Discovery and Characterization of AMPA Receptor Modulators Selective for TARP- 8

Abstract

Members of the a-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of ionotropic glutamate receptors mediate the majority of fast synaptic transmission within the mammalian brain and spinal cord, representing attractive targets for therapeutic intervention. Here, we describe novel AMPA receptor modulators that require the presence of the accessory protein CACNG8, also known as transmembrane AMPA receptor regulatory protein g8 (TARP-g8). Using calcium flux, radioligand binding, and electrophysiological assays of wild-type and mutant forms of TARP-g8, we demonstrate that these compounds possess a novel mechanism of action consistent with a partial disruption of the interaction between the TARP and the pore-forming subunit of the channel. One of the molecules, 5-[2-chloro-6-(trifluoromethoxy)phenyl]-1,3-dihydrobenzimidazol-2-one (JNJ-55511118), had excellent pharmacokinetic properties and achieved high receptor occupancy following oral administration. This molecule showed strong, dose-dependent inhibition of neurotransmission within the hippocampus, and a strong anticonvulsant effect. At high levels of receptor occupancy in rodent in vivo models, JNJ-55511118 showed a strong reduction in certain bands on electroencephalogram, transient hyperlocomotion, no motor impairment on rotarod, and a mild impairment in learning and memory. JNJ-55511118 is a novel tool for reversible AMPA receptor inhibition, particularly within the hippocampus, with potential therapeutic utility as an anticonvulsant or neuroprotectant. The existence of a molecule with this mechanism of action demonstrates the possibility of pharmacological targeting of accessory proteins, increasing the potential number of druggable targets.

Control of AMPA Receptor Activity by the Extracellular Loops of Auxiliary Proteins

“…The molecular nature of the interactions we have identified here raise the intriguing possibility that acute disassembly of complexes, rather than modulation, might be the target of recent subtype specific drugs (Maher et al, 2016;Kato et al, 2016).…”

“…The physiological importance of modulation is likely to be the specialization of particular codes of short-term plasticity, in the hippocampus and cerebellum at least (von Engelhardt et al, 2010;Klaassen et al, 2016;Khodosevich et al, 2014;Devi et al, 2016). Recently, antagonists of AMPA receptors that target GluA2-g8 complexes were described (Maher et al, 2016;Kato et al, 2016), further enhancing interest in the molecular basis of complexes of GluA subunits and their auxiliary proteins as potential drug targets.…”

Reply to "A Comment on 'Discovery and Characterization of AMPA Receptor Modulators Selective for TARP- 8"

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Thank you for the opportunity to reply to the comment by Witkin and Gardinier (2016) regarding our recent article, "Discovery and Characterization of AMPA Receptor Modulators Selective for TARP-g8" (Maher et al, 2016). It is scientifically reassuring when two independent lines of research converge to very common conclusions and when distinct chemical entities independently replicate exciting pharmacological findings.

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A Comment on "Discovery and Characterization of AMPA Receptor Modulators Selective for TARP- 8"

“…In this article, Maher et al (2016) describe a molecule that selectively blocks a-amino-3-hydroxyl-5-methyl-4-isoxazole-propionic acid (AMPA) receptors associated with the auxiliary protein transmembrane AMPA receptor regulatory protein (TARP)-g8. Given the unique localizations of these AMPA receptors in the brain, the molecule was anticonvulsant and had fewer motor-impacting effects than non-TARP-dependent AMPA receptor antagonists.…”

“…We would like to make the readers of JPET aware of literature precedents for the very exciting work recently published by Maher et al (2016) ("Discovery and Characterization of AMPA Receptor Modulators Selective for TARP-g8") in JPET. In this article, Maher et al (2016) describe a molecule that selectively blocks a-amino-3-hydroxyl-5-methyl-4-isoxazole-propionic acid (AMPA) receptors associated with the auxiliary protein transmembrane AMPA receptor regulatory protein (TARP)-g8.…”