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Deciphering Ibogaine’s Matrix Pharmacology:
Multiple Transporter Modulation at Serotonin
Synapses
Christopher Hwu1,†, Václav Havel1,†, Xavier Westergaard2,3,†, Adriana M. Mendieta1, Inis
C. Serrano1, Jennifer Hwu1, Donna Walther4, David Lankri1, Tim Luca Selinger1, Keer
He1, Rose Liu5, Tyler P. Shern1, Steven Sun1, Boxuan Ma2, Bruno González1, Hannah J.
Goodman1, Mark S. Sonders6, Michael H. Baumann4, Ignacio Carrera7, David
Sulzer3,6,8,9, Dalibor Sames1,10,*
1 Department of Chemistry, Columbia University, New York, New York 10027, United
States.
2 Department of Biological Sciences, Columbia University, New York, New York 10027,
United States.
3 Department of Psychiatry, Columbia University Irving Medical Center, New York, New
York 10032, United States.
4 Designer Drug Research Unit, Intramural Research Program, National Institute on Drug
Abuse, National Institutes of Health, Baltimore, Maryland 21224, United States.
5 Department of Biology, Barnard College, New York, New York 10027, United States.
6 Division of Molecular Therapeutics, New York State Psychiatric Institute, New York, New
York 10032, United States.
7 Laboratorio de Síntesis Orgánica, Departamento de Química Orgánica, Facultad de
Química, Universidad de la República, Montevideo, Uruguay 11200.
8 Department of Neurology, Columbia University Irving Medical Center, New York, New
York 10032, United States.
9 Department of Molecular Pharmacology and Therapeutics, Columbia University Irving
Medical Center, New York, New York 10032, United States.
10 Zuckerman Mind Brain Behavior Institute, Columbia University, New York, New York
10027, United States.
† These authors contributed equally.
*Correspondence should be addressed to D. Sames (ds584@columbia.edu).
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Abstract
Ibogaine is the main psychoactive alkaloid produced by the iboga tree (Tabernanthe
iboga) that has a unique therapeutic potential across multiple indications, including opioid
dependence, substance use disorders, depression, anxiety, posttraumatic stress disorder
(PTSD), and traumatic brain injury (TBI). We systematically examined the effects of
ibogaine, its main metabolite noribogaine, and a series of iboga analogs at monoamine
neurotransmitter transporters, some which have been linked to the oneiric and therapeutic
effects of these substances. We report that ibogaine and noribogaine inhibit the transport
function of the vesicular monoamine transporter 2 (VMAT2) with sub-micromolar potency
in cell-based fluorimetry assays and at individual synaptic vesicle clusters in mouse brain
as demonstrated via two-photon microscopy. The iboga compounds also inhibit the
plasma membrane monoamine transporters (MATs), prominently including the serotonin
transporter (SERT), and a novel iboga target, the organic cation transporter 2 (OCT2).
SERT transport inhibition was demonstrated in serotonin axons and soma in the brain
and in rat brain synaptosomes, where ibogaine and its analogs did not act as substrate-
type serotonin releasers. Noribogaine showed dual inhibition of VMAT2 and SERT with
comparable potency, providing an explanatory model for the known neurochemical effects
of ibogaine in rodents. Together, the updated profile of the monoamine transporter
modulation offers insight into the complexity of the iboga pharmacology, which we termed
“matrix pharmacology”. The matrix pharmacology concept is outlined and used to explain
why ibogaine and noribogaine do not induce catalepsy, as demonstrated in our study, in
contrast to other VMAT2 inhibitors.
Introduction
Ibogaine is the main psychoactive principle of the iboga plant (Tabernanthe iboga),
indigenous to West Central Africa.1 The iboga root has been used for centuries to induce
visionary states and transpersonal spiritual experiences during ceremonies and has
served as a center piece for indigenous religions and spiritual practices.2 Outside
traditional use, ibogaine and iboga were reported to interrupt dependence on opioids and
other reinforcing drugs, including alcohol and cocaine.3,4 Through the work of several
generations of pioneers, pursued mostly outside the mainstream medical system,
ibogaine has provided a new paradigm for treating substance use disorders (SUDs) –
albeit a controversial one due to its adverse cardiac effects.5,6 This paradigm consists of
one or a few treatment sessions with ibogaine, which have acute and long-lasting effects
as reported in numerous observational surveys and case studies.3,7 Acute effects include
dream-like experiences (oneiric effects) that often provide deep psychological insights
reduced physiological drug dependence (i.e., large effects in reducing acute withdrawal
symptoms). Long-term effects include attenuation of drug craving, and improvement in
mood and anxiety symptoms. It may be that ibogaine provides a multi-faceted, global
treatment that addresses the core aspects of SUDs.8,9 The clinical observations have
been supported by numerous preclinical studies showing therapeutic-like effects of
ibogaine in rodent models of SUDs and depression.10,11
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However, administration of ibogaine or iboga materials can lead to rare but severe cardiac
adverse effects and sudden death, which have presented substantial obstacles to the
development of ibogaine as an FDA-approved medication.12 Nevertheless, many
individuals desperate for relief from their suffering have sought ibogaine treatment in
clinics abroad, a growing trend that has provided pilot clinical observations.13
In addition to the anti-addiction effects of ibogaine, its putative therapeutic scope
encompasses other psychiatric and neurological conditions, often co-morbid with SUDs,
including PTSD and mild traumatic brain injury (mTBI), according to recent surveys of
combat veterans with blast exposures.14,15 Although the clinical data supporting
therapeutic efficacy of ibogaine are almost exclusively based on open label observational
studies, the reported effect sizes are notably large across neurological and mental health
assessment scales (for example, >90% response rates and 80% remission after a single
treatment).15 Collectively, the current evidence indicates a trans-diagnostic therapeutic
potential of ibogaine rooted in profound neurorestorative effects across biological scales
(the molecular, physiological, psychological, and social-spiritual domains).
The emerging therapeutic profile of ibogaine leads to a fundamental question of how such
a range of neurorestorative effects may be induced and mediated on a molecular level.
Ibogaine is metabolized in vivo to form noribogaine, in both humans and rodents, where
these two compounds act in tandem due to overlapping pharmacokinetic profiles.11,16–18
The reported pharmacological targets and associated effects provide a window on the
complexity of signaling pathways that ibogaine and noribogaine engage. The combined
action of these two compounds modulates several classes of molecular targets and
pathways, including ion channels, neurotransmitter transporters, G protein coupled
receptors (GPCRs) and their signaling, and kinase signaling pathways via several modes
of action such as ion channel blockade,19 monoamine transporter inhibition via an atypical
mechanism,20 monoamine transporter pharmaco-chaperoning effect,21,22 and kinase
signaling pathway potentiation.23 Interestingly, Interestingly, these wide-ranging effects
typically involve low potency drug interactions in the micromolar range (Figure 1).24–27
Here, we introduce the term “matrix pharmacology” – to describe this mechanistic model,
defined as modulation of many molecular targets and signaling pathways via multiple
modes of action with weak or modest-potency molecular interactions. As the collective
data suggests that iboga compounds act throughout the signalome’s information-
processing matrix, we wish to differentiate this mechanistic model (matrix pharmacology)
from “selective polypharmacology”, which is characterized by potent agonism or
antagonism at several targets, such as G protein coupled receptors (GPCRs), as
exemplified by LSD.28,29 A molecular logic of iboga matrix pharmacology is emerging
where iboga compounds do not modulate GPCRs directly (with some exceptions) but
rather 1) modulate neurotransmitter dynamics via direct inhibition and modulation of the
monoamine transporters, 2) engage ion channels as channel blockers and or antagonists,
and 3) potentiate downstream signaling pathways of GPCRs and receptor tyrosine
kinases (RTKs).
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As downstream effectors activated by the primary pharmacology, iboga compounds
modulate gene expression and protein levels of neurotrophic factors in several brain
regions with relevance to SUDs and other mental health disorders.30,31 Upregulation of
myelination markers was reported in morphine-dependent mice after a single ibogaine
administration, indicating the possibility of white matter restoration.32 It was also
suggested that ibogaine may increase oxytocin gene expression,33 while another report
demonstrated induction of metaplasticity states in the nucleus accumbens (NAc) that
sensitize the local synaptic connections to oxytocin, which jointly correlates with
reopening a critical learning period for social reward in adult mice (Figure 1).34 These
results, together with behavioral effects, indicate induction of both specific and broad
restorative programs and processes (e.g. reversal of drug dependence phenotype and
induction of metaplasticity and neurorestoration states).
In this report, we focus on mapping the actions of iboga compounds at the monoamine
transporters, some of which have previously been implicated in ibogaine’s anti-addiction
and oneirogenic effects.20 The plasma membrane monoamine transporters (MATs),
including the dopamine transporter (DAT), norepinephrine transporter (NET), and
serotonin transporter (SERT), are essential components of monoamine
neurotransmission, as they directly modulate the magnitude and duration of the synaptic
activity by rapid removal and recycling of the monoamine neurotransmitters from the
extracellular space. They constitute a branch of a solute carriers 6 family (SLC6; also
known as neurotransmitter sodium symporters, or NSS) that mediate a directional
transport coupled to the membrane ion gradient by co-transporting the endogenous
monoamine transmitters and sodium ions.35,36 DAT and NET are located in the
corresponding catecholamine neurons, whereas SERT is expressed in 5-HT neurons,
blood-brain barrier (BBB) cells, endochromaffin cells, and blood platelets.37,38 MATs are
prominent targets of psychoactive substances and medications that inhibit one or more
monoamine transporters, including cocaine, methylphenidate, tricyclic antidepressants,
and selective serotonin reuptake inhibitors.39–41 There are also targets for monoamine
releasers, such as amphetamine and MDMA, that act as MAT substrates and induce
efflux of native monoamine transmitters via these transporters, often referred to as
“reverse transport”.42
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Figure 1. Proposed global model of ibogaine’s pharmacology, downstream
molecular signaling, neuro-restorative processes, and clinical therapeutic and
adverse effects. (A) Ibogaine is metabolized to noribogaine and both compounds
contribute to the complex pharmacology. (B) Examples of known primary molecular
targets; the present study focuses on monoamine transporters including the vesicular
monoamine transporter 2 (VMAT2) and organic cation transporter 2 (OCT2), disclosed as
novel targets in this study. Ibogaine and noribogaine act as weak and modest potency
modulators of several targets and signaling pathways, via multiple modes of action, such
as blockers of ion channels, atypical inhibitors of monoamine transporters, pharmaco-
chaperones of monoamine transporters (SERT and DAT), and potentiators of
downstream signaling pathways – a functional profile termed “matrix pharmacology”. (C)
The downstream effects include, for example, expression changes of neurotrophic factors
such as glial cell derived neurotrophic factor (GDNF) and brain derived neurotrophic
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factor (BDNF), and potentiation of receptor tyrosine kinase signaling pathways. Oxytocin
(OT) signaling has been implicated in mediating reopening of the critical development-
like learning states. (D) According to this mechanistic model, the indicated pathways
mediate the neuroplasticity and neurorestorative processes, where the oneiric and
psychedelic states likely contribute as well. (E) These processes collectively likely
mediate the profound therapeutic effects across biological scales.
The functional dynamic range of MAT transporters, described as high-affinity, low-
capacity transporters (uptake 1 system) is complemented by the low-affinity, high-
capacity transporters (uptake 2 system) comprised of transporters from several different
SLC families including organic cation transporters 1-3 (OCT1-3, SLC22A1-3), plasma
membrane monoamine transporter (PMAT, SLC29A4), and other more recently identified
transporters.43 These transporters generally show much lower apparent affinity for
biogenic monoamines (as much as two orders of magnitude), but greater maximal
transport velocity than MATs, and are driven by the concentration gradient of the
substrates (equilibrative transporters). OCT1-3 and PMAT have distinct but often
overlapping expression patterns in the CNS on neurons (presynaptic and postsynaptic)
and glial cells (Figure 2).43
MATs work in tandem with the vesicular monoamine transporters, VMAT1 (SLC18A1)
and VMAT2 (SLC18A2), which load synaptic vesicles or large dense core vesicles with
monoamine neurotransmitters as an essential step prior to activity-dependent release via
exocytosis (Figure 2B). VMAT1 is expressed in neuroendocrine cells, while VMAT2 is
largely found in neurons in the CNS. Both transporters concentrate neurotransmitters in
the vesicle lumen, driven by the proton gradient between the cytoplasm and vesicular
lumen, via an amine-proton antiport mechanism.44,45 The cytosolic monoamines that are
not packaged into synaptic vesicles are oxidatively deaminated by the monoamine
oxidases. Reserpine and tetrabenazine are classical VMAT2 inhibitors; reserpine (a dual
VMAT1 and 2 inhibitor) has been used in the past to treat hypertension and psychosis,
while TBZ (and its deuterated analog, selective VMAT2 inhibitors) are prescribed to treat
chorea associated with the Huntington’s disease.46
The VMAT2 and the plasma membrane uptake 1 and uptake 2 transporters jointly shape
the spatial and temporal landscape of monoamine neurotransmission in the CNS and its
perturbation by pharmaceutical agents. Biogenic monoamines act as modulatory
neurotransmitters via their respective receptors by augmenting or attenuating the
excitatory and inhibitory synapses and serve as critical neuroplasticity mediators.47
Guided by the framework of matrix pharmacology and the substantial corpus of
neurochemical studies with ibogaine and noribogaine in rodents, we hypothesized that
there are one or more important molecular targets of iboga alkaloids in the monoamine
transporter families, which have not been examined in detail previously (the “iboga X
project”). The effects of ibogaine or noribogaine on monoamine neurotransmitter
dynamics in vivo are complex; for example, the brain tissue analysis in mice and rats
showed, in terms of total tissue concentrations, a decrease in dopamine and increase in
the dopamine metabolite, DOPAC (dihydroxyphenylacetic acid), which is a tell-tale sign
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of VMAT2 inhibition.20 Weak binding affinities of ibogaine and noribogaine at VMAT2 in
human brain striatal homogenates (ibogaine, IC50 = 14.6 μM; and noribogaine, IC50 = 29.5
μM) have been reported, supporting the hypothesis that VMAT2 may be directly inhibited
by the iboga compounds.48 Ibogaine and noribogaine were also reported to acutely raise
extracellular 5-HT levels in the Nucleus accumbens (NAc), while the total tissue content
analysis revealed minimal or no 5-HT decrease and a more pronounced decrease of the
5-HT metabolite, 5-HIAA (5-hydroxyindolylacetic acid), consistent with SERT inhibition.20
These measurements indicate a complex monoamine modulation scenario and provides
a rationale to systematically examine monoamine transporters, including VMAT2 and the
uptake 1 and uptake 2 plasma membrane monoamine transporters.
