Low- and high-cocaine intake affects the spatial and temporal dynamics of class IIa HDAC expression-activity in the nucleus accumbens and hippocampus of male rats as measured by [18F]TFAHA PET/CT neuroimaging.

Repeated cocaine alters neuronal function in the nucleus accumbens (NAc), a brain region involved in cocaine taking, and in hippocampus (HC), known for contextual and associative learning. [18F]TFAHA is a histone deacetylase (HDAC) class IIa-specific radiotracer for positron emission tomography (PET)-imaging developed by our group to study epigenetic mechanisms. Here, [18F]TFAHA was used to conduct PET-imaging coupled with computed tomography (CT) of rat brains at baseline and after repeated cocaine intravenous self-administration (cocaine-IVSA) in low-intake versus high-intake cocaine groups. A 3 h-access FR1-schedule of cocaine-IVSA (0.5 mg/kg/infusion) for 12 continuous days was used with male Sprague Dawley rats following jugular vein catheterization. PET/CT neuroimaging with [18F]TFAHA was acquired in a dynamic mode over 40 min post-radiotracer administration at baseline and on day 12 of cocaine-IVSA using a longitudinal, repeated design. This study shows that high-cocaine intake significantly decreases class IIa HDAC expression-activity in NAc, while low-cocaine intake significantly decreases expression-activity in HC in male rats. These findings suggest the individual rats with low-cocaine intake had epigenetic changes in HC, where drug-associative changes occur. Alternatively, individuals with high-cocaine intake had robust epigenetic changes in NAc, where rewared-related behaviors originate. These findings are the first longitudinal data obtained in vivo to implicate class IIa HDACs in the persistent behavioral effects of cocaine. Furthermore, our results are consistent with published research implicating class IIa HDACs in cocaine-induced brain changes and studies suggesting a relationship between an individual's drug-taking behavior and regional pattern of epigenetic changes in the brain.

Benzimidazolone-based selective σ2 receptor ligands: Synthesis and pharmacological evaluation.

Sigma receptors (σRs) are considered to be a significant and valid target for developing new medications to address several diseases. Their potential involvement in numerous central nervous system disorders, neuropathic pain, addiction, and cancer has been extensively reported. In particular, the σ2R has been identified as potential target for the development of pharmaceutical agents intended to treat the negative effects associated with drugs of abuse. As a continuation of our previous efforts to develop new selective σ2R ligands, a series of benzimidazolone derivatives were designed, synthesized, and characterized. The newly synthesized ligands were evaluated through in vitro radioligand binding assays to determine their affinity and selectivity towards both σ1 and σ2 receptors. Several derivatives displayed high affinity for the σ2R (Ki = 0.66-68.5 nM) and varied from preferring to selective, compared to σ1R (σ1/σ2 = 5.8-1139). Among them, compound 1-{4-[4-(4-fluorophenyl)piperazin-1-yl]butyl}-3-propyl-1,3-dihydrobenzimidazol-2-one dihydrochloride (14) displayed the ability to produce a dose-dependent reduction in the convulsive effects of cocaine in a rodent model after injecting 10 mg/kg (i.p.). These preliminary results support the use of selective σ2R ligands in the development of useful pharmacological tools or potential pharmacotherapies for cocaine toxicity.

Divergent Cytotoxic and Metabolically Stimulative Functions of Sigma-2 Receptors: Structure-Activity Relationships of 6-Acetyl-3-(4-(4-(4-fluorophenyl)piperazin-1-yl)butyl)benzo[d]oxazol-2(3H)-one (SN79) Derivatives.

Sigma-2 receptors, recently identified as TMEM97, have been implicated in cancer and neurodegenerative disease. Structurally distinct sigma-2 receptor ligands induce cell death in tumor cells, linking sigma-2 receptors to apoptotic pathways. Recently, we reported that sigma-2 receptors can also stimulate glycolytic hallmarks, effects consistent with a prosurvival function and upregulation in cancer cells. Both apoptotic and metabolically stimulative effects were observed with compounds related to the canonical sigma-2 antagonist SN79. Here we investigate a series of 6-substituted SN79 analogs to assess the structural determinants governing these divergent effects. Substitutions on the benzoxazolone ring of the core SN79 structure resulted in high-affinity sigma-2 receptor ligands (K i = 0.56-17.9 nM), with replacement of the heterocyclic oxygen by N-methyl (producing N-methylbenzimidazolones) generally decreasing sigma-1 affinity and a sulfur substitution (producing benzothiazolones) imparting high affinity at both subtypes, lowering subtype selectivity. Substitution at the 6-position with COCH3, NO2, NH2, or F resulted in ligands that were not cytotoxic. Five of these ligands induced an increase in metabolic activity, as measured by increased reduction of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) in human SK-N-SH neuroblastoma cells, further supporting a role for sigma-2 receptors in metabolism. Substitution with 6-isothiocyanate resulted in ligands that were sigma-2 selective and that irreversibly bound to the sigma-2 receptor, but not to the sigma-1 receptor. These ligands induced cell death upon both acute and continuous treatment (EC50 = 7.6-32.8 µM), suggesting that irreversible receptor binding plays a role in cytotoxicity. These ligands will be useful for further study of these divergent roles of sigma-2 receptors.

Structure-Based Identification of Potent Natural Product Chemotypes as Cannabinoid Receptor 1 Inverse Agonists.

Natural products are an abundant source of potential drugs, and their diversity makes them a rich and viable prospective source of bioactive cannabinoid ligands. Cannabinoid receptor 1 (CB1) antagonists are clinically established and well documented as potential therapeutics for treating obesity, obesity-related cardiometabolic disorders, pain, and drug/substance abuse, but their associated CNS-mediated adverse effects hinder the development of potential new drugs and no such drug is currently on the market. This limitation amplifies the need for new agents with reduced or no CNS-mediated side effects. We are interested in the discovery of new natural product chemotypes as CB1 antagonists, which may serve as good starting points for further optimization towards the development of CB1 therapeutics. In search of new chemotypes as CB1 antagonists, we screened the in silico purchasable natural products subset of the ZINC12 database against our reported CB1 receptor model using the structure-based virtual screening (SBVS) approach. A total of 18 out of 192 top-scoring virtual hits, selected based on structural diversity and key protein⁻ligand interactions, were purchased and subjected to in vitro screening in competitive radioligand binding assays. The in vitro screening yielded seven compounds exhibiting >50% displacement at 10 µM concentration, and further binding affinity (Ki and IC50) and functional data revealed compound 16 as a potent and selective CB1 inverse agonist (Ki = 121 nM and EC50 = 128 nM) while three other compounds-2, 12, and 18-were potent but nonselective CB1 ligands with low micromolar binding affinity (Ki). In order to explore the structure⁻activity relationship for compound 16, we further purchased compounds with >80% similarity to compound 16, screened them for CB1 and CB2 activities, and found two potent compounds with sub-micromolar activities. Most importantly, these bioactive compounds represent structurally new natural product chemotypes in the area of cannabinoid research and could be considered for further structural optimization as CB1 ligands.