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Targeting ligand-gated ion channels in neurology and psychiatry: Is pharmacological promiscuity an obstacle or an opportunity?


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The traditional emphasis on developing high specificity pharmaceuticals ("magic bullets") for the treatment of Neurological and Psychiatric disorders is being challenged by emerging pathophysiology concepts that view disease states as abnormal interactions within complex networks of molecular and cellular components. So-called network pharmacology focuses on modifying the behavior of entire systems rather than individual components, a therapeutic strategy that would ideally employ single pharmacological agents capable of interacting with multiple targets ("magic shotguns"). For this approach to be successful, however, a framework for understanding pharmacological "promiscuity"--the ability of individual agents to modulate multiple molecular targets--is needed. Pharmacological promiscuity is more often the rule than the exception for drugs that target the central nervous system (CNS). We hypothesize that promiscuity is an important contributor to clinical efficacy. Modulation patterns of existing therapeutic agents may provide critical templates for future drug discovery in Neurology and Psychiatry. To demonstrate the extent of pharmacological promiscuity and develop a framework for guiding drug screening, we reviewed the ability of 170 therapeutic agents and endogenous molecules to directly modulate neurotransmitter receptors, a class of historically attractive therapeutic targets in Neurology and Psychiatry. The results are summarized in the form of 1) receptor-centric maps that illustrate the degree of promiscuity for GABA-, glycine-, serotonin-, and acetylcholine-gated ion channels, and 2) drug-centric maps that illustrated how characterization of promiscuity can guide drug development. Developing promiscuity maps of approved neuro-pharmaceuticals will provide therapeutic class-based templates against which candidate compounds can be screened. Importantly, compounds previously rejected in traditional screens due to poor specificity could be reconsidered in this framework. Further testing will require high throughput assays to systematically characterize interactions between available CNS-active drugs and surface receptors, both ionotropic and metabotropic.
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Targeting ligand-gated ion channels in neurology
and psychiatry: is pharmacological promiscuity an
obstacle or an opportunity?
Matt T Bianchi
, Emmanuel J Botzolakis
Background: The traditional emphasis on developing high specificity pharmaceuticals ("magic bullets) for the
treatment of Neurological and Psychiatric disorders is being challenged by emerging pathophysiology concepts
that view disease states as abnormal interactions within complex networks of molecular and cellular components.
So-called network pharmacology focuses on modifying the behavior of entire systems rather than individual
components, a therapeutic strategy that would ideally employ single pharmacological agents capable of
interacting with multiple targets ("magic shotguns ). For this approach to be successful, however, a framework for
understanding pharmacological promiscuity - the ability of individual agents to modulate multiple molecular
targets - is needed.
Presentation of the Hypothesis: Pharmacological promiscuity is more often the rule than the exception for drugs
that target the central nervous system (CNS). We hypothesize that promiscuity is an important contributor to
clinical efficacy. Modulation patterns of existing therapeutic agents may provide critical templates for future drug
discovery in Neurology and Psychiatry.
Testing the Hypothesis: To demonstrate the extent of pharmacological promiscuity and develop a framework for
guiding drug screening, we reviewed the ability of 170 therapeutic agents and endogenous mol ecules to directly
modulate neurotransmitter receptors, a class of historically attractive therapeutic targets in Neurology and
Psychiatry. The results are summarized in the form of 1) receptor-centric maps that illustrate the degree of
promiscuity for GABA-, glycine-, serotonin-, and acetylcholine-gated ion channels, and 2) drug-centric maps that
illustrated how characterization of promiscuity can guide drug development.
Implications of the Hypothesis: Developing promiscuity maps of approved neuro-pharmaceuticals will provide
therapeutic class-based templates against which candidate compounds can be screened. Importantly, compounds
previously rejected in traditional screens due to poor specificity could be reconsidered in this framework. Further
testing will require high throughput assays to systematically characterize interactions between availabl e CNS-active
drugs and surface receptors, both ionotropic and metabotropic.
A co mmon assumption und erlying drug discovery is
that therapeutic agents with h igher specificity for their
molecular t argets confer better efficacy and fewer side
effects. Indeed, drug disco very efforts traditionally focus
on developing magic bullets - agents that provide the
proverbial surgical strike against critica l players in a
disease process while minimizing collateral damage.
However, there is growing interest in the possibility that
drug promiscuity (defined as clinically meaningful inter-
action between a drug and m ultiple molecular targets)
may actually represent a therapeutic benefit rather than
a liability. If true, then screening for magic shotguns -
therapeutic agents that are rationally promiscuous -
could be a more effective drug discovery strategy [1-6].
This concept is supported by both theoretical and
empirical studies, and is congruent with our current
understanding of biology in general: that is, genes,
* Correspondence:
Neurology Department, Sleep Division, Massachusetts General Hospital,
Boston, MA, USA
Bianchi and Botzolakis BMC Pharmacology 2010, 10:3
© 2010 Bianchi and Botzolakis; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
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proteins, and signaling molecules are multi-functional
and comprise a complex network of interactions
[3,4,7-9]. In sight into the effects of therapeutic agents
upon these networks has been fueled by the recent
explosion in genomic and proteomic investigations,
which have elucidated the complex molecular interac-
tions in disease states[9]. Similarly, protein-protein
interaction networks have yielded elaborate datasets
from organisms spanning yeast, nematodes, and
humans, revealing novel sets of potential therapeutic
targets for disease processes [10-12].
