Abstracts

Rationale: Epileptic patients suffer from comorbidities of depression and anxiety more so than the general population. Kv7 channel opening is a validated target for epilepsy with the approval of ezogabine (EZG) in 2011 as a first-in-class molecule; it was removed from the market in 2017. Kv7 openers BHV7000 and azetukalner (XEN1101) are currently in clinical development. This Kv7 program addresses potency and posology with novel, selective, Kv7 openers for epilepsy and other neurological diseases.

Methods: Xyzagen developed a compound library of Kv7 channel openers based on rational chemical design. Initial screening was conducted by rubidium (Rb(+)) efflux assay using HEK293 cells expressing Kv7.2. Secondary Kv7.2/7.3 in vitro testing was by whole cell patch clamp for activity and ½ Vmax shift. Anti-seizure efficacy was tested by a MES model in rats and mice. GABAA binding and PK studies for plasma and brain exposure were conducted in rats and mice and drug levels were analyzed by LC/MS/MS in stand-alone studies or after MES. A 2-species, 2-compartment allometric scaling model with extravascular dosing was applied for the simulation of human exposure.

Results: Lead molecules exhibited a 200+-fold shift in Kv7.2 EC50 with a >25% increase in Emax over EZG and >5-fold more potent than aztukalner. In the secondary screen, lead molecules were >20-fold more potent than EZG and > 33% more potent than aztukalner. In the ½ Vmax shift assay, lead molecules exhibited a shift in activation by >7 mV at concentrations < 100 nM, which is considered clinically effective for EZG at conc. >400 nM. No GABAA binding was observed. A lead molecule, in mice, 7 mg/kg PO 30 min post-dose delivered full protection from MES and at 0.3 mg/kg 25% were protected. Mean brain levels in protected mice were 115 nM with a minimum of 21 nM required for protection. In rats, 0.1 mg/kg PO at 30 min protected 3/4 animals from MES with 0.03 mg/kg demonstrating statistically significant prolongation over the vehicle, and was tolerated at concentrations up to 3 mg/kg (30-fold). Brain concentrations in the protected rats were as low as 21 nM, as seen in mice. A lead molecule exhibits a T1/2 of 4.5 h and 8.3 h in mice and rats, respectively, with a brain-to-plasma ratio > 0.7 from 1-4 h. The allometrically scaled model suggests a 5 mg dose in humans may deliver a Cmax of 330 nM, a T1/2 of ~1.5 days, and time above ~30 nM for 5 days. At 5 mg QD dosing, steady-state trough levels are >500 nM with a swing of 40% between peak to trough.

Conclusions: In vivo, PO efficacy in rodent MES is >10-fold over aztukalner (ED50 > 4 mg/kg) and BHV7000 (full protection at 3 mg/kg). It is anticipated that the lead molecule, based on an in vivo minimum effective brain concentration of >20 nM for MES in mice and rats, a half maximal voltage shift of ~7 mV at < 50 nM, and a brain:plasma ratio of >0.7 in rodents, may be effective at a plasma conc. of 30 nM, as a threshold conc., for clinical seizure protection in humans. Molecules are currently enrolled in the NINDS PSPP, ETSP, and NIDA SUD programs.

Funding: None