Antipsychotic potential of the type 1 cannabinoid receptor positive allosteric modulator GAT211: preclinical in vitro and in vivo studies

Cannabinoid receptor 1 positive allosteric modulator ZCZ011 shows differential effects on behavior and the endocannabinoid system in HIV-1 Tat transgenic female and male mice

The cannabinoid receptor type 1 (CB1R) is a promising therapeutic target for various neurodegenerative diseases, including HIV-1-associated neurocognitive disorder (HAND). However, the therapeutic potential of CB1R by direct activation is limited due to its psychoactive side effects. Therefore, research has focused on indirectly activating the CB1R by utilizing positive allosteric modulators (PAMs). Studies have shown that CB1R PAMs (ZCZ011 and GAT211) are effective in mouse models of Huntington's disease and neuropathic pain, and hence, we assess the therapeutic potential of ZCZ011 in a well-established mouse model of neuroHIV. The current study investigates the effect of chronic ZCZ011 treatment (14 days) on various behavioral paradigms and the endocannabinoid system in HIV-1 Tat transgenic female and male mice. Chronic ZCZ011 treatment (10 mg/kg) did not alter body mass, locomotor activity, or anxiety-like behavior regardless of sex or genotype. However, differential effects were noted in hot plate latency, motor coordination, and recognition memory in female mice only, with ZCZ011 treatment increasing hot plate latency and improving motor coordination and recognition memory. Only minor effects or no alterations were seen in the endocannabinoid system and related lipids except in the cerebellum, where the effect of ZCZ011 was more pronounced in female mice. Moreover, AEA and PEA levels in the cerebellum were positively correlated with improved motor coordination in female mice. In summary, these findings indicate that chronic ZCZ011 treatment has differential effects on antinociception, motor coordination, and memory, based on sex and HIV-1 Tat expression, making CB1R PAMs potential treatment options for HAND without the psychoactive side effects.

The endocannabinoid system as a putative target for the development of novel drugs for the treatment of psychiatric illnesses

Cannabis is well established to impact affective states, emotion and perceptual processing, primarily through its interactions with the endocannabinoid system. While cannabis use is quite prevalent in many individuals afflicted with psychiatric illnesses, there is considerable controversy as to whether cannabis may worsen these conditions or provide some form of therapeutic benefit. The development of pharmacological agents which interact with components of the endocannabinoid system in more localized and discrete ways then via phytocannabinoids found in cannabis, has allowed the investigation if direct targeting of the endocannabinoid system itself may represent a novel approach to treat psychiatric illness without the potential untoward side effects associated with cannabis. Herein we review the current body of literature regarding the various pharmacological tools that have been developed to target the endocannabinoid system, their impact in preclinical models of psychiatric illness and the recent data emerging of their utilization in clinical trials for psychiatric illnesses, with a specific focus on substance use disorders, trauma-related disorders, and autism. We highlight several candidate drugs which target endocannabinoid function, particularly inhibitors of endocannabinoid metabolism or modulators of cannabinoid receptor signaling, which have emerged as potential candidates for the treatment of psychiatric conditions, particularly substance use disorder, anxiety and trauma-related disorders and autism spectrum disorders. Although there needs to be ongoing clinical work to establish the potential utility of endocannabinoid-based drugs for the treatment of psychiatric illnesses, the current data available is quite promising and shows indications of several potential candidate diseases which may benefit from this approach.

Cannabinoid receptor 1 positive allosteric modulator (GAT229) attenuates cisplatin-induced neuropathic pain in mice

