Modification on the 1,2-dihydro-2-oxo-pyridine-3-carboxamide core to obtain multi-target modulators of endocannabinoid system

Novel Orthosteric/Allosteric Ligands of Cannabinoid Receptors: An Unexpected Pharmacological Profile

The design of dualsteric/bitopic receptor ligands as compounds capable of simultaneously interacting with both the orthosteric and an allosteric binding site has gained importance to achieve enhanced receptor specificity and minimize off-target effects. In this work, we reported the synthesis and biological evaluation of a new series of compounds, namely, the RF series, obtained by chemically combining the CB1R ago-positive allosteric modulators (PAM) GAT211 with the cannabinoid receptors (CBRs) orthosteric agonist FM6b. Therefore, RF compounds were designed as dualsteric/bitopic ligands for hCB1R with the aim of obtaining stronger hCB1R agonists or ago-PAMs, with improved receptor subtype selectivity and reduction of central side effects. Unexpectedly, in vitro assays on hCB1R indicated RF compounds were inverse agonists/antagonists, exhibiting different profiles compared to those of parent compounds FM6b and GAT211 and, furthermore, two compounds behaved as hCB2R PAMs. The unpredictable change in the function of these new ligands suggests that the function of cannabinoids is not simply predicted.

The cannabinoid CB2 receptor positive allosteric modulator EC21a exhibits complicated pharmacology in vitro

Schizophrenia is a complex disease involving the dysregulation of numerous brain circuits and patients exhibit positive symptoms (hallucinations, delusions), negative symptoms (anhedonia), and cognitive impairments. We have shown that the antipsychotic efficacy of positive allosteric modulators (PAMs) of both the M4 muscarinic receptor and metabotropic glutamate receptor 1 (mGlu1) involve the retrograde activation of the presynaptic cannabinoid type-2 (CB2) receptor, indicating that CB2 activation or potentiation could result in a novel therapeutic strategy for schizophrenia. We used two complementary assays, receptor-mediated phosphoinositide hydrolysis and GIRK channel activation, to characterize a CB2 PAM scaffold, represented by the compound EC21a, to explore its potential as a starting point to optimize therapeutics for schizophrenia. These studies revealed that EC21a acts as an allosteric inverse agonist at CB2 in both assays and exhibits a mixed allosteric agonist/negative allosteric modulator profile at CB1 depending upon the assay used for profiling. A series of compounds related to EC21a also functioned as CB2 inverse agonists. Overall, these results suggest that EC21a exhibits complicated and potentially assay-dependent pharmacology, which may impact interpretation of in vivo studies.

New Insights into Bitopic Orthosteric/Allosteric Ligands of Cannabinoid Receptor Type 2

Very recently, we have developed a new generation of ligands targeting the cannabinoid receptor type 2 (CB2R), namely JR compounds, which combine the pharmacophoric portion of the CB2R positive allosteric modulator (PAM), EC21a, with that of the CB2R selective orthosteric agonist LV62, both synthesized in our laboratories. The functional examination enabled us to identify JR14a, JR22a, and JR64a as the most promising compounds of the series. In the current study, we focused on the assessment of the bitopic (dualsteric) nature of these three compounds. Experiments in cAMP assays highlighted that only JR22a behaves as a CB2R bitopic (dualsteric) ligand. In parallel, computational studies helped us to clarify the binding mode of these three compounds at CB2R, confirming the bitopic (dualsteric) nature of JR22a. Finally, the potential of JR22a to prevent neuroinflammation was investigated on a human microglial cell inflammatory model.

Development of N-(1-Adamantyl)benzamides as Novel Anti-Inflammatory Multitarget Agents Acting as Dual Modulators of the Cannabinoid CB2 Receptor and Fatty Acid Amide Hydrolase

Cannabinoid type 2 receptor (CB2R), belonging to the endocannabinoid system, is overexpressed in pathologies characterized by inflammation, and its activation counteracts inflammatory states. Fatty acid amide hydrolase (FAAH) is an enzyme responsible for the degradation of the main endocannabinoid anandamide; thus, the simultaneous CB2R activation and FAAH inhibition may be a synergistic anti-inflammatory strategy. Encouraged by principal component analysis (PCA) data identifying a wide chemical space shared by CB2R and FAAH ligands, we designed a small library of adamantyl-benzamides, as potential dual agents, CB2R agonists, and FAAH inhibitors. The new compounds were tested for their CB2R affinity/selectivity and CB2R and FAAH activity. Derivatives 13, 26, and 27, displaying the best pharmacodynamic profile as CB2R full agonists and FAAH inhibitors, decreased pro-inflammatory and increased anti-inflammatory cytokines production. Molecular docking simulations complemented the experimental findings by providing a molecular rationale behind the observed activities. These multitarget ligands constitute promising anti-inflammatory agents.

Design, Synthesis, and Biological Activity of New CB2 Receptor Ligands: from Orthosteric and Allosteric Modulators to Dualsteric/Bitopic Ligands

The design of dualsteric/bitopic agents as single chemical entities able to simultaneously interact with both the orthosteric and an allosteric binding site represents a novel approach in medicinal chemistry. Biased dualsteric/bitopic agents could enhance certain signaling pathways while diminishing the others that cause unwanted side effects. We have designed, synthesized, and functionally characterized the first CB2R heterobivalent bitopic ligands. In contrast to the parent orthosteric compound, our bitopic ligands selectively target CB2R versus CB1R and show a functional selectivity for the cAMP signaling pathway versus βarrestin2 recruitment. Moreover, the most promising bitopic ligand FD-22a displayed anti-inflammatory activity in a human microglial cell inflammatory model and antinociceptive activity in vivo in an experimental mouse model of neuropathic pain. Finally, computational studies clarified the binding mode of these compounds inside the CB2R, further confirming their bitopic nature.

