In a program to identify pain treatments with low addiction potential, we isolated five steroids, conosteroids A-E (1-5), from the hypobranchial gland of the mollusk Conus geographus. Compounds 1-5 were active in a mouse dorsal root ganglion (DRG) assay that suggested that they might be analgesic. A synthetic analogue 6 was used for a detailed pharmacological study. Compound 6 significantly increased the pain threshold in mice in the hot-plate test at 2 and 50 mg/kg. Compound 6 at 500 nM antagonizes type-A γ-aminobutyric acid receptors (GABAARs). In a patch-clamp experiment, out of the six subunit combinations tested, 6 exhibited subtype selectivity, most strongly antagonizing α1ß1γ2 and α4ß3γ2 receptors (IC50 1.5 and 1.0 µM, respectively). Although the structures of 1-6 differ from those of known neuroactive steroids, they are cell-type-selective modulators of GABAARs, expanding the known chemical space of neuroactive steroids.
Analgesics/chemistry , Conus Snail/chemistry , GABA Antagonists/chemistry , Neurosteroids/chemistry , Receptors, GABA/chemistry , Action Potentials/drug effects , Analgesics/chemical synthesis , Analgesics/pharmacology , Analgesics/therapeutic use , Animals , Conus Snail/metabolism , Disease Models, Animal , GABA Antagonists/isolation & purification , GABA Antagonists/pharmacology , GABA Antagonists/therapeutic use , Ganglia, Spinal/cytology , Ganglia, Spinal/drug effects , Ganglia, Spinal/physiology , Mice , Mice, Inbred C57BL , Molecular Conformation , Neurosteroids/isolation & purification , Neurosteroids/pharmacology , Neurosteroids/therapeutic use , Pain/chemically induced , Pain/drug therapy , Pain/pathology , Protein Subunits/chemistry , Protein Subunits/metabolism , Receptors, GABA/metabolism
