Assessing seizure protection in preclinical models by transmembrane AMPA receptor regulatory protein γ8 (TARPγ8) negative allosteric modulators (NAMs).

TARPγ8, enriched in the cortex, amygdala, and hippocampus with little to no expression in the hindbrain, provides a target for seizure protection with improved tolerability.

Subjects were adult male CF-1 mice (Charles River, Portage, MI).

Antiseizure effects of RAP-219 and RTX-1738 were assessed in the pentylenetetrazol (PTZ) and corneal kindling (CK) mouse models. PTZ was infused 2h after RAP-129 (0.01-1mg/kg) or vehicle administration. Seizure threshold was assessed via time to first twitch or onset of sustained clonus. For CK studies, fully kindled mice were treated with RAP-219 (0.01-3mg/kg), RTX-1738 (0.003-0.3mg/kg; single dose and 7d QD), or vehicle. Seizure protection was assessed 2h post-dose. Motoric impairment was assessed via rotarod 2h post—RAP-219 administration; locomotor activity was assessed via open-field following 7d RTX-1738 administration. Receptor occupancy (RO) was determined using ex vivo autoradiography studies.

RAP-219—treated mice (0.1 and 1mg/kg) had significantly higher seizure threshold (PTZ) vs vehicle (P<0.01). RAP-219 ED₅₀ for twitch and clonus were 0.02mg/kg (EC₅₀=2.9ng/mL) and 0.02mg/kg (EC₅₀=2.4ng/mL), respectively. In CK, RAP-219 was associated with dose-dependent seizure protection (ED₅₀=0.02mg/kg, EC₅₀=2.3ng/mL) with minimal, non-dose-dependent failures on the rotarod (therapeutic index>150).

RTX-1738 was associated with seizure protection in CK after single-dose (ED₅₀=0.05mg/kg, EC₅₀=4.7ng/mL) and 7d QD administration (ED₅₀=0.01mg/kg, EC₅₀=3.6ng/mL) with no differences in locomotor activity.

RO EC₅₀ was 3.3ng/mL for RAP-219 and 3.2ng/mL for RTX-1738, with full protection at 70% RO (7ng/mL) and 90% RO (10ng/mL), respectively.

TARPγ8 NAMs provided potent, dose-dependent antiseizure effects maintained after 7d in preclinical focal and generalized seizure models without impairing motor function, yielding a high therapeutic index. TARPγ8 NAMs may provide a new precision medicine option with improved tolerability for patients with epilepsy.