David B. Finlay

Bio: David B. Finlay is an academic researcher from University of Otago. The author has contributed to research in topics: Cannabinoid receptor & Cannabinoid. The author has an hindex of 10, co-authored 22 publications receiving 423 citations. Previous affiliations of David B. Finlay include University of Auckland, Faculty of Medical and Health Sciences & University of Auckland.

Cannabinoid CB2 receptor ligand profiling reveals biased signalling and off-target activity

Abstract: The cannabinoid CB2 receptor (CB2R) represents a promising therapeutic target for various forms of tissue injury and inflammatory diseases. Although numerous compounds have been developed and widely used to target CB2R, their selectivity, molecular mode of action and pharmacokinetic properties have been poorly characterized. Here we report the most extensive characterization of the molecular pharmacology of the most widely used CB2R ligands to date. In a collaborative effort between multiple academic and industry laboratories, we identify marked differences in the ability of certain agonists to activate distinct signalling pathways and to cause off-target effects. We reach a consensus that HU910, HU308 and JWH133 are the recommended selective CB2R agonists to study the role of CB2R in biological and disease processes. We believe that our unique approach would be highly suitable for the characterization of other therapeutic targets in drug discovery research.

Gαs signalling of the CB1 receptor and the influence of receptor number.

Abstract: BACKGROUND AND PURPOSE CB1 cannabinoid receptor signalling is canonically mediated through inhibitory Gαi proteins, but signalling through other G proteins occurs under some circumstances; Gαs being the most characterised secondary pathway. Determinants of this signalling switch identified to date include Gαi blockade, CB1/D2 dopamine receptor co-stimulation, CB1 agonist class, and cell background. The aim of this study was to examine the effects of receptor number and ligand dependence on CB1 signalling. EXPERIMENTAL APPROACH CB1 was expressed in HEK cells at different levels, and signalling characterisation was performed for cAMP by real-time BRET biosensor – CAMYEL – and for phospho-ERK by AlphaScreen. Characterisation of a novel irreversible antagonist of CB1, AM6544, was performed by homogenate and whole cell radioligand binding assays. KEY RESULTS In HEK cells expressing high levels of CB1, agonist treatment resulted in cAMP stimulation; a response not previously known to be mediated by receptor number. Δ9-THC and BAY59-3074 increased cAMP only in high-expressing cells that had been pre-treated with pertussis toxin, and agonists demonstrated more diverse signalling profiles in the stimulatory pathway than they elicited in the canonical inhibitory pathway. CB1 pharmacological knockdown and Gαi1 supplementation were sufficient to restore canonical Gαi signalling to high expressing cells. Constitutive signalling in both lower- and higher-expressing cells was Gαi-mediated. CONCLUSION AND IMPLICATIONS CB1 coupling to opposing G proteins is determined by both receptor and G protein number, and this underpins a mechanism for non-canonical signalling in a fashion consistent with Gαs signalling. CB1 is known to mediate opposite consequences in endpoints such as tumour viability receptor number-dependently, and our study may help to explain such effects at the level of G protein coupling.

Terpenoids From Cannabis Do Not Mediate an Entourage Effect by Acting at Cannabinoid Receptors.

Abstract: The entourage effect was a proposed explanation for biological observations that endocannabinoid ligand activities can be modified by other lipids released from cells at the same time. An increasing volume of anecdotal reports and interest in the plant have provoked research into the activity of minor chemical constituents of the plant-including volatile terpenoids such as myrcene, α- and β- pinene, β-caryophyllene, and limonene. However, to date, no clear interaction has been identified. The current study was designed to determine whether terpenes in the cannabis plant have detectable receptor-mediated activity, or modify the activity of Δ9-tetrahydrocannabinol, cannabidiol, or the endocannabinoid 2-arachidonylglycerol at the cannabinoid receptors. In addition, we have utilized a standard radioligand binding paradigm with ability to detect orthosteric and allosteric interactions of test compounds. With the possible exception of a weak interaction of β-caryophyllene with CB2, no data were produced to support the hypothesis that any of the five terpenes tested (either alone or in mixtures) have direct interactions with CB1 or CB2, as the binding of radioligand ([3H]-CP55,940), Δ9-tetrahydrocannabinol, and cannabidiol were unaltered by the presence of terpenes. Similarly, terpene functional effects were also not detected, either alone or in combination with Δ9-tetrahydrocannabinol, cannabidiol, or 2-arachidonoylglycerol. This study adds to the evidence that the putative entourage effect cannot be explained by direct effects at CB1 or CB2.