Presentation of the Hypothesis
For disorders of the central nervous system ( CNS),
where highly complex interactions underlie normal
function, drug pro miscuity may be parti cularly relevant.
Drug promiscuity is already well-reco gnized among cer-
tain classes of CNS-active modulators such as general
anesthetics [13,14], anticonvulsants [15], and antipsycho-
tics - and this property may extend to other therapeutic
classes such as anti-dementia drugs [16] and even pur-
portedly high-specificity agents such as selective seroto-
nin re-uptake inhibitors (SSRIs) [17,18]. However, it
remains uncertain which subset of promiscuous interac-
tions is important for clinical efficacy. Potential contri-
butors to th is uncertainty include the fruitful history of
linking off-target interactions with side effects, as well as
the e mphasis on high specificity compounds in drug
development. Despite the clear importance of off-target
interactions with side effects, many drugs acting in the
CNS (including some purported to have high specificity)
have been shown to i nteract with multiple targets at
therapeutically relevant concentrations. One approach to
potentially harness promiscuity as a tool for drug dis-
covery is to ascertain which targets are common among
different drugs in a t herapeutic class, thereby e nriching
for the subset of interactions most likely to be therapeu-
tically relevant. We hypothesize that drug discovery stra-
tegies developed to screen for such rational
promiscuity may reveal novel compounds with thera-
peutic efficacy in diseases of the CNS.
Testing the Hypo thesis
To demonstrate that CNS drugs are generally promiscu-
ous agents and illustrate how mapping promiscuity can
guide drug discovery, we collected published examples
of acute, direct funct ional modulation of ligand-gated
ion channels (LGICs) by a total of 170 pharmaceutical
and endogenous molecules, as demonstrated by in vitro
electrophysiology. Although indirect (signal transduc-
tion) and subacute/chronic (plasticity, gene expression)
effects also likely contribute to the clinical efficacy of
many CNS-active drugs, we focused only on direct func-
tional interactions demons trated with physiological
measurements (ion flux and binding data were consid-
ered insufficient). Although the actions of these 170
modulators on the selected LGICs may or may not b e
functionally relevant in vivo , the degr ee of promiscu ity
illustrates the capacity of this c lass of protein targets to
interact with diverse compounds. The potential drug
discovery impact of recognizing clinically relevant pro-
miscuity includes the idea that compound library mole-
cules previously rejected on account of poor specificity
by in vitro screening could be reconsidered in the con-
text of rational promiscuity.
The ligand-gated ion channel family:
evidence for promiscuous modulation
Figure 1 illustrates the promiscuous modulation of four
, acetylcholine, glycine, and 5HT-3
receptors) by 170 compounds identified in a systematic
manual se arch of the PubMe d database between 1970
and 2008, as demonstrated by in vit ro electrophysiology
studies. These compounds span categories of psychiatric
medications (Additional File 1: Supplementary Table
S1), anesthetics (Additional File 1: Supplementary Table
S2), anticonvulsants (Additional File 1: Supplementary
Table S3), natural extracts (Additional File 1: Supple-
mentary Table S4), am ino acids and ions (Additio nal
File 1: Supplementary Table S5), steroids (Additional
File 1: Supplemen tary Table S6), endogenous substances
(Additional File 1: Supplementary Table S7), drugs of
abuse (Additional File 1: Supplem entary Table S8), mis-
cellaneous medications (Additional F ile 1: S upplemen-
tary Table S9). The EC
, and modulation
percentage are referenced in these tables.
receptors, 56% at nicotinic acetylcholine receptors, 40%
at glycine receptors, and 40% at 5HT-3 receptors. 4 2%
of the compounds interacted with only one LGIC
(located in the four corners of Figure 1), 30% interacted
with two LGICs, 16.5% interacted with three LGICs, and
11% interacted with all four LGICs (located in the cen-
ter of Figure 1). Additional connections may exist, as
not every molecule was tested systematica lly across
these four LGICs. M odulators spanned several cate-
gories, inc luding endogenous species (e.g., amino acids,
ions, steroids) and exogenous molecules (e.g., psychotro-
pic, anticonvulsant, anesthetic, and other FDA-approved
medications). While some of these interactions are
thought to be responsible for clinical efficacy (such as
benzodiazepines potentiating GABA
receptors) or side
effects (such as antibiotics ant agonizing GABA
tors), the physiological relevance (if any) of many of
these interactions is unknown. However, the extent of
promiscuity emphasizes the need for systematic charac-
terization if the hypothesis is to be investigated for drug
discovery purposes. Since the evidence for modulation
Bianchi and Botzolakis BMC Pharmacology 2010, 10:3
Page 2 of 8
was derived from a wide vari ety of sources not explicitly
designed to test for promiscuity, meaningful comparison
of the affinity and efficacy of modulation wa s not possi-
ble (values are neverthele ss shown in Supplemental
Tables, Additional file 1).
