Abstracts

Rationale: Because of their powerful inhibitory control over network function, GABA-A alpha subtype-receptor modulators are attractive targets for management of epilepsy. It is well known that α1-α3 subunits play a significant role in anticonvulsant activity of benzodiazepines. However, modulation of GABA-A receptors containing α1 subunits is responsible for a number of undesirable side effects of benzodiazepines, including somnolence, dizziness, cognitive impairment, and addiction. With the goal of mitigating these side effects while maintaining anticonvulsant efficacy, we developed an α2/3/5-subtype selective GABA-A partial PAM, PF-06372865, with minimal functional activity at α1-containing receptors. Methods: Rat or human GABA-A α1β3γ2-, α2β2γ2-, α3β3γ2-, α4β3γ2-, or α5β2γ2-expressing HEK293 cells were used for functional activity, measured using whole cell manual patch and high-throughput electrophysiology. Locomotor activity (horizontal and vertical movements) was collected over 30 minutes using an open-field photobeam monitoring system. Motor function was tested using the accelerating rotorod in mice. The pentylenetetrazol (PTZ) and amygdala kindling (AK) models were used to assess anticonvulsant in vivo efficacy.  Results: Selectivity was confirmed using whole cell electrophysiology to assess functional activity. Although the functional activity over the α1 subunit was ~5-fold, non-functional binding was present. GABA-mediated currents from α1β2γ2-containing receptors that were enhanced by the non-selective benzodiazepine, lorazepam, could not be antagonized by the presence of PF-06372865. These results indicate that PF-06372865 binding does not affect functional activity at α1β2γ2 receptors.PF-06372865 at ≤20 mg/kg did not result in any significant changes in locomotor activity. In addition, PF-06372865 had no effect on fall latency on the rotorod, whereas diazepam (10 mg/kg) resulted in a significantly shorter latency (p Conclusions: PF-06372865 shows clear functional selectivity over the α1 subunit. In the amygdala kindling and pentylenetetrazol models of seizure/convulsion, PF-06372865 showed robust efficacy. Our results show that selective partial modulation of α2/3/5 is sufficient to abolish seizure-like activity in two preclinical models of epilepsy. Data indicate that PF-06372865 may have potent anti-seizure activity in humans with fewer undesirable side effects than classic non-selective benzodiazepines. Funding: All funding was provided by Pfizer, Inc. World Research and Development