GPR18 undergoes a high degree of constitutive trafficking but is unresponsive to N-Arachidonoyl Glycine

Abstract: The orphan receptor GPR18 has become a research target following the discovery of a putative endogenous agonist, N-arachidonoyl glycine (NAGly). Chemical similarity between NAGly and the endocannabinoid anandamide suggested the hypothesis that GPR18 is a third cannabinoid receptor. GPR18-mediated cellular signalling through inhibition of cyclic adenosine monophosphate (cAMP) and phosphorylation of extracellular signal-regulated kinase (ERK), in addition to physiological consequences such as regulation of cellular migration and proliferation/apoptosis have been described in response to both NAGly and anandamide. However, discordant findings have also been reported. Here we sought to describe the functional consequences of GPR18 activation in heterologously-expressing HEK cells. GPR18 expression was predominantly intracellular in stably transfected cell lines, but moderate cell surface expression could be achieved in transiently transfected cells which also had higher overall expression. Assays were employed to characterise the ability of NAGly or anandamide to inhibit cAMP or induce ERK phosphorylation through GPR18, or induce receptor trafficking. Positive control experiments, which utilised cells expressing hCB1 receptors (hCB1R), were performed to validate assay design and performance. While these functional pathways in GPR18-expressing cells were not modified on treatment with a panel of putative GPR18 ligands, a constitutive phenotype was discovered for this receptor. Our data reveal that GPR18 undergoes rapid constitutive receptor membrane trafficking-several-fold faster than hCB1R, a highly constitutively active receptor. To enhance the likelihood of detecting agonist-mediated receptor signalling responses, we increased GPR18 protein expression (by tagging with a preprolactin signal sequence) and generated a putative constitutively inactive receptor by mutating the hGPR18 gene at amino acid site 108 (alanine to asparagine). This A108N mutant did cause an increase in surface receptor expression (which may argue for reduced constitutive activity), but no ligand-mediated effects were detected. Two glioblastoma multiforme cell lines (which endogenously express GPR18) were assayed for NAGly-induced pERK phosphorylation, with negative results. Despite a lack of ligand-mediated responses in all assays, the constitutive trafficking of GPR18 remains an interesting facet of receptor function and will have consequences for understanding the role of GPR18 in physiology.

Cannabinoid CB1 and CB2 Receptor-Mediated Arrestin Translocation: Species, Subtype, and Agonist-Dependence.

Abstract: Arrestin translocation and signaling have come to the fore of the G protein-coupled receptor molecular pharmacology field. Some receptor-arrestin interactions are relatively well understood and considered responsible for specific therapeutic or adverse outcomes. Coupling of arrestins with cannabinoid receptors 1 (CB1) and 2 (CB2) has been reported, though the majority of studies have not systematically characterized the differential ligand dependence of this activity. In addition, many prior studies have utilized bovine (rather than human) arrestins, and the most widely applied assays require reporter-tagged receptors, which prevent meaningful comparison between receptor types. We have employed a bioluminescence resonance energy transfer (BRET) method that does not require the use of tagged receptors and thereby allows comparisons of arrestin translocation between receptor types, as well as with cells lacking the receptor of interest - an important control. The ability of a selection of CB1 and CB2 agonists to stimulate cell surface translocation of human and bovine β-arrestin-1 and -2 was assessed. We find that some CB1 ligands induce moderate β-arrestin-2 translocation in comparison with vasopressin V2 receptor (a robust arrestin recruiter); however, CB1 coupling with β-arrestin-1 and CB2 with either arrestin elicited low relative efficacies. A range of efficacies between ligands was evident for both receptors and arrestins. Endocannabinoid 2-arachidonoylglycerol stood out as a high efficacy ligand for translocation of β-arrestin-2 via CB1. Δ9-tetrahydrocannabinol was generally unable to elicit translocation of either arrestin subtype via CB1 or CB2; however, control experiments revealed translocation in cells not expressing CB1/CB2, which may assist in explaining some discrepancy with the literature. Overexpression of GRK2 had modest influence on CB1/CB2-induced arrestin translocation. Results with bovine and human arrestins were largely analogous, but a few instances of inconsistent rank order potencies/efficacies between bovine and human arrestins raise the possibility that subtle differences in receptor conformation stabilized by these ligands manifest in disparate affinities for the two arrestin species, with important potential consequences for interpretation in ligand bias studies. As well as contributing important information regarding CB1/CB2 ligand-dependent arrestin coupling, our study raises a number of points for consideration in the design and interpretation of arrestin recruitment assays.

Cannabinoids and the expanded endocannabinoid system in neurological disorders.