It is worth noting that each of these LGICs is actually
comprised of multiple subtypes, each having distinct func-
tional and pharmacological properties. Similar to a recent
pharmacological int eraction network based on databases
of FDA-approved drugs and the ir t argets [19], we have
not presented receptor sub-types, which can have pro-
found influence on modulation. For example, GABA
receptors are assembled as heteropentamers from a neu-
ronal repertoire of 19 subunit genes, and subunit compo-
sition is known to influence modulation[20]. The level of
complexity further increases when the promiscuous nat-
ure of the neurotransmitters themselves is considered.
For example, in addition to binding to GABA
receptor s,
the neurotransmitter GABA binds to two additional
receptor classes (metabotropic GABA
and ionotropic
receptors), as well as to a subset of glycine recep-
tors in vivo [21,22]. In fact, the ability of classical neuro-
transmitters to interact directly with non-canonical
targets is well- recognized: glycine is a co-agonist for
NMDA-type glutamate receptors, serotonin can activate
nicotinic acetylcholine receptors, and dopamine is an ago-
nist at serotonin re ceptors. Mo reover, experimental mea-
surements o f modulation are themselves influenced by
receptor properties s uch a s agonist affinity, efficacy, and
desensitization [23,24]. Modulation mechanisms can be
influenced by the modulator concentration: neurosteroids
and barbiturates allosterically modulate GABA
at low concentrations, act as direct agonists as higher
concentrations, and open channel blockers at even higher
concentrations concentrations [25-27]. Direct receptor-
receptor interac tions, independent of second messenger
systems, also contributes to complexity [28-31]. Local
drug concentration profiles may also exhibit complex reg-
ulation within and outside synapses, or via lipid rafts that
alter their effective concentration [32].
Figure 1 Promiscuous modulation of ligand-gated ion channels. The four members of the cys-loop family of ligand gated ion channels are
shown as black nodes. Endogenous and exogenous modulators exhibiting electrophysiologically confirmed modulation of one or more of these
channel classes are indicated by a blue line connecting the modulator to the receptor(s). Modulators in the four corners are those showing
documented modulation of only one channel class, while those centrally located modulate all four classes. Endog, endogenous; AA, amion acids;
misc, miscellaneous; anesth, anesthetics; AED, anti-epileptic drug; psych, psychiatric. This figure was generated using Cytoscape software.
Bianchi and Botzolakis BMC Pharmacology 2010, 10:3
Page 3 of 8
Drug-centric promiscuity maps
Drug promiscuity can also be evaluated from the reverse
perspective, focusing i nstead on the ability of a single
therapeutic agent to interact with multiple protein tar-
gets. The most comprehensive approach, illustrated in
Figure 2A using t he example of SSRIs, is to include
both d irect and indirect ta rgets. Although cl assically
thought to be highly selective agents, three points are
immediately apparent from the SSRI map. First, promis-
cuity exists a t the level of direct interactions of SSRIs
with CNS targets [17] . Second, one of th e direct targets,
the rate-limiting step in neurosteroid biosynthesis, leads
to the production of additional promiscuous modulators,
each of which affects various downstream targets.
Finally, the SSRI-induced increase in serotonin concen-
tration potentially impacts numerous serotonin receptor
Figure 2 Promiscuity maps. A. SSRIs interact with multiple classes of ion channels, and increases neurosteroid synthesis (by directly modulating
a rate limiting enzyme activity), in addition to its activity on the serotonin reuptake transporter (SERT). Neurosteroids are themselves promiscuous
modulators of ion channels, and some of these interactions are shown (dotted lines from purple box). The impact of increasing serotonin is
manifest at potentially any of seven categories of serotonin receptor (each with several subtypes), spanning ionotropic, metabotropic, varying
localization, and different second messenger cascades. B. Promiscuity map of direct interactions of SSRIs with various metabotropic receptors and
transporters (polygons), as well as ion channels (rectangles) including K channels (blue), Ca channels (green), LGICs (yellow). Distance from the
central SSRI node approximates the log-scaled affinity of SSRI for the various targets. Concentric dotted circles reflect 3 orders of concentration
magnitude (0.1, 1, and 10 μM). Therapeutic SSRI concentration in vivo is between 1-10 μM, that is, between the middle and outer circle. This
figure was generated using CellDesigner software.