Our previous work revealed that even small structural perturbations of the iboga system
can have large effects on in vitro and in vivo pharmacology, as demonstrated by the oxa-
iboga class of compounds (benzofuran-based iboga analogs).31 We therefore examined
a focused SAR space of the ibogamine core in terms of the monoamine transporter
activity.
Results
Ibogaine and noribogaine inhibit the function of multiple monoamine transporters.
To examine the effect of ibogaine and noribogaine on human VMAT2 (hVMAT2), we used
HEK293 (human embryonic kidney 293) cells stably transfected with hVMAT2 (hVMAT2-
HEK cells) and a VMAT2 fluorescent substrate, FFN206 (Figures S2).49 For uptake 1
plasma membrane monoamine transporters, we used APP+ [4-(4-dimethylamino)phenyl-
1-methylpyridinium] as the validated fluorescent substrate and the corresponding stably
transfected HEK cells (hSERT-HEK, hDAT-HEK, and hNET-HEK). These cell-based
assays provide an optical readout for the fluorescent substrate uptake (fluorescence
units) mediated by the selected transporter.50 The extent of inhibition induced by the
tested compounds is quantified by the difference in the fluorescence signal between the
vehicle and the iboga compound treatments (Figures S1, S4, and S5). Similar protocols
were developed for the uptake 2 transporters, OCT1-3 and PMAT, using APP+ (OCT1
and PMAT) and ASP+ (4-[4-(dimethylamino)styryl]-N-methylpyridium; OCT2-3) as
fluorescent substrates (Figures S6-S9). Established transporter inhibitors, including
indatraline (DAT; Figure S4), reboxetine (NET; Figure S5), imipramine (SERT; Figures 3
and S1), tetrabenazine (VMAT2; Figures 3 and S2), and decynium-22 (OCT1-3 and
PMAT; Figures S6-S9) were used for each transporter as positive controls.51
We found that both ibogaine and noribogaine inhibit hVMAT2 transport with comparable
potency (IC50, ibogaine, hVMAT2 = 390 nM, IC50, noribogaine, hVMAT2 = 570 nM, Figure 2A, Figure 3,
and Figure S2). The values indicate more potent inhibition effect than those previously
reported for hVMAT2 binding in a radioligand displacement assay in post-mortem human
brain (IC50, ibogaine, striatum = 14.6 μM and IC50, noribogaine, striatum = 29.5 μM).48 Ibogaine shows
approximately a one-log higher affinity for hVMAT2 over hSERT (IC50, hSERT = 2980 nM)
and NET (IC50, hNET = 3670 nM) (Figures 3, S1, and S5). Noribogaine inhibits hVMAT2
(IC50, hVMAT2 = 570 nM) and SERT (IC50, hSERT = 280 nM) with comparable potency, which
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represents an unusual pharmacological profile (Figures 2-3, and S1-S2). The VMAT2 and
SERT dual inhibition is over 10-fold more potent than the effect of noribogaine at DAT
(IC50, DAT = 6760 nM) (Figure S4). In terms of uptake 2 transporters, we found that ibogaine
(IC50, OCT2 = 9310 nM) and noribogaine (IC50, OCT2 = 6180 nM) inhibit transport by hOCT2
with weak but measurable potency, while showing no inhibition below 10 μM at other
uptake 2 transporters examined (Figures 2A and S6-S9).
Figure 2. Ibogaine and noribogaine exert dual inhibition of vesicular and plasma
membrane transporters.
(A) Graphical representation of ibogaine’s (left panel) and noribogaine’s (right panel)
inhibitory profile at the vesicular monoamine transporter 2 (VMAT2), uptake 1 and uptake
2 monoamine transporters. Ibogaine inhibits hVMAT2 with submicromolar potency (IC50,
hVMAT2 = 390 nM) and modest selectivity of around one log unit over hSERT (IC50, hSERT =
2980 nM) and hNET (IC50, hNET = 3670 nM), while having a weak effect at hOCT2 (IC50,
hOCT2 = 9310 nM). Noribogaine inhibits hVMAT2 (IC50, hVMAT2 = 570 nM) and hSERT (IC50,
hSERT = 280 nM) with comparable potency. This dual activity is separated by more than
one log unit from the effect of noribogaine at hDAT (IC50, hDAT = 6760 nM) and hOCT2
(IC50, hOCT2 = 6180 nM). (B) A schematic showing a 5-HT axon (blue line), 5-HT release
sites (blue dots) and 5-HT synapses (lighter and larger blue dots) on a pyramidal neuron’s
soma and dendrite (left graphic). A pictorial representation of 5-HT synapse and location
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of VMAT2 on synaptic vesicles, SERT on presynaptic boutons, and uptake 2 transporters
OCT2 and PMAT on presynaptic and postsynaptic cells (localization on glial cells is
omitted for clarity). Noribogaine has a dual inhibitory effect on VMAT2 and SERT,
suggesting complex, non-linear effects on 5-HT and monoamine neurotransmission.
Synaptic reuptake inhibitors (SynRIs) are defined by dual inhibition of the vesicular
monoamine transporter 2 and a plasma membrane monoamine transporter with
comparable inhibitory potencies. The inhibition of both VMAT2 and a plasma
membrane monoamine transporter is relatively uncommon in the pharmacopeia. The
potent VMAT2 inhibitors such as reserpine or tetrabenazine (TBZ) are selective for
VMAT2 versus plasma membrane monoamine transporters (>1000-fold potency
differences for reserpine and >70-fold for TBZ, Figure S10),52 while potent SERT inhibitors
such as imipramine and fluoxetine are selective for SERT over VMAT2 (typically >100-
fold, Figure S10).53–56 Although there are reports that suggest the possibility of cross-
activity between the MATs and VMAT2 for the classical compounds,55,57 VMAT2 inhibitors
do not block MATs in brain tissue or in vivo at concentration exposures that lead to
vesicular depletion.52,58 We therefore propose a new class of pharmacological agents -
termed “synaptic reuptake inhibitors” or “SynRIs” – as agents exerting dual inhibition of
VMAT2 and SERT (or the other plasma membrane monoamine transporters including
DAT or NET) with comparable inhibitory potencies (within a half log in IC50 values, Figures
3, S1-S2, and S4-S5). The dual transporter inhibition profile suggests complex effects at
5-HT synapses and release sites, as well as other monoamine synapses, as noribogaine
directly modulates the synaptic vesicular, cytoplasmic, and extracellular pools of 5-HT
(Figure 2B). Some of the in vivo neurochemical measurements reported previously are
consistent with this pharmacological profile (see Introduction and Discussion).
There is a precedent for VMAT2 inhibitors that also block DAT transport with comparable
potencies, as exemplified by deoxygenated lobeline analogs.59 S-amphetamine has
comparable potency as a [3H] 5-HT releaser via SERT in rat synaptosomes (EC50 = 1.8
µM) and uptake blocker at VMAT2 (IC50 = 3.3 µM) in crude vesicular rat brain fractions;
whereas its releasing potency was reported to be much greater at NET and DAT in
synaptosomes (EC50, NET = 7.1 nM and EC50, DAT = 24.8 nM, respectively).42,60
Synthesis of iboga alkaloids and their analogs from natural voacangine. We next
examined the effect of substitution in the 1-position and 5-position (indole substituents)
on the balance between the VMAT2 and SERT inhibition (we propose a new, more logical
iboga system numbering as shown in Figure 3A). These two structural positions are
readily modifiable via late-stage functionalization of naturally derived iboga alkaloids
(Scheme 1), with the exception of (±)-oxa-noribogaine and (-)-fluoro-ibogamine analogs,
which required a total synthesis as reported previously.23,31,61,62,63 We do not use
Tabernanthe iboga materials for analog synthesis for eco-cultural reasons (to avoid
overharvesting this resource); instead, we used natural (-)-voacangine obtained by
extraction from the root bark of Voacanga Africana (Scheme 1).31,64 Voacangine was
converted to desmethyl voacangine, using ethanethiol and boron tribromide, and its
subsequent hydrolysis and decarboxylation yielded noribogaine. We used noribogaine as
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the starting point to generate a number of readily accessible derivatives, by taking
advantage of reactive sites on the indole core.
The phenol moiety can be derivatized selectively under mild basic conditions to obtain
alkoxy analogs (with alkyl halide, carbonate) or the reactive triflate intermediate [by
bis(trifluoromethanesulfonyl)aniline, tertiary amine base). 5-Triflate-ibogamine can be
further transformed by palladium-mediated hydrogenation into ibogamine,65 a substantial
component of the total iboga alkaloid content of Tabernanthe iboga, but not produced by
Voacanga africana plants in sufficient quantity to support cost-effective direct isolation.
The nitrile group is a prominent feature of the selective SERT inhibitor citalopram, as such
we hypothesized that this group could have a dramatic effect on ibogamine’s SERT
inhibition. Aryl halides and pseudohalides, like triflates can be transformed into nitriles by
a widely used palladium-mediated reaction using a suitable nitrile source (zinc cyanide),
carried at elevated temperatures (80 – 160°C). However, we found that a prolonged
reaction time and high excess of reagents were required to achieve a desirable level of
conversion at a lower temperature range required to limit degradation.
Indole nitrogen is rapidly alkylated in good yields when treated with alkyl halide in
dimethylsulfoxide in the presence of potassium hydroxide. Milder alkylation conditions
(metal carbonate in hot acetonitrile) can be used to N-alkylate more labile analogs, that
would not tolerate the harsher KOH/DMSO conditions. For analogs where restoring the
free phenol group was desirable, the alkoxy group was cleaved using ethanethiol and
boron tribromide.
Oxa-noribogaine was prepared and characterized as a racemate by a total synthesis as
reported previously,31 while (-)-5- and (-)-6-fluoro-ibogamine analogs were prepared from
a chromatographically resolved isoquinuclidine intermediate to match the natural iboga
stereochemistry.
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Scheme 1. Synthesis of iboga analogs via late-stage functionalization of natural
voacangine. Noribogaine, accessible semi-synthetically from voacangine isolated from
root bark of Voacanga Africana, serves as a versatile intermediate for preparation of
analogs with amplified and targeted transporter inhibitory profiles. Detailed synthetic
procedures are provided in supplementary information.
Structure-activity relationship (SAR) of iboga alkaloids at hVMAT2 and hSERT.
Removal of the methyl group in the 5-position transforms VMAT2-prefering activity of
ibogaine to a balanced inhibitory profile of noribogaine, by increasing the SERT potency
10-fold (Figures 2-3 and S1-S2). Excision of the entire 5-methoxy group of ibogaine,
rendering another natural iboga alkaloid, ibogamine, inverts the ratio of the two activities
by shifting the potency about 10-fold at each target, giving a SERT-preferring
pharmacological profile (IC50, hSERT = 330 nM, IC50, hVMAT2 = 3010 nM; Figures 2-3 and S1-
S2). In contrast, extending the steric bulk of the methoxy to ethoxy group in the same
position, accomplished by synthesizing 5-ethoxyibogamine, affords a potent VMAT2
inhibitor with more than 100-fold selectivity over SERT (IC50,hVMAT2 = 80 nM, IC50,SERT =
9030 nM, Figures 3A-C and S1-S2). In further contrast, placing a nitrile group in the 5-
position gives 5-cyano-ibogamine, which is a potent SERT inhibitor with high selectivity
over VMAT2 (IC50, hSERT = 26 nM, IC50, hVMAT2 = 3340 nM, Figures 3A-B and S1-S2). Thus,
the 5-position has a strong effect on both transporters and the observed relative inhibitory
potencies. The hydroxy or alkoxy group is important for the observed sub-micromolar
inhibitory potency at hVMAT2, as the corresponding 5-fluoroibogamine analogs and
ibogamines (H in the 5-position) are weak hVMAT2 inhibitors (Figure 3A and Figure S2).
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With respect to hSERT activity, the nitrile and fluorine 5-substituents give potent, low
nanomolar hSERT inhibitors (Figure 3A and Figure S1).
N-alkylation of the indole nitrogen (1-position) can also have robust SAR effects. For
example, N-methylation of noribogaine resulted in increasing the potency two- to three-
fold at both targets, giving a SynRI ligand, N-methyl-noribogaine (IC50, hVMAT2 = 59 nM,
IC50, SERT = 170 nM, Figures 3A-C and S1-S2). Conversely, N-ethyl-noribogaine is a potent
hVMAT2 compound with good selectivity over hSERT (IC50,hVMAT2 = 70 nM, IC50,SERT =
1860 nM, Figures 3A-C and S1-S2). N-methylation of the potent hSERT inhibitor 5-cyano-
ibogamine further increases the inhibitory potency at hSERT, yielding a compound with
low nanomolar potency at hSERT (IC50, SERT = 5 nM, IC50, hVMAT2 = 440 nM; Figures 3A-B
and S1-S2). Replacing the nitrogen with oxygen, rendering the oxa-iboga system, as
exemplified by oxa-noribogaine (IC50, SERT = 900 nM, IC50, hVMAT2 = 670 nM; Figures 3A-C
and S1-S2) results in a nearly perfect balance between hSERT and hVMAT2 due to a
modest decrease of the hSERT potency versus noribogaine.
We found that hOCT2 has its own SAR trends. Removal of the 5-methoxy group or N-
methylation of ibogaine, yielding ibogamine (IC50, hOCT2 = 2.0 μM) and N-methyl-ibogaine
(IC50, hOCT2 = 2.3 μM), respectively, gives the most potent compounds of the series at
hOCT2 in the range of low micromolar inhibitory potencies (Figure S6).
