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Molecular Pharmacology
of Phytocannabinoids
Sarah E. Turner, Claire M. Williams, Leslie Iversen,
and Benjamin J. Whalley
Contents
1 Introduction . . ................................................................................. 62
2Δ
9
-trans-Tetrahydrocannabinol . ............................................................. 63
2.1 Activity at Cannabinoid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 64
2.2 Cannabinoid Receptor Independent Activity .......................................... 68
3Δ
9
-Tetrahydrocannabivarin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.1 Activity at Cannabinoid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 71
3.2 Cannabinoid Receptor Independent Activity .......................................... 73
4 Cannabinol .................................................................................... 74
4.1 Activity at Cannabinoid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.2 Cannabinoid Receptor Independent Activity .......................................... 75
5 Cannabidiol ................................................................................... 76
5.1 Activity at Cannabinoid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 76
5.2 Cannabinoid Receptor Independent Activity .......................................... 77
6 Cannabidivarin . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 83
6.1 Activity at Cannabinoid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 84
6.2 Cannabinoid Receptor Independent Activity .......................................... 84
7 Cannabigerol .................................................................................. 86
7.1 Activity at Cannabinoid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 86
7.2 Cannabinoid Receptor Independent Activity .......................................... 87
S.E. Turner • C.M. Williams
School of Psychology and Clinical Language Sciences and School of Pharmacy, University of
Reading, Earley Gate, Whiteknights, Reading RG6 6AL, UK
e-mail: s.glyn@pgr.reading.ac.uk;claire.williams@reading.ac.uk
L. Iversen (*)
Department of Pharmacology, Oxford University, Mansfield Road, Oxford OX1 3QT, UK
e-mail: les.iversen@pharm.ox.ac.uk
B.J. Whalley
School of Pharmacy, University of Reading, Whiteknights, Reading RG6 6AP, UK
e-mail: b.j.whalley@reading.ac.uk
©Springer International Publishing Switzerland 2017
A.D. Kinghorn, H. Falk, S. Gibbons, J. Kobayashi (eds.), Phytocannabinoids,
Progress in the Chemistry of Organic Natural Products 103,
DOI 10.1007/978-3-319-45541-9_3
61
8 Cannabichromene . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . 88
8.1 Activity at Cannabinoid Receptors . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.2 Cannabinoid Receptor Independent Activity .......................................... 88
9 Conclusions ................................................................................... 90
References . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
1 Introduction
Cannabis sativa contains about 120 phytocannabinoids, which are the C
21
terpenophenolic constituents making up approximately 24% of the total natural
products of the plant [1]. To date, eleven different chemical classes of
phytocannabinoids have been identified (Table 1). The Δ
9
-tetrahydrocannabinol
(1) type class represents the largest proportion, comprising 17.3% of the total
phytocannabinoid content, closely followed by the cannabigerol (6) type (see [1]
for a detailed review of these different classes). The proportion of each chemical
class in the cannabis plant is, however, dependent on the growing conditions,
geographical location, plant processing methods, and plant variety or chemotype.
Thus, these factors influencing the relative proportions of each phytocannabinoid
type will additionally influence the pharmacological effects of whole cannabis
extracts, either through a polypharmacological effect of the phytocannabinoids
themselves, or through modulation of phytocannabinoid effects by the
non-cannabinoid content of the plant [2]. These variances are therefore important
to take into account when assessing the effects of whole cannabis plant extracts. In
this chapter, focus will be made on the seven individual phytocannabinoids that
have been the most thoroughly studied.
Table 1 Constituents of
Cannabis sativa
L. represented as a percentage
of the total phytocannabinoid
content. Adapted from [1]
Chemical class type
Percent of total
phytocannabinoid content (%)
a
1type 17.3
Δ
8
-THC type 1.9
3type 9.6
4type 7.7
7type 7.7
6type 16.3
CBND type 1.9
CBE type 4.8
CBL type 2.9
CBT type 8.7
Miscellaneous type 21.2
a
Total phytocannabinoid content ¼ca. 120
62 S.E. Turner et al.
Phytocannabinoids have been of recreational, therapeutic, and other interest for
thousands of years [3,4]. Elucidation of the structure of the main phytocannabinoid
obtained from cannabis, 1[5], was reported in 1971. This discovery paved the way
for further research that ultimately led to the discovery of the cannabinoid recep-
tors, CB
1
[6], which predominates in the central nervous system, and the principally
peripheral cannabinoid receptor, CB
2
[5]. The mammalian endocannabinoid system
was then discovered [6], including the endogenous cannabinoid receptor ligands
arachidonylethanolamide (AEA) and 2-arachidonylglycerol (2-AG) [7–9]. The
psychotropic effect of 1, mediated by its partial agonist activity at CB
1
receptors,
has limited the extent of its use medicinally and it was removed from the British
Pharmacopeia in 1971, and was declared of no medical benefit and placed under
control in the Misuse of Drugs Act 1971 of the United Kingdom [10]. Despite this,
patient-led self-medication campaigns claimed various therapeutic benefits, such as
control of pain and emesis [11–15], control of seizures [16–21], and anti-
inflammatory properties [17,22], among others. This drove further investigation,
leading to some licensed medications containing 1being now available, such as
Sativex®, which is used for the treatment of spasticity associated with multiple
sclerosis. Although 1also exerts some effects through non-CB receptor targets, the
absence of psychotropic effects associated with the other phytocannabinoids pre-
sent in cannabis has driven research into their discrete pharmacology and molecular
targets that lie outside of the endocannabinoid system.
Over the years, a variety of molecular targets for plant cannabinoids outside the
endocannabinoid system have been identified, such as ion channels, non-CB
1
or CB
2
G-protein coupled receptors, enzymes, and transporters. In this chapter, an overview
of the molecular pharmacology of phytocannabinoids is presented, describing both
targets within the endocannabinoid system and a wide range of other molecular
targets. Since ca. 120 phytocannabinoids have now been identified and many have, as
yet, poorly defined or unknown pharmacological profiles, particular focus is paid to
phytocannabinoids that: (a) are reported to exert a behavioral effect in animal models
or clinical reports, and (b) exert effects via specific molecular targets at sub-
micromolar to low micromolar concentrations, which can realistically be achieved
in vivo due to the lipophilic nature of these compounds [23].
2Δ
9
-trans-Tetrahydrocannabinol
O
OH
1
9
Molecular Pharmacology of Phytocannabinoids 63
2.1 Activity at Cannabinoid Receptors
In 1986, Howlett and colleagues developed a biochemical model system that
allowed the indirect identification of cannabimimetic drugs, i.e. those exhibiting
properties like 1(cAMP assay) [24]. This system provided an indication of canna-
binoid receptor activation by monitoring the ability of a compound to inhibit
forskolin-induced stimulation of cyclic adenosine monophosphate (cAMP) produc-
tion. Along with the many synthetic CB
1
receptor agonists now developed [6,25,
26], 1can inhibit the activity of adenylate cyclase that synthesizes cyclic AMP.
However, in this assay, 1does not inhibit adenylate cyclase to the same extent as
several other synthetic CB
1
receptor agonists, which led to its classification as a
partial agonist at this receptor [27].
Two years later, in 1988, Devane and co-workers developed a radioligand
displacement binding assay using the highly potent, synthetic CB
1
receptor agonist,
CP-55940 [28]. In this assay, 1effectively displaced radiolabeled CP-55940 and
showed low micromolar affinity at the CB
1
receptor (Table 2). The properties of
1as a CB
1
receptor partial agonist were further exemplified in binding assays
assessing ligand-induced changes in GTPγS binding in cell membranes [27,29,
30]. Here, the synthetic CB
1
receptor agonist, JWH-018, increased GTPγS binding
in mouse brain membranes to a much greater extent than 1[29].
Importantly, 1not only activates CB
1
receptors in vitro but also in vivo as well.
In vivo activity of 1at CB
1
receptors was tested in a battery of animal behavior
tasks known to produce outcomes associated with CB
1
receptor activation
[31,32]. The four simple behavioral tests in mice known as the “Billy Martin
Tetrad” were reported, and these are: inhibition of locomotor activity; reduced
sensitivity to pain; reduced body temperature; and immobility (catalepsy) [31]. At
doses of 0.03–20 mg kg
1
(i.v.), 1was active in all of these tests, and the effects
were blocked by the CB
1
receptor antagonist, rimonabant (10 mg kg
1
)[31–
33]. However, it should be noted that rimonabant is not a specific ligand for the
CB
1
receptor when employed at concentrations of >1μM[34,35] and, therefore, at
the concentrations reached in vivo.
With this dose, functional antagonism of these effects could also have been
mediated by other targets of rimonabant such as agonism or antagonism of GPR55
receptors [36], antagonism of A1 adenosine receptors [37], and antagonism of
TRPV1 channels [38].
In a feeding study in rats, 1(0.5–4.0 mg kg
1
) stimulated hyperphagia.
However, while rimonabant predictably inhibited hyperphagia at doses of
>0.67 mg kg
1
, it also stimulated hyperphagia at lower doses. There was no significant
difference in food intake between these two groups and this may be due to the
differences in the feeding pattern being masked by effects on non-specific behavioral
effects such as reduced motor co-ordination induced by 1treatment [39].