Chemotherapy-induced peripheral neuropathy (CIPN) is one of chemotherapies' most often documented side effects. Patients with CIPN experience spontaneous burning, numbness, tingling, and neuropathic pain in their feet and hands. Currently, there is no effective pharmacological treatment to prevent or treat CIPN. Activating the cannabinoid receptor type 1 (CB₁) by orthosteric agonists has shown promising results in alleviating the pain and neuroinflammation associated with CIPN. However, the use of CB₁ orthosteric agonists is linked to undesirable side effects. Unlike the CB₁ orthosteric agonists, CB₁ positive allosteric modulators (PAMs) don't produce any psychoactive effects, tolerance, or dependence. Previous studies have shown that CB₁ PAMs exhibit antinociceptive effects in inflammatory and neuropathic rodent models. This study aimed to investigate the potential benefits of the newly synthesized GAT229, a pure CB₁ PAM, in alleviating neuropathic pain and slowing the progression of CIPN. GAT229 was evaluated in a cisplatin-induced (CIS) mouse model of peripheral neuropathic pain (3 mg/kg/d, 28 d, i.p.). GAT229 attenuated and slowed the progression of thermal hyperalgesia and mechanical allodynia induced by CIS, as evaluated by the hotplate test and von Frey filament test. GAT229 reduced the expression of proinflammatory cytokines in the dorsal root ganglia (DRG) neurons. Furthermore, GAT229 attenuated nerve injuries by normalizing the brain-derived neurotrophic factor and the nerve growth factor mRNA expression levels in the DRG neurons. The CB₁ receptor antagonist/inverse agonist AM251 blocked GAT229-mediated beneficial effects. According to our data, we suggest that CB₁ PAMs might be beneficial in alleviating neuropathic pain and slowing the progression of CIPN.

Endocannabinoid signaling in the central nervous system

It is hard to overestimate the influence of the endocannabinoid signaling (ECS) system on central nervous system (CNS) function. In the 40 years since cannabinoids were found to trigger specific cell signaling cascades, studies of the ECS system continue to cause amazement, surprise, and confusion! CB1 cannabinoid receptors are expressed widely in the CNS and regulate cell-cell communication via effects on the release of both neurotransmitters and gliotransmitters. CB2 cannabinoid receptors are difficult to detect in the CNS but seem to "punch above their weight" as compounds targeting these receptors have significant effects on inflammatory state and behavior. Positive and negative allosteric modulators for both receptors have been identified and examined in preclinical studies. Concentrations of the endocannabinoid ligands, N-arachidonoylethanolamine and 2-arachidonoylglycerol (2-AG), are regulated by a combination of enzymatic synthesis and degradation and inhibitors of these processes are available and making their way into clinical trials. Importantly, ECS regulates many essential brain functions, including regulation of reward, anxiety, inflammation, motor control, and cellular development. While the field is on the cusp of preclinical discoveries providing impactful clinical and therapeutic insights into many CNS disorders, there is still much to be learned about this remarkable and versatile modulatory system.

Design, synthesis, and pharmacological profiling of cannabinoid 1 receptor allosteric modulators: Preclinical efficacy of C2-group GAT211 congeners for reducing intraocular pressure

Allosteric modulators of cannabinoid 1 receptor (CB1R) show translational promise over orthosteric ligands due to their potential to elicit therapeutic benefit without cannabimimetic side effects. The prototypic 2-phenylindole CB1R allosteric modulator, GAT211 (1), demonstrates preclinical efficacy in various disease models. The limited systematic structure-activity relationship (SAR) data at the C2 position of the indole ring within GAT211 invites the opportunity for further modifications to improve GAT211's pharmacological profile while serving to amplify and variegate this library of therapeutically attractive agents. These considerations prompted this focused SAR study in which we substituted the GAT211 C2-phenyl ring with heteroaromatic substituents. The synthesized GAT211 analogs were then evaluated in vitro as CB1R allosteric modulators in cAMP and β-arrestin2 assays with CP55,940 as the orthosteric ligand. Furan and thiophene rings (15c-f and 15m) were the best-tolerated substituents at the C2 position of GAT211 for engagement with human CB1R (hCB1R). The SAR around the novel ligands reported allowed direct experimental characterization of the interaction profile of that pharmacophore with its binding domain in functional, human CB1R, thus offering guidance for accessing subsequent-generation hCB1R allosteric modulators as potential therapeutics. The most potent analog, 15d, markedly promoted orthosteric ligand binding to hCB1R. Pharmacological profiling in the GTPγS and mouse vas deferens assays demonstrated that 15d behaves as a CB1R agonist-positive allosteric modulator (ago-PAM), as confirmed electrophysiologically in autoptic neurons. In vivo, 15d was efficacious as a topical agent that significantly reduced intraocular pressure (IOP) in the ocular normotensive murine model of glaucoma. Since elevated IOP is a decisive risk factor for glaucoma and attendant vision loss, our data support the proposition that the 2-phenylindole class of CB1R ago-PAMs has therapeutic potential for glaucoma and other diseases where potentiation of CB1R signaling may be therapeutic.