The combined SAR at these two positions enabled us to generate a series of iboga
compounds with a broad range of activities, including potent hVMAT2 or hSERT inhibitors,
balanced SynRI compounds (Figure 3C), and compounds with varying relative potencies
at these two targets. The rest of monoamine transporters were also examined for each of
the featured compounds (Figures S1-S2 and S4-S9). The data discussed above was
obtained by fluorimetry of the transfected cells using a plate reader. We confirmed these
results with epifluorescence and confocal fluorescence microscopy, which showed that
the fluorescence signals originate from intracellular localization of the fluorescent
substrates, which is dependent on the function of relevant transporters (Figure S3).
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Figure 3. Iboga compounds define a new class of pharmacological agents, termed
“synaptic reuptake inhibitors” or “SynRIs”. (A) Structure-activity relationship (SAR)
examination of two positions of ibogamine and oxa-ibogamine (indicated on top, the 5-
position in blue, the 1-position in yellow and purple) with respect to VMAT2 and SERT
transport. We introduce a new numbering system in line with the numbering of simple
tryptamines and indoles. The table provides IC50 values for transport inhibition obtained
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by fluorimetry based on inhibition of uptake of fluorescent substrates, APP+ for hSERT
and FFN206 for hVMAT2, n = 4 biological replicates, mean ± SEM. Brick red shading
highlights SynRI compounds with balanced inhibitory profiles; i.e., with IC50 values for
SERT and VMAT2 that fall within a three-fold range (one-half log). (B) Dose-response
curves for control inhibitor (for hSERT: imipramine and for hVMAT2: tetrabenazine) and
selected compounds in hSERT-HEK cells (left panel) and hVMAT2-HEK cells (right
panel). The y-axis shows normalized inhibition of fluorescent substrate uptake
(uninhibited – inhibited) ± SEM, derived from four separate experiments (n = 4). (C)
Graphical representation of the dual inhibitory activity at SERT and VMAT2 exhibited by
noribogaine, N-methyl-ibogaine, N-methyl-noribogaine, and oxa-noribogaine. Minor
modifications of the iboga structure yield a range of activities in the SERT and VMAT2
continuum including potent and selective SERT inhibitors and VMAT2 inhibitors, as well
as balanced SynRI compounds.
Iboga alkaloids inhibit uptake but do not induce release of serotonin (5-HT) in brain
synaptosomes. We next examined the effect of iboga compounds on monoamine
transporters natively expressed in rat brain tissue preparations. For this purpose,
synaptosomes have been used with much success enabling measurements of both
uptake and release of radiolabeled neurotransmitters; namely, tritiated dopamine, [3H]DA,
norepinephrine, [3H]NE, and serotonin, [3H]5-HT.42 Synaptosomes are prepared by
fractionation of brain tissue. Caudate tissue was used for DAT assays whereas whole
brain minus caudate and cerebellum was used for NET and SERT assays. Synaptosomes
preserve much of the molecular machinery and physiological functions of presynaptic
boutons, such as respiration, membrane potential, depolarization-induced exocytosis,
neurotransmitter uptake, and pharmacologically induced monoamine efflux.66
We examined a set of iboga compounds on [3H]5-HT uptake in synaptosomes, in the
presence of DAT and NET inhibitors, effectively examining the function of native rat SERT
(rSERT, Table 1).67 Noribogaine was about 10-fold more potent than ibogaine in this
assay, consistent with the literature and the inhibitory potency values determined in the
optical assays with hSERT-transfected cells as detailed above (ibogaine: IC50, rSERT = 3037
nM versus IC50, hSERT = 2980 nM; noribogaine: IC50, rSERT = 326 nM versus IC50, hSERT = 280
nM, Tables 1 and Figure S12). Both sets of values are similar to those reported previously
in rat synaptosomes (ibogaine: IC50, rSERT = 3150 nM, noribogaine: IC50, rSERT = 330 nM).17
Close similarities of the obtained values are noteworthy considering the differences
between these two assays. For the other iboga analogs, the values between the
synaptosome and fluorescence assays also matched well, except for N-ethyl-noribogaine
where the inhibition of [3H]5-HT uptake in synaptosomes was more than 20-fold more
potent than the fluorescent SERT substrate inhibition in transfected cells (IC50, rSERT = 80
nM versus IC50, hSERT = 1860 nM, Table 1B and Figure S12). The reasons for the large
difference in potency for this specific compound are unclear; however, we note that N-
ethyl-noribogaine differs from the rest of tested compounds by its high potency of VMAT2
inhibition. The greater relative potency of N-ethyl-noribogaine in synaptosomes versus
transfected cells was also found at NET and DAT (Figure S12). This leads to a speculation
that the increased potency at MATs may be due to a functional coupling between the
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VMAT2 and MAT transporters in the native system but not in the singly transfected cell
lines, rather than species differences (rat versus human). The source of this discrepancy
is unclear.
Generally, transporter substrates differ from non-transported inhibitors by stimulating the
efflux of pre-accumulated substrates (“trans-acceleration” in the terminology of W.
Stein).68 Synaptosomes allow compounds to be assayed for promoting the release of
preloaded [3H]5-HT, which would be indicative of acting as SERT substrates. A previous
study showed that ibogaine did not release [3H]5-HT from synaptosomes, but noribogaine
was not tested.69 Considering the ability of ibogaine and noribogaine to stabilize
conformations of SERT distinct from those induced by SSRIs, and their SERT
pharmacochaperone activity,20–22 we re-examined this question with a wider set of iboga
analogs (Table 1 and Figure S12). No [3H]5-HT release was observed for ibogaine,
noribogaine, or ibogamine; nor for any of the synthetic iboga analogs tested. This
contrasts with the robust [3H]5-HT release by amphetamine, a drug shown to be a SERT
substrate by numerous lines of evidence (positive control, Table 1 and Figure S12).42
The ratio of binding to uptake inhibitory constants at SERT is low (~ 1) which also supports
the model where ibogaine and noribogaine are non-transported SERT inhibitors. In
contrast, transporter substrates typically exhibit large ratios (10s-100s) due to markedly
weaker potency in ligand binding displacement assays relative to the potency obtained in
uptake inhibition assays.17
Table 1. Effect of iboga alkaloids on SERT-mediated uptake and release.
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(A) Iboga analogs inhibit SERT-mediated [3H]5-HT uptake (n = 3) in rat-derived brain
synaptosomes, but do not initiate its release (n = 3). (B) Comparison of inhibitory activity
determined for iboga analogs in cell-based fluorescent uptake assay (n = 4) with values
observed in rat brain synaptosomes presented on panel A.
Imaging SERT and VMAT2 inhibition by iboga alkaloids with subcellular resolution
in mouse brain. We next set out to examine SERT inhibition by the iboga compounds in
acutely sectioned living brain slices in several brain regions containing different parts of
serotonin neurons (cell bodies, dendrites, and axons). For this purpose, we used the
recently reported molecular probe, SERTlight, which is a selective fluorescent SERT
substrate that labels 5-HT neurons in mouse brain with good morphological fidelity in a
SERT-dependent manner (Figure 4A).50 This imaging probe enables visualization of
SERT function in the context of 5-HT neuronal morphology by incubating brain slices with
SERTlight (10 μM, 30 min incubation), or injecting SERTlight into the brain in living
animals, and acquiring images inside tissue via two-photon fluorescence microscopy. The
cell bodies and dendrites were imaged in the dorsal raphe (DR), the location of a majority
of 5-HT neuronal cell bodies that project throughout the forebrain (Figure 4A, F). The 5-
HT axonal projections appearing as punctate strings were imaged in the substantia nigra
pars reticulata (SNpr) and dorsal striatum (DS), regions with relatively high density of 5-
HT axons, and somatosensory cortex (SS, or barrel cortex), that has sparse 5-HT axonal
innervation (Figure 4A-E). In the 5-HT axons in these regions, citalopram (2 μM, pre- and
co-incubation with SERTlight) used as a positive control resulted in complete suppression
of SERTlight labeling, consistent with in situ axonal SERT inhibition. In contrast, ibogaine
(2 μM) had no effect on SERTlight labeling using the same concentration and incubation
protocol as for citalopram, consistent with a relatively weak, micromolar inhibitory effect
of ibogaine as determined in the cell assays and synaptosomes (Figure 4B, C, E). On the
other hand, noribogaine (2 μM) showed a complete inhibition of SERTlight signal in the
axons, in line with its sub-micromolar SERT inhibition potency (Figure 4B, C, E, F).
Similarly, the potent SERT inhibitor, 5-cyano-noribogaine (2 μM), fully inhibited SERTlight
uptake; and a qualitative dose-response study indicated a marked suppression of
SERTlight fluorescent labeling at 200 nM concentration of this iboga analog (Figure 4D).
These results indicate that noribogaine, and its more potent analog, 5-cyano-noribogaine,
can inhibit axonal SERT function in native brain tissue in a concentration range that
matches the brain exposures of free drug at behaviorally active doses (> 2 μM, see the
pharmacokinetic studies below).
In the DR, the somatodendritic labeling pattern of SERTlight was completely inhibited by
citalopram (2 μM); however, noribogaine showed no effect at 2 μM and 10 μM
concentrations, with the latter concentration being five-fold higher than a concentration
effecting complete SERTlight labeling suppression in 5-HT axons (Figure 4F). A dose-
response study demonstrated that even 30 μM concentration of noribogaine had no
apparent effect on the somatodendritic SERT function. A clear inhibition was only
achieved at 100 μM concentration of noribogaine (Figure 4F). Thus, in semi-quantitative
terms, there is more than 50-fold difference in the inhibitory potency of noribogaine
between the axonal and somato-dendritic brain regions. A simple explanation that the cell
bodies and dendrites of 5-HT neurons express other transporter(s), which take up
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SERTlight but are noribogaine-insensitive, was eliminated by showing that: 1) there was
no SERTlight somatodendritic labeling in SERT knock-out (SERT-KO) mice, 2) SERTlight
was not a substrate for DAT, NET, or any of the uptake 2 transporters.50 Instead, our
results indicate that noribogaine may have the ability to “read” a different functional status
of the SERT molecules in cell bodies versus axons, embodying essentially an “axon-
selective” or “brain-region-selective” SERT inhibitor.
Figure 4. Inhibition of SERT in axons, cell bodies, and dendrites of 5-HT neurons in
mouse brain visualized by SERTlight and two-photon imaging. (A) Left panel: A
schematic graphic of the concept of the imaging method. A 5-HT axonal bouton and
release site is shown featuring SERT in the plasma membrane, which transports 5-HT
and SERTlight (as the fluorescent substrate) to yield fluorescently labeled 5-HT neurons.
Inhibition of SERT with noribogaine or other iboga analogs diminishes the labeling of 5-
HT neurons. Examples of the other transporters examined in this study (OCT2 and PMAT)
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are also shown. Right panel: A schematic representation of a sagittal slice of mouse brain
(Allen Brain Atlas) showing the brain areas chosen for imaging, including dorsal raphe
(DR), the seat of 5-HT cell bodies and dendrites; substantia nigra pars reticulata (SNpr)
and dorsal striatum (DS), the regions with relatively dense 5-HT axonal innervation; and
somatosensory cortex layers 2/3 (SSp2/3), a location with relatively sparse 5-HT axons.
(B) Left, zoomed-out microscopy image in SNpr (Scale bar: 20 μm) showing axonal
strings and the location of the inset image shown right (Scale bar: 7 μm). In-between the
microscopy images, mouse brain atlas image highlighting the SNpr region (Bregma: 1.8
mm, Allen Brain Institute). For the inset images to the right, SERTlight (10 μM for 30
minutes) accumulates in 5-HT axons in WT mice. Co-incubation of acute mouse brain
slices with the SERT inhibitor citalopram (2 μM for 30 minutes) and SERTlight (10 μM for
30 minutes) inhibited SERTlight uptake (positive control). Co-incubation of acute mouse
brain slices with ibogaine (2 μM for 30 minutes) and SERTlight (10 μM for 30 minutes)
did not alter probe uptake into 5-HT axons, but co-incubation with noribogaine (2 μM for
30 minutes) or 5-cyano-ibogamine (2 μM for 30 minutes) ablated SERTlight probe uptake.
(C) Left, zoomed-out microscopy image in DS (Scale bar: 20 μm) showing axonal strings
and the location of the inset image shown to the right (Scale bar: 7 μm). In-between
images, a mouse brain atlas representation highlighting the dorsal striatum (DS) in red
(Bregma: -3.3 mm, Allen Brain Institute). For the inset images to the right, the same
treatment conditions as in B above.
(D) Two-photon images in DS showing the dose-response of co-incubating SERTlight (10
μM for 30 minutes) with 5-cyano-ibogamine. Marked labeling inhibition is observed at 0.2
μM concentration of 5-cyano-ibogamine.
(E) Left, mouse brain atlas image highlighting the barrel cortex (SSp2/3) region containing
sparse 5-HT axonal projections (Bregma: -1.0 mm, Allen Institute). Images to right (scale
bar: 7 μm), the same treatment conditions as in B above.
(F) Vertical organization of panels, top: mouse brain atlas image highlighting the small
DR region (Bregma: -4.5 mm, Allen Brain Institute). Image below shows SERTlight
staining of 5-HT neuronal cell bodies, the larger objects with darker nuclei, and punctate
staining of dendrites. From top to bottom, co-incubation of SERTlight with citalopram
(positive control) and increasing concentrations of noribogaine (10, 30, 50, and 100 μM)
shows weak inhibitory potency of noribogaine, but not citalopram, in this brain region. For
all panels, representative images from n = 3 mice, three slices per mouse per region.
We next examined the effect of ibogaine, noribogaine, and 5-cyano-ibogamine on mouse
VMAT2 (mVMAT2) function in acute mouse brain slices using the fluorescent VMAT2
substrate, FFN200. We previously demonstrated that FFN200 labels synaptic vesicle
clusters in a mVMAT2-dependent manner in the monoaminergic axons in the striatum
(Figure 5A).70 FFN200 affords a highly dense punctate labeling pattern which is
attenuated by VMAT2 inhibitors, such as dihydrotetrabenazine (dhTBZ, 2 μM), (Figure
5b). In addition to a qualitative assessment, the punctate pattern was quantified (see
Methods for details) and confirmed large inhibitory effects by ibogaine and noribogaine
(each at 2 μM), consistent with their sub-micromolar potency at VMAT2. In comparison,
the weaker VMAT2 inhibitor, 5-cyano-ibogamine (2 μM), showed no inhibitory effects at
the equivalent concentration. These outcomes support the mechanistic model in which
ibogaine and noribogaine directly inhibit VMAT2, an intracellular molecular target
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expressed on monoamine synaptic vesicles, and thus are expected to limit the synaptic
vesicular neurotransmitter pools by drug exposures reached by administering biologically
active doses (> 2 μM, after 10 mg/kg, see pharmacokinetics results below).