There is also in vitro and in vivo evidence that 1binds to, and activates the CB
2
receptor. The binding affinity of 1at CB
2
receptors is, however, lower than that at
CB
1
receptors, as shown in Table 2[29,40]. Evidence of a partial agonist effect of
64 S.E. Turner et al.
Table 2 Examples of K
i
values of Δ
9
-trans-tetrahydrocannibinol (1), Δ
9
-trans-tetra-
hydrocannabivarin (2), cannabinol (3), cannabidiol (4), cannabidivarin (5), cannabigerol (6), and
cannabichromene (7) and half maximal responses where described
K
i
/μM
EC
50
/
IC
50
Assay Cell type Ref.
Δ
9
-Tetrahydrocannabinol (1)
CB
1
0.0061 ND [
3
H] CP55-940 binding assay Whole brain/Rat [28]
0.005 ND [
3
H] CP55-940 binding assay CHO cell membrane/
Human
[158]
0.008 ND [
3
H] CP55-940 binding assay CHO cell membrane/
Mouse
0.013 ND [
3
H] CP55-940 binding assay CHO cell membrane/
Rat
0.021 ND Filtration assay Brain membranes/Rat [86]
0.035 ND [
3
H] CP55-940 binding assay Brain synaptosomal
membrane/Rat
[35]
0.0395 0.013 [
3
H] HU-243 binding assay COS-7 cells/Rat [40]
0.0477 ND [
3
H] CP55-940 binding assay Whole brain/Mouse [90]
0.053 0.0165 [
3
H] CP55-940 binding assay Fibroblast L cells/Rat [87]
0.065 ND [
3
H] HU-243 binding assay Synaptosomal brain
membrane/Rat
[85]
0.08 ND [
3
H] HU-243 binding assay COS-7 cells/Rat
0.0356 0.087 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
CB
2
0.003 ND [
3
H] CP55-940 binding assay CHO cell membrane/
Human
[158]
0.0017 ND [
3
H] CP55-940 binding assay CHO cell membrane/
Mouse
0.0068 ND [
3
H] CP55-940 binding assay CHO cell membrane/
Rat
0.036 ND Filtration assay Spleen membrane/Rat [86]
0.0039 ND [
3
H] CP55-940 binding assay Spleen membrane/Rat [35]
0.040 ND [
3
H] HU-243 binding assay CHO cell/Rat [40]
0.075 0.0418 [
3
H] CP55-940 binding assay CHO cell membrane/
Rat
[87]
0.032 ND [
3
H] HU-243 binding assay COS-7 cells/Rat [85]
0.0084 0.061 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
Δ
9
-Tetrahydrocannabivarin (2)
CB
1
0.075 ND [
3
H] CP55-940 binding assay Whole brain mem-
branes/Mouse
[73]
0.047 ND [
3
H] CP55-940 binding assay Cortical brain mem-
branes/Rat
[72]
0.286 ND [
3
H] rimonabant binding assay Cortical brain mem-
branes/Rat
[160]
0.046 ND [
3
H] CPP-940 binding assay Whole brain/Mouse [90]
(continued)
Molecular Pharmacology of Phytocannabinoids 65
Table 2 (continued)
K
i
/μM
EC
50
/
IC
50
Assay Cell type Ref.
CB
2
0.225 0.038 [
3
H] CP55-940 binding assay CHO cell membrane/
Human
[70]
0.145 0.143 [
3
H] CP55-940 binding assay CHO cell membrane/
Human
[41]
Cannabinol (3)
CB
1
0.326 ND Filtration assay Brain/Rat [86]
0.129 ND [
3
H] CPP-940 binding assay Whole brain/Mouse [90]
1.13 >1[
3
H] CPP-940 binding assay Fibroblast L cells/Rat [87]
0.392 ND [
3
H] HU-243 binding assay Synaptosomal brain
membrane/Rat
[85]
0.211 ND [
3
H] HU-243 binding assay COS-7 cells/Rat
3.2 ND [
3
H] CP55-940 binding assay Sectioned brain/Rat [25]
0.25 ND [
3
H] CP55-940 binding assay Whole brain/Rat [161]
0.74 ND [
3
H] rimonabant binding assay Whole brain/Rat
0.012 0.017 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
0.069 ND [
3
H] CP55-940 binding assay CHO cell/Human [88]
CB
2
0.096 ND Filtration assay Spleen/Rat [86]
0.301 >1[
3
H] CPP-940 binding assay CHO cell membrane/
Rat
[87]
0.126 ND [
3
H] HU-243 binding assay COS-7 cells/Rat [85]
0.016 0.055 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
0.07 0.062 [
3
H] CP55-940 binding assay CHO cell/Human [88]
Cannabidiol (4)
CB
1
>10 ND [
3
H] CP55-940 binding assay Whole brain/Mouse [90]
0.073 ND [
3
H] 50-trimethylammonium-Δ
9
-
THC binding assay
Whole brain/Rat [162]
>0.5 ND [
3
H] CP55-940 binding assay Whole brain/Rat [28]
53 ND [
3
H] CPP-940 binding assay Sectioned brain/Rat [25]
4.3 ND [
3
H] CP55-940 binding assay Cortical brain mem-
branes/Rat
[163]
2.3 ND [
3
H] CP55-940 binding assay Whole brain/Rat [161]
1.3 ND [
3
H] rimonabant binding assay Whole brain/Rat
>10 ND [
3
H] HU-243 binding assay Whole brain/Rat [136]
4.9 ND [
3
H] HU-243 binding assay Whole brain/Mouse [104]
1.8 ND/
NE
[
3
H] rimonabant binding assay Brain cortical mem-
branes/Rat
[164]
4.7 ND [
3
H] CP55-940 binding assay Whole brain mem-
branes/Mouse
[118]
1.45 3.86 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
CB
2
>10 ND [
3
H] HU-243 binding assay COS-7 cells/Rat [136]
2.86 ND [
3
H] CP55-940 binding assay CHO cell/Human [86]
4.2 0.503 [
3
H] CP55-940 binding assay CHO cell/Human [104]
(continued)
66 S.E. Turner et al.
1at CB
2
receptors came from a study where 1antagonized the inhibition of
adenylate cyclase in CHO cells transfected with human CB
2
receptors induced by
the agonists HU-293a and HU-210 (Table 2)[40].
As is typical of a partial agonist, 1has a mixed agonist–antagonist effect. This is
likely dependent on the proportion of cannabinoid receptors that are in the “active”
state in tissues, coupled to their effector mechanisms, or in the “inactive” state,
uncoupled to their effector mechanisms [41]. Moreover, it would also depend on the
presence of other synthetic or endogenous cannabinoid receptor agonists, and
possibly species differences between studies. As a partial agonist, 1can be expected
to antagonize the actions of full agonists. In a mouse model of hypothermia, 1alone
acted as a partial agonist with less efficacy than the cannabinoid receptor full
agonist, AM2389, but when co-administered with this compound, 1antagonized
AM2389’s hypothermic effects [42].
In an in vitro study using the GTPγS binding assay in rat brain membranes from
rats chronically treated with 10 mg kg
1
1for 21 days, the stimulation of GTPγS
binding by WIN 55212–2 was reduced by up to 70%, suggesting that chronic
exposure to 1led to a desensitization of cannabinoid-activated signal transduction.
In healthy human subjects, the intravenous administration of 1caused acute
psychotic reactions and a temporary decline in cognitive functioning [43].
Table 2 (continued)
K
i
/μM
EC
50
/
IC
50
Assay Cell type Ref.
2.86 ND [
3
H] CP55-940 binding assay E. coli cell membranes/
Human
[118]
0.37 2.27 [
3
H] CP55-940 binding assay Sf9 cells/ Human [159]
Cannabichromene (7)
CB
1
>10 ND [
3
H] CP55-940 binding assay Whole brain/Mouse [90]
0.71 1.68 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
CB
2
0.256 1.30 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
Cannabigerol (6)
CB
1
275 ND [
3
H] CP55-940 binding assay Sectioned brain/Rat [25]
0.896 1.12 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
CB
2
0.153 0.85 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
Cannabidivarin (5)
CB
1
14.7 13.80 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
0.127
*
ND [
3
H] CP55-940 binding assay MF1 brain membranes/
Mouse
[2]
CB
2
0.57 3.45 [
3
H] CP55-940 binding assay Sf9 cells/Human [159]
ND, not described; CHO, Chinese hamster ovary; COS, CV1 in origin with SV40 genes; Sf,
Spodoptera frugiperda
Molecular Pharmacology of Phytocannabinoids 67
2.2 Cannabinoid Receptor Independent Activity
The well-known psychotropic effect of 1is mediated by its partial agonist activity
at CB
1
receptors. However, 1also exerts effects at molecular targets outside of the
endocannabinoid system. Some of the physiological effects of 1may be mediated
by more than one target, as detailed below.
In this regard, 1has been proposed to act in an allosteric manner on specific
receptors outside of the endocannabinoid system. In vitro, 1potently inhibited
5HT
3A
-induced currents in HEK293 cells transfected with 5HT
3A
receptor cDNA
[44], similar to the reported effect of the synthetic cannabinoid receptor agonist,
WIN 55212–2,and also in cultured rat trigeminal ganglion neurons (Table 3)
[44,45]. Together with 1, other cannabinoids such as WIN 55212–2, anandamide,
JWH-015, and CP-55940, have been shown to stereoselectively inhibit currents at
this receptor [44].
Cannabinoid receptors and 5HT
3
receptors are both involved in control of pain
and emesis [11–14]. The results above show that the activity of cannabinoid
receptor agonists on the control of pain and emesis may be shared by their
antagonistic effect on 5HT
3
receptors [46–50]. This highlights the possibility of a
ligand having a physiological effect that can be mediated by multiple targets.
Therefore, an effect proven to be mediated through one target does not mean that
other targets of the ligand mediating the same physiological effect can be ruled out.