Bianchi and Botzolakis BMC Pharmacology 2010, 10:3
Page 4 of 8
subtypes, spanning multiple signaling processes (pre-
and post-synaptic, excitatory and inhibitory, ionotropic
and metabotropic, and different second messenger
For drug screening purposes, however, mapping only
direct interactions may be more explicitly useful. An
example is shown in Figure 2B, where the direct modu-
lation of multiple targets by SSRIs is illustrated. The
or IC
of SSRIs for each target is approximated
by the radial distance from the center of the map (based
on electr ophysiology dat a for the ion channel tar gets
and on binding data for the metabotropic target recep-
tors). The radius of the outer two concentric circles
spans the range of estimated the rapeutic CNS concen-
tration (1-10 μM) [17]. With this approach, the extent
of drug pro miscuity can easi ly be visualized in reference
to therapeu tically relevant concentrations. Of note,
while the affinity of SSRIs for the primary target, the
serotonin transporter, is ~50 nM, the therapeutic CNS
concentration range in humans is estimated to be more
than 10-fold higher, r aising the possibility of clinically
important interactions with numerous other t argets. It
should also be emphasized that affinity doe s not entirely
capture the potential for significant interaction. For
example, although the EC
for fluoxetine enhancement
receptors was 128 μM, the enhancement was
large (350%), suggesting mod ulation could occur at con-
major metabolite norfluoxetine was over 100× more
potent in the same study (EC
0.7 μM).
Using promiscuity mapping to guide drug discovery
Using promiscuity maps to guide drug discovery cou ld
proceed as follows. First, a drug-centric promiscuity
map akin to that shown in Figure 2B w ould be gener-
ated for each drug in a therapeutic class, possibly group-
ing drugs with similar clinical efficacy (Figure 3). Then,
targets shared by all members of the class would be
identified, thus representing the subset of interactions
presumably linked t o the desired clinical effect. Non-
shared targets would also be identified, as these are pre -
sumably less ther apeutically relevant and/or responsible
Figure 3 A rational promiscuity approach to drug screening. Coverage maps a re generated for individual drugs, here plotted a s relative
affinity for targets A-J indicated by radial distance from the origin (in arbitrary units). Combining the maps clearly illustrates that targets A-F are
shared by all 3 drugs (dotted line). Subsequent screening algorithms would enrich for targets A-F, while avoiding non-shared targets G-J.
Bianchi and Botzolakis BMC Pharmacology 2010, 10:3
Page 5 of 8
for drug-specific side effects. Screening (or design) of
rationally promiscuous drugs would then aim to
reproduce the shared interactions across similarly effica-
cious compounds, while avoiding non-shared targets
(Figure 3). Granted, this strategy may be somewhat
oversimplified sinc e side effects could be shared and
thus selected for in such a prom iscuity analysis. Addi-
tionally, it is conceivable that targets not shar ed by all
members of a class could be relevant for individual
patient differences in efficacy seen clinically. Howeve r,
these are both potentially testable hypotheses through
systematic analysis of promiscuity, followed by rational
design of drugs exhibiting distinct coverage maps. The
currently sparse experimental coverage of possible inter-
actions precludes even preliminary estimates of sha red
targets. Advances in high throughput electrophysiology
will facilitate implementation of this screening strategy.
Implications of the Hypothesis
The in vivo cellular and molecular milieu involves com-
plex interactions between cellular and molecular compo-
nent s. However, because these components are typically
studied experimentally in is olation, it remains largely
uncertain how such complexity influences signaling dur-
ing normal brain funct ion or disease states. Moreover,
few studies have endeavored to explore the effect of
simultaneous endogenous and pharmacological modula-
tors acting on a receptor target, mainly because of the
cumbersome combinatorial nature of studying even a
subset of the possible interactions. Given the evidence
for promiscuity of endogenous as well as therapeutic
modulators of neurotransmitter receptors highlighted
here, we propose that such information may be biologi-
cally and clinically relevant.Indeed,byaimingvarious
high throughput functional assays toward the systematic
elucidation of promiscuity maps, we anticipate that new
vistas of drug disco very will be revealed. One imp ortant
implication of this strategy is that one can re-investigate
existing compounds that have been discarded in early
preclinical studies solely on the basis of failing high spe-
cificity criteria.
The magic shotgun approach to complex disease
Three lines of reasoning argue against the assump-
tion that higher specificity drugs will necessarily confer
increased therapeutic efficacy. First, endogenous
receptors and signaling molecules are themselves
multi-functional, exhibiting b oth ligand-centric and
receptor-centric p romiscuity. Thus, even theoretically
high specificity agents could have unpredictable biologi-
cal impact, if the intended target were involved in many
functions. Second, target promiscuity may be more com-
mon than recognized for many CNS-active therapeutics
[14,15,17,18], raising the possibility that promiscuity in
fact contributes to the clinical efficacy. Finally, there is
growi ng evidence that complex networks are more opti-
mally modulated by mult i-target appr oaches [8], su g-
gesting a paradigm shift from the dominant magic
bullet strategy to what has become known as the
magic sho tgun approach to therapy[3,4,7,34]. Indeed,
to treat most CNS disorders, drugs must limit patholo-
gical neur onal activ ity without disrupting the rich
underlying functionality of the brain. The existing e vi-
dence for promiscuity raises the possibility that m odu-
lating multiple nodes of a ne twork of i nteracting
components may be more appro priate for the complex
pathophysiology of CNS diseases. An intriguing specula-
tion is that highly s pecific drugs could invoke greater
compensatory homeostatic processes, which may relate
to tolerance and/or to side effects. Is it possible that a
multi-pronged modulati on strat egy, with ea ch prong
perhaps providing a relatively small effect (that evades
large homeostatic cellular responses), would not only be
more efficacious, but potentially also reduce side effects?