Design, Synthesis, and Evaluation of Anticonvulsant Activities of New Triazolopyrimidine Derivatives

Epilepsy, a severe brain disease affecting a large population, is treated mainly by antiepileptic drugs (AEDs). However, toxicity, intolerance, and low efficiency of the available AEDs have prompted the continual attempts in the discovery of new AEDs. In this study, we discovered a skeleton of triazolopyrimidine for the development of new AEDs. The design, synthesis, in vivo anticonvulsant activity evaluation of triazolopyrimidines (3a–3i and 6a–6e), and pyrazolopyrimidines (4a–4i) are reported. We found that most triazolopyrimidines showed anticonvulsive activity in the maximal electroshock (MES) and pentetrazol (PTZ)-induced seizure models. On the contrary, pyrazolopyrimidines (4a–4i) showed weak or no protective effects. Among the tested derivatives, compound 6d, holding a median effective dose (ED₅₀₎ of 15.8 and 14.1 mg/kg against MES and PTZ-induced seizures, respectively, was found to be the most potent one. Moreover, the protection index (PI) value of 6d was significantly higher than that of the available AEDs such as valproate, carbamazepine, and diazepam. The antiepileptic efficacy of compound 6d was also observed in the 3-mercaptopropionic acid and bicuculline-induced seizure models. Antagonistic effects of flumazenil and 3-MP for the anticonvulsive activity of 6d and also the radioligand-binding assay confirmed the involvement of GABA receptors, at least benzodiazepine (BZD) receptor, in the anticonvulsant activity of compound 6d. The docking study of compounds 4e and 6d with GABA_A receptor confirmed and explained their affinity to the BZD receptors.

Δ9-cis-Tetrahydrocannabinol: Natural Occurrence, Chirality, and Pharmacology

The cis-stereoisomers of Δ⁹-THC [(-)-3 and (+)-3] were identified and quantified in a series of low-THC-containing varieties of Cannabis sativa registered in Europe as fiber hemp and in research accessions of cannabis. While Δ⁹-cis-THC (3) occurs in cannabis fiber hemp in the concentration range of (-)-Δ⁹-trans-THC [(-)-1], it was undetectable in a sample of high-THC-containing medicinal cannabis. Natural Δ⁹-cis-THC (3) is scalemic (ca. 80-90% enantiomeric purity), and the absolute configuration of the major enantiomer was established as 6aS,10aR [(-)-3] by chiral chromatographic comparison with a sample available by asymmetric synthesis. The major enantiomer, (-)-Δ⁹-cis-THC [(-)-3], was characterized as a partial cannabinoid agonist in vitro and elicited a full tetrad response in mice at 50 mg/kg doses. The current legal discrimination between narcotic and non-narcotic cannabis varieties centers on the contents of "Δ⁹-THC and isomers" and needs therefore revision, or at least a more specific wording, to account for the presence of Δ⁹-cis-THCs [(+)-3 and (-)-3] in cannabis fiber hemp varieties.

Novel approaches and current challenges with targeting the endocannabinoid system

INTRODUCTION

The pathophysiological relevance of the endocannabinoid system has been widely demonstrated in a variety of diseases including cancer, neurological disorders, and metabolic issues. Therefore, targeting the receptors and the endogenous machinery involved in this system can provide a successful therapeutic outcome. Ligands targeting the canonical cannabinoid receptors, CB1 and CB2, along with inhibitors of the endocannabinoid enzymes have been thoroughly studied in diverse disease models. In fact, phytocannabinoids such as cannabidiol or Δ9-tetrahydrocannabinol are currently on the market for the management of neuropathic pain due to spasticity in multiple sclerosis or seizures in children epilepsy amongst others.

AREAS COVERED

Challenges in the pharmacology of cannabinoids arise from its pharmacokinetics, off-target effects, and psychoactive effects. In this context, the current review outlines the novel molecular approaches emerging in the field discussing their clinical potential.

EXPERT OPINION

Even if orthosteric CB1 and CB2 ligands are on the forefront in cannabinoid clinical research, emerging strategies such as allosteric or biased modulation of these receptors along with controlled off-targets effects may increase the therapeutic potential of cannabinoids.

Advances in the discovery of fatty acid amide hydrolase inhibitors: what does the future hold?

INTRODUCTION

Fatty acid amide hydrolase (FAAH) is a membrane-bound enzyme, that inactivates endogenous signaling lipids of the fatty acid amide family, including the endocannabinoid anandamide (N-arachidonoylethanolamine, AEA). The latter compound has been shown to regulate a number of important pathophysiological conditions in humans, like feeding, obesity, immune response, reproductive events, motor coordination, and neurological disorders. Hence, direct manipulation of the endocannabinoid tone is thought to have therapeutic potential. A new opportunity to develop effective drugs may arise from multi-target directed ligand (MTDL) strategies, which brings the concept that a single compound can recognize different targets involved in the cascade of pathophysiological events.

AREAS COVERED

This review reports the latest advances in the development of new single targeted and dual-targeted FAAH inhibitors over the past 5 years.

EXPERT OPINION

In recent years, several FAAH inhibitors have been synthesized and investigated, yet to date none of them has reached the market as a systemic drug. Due to the diligence of inherent redundancy and robustness in many biological networks and pathways, multitarget inhibitors present a new prospect in the pharmaceutical industry for treatment of complex diseases.