At glycine receptors, low concentrations of 1also acted through a possible
allosteric mechanism by potentiating the amplitude of glycine-activated currents
in rat isolated ventral tegmental area neurons via a cannabinoid receptor-
independent mechanism (Table 3)[51]. Glycine receptor function was potentiated
by 1at physiologicallyrelevant concentrations. Glycine receptors are involved in
pain transmission [52,53] and dopamine release from ventral tegmental area
neurons [54,55], thus 1may be important for analgesia and drug addiction.
Analgesia is also produced through 1activity at cannabinoid receptors [11,12]
but some of this analgesic effect may be mediated through glycine receptors as
well. This again shows a physiological effect being mediated by more than one
target of the same ligand.
Compound 1(0.1–10 μM) is a peroxisome proliferator-activated receptor
gamma (PPARγ) agonist. The studies below outline the relevance of the agonist
effect at this nuclear receptor in the cardiovascular system and potentially in cancer
treatment. Through agonism of the PPARγreceptor, 1has time-dependent effects
on vasorelaxation of the aorta and superior mesenteric arteries in a dose-dependent
manner [56]. This relaxation effect of 1was similar to the vascular relaxation effect
of the PPARγligand rosiglitazone (46.7% and 69.7% respectively). Another study
by the same group showed differences in the time-dependent effect of 1on
vasorelaxation in different vessel types; in resistance mesenteric arteries no time-
dependent effect of 1on PPARγmediated vasorelaxation was noted [57]. These
studies show that the effect of 1on endothelium-dependent vasorelaxation is
dependent on the predominant relaxing factor in a given artery. Agonism of
68 S.E. Turner et al.
Table 3 A comparison of select in vitro studies showing cannabinoid receptor independent
activity of Δ
9
-trans-tetrahydrocannabinol (1) according to concentrations, assay types, and cell
types used
Target
Concentration/
μM
EC
50
/
μM
IC
50
/
μMAssay Cell line Ref.
GPR55 <1 0.008 GTPγS binding assay HEK293/Human [67]
1–10 5 [Ca
2+
] mobilization
assay
HEK293/Human [165]
<1 0.64 ERK1/2 MAPK
phosphorylation
HEK293/Human [69]
1 ND ERK1/2 MAPK
phosphorylation
HEK293/Human
ND B-arrestin assay HEK293/ND [66]
GPR18 <1 0.96 MAPK activation
assay
HEK293/ Human [62]
5HT
3A
<1 0.038 Voltage clamp HEK293/Human [44]
Glycine ligand gated ion channels
α1<1 0.086 Whole cell patch
clamp
Xenopus laevis
oocytes/
Human
[51]
α1β1<1 0.073 Whole cell patch
clamp
0.115 Ventral tegmen-
tal area neurons/
Rat
PPARγ
nuclear
receptor
<1 ND Contraction HEK293/ND [166]
TRP cation channels
TRPA1 <1 0.23 Ca
2+
Fluorescence
assay
HEK293/Rat [80]
TRPV2 0.65 HEK293/Rat
TRPM8 0.16 HEK293/Rat
0.15 HEK293/Rat [79]
TRPV3 1–10 9.5 HEK293/Rat [81]
TRPV4 8.5 HEK293/Rat
CYP1A1 1–10 0.53 Fluorescence assay-
FLUOSTAR
OPTIMA
Recombinant/
Human
[167]
CYP1A2 4.59
CYP1B1 1.39
CYP2C9 1–10 2.84 HPLC Recombinant/
Human
[168]
Adenosine
uptake
<1 0.27 Scintillation counting
[
3
H]adenosine
EOC-20 microglia [116]
0.334 Scintillation counting
[
3
H]adenosine
RAW264.7
macrophages
GPR, G-protein-coupled receptor; 5HT, 5-hydroxytryptamine; PPAR, peroxisome proliferator-
activated receptor; TRP, transient receptor potential; CYP, cytochrome P450; HEK, human
embryonic kidney; GTPγS, guanosine 50-O-(3-thiotriphosphate); Ca
2+
, Calcium; ERK, extracel-
lular signal-regulated kinases; MAPK, mitogen-activated protein kinase; also see footnote for
Table 1
Molecular Pharmacology of Phytocannabinoids 69
PPARγby 1leads to an increase in superoxide dismutase activity, thus leading to an
increase in hydrogen peroxide (H
2
O
2
). In superior mesenteric arteries, H
2
O
2
is the
predominant relaxing factor and therefore 1enhances endothelium-dependent
vasorelaxation. In resistance mesenteric arteries, however, where endothelium-
derived hyperpolarizing factor (EDHF) is the predominant relaxing factor, 1inhibits
EDHF production and therefore inhibits vasorelaxation in these arteries [57].
In vivo,1acts via the PPARγmechanism to reduce tumor growth rate. In mice
with induced tumour xenografts, 1(15 mg kg
1
) showed antitumor properties by
reducing tumor growth rate, which was prevented by co-administration with the
PPARγantagonist, GW9662 [58]. However, an antagonist-only treatment group
was not included in this study and therefore the effect of 1on tumor growth has not
been validated as being mediated by PPARγand so, as yet, can be considered a
functional, rather than molecular antagonism.
Moreover, PPARγis not only involved in the physiological roles outlined above.
It is also involved in adipogenesis, where it is highly expressed, and in the treatment
of type 2 diabetes [59,60] and gastro-inflammatory disorders [61]. Compound
1may therefore have as yet unproven effects on these disorders. There are other G
i/o
coupled receptors (GPCR) that are thought to be novel cannabinoid receptors.
These are GPR18 and GPR55 [29,30,62,63]. These receptors belong to the
same class as CB
1
and CB
2
receptors but do not share many structural similarities
[64], which would likely result in differing ligands and physiological effects at
these receptors compared to CB
1
and CB
2
receptors.
In HEK293 cells transfected with the novel G
i/0
coupled GPCR cannabinoid
receptor, GPR18, 1acts as a potent agonist (Table 3)[62]. Interestingly, the
phytocannabinoid cannabidiol (4) can antagonize the effect of the agonists such
as 1at this receptor [62,63].
There are conflicting reports on the activity of 1at the GPR55 receptor in vitro.
This receptor has been claimed, by many authors, to be a third cannabinoid receptor
[29–31,65]. Using two different assays in the same cell line (HEK293) transfected
with human GPR55, 1weakly activated GPR55 in a β-arrestin assay [66], but
potently activated it in a GTPγS binding assay with a submicromolar half maximal
response (Table 3)[67]. However, using the same cell line transfected with human
GPR55 and the β-arrestin assay, Kapur and co-workers found no detectable activity
of 1at this receptor [68]. Moreover, again in the same cell line also transfected with
human GPR55, 1has been reported to exhibit differential effects in a concentration-
dependent fashion. It was reported in the same study that 1is an inhibitor of the
proposed endogenous agonist of GPR55, lysophosphatidylinositol (LPI), at con-
centrations of 1 μM, by inducing a rightward shift in the log concentration-response
70 S.E. Turner et al.
curve of LPI as well as activating this receptor at micromolar concentrations
[69]. These findings of agonism and inhibition suggest that there could be two
distinct binding sites on GPR55 receptors. By itself, 1may bind to either an
orthosteric binding site or an allosteric binding site producing agonism of the
receptor or, by binding to an allosteric site, produces a conformational change in
the orthosteric binding site, thus reducing the effect of LPI [69]. The binding of 1to
a particular binding site may be dependent on the concentrations used.
Even though 1has undesirable psychotropic effects, mediated by CB
1
receptors,
it is important to remember that this phytocannabinoid has a range of important
therapeutic benefits. These effects may be mediated both by cannabinoid receptors,
either CB
1
and CB
2
receptors or novel GPCRs, and non-cannabinoid targets.
3Δ
9
-Tetrahydrocannabivarin
O
OH
2
Δ
9
-Tetrahydrocannabivarin (2) is included in the Δ
9
-THC chemical class which, as
mentioned earlier, constitutes the majority of the phytocannabinoid content [1]of
C. sativa. This phytocannabinoid is the n-propyl analog of 1, with the slight
structural change resulting in some different molecular targets and physiological
effects when compared to 1.
3.1 Activity at Cannabinoid Receptors
In vitro, 2is a CB
2
receptor partial agonist, as shown by its lower efficacy at CB
2
receptors than the agonist CP-55940 in both CHO cells transfected with human CB
2
receptors and in the GTPγS binding assay in membranes from these cells, as shown
in Table 2[70].
Importantly, there is also in vivo evidence of 2as a CB
2
receptor partial agonist.
Garcia and co-workers showed that 2(2 mg kg
1
) can show signs of
neuroprotection in a model of Parkinson’s disease in mice that have received
Molecular Pharmacology of Phytocannabinoids 71
intrastriatal injections of lipopolysaccharide (LPS), similar to the effects shown by
the CB
2
selective agonist HU-308 [71]. CB
2
receptor-deficient mice were more
vulnerable to LPS-induced lesions, which supports the effects of 2being mediated,
at least in part, by agonism at CB
2
receptors.
At low concentrations (0.1–5 μM), 2blocks CB
1
receptors both in vitro and
in vivo, but interestingly at high doses acts as a CB
1
agonist in vivo but not in vitro.