Recent advances in imaging large networks of neuronal
firing may shed light on the network-level impact of
drugs thought to interact with multiple targets in clini-
cally relevant situations such as depression models [35].
Promiscuity and clinical efficacy of CNS-active drugs
Rational approaches to promiscuity may inform poten-
tial drug discovery strategies that c onsider the patterns
of target modulation in relation to pharmaceutical effi-
cacy as well as side effects. Endogenous signal transduc-
tion pathways, such as G-protein coupled receptors and
receptor kinases, likely also demonstrate modulator pro-
miscuity, and should be considered in addition to ion
channel targets. Several models have been proposed to
address the potential molecular basis of target-receptor
promiscuity based on atomic-level interactions [36], as
well as the propensity for promiscuous versus specific
protein-protein interactions in crowded cellular envir-
onments [37]. Other analysis, arguing in favor of the
importance of specificity, suggested that promiscuity
was more commonly evident in drugs that did not reach
the clinic[38], perhap s due to side effects. Finally, a
recent repor t used ligand-recep tor interaction models to
explore previously unknown off-target interactions
experimentally [5].
The f undamental challenge of m odern CNS pharma-
cology is to determine which aspects of drug promiscu-
ity contribute to clinical efficacy, and which aspects are
responsible for unwanted side effects[39]. To gain novel
insight into normal and pathological physiology as well
as potential therapeutic interventions, a multidisciplinary
effort is required that combines high throughput techni-
ques and informatics approaches. Rational exploration
Bianchi and Botzolakis BMC Pharmacology 2010, 10:3
Page 6 of 8
of the promiscuity parameter space represents one strat-
egy for improvi ng drug d iscovery by usi ng existing drug
classes as a template for future rational design.
Additional file 1: Tables of modulator-target interactions.EC
percent modulation, and references for each modulator-target
Click here for file
S1.DOC ]
The authors thank Drs. Sydney Cash and Verne Caviness for valuable
comments and discussion. MTB receives funding from the Department of
Neurology, Massachusetts General Hospital, and the Clinical Investigator
Training Program: Harvard/MIT Health Sciences and Technology - Beth Israel
Deaconess Medical Center, in collaboration with Pfizer, Inc. and Merck & Co;
EJB receives funding from NIH T32-GM07347 to the Vanderbilt Medical
Scientist Training Program (MSTP).
Author details
Neurology Department, Sleep Division, Massachusetts General Hospital,
Boston, MA, USA.
Medical Scientist Training Program, Vanderbilt University
School of Medicine, Nashville, TN, USA.
Authors contributions
MTB and EJB contributed equally to conceiving the study and its design,
interpretation, figure development, and drafting of the manuscript. MTB
carried out the primary literature analysis. Both authors read and approved
the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 13 October 2009
Accepted: 2 March 2010 Published: 2 March 2010
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Cite this article as: Bianchi and Botzolakis: Targeting ligand-gated ion
channels in neurology and psychiatry: is pharmacological promiscuit y
an obstacle or an opportunity?. BMC Pharmacology 2010 10:3.
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Supplementary resource (1)

... The fusion of network science and drug research was first conceptualized by Andrew L. Hopkins based on the premise of poly-pharmacology-one drug, multiple targets [24]. This holistic view has been appreciated in psychiatry, in which many psychotropic drugs have been shown to exhibit promiscuity as an intrinsic feature of their therapeutic effects [25]. Antipsychotics are prominent examples. ...
Full-text available
Despite advances in pharmacology and neuroscience, the path to new medications for psychiatric disorders largely remains stagnated. Drug repurposing offers a more efficient pathway compared with de novo drug discovery with lower cost and less risk. Various computational approaches have been applied to mine the vast amount of biomedical data generated over recent decades. Among these methods, network-based drug repurposing stands out as a potent tool for the comprehension of multiple domains of knowledge considering the interactions or associations of various factors. Aligned well with the poly-pharmacology paradigm shift in drug discovery, network-based approaches offer great opportunities to discover repurposing candidates for complex psychiatric disorders. In this review, we present the potential of network-based drug repurposing in psychiatry focusing on the incentives for using network-centric repurposing, major network-based repurposing strategies and data resources, applications in psychiatry and challenges of network-based drug repurposing. This review aims to provide readers with an update on network-based drug repurposing in psychiatry. We expect the repurposing approach to become a pivotal tool in the coming years to battle debilitating psychiatric disorders.
... Ionotropic receptors have a variety of triggering mechanisms, including ligand-gated, mechanosensitive, and chemosensitive. The ligand-gated ionotropic channels are highly expressed in a wide variety of tissues and have been successfully targeted to modulate their function since the 1950s (Bianchi and Botzolakis, 2010). ...
