GABA_A receptor modulators are structurally almost as diverse as their target protein. A plethora of heterocyclic scaffolds has been described as modulating this extremely important receptor family. Some made it into clinical trials and, even on the market, some were dismissed. This review focuses on the synthetic accessibility and potential for library synthesis of GABA_A receptor modulators containing at least one heterocyclic scaffold, which were disclosed within the last 10 years.

The GABRA1 gene encodes one of the most conserved and highly expressed subunits of the GABA_A receptor family. Variants in this gene are causatively implicated in different forms of epilepsy and also more severe epilepsy-related neurodevelopmental syndromes. Here we study functional consequences of a novel de novo missense GABRA1 variant, p.(Ala332Val), identified through exome sequencing in an individual affected by early-onset syndromic epileptic encephalopathy. The variant is localised within the transmembrane domain helix 3 (TM3) and in silico prediction algorithms suggested this variant to be likely pathogenic. In vitro assessment revealed unchanged protein levels, regular assembly and forward trafficking to the cell surface. On the functional level a significant left shift of the apparent GABA potency in two-electrode voltage clamp electrophysiology experiments was observed, as well as changes in the extent of desensitization. Additionally, apparent diazepam potency was left shifted in radioligand displacement assays. During prenatal development mainly alpha2/3 subunits are expressed, whereas after birth a switch to alpha1 occurs. The expression of alpha1 in humans is upregulated during the first years. Thus, the molecular change of function reported here supports pathogenicity and could explain early-onset of seizures in the affected individual.

Drug-induced Mood- and Cognition-related adverse events (MCAEs) are often only detected during the clinical trial phases of drug development, or even after marketing, thus posing a major safety concern and a challenge for both pharmaceutical companies and clinicians. To fill some gaps in the understanding and elucidate potential biological mechanisms of action frequently associated with MCAEs, we present a unique workflow linking observational population data with the available knowledge at molecular, cellular, and psychopharmacology levels. It is based on statistical analysis of pharmacovigilance reports and subsequent signaling pathway analyses, followed by evidence-based expert manual curation of the outcomes. Our analysis: (a) ranked pharmaceuticals with high occurrence of such adverse events (AEs), based on disproportionality analysis of the FDA Adverse Event Reporting System (FAERS) database, and (b) identified 120 associated genes and common pathway nodes possibly underlying MCAEs. Nearly two-thirds of the identified genes were related to immune modulation, which supports the critical involvement of immune cells and their responses in the regulation of the central nervous system function. This finding also means that pharmaceuticals with a negligible central nervous system exposure may induce MCAEs through dysregulation of the peripheral immune system. Knowledge gained through this workflow unravels putative hallmark biological targets and mediators of drug-induced mood and cognitive disorders that need to be further assessed and validated in experimental models. Thereafter, they can be used to substantially improve in silico/in vitro/in vivo tools for predicting these adversities at a preclinical stage.

Background and Purpose Many psychotherapeutic drugs, including clozapine, display polypharmacology and act on GABA_A receptors. Patients with schizophrenia show alterations in function, structure and molecular composition of the hippocampus, and a recent study demonstrated aberrant levels of hippocampal α5 subunit-containing GABA_A receptors. The purpose of this study is to investigate tricyclic compounds in α5 subunit-containing receptor subtypes. Experimental Approach Functional studies of effects by seven antipsychotic and antidepressant medications were performed in several GABA_A receptor subtypes by two-electrode voltage-clamp electrophysiology using Xenopus laevis oocytes. Computational structural analysis was employed to design mutated constructs of the α5 subunit, probing a novel binding site. Radioligand displacement data complemented the functional and mutational findings. Key Results We show that the antipsychotic drugs clozapine and chlorpromazine exert functional inhibition on multiple GABA_A receptor subtypes, including α5-containing ones. Based on a chlorpromazine binding site observed in a GABA-gated bacterial homologue, we identified a novel site in α5 GABA_A receptor subunits and demonstrate differential usage of this and the orthosteric sites by these ligands. Conclusion and Implications Despite high molecular and functional similarities among the tested ligands, they reduce GABA currents by differential usage of allosteric and orthosteric sites. The chlorpromazine site we describe here is a new potential target for optimizing antipsychotic medications with beneficial polypharmacology. Further studies in defined subtypes are needed to substantiate mechanistic links between the therapeutic effects of clozapine and its action on certain GABA_A receptor subtypes.

Background and Purpose: Many psychotherapeutic drugs, including clozapine, display polypharmacology and act on GABA _A receptors. Patients with schizophrenia show alterations in function, structure and molecular composition of the hippocampus, and a recent study demonstrated aberrant levels of hippocampal a5 subunit-containing GABA _A receptors. The purpose of this study is to investigate tricyclic compounds in a5 subunit-containing receptor subtypes. Experimental Approach: Functional studies of effects by seven antipsychotic and antidepressant medications were performed in several GABA _A receptor subtypes by two‐electrode voltage‐clamp electrophysiology using Xenopus laevis oocytes. Computational structural analysis was employed to design mutated constructs of the a5 subunit, probing a novel binding site. Radioligand displacement data complemented the functional and mutational findings. Key Results: We show that the antipsychotic drugs clozapine and chlorpromazine exert functional inhibition on multiple GABA _A receptor subtypes, including a5-containing ones. Based on a chlorpromazine binding site observed in a GABA-gated bacterial homologue, we identified a novel site in a5 GABA _A receptor subunits and demonstrate differential usage of this and the orthosteric sites by these ligands. Conclusion and Implications:  Despite high molecular and functional similarities among the tested ligands, they reduce GABA currents by differential usage of allosteric and orthosteric sites. The C C C C C C site we describe here is a new potential target for optimizing antipsychotic medications with beneficial polypharmacology. Further studies in defined subtypes are needed to substantiate mechanistic links between the therapeutic effects of clozapine and its action on certain GABA _A receptor subtypes.