Two studies reported that 2blocks the agonist effects of CP-55940- and (+)-(R)-
WIN55212-induced stimulation of GTPγS binding to mouse whole membranes at a
low concentration of 1 μM(Table 2)[72,73], while Dennis and co-workers showed,
using the same assay, this antagonistic effect of 2from the lower concentration of
0.1 μMup to 5 μMon (+)-(R)-WIN55212 in the mouse cerebellum and piriform
cortex membranes [74]. The antagonist effect of 2is the same as two established
CB
1
receptor-selective antagonists, rimonabant and AM251 [72,73,75,76]. Thus,
antagonism of CB
1
receptors by 2modulates inhibitory neurotransmission in the
cerebellum [76].
In vivo, 2acts as both an antagonist and agonist at low doses and high doses,
respectively. This antagonist and agonist phenomenon results in opposing effects
on antinociception and on locomotor activity depending on the concentration used.
This disparity in pharmacological effect of 2, dependent upon the concentration
used, highlights the importance of knowing the concentration of each phyto-
cannabinoid in whole cannabis plant material and extracts when this is being
used for therapeutic use.
At low doses of 0.3 and 3 mg kg
1
,2blocks the antinociceptive effect of 1in a
mouse model of acute pain and hypothermia [72]. Using the same model, 2also
partially antagonized the CB
1
agonist effects of CP-55940 at a dose of 2 mg kg
1
and also partially antagonized CP-55940-induced inhibition of rat locomotor activ-
ity in a model of Parkinson’s disease [71]. There was no effect of 2treatment alone
on either of these parameters and therefore these studies support the molecular
antagonism of 2at CB
1
receptors.
At higher doses of 3, 10, 30, and 56 mg kg
1
,2acts as an agonist by producing
antinociception in an acute model of pain and causes immobility in the ring test
(a quantitative test for measuring catalepsy [65]) [72]. In this study, the CB
1
receptor antagonist rimonabant blocked the agonist effect of 2on antinociception
but not on immobility in the ring test. A rimonabant-only treatment group was not
included in this study to rule out whether this antagonist worsens nociceptive pain.
It is therefore not clear from this study whether the effect found is functional or
molecular.
In other in vivo experiments, 2(3, 10, 30 mg kg
1
) suppressed food consumption
in non-fasted mice, similar to the CB
1
-selective antagonist AM251 [77]. Signs of
motor inhibition, induced by 6-hydroxydopamine, were reduced by 2(2 mg kg
1
),
similar to the effect of the CB
1
antagonist, rimonabant [71]. It is unclear without
further investigation whether this effect of 2is via inverse agonism of the CB
1
receptor, competitive inhibition with endogenous cannabinoids at CB
1
receptors or
by activity at another target, since comparisons made were based on functional
effects of the compounds without confirmation of the molecular targets [78].
72 S.E. Turner et al.
3.2 Cannabinoid Receptor Independent Activity
There is little available evidence to suggest that 2acts at CB
1
or CB
2
receptor-
independent targets but it may have other targets within the cannabinoid system,
such as the novel cannabinoid receptor GPR55 [69]. There is, however, only one
study to date describing agonism of GPR55 receptors by 2[69]. In this investiga-
tion, 2was an agonist of GPR55 in HEK293 cells expressing human GPR55 with a
similar potency to 1(Table 4) and 1 μM2was shown to inhibit LPI induced
stimulation of GPR55 with 50% efficacy, higher than that of 1[69].
The evidence of 2acting at targets outside the cannabinoid system comes from
the proven interaction between 2and transient receptor potential (TRP) cation
channels at higher concentrations than at which it acts at CB
1
or CB
2
receptors
[79–81].
Despite there being limited known pharmacological targets for 2, its activity at
TRP channels may have wide-reaching physiological effects. These TRP channels
are present in the plasma membrane of a broad range of cell types in many tissues and
act as ligand-gated, non-selective cation channels permeable to sodium, calcium and
magnesium ions, thereby being powerful regulators of many cell functions [82].
De Petrocellis and co-workers studied the efficacy and potency of numerous
phytocannabinoids at various TRP channels [79–81]. At TRPA1 and TRPV1 cation
channels, 2is an agonist with the same high potency and at TRPV2 with a slightly
Table 4 A comparison of selected in vitro studies showing cannabinoid receptor independent
activity of Δ
9
-trans-tetrahydrocannabivarin (2) according to concentrations, assay types, and cell
types used
Target
Concentration/
μM
EC
50
/
μM
IC
50
/
μMAssay Cell type Ref.
GPR55 >1 0.88 ERK1/2 MAPK
phosphorylation
HEK293/Human [69]
1 ND ERK1/2 MAPK
phosphorylation
HEK293/
Human
5HT
1A
<1 5.4 GTPγS binding assay
8-OH-DPAT
Brainstem mem-
branes/Rat
[169]
28.3 GTPγS binding assay
8-OH-DPAT
CHO cells/
Human
TRP cation channels
TRPA1 1–10 1.5 Ca
2+
fluorescence
assay
HEK293/Rat [80]
TRPM8 <1 0.87 HEK293/Rat
TRPV1 1–10 1.5 HEK293/
Human
TRPV2 4.1 HEK293/Rat
TRPV3 3.8 HEK293/Rat [81]
TRPV4 6.4 HEK293/Rat
See Tables 1and 2
Molecular Pharmacology of Phytocannabinoids 73
lower potency. The TRPM8 cation channels are blocked by 2with relatively high
potency (Table 4)[80].
In summary, 2is known to be an antagonist at CB
1
receptors at low concentra-
tions both in vitro and in vivo but at high concentrations it shows agonistic effects at
CB
1
receptors only in vivo. This antagonistic effect at CB
1
receptors has been
shown to have adverse effects in the clinic, with removal of the CB
1
receptor
antagonist, rimonabant, from the market due to adverse psychological effects
[83]. In vivo and in vitro evidence supports partial agonism activity at CB
2
receptors and at higher concentrations than at which it activates cannabinoid
receptors it has activity at TRP cation channels, which may have benefits for
regulating a variety of cell functions.
4 Cannabinol
OH
O
3
Cannabinol (3) is an oxidation product of 1and is found in large quantities in dried
and aged cannabis material [84]. The acid form of 3is also found in large quantities
in the cannabis plant but upon heating this acid is decarboxylated to 3[84]. This is
important to take into account when considering how cannabis that is being used
for medicinal or recreational purposes is processed, and stored, and how it is
administered.
4.1 Activity at Cannabinoid Receptors
Cannabinol (3) like 1, acts at both CB
1
and CB
2
receptors but with higher affinity
for CB
2
than CB
1
receptors, as shown in Table 2[85–87]. It is an agonist at CB
1
receptors [29], but there are conflicting reports about its activity at CB
2
receptors. In
COS-7 cells transfected with rat CB
2
receptors, 3acted as a CB
2
receptor agonist in
the cyclic AMP assay at 1 μM[85] but in another study performed in CHO cells
transfected with human CB
2
receptors, 3acted as an inverse agonist in the GTPγS
binding assay at submicromolar concentrations [88]. These discrepancies may be
due to the differences in concentrations of 3used between the studies and could also
depend on the conformational state of the receptors in the tissues. Receptors can
either be in the active conformational state, where G-proteins are activated and
74 S.E. Turner et al.
elicit a physiological response, or the inactive conformational state, where there is
no activation of G-proteins. The amount of receptors in either state can differ in
different tissues and under different conditions. If a ligand has a greater affinity for
a specific conformational state (active or inactive), then the presence of the ligand
will cause a redistribution of the concentrations of each conformational state. Thus,
the concentration of ligand present will dictate the distribution of the receptor
conformational state and either induce or inhibit a physiological response [89]. Fur-
ther investigations are warranted to determine the activity of 3at CB
2
receptors.
In vivo, 3(50 mg kg
1
) has been shown to be a CB
1
receptor agonist by
suppressing acetic acid-induced abdominal stretching behavior in mice, which
was blocked by the CB
1
antagonist, rimonabant. The administration of rimonabant
alone did not significantly affect abdominal stretching, indicating that this effect of
3is likely to be a molecular one [90]. Moreover, in this study, the effect of 3on
locomotor suppression was also investigated. This was performed to determine
whether the effect of 3on hypomotility could be excluded from the observed effect
of 3on abdominal stretching behavior. The dose of 3used (50 mg kg
1
) did not
elicit locomotor suppression thereby indicating the suppression of abdominal
stretching was not due to motor dysfunction [90].
Additionally, 3(0.26–26.0 mg kg
1
p.o.) exerts CB
1
receptor-dependent effects
on rat feeding behavior by decreasing latency to feed and increasing food con-
sumption over the whole test period with these effects being abolished in the
presence of rimonabant [91]. However, a rimonabant-only treatment group was
not included in this study and therefore it is not clear whether this effect of 3is via
functional mechanisms or molecular mechanisms. In numerous other feeding
studies rimonabant decreases food consumption [92–94], but there is speculation
as to whether this is due to suppressive effects of rimonabant on spontaneous
locomotion [95,96] and stimulation of emesis and nausea [97–99]. Together with
these studies it is unclear whether the effects of 3and rimonabant on feeding are
mediated via molecular mechanisms.
For further information on binding affinities of 3at CB
1
and CB
2
receptors, see
Table 2.
4.2 Cannabinoid Receptor Independent Activity
Cannabinol also acts at targets outside of the endocannabinoid system. It is a potent
agonist of TRPA1 cation channels, potently blocks TRPM8 cation channels, and
also desensitizes TRPA1 cation channels to activation by the agonist allyl isothio-
cyanate (Table 5)[80].
There is little recent literature on the pharmacology of 3and thus further
investigations need to be conducted to determine whether this compound has
other therapeutic or recreational effects and how it modulates or enhances the
physiological effects of whole cannabis-derived preparations.
