Molecular Pharmacology of Selective Na V 1.6 and Dual Na V 1.6/Na V 1.2 Channel Inhibitors that Suppress Excitatory Neuronal Activity Ex Vivo.

Voltage-gated sodium channel (Na _V ) inhibitors are used to treat neurological disorders of hyperexcitability such as epilepsy. These drugs act by attenuating neuronal action potential firing to reduce excitability in the brain. However, all currently available Na _V -targeting antiseizure medications nonselectively inhibit the brain channels Na _V 1.1, Na _V 1.2, and Na _V 1.6, which potentially limits the efficacy and therapeutic safety margins of these drugs. Here, we report on XPC-7724 and XPC-5462, which represent a new class of small molecule Na _V -targeting compounds. These compounds specifically target inhibition of the Na _V 1.6 and Na _V 1.2 channels, which are abundantly expressed in excitatory pyramidal neurons. They have a > 100-fold molecular selectivity against Na _V 1.1 channels, which are predominantly expressed in inhibitory neurons. Sparing Na _V 1.1 preserves the inhibitory activity in the brain. These compounds bind to and stabilize the inactivated state of the channels thereby reducing the activity of excitatory neurons. They have higher potency, with longer residency times and slower off-rates, than the clinically used antiseizure medications carbamazepine and phenytoin. The neuronal selectivity of these compounds is demonstrated in brain slices by inhibition of firing in cortical excitatory pyramidal neurons, without impacting fast spiking inhibitory interneurons. XPC-5462 also suppresses epileptiform activity in an ex vivo brain slice seizure model, whereas XPC-7224 does not, suggesting a possible requirement of Nav1.2 inhibition in 0-Mg ²⁺ - or 4-AP-induced brain slice seizure models. The profiles of these compounds will facilitate pharmacological dissection of the physiological roles of Na _V 1.2 and Na _V 1.6 in neurons and help define the role of specific channels in disease states. This unique selectivity profile provides a new approach to potentially treat disorders of neuronal hyperexcitability by selectively downregulating excitatory circuits.