The results obtained with SERTlight and FFN200 support a model in which noribogaine
modulates both SERT and VMAT2 in the 5-HT presynaptic boutons, as well as VMAT2 in
the DA and NE presynaptic boutons and release sites at relevant brain exposures (Figure
2B).
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Figure 5. Inhibition of VMAT2 by iboga alkaloids visualized with resolution of
individual synaptic vesicle clusters of monoamine axons in the brain.
(A) A graphical sketch of the imaging method visualizing VMAT2 transport in the brain. A
monoaminergic axonal bouton and release site (in either 5-HT, DA, or NE axons) where
intracellular neurotransmitter or FFN200 (as a fluorescent substrate) are transported into
the synaptic vesicles. The puncta in the microscopy images represent individual axonal
vesicle clusters.
(B) Left panel, mouse brain atlas image highlighting the dorsal striatum (DS) region
containing high density of DA, but also 5-HT and NE neuronal axonal projections
(Bregma: -3.3 mm, Allen Brain Institute). Top middle panel (vehicle, DMSO), incubation
of acute mouse brain slices with FFN200 (10 μM for 30 minutes) leads to probe
accumulation in VMAT2-expressing vesical clusters in WT mice giving a dense punctate
pattern imaged by two-photon microscopy. Top right panel (dhTBZ), co-incubation of
acute mouse brain slices with FFN200 (10 μM for 30 minutes) and the VMAT2 inhibitor
dhTBZ (2 μM for 30 minutes) inhibited the labeling pattern (positive control). Bottom right
and middle panels: co-incubation of FFN200 (10 μM for 30 minutes) with ibogaine (2 μM
for 30 minutes) or noribogaine (2 μM for 30 minutes) completely inhibited FFN200 uptake.
Bottom left panel: coincubation with 5-cyano-ibogamine (2 μM for 30 minutes) under the
same conditions as above had no effect on labeling pattern of FFN200.
(C) Quantification of the number of puncta per image under different conditions. Ex./em.
for FFN200: 740 nm/460±25 nm. Scale bar for images: 20 μm. Representative images
from n = 3 mice, three slices per mouse.
Ibogaine and noribogaine do not induce catalepsy despite their VMAT2 inhibitory
activity. VMAT2 inhibitors at sufficient doses induce catalepsy in humans and animals,
characterized by an immobile position and lack of volitional motor behavior, a
consequence of dopamine depletion in the striatum and basal ganglia. We used a simple
bar test to determine catalepsy in mice where the animals are situated in the instrument
in a rearing position with the front paws placed on an elevated bar (Figure 6A). Under
vehicle control conditions, animals come off the bar immediately (< 2 – 4 seconds),
whereas the cataleptic state is determined by a time threshold (30 – 60 s) of remaining
with both paws on the bar.71,72 In this manner, catalepsy in mice can be readily
differentiated from sedation, which is a non-specific readout of suppression of
spontaneous locomotor behavior as measured by placing animals in a novel arena (open
field, OF, test, (Figure 6A)).73
We used TBZ, an established selective VMAT2 inhibitor, as a positive control. As
expected, TBZ induced both sedation in the open field test and catalepsy in the bar test
in a dose-dependent manner (Figure 6A). In contrast, noribogaine did not induce
catalepsy even at high doses (30, 50 and 80 mg/kg, s.c.), whereas the locomotion was
strongly suppressed already at 30 mg/kg in both male and female mice (Figure 6B).
Similarly, ibogaine did not induce catalepsy while suppressing locomotion, but the
assessment of catalepsy at higher doses (30 mg/kg and higher) was prevented by strong
tremors, a recognized effect of ibogaine and several other natural iboga alkaloids (Figures
S13-S15).74 After administration of high doses of noribogaine or other iboga compounds,
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we did not observe a loss of righting reflex (LORR), indicating that the heavy sedation
and catalepsy states were not confounded by anesthesia (Figure 7).75–77
The potent VMAT2 inhibitor, N-ethyl-noribogaine, also showed a lack of catalepsy up to
30 mg/kg, while this dose completely suppressed locomotion. However, at an even higher
dose of 50 mg/kg, catalepsy was induced at the 60-minute mark, while trending toward
cataleptic states at the 30 and 90 minutes post drug administration (Figure 6C). The
difference in cataleptic effects between noribogaine and N-ethyl-noribogaine is not due to
a relatively lower brain penetration by noribogaine, as both compounds produce
comparable total brain concentrations (Figure S11). However, due to significantly higher
nonspecific protein retention of N-ethyl-noribogaine (both in plasma and tissue),
noribogaine at the same dose shows a nearly three-fold greater estimated free drug
exposure in the brain, in terms of both maximum concentration (Cmax ) and total drug
exposure (AUC, area under the curve, Figure S11) (given 50 mg/kg of each compound,
s.c.: Cmax, noribogaine = 31 μM versus Cmax, N-Et-noribogaine = 11 μM (Figure 6D)). Thus, the
greater VMAT2 inhibitory potency of N-ethyl-noribogaine (IC50, hVMAT2 = 70 nM) versus
noribogaine IC50, hVMAT2 = 570 nM), as determined in vitro, likely underlies the observed
differences in catalepsy in vivo.
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✱✱
✱
✱✱✱✱
noribogaine
(VMAT2 ≈ SERT)
✱✱✱
✱✱✱
✱✱✱✱
Figure 6. Ibogaine and noribogaine do not show behavioral signs of monoamine
depletion.
(A) Tetrabenazine acutely induces catalepsy as evidenced by the catalepsy bar test for
over 90 min (n = 5), with the severity following a dose-response trend (n = 5 - 9). This
diminishes also the observed locomotor activity in an open-field test (n = 4 - 8). (B)
Noribogaine administration does not result in catalepsy in male (n = 5), nor female mice
(n = 4), but produce sedation-like behavior resulting in diminished ambulatory behavior
(n = 4 - 8), presented as total distance traveled over 60 min. (C) High doses of N-ethyl-
noribogaine induces catalepsy (n = 4 - 9) and suppresses locomotor activity in an open
field (n = 4 - 8). (D) Noribogaine administration rapidly produces high, freely available
brain concentration levels. N-ethyl-noribogaine is no less brain penetrant, but significantly
less available compared to noribogaine due to its high nonspecific brain tissue
homogenate binding. Pharmacokinetic data and derived parameters are available in the
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supplementary information file (Figure S11). Compounds were administered by s.c.
injection. Data were analyzed using one-way ANOVA followed by Dunnett’s post hoc test.
All values represented as mean ± SEM, ****p < 0.0001, ***p < 0.001, **p < 0.01, *p <
0.05.
The observation that N-ethyl-noribogaine, a potent VMAT2 inhibitor with high brain
bioavailability, requires high doses and brain concentrations to induce catalepsy suggests
that the iboga matrix pharmacology, the complex pharmacological background of iboga
alkaloids, exerts a protective effect against monoamine tissue depletion and catalepsy.
To test this hypothesis, we examined the effect of noribogaine on TBZ-induced catalepsy
in mice. First, we used a sub-threshold dose of TBZ to be able to observe effects in either
direction, namely the suppression or amplification of catalepsy (10 mg/kg TBZ). Indeed,
we found that noribogaine alleviated the cataleptic activity of TBZ (Figure 7A). At a higher
dose of TBZ (20 mg/kg) that induces full expression of catalepsy, noribogaine still showed
a dose-dependent trend, and a statistically significant effect at a high dose (50 mg/kg),
toward attenuating the TBZ-induced cataleptic effects. Ibogaine had a similar attenuating
effect even at low dose (3 mg/kg, Figure S13). Thus, the catalepsy protection hypothesis
of iboga compounds is supported by three points: 1) noribogaine does not induce
catalepsy by itself even at high non-toxic doses, 2) noribogaine and ibogaine attenuates
TBZ-induced catalepsy, and 3) N-ethyl-noribogaine (a potent VMAT2 blocker) only
induces catalepsy at high doses and brain concentrations (Figure S14). For comparison,
we also examined the effect of a selective SERT inhibitor (citalopram, 10 mg/kg, S.C.) on
a sub-threshold TBZ dose, which showed an opposite effect to that of noribogaine,
leading to amplification of TBZ’s cataleptic effects (Figure 7B). This observation is
consistent with previous reports in rodents in which SSRIs increased the catalepsy and
other motor effects such as oral tremors induced by TBZ or haloperidol;71,78 and humans
in which SSRIs have been reported to exacerbate the motor deficits in a segment of
Parkinson’s patients.79 Our results indicate that the SERT blockade and transient
elevation of 5-HT induced by noribogaine in the NAc and striatum cannot explain its
catalepsy mitigating effects. Instead, we propose that there is a functional interplay
between VMAT2 inhibition and the iboga matrix pharmacology that moderates the
monoamine levels and or monoamine receptor signaling in vivo. Previous neurochemistry
studies showed that ibogaine and noribogaine induced a transient decrease of
extracellular dopamine concentration in the striatum, as well as a strong tissue reduction
of dopamine throughout the brain.20 However, at these doses, ibogaine (e.g., 40 mg/kg)
did not induce a complete dopamine depletion and catalepsy. To our knowledge,
catalepsy had not been previously described for ibogaine or noribogaine in rodents. In
humans, high doses of ibogaine (> 10 mg/kg, P.O.) can induce ataxia, but not catalepsy.18
Anecdotally, very high doses of ibogaine (> 20 mg/kg) can lead to anesthesia-like states,
but catalepsy has not been reported.8
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Figure 7. Ibogaine and noribogaine attenuate tetrabenazine-induced catalepsy.
(A) Effect of noribogaine administration on TBZ-induced catalepsy at sub-threshold (10
mg/kg) and full effect (20 mg/kg) doses (all groups n = 10). (B) Citalopram potentiated
catalepsy effect of TBZ 10 mg/kg (n = 10, except veh+CIT n = 5). (C) Loss of righting
reflex (LORR) was assessed one-hour post injection (n = 3). Data analyzed using one-
way ANOVA followed by Dunnett’s post hoc test. All values represented as mean ± SEM,
*p < 0.05.
Discussion
In this report, we examine the pharmacological profile of iboga alkaloids at monoamine
neurotransmitter transporters, with a focus on the parent compound, ibogaine, its main
metabolite, noribogaine, and a small series of iboga analogs. We find that ibogaine and
noribogaine exhibit a complex monoamine modulatory profile by inhibiting three or more
transporters within a pharmacologically relevant concentration range.
Specifically, we demonstrated that ibogaine and noribogaine inhibit the transport function
of the vesicular transporter VMAT2 with sub-micromolar potency, using a fluorescent
VMAT2 substrate (FFN206) in cell-based assays. We also demonstrated the inhibition of
VMAT2 by ibogaine and noribogaine in synaptic vesicle clusters of intact monoamine
axons in mouse brain, using two-photon microscopy imaging. Thus, we provide evidence
for VMAT2 transport inhibition by iboga alkaloids and the potency range of this effect (sub-
micromolar to low micromolar, Figure 5) in two experimental systems. Ibogaine (IC50,
hVMAT2 = 390 nM) and noribogaine (IC50, hVMAT2 = 570 nM) have similar inhibitory potency
at VMAT2. We did not elucidate the exact mechanism of this inhibitory effect, as it could
✱
✱
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B) C)
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result from the iboga alkaloids acting as 1) VMAT2 non-substrate inhibitors, 2) substrate
inhibitors, or 3) lipophilic bases that diminish the vesicular pH gradient. The third option
is less likely for ibogaine and noribogaine since these two alkaloids possess markedly
different lipophilicity while exerting comparable potencies on the uptake of VMAT2
fluorescent substrates. However, the base effect can contribute to the greater potency of
more lipophilic N-ethyl-noribogaine and 10-ethoxy-ibogamine, in a similar manner as
proposed for amphetamine, which functions, at least in part, as a lipophilic base at
synaptic vesicles.80 This question will be addressed in future studies.