Molecular Pharmacology of Phytocannabinoids 75
5 Cannabidiol
OH
HO
4
Cannabidiol (4) is a non-psychotropic phytocannabinoid and the 4chemical class
type of phytocannabinoids is currently the third most abundant chemical class type
in cannabis, after 1and 6[1]. Another phytocannabinoid in this class,
cannabimovone, was isolated in 2010 [100], thereby increasing the number of
phytocannabinoids of this type from seven in 2005 [101] to eight [1]. This class
now makes up 7.7% of phytocannabinoid content (Table 1).
5.1 Activity at Cannabinoid Receptors
Cannabidiol (4) has been investigated in a number of studies to determine its
activity at cannabinoid receptors and shows very low affinity at these receptors
(Table 2)[102,103]. There has been a single report where 4was shown to act as an
antagonist of both CB
1
and CB
2
receptors at submicromolar concentrations
[104]. However, a meta-analysis examining interspecies differences in ligand-
binding affinity and receptor distribution identified eight methodological covariates
Table 5 A comparison of selected in vitro studies showing cannabinoid receptor independent
activity of cannabinol (3) according to concentrations, assay types, and cell types used
Target
Concentration/
μM
EC
50
/
μM
IC
50
/
μMAssay Cell type Ref.
TRP cation channels
TRPA1 <1 0.18 0.4 Ca
2+
fluorescence assay HEK293/Rat [80]
TRPM8 0.21 HEK293/Rat
TRPV1 1–10 6.2 HEK293/
Human
TRPV2 >10 19.0
TRPV3 1–10 5.3 HEK293/Rat [81]
TRPV4 >10 16.1 HEK293/Rat
CYP1A1 1–10 0.685 fluorescence assay—
FLUOSTAR OPTIMA
Recombinant/
Human
[167]
CYP1A2 3.92
CYP1B1 1.50
CYP2C9 1–10 2.86 HPLC Recombinant/
Human
[168]
See Tables 1and 2
76 S.E. Turner et al.
that could explain the discrepancies between results from various studies on
cannabinoid receptor affinity for 4[105]. A more recent meta-analysis from the
same group concluded that 4has very low affinity as an orthosteric ligand for CB
1
receptors (Table 2), but may affect CB
1
receptor activity in vivo via an indirect
mechanism [78]. However, a study recently published showed that 4can act as a
negative allosteric modulator of CB
1
receptors [106]. Allosteric modulators alter
the potency and efficacy of the orthosteric ligands but do not activate the receptor
themselves. The allosteric effects of 4were studied using an operational model of
allosterism [107] and the effects of 4treatment compared to the well-characterized
negative allosteric modulators ORG2759 and PSNGBAM-1 [108–111]. The effi-
cacy of both of the orthosteric ligands, 1and 2-AG, was reduced by 4(<1μM) and
4displayed negative co-operativity for binding of these ligands. Moreover, 4-
treatment reduced G-protein dependent signaling and arrestin 2 recruitment, similar
to the effects of the negative allosteric modulators ORG2759 and PSNCBAM-1
[109,112]. This allosteric modulation of CB
1
receptors needs to be validated by
further studies, but the results from this study could explain the reported ability of
4to functionally antagonize some effects of 1in animal studies and clinical studies
in humans (for a review see [113]).
Compound 4has an effect in vitro of inhibiting anandamide uptake and therefore
affecting endocannabinoid tone by increasing availability of anandamide. The
concentration at which 4exerts its half maximal response, however, is higher
than what would be relevant for a physiological effect in vivo [80].
5.2 Cannabinoid Receptor Independent Activity
Despite 4showing very little affinity for CB
1
and CB
2
receptors, as described
above, there is evidence of an antagonist effect of 4at the novel cannabinoid
receptor GPR55 both in vitro and in vivo. At a concentration of 1 μM,4suppressed
the activation of GPR55 in rat hippocampal slices, thus suppressing excitatory
output from pyramidal cells [114]. In a GTPγS-binding assay, 4had potent antag-
onist effects at GPR55 with a submicromolar half maximum response (Table 6)
[67]. Whyte and co-workers have shown a role for GPR55 in bone physiology,
regulating osteoclast formation and function and bone mass [115]. This group
reported that administration of 4(10 mg kg
1
) to mice three times daily for
8 weeks significantly reduced bone resorption in these mice.
Outside of the endocannabinoid system, 4has numerous targets and its activity
at these targets results in a variety of physiological effects. Some of these physio-
logical effects may be mediated by more than one target, such as the anti-
inflammatory and immunosuppressive effect of 4. These effects are mediated by
both adenosine mechanisms and via strychnine-sensitive glycine receptors, as
detailed in the following paragraphs.
Molecular Pharmacology of Phytocannabinoids 77
Table 6 A comparison of select in vitro studies showing cannabinoid receptor independent activity of cannabidiol (4) according to concentrations, assay
types, and cell types used
Target
Concentration/
μMEC
50
/μMIC
50
/μMAssay Cell line Ref.
GPR55 <1 ND Two photon Ca
2+
imaging Hippocampal slices/Rats [114]
<1 0.45 GTPγS binding assay HEK293/Human [67]
<1 0.45 Rho/ERK1/2 activation Human osteoclasts [115]
Glycine receptors
α1 subunit 1–300 12.3
(allosteric)
Patch clamp HEK293/ND [117]
132.4
(direct)
α1βsubunit 1–300 18.1
(allosteric)
Patch clamp HEK293/ND
144.3
(direct)
α3 subunit 0.01–50 3
(direct)
Patch clamp HEK293/ND [118]
5HT
1A
<1 0.007 GTPγS binding assay Rat brainstem [123]
>10 ND ND [3H]-8-OH-DPAT ligand binding CHO/Human [122]
[35S]-GTPγS assay
Forskolin
5HT
2A
>10 ND ND [
3
H]-Ketanserin NIH 3 T3 membrane/rat
5HT
3A
<1 0.6 Patch clamp Xenopus laevis oocytes [135]
PPARγ1–10 5 Contraction Aorta/rat [166]
78 S.E. Turner et al.
Mitochondrial
Complex I
Complex II
Complex IV
1–10, >10 High resolution respirometry Brain cortex/Pig [170]
8.2
19.1
18.8
CYP2C19
CYP3A5
CYP2C9
CYP1A1
1–10 0.5–2.7 HPLC, Fluorescence FLUOSTAR
OPTIMA
Recombinant/Human liver
microsomes
[167,168,171,
172]
Cav3.1–3.3 T-
type
1–10 0.78–3.7 Whole cell patch clamp HEK293/Human, Sensory neu-
rons/Mouse
[173]
TRPA1 <1 0.096 Ca
2+
Fluorescence assay HEK293/Rat [79]
0.11 0.06 HEK293/Rat [80]
TRPM8 <1 0.14 Ca
2+
Fluorescence HEK293/Rat [79]
0.06 HEK293/Rat [80]
TRPV1 1–10 3.5 Ca
2+
Fluorescence assay HEK293/Human [136]
1–10 1 HEK293/Human [80]
TRPV2 1–10 1.25 Ca
2+
Fluorescence HEK293/Rat
>10 22.2 Ca
2+
mobilization U87MG/Human [174]
TRPV3 1–10 3.7 Ca
2+
Fluorescence HEK293/Rat [81]
TRPV4 1–10 0.8 HEK293/Rat
Adenosine
uptake
<1 0.12 Scintillation counting [
3
H]
Adenosine
EOC-20 microglia [116]
0.19 Scintillation counting [
3
H]
Adenosine
RAW264.7 macrophages
1–10 3.5 Dual label counting [
3
H] Adenosine Striatal tissue synaptosome/
Mouse, Rat
[175]
8-OH-DPAT, 8-hydroxy-2-(dipropylamino)-tetralinhydrobromide; HPLC, high-performance liquid chromatography; also see Tables 1and 2
Molecular Pharmacology of Phytocannabinoids 79
Activity of 4at one target may also elicit various physiological effects. This is
shown by 4having anti-inflammatory effects and antiarrhythmic effects both
mediated by adenosine mechanisms. Another example refers to the 5HT serotonin
receptors of a target where 4acts to mediate multiple physiological effects such as
acute autonomic responses to stress, nausea and vomiting, cerebral infarction and
anxiolytic, panicolytic, and antidepressant effects. The sections below will describe
in more detail the studies that support evidence for the numerous and varied
physiological targets of 4.
It is known that 4has anti-inflammatory and immunosuppressive effects, but
these effects have been shown to be mediated by multiple pharmacological targets,
as detailed below. The mechanisms by which 4possibly mediate anti-inflammatory
and immunosuppressive effects include: activity at A
1A
and A
2A
adenosine recep-
tors and the inhibition of the equilibrative nucleoside transporter [116] and the
activation of strychnine-sensitive α
1
and α
1
βglycine receptors [117,118].
The effects of 4mediated via adenosine have been shown in both in vitro and
in vivo studies. Uptake of [
3
H] adenosine was inhibited by 4in murine microglia
and RAW264.7 macrophages by a mechanism of binding to the equilibrative
nucleoside transporter 1 (ENT1) and competitively inhibiting this nucleoside trans-
porter with a K
i
value of less than 0.25 μMand a submicromolar half maximal
response [116] (Table 6). In addition to inhibition of ENT1 uptake of adenosine, the
authors also documented in vivo that 4could bind and activate the A
2A
receptor,
since the effects of 4on tumor necrosis factor α(TNF α) were abolished by an A
2A
receptor antagonist and by genetic deletion of this receptor [116]. An in vivo effect
of 4on anti-inflammatory effects mediated by the A
2A
receptor was shown with
lipopolysaccharide-induced inflammation in the rat retina [119] and in the mouse
lung [120], both using the A
2A
receptor antagonist ZM241385. The study by Liou
and co-workers that indicated inhibition of adenosine uptake by ENT1 is important
in the anti-inflammatory effects of 4both in vitro and in vivo in the rat retina [119].
