Neurosteroid Analogues. 17. Inverted Binding Orientations of Androsterone Enantiomers at the Steroid Potentiation Site on γ-Aminobutyric Acid Type A Receptors

• Published in: Journal of medicinal chemistry Vol. 55; no. 3; pp. 1334 - 1345
• Main Authors: Krishnan, Kathiresan, Manion, Brad D, Taylor, Amanda, Bracamontes, John, Steinbach, Joseph H, Reichert, David E, Evers, Alex S, Zorumski, Charles F, Mennerick, Steven, Covey, Douglas F
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 09-02-2012
• Subjects: Allosteric Site; Androsterone - analogs & derivatives; Androsterone - chemistry; Androsterone - pharmacology; Animals; Binding, Competitive; Brain - metabolism; Female; In Vitro Techniques; Larva - drug effects; Larva - physiology; Models, Molecular; Neurotransmitter Agents - chemistry; Neurotransmitter Agents - pharmacology; Oocytes - metabolism; Patch-Clamp Techniques; Protein Binding; Radioligand Assay; Rats; Receptors, GABA-A - metabolism; Reflex - drug effects; Stereoisomerism; Structure-Activity Relationship; Xenopus laevis - physiology
• ISSN: 0022-2623; 1520-4804
• DOI: 10.1021/jm2014925

The enantiomer pair androsterone and ent-androsterone are positive allosteric modulators of γ-aminobutyric acid (GABA) type A receptors. Each enantiomer was shown to bind at the same receptor site. Binding orientations of the enantiomers at this site were deduced using enantiomer pairs containing OBn substituents at either C-7 or C-11. 11β-OBn-substituted steroids and 7α-OBn-substituted ent-steroids potently displace [35S]-tert-butylbicyclophosphorothionate, augment GABA currents, and anesthetize tadpoles. In contrast, 7β-OBn-substituted steroids and 11α-OBn-substituted ent-steroids have diminished actions. The results suggest that the binding orientations of the active analogues are inverted relative to each other with the 7α- and 11β-substituents similarly located on the edges of the molecules not in contact with the receptor surface. Analogue potentiation of the GABA current was abrogated by an α1 subunit Q241L mutation, indicating that the active analogues act at the same sites in α1β2γ2L receptors previously associated with positive neurosteroid modulation.