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Forebrain-selective AMPA-receptor antagonism guided by TARP γ-8 as an antiepileptic mechanism

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Abstract

Pharmacological manipulation of specific neural circuits to optimize therapeutic index is an unrealized goal in neurology and psychiatry. AMPA receptors are important for excitatory synaptic transmission1, and their antagonists are antiepileptic2. Although efficacious, AMPA-receptor antagonists, including perampanel (Fycompa), the only approved antagonist for epilepsy, induce dizziness and motor impairment3,4. We hypothesized that blockade of forebrain AMPA receptors without blocking cerebellar AMPA receptors would be antiepileptic and devoid of motor impairment. Taking advantage of an AMPA receptor auxiliary protein, TARP γ-8, which is selectively expressed in the forebrain and modulates the pharmacological properties of AMPA receptors5, we discovered that LY3130481 selectively antagonized recombinant and native AMPA receptors containing γ-8, but not γ-2 (cerebellum) or other TARP members. Two amino acid residues unique to γ-8 determined this selectivity. We also observed antagonism of AMPA receptors expressed in hippocampal, but not cerebellar, tissue from an patient with epilepsy. Corresponding to this selective activity, LY3130481 prevented multiple seizure types in rats and mice and without motor side effects. These findings demonstrate the first rationally discovered molecule targeting specific neural circuitries for therapeutic advantage.

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Figure 1: Identification of γ-8-selective AMPA-receptor antagonists.
Figure 2: LY3130481 potently and selectively blocks all AMPA-receptor complexes that contain γ-8.
Figure 3: LY3130481 potently and partially blocks native γ-8-containing, but not γ-8-lacking, AMPA receptors.
Figure 4: Anticonvulsant effects of LY3130481, on motor performance and on excitatory currents from AMPA receptors expressed in human hippocampal epileptic tissue.

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Acknowledgements

We are grateful to the US National Institutes of Health Anticonvulsant Screening Program of the US National Institutes of Neurological Disorders and Stroke, National Institutes of Health (http://www.ninds.nih.gov/research/asp/), for their help with the mesial temporal lobe assessments. In particular, we are grateful for the expert support of T. Chen, S. Raeissi and program director J. Kehne and to their associated laboratories at the University of Utah, directed by H.S. White. We also thank Covance Laboratories, particularly D. Modlin, for their assistance with the amygdala kindling studies, and M.W. Jeffries (Eli Lilly) for transfection. While this manuscript was under review, the following manuscripts were published: Gardinier et al., 2016 (ref. 9), describing the synthesis of LY3130481; Maher et al., 2016 (ref. 20), describing an alternative molecule with TARP γ-8 selectivity and anticonvulsant activity; and Witkin and Gardinier, 2016 (ref. 21), detailing discovery and disclosure dates for LY3130481 as the first TARP-dependent antagonist. On 26 September 2016, Cerecor Inc. announced the acquisition of LY3130481 (now CERC-611) from Eli Lilly and Company for development in patients with epilepsy.

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Contributions

J.M.W. designed the anticonvulsant and behavioral experiments and interpreted the associated data, wrote the manuscript and served as the biological leader of the project. A.S.K. designed, performed and interpreted the data from most of the electrophysiological and biochemical experiments, and wrote the manuscript. K.D.B., C.D., Y.T., D.A.S. and H.Y. designed, performed and interpreted the data from the FLIPR screening experiments. K.M.G. (chemistry leader), D.L.G., W.J.P., J.R., B.A.H. and P.L.O. performed chemical design and synthesis of LY3130481. F.P. and S.M.F. contributed electrophysiological recordings from hippocampal slices. R.Z. and E.S. designed and performed the Xenopus oocyte experiment. Y.Q., H.W. and M.R.L. designed and constructed the TARP mutant cDNAs. T.E.F. and K.R. designed and performed in vivo electrophysiological recordings. S.D.G. and K.A.W. designed and conducted anticonvulsant and behavioral studies. J.T.C. planned and executed experiments on tissue permeability. J.T.R.I. and E.S.N. designed electrophysiological experiments and provided expert advice. D.S.B. initiated the project with the key concept of this study.

Corresponding authors

Correspondence to Akihiko S Kato or Jeffrey M Witkin.

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Competing interests

All of the authors were employees of Eli Lilly and Company. This work was supported by Eli Lilly and Company.

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Supplementary Figures 1–12 and Supplementary Tables 1–3 (PDF 2092 kb)

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Kato, A., Burris, K., Gardinier, K. et al. Forebrain-selective AMPA-receptor antagonism guided by TARP γ-8 as an antiepileptic mechanism. Nat Med 22, 1496–1501 (2016). https://doi.org/10.1038/nm.4221

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