Abstracts

Rationale: Cholesterol 24-hydroxylase (CH24H) is a brain specific CYP450 family enzyme which converts cholesterol to 24S-hydroxycholesterol (24HC). 24HC was recently reported to be a positive allosteric modulator of N-methyl-D-aspartate (NMDA) receptors. TAK-935 was identified as a novel and highly selective CH24H inhibitor and is being explored as a potential CNS therapeutic in the treatment of epileptic encephalopathies. In this study, we characterized the pharmacodynamic (PD) effects of TAK-935 and demonstrated target engagement of TAK-935 in rodents and primates. Methods: CH24H WT/KO mice and normal rats were treated with TAK-935 by subcutaneous infusion for 7 days. The concentrations of TAK-935 in the plasma and brain were measured. Brain and plasma 24HC levels were also measured and their correlation with TAK-935 exposure levels were assessed. For the target engagement of TAK-935, in vitro autoradiography (ARG) studies using [3H]T-008 ([18F]MNI-792), a selective tracer for CH24H, were conducted in CH24H WT/KO mouse brain sections. Brain PET studies of [18F]T-008, baseline and blocking study with TAK-935 (0.90 mg/kg, i.v., 30 min pre-treatment), were also conducted to evaluate the enzyme occupancy of TAK-935 in rhesus monkeys. Results: TAK-935 exhibited CH24H specific uptake into the mouse brain in the distribution study using CH24H WT/KO mice. Furthermore, TAK-935 reduced brain 24HC levels in WT mice and rats (brain 24HC reduction in mice: EC50=6.0 nM), which were highly correlated with the unbound plasma exposure level of TAK-935 at steady-state. Plasma 24HC levels in rats showed good correlation with brain 24HC levels. TAK-935 blocked the CH24H specific binding of [3H]T-008 in ARG study. In brain PET studies, TAK-935 blocked the signal of [18F]T-008 in all brain regions in rhesus monkeys (occupancy: 97-100 %). Conclusions: TAK-935 is a potent and selective CH24H inhibitor. Observed reduction in brain 24HC levels were highly correlated with TAK-935 systemic exposures in rodents. Furthermore, [18F]T-008 appears to be a powerful tool to relate brain enzyme occupancy, reduction in 24HC levels and efficacy of TAK-935, providing preclinical evidence of biological activity for guiding optimal dosing in humans. Funding: This study was funded by TAKEDA Pharmaceitical Company Limited.