Basmisanil, an α5-GABAAR negative allosteric modulator, produces rapid and sustained antidepressant-like responses in male mice

There is a critical need for safer and better-tolerated alternatives to address the current limitations of antidepressant treatments for major depressive disorder. Recently, drugs targeting the GABA system via α5-containing GABAA receptors (α5-GABAAR) as negative allosteric modulators (α5-NAMs) have shown promise in alleviating stress-related behaviors in preclinical studies, suggesting that α5-NAMs may have translational relevance as novel antidepressant medications. Here, we evaluated the efficacy of Basmisanil, an α5-NAM that has been evaluated in Phase 2 clinical studies as a cognitive enhancer, in a battery of behavioral tests relevant to coping strategies, motivation, and aversion in male mice, along with plasma and brain pharmacokinetic measurements. Our findings reveal that Basmisanil induces dose-dependent rapid antidepressant-like responses in the forced swim test and sucrose splash test without promoting locomotor stimulating effects. Furthermore, Basmisanil elicits sustained behavioral responses in the female urine sniffing test and sucrose splash test, observed 24 h and 48 h post-treatment, respectively. Bioanalysis of plasma and brain samples confirms effective blood-brain barrier penetration by Basmisanil and extrapolation to previously published data suggest that effects were observed at doses (10 and 30 mg/kg i.p.) corresponding to relatively modest levels of α5-GABAAR occupancy (40-65 %). These results suggest that Basmisanil exhibits a combination of rapid and sustained antidepressant-like effects highlighting the potential of α5-NAMs as a novel therapeutic strategy for depression.

HIV gp120 upregulates tonic inhibition through α5-containing GABAARs

HIV-Associated Neurocognitive disorder (HAND) affects nearly half of infected patients. The HIV envelope protein gp120 is shed by infected cells and is a potent neurotoxin in vitro that reproduces many aspects of HAND when expressed in vivo. Here, we show that HIV gp120 increases the amplitude of a tonic current mediated by γ-aminobutyric acid type-A receptors (GABA_ARs). Treating rat hippocampal cultures with 600 pM gp120_IIIB for 4 h increased a tonic bicuculline-sensitive current, which remained elevated for 24 h. The increased current resulted from upregulation of extrasynaptic α5-containing GABA_ARs, as indicated by inhibition with the selective inverse agonist basmisanil. Treatment with gp120 increased α5-GABA_AR immunoreactivity on the cell surface without new protein synthesis. The increase in tonic inhibition was prevented by a C-X-C chemokine receptor type 4 (CXCR4) antagonist or elimination of microglia from the culture. Treatment with interleukin-1β (IL-1β) increased the tonic current and an IL-1 receptor antagonist blocked the gp120-evoked response. Pharmacological or genetic inhibition of p38 mitogen-activated protein kinase (MAPK) prevented the gp120-evoked increase in tonic current and direct activation of a mutant form of p38 MAPK expressed in neurons increased the current. Collectively, these data show that gp120 activates CXCR4 to stimulate microglia to release IL-1β. Subsequent stimulation of IL-1 receptors activates p38 MAPK in neurons leading to the upregulation of α5-containing GABA_ARs. Increased tonic inhibition impairs neuroplasticity and inhibition of α5-containing GABA_ARs improves cognitive function in disease models. Thus, gp120-induced upregulation of α5-containing GABA_ARs presents a novel therapeutic target for HAND.

Stability and compatibility of Basmisanil granules co-administered with soft food

Co-administration of solid oral dosage forms with soft food or beverages is commonly used to facilitate administration and to improve compliance in the paediatric and geriatric population and in patient groups with swallowing difficulties. The present case study was conducted to investigate the compatibility, stability and dissolution of Basmisanil administered as granules mixed with different soft food matrices. The data were generated to justify dosing instructions, according which Basmisanil should be sprinkled on or mixed with one tablespoon of soft food to aid swallowing. Different soft food types were selected to cover a broad range of various food components (e.g. fat, protein, carbohydrates, fiber and water) and pH. Active content and degradation products of the active substance were determined after mixing the granules with the semisolid food matrix and after two hours of storage under ambient conditions, respectively. In-vitro dissolution tests of granule/food mixtures were also conducted. Furthermore, the stability of the API polymorph was evaluated. Basmisanil shows good chemical stability when the granules are mixed with soft food and consumed within two hours. No polymorphic conversion (anhydrate to monohydrate) could be detected in the granule/food mixtures after preparation and after storage up to 24 h. The in-vitro dissolution of the API from the granules was not adversely affected by the presence of the food matrix. All results were comparable regardless of the tested food matrix. The results do not prohibit the administration of the granules with soft food to the patient.