We also examined the effect of iboga compounds on two types of monoamine plasma
membrane transporters, the uptake 1 and uptake 2 transporters. In line with previous
results reported in the literature,20 we show that noribogaine is about 10-fold more potent
than ibogaine at inhibiting hSERT as determined using the SERT fluorescent substrate
APP+ in cell-based assays. Noribogaine has a comparable inhibitory potency at hSERT
(IC50, hSERT = 280 nM) and hVMAT2 (IC50, hSERT = 570 nM, Figures 3 and S1), exhibiting an
uncommon pharmacological profile of dual inhibition of these two critical transporters at
5-HT synapses and release sites. We proposed the term “synaptic reuptake inhibitors” or
“SynRIs” to highlight this interesting mechanistic feature and contrast it to the well-known
VMAT2 inhibitors and SSRIs (Figures 3 and S10). The inhibition of OCT2, identified here
as a novel molecular target of iboga alkaloids, may be pharmacologically relevant in vivo,
considering the estimated free brain concentrations of noribogaine based on the
pharmacokinetic studies reported here (Cmax ~ 6.6 μM after 10 mg/kg, and 31 μM after 50
mg/kg, s.c., Figures 6 and S11), and previous reports in humans (Cmax ~ low micromolar
after 10 mg/kg of oral ibogaine in opioid-dependent individuals).18 OCT2 certainly needs
to be entered into the iboga matrix of known targets, particularly for SAR studies with new
analogs.81
The presented SAR study showed that the relative potencies at SERT and VMAT2 can
be tuned over a broad range, identifying analogs with a balanced SynRI profile (e.g.,
noribogaine, oxa-noribogaine), dominant VMAT2 (N-ethyl-noribogaine), and dominant
SERT (5-cyano-ibogamine) (Figures 3 and S1-S2). We also determined that none of the
iboga compounds - with varying SERT inhibitory potency - induce release of [3H] 5-HT in
synaptosomes, confirming the non-substrate inhibitory effect at SERT, consistent with a
previous report on ibogaine (Figure S12).69 The structural dimensions of the iboga
compounds, in which the aliphatic amino group of the tryptamine unit is embedded in the
bulky isoquinuclidine ring system, are too large for the transport to take place through
SERT on a reasonable time scale, in contrast to the smaller known SERT substrates and
5-HT releasers. However, a recent report claimed a partial [3H] 5-HT release (Emax~30%)
induced by noribogaine in SERT-transfected cells.63 With regard to in vivo
neurochemistry, although there is a single report claiming a 5-HT release induced by
ibogaine in nucleus accumbens,82 other studies described results consistent with a SERT
non-substrate inhibition profile.17,20
We further probed the effect of iboga alkaloids on SERT transport in acute mouse brain
tissue with subcellular spatial resolution enabled by the state-of-the-art imaging probe,
SERTlight, and two-photon microscopy.50 While noribogaine (2 μM) completely inhibited
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the axonal SERT in three different brain regions, as expected, it was far less potent at
inhibiting SERT in 5-HT neuronal cell bodies and dendritic compartments (> 50-fold
difference; Figure 4). While this finding was surprising, there is a precedent for different
binding potencies of noribogaine at VMAT2 in distinct human brain regions (IC50, binding,
striatum = 29.5 μM versus IC50, binding, cortex = 5 μM).48 It has been previously demonstrated
that ibogaine is an atypical SERT inhibitor (non-competitive inhibition) that binds and
stabilizes SERT in inward-open conformational states, in contrast to cocaine-based
blockers or SSRIs that bias the SERT conformational dynamics toward outward-facing
conformations.83,84 It has been proposed that the pharmaco-chaperone effect of iboga
compounds at SERT (along with DAT and likely NET) is related to the stabilization of
inward-open conformational states sampled by the transporter in its folding and trafficking
pathway.85 Inspired by the ibogaine’s mode of action, more potent SERT
pharmacochaperones were generated and conformation-selective SERT ligands were
developed via computational methods.22,86 On this background of rich iboga SERT
pharmacology, we speculate that noribogaine “detects” different SERT conformational or
functional states in the brain, which may be related to post-translational modifications and
or complexation dynamics with ancillary proteins, transporter-associated chaperones, or
cytoskeleton proteins, as part of the local membrane composition and cellular functional
states.87,88
Considering the findings of this study and prior literature, a complex picture of monoamine
neurotransmission modulation by ibogaine and noribogaine emerges (Figure 2). The
iboga compounds inhibit monoamine transporters known to play critical roles in
monoamine neurotransmission, including the synaptic vesicle transporter VMAT2, plasma
membrane monoamine transporters of uptake 1 family (most notably SERT), and the
uptake 2 transporter OCT2, expressed on neuronal and glial cells. The dual or multiple
site modulation predicts complex, non-linear effects on neurotransmission, especially
when considering functional couplings between the different neurotransmitter pools (i.e.
vesicular, cytoplasmic, and extracellular) and the complex mutual interactions between 5-
HT and catecholamines.89–91
The updated monoamine transporter profile of the iboga compounds provides a new
explanatory model for the questions posed previously based on the extensive body of
neurochemical literature: namely, why do iboga compounds have such a profound effect
on dopamine metabolism (a strong dopamine decrease and metabolite DOPAC increase
in total tissue content in most brain regions), while the effect on 5-HT metabolism is
modest (no or small decrease in 5-HT and a modest decrease of metabolite 5-HIAA).20
The direct inhibition of VMAT2 has an important role in the explanatory hypothesis; while
ibogaine and noribogaine act as VMAT2 transport inhibitors in vitro and in vivo, they do
not appear to inhibit DAT in vivo (in vitro inhibition potency at DAT is more than one log
unit weaker compared to VMAT2; Figure S4). Thus, the effect of the iboga compounds on
dopamine metabolism and neurotransmission is dominated by the VMAT2 inhibitory effect
and largely the absence of DAT inhibition. This model is also consistent with the effect of
ibogaine and noribogaine on extracellular dopamine: generally, a decrease in striatum,
and no effect or a decrease in NAc, as well as attenuation of cocaine-induced dopamine
increase in NAc and striatum.20,92 The lack of DAT inhibition by iboga compounds in vivo,
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and VMAT2-mediated depletion of vesicular dopamine pools explains the behavioral
effects in which ibogaine decreases the ambulatory stimulation by cocaine, an effect
dependent on the vesicular release of dopamine via exocytosis.20 Thus, ibogaine and
noribogaine as VMAT2 inhibitors limit the accumulation of DA into synaptic vesicles,
resulting in increased metabolism of dopamine and the neurochemical signature of
VMAT2 inhibitors (decreased tissue dopamine and increased dopamine metabolites,
Figure 5).
In contrast, at 5-HT axonal release sites, noribogaine acts as a SynRI, a dual inhibitor of
VMAT2 and SERT. In this manner, the re-uptake of 5-HT released via activity-dependent
exocytosis is limited by SERT inhibition (and potentially OCT2 inhibition), which protects
5-HT from extensive metabolism within 5-HT neurons. VMAT2 inhibition likely contributes
to the temporal profile and firing pattern of 5-HT transmission (transient increase of
extracellular 5-HT in NAc and striatum) post ibogaine or noribogaine administration
(Figure 5).58
We propose that the complexity of iboga’s modulation of monoamine neurotransmission
provides clues and insights about the global picture of the iboga matrix pharmacology.
The present results do not suggest non-discriminate inhibition or activation of many
random targets by iboga substances, but rather modulation of a combination of molecular
targets that are functionally coupled in critical and highly tuned processes, such as
monoamine neurotransmission (e.g., SERT/OCT2 and VMAT2, Figure 2). Furthermore,
the effects at certain individual targets are atypical revealing higher order molecular
functions. The prime exhibit is SERT, a pivotal element of serotonergic transmission, in
which several modes of action of the iboga compounds have been reported: including the
acute inhibition of SERT via distinct conformational states, pharmaco-chaperone effect
(the latter effects may modulate the long-term function of SERT), and now the axon
specific inhibitory effects (which may lead to targeted 5-HT circuit modulation). Hence, we
extrapolate the existing evidence and speculate that the iboga matrix pharmacology may
have a deep sophisticated logic based on unique molecular effects at specific targets and
complex combinations of molecular targets and interventions.
A previous study reported displacement of tritiated vesamicol by ibogaine in human brain
(IC50 ≤ 10 μM), suggesting inhibition of the vesicular acetylcholine transporter (VAChT),48
and hence, a likely effect on the vesicular pools and neurotransmission of acetylcholine.
This effect – coupled with the well-established action of iboga compounds as antagonists
of several nicotinic acetylcholine receptors (nAChRs) – indicates multi-pronged
modulation of the cholinergic neurotransmission.93–96 The inhibition of NMDAR by the
iboga compounds as channel blockers is also well documented and adds the glutamate
neurotransmission to the list of critical neurotransmission posts modulated by the iboga
alkaloids.19 Finally, we reported previously that iboga compounds potentiate kinase
signaling pathways activated by the fibroblast growth factor receptors (FGFRs),
suggesting modulation of downstream effectors of receptor tyrosine kinases and
neurotrophic factors, together with the reported re-casting of neurotrophin expression
levels.23,30
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Based on these observations and extrapolations, we put forth a theory that predicts that
the molecular targets or signaling processes reported for the iboga compounds represent
a fragment or a preview of the full pharmacological profile of unprecedented complexity
– which we termed “matrix pharmacology”. We defined this pharmacological category as
modulation of multitudes of molecular targets (often targets that are functionally coupled),
via multiple modes of action, and via weak potency molecular interactions that permeate
the entire information and bioenergy processing matrix. We also propose that this new
concept, or a new pharmacological category, is essential for the interpretation and re-
interpretation of the experimental results in the iboga space. For example, selective
single-target perturbations ought not to be considered in isolation, but in context of the
iboga matrix pharmacology. This is a challenging task that will ultimately require
computational models, to interpret and potentially predict experimental outcomes of
modifications of the iboga matrix pharmacology.
The iboga analogs with a single dominant target are useful tools for stepwise probing and
deciphering the iboga matrix mechanisms. We recently introduced the oxa-iboga
compounds (benzofuran iboga analogs) that have KOR as the dominant target (greater
than one log more potent at KOR versus at other examined targets). These analogs show
atypical signaling and behavioral characteristics (e.g. lack of aversion or pro-depressive
effects in mice) in contrast to standard KOR agonists, which we ascribed, at least in part,
to the interactions of KOR with the iboga matrix pharmacology.31 In the present article,
we introduce additional examples of such iboga analogs with one or two dominant targets:
for example, 5-cyano-ibogamine as a potent SERT inhibitor, and N-ethyl-noribogaine as
an analog with dominant VMAT2 (based on the human receptor profile, or dominant
VMAT2/SERT activity based on rat synaptosomes, Figures 3 and S1-S2 and Table 1).
In this context, the conceptual framework of matrix pharmacology may be useful for
explaining why ibogaine or noribogaine do not induce catalepsy even at high doses, in
contrast to the standard VMAT2 inhibitors. To this end, we examined the effect of varying
VMAT2 potency within the iboga system on mouse behavior. We confirmed that catalepsy
can be readily induced in mice by TBZ, a potent VMAT2 inhibitor, as determined by using
a bar test (Figure 6). Unlike the TBZ positive control, noribogaine did not show any
catalepsy even at very high doses (50 and 80 mg/kg, s.c.) where the 50 mg/kg dose
resulted in > 20 μM estimated maximum concentration of free drug in the brain (Figure
6D), which is 10-times greater than the concentration effecting complete inhibition of
VMAT2 transport in striatal brain slices (2 μM, Figure 5). Examining N-ethyl-noribogaine,
a compound with high VMAT2 potency, catalepsy was not induced by 10 and 30 mg/kg
doses, but only by the top administered dose of 50 mg/kg (Figure S14). Remarkably, a
nanomolar VMAT2 inhibitor, N-ethyl-noribogaine (IC50, hVMAT2 = 70 nM in vitro), did not
induce catalepsy at the estimated maximum brain exposure of 7,000 nM of free drug (30
mg/kg dose). The SynRI profile, the dual VMAT2-SERT inhibition cannot explain these
findings as citalopram had the opposite effect, increasing the catalepsy of TBZ (Figure 7).
We therefore propose that the background iboga matrix pharmacology mitigates or
integrates the consequences of the VMAT2 inhibition effect. This hypothesis was further
supported by demonstrating that noribogaine attenuated the cataleptic effects of TBZ.
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The effect of VMAT2 inhibitors on dopamine levels is well established, as discussed
above, leading to dose-dependent dopamine depletion and catalepsy.97 Simple
explanations based on known effects that mitigate those of TBZ, such as monoamine
oxidases inhibition, DAT blockade, or direct dopamine receptor agonism do not apply in
this case, as ibogaine and noribogaine also buffer the opposite effect of a transient
dopamine increase induced by cocaine (DAT inhibitor) or opioids (indirect circuit
mechanism).20,98 Hence, evidence points to a complex multi-factorial mechanism that
restrains both neurochemical extremes – high and low dopamine levels – and the
behavioral consequences as demonstrated by attenuating the effects of both DAT and
VMAT2 inhibition. Our discussion here focuses on the acute (drug-on) neurochemical and
behavioral effects, which likely shape the long-term sequels of iboga compounds.30 While
much work lies ahead on the path toward elucidation of the full complexity and
sophistication of iboga matrix pharmacology, the observed mitigation of behavioral
consequences of VMAT2 inhibition is an important example.
Conclusions
In summary, the present study brings two major contributions. First, we provide a
comprehensive map of monoamine transporters as primary pharmacological targets of
the iboga alkaloids. For this task, we used a combination of in vitro and ex vivo
experimental methods, including the state-of-the-art optical imaging of transporter
function in brain tissue, to provide the first direct evidence for VMAT2 and OCT2 inhibition.
Second, we propose the concept of iboga matrix pharmacology to advance the
understanding of molecular mechanisms, interpretation of results including the
therapeutic and psycho-spiritual effects, and development of novel iboga analogs. Our
results support the proposed theory that ibogaine and iboga alkaloids are molecular
entities operating via a novel, unprecedented mechanism that likely underlies their
remarkable therapeutic and healing effects.
In the reports of past ethnographers and ethnobotanists, we find descriptions of a
spectrum of effects induced by consumption of the iboga root bark by the indigenous
groups in Gabon; for example, central stimulant (at low doses) or intense psychedelic and
visionary (at high doses) activities. Iboga was characterized as a substance with a major
social impact, serving as a central, unifying agent to local communities.2,99 They speak of
iboga’s ability to transform one’s subjective views of self and the world, release individuals
and social groups from the trauma and difficult living circumstances of post colonialism,
and restore clarity and calm amidst a rapidly changing world and culture around them –
in essence describing, in our interpretation, a unique psycho-social restorative
“technology”. More recently and largely outside Africa, reports suggest profound
therapeutic and healing capabilities of ibogaine across therapeutic indications. These
include substance use disorders (with opioid, cocaine and alcohol), depression and
anxiety, PTSD, mTBI, and potentially chronic traumatic encephalopathy
(CTE).3,4,14,15,100,101 The recent narratives from volunteers across the world, recounting
their subjective experiences during and post ibogaine treatment, are in conceptual
themes similar to the conclusions of the ethnographic studies focused on the African
indigenous communities carried out in the 1950-1960’s that describe personality
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reformatting, worldview resetting, and psychosocial restorative effects.8,102 If the past and
contemporary reports are confirmed in rigorous studies and safe use of ibogaine and
iboga analogs, then these substances would constitute a unique class of therapeutics
and molecular technologies. The present study adds a few new cornerstones to the
molecular puzzle of the iboga pharmacology and puts forth a conceptual framework for
the mechanistic complexity it presents.
TOC Graphic
Associated Content
Supporting Information
The Supporting Information is available free of charge at the following link.
Experimental details including in vitro functional assays, rat brain synaptosome
radioligand uptake and release, and behavioral catalepsy and locomotor activity
evaluation protocols, data analysis, and results, synthetic schemes and protocols,
and NMR spectra.
Author Information
Corresponding Authors
Dalibor Sames - Department of Chemistry and The Zuckerman Mind Brain Behavior
Institute, Columbia University, New York, New York 10027, United States;
orcid.org/0000-0001-6911-2260; Email: ds584@columbia.edu
Authors
Christopher Hwu - Department of Chemistry, Columbia University, New York, New York
10027, United States.