Full-text available
Ligand-gated ion channels are an ionotropic receptor subtype characterized by the binding of an extracellular ligand, followed by the transient passage of ions through a transmembrane pore. Ligand-gated ion channels are commonly subcategorized into three superfamilies: purinoreceptors, glutamate receptors, and Cys-loop receptors. This classification is based on the differing topographical morphology of the receptors, which in turn confers functional differences. Ligand-gated ion channels have a diverse spatial and temporal expression which implicate them in key cellular processes. Given that the transcellular electrochemical gradient is finely tuned in eukaryotic cells, any disruption in this homeostasis can contribute to aberrancies, including altering the activity of pro-tumorigenic molecular pathways, such as the MAPK/ERK, RAS, and mTOR pathways. Ligand-gated ion channels therefore serve as a potential targetable system for cancer therapeutics. In this review, we analyze the role that each of the three ligand-gated ion channel superfamilies has concerning tumor proliferation and as a target for the treatment of cancer symptomatology.
... Antidepressant medications are remarkably pleiotropic in their effects. In addition to binding to serotonin and/or norepinephrine transporters (SERT and NET, respectively), their affinity for other neurotransmitter receptors and ligand-gated ion channels may be relevant to their effects (Bianchi and Botzolakis, 2010). In addition, the acute effect on aminergic signaling has the potential to influence a wide range of downstream genetic pathways implicated in neurogenesis, synaptic plasticity, neuronal excitability, and metabolism (Baudry et al., 2011). ...
Full-text available
Changes in gene expression (GE) during antidepressant treatment may increase understanding of the action of antidepressant medications and serve as biomarkers of efficacy. GE changes in peripheral blood are desirable because they can be assessed easily on multiple occasions during treatment. We report here on GE changes in 68 individuals who were treated for 8 weeks with either escitalopram alone, or escitalopram followed by bupropion. GE changes were assessed after 1, 2, and 8 weeks of treatment, with significant changes observed in 156, 121, and 585 peripheral blood gene transcripts, respectively. Thirty-one transcript changes were shared between the 1- and 8-week time points (seven upregulated, 24 downregulated). Differences were detected between the escitalopram- and bupropion-treated subjects, although there was no significant association between GE changes and clinical outcome. A subset of 18 genes overlapped with those previously identified as differentially expressed in subjects with MDD compared with healthy control subjects. There was statistically significant overlap between genes differentially expressed in the current and previous studies, with 10 genes overlapping in at least two previous studies. There was no enrichment for genes overexpressed in nervous system cell types, but there was a trend toward enrichment for genes in the WNT/β-catenin pathway in the anterior thalamus; three genes in this pathway showed differential expression in the present and in three previous studies. Our dataset and other similar studies will provide an important source of information about potential biomarkers of recovery and for potential dysregulation of GE in MDD.
... In this context, it may be important that ADs are promiscuous drugs, and resolving the molecular basis for drug promiscuity may help guide drug development toward either a "magic bullet" (targeting one specific protein) or a "magic shotgun" (targeting multiple proteins; Roth et al., 2004;Hopkins et al., 2006;Bianchi and Botzolakis, 2010;Peters, 2013;Reddy and Zhang, 2013). Targeting multiple molecular pathways and networks, rather than individual proteins (i.e., exploiting drug promiscuity [or polypharmacology]) has proven advantageous (e.g., Ciceri et al., 2014), though the molecular properties that confer polypharmacological promise also may confer risk of toxicity (Peters, 2013). ...
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The two major classes of antidepressants, tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs), inhibit neurotransmitter reuptake at synapses. They also have off-target effects on proteins other than neurotransmitter transporters, which may contribute to both desired changes in brain function and the development of side effects. Many proteins modulated by antidepressants are bilayer spanning and coupled to the bilayer through hydrophobic interactions such that the conformational changes underlying their function will perturb the surrounding lipid bilayer, with an energetic cost (Δ Gdef ) that varies with changes in bilayer properties. Here, we test whether changes in Δ Gdef caused by amphiphilic antidepressants partitioning into the bilayer are sufficient to alter membrane protein function. Using gramicidin A (gA) channels to probe whether TCAs and SSRIs alter the bilayer contribution to the free energy difference for the gramicidin monomer⇔dimer equilibrium (representing a well-defined conformational transition), we find that antidepressants alter gA channel activity with varying potency and no stereospecificity but with different effects on bilayer elasticity and intrinsic curvature. Measuring the antidepressant partition coefficients using isothermal titration calorimetry (ITC) or cLogP shows that the bilayer-modifying potency is predicted quite well by the ITC-determined partition coefficients, and channel activity is doubled at an antidepressant/lipid mole ratio of 0.02–0.07. These results suggest a mechanism by which antidepressants could alter the function of diverse membrane proteins by partitioning into cell membranes and thereby altering the bilayer contribution to the energetics of membrane protein conformational changes.
... As roles for serotonin in β-cell function are also inconclusive ( Isaac et al., 2013;Ohara-Imaizumi et al., 2013), further study will be required to clarify whether serotonergic signaling is a viable therapeutic target for diabetic patients. In addition, neuromodulator drugs are known to be highly promiscuous ( Bianchi and Botzolakis, 2010), therefore, it will be important to test whether other neurotransmitter pathways also affect islet structure and/or β-cell proliferation. This is also emphasized by the fact that neuromodulators make up the largest subcategory among the 131 ARQiv Call compounds, which remain to be further evaluated (>20 compounds, first shaded set in Supplementary file 2). ...
