Null Allosteric Ligands of GABAA Receptors: Design, Synthesis, Molecular Pharmacology and Applications

Indulged by the pharmacology of γ-aminobutyric acid type A receptors (GABAA receptors), we aimed to understand their allosterism, gain mechanistic insights into their function, and design and develop anesthetic antagonists, the first non-sedative antiepileptics, and nootropics. GABAA receptors are ligand-gated ion channels that regulate GABA-mediated inhibitory signals in the brain. Their extensive pharmacology is evident from the wide range of agents interacting with them, including general anesthetics, sedatives, antiepileptics, anxiolytics, and nootropics. We aimed to design and develop allosteric ligands of GABAA receptors that act as reversal agents for general anesthesia and potentially non-sedative antiepileptics. These agents could mitigate postoperative anesthesia-related complications, such as memory loss and confusion, by expediting recovery from general anesthesia. We report the discovery of a new class of GABAA receptor ligands with novel pharmacology, the null allosteric ligands (NALs). These ligands bind to a previously undiscovered allosteric site in the extracellular domain (ECD) and exert a global effect on the receptor. Through SAR studies, we developed the first spiro-barbiturate and spiro-hydantoin NALs that reverse the enhancement of desensitization in GABAA receptors caused by R-mTFD-MPAB, etomidate, and alfaxalone while having only a marginal effect on the binding of the agonist [3H]muscimol. The development of these NALs, which reverse the action of anesthetics on GABAA receptors, will potentially lead to reversal agents for general anesthesia and other GABAergic CNS drugs, enhancing our understanding of GABAergic actions in the CNS. This work is the result of a collaboration among three labs: the UIC Dr. K. S. Bruzik Lab, where we designed and synthesized these novel molecules; the MGH Dr. K. W. Miller Lab, which conducted biochemical evaluations; and the MRC Dr. A. R. Aricescu Lab, which performed structural studies.