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Václav Havel - Department of Chemistry, Columbia University, New York, New York
10027, United States.
Xavier Westergaard - Department of Biological Sciences, Columbia University, New
York, New York 10027, United States;
Department of Psychiatry, Columbia University Irving Medical Center, New York, New
York 10032, United States.
Adriana M. Mendieta - Department of Chemistry, Columbia University, New York, New
York 10027, United States.
Inis C. Serrano - Department of Chemistry, Columbia University, New York, New York
10027, United States.
Jennifer Hwu - Department of Chemistry, Columbia University, New York, New York
10027, United States.
Donna Walther - Designer Drug Research Unit, Intramural Research Program, National
Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland 21224,
United States.
David Lankri - Department of Chemistry, Columbia University, New York, New York
10027, United States.
Tim Luca Selinger - Department of Chemistry, Columbia University, New York, New
York 10027, United States.
Keer He - Department of Chemistry, Columbia University, New York, New York 10027,
United States; orcid.org/0009-0005-2006-4970.
Rose Liu - Department of Biology, Barnard College, New York, New York 10027, United
States.
Tyler P. Shern - Department of Chemistry, Columbia University, New York, New York
10027, United States.
Steven Sun - Department of Chemistry, Columbia University, New York, New York
10027, United States.
Boxuan Ma - Department of Biological Sciences, Columbia University, New York, New
York 10027, United States.
Bruno González - Department of Chemistry, Columbia University, New York, New York
10027, United States.
Hannah J. Goodman - Department of Chemistry, Columbia University, New York, New
York 10027, United States.
Mark S. Sonders - Division of Molecular Therapeutics, New York State Psychiatric
Institute, New York, New York 10032, United States.
Michael H. Baumann - Designer Drug Research Unit, Intramural Research Program,
National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland
21224, United States.
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Ignacio Carrera - Laboratorio de Síntesis Orgánica, Departamento de Química
Orgánica, Facultad de Química, Universidad de la República, Montevideo, Uruguay
11200.
David Sulzer - Department of Psychiatry, Department of Neurology, Department of
Molecular Pharmacology and Therapeutics, Columbia University Irving Medical
Center, New York, New York 10032, United States;
Division of Molecular Therapeutics, New York State Psychiatric Institute, New York,
New York 10032, United States.
Complete contact information is available at the following link.
Author Contributions
† C.H., V.H., and X.W. contributed equally to this work.
Notes
D. Sames, V.H., C.H., D.L., I.C.S and B.G. are inventors on iboga-related patents. D.
Sames is a co-founder of Gilgamesh Pharmaceuticals. The other authors declare no
competing financial interest.
Acknowledgments
This work was supported by The G Harold & Leila Y Mathers Charitable Foundation (MF-
2107-01880, Iboga X Project, D.Sames. and V.H.), and the National Institute on Drug
Abuse (NIDA) (R01-DA050613 to D. Sames) of the National Institutes of Health (NIH),
and the NIDA Intramural Research Program (NIDA ZIADA00052-17, M.H.B.). We would
like to thank the following philanthropists for the timely support of the Sames iboga
research program: Monica Winsor (Trustee of the William H. Donner Foundation), Jeffrey
C. Walker (Walker Family Foundation), Austin Hearst (The Austin & Gabriela Hearst
Foundation), Scott and Kristin Edmondson (Scott and Kristin Edmondson Charitable Gift
Fund), Zaki Manian, Joshua Mailman (The Joshua Mailman Foundation), and an
anonymous funder. This work was also supported in part by the National Institutes of
Mental Health (NIMH) of the National Institutes of Health (NIH), grant R01MH108186
(awarded to D. Sames and D. Sulzer), and R01DA07418 and the Freedom Together
Foundation (awarded to D. Sulzer). Research reported in this publication was supported
by the Office of The Director, National Institutes of Health of the National Institutes of
Health under Award Number S10OD026749. The content is solely the responsibility of
the authors and does not necessarily represent the official views of the National Institutes
of Health. The authors thank Dr. Gary W. Miller and Mr. Joshua M. Bradner of the
Department of Environmental Health Sciences of Columbia University Mailman School of
Public Health for their gift of hVMAT2-HEK cell cultures that were instrumental to this
work, and Dr. Daniel Wacker and Ms. Audrey Warren of the Departments of
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Pharmacological Sciences, Neuroscience, and Genetics and Genomic Sciences of Icahn
School of Medicine at Mount Sinai for their gift of hOCT1-3-HEK and hPMAT-HEK cell
cultures.
Illustrations presented on Figures 6, 7, S13, S14, and S15 were created from icons
obtained from Biorender.com (Publication License GM27SS5YWS).
References
(1) Bartlett, M. F.; Dickel, D. F.; Taylor, W. I. The Alkaloids of Tabernanthe Iboga. Part
IV.1 The Structures of Ibogamine, Ibogaine, Tabernanthine and Voacangine. J. Am.
Chem. Soc. 1958, 80 (1), 126–136. https://doi.org/10.1021/ja01534a036.
(2) Pope, H. G. Tabernanthe Iboga: An African Narcotic Plant of Social Importance.
Econ Bot 1969, 23 (2), 174–184. https://doi.org/10.1007/BF02860623.
(3) Mash, D. C.; Duque, L.; Page, B.; Allen-Ferdinand, K. Ibogaine Detoxification
Transitions Opioid and Cocaine Abusers Between Dependence and Abstinence:
Clinical Observations and Treatment Outcomes. Front. Pharmacol. 2018, 9, 529.
https://doi.org/10.3389/fphar.2018.00529.
(4) Alper, K. R. Chapter 1 Ibogaine: A Review. In The Alkaloids: Chemistry and
Biology; Academic Press, 2001; Vol. 56, pp 1–38. https://doi.org/10.1016/S0099-
9598(01)56005-8.
(5) Alper, K. R.; Lotsof, H. S.; Kaplan, C. D. The Ibogaine Medical Subculture. Journal
of Ethnopharmacology 2008, 115 (1), 9–24.
https://doi.org/10.1016/j.jep.2007.08.034.
(6) Alper, K.; Bai, R.; Liu, N.; Fowler, S. J.; Huang, X.-P.; Priori, S. G.; Ruan, Y. hERG
Blockade by Iboga Alkaloids. Cardiovasc Toxicol 2016, 16 (1), 14–22.
https://doi.org/10.1007/s12012-015-9311-5.
(7) Rocha, J. M.; Reis, J. A. S.; Bouso, J. C.; Hallak, J. E. C.; dos Santos, R. G.
Identifying Setting Factors Associated with Improved Ibogaine Safety: A Systematic
Review of Clinical Studies. Eur Arch Psychiatry Clin Neurosci 2023, 273 (7), 1527–
1542. https://doi.org/10.1007/s00406-023-01590-1.
(8) Schenberg, E. E.; De Castro Comis, M. A.; Alexandre, J. F. M.; Tófoli, L. F.;
Chaves, B. D. R.; Da Silveira, D. X. A Phenomenological Analysis of the Subjective
Experience Elicited by Ibogaine in the Context of a Drug Dependence Treatment.
Journal of Psychedelic Studies 2017, 1 (2), 74–83.
https://doi.org/10.1556/2054.01.2017.007.
(9) Brown, T. K.; Noller, G. E.; Denenberg, J. O. Ibogaine and Subjective Experience:
Transformative States and Psychopharmacotherapy in the Treatment of Opioid
Use Disorder. Journal of Psychoactive Drugs 2019, 51 (2), 155–165.
https://doi.org/10.1080/02791072.2019.1598603.
(10) Belgers, M.; Leenaars, M.; Homberg, J. R.; Ritskes-Hoitinga, M.; Schellekens, A. F.
A.; Hooijmans, C. R. Ibogaine and Addiction in the Animal Model, a Systematic
Review and Meta-Analysis. Transl Psychiatry 2016, 6 (5), e826–e826.
https://doi.org/10.1038/tp.2016.71.
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
(11) Rodrıguez, P.; Urbanavicius, J.; Prieto, J. P.; Fabius, S.; Reyes, A. L.; Havel, V.;
Sames, D.; Scorza, C.; Carrera, I. A Single Administration of the Atypical
Psychedelic Ibogaine or Its Metabolite Noribogaine Induces an Antidepressant-Like
Effect in Rats. ACS Chem. Neurosci. 2020, 11 (11), 1661–1672.
https://doi.org/10.1021/acschemneuro.0c00152.
(12) Koenig, X.; Hilber, K. The Anti-Addiction Drug Ibogaine and the Heart: A Delicate
Relation. Molecules 2015, 20 (2), 2208–2228.
https://doi.org/10.3390/molecules20022208.
(13) Oaklander, M. Inside Ibogaine, One of the Most Promising and Perilous
Psychedelics for Addiction. Time Magazine. April 2021.
https://time.com/5951772/ibogaine-drug-treatment-addiction/ (accessed 2021-07-
05).
(14) Davis, A. K.; Averill, L. A.; Sepeda, N. D.; Barsuglia, J. P.; Amoroso, T. Psychedelic
Treatment for Trauma-Related Psychological and Cognitive Impairment Among US
Special Operations Forces Veterans. Chronic Stress 2020, 4, 247054702093956.
https://doi.org/10.1177/2470547020939564.
(15) Cherian, K. N.; Keynan, J. N.; Anker, L.; Faerman, A.; Brown, R. E.; Shamma, A.;
Keynan, O.; Coetzee, J. P.; Batail, J.-M.; Phillips, A.; Bassano, N. J.; Sahlem, G. L.;
Inzunza, J.; Millar, T.; Dickinson, J.; Rolle, C. E.; Keller, J.; Adamson, M.; Kratter, I.
H.; Williams, N. R. Magnesium–Ibogaine Therapy in Veterans with Traumatic Brain
Injuries. Nat Med 2024, 30 (2), 373–381. https://doi.org/10.1038/s41591-023-
02705-w.
(16) Mash, D. C.; Staley, J. K.; Baumann, M. H.; Rothman, R. B.; Lee Hearn, W.
Identification of a Primary Metabolite of Ibogaine That Targets Serotonin
Transporters and Elevates Serotonin. Life Sciences 1995, 57 (3), PL45–PL50.
https://doi.org/10.1016/0024-3205(95)00273-9.
(17) Baumann, M. H.; Rothman, R. B.; Pablo, J. P.; Mash, D. C. In Vivo Neurobiological
Effects of Ibogaine and Its O-Desmethyl Metabolite, 12-Hydroxyibogamine
(Noribogaine), in Rats. The Journal of Pharmacology and Experimental
Therapeutics 2001, 297 (2), 531–539. https://doi.org/10.1016/S0022-
3565(24)29567-7.
(18) Knuijver, T.; ter Heine, R.; Schellekens, A. F. A.; Heydari, P.; Lucas, L.; Westra, S.;
Belgers, M.; van Oosteren, T.; Verkes, R. J.; Kramers, C. The Pharmacokinetics
and Pharmacodynamics of Ibogaine in Opioid Use Disorder Patients. J
Psychopharmacol 2024, 38 (5), 481–488.
https://doi.org/10.1177/02698811241237873.
(19) Popik, P.; Layer, R. T.; Fossom, L. H.; Benveniste, M.; Geter-Douglass, B.; Witkin,
J. M.; Skolnick, P. NMDA Antagonist Properties of the Putative Antiaddictive Drug,
Ibogaine. J Pharmacol Exp Ther 1995, 275 (2), 753–760.
(20) Baumann, M. H.; Pablo, J.; Ali, S. F.; Rothman, R. B.; Mash, D. C. Chapter 5
Comparative Neuropharmacology of Ibogaine and Its O-Desmethyl Metabolite,
Noribogaine. In The Alkaloids: Chemistry and Biology; Elsevier, 2001; Vol. 56, pp
79–113. https://doi.org/10.1016/S0099-9598(01)56009-5.
(21) El-Kasaby, A.; Just, H.; Malle, E.; Stolt-Bergner, P. C.; Sitte, H. H.; Freissmuth, M.;
Kudlacek, O. Mutations in the Carboxyl-Terminal SEC24 Binding Motif of the
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
Serotonin Transporter Impair Folding of the Transporter. J Biol Chem 2010, 285
(50), 39201–39210. https://doi.org/10.1074/jbc.M110.118000.
(22) Bhat, S.; Guthrie, D. A.; Kasture, A.; El-Kasaby, A.; Cao, J.; Bonifazi, A.; Ku, T.;
Giancola, J. B.; Hummel, T.; Freissmuth, M.; Newman, A. H. Tropane-Based
Ibogaine Analog Rescues Folding-Deficient Serotonin and Dopamine Transporters.
ACS Pharmacol. Transl. Sci. 2021, 4 (2), 503–516.
https://doi.org/10.1021/acsptsci.0c00102.
(23) Gassaway, M. M.; Jacques, T. L.; Kruegel, A. C.; Karpowicz, R. J.; Li, X.; Li, S.;
Myer, Y.; Sames, D. Deconstructing the Iboga Alkaloid Skeleton: Potentiation of
FGF2-Induced Glial Cell Line-Derived Neurotrophic Factor Release by a Novel
Compound. ACS Chem. Biol. 2016, 11 (1), 77–87.
https://doi.org/10.1021/acschembio.5b00678.
(24) Popik, P.; Layer, R. T.; Skolnick, P. 100 Years of Ibogaine: Neurochemical and
Pharmacological Actions of a Putative Anti-Addictive Drug. Pharmacol Rev 1995,
47 (2), 235–253.
(25) Mash, D. C. IUPHAR – Invited Review - Ibogaine – A Legacy within the Current
Renaissance of Psychedelic Therapy. Pharmacological Research 2023, 190,
106620. https://doi.org/10.1016/j.phrs.2022.106620.
(26) Glick, S. D.; Maisonneuve, I. M.; Szumlinski, K. K. Chapter 2 Mechanisms of Action
of Ibogaine: Relevance to Putative Therapeutic Effects and Development of a
Safer Iboga Alkaloid Congener. In The Alkaloids: Chemistry and Biology; Elsevier,
2001; Vol. 56, pp 39–53. https://doi.org/10.1016/S0099-9598(01)56006-X.