... The observation that fluoxetine can trigger seizures so acutely while its antidepressant effects take weeks to develop is surprising. However, it must be noted that fluoxetine is a highly promiscuous drug, binding the serotonin transporter, but also to muscarinic, histaminic, dopaminergic receptors, as well as ion channels [38,39]. As other drug-induced seizures often arise from an overdose of antimuscarinic or antihistaminic drugs [29,39], one could speculate that fluoxetine activation of these receptors could underlie the observed seizures in our mouse model. ...
Treatment of Alzheimer's disease (AD) patients with the antidepressant fluoxetine is known to improve memory and cognitive function. However, the mechanisms underlying these effects are largely unknown. To unravel these mechanisms, we aimed to treat APPswe/PS1dE9 mice with fluoxetine. Unexpectedly, with time, an increased number of animals displayed seizure behavior and died. Although spontaneous behavioral seizures have been reported previously in this mouse model, the observation of seizures and death consequential to fluoxetine treatment is new. Our results warrant further research on the underlying mechanisms as this may refine the treatment of AD patients.
Whole-organism chemical screening can circumvent bottlenecks that impede drug discovery. However, in vivo screens have not attained throughput capacities possible with in vitro assays. We therefore developed a method enabling in vivo high-throughput screening (HTS) in zebrafish, termed automated reporter quantification in vivo (ARQiv). In this study, ARQiv was combined with robotics to fully actualize whole-organism HTS (ARQiv-HTS). In a primary screen, this platform quantified cell-specific fluorescent reporters in textgreater500,000 transgenic zebrafish larvae to identify FDA-approved (Federal Drug Administration) drugs that increased the number of insulin-producing $beta$ cells in the pancreas. 24 drugs were confirmed as inducers of endocrine differentiation and/or stimulators of $beta$-cell proliferation. Further, we discovered novel roles for NF-$kappa$B signaling in regulating endocrine differentiation and for serotonergic signaling in selectively stimulating $beta$-cell proliferation. These studies demonstrate the power of ARQiv-HTS for drug discovery and provide unique insights into signaling pathways controlling $beta$-cell mass, potential therapeutic targets for treating diabetes.
The increased versatility of frontal and zonal chromatography has become increasingly evident with mass spectrometry. In this chapter we discuss the principles of frontal and zonal affinity chromatography, including their uses in binding affinity determination and binding kinetics. The more recent uses with frontal and zonal-MS applications will also be discussed, including simultaneous frontal affinity chromatography, multiple binding site characterization, receptor subtype confirmation, multiple protein confirmation analysis.
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Although drugs are intended to be selective, at least some bind to several physiological targets, explaining side effects and efficacy. Because many drug-target combinations exist, it would be useful to explore possible interactions computationally. Here we compared 3,665 US Food and Drug Administration (FDA)-approved and investigational drugs against hundreds of targets, defining each target by its ligands. Chemical similarities between drugs and ligand sets predicted thousands of unanticipated associations. Thirty were tested experimentally, including the antagonism of the beta(1) receptor by the transporter inhibitor Prozac, the inhibition of the 5-hydroxytryptamine (5-HT) transporter by the ion channel drug Vadilex, and antagonism of the histamine H(4) receptor by the enzyme inhibitor Rescriptor. Overall, 23 new drug-target associations were confirmed, five of which were potent (<100 nM). The physiological relevance of one, the drug N,N-dimethyltryptamine (DMT) on serotonergic receptors, was confirmed in a knockout mouse. The chemical similarity approach is systematic and comprehensive, and may suggest side-effects and new indications for many drugs.
Full-text available
Current yeast interactome network maps contain several hundred molecular complexes with limited and somewhat controversial representation of direct binary interactions. We carried out a comparative quality assessment of current yeast interactome data sets, demonstrating that high-throughput yeast two-hybrid (Y2H) screening provides high-quality binary interaction information. Because a large fraction of the yeast binary interactome remains to be mapped, we developed an empirically controlled mapping framework to produce a “second-generation” high-quality, high-throughput Y2H data set covering ∼20% of all yeast binary interactions. Both Y2H and affinity purification followed by mass spectrometry (AP/MS) data are of equally high quality but of a fundamentally different and complementary nature, resulting in networks with different topological and biological properties. Compared to co-complex interactome models, this binary map is enriched for transient signaling interactions and intercomplex connections with a highly significant clustering between essential proteins. Rather than correlating with essentiality, protein connectivity correlates with genetic pleiotropy.
