While allopregnanolone’s GABAA modulatory activity is well documented, allopregnanolone has the potential to convert back to its metabolic precursor, progesterone, which could lead to hormonal side effects. Ganaxolone has been designed with an added methyl group that prevents back conversion to an active steroid, which unlocks ganaxolone’s potential for chronic use. In preclinical studies, ganaxolone exhibited potency and efficacy comparable to allopregnanolone.
GABA (gamma-aminobutyric acid) is the chief inhibitory neurotransmitter in the brain. One of the subclasses of receptors that respond to GABA is the GABAA receptor. When activated, these receptors selectively conduct chloride ions through a pore that results in the inhibitory effect of hyperpolarization of the neuron. Synaptic GABAA receptors respond quickly to inhibit neurotransmission, while extrasynaptic GABAA receptors provide ambient tonic inhibition.
Both ganaxolone and allopregnanolone bind to GABAA at the synaptic and extrasynaptic binding sites. Activity with extrasynaptic GABAA receptors is of particular importance for treating patients who developed tolerance to benzodiazepines and barbiturates. Ganaxolone binds to the GABAA receptors, which opens the pore to allow chloride ions to move into the postsynaptic neuron, leading to the inhibition of neurotransmission.