Anticonvulsive properties of soticlestat, a novel cholesterol 24-hydroxylase inhibitor

Abstract

Objective: The formation of 24S-hydroxycholesterol is a brain-specific mechanism of cholesterol catabolism catalyzed by cholesterol 24-hydroxylase (CYP46A1, also known as CH24H). CH24H has been implicated in various biological mechanisms, whereas pharmacological lowering of 24S-hydroxycholesterol has not been fully studied. Soticlestat is a novel small-molecule inhibitor of CH24H. Its therapeutic potential was previously identified in a mouse model with an epileptic phenotype. In the present study, the anticonvulsive property of soticlestat was characterized in rodent models of epilepsy that have long been used to identify antiseizure medications.

Methods: The anticonvulsive property of soticlestat was investigated in maximal electroshock seizures (MES), pentylenetetrazol (PTZ) acute seizures, 6-Hz psychomotor seizures, audiogenic seizures, amygdala kindling, PTZ kindling, and corneal kindling models. Soticlestat was characterized in a PTZ kindling model under steady-state pharmacokinetics to relate its anticonvulsive effects to pharmacodynamics.

Results: Among models of acutely evoked seizures, whereas anticonvulsive effects of soticlestat were identified in Frings mice, a genetic model of audiogenic seizures, it was found ineffective in MES, acute PTZ seizures, and 6-Hz seizures. The protective effects of soticlestat against audiogenic seizures increased with repetitive dosing. Soticlestat was also tested in models of progressive seizure severity. Soticlestat treatment delayed kindling acquisition, whereas fully kindled animals were not protected. Importantly, soticlestat suppressed the progression of seizure severity in correlation with 24S-hydroxycholesterol lowering in the brain, suggesting that 24S-hydroxycholesterol can be aggressively reduced to produce more potent effects on seizure development in kindling acquisition.

Significance: The data collectively suggest that soticlestat can ameliorate seizure symptoms through a mechanism distinct from conventional antiseizure medications. With its novel mechanism of action, soticlestat could constitute a novel class of antiseizure medications for treatment of intractable epilepsy disorders such as developmental and epileptic encephalopathy.

Keywords: CYP46A1; anticonvulsants; cholesterol 24-hydroxylase; epilepsy; soticlestat.

FIGURE 1

Dose‐ and time‐dependent effects of soticlestat on audiogenic seizures (AGS) in Frings mice. (A) Experimental design and the overall seizure protection by soticlestat. Each of the black arrows in the pentagonal diagrams on the left‐hand side indicates soticlestat administration, which was given at 3, 10, and 30 mg/kg (orally once daily [POQD]) singly or three times before seizure induction. The numbers in the diagrams indicate hours prior to auditory seizure induction. The pie charts on the right‐hand side indicate the proportion of mice protected from AGS in each different dosing condition. The data are given in Table S1. (B) Effects of soticlestat on the time spent in wild‐running behaviors. (C) Effects of soticlestat on the time spent in tonic‐extension seizures (TE). Data are mean ± SEM (n = 8–13). *, **, ***p < .05, .01, .001, respectively, compared to the vehicle control group in the same treatment paradigm (two‐way analysis of variance followed by Bonferroni posttest)

FIGURE 2

Time course of soticlestat effects on seizure progression in the rat amygdala kindling model. Treatment was started on the first day of kindling stimulation and maintained once daily over the study period. Statistical analyses were performed on various indices and shown in Table 2. (A) Change of Racine seizure severity scores over the course of kindling stimulation in parallel with soticlestat administration (100 mg/kg orally once daily [POQD]). (B) Change of afterdischarge duration during the development of kindling. Data are plotted as mean ± SEM (n = 12)

FIGURE 3

Soticlestat pharmacokinetics/pharmacodynamics and treatment effects on seizure progression in the mouse pentylenetetrazol (PTZ) kindling model. (A) Plasma and (B) brain soticlestat exposure levels during the 24 h following a single administration of soticlestat to kindled mice (10 and 30 mg/kg orally once daily [POQD]). (C) Effects of repetitive soticlestat treatments on the brain level of 24S‐hydroxycholesterol (24HC; 10 and 30 mg/kg POQD for 3 days). (D) Effects of soticlestat (30 mg/kg POQD) on the progression of seizure severity over the course of PTZ stimulation. Treatment was started on the first day of kindling stimulation and maintained once daily over the study period. (E) Cumulation of Racine scores. *p < .05 compared with the vehicle‐treated control group (Student t‐test). Data are mean ± SEM

FIGURE 4

Steady‐state soticlestat pharmacokinetics (PK)/pharmacodynamics (PD) and treatment effects on seizure progression in the mouse pentylenetetrazol (PTZ) kindling model. To investigate a steady‐state PK/PD relationship, soticlestat treatment was maintained through subcutaneous infusion over the study period (SC inf). (A) Effects of soticlestat on the progression of seizure severity over the four PTZ stimulations (.03, .3, 1, 3 and 10 mg/kg/day SC inf). The vehicle treatment is indicated as 0 mg/kg soticlestat. (B) Distribution of the Racine scores obtained over the total experiment period. (C) Cumulative seizure scores obtained over the total experimental period. #p < .025 compared to the vehicle‐controlled group (one‐tailed Williams test). (D) Brain 24S‐hydroxycholesterol (24HC)‐lowering effects evaluated at the study endpoint. #p < .025 compared to the vehicle‐controlled group (one‐tailed Williams test). (E) Correlation between brain 24HC‐lowering and antiseizure effects of soticlestat. The dashed lines define the 95% confidence band in linear regression. (F) Correlation between brain 24HC lowering and brain soticlestat levels determined at the study endpoint. The dashed lines define the 95% confidence band in nonlinear regression