Recent advances in molecular biology and complementary information derived from neuropharmacology, biochemistry and behavior have dramatically increased our understanding of various aspects of GABAA receptors. These studies have revealed that the GABAA receptor is derived from various subunits such as α1–α6, β1–β3, γ1–γ3, δ, ε, π, and ρ1–3. Furthermore, two additional subunits (β4, γ4) of GABAA receptors in chick brain, and five isoforms of the ρ-subunit in the retina of white perch (Roccus americana) have been identified. Various techniques such as mutation, gene knockout and inhibition of GABAA receptor subunits by antisense oligodeoxynucleotides have been used to establish the physiological/pharmacological significance of the GABAA receptor subunits and their native receptor assemblies in vivo. Radioligand binding to the immunoprecipitated receptors, co-localization studies using immunoaffinity chromatography and immunocytochemistry techniques have been utilized to establish the composition and pharmacology of native GABAA receptor assemblies. Partial agonists of GABAA receptors are being developed as anxiolytics which have fewer and less severe side effects as compared to conventional benzodiazepines because of their lower efficacy and better selectivity for the GABAA receptor subtypes. The subunit requirement of various drugs such as anxiolytics, anticonvulsants, general anesthetics, barbiturates, ethanol and neurosteroids, which are known to elicit at least some of their pharmacological effects via the GABAA receptors, have been investigated during the last few years so as to understand their exact mechanism of action. Furthermore, the molecular determinants of clinically important drug-targets have been investigated. These aspects of GABAA receptors have been discussed in detail in this review article.
There is growing interest in the concept of network pharmacology, as opposed to specific pharmacological targets, as an important drug discovery paradigm. Also known as the "magic shotgun" paradigm, this strategy involves individual drugs interacting with multiple targets to achieve clinical benefit. Pharmacological promiscuity consistent with this paradigm has been suggested in vitro for antidepressants and anticonvulsants, which interact with many classes of ion channels (among other receptor targets). Although the link between certain "off-target" interactions and drug side effects is well-accepted, the potential linkage between promiscuity and clinical efficacy remains poorly understood. Here we summarize interactions of clinically useful anti-psychotic and anti-dementia medications with a diverse array of ligand- and voltage-gated ion channels. We hypothesize that promiscuous ion channel modulation may contribute to the efficacy of drugs used to treat psychosis and dementia.
Molecular recognition between proteins and their interacting partners underlies the biochemistry of living organisms. Specificity in this recognition is thought to be essential, whereas promiscuity is often associated with unwanted side effects, poor catalytic properties and errors in biological function. Recent experimental evidence suggests that promiscuity, not only in interactions but also in the actual function of proteins, is not as rare as was previously thought. This has implications not only for our fundamental understanding of molecular recognition and how protein function has evolved over time but also in the realm of biotechnology. Understanding protein promiscuity is becoming increasingly important not only to optimize protein engineering applications in areas as diverse as synthetic biology and metagenomics but also to lower attrition rates in drug discovery programs, identify drug interaction surfaces less susceptible to escape mutations and potentiate the power of polypharmacology.
Medical management and drug development for epilepsy emphasizes increasing pharmacological specificity to improve efficacy while minimizing side effects. However, growing evidence supports potential benefits of "magic shotgun" over "magic bullet" approaches to treatment of complex disease processes. We discuss experimental and theoretical evidence suggesting that seizures may be more amenable to a multi-target rather than a high-specificity approach, including evidence that individual anticonvulsants directly modulate a variety ion channel targets, the most direct determinants of neuronal excitability. Although the relevance of this promiscuity remains untested, it may contribute to anticonvulsant efficacy and should therefore be considered in drug development strategies and in therapeutic decision making.
Chemical biology and systems biology have grown and evolved in parallel during the past decade, but the mindsets of the two disciplines remain quite different. As the inevitable intersections between the disciplines become more frequent, chemical biology has an opportunity to assimilate the most powerful ideas from systems biology. Can the integrationist mindset of systems biology liberate chemical biology from the compulsion to reduce everything to individual small molecule-target pairings?
This study investigates the antinociception caused by intradermal (i.d) or intracerebroventricular (i.c.v.) injection of the capsaicin receptor antagonist capsazepine (CPZ), and ruthenium red (RR) (a cation-selective antagonist coupled to vanilloid receptor of capsaicin), on the chemical nociception caused by i.d. injection of formalin (FM) and capsaicin (CAP) into the mouse paw. The i.d. injection of either CPZ or RR in association with FM or CAP, inhibited the early phase, and to a lesser extent the late phase, of the FM, as well as CAP-induced nociception. Given i.c.v., both CPZ and RR caused discrete antinociception in the FM (both phases), while producing graded inhibition of CAP. The actions of CPZ and RR were insensitive to i.p. injection of naloxone (5 mg/kg). These results indicate that i.d. injection of CPZ and RR produce marked antinociception in chemical models of neurogenic pain induced by CAP and FM in mice. However, administered by supraspinal site, both CPZ and RR were inactive in inhibiting FM, but prevented, in a graded manner, CAP-induced algesic response, suggesting the participation of distinct mechanisms in the nociception induced by FM and CAP. Thus, vanilloid selective antagonists seem to be useful tools for investigating the nociception elicited by CAP and FM.
Steady progress in the identification of human pharmacogenetic variants and new discoveries of disease susceptibility genes makes the old notion of one disease/one drug untenable. Advances in the ability to rapidly identify these variants, when coupled with appropriate drug delivery systems, should revolutionize pharmacotherapy.