Kainate Receptors as a Target for the Anticonvulsant Perampanel

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SUMMARY Perampanel (PMP) is a third-generation anticonvulsant that acts as a noncompetitive allosteric modulator (NAM) of AMPA receptors, the ionotropic glutamate receptors (iGluRs) that serve as principle mediators of excitatory neurotransmission in the CNS. Its anticonvulsant activity is thought to result from dampening hyperexcitability in an epileptic brain through AMPA receptor inhibition. The recent structural resolution of the binding site for PMP on the GluA2 AMPA receptor subunit revealed fine details into determinants of its NAM activity but also underscored the conservation of critical binding residues in AMPA and kainate receptor (KAR) subunits, a distinct but related family of iGluRs. KARs serve a variety of functions in the CNS that are generally characterized as modulating a balance between excitation and inhibition tone. We hypothesize that PMP acts as a NAM on KARs and that this activity in part contributes to its therapeutic efficacy. Our preliminary results provide initial tentative support for this hypothesis and additionally reveal that PMP inhibition depends on the incorporation of a specific KAR subunit, GluK5, into the receptor complex. In this project, we propose to explore this observation further in three related aims. In Specific Aim 1, we will test the hypothesis that PMP is a subunit-selective noncompetitive antagonist of KARs and explore the importance of key amino acid residues in the PMP binding domains that control sensitivity of KARs to the modulator. In Specific Aim 2, we will test if PMP inhibits neuronal KARs at hippocampal mossy fiber synapses on CA3 pyramidal neurons and in dorsal root ganglion neurons. Both of these types of neuronal receptors are known to contain the GluK5 subunit. We will compare relative inhibition of receptors in wildtype and GluK5-/- mice to test the hypothesis that GluK5 forms a key substrate for PMP inhibition in the CNS. In Specific Aim 3, we will discriminate between modulatory activity on AMPA vs. kainate receptors by comparing potency of PMP in wildtype and GluK5-/- knockout mice in animal seizure, anxiety, and pain models, indications in which PMP shows efficacy. These objectives are significant because they could change our understanding of the mechanism of action of the third-generation anticonvulsant perampanel. Optimization of inhibitors that effectively discriminate between AMPA and kainate receptors could lead to a new generation of drugs with larger therapeutic indices.