Abstract: Anecdotal evidence that cannabis preparations have medical benefits together with the discovery of the psychotropic plant cannabinoid Δ9-tetrahydrocannabinol (THC) initiated efforts to develop cannabinoid-based therapeutics. These efforts have been marked by disappointment, especially in relation to the unwanted central effects that result from activation of cannabinoid receptor 1 (CB1), which have limited the therapeutic use of drugs that activate or inactivate this receptor. The discovery of CB2 and of endogenous cannabinoid receptor ligands (endocannabinoids) raised new possibilities for safe targeting of this endocannabinoid system. However, clinical success has been limited, complicated by the discovery of an expanded endocannabinoid system — known as the endocannabinoidome — that includes several mediators that are biochemically related to the endocannabinoids, and their receptors and metabolic enzymes. The approvals of nabiximols, a mixture of THC and the non-psychotropic cannabinoid cannabidiol, for the treatment of spasticity and neuropathic pain in multiple sclerosis, and of purified botanical cannabidiol for the treatment of otherwise untreatable forms of paediatric epilepsy, have brought the therapeutic use of cannabinoids and endocannabinoids in neurological diseases into the limelight. In this Review, we provide an overview of the endocannabinoid system and the endocannabinoidome before discussing their involvement in and clinical relevance to a variety of neurological disorders, including Parkinson disease, Alzheimer disease, Huntington disease, multiple sclerosis, amyotrophic lateral sclerosis, traumatic brain injury, stroke, epilepsy and glioblastoma. In this Review, Cristino, Bisogno and Di Marzo outline the biology of cannabinoids, the endocannabinoid system and the expanded endocannabinoid system and discuss the involvement of these systems and the therapeutic potential of cannabinoids across the spectrum of neurological disease.

Cannabinoid ligands targeting TRP channels

Abstract: Transient receptor potential (TRP) channels are a group of membrane proteins involved in the transduction of a plethora of chemical and physical stimuli. These channels modulate ion entry, mediating a variety of neural signaling processes implicated in the sensation of temperature, pressure, and pH, as well as smell, taste, vision, and pain perception. Many diseases involve TRP channel dysfunction, including neuropathic pain, inflammation, and respiratory disorders. In the pursuit of new treatments for these disorders, it was discovered that cannabinoids can modulate a certain subset of TRP channels. The TRP vanilloid (TRPV), TRP ankyrin (TRPA), and TRP melastatin (TRPM) subfamilies were all found to contain channels that can be modulated by several endogenous, phytogenic, and synthetic cannabinoids. To date, six TRP channels from the three subfamilies mentioned above have been reported to mediate cannabinoid activity: TRPV1, TRPV2, TRPV3, TRPV4, TRPA1, and TRPM8. The increasing data regarding cannabinoid interactions with these receptors has prompted some researchers to consider these TRP channels to be "ionotropic cannabinoid receptors." Although CB1 and CB2 are considered to be the canonical cannabinoid receptors, there is significant overlap between cannabinoids and ligands of TRP receptors. The first endogenous agonist of TRPV1 to be discovered was the endocannabinoid, anandamide (AEA). Similarly, N-arachidonyl dopamine (NADA) and AEA were the first endogenous TRPM8 antagonists discovered. Additionally, Δ9-tetrahydrocannabinol (Δ9-THC), the most abundant psychotropic compound in cannabis, acts most potently at TRPV2, moderately modulates TRPV3, TRPV4, TRPA1, and TRPM8, though Δ9-THC is not reported to modulate TRPV1. Moreover, TRP receptors may modulate effects of synthetic cannabinoids used in research. One common research tool is WIN55,212-2, a CB1 agonist that also exerts analgesic effects by desensitizing TRPA1 and TRPV1. In this review article, we aim to provide an overview and classification of the cannabinoid ligands that have been reported to modulate TRP channels and their therapeutic potential.

New approaches and challenges to targeting the endocannabinoid system.

Abstract: The endocannabinoid signalling system was discovered because receptors in this system are the targets of compounds present in psychotropic preparations of Cannabis sativa. The search for new therapeutics that target endocannabinoid signalling is both challenging and potentially rewarding, as endocannabinoids are implicated in numerous physiological and pathological processes. Hundreds of mediators chemically related to the endocannabinoids, often with similar metabolic pathways but different targets, have complicated the development of inhibitors of endocannabinoid metabolic enzymes but have also stimulated the rational design of multi-target drugs. Meanwhile, drugs based on botanical cannabinoids have come to the clinical forefront, synthetic agonists designed to bind cannabinoid receptor 1 with very high affinity have become a societal threat and the gut microbiome has been found to signal in part through the endocannabinoid network. The current development of drugs that alter endocannabinoid signalling and how this complex system could be pharmacologically manipulated in the future are described in this Opinion article.