The Endocannabinoid System: A Potential Target for the Treatment of Various Diseases

The Endocannabinoid System (ECS) is primarily responsible for maintaining homeostasis, a balance in internal environment (temperature, mood, and immune system) and energy input and output in living, biological systems. In addition to regulating physiological processes, the ECS directly influences anxiety, feeding behaviour/appetite, emotional behaviour, depression, nervous functions, neurogenesis, neuroprotection, reward, cognition, learning, memory, pain sensation, fertility, pregnancy, and pre-and post-natal development. The ECS is also involved in several pathophysiological diseases such as cancer, cardiovascular diseases, and neurodegenerative diseases. In recent years, genetic and pharmacological manipulation of the ECS has gained significant interest in medicine, research, and drug discovery and development. The distribution of the components of the ECS system throughout the body, and the physiological/pathophysiological role of the ECS-signalling pathways in many diseases, all offer promising opportunities for the development of novel cannabinergic, cannabimimetic, and cannabinoid-based therapeutic drugs that genetically or pharmacologically modulate the ECS via inhibition of metabolic pathways and/or agonism or antagonism of the receptors of the ECS. This modulation results in the differential expression/activity of the components of the ECS that may be beneficial in the treatment of a number of diseases. This manuscript in-depth review will investigate the potential of the ECS in the treatment of various diseases, and to put forth the suggestion that many of these secondary metabolites of Cannabis sativa L. (hereafter referred to as "C. sativa L." or "medical cannabis"), may also have potential as lead compounds in the development of cannabinoid-based pharmaceuticals for a variety of diseases.

Positive allosteric modulation of type 1 cannabinoid receptors reduces spike-and-wave discharges in Genetic Absence Epilepsy Rats from Strasbourg

Childhood Absence Epilepsy (CAE) accounts for approximately 10% of all pediatric epilepsies. Current treatments for CAE are ineffective in approximately 1/3 of patients and can be associated with severe side effects such as hepatotoxicity. Certain cannabinoids, such as cannabidiol (CBD), have shown promise in the treatment of pediatric epilepsies. However, CBD remains limited or prohibited in many jurisdictions, and has not been shown to have efficacy in CAE. Modulation of the type 1 cannabinoid receptor (CB1R) may provide more desirable pharmacological treatments. Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model many aspects of CAE, including cortical spike and wave discharges (SWDs). We have recently demonstrated that Δ⁹-tetrahydrocannabinol (THC) increases SWDs in GAERS whereas CBD decreases these events. Here, we characterized aspects of the endocannabinoid system in brain areas relevant to seizures in GAERS and tested whether positive allosteric modulators (PAMs) of CB1R reduced SWDs. Both female and male GAERS had reduced (>50%) expression of CB1R and elevated levels of the endocannabinoid 2-AG in cortex compared to non-epileptic controls (NEC). We then administered the CB1R PAMs GAT211 and GAT229 to GAERS implanted with cortical electrodes. Systemic administration of GAT211 to male GAERS reduced SWDs by 40%. Systemic GAT229 administration reduced SWDs in female and male GAERS. Intracerebral infusion of GAT229 into the cortex of male GAERS reduced SWDs by >60% in a CB1R-dependent manner that was blocked by SR141716A. Together, these experiments identify altered endocannabinoid tone in GAERS and suggest that CB1R PAMs should be explored for treatment of absence seizures.