These studies clearly indicated that 4has immunosuppressive effects that are
mediated via adenosine mechanisms. This immune-suppressive effect is important
in limiting cellular stress and inflammation and perhaps explains the effect of 4on
improving arthritis and multiple sclerosis symptoms. Its immunosuppressive effects
in microglia would have considerable benefits for a number of neurodegenerative
conditions.
The anti-inflammatory effects of 4mediated through strychnine-sensitive α
1
and
α
1
βglycine receptors have also been shown in in vitro and in vivo studies but the
in vitro study detailed below would be physiologically irrelevant due to the high
concentrations used to elicit an effect that would not be achieved in vivo. The study
used a whole cell patch clamp technique to show that 4, at a mid-micromolar range,
had positive allosteric modulating effects at these glycine receptor subunits and at
higher concentrations showed direct activation of these receptor subunits
(Table 6)[117].
It has also been reported that 4has anti-inflammatory actions and suppresses
neuropathic pain in vivo, mediated by glycine receptors. In α3 glycine channel
knockout mice injected with Freund’s adjuvant into the hind paw, the anti-
80 S.E. Turner et al.
inflammatory effects of 4(50 mg kg
1
i.p.) in this model of inflammatory pain were
abolished [118].
Another physiological effect of 4mediated via adenosine mechanisms is its
antiarrythmic effect, shown by inhibiting ventricular tachycardia in rats [121]. This
effect was shown using a low dose of 4of 50 μgkg
1
and agonism of the A
1A
receptor by 4was validated by administration of the selective antagonist,
8-cyclopentyl-1,3-dipropylxanthine (DPCPX), at 100 μgkg
1
. In the presence of
this selective antagonist, these effects of 4were abolished [121]. Importantly, this
effect was also determined to be a molecular effect rather than a functional one
since a DCPX-only treatment group showed no effect on the incidence or duration
of arrhythmias.
Significant evidence supports 4producing its effects via serotonin (5-HT)
receptors, predominantly the 5HT
1A
receptor subtype but also the 5HT
3A
receptor
and less so at the 5HT
2A
receptor. As described above, activity at these receptors
mediates a variety of physiological responses.
In two in vitro studies, first in Chinese hamster ovary (CHO) cells [122] and
more recently using rat brainstem membranes [123], 4was found to enhance the
ability of a 5HT
1A
agonist, 8-OH-DPAT, to stimulate GTPγS binding at
submicromolar concentrations (Table 6).
In vivo, 4induces various 5HT
1A
-mediated physiological responses. These
include attenuation of: acute autonomic responses to stress, nausea and vomiting,
and cerebral infarction, and induction of anxiolytic, panicolytic, and antidepressant
effects [123–133]. Studies with evidence supporting these effects are detailed
below.
At doses of 1, 10, or 20 mg kg
1
(i.p.) of 4in male Wistar rats, this compound
dose-dependently reduced the acute autonomic response to restraint stress and
reduced the anxiety behavior caused by previous exposure to restraint
[124]. These effects of 4were blocked by the 5HT
1A
receptor antagonist,
WAY100635 (0.1 mg kg
1
), while by itself WAY100635 did not have an effect
on cardiovascular or anxiogenic responses, indicating this to be a molecular effect
[124]. Another study reported that 4administration directly into the dorsal
periaqueductal gray via an implanted cannula in rats elicits panicolytic effects by
inhibiting escape responses in the elevated T maze via 5HT
1A
mediated responses.
These responses were blocked by treatment with WAY100635 [125]. In both of
these studies, a WAY100635-only treatment group was not used and therefore these
results are not indicative of a molecular effect.
Activation of 5HT
1A
receptors has been regularly related to the therapeutic
effect of antidepressant treatments [130] and a reduced number/affinity of postsyn-
aptic 5HT
1A
receptors in the brains of depressed individuals has been reported by a
number of studies [131,132]. The first study to investigate whether there is a link
between these receptors and the antidepressant effects of 4was conducted quite
recently by Zanelati and co-workers [126]. Mice received i.p. injections of 3, 10,
30, and 100 mg kg
1
4and were then subjected to the forced swimming test. This
test is predictive of antidepressant-like activity [133]. Immobility time was reduced
by 4and showed a bell-shaped response, since 4was only effective at 30 mg kg
1
Molecular Pharmacology of Phytocannabinoids 81
and not at the lower or higher doses [126]. The 5HT
1A
receptor antagonist
WAY100635 blocked the effects of 4on antidepressant-like activity but mediation
of this effect by 5HT
1A
receptors was not validated by use of a WAY100635-only
treatment group.
Various studies have reported 4to have antiemetic- and antinausea-like effects
and this is thought to be mediated by 5HT
1A
receptors. Unlike 1, for which the
antiemetic effects are mediated by both CB
1
receptors and 5HT receptors
(as described in Sect. 2.2), it appears that 4exerts its antiemetic effects primarily
through 5HT receptors. Three studies showed that a low dose of 4(5 mg kg
1
i.p.)
suppressed nicotine, cisplatin, and lithium chloride-induced vomiting in house
musk shrews (Suncus murinus)[123,127,128] and lithium chloride-conditioned
gaping in rats [123]. This suppression of vomiting and conditioned gaping was
abolished by pre-treatment with the 5HT
1A
receptor antagonists, WAY100135 and
WAY100635 [123], but since an antagonist-only treatment group was not included
in this study, an effect of 4being mediated by 5HT
1A
receptors has not been
validated and it only showed a functional effect.
Neuroprotective effects of 4have been shown through increasing cerebral blood
flow and reducing infarct volume in a mouse model of middle cerebral artery
occlusion [129]. This effect has been claimed to be CB
1
receptor independent
[134] and in this study the effects of 4were opposed by WAY100135 but not by
the CB
1
receptor antagonist, rimonabant [129]. The neuroprotective effects of
4have been claimed here to be mediated by 5HT
1A
receptors but since a
WAY100135-only treatment group was not included, this effect may be functional
rather than molecular.
The only study to date investigating 4activity at 5HT
3A
receptors in vitro was
conducted using Xenopus laevis oocytes expressing mouse 5HT
3A
receptors using
two electrode voltage clamp techniques [135]. In this study, 4reversibly inhibited
5HT evoked currents in a concentration-dependent manner, which indicated that
4is a non-competitive antagonist of 5HT
3A
receptors (Table 6)[135]. This antag-
onist activity of 4at 5HT
3A
receptors may also be involved in the control of pain
and emesis as described for 1[46–50].
Activity of 4at 5HT
2A
receptors seems to be minimal and studies to date are not
physiologically relevant, as shown with the high concentrations used in the follow-
ing study. Using NIH/3 T3 cells expressing rat 5HT
2A
receptors, 4showed activity
as a partial agonist but only at a concentration of 32 μMand furthermore it only had
50% efficacy at displacing [
3
H]-ketanserin [122]. The concentration used here
would not be reached in vivo.
Unlike most of the other phytocannabinoids, 4has been reported to act at TRP
cation channels not just in vitro but in vivo as well. In vitro, 4has been reported by
numerous studies to activate TRPV1, TRPV2, and TRPA1 channels [80,136–139]
in HEK293 cells expressing these channels (Table 6). The TRPA1 channels are
potently activated by 4, with this compound being the second most potent agonist at
this channel of all the phytocannabinoids tested in this study (Table 6)[80]. Indeed,
all phytocannabinoids mentioned in this chapter, except cannabichromene (7),
antagonize the Ca
2+
elevation response induced by the agonist icilin [79,80], but
82 S.E. Turner et al.
4is the most potent antagonist at this channel (Table 6)[80]. Moreover, in a recent
study using whole cell patch clamp techniques on HEK293 transfected cells, it was
shown that 4(3, 10, 30 μM) dose-dependently activated and rapidly desensitized
TRPV1, TRPV2, and TRPA1 channels [139]. The TRPV3 channels are activated by
4with high efficacy (50% higher than that of ionomycin) and high potency
(Table 6)[81].
In vivo, 4shows possible activity at TRPV1 channels in mice and rats [102–104]
and TRPA1 channels in rats [140]. The effects of 4in one of these studies was
blocked by the TRPA1 selective antagonist, AP18, and by the TRPV1 selective
antagonist, 5-iodo-resiniferatoxin, indicating involvement of these channels in the
tail-flick related antinociception effects of 4in anesthetized rats [140]. However,
these antinociceptive effects were also blocked by the CB
1
receptor-selective
antagonist, AM251, the 5HT
1A
receptor antagonist, WAY100635, and also the
adenosine A
1
-selective antagonist [140]. This indicated that the descending path-
way of antinociception in rats is possibly mediated by various mechanisms and the
mechanism by which 4mediates antinociception needs to be explored further.