(27) Ona, G.; Reverte, I.; Rossi, G. N.; dos Santos, R. G.; Hallak, J. E.; Colomina, M. T.;
Bouso, J. C. Main Targets of Ibogaine and Noribogaine Associated with Its Putative
Anti-Addictive Effects: A Mechanistic Overview. J Psychopharmacol 2023, 37 (12),
1190–1200. https://doi.org/10.1177/02698811231200882.
(28) Rickli, A.; Moning, O. D.; Hoener, M. C.; Liechti, M. E. Receptor Interaction Profiles
of Novel Psychoactive Tryptamines Compared with Classic Hallucinogens. Eur
Neuropsychopharmacol 2016, 26 (8), 1327–1337.
https://doi.org/10.1016/j.euroneuro.2016.05.001.
(29) Glatfelter, G. C.; Pottie, E.; Partilla, J. S.; Stove, C. P.; Baumann, M. H.
Comparative Pharmacological Effects of Lisuride and Lysergic Acid Diethylamide
Revisited. ACS Pharmacol. Transl. Sci. 2024, 7 (3), 641–653.
https://doi.org/10.1021/acsptsci.3c00192.
(30) Marton, S.; González, B.; Rodríguez-Bottero, S.; Miquel, E.; Martínez-Palma, L.;
Pazos, M.; Prieto, J. P.; Rodríguez, P.; Sames, D.; Seoane, G.; Scorza, C.;
Cassina, P.; Carrera, I. Ibogaine Administration Modifies GDNF and BDNF
Expression in Brain Regions Involved in Mesocorticolimbic and Nigral
Dopaminergic Circuits. Front. Pharmacol. 2019, 10, 193.
https://doi.org/10.3389/fphar.2019.00193.
(31) Havel, V.; Kruegel, A. C.; Bechand, B.; McIntosh, S.; Stallings, L.; Hodges, A.;
Wulf, M. G.; Nelson, M.; Hunkele, A.; Ansonoff, M.; Pintar, J. E.; Hwu, C.; Ople, R.
S.; Abi-Gerges, N.; Zaidi, S. A.; Katritch, V.; Yang, M.; Javitch, J. A.; Majumdar, S.;
Hemby, S. E.; Sames, D. Oxa-Iboga Alkaloids Lack Cardiac Risk and Disrupt
Opioid Use in Animal Models. Nat Commun 2024, 15 (1), 8118.
https://doi.org/10.1038/s41467-024-51856-y.
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
(32) Govender, D.; Moloko, L.; Papathanasopoulos, M.; Tumba, N.; Owen, G.; Calvey,
T. Ibogaine Administration Following Repeated Morphine Administration
Upregulates Myelination Markers 2′, 3′-Cyclic Nucleotide 3′-Phosphodiesterase
(CNP) and Myelin Basic Protein (MBP) mRNA and Protein Expression in the
Internal Capsule of Sprague Dawley Rats. Front. Neurosci. 2024, 18, 1378841.
https://doi.org/10.3389/fnins.2024.1378841.
(33) Biosca-Brull, J.; Ona, G.; Alarcón-Franco, L.; Colomina, M. T. A Transcriptomic
Analysis in Mice Following a Single Dose of Ibogaine Identifies New Potential
Therapeutic Targets. Transl Psychiatry 2024, 14 (1), 41.
https://doi.org/10.1038/s41398-024-02773-7.
(34) Nardou, R.; Sawyer, E.; Song, Y. J.; Wilkinson, M.; Padovan-Hernandez, Y.; De
Deus, J. L.; Wright, N.; Lama, C.; Faltin, S.; Goff, L. A.; Stein-O’Brien, G. L.; Dölen,
G. Psychedelics Reopen the Social Reward Learning Critical Period. Nature 2023,
618 (7966), 790–798. https://doi.org/10.1038/s41586-023-06204-3.
(35) Kristensen, A. S.; Andersen, J.; Jørgensen, T. N.; Sørensen, L.; Eriksen, J.; Loland,
C. J.; Strømgaard, K.; Gether, U.; Simonsen, U. SLC6 Neurotransmitter
Transporters: Structure, Function, and Regulation. Pharmacological Reviews 2011,
63 (3), 585–640. https://doi.org/10.1124/pr.108.000869.
(36) Yang, D.; Gouaux, E. Illumination of Serotonin Transporter Mechanism and Role of
the Allosteric Site. Sci Adv 2021, 7 (49), eabl3857.
https://doi.org/10.1126/sciadv.abl3857.
(37) Belmer, A.; Klenowski, P. M.; Patkar, O. L.; Bartlett, S. E. Mapping the Connectivity
of Serotonin Transporter Immunoreactive Axons to Excitatory and Inhibitory
Neurochemical Synapses in the Mouse Limbic Brain. Brain Struct Funct 2017, 222
(3), 1297–1314. https://doi.org/10.1007/s00429-016-1278-x.
(38) Young, L. W.; Darios, E. S.; Watts, S. W. An Immunohistochemical Analysis of
SERT in the Blood-Brain Barrier of the Male Rat Brain. Histochem Cell Biol 2015,
144 (4), 321–329. https://doi.org/10.1007/s00418-015-1343-1.
(39) Rothman, R. B.; Baumann, M. H. Monoamine Transporters and Psychostimulant
Drugs. European Journal of Pharmacology 2003, 479 (1), 23–40.
https://doi.org/10.1016/j.ejphar.2003.08.054.
(40) Aggarwal, S.; Mortensen, O. V. Overview of Monoamine Transporters. Current
Protocols in Pharmacology 2017, 79 (1), 12.16.1-12.16.17.
https://doi.org/10.1002/cpph.32.
(41) Torres, G. E.; Gainetdinov, R. R.; Caron, M. G. Plasma Membrane Monoamine
Transporters: Structure, Regulation and Function. Nat Rev Neurosci 2003, 4 (1),
13–25. https://doi.org/10.1038/nrn1008.
(42) Rothman, R.; Baumann, M. Therapeutic Potential of Monoamine Transporter
Substrates. CTMC 2006, 6 (17), 1845–1859.
https://doi.org/10.2174/156802606778249766.
(43) Organic Cation Transporters in the Central Nervous System; Daws, L. C., Ed.;
Handbook of Experimental Pharmacology; Springer International Publishing:
Cham, 2021; Vol. 266. https://doi.org/10.1007/978-3-030-82984-1.
(44) Yaffe, D.; Forrest, L. R.; Schuldiner, S. The Ins and Outs of Vesicular Monoamine
Transporters. J Gen Physiol 2018, 150 (5), 671–682.
https://doi.org/10.1085/jgp.201711980.
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
(45) Wu, D.; Chen, Q.; Yu, Z.; Huang, B.; Zhao, J.; Wang, Y.; Su, J.; Zhou, F.; Yan, R.;
Li, N.; Zhao, Y.; Jiang, D. Transport and Inhibition Mechanisms of Human VMAT2.
Nature 2024, 626 (7998), 427–434. https://doi.org/10.1038/s41586-023-06926-4.
(46) Chen, J. J.; Ondo, W. G.; Dashtipour, K.; Swope, D. M. Tetrabenazine for the
Treatment of Hyperkinetic Movement Disorders: A Review of the Literature. Clin
Ther 2012, 34 (7), 1487–1504. https://doi.org/10.1016/j.clinthera.2012.06.010.
(47) Lesch, K.-P.; Waider, J. Serotonin in the Modulation of Neural Plasticity and
Networks: Implications for Neurodevelopmental Disorders. Neuron 2012, 76 (1),
175–191. https://doi.org/10.1016/j.neuron.2012.09.013.
(48) Staley, J. K.; Ouyang, Q.; Pablo, J.; Hearn, W. L.; Flynn, D. D.; Rothman, R. B.;
Rice, K. C.; Mash, D. C. Pharmacological Screen for Activities of 12-
Hydroxyibogamine: A Primary Metabolite of the Indole Alkaloid Ibogaine.
Psychopharmacology 1996, 127 (1), 10–18. https://doi.org/10.1007/BF02805969.
(49) Hu, G.; Henke, A.; Karpowicz, R. J.; Sonders, M. S.; Farrimond, F.; Edwards, R.;
Sulzer, D.; Sames, D. New Fluorescent Substrate Enables Quantitative and High-
Throughput Examination of Vesicular Monoamine Transporter 2 (VMAT2). ACS
Chem Biol 2013, 8 (9), 1947–1954. https://doi.org/10.1021/cb400259n.
(50) Lee, W.-L.; Westergaard, X.; Hwu, C.; Hwu, J.; Fiala, T.; Lacefield, C.; Boltaev, U.;
Mendieta, A. M.; Lin, L.; Sonders, M. S.; Brown, K. R.; He, K.; Asher, W. B.;
Javitch, J. A.; Sulzer, D.; Sames, D. Molecular Design of SERTlight: A Fluorescent
Serotonin Probe for Neuronal Labeling in the Brain. J Am Chem Soc 2024, 146
(14), 9564–9574. https://doi.org/10.1021/jacs.3c11617.
(51) Warren, A. L.; Lankri, D.; Cunningham, M. J.; Serrano, I. C.; Parise, L. F.; Kruegel,
A. C.; Duggan, P.; Zilberg, G.; Capper, M. J.; Havel, V.; Russo, S. J.; Sames, D.;
Wacker, D. Structural Pharmacology and Therapeutic Potential of 5-
Methoxytryptamines. Nature 2024, 630 (8015), 237–246.
https://doi.org/10.1038/s41586-024-07403-2.
(52) Tod, P.; Varga, A.; Román, V.; Lendvai, B.; Pálkovács, R.; Sperlágh, B.; Vizi, E. S.
Tetrabenazine, a Vesicular Monoamine Transporter 2 Inhibitor, Inhibits Vesicular
Storage Capacity and Release of Monoamine Transmitters in Mouse Brain Tissue.
Br J Pharmacol 2024, 181 (24), 5094–5109. https://doi.org/10.1111/bph.17348.
(53) Tatsumi, M.; Groshan, K.; Blakely, R. D.; Richelson, E. Pharmacological Profile of
Antidepressants and Related Compounds at Human Monoamine Transporters. Eur
J Pharmacol 1997, 340 (2–3), 249–258. https://doi.org/10.1016/s0014-
2999(97)01393-9.
(54) Owens, M. J.; Morgan, W. N.; Plott, S. J.; Nemeroff, C. B. Neurotransmitter
Receptor and Transporter Binding Profile of Antidepressants and Their
Metabolites. J Pharmacol Exp Ther 1997, 283 (3), 1305–1322.
(55) Yasumoto, S.; Tamura, K.; Karasawa, J.; Hasegawa, R.; Ikeda, K.; Yamamoto, T.;
Yamamoto, H. Inhibitory Effect of Selective Serotonin Reuptake Inhibitors on the
Vesicular Monoamine Transporter 2. Neurosci Lett 2009, 454 (3), 229–232.
https://doi.org/10.1016/j.neulet.2009.03.049.
(56) Wang, X.; Marmouzi, I.; Finnie, P. S. B.; Bucher, M. L.; Yan, Y.; Williams, E. Q.;
Støve, S. I.; Lipina, T. V.; Ramsey, A. J.; Miller, G. W.; Salahpour, A. Tricyclic and
Tetracyclic Antidepressants Upregulate VMAT2 Activity and Rescue Disease-
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
Causing VMAT2 Variants. Neuropsychopharmacology 2024, 49 (11), 1783–1791.
https://doi.org/10.1038/s41386-024-01914-2.
(57) Meyer, A. C.; Horton, D. B.; Neugebauer, N. M.; Wooters, T. E.; Nickell, J. R.;
Dwoskin, L. P.; Bardo, M. T. Tetrabenazine Inhibition of Monoamine Uptake and
Methamphetamine Behavioral Effects: Locomotor Activity, Drug Discrimination and
Self-Administration. Neuropharmacology 2011, 61 (4), 849–856.
https://doi.org/10.1016/j.neuropharm.2011.05.033.
(58) German, D. C.; McMillen, B. A.; Sanghera, M. K.; Saffer, S. I.; Shore, P. A. Effects
of Severe Dopamine Depletion on Dopamine Neuronal Impulse Flow and on
Tyrosine Hydroxylase Regulation. Brain Res Bull 1981, 6 (2), 131–134.
https://doi.org/10.1016/s0361-9230(81)80037-8.
(59) Nickell, J. R.; Krishnamurthy, S.; Norrholm, S.; Deaciuc, G.; Siripurapu, K. B.;
Zheng, G.; Crooks, P. A.; Dwoskin, L. P. Lobelane Inhibits Methamphetamine-
Evoked Dopamine Release via Inhibition of the Vesicular Monoamine Transporter-
2. J Pharmacol Exp Ther 2010, 332 (2), 612–621.
https://doi.org/10.1124/jpet.109.160275.
(60) Partilla, J. S.; Dempsey, A. G.; Nagpal, A. S.; Blough, B. E.; Baumann, M. H.;
Rothman, R. B. Interaction of Amphetamines and Related Compounds at the
Vesicular Monoamine Transporter. J Pharmacol Exp Ther 2006, 319 (1), 237–246.
https://doi.org/10.1124/jpet.106.103622.
(61) Kruegel, A. C.; Rakshit, S.; Li, X.; Sames, D. Constructing Iboga Alkaloids via C–H
Bond Functionalization: Examination of the Direct and Catalytic Union of
Heteroarenes and Isoquinuclidine Alkenes. J. Org. Chem. 2015, 80 (4), 2062–
2071. https://doi.org/10.1021/jo5018102.
(62) Hughes, A. J.; Hamelink, C. R.; Townsend, S. D. Disrupting Substance Use
Disorder: The Chemistry of Iboga Alkaloids. European Journal of Organic
Chemistry 2024, 27 (36), e202400432. https://doi.org/10.1002/ejoc.202400432.
(63) Iyer, R. N.; Favela, D.; Domokos, A.; Zhang, G.; Avanes, A. A.; Carter, S. J.;
Basargin, A. G.; Davis, A. R.; Tantillo, D. J.; Olson, D. E. Efficient and Modular
Synthesis of Ibogaine and Related Alkaloids. Nat. Chem. 2025, 1–9.
https://doi.org/10.1038/s41557-024-01714-7.
(64) González, B.; Fagúndez, C.; Peixoto de Abreu Lima, A.; Suescun, L.; Sellanes, D.;
Seoane, G. A.; Carrera, I. Efficient Access to the Iboga Skeleton: Optimized
Procedure to Obtain Voacangine from Voacanga Africana Root Bark. ACS Omega
2021, 6 (26), 16755–16762. https://doi.org/10.1021/acsomega.1c00745.
(65) Mori, A.; Mizusaki, T.; Ikawa, T.; Maegawa, T.; Monguchi, Y.; Sajiki, H. Palladium on
Carbon-Diethylamine-Mediated Hydrodeoxygenation of Phenol Derivatives under
Mild Conditions. Tetrahedron 2007, 63 (5), 1270–1280.
https://doi.org/10.1016/j.tet.2006.11.060.
(66) Whittaker, V. P. Thirty Years of Synaptosome Research. J Neurocytol 1993, 22 (9),
735–742. https://doi.org/10.1007/BF01181319.
(67) Johnson, C. B.; Walther, D.; Baggott, M. J.; Baker, L. E.; Baumann, M. H. Novel
Benzofuran Derivatives Induce Monoamine Release and Substitute for the
Discriminative Stimulus Effects of 3,4-Methylenedioxymethamphetamine. J
Pharmacol Exp Ther 2024, 391 (1), 22–29.
https://doi.org/10.1124/jpet.123.001837.
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
(68) Stein, W. The Movement Of Molecules Across Cell Membranes; Academic Press:
New York, 1967.
(69) Wells, G. B.; Lopez, M. C.; Tanaka, J. C. The Effects of Ibogaine on Dopamine and
Serotonin Transport in Rat Brain Synaptosomes. Brain Res Bull 1999, 48 (6), 641–
647. https://doi.org/10.1016/s0361-9230(99)00053-2.
(70) Pereira, D. B.; Schmitz, Y.; Mészáros, J.; Merchant, P.; Hu, G.; Li, S.; Henke, A.;
Lizardi-Ortiz, J. E.; Karpowicz, R. J.; Morgenstern, T. J.; Sonders, M. S.; Kanter, E.;
Rodriguez, P. C.; Mosharov, E. V.; Sames, D.; Sulzer, D. Fluorescent False
Neurotransmitter Reveals Functionally Silent Dopamine Vesicle Clusters in the
Striatum. Nat Neurosci 2016, 19 (4), 578–586. https://doi.org/10.1038/nn.4252.
(71) Tatara, A.; Shimizu, S.; Shin, N.; Sato, M.; Sugiuchi, T.; Imaki, J.; Ohno, Y.
Modulation of Antipsychotic-Induced Extrapyramidal Side Effects by Medications
for Mood Disorders. Prog Neuropsychopharmacol Biol Psychiatry 2012, 38 (2),
252–259. https://doi.org/10.1016/j.pnpbp.2012.04.008.
(72) Mann, A.; Chesselet, M.-F. Chapter 8 - Techniques for Motor Assessment in
Rodents. In Movement Disorders (Second Edition); LeDoux, M. S., Ed.; Academic
Press: Boston, 2015; pp 139–157. https://doi.org/10.1016/B978-0-12-405195-
9.00008-1.
(73) Cunningham, M. J.; Bock, H. A.; Serrano, I. C.; Bechand, B.; Vidyadhara, D. J.;
Bonniwell, E. M.; Lankri, D.; Duggan, P.; Nazarova, A. L.; Cao, A. B.; Calkins, M.
M.; Khirsariya, P.; Hwu, C.; Katritch, V.; Chandra, S. S.; McCorvy, J. D.; Sames, D.
Pharmacological Mechanism of the Non-Hallucinogenic 5-HT2A Agonist Ariadne
and Analogs. ACS Chem Neurosci 2023, 14 (1), 119–135.
https://doi.org/10.1021/acschemneuro.2c00597.
(74) González, J.; Prieto, J. P.; Rodríguez, P.; Cavelli, M.; Benedetto, L.; Mondino, A.;
Pazos, M.; Seoane, G.; Carrera, I.; Scorza, C.; Torterolo, P. Ibogaine Acute
Administration in Rats Promotes Wakefulness, Long-Lasting REM Sleep
Suppression, and a Distinctive Motor Profile. Front Pharmacol 2018, 9, 374.
https://doi.org/10.3389/fphar.2018.00374.
(75) Ma, X.; Peng, J.; Chen, Y.; Wang, Z.; Zhou, Q.; Yan, J.; Jiang, H. Esketamine
Anesthetizes Mice With a Similar Potency to Racemic Ketamine. Dose Response
2023, 21 (1), 15593258231157563. https://doi.org/10.1177/15593258231157563.
(76) Franks, N. P. General Anaesthesia: From Molecular Targets to Neuronal Pathways
of Sleep and Arousal. Nat Rev Neurosci 2008, 9 (5), 370–386.
https://doi.org/10.1038/nrn2372.
(77) Teng, M. Z.; Merenick, D.; Jessel, A.; Ganshorn, H.; Pang, D. S. J. Consistency in
Reporting of Loss of Righting Reflex for Assessment of General Anesthesia in Rats
and Mice: A Systematic Review. Comp Med 2024, 74 (1), 12–18.
https://doi.org/10.30802/AALAS-CM-23-000063.
(78) Podurgiel, S. J.; Milligan, M. N.; Yohn, S. E.; Purcell, L. J.; Contreras-Mora, H. M.;
Correa, M.; Salamone, J. D. Fluoxetine Administration Exacerbates Oral Tremor
and Striatal Dopamine Depletion in a Rodent Pharmacological Model of
Parkinsonism. Neuropsychopharmacology 2015, 40 (9), 2240–2247.
https://doi.org/10.1038/npp.2015.69.
(79) Leo, R. J. Movement Disorders Associated with the Serotonin Selective Reuptake
Inhibitors. Journal of Clinical Psychiatry 1996, 57 (10), 449–454.
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
(80) Sulzer, D.; Sonders, M. S.; Poulsen, N. W.; Galli, A. Mechanisms of
Neurotransmitter Release by Amphetamines: A Review. Progress in Neurobiology
2005, 75 (6), 406–433. https://doi.org/10.1016/j.pneurobio.2005.04.003.
(81) Couroussé, T.; Bacq, A.; Belzung, C.; Guiard, B.; Balasse, L.; Louis, F.; Le
Guisquet, A.-M.; Gardier, A. M.; Schinkel, A. H.; Giros, B.; Gautron, S. Brain
Organic Cation Transporter 2 Controls Response and Vulnerability to Stress and
GSK3β Signaling. Mol Psychiatry 2015, 20 (7), 889–900.
https://doi.org/10.1038/mp.2014.86.
(82) Wei, D.; Maisonneuve, I. M.; Kuehne, M. E.; Glick, S. D. Acute Iboga Alkaloid
Effects on Extracellular Serotonin (5-HT) Levels in Nucleus Accumbens and
Striatum in Rats. Brain Res 1998, 800 (2), 260–268. https://doi.org/10.1016/s0006-
8993(98)00527-7.
(83) Bulling, S.; Schicker, K.; Zhang, Y.-W.; Steinkellner, T.; Stockner, T.; Gruber, C. W.;
Boehm, S.; Freissmuth, M.; Rudnick, G.; Sitte, H. H.; Sandtner, W. The
Mechanistic Basis for Noncompetitive Ibogaine Inhibition of Serotonin and
Dopamine Transporters. J Biol Chem 2012, 287 (22), 18524–18534.
https://doi.org/10.1074/jbc.M112.343681.
(84) Coleman, J. A.; Yang, D.; Zhao, Z.; Wen, P.-C.; Yoshioka, C.; Tajkhorshid, E.;
Gouaux, E. Serotonin Transporter–Ibogaine Complexes Illuminate Mechanisms of
Inhibition and Transport. Nature 2019, 569 (7754), 141–145.
https://doi.org/10.1038/s41586-019-1135-1.
(85) El-Kasaby, A.; Koban, F.; Sitte, H. H.; Freissmuth, M.; Sucic, S. A Cytosolic Relay
of Heat Shock Proteins HSP70-1A and HSP90β Monitors the Folding Trajectory of
the Serotonin Transporter. J Biol Chem 2014, 289 (42), 28987–29000.
https://doi.org/10.1074/jbc.M114.595090.
(86) Singh, I.; Seth, A.; Billesbølle, C. B.; Braz, J.; Rodriguiz, R. M.; Roy, K.; Bekele, B.;
Craik, V.; Huang, X.-P.; Boytsov, D.; Pogorelov, V. M.; Lak, P.; O’Donnell, H.;
Sandtner, W.; Irwin, J. J.; Roth, B. L.; Basbaum, A. I.; Wetsel, W. C.; Manglik, A.;
Shoichet, B. K.; Rudnick, G. Structure-Based Discovery of Conformationally
Selective Inhibitors of the Serotonin Transporter. Cell 2023, 186 (10), 2160-
2175.e17. https://doi.org/10.1016/j.cell.2023.04.010.
(87) Rudnick, G.; Krämer, R.; Blakely, R. D.; Murphy, D. L.; Verrey, F. The SLC6
Transporters: Perspectives on Structure, Functions, Regulation, and Models for
Transporter Dysfunction. Pflugers Arch 2014, 466 (1), 25–42.
https://doi.org/10.1007/s00424-013-1410-1.
(88) Zhang, Y.-W.; Turk, B. E.; Rudnick, G. Control of Serotonin Transporter
Phosphorylation by Conformational State. Proc Natl Acad Sci U S A 2016, 113
(20), E2776-2783. https://doi.org/10.1073/pnas.1603282113.
(89) Courtiol, E.; Menezes, E. C.; Teixeira, C. M. Serotonergic Regulation of the
Dopaminergic System: Implications for Reward-Related Functions. Neurosci
Biobehav Rev 2021, 128, 282–293.
https://doi.org/10.1016/j.neubiorev.2021.06.022.
(90) Peters, K. Z.; Cheer, J. F.; Tonini, R. Modulating the Neuromodulators: Dopamine,
Serotonin, and the Endocannabinoid System. Trends Neurosci 2021, 44 (6), 464–
477. https://doi.org/10.1016/j.tins.2021.02.001.
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
(91) Dagher, M.; Perrotta, K. A.; Erwin, S. A.; Hachisuka, A.; Iyer, R.; Masmanidis, S. C.;
Yang, H.; Andrews, A. M. Optogenetic Stimulation of Midbrain Dopamine Neurons
Produces Striatal Serotonin Release. ACS Chem Neurosci 2022, 13 (7), 946–958.
https://doi.org/10.1021/acschemneuro.1c00715.
(92) Maisonneuve, I. M.; Keller, R. W.; Glick, S. D. Interactions between Ibogaine, a
Potential Anti-Addictive Agent, and Morphine: An in Vivo Microdialysis Study. Eur J
Pharmacol 1991, 199 (1), 35–42. https://doi.org/10.1016/0014-2999(91)90634-3.
(93) Chang, Q.; Hanania, T.; Mash, D. C.; Maillet, E. L. Noribogaine Reduces Nicotine
Self-Administration in Rats. J Psychopharmacol 2015, 29 (6), 704–711.
https://doi.org/10.1177/0269881115584461.
(94) Arias, H. R.; Targowska-Duda, K. M.; Feuerbach, D.; Jozwiak, K. Coronaridine
Congeners Inhibit Human Α3β4 Nicotinic Acetylcholine Receptors by Interacting
with Luminal and Non-Luminal Sites. The International Journal of Biochemistry &
Cell Biology 2015, 65, 81–90. https://doi.org/10.1016/j.biocel.2015.05.015.
(95) Maisonneuve, I. M.; Glick, S. D. Anti-Addictive Actions of an Iboga Alkaloid
Congener: A Novel Mechanism for a Novel Treatment. Pharmacol Biochem Behav
2003, 75 (3), 607–618. https://doi.org/10.1016/s0091-3057(03)00119-9.
(96) Williams, B. M.; Steed, N. D.; Woolley, J. T.; Moedl, A. A.; Nelson, C. A.; Jones, G.
C.; Burris, M. D.; Arias, H. R.; Kim, O.-H.; Jang, E. Y.; Hone, A. J.; McIntosh, J. M.;
Yorgason, J. T.; Steffensen, S. C. Catharanthine Modulates Mesolimbic Dopamine
Transmission and Nicotine Psychomotor Effects via Inhibition of Α6-Nicotinic
Receptors and Dopamine Transporters. ACS Chem Neurosci 2024, 15 (9), 1738–
1754. https://doi.org/10.1021/acschemneuro.3c00478.
(97) Quinn, G. P.; Shore, P. A.; Brodie, B. B. Biochemical and Pharmacological Studies
of RO 1-9569 (Tetrabenazine), a Nonindole Tranquilizing Agent with Reserpine-like
Effects. J Pharmacol Exp Ther 1959, 127, 103–109.
(98) Pletscher, A. The Discovery of Antidepressants: A Winding Path. Experientia 1991,
47 (1), 4–8. https://doi.org/10.1007/BF02041242.
(99) Fernandez, J. W.; Fernandez, R. L. “Returning to the Path”: The Use of Iboga[Ine]
in an Equatorial African Ritual Context and the Binding of Time, Space, and Social
Relationships. Alkaloids Chem Biol 2001, 56, 235–247.
https://doi.org/10.1016/s0099-9598(01)56017-4.
(100) Philipps, D.; Abramson, M. Seeking Relief From Brain Injury, Some Veterans
Turn to Psychedelics. The New York Times. Tijuana, Mexico December 16, 2024.
https://www.nytimes.com/2024/12/16/us/psycjedelic-ibogaine-veteran-brain-injury-
ptsd.html.
(101) Philipps, D. Chronic Brain Trauma Is Extensive in Navy’s Elite Speedboat Crews.
The New York Times. San Diego November 12, 2024.
https://www.nytimes.com/2024/11/12/us/brain-trauma-cte-navy-speedboat.html.
(102) The Teafaerie. Teatime» Hard Reset.
https://www.erowid.org/columns/teafaerie/2014/12/18/hard-reset/ (accessed 2025-
01-17).
(which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission.
The copyright holder for this preprintthis version posted March 10, 2025. ; https://doi.org/10.1101/2025.03.04.641351doi: bioRxiv preprint