The non-psychotropic quality of 4provides promise for its use in the clinic
and its “taming” of the effects of 1have also proven beneficial in a licensed
cannabis extract medication currently on the market in several countries,
Sativex®. This medication is for the treatment of spasticity in multiple sclerosis
patients and contains equal ratios of 4and 1.Here4functionally, not molecu-
larly, antagonizes the undesirable effects of 1, thus increasing its therapeutic
index [113]. This reported “antagonism” may be explained by the negative
allosteric modulation of CB
1
receptors as described in Sect. 5.1.Underthe
names Epidiolex®[141] and Cannabidiol Oral solution [142], 4has been
granted Orphan Drug designation by the U.S. FDA for treatment of Dravet
syndrome and Lennox-Gastaut syndrome, both of which being forms of
childhood-onset epilepsy. Epidiolex is in Phase 3 trials for Dravet syndrome
and Lennox-Gastaut syndrome and Cannabidiol Oral Solution is in Phase 1 clin-
ical trials for both these syndromes [141,142]. Epidiolex is also nearing the end
of Phase 2 trials for tuberous sclerosis, a genetic disease that results in benign
tumorgrowthinthebrainandothervital organs. Novagant Corp. has released
GoldenCBD™in capsule and liquid form. This is cannabidiol-rich hemp oil that
is being marketed as medical marijuana for people living outside the states of
WashingtonandColoradointheUSA[143].
6 Cannabidivarin
OH
HO
5
Molecular Pharmacology of Phytocannabinoids 83
Cannabidivarin (5) is the n-propyl analog of 4, therefore being part of the 4chemical
class type (Table 1) and like 4it is non-psychotropic. Little is known about the
pharmacological properties of 5[103] and how it exerts its therapeutic benefits. It
was first isolated in 1969 by Vollner and co-workers [103], but, since its classifi-
cation, relatively few studies have been conducted to determine its pharmacological
profile.
6.1 Activity at Cannabinoid Receptors
Pure 5and 5-enriched cannabis extracts are known to be CB
1
independent due to
the lack of effect on motor function in a battery of motor tasks [2,144]. Additionally,
in a CP-55940 radioligand-binding assay using MF1 whole mouse brain and in
CHO cells expressing human CB
1
receptors, pure 5only displaced CP-55940 at the
highest concentration tested (10 μM) and a 5-enriched extract showed very weak
affinity for CB
1
receptors, displacing CP-55940 only weakly [2]. For a summary of
5binding affinities to CB
1
and CB
2
receptors, see Table 2.
6.2 Cannabinoid Receptor Independent Activity
De Petrocellis and co-workers showed 5to have agonist and antagonist effects at
(TRP) cation channels. At human TRPA1 channels, 5is a potent agonist and a less
potent agonist at human TRPV1 and TRPV2 channels [80]. In this study, when
5was given to TRPM8 transfected HEK293 cells, it antagonized the Ca
2+
elevation
response elicited by the agonist icilin. With the same potency, 5induced
intracellular Ca
2+
elevation at the TRPV4 channel and is also an agonist at
TRPV3 channels (Table 7)[81].
A recent study using whole cell patch clamp techniques on HEK293 transfected
cells reported that 5(3, 10, 30 μM) dose-dependently activated, and rapidly
desensitized, TRPV1, TRPV2, and TRPA1 channels [139]. Previous work has
shown 5to have antiepileptiform activity in rat hippocampal slices [144] and
Iannotti and co-workers showed there to be significant TRPV1 transcript expression
in rat hippocampal slices [139]. This group therefore conducted multi-electrode
array (MEA) experiments, which showed that 5and the TRPV1 agonist, capsaicin,
84 S.E. Turner et al.
produced similar effects on epileptiform activity induced in rat hippocampal slices.
The effects of capsaicin on burst amplitude were reversed by the selective TRPV1
antagonist, IRTX, but the effects of 5were not. This indicated that the anti-
epileptiform effects of 5are not mediated by activity at TRPV1 channels [139].
In vivo, 5has been shown to display anticonvulsant properties in various acute
animal models of seizure [144] and is currently in Phase 2 clinical trials as an
antiepileptic drug [141]. The mechanism of action underlying these effects, how-
ever, is yet to be determined. In the pentylenetetrazole (PTZ) model of acute
seizure, 5(400 mg kg
1
p.o.) exhibited anticonvulsant effects by significantly
reducing PTZ-induced seizure activity, in male Wistar rats, which was correlated
with changes in gene expression of various epilepsy-related genes [145]. Of note is
the clinical relevance of the route of administration used in this study (per os)
compared to other in vivo studies where administration is via non-clinically rele-
vant routes. The mechanism by which 5induces changes in these epilepsy-related
genes requires investigation.
Apart from currently being in clinical trials for epilepsy, 5is also in clinical trials
for glioma, type-2 diabetes and schizophrenia and has received U.S. FDA Orphan
Drug Designation for neonatal hypoxic-ischemic encephalopathy [141]. This
phytocannabinoid, like 4, is therefore proving to be a promising therapeutic con-
stituent of cannabis.
Table 7 A comparison of selected in vitro studies showing cannabinoid receptor independent
activity of cannabidivarin (5) according to concentrations, assay types, and cell types used
Target
Concentration/
μM
EC
50
/
μM
IC
50
/
μMAssay Cell type Ref.
GPR55 <1 0.4 ERK1/2 MAPK
phosphorylation
HEK293/
Human
[69]
TRP cation channels
TRPA1 1–10 ND ND Whole cell patch
clamp
Hipocampal
slices/Rat
[139]
<1 0.42 Ca
2+
Fluorescence
assay
HEK293/Rat [80]
TRPM8 0.9 HEK293/Rat
TRPV1 1–10 3.6 HEK293/
Human
1–10 ND ND Whole cell patch
clamp
Hippocampal
slices/Rat
[139]TRPV2
1–10 7.3 Ca
2+
Fluorescence
assay
HEK293/Rat [80]
TRPV3 1.7 HEK293/Rat [81]
TRPV4 <1 0.9 HEK293/Rat
See Tables 1and 2
Molecular Pharmacology of Phytocannabinoids 85
7 Cannabigerol
6
OH
HO
Cannabigerol (6) is another non-psychotropic phytocannabinoid and its chemical
class type is the second most abundant in the cannabis plant, making up 16.3% of
the phytocannabinoid content [1]. The carboxylic acid form of this phyto-
cannabinoid, cannabigerolic acid (CBGA), is very important for the synthesis of
other phytocannabinoids. In fresh cannabis plant material, phytocannabinoids are
present in their carboxylic acid forms [146]. Cannabigerolic acid is the precursor to
the acid forms of three phytocannabinoids: Δ
9
-tetrahydrocannabinolic acid (Δ
9
-
THCA), cannabidiolic acid (CBDA), and cannabichromenic acid (CBCA) [147–
149]. Cannabigerovaric acid (CBGVA) is the precursor of the n-propyl analogues
of the carboxylic acid derivatives Δ
9
-THCVA, CBDVA, and CBCVA [146]. Upon
heating and storage of cannabis plant material these acid forms undergo decarbox-
ylation to produce the non-acid forms, such as 1and 2[150]. Furthermore, under
prolonged storage and drying some of these non-acid forms undergo oxidative
catabolism to other phytocannabinoids. An example of this is oxidative catabolism
of 1to 3, as described in Sect. 4[84]. This phytocannabinoid was first isolated by
Gaoni and Mechoulam in 1964 [151] and since then only a few studies have been
conducted to investigate its pharmacological actions.
7.1 Activity at Cannabinoid Receptors
The non-psychotropic effect of 6is explained by its low affinity for CB
1
receptors (Table 2)[103] and it has been shown in vivo to not produce
psychotropic effects like 1[152]. It does however affect endocannabinoid tone
indirectly by inhibiting anandamide uptake, thereby increasing levels of anan-
damide, as shown in Table 8.
86 S.E. Turner et al.
7.2 Cannabinoid Receptor Independent Activity
Despite the relatively few investigational studies conducted, there is evidence of
pharmacological actions at a number of targets. In a study using mouse brain
membranes, 6acted as a potent α2 adrenoceptor agonist [153]. The same study
found 6to moderately block 5HT
1A
receptors with a K
B
value of 0.0519 μM.This
effect is opposite to that of 4on 5HT
1A
receptors and explains the ability of 6to
antagonize the antinausea and antiemetic effect of 4[154].
Like many phytocannabinoids, 6interacts with numerous TRP cation channels.
It is a potent TRPA1 agonist, a weak agonist at TRPV1 and TRPV2 and a potent
TRPM8 antagonist (Table 8)[80].
Table 8 A comparison of selected in vitro studies showing cannabinoid receptor independent
activity of cannabigerol (6) according to concentrations, assay types, and cell types used
Target
Concentration/
μM
EC
50
/
μM
IC
50
/
μMAssay Cell type Ref.
GPR55 1–10 2.16 ERK1/2 MAPK
phosphorylation
HEK293/
Human
[69]
α2
adrenoceptor
<1 0.0002 GTPγS binding
assay
Brain mem-
branes/Mouse
[153]
0.072 Electrically
invoked
contractions
Vas deferens/
Mouse
TRP cation channels
TRPA1 1–10 3.4 Ca
2+
Fluorescence
assay
HEK293/Rat [79]
<1 0.7 HEK293/Rat [80]
TRPM8 0.16 HEK293/Rat [79]
0.16 HEK293/Rat [80]
TRPV1 1–10 1.3 HEK293/
Human
TRPV2 1.72 HEK293/Rat
TRPV3 1.0 HEK293/Rat [81]
TRPV4 5.1 HEK293/Rat
Anandamide
uptake
11.3 [
14
C]-AEA uptake RBL-2H3
cells/Rat
[80]
AEA, anandamide (arachidonoylethanolamine); also see Tables 1and 2
Molecular Pharmacology of Phytocannabinoids 87
8 Cannabichromene
O
OH
7
Cannabichromene (7) is one of the most abundant phytocannabinoids naturally
occurring in the cannabis plant, with its chemical class type making up the same
percentage as that of the 4chemical class type (Table 1)[1,151,155]. It was
discovered independently by Claussen and co-workers and Gaoni and Mechoulam
in 1966 [103].
8.1 Activity at Cannabinoid Receptors
Cannabichromene has not been found to have significant affinity for CB
1
or CB
2
receptors as shown in Table 2but it does, however, affect endocannabinoid tone
indirectly by inhibiting cellular uptake of anandamide (Table 9)[80].
8.2 Cannabinoid Receptor Independent Activity
The most notable pharmacological action of 7to date is most likely its effect at TRP
cation channels. At TRPA1 channels, 7was found to be the most potent agonist of
all the phytocannabinoids tested and also desensitized the TRPA1 channel to
activation by the agonist allyl isothiocyanate [80]. At a lower potency, but still
within the lower micromolar range, 7was able to activate TRPV3 and TRPV4
channels and also desensitize TRPV4 channels to an agonist (9.9 μM)[81]. At the
TRPV2 channel, 7was only found to desensitize the channel and although 7was
found to block TRPM8 channel activation, this was at a very low potency [80] and
would not be deemed physiologically relevant in vivo (Table 9)[23].
At a concentration of 1 μM,7has also been reported to act via ATP upregulation
and adenosine signaling to raise the viability of adult mouse neural stem/progenitor
cells (NSPCs) during differentiation [156]. The adenosine A
1A
receptor selective
antagonist, DPCPX, countered the stimulation of ERK1/2 phosphorylation by 7and
the upregulation of the astrocyte marker nestin by 7.
88 S.E. Turner et al.
Table 9 A comparison of selected in vitro studies showing cannabinoid receptor independent activity of cannabichromene (7) according to concentrations,
assay types, and cell types used
Target Concentration/μMEC
50
/μmol IC
50
/μMAssay Cell type Ref.
TRP cation channels
TRPA1 <1 0.06 Ca
2+
Fluorescence assay HEK293/Rat [79]
0.09 HEK293/Rat [80]
TRPM8 >10 40.7 HEK293/Rat
TRPV1 24.2 HEK293/Human
TRPV3 1–10 1.9 HEK293/Rat [81]
TRPV4 <1 0.6 HEK293/Rat
Anandamide uptake >10 12.3 [
14
C]-AEA uptake RBL-2H3 cells/Rat [80]
Adenosine A
1A
receptor ND MTT (viability) assay Neuroprogenitor cells (NSPCs)/Mouse [156]
See Tables 1and 2
Molecular Pharmacology of Phytocannabinoids 89
9 Conclusions
This chapter has reviewed the molecular pharmacology of the seven most thor-
oughly studied phytocannabinoids and demonstrated that each has a diverse set of
pharmacological targets with varying therapeutic, recreational and toxicological
effects. Even slight structural differences between the phytocannabinoids can
produce very diverse and competing physiological effects. Investigations into
some of the phytocannabinoids have produced conflicting results, as mentioned in
this chapter. Thus, it is critical to take into account the differences in assays used,
the species from which the target is taken and the concentrations used in in vitro
studies in order to predict the pharmacology of the phytocannabinoids at the system
level. It is important that the concentrations used to elicit a response in vitro are
indicative of the levels that will be reached after administration in animal models or
in the clinic, otherwise no predictions can be made on the physiological relevance
of results from in vitro studies. As highlighted by McPartland and co-workers, it is
imperative that when analyzing the results of various studies one takes into account
interspecies differences in receptor distribution and differences among different
tissues and cell types [105]. Moreover, it is also important when designing exper-
iments to look at the therapeutic benefits of a phytocannabinoid that the species
used, route of administration of the compound, and concentrations used are clini-
cally relevant, i.e. applicable to the end target species. It is therefore important to
assess species differences in receptor orthologues and distribution, remembering
that there are molecular divergences between human and rodent orthologues such
as, for example, within the endocannabinoid system [157].
This chapter has also highlighted the importance of each individual phyto-
cannabinoid in mediating the therapeutic and recreational effects of cannabis.
Two phytocannabinoids, 4and 5, may prove to be clinically useful constituents
of cannabis. Both phytocannabinoids have been granted Orphan Drug designation
by the U.S. FDA for a number of seizure-related disorders and, as a result, Phase II
and III clinical trials are underway [141–143]. The conduct of formal clinical trials
using these non-Δ
9
-tetrahydrocannabinol phytocannabinoids could stimulate new
research of cannabis and its constituents and see additional phytocannabinoids
objectively assessed for therapeutic potential. Even though research on individual
phytocannabinoids has been conducted for many years, still much more research is
warranted. The cannabis plant contains about 120 phytocannabinoids, which shows,
in reality, how little research has been conducted on these compounds.
Further research on the “known” phytocannabinoids as well as the “unknown”
phytocannabinoids would greatly advance our understanding of these substances
alone as well as in conjunction with each other or as part of a whole in cannabis.
Acknowledgements We would like to thank Prof. Simon Gibbons for providing the figures of the
phytocannabinoid structures.
90 S.E. Turner et al.
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Molecular Pharmacology of Phytocannabinoids 99
Sarah E. Turner is undertaking her Ph.D. in neurophar-
macology at the University of Reading under the guidance of
Prof. Claire M. Williams and Prof. Benjamin J. Whalley. Her
work involves investigation of the antiepileptic mechanism
of action of two phytocannabinoids. She received a B.Sc.
(Hons) degree in Animal Science from the University of
Pretoria, South Africa in 2009. Since moving to the United
Kingdom in 2010, she worked as a research technician at the
University of Reading for three years in Prof. Benjamin
J. Whalley and Prof. Claire M. Williams’s research group.
She has extensive experience in behavioral neuroscience,
investigating the effects of phytocannabinoids on acute sei-
zures and epilepsy in various animal models and investigat-
ing the effects of phytocannabinoid treatment and the
comorbidity effects of epilepsy on motor function and cog-
nition. This work led to being named as a co-author on two peer-reviewed papers. Her main interests
lie in investigating the therapeutic benefits of phytocannabinoids in various diseases and disorders
and driving phytocannabinoid treatment through clinical trials.
Claire Williams is a behavioral pharmacologist with
research interests that explore the role of natural phyto-
(plant derived) chemicals for biomedical research and
developing novel dietary or therapeutic strategies to
improve health. After studying for a B.Sc. (Hons) degree
in Applied Biology from Nottingham Trent University,
Claire moved to the School of Psychology and Clinical
Language Sciences at the University of Reading in 1996 to
study for a Ph.D. investigating the role of the cannabinoid
system in feeding behavior, graduating in 2000. After
receiving her Ph.D., she began a postdoctoral research posi-
tion at the University of Reading continuing the work from
her Ph.D. on cannabinoid-induced feeding. In October 2002
she was awarded tenure working as a Lecturer (2002–2010),
Associate Professor (2010–2015) and Professor (2015–pre-
sent) within the School of Psychology and Clinical Lan-
guage Sciences at the University of Reading. She has been
awarded grant funding from several UK research councils and has established extensive research
collaborations with industry. To date, Professor Williams has published over 40 research articles in
peer-reviewed journals, four invited book chapters, and has been named as co-inventor on several
patents.
100 S.E. Turner et al.
Leslie Iversen, Ph.D., F.R.S, C.B.E. is Visiting Professor
at the Department of Pharmacology, University of Oxford.
He was previously Director of the Wolfson Centre for
Research on Age Related diseases at Kings College
London (1999–2004), Director of the Neuroscience
Research Centre for Merck & Co. Inc. in the UK
(1983–1995), and Director of the Medical Research Coun-
cil Neurochemical Pharmacology Unit in Cambridge,
England (1970–1983). He is well known for his research
on how drugs interact with chemical messengers in the
nervous system and has published more than 300 scientific
papers on this topic and is the author of “The Science of
Marijuana, 2nd Ed.”, 2007; “Speed, Ecstasy, and Ritalin:
the Science of Amphetamines”, 2007; “Introduction to
Neuropsychopharmacology”, 2008; and “Very Short Intro-
duction Drugs” (2nd Edition), 2016, Oxford University Press. He is a Fellow of the Royal
Society London, and a Foreign Associate of the US National Academy of Sciences.
Benjamin J. Whalley is a Professor of Neuropharmacol-
ogy at the Reading School of Pharmacy. He received a
B. Pharm. (Hons) degree from the London School of Phar-
macy, University of London in 1992. Since registering as a
pharmacist since 1993, he worked in community and pri-
mary care trust pharmacy for several years before undertak-
ing a Ph.D. in Neuroscience at the London School of
Pharmacy, University of London. He was subsequently
appointed as a Lecturer at the Reading School of Pharmacy
in 2005. He is a member of the UK Advisory Council on the
Misuse of Drugs. His research interests lie in investigating
neuronal processes that underlie complex physiological
functions such as neuronal hyperexcitability states and
their consequential disorders (e.g. epilepsy and ataxia).
This work has helped to determine cellular mechanisms
that underlie the effects of antiepileptic drugs in clinical use
or currently in clinical trials, particularly non-psychoactive
components of cannabis drugs for which he received the 2014 Royal Pharmaceutical Society’s
Science Award. A further significant component of his research has been the development of
experimental platforms that combine biological (neuronal cell culture, including human stem cell-
based networks) and machine systems to produce tools for investigating the cellular correlates of
complex CNS function and dysfunction.
Molecular Pharmacology of Phytocannabinoids 101
