Molecular pharmacodynamics of emixustat in protection against retinal degeneration

Jianye Zhang

Philip Kiser

Mohsen Badiee

Grazyna Palczewska

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^{Department of Pharmacology, Cleveland Center for Membrane and Structural Biology, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA.}

^{Louis Stokes Cleveland VA Medical Center, Cleveland, Ohio, USA.}

^{Department of Chemistry, Case Western Reserve University, Cleveland, Ohio, USA.}

^{Polgenix Inc., Cleveland, Ohio, USA.}

Address correspondence to: Krzysztof Palczewski, Department of Pharmacology, School of Medicine, Case Western Reserve University, 10900 Euclid Ave., Cleveland, Ohio 44106, USA. Phone: 216.368.4631; E-mail: ude.esac@56pxk.

Authorship note: Jianye Zhang and Philip D. Kiser contributed equally to this work.

Received 2015 Jan 13; Accepted 2015 May 12.

Abstract

Emixustat is a visual cycle modulator that has entered clinical trials as a treatment for age-related macular degeneration (AMD). This molecule has been proposed to inhibit the visual cycle isomerase RPE65, thereby slowing regeneration of 11-cis-retinal and reducing production of retinaldehyde condensation byproducts that may be involved in AMD pathology. Previously, we reported that all-trans-retinal (atRAL) is directly cytotoxic and that certain primary amine compounds that transiently sequester atRAL via Schiff base formation ameliorate retinal degeneration. Here, we have shown that emixustat stereoselectively inhibits RPE65 by direct active site binding. However, we detected the presence of emixustat-atRAL Schiff base conjugates, indicating that emixustat also acts as a retinal scavenger, which may contribute to its therapeutic effects. Using agents that lack either RPE65 inhibitory activity or the capacity to sequester atRAL, we assessed the relative importance of these 2 modes of action in protection against retinal phototoxicity in mice. The atRAL sequestrant QEA-B-001-NH2 conferred protection against phototoxicity without inhibiting RPE65, whereas an emixustat derivative incapable of atRAL sequestration was minimally protective, despite direct inhibition of RPE65. These data indicate that atRAL sequestration is an essential mechanism underlying the protective effects of emixustat and related compounds against retinal phototoxicity. Moreover, atRAL sequestration should be considered in the design of next-generation visual cycle modulators.

Abstract

Acknowledgments

We thank Leslie T. Webster Jr. and members of the Palczewski laboratory for helpful comments on this manuscript. This work was supported by funding from the NIH ({"type":"entrez-nucleotide","attrs":{"text":"EY009339","term_id":"159072030","term_text":"EY009339"}}EY009339 and {"type":"entrez-nucleotide","attrs":{"text":"EY021126","term_id":"159085873","term_text":"EY021126"}}EY021126, to K. Palczewski; {"type":"entrez-nucleotide","attrs":{"text":"CA157735","term_id":"35068310","term_text":"CA157735"}}CA157735, to G.P. Tochtrop; {"type":"entrez-nucleotide","attrs":{"text":"EY025451","term_id":"169228729","term_text":"EY025451"}}EY025451 and {"type":"entrez-nucleotide","attrs":{"text":"AG043645","term_id":"16572370","term_text":"AG043645"}}AG043645, to G. Palczewska; and {"type":"entrez-nucleotide","attrs":{"text":"EY023948","term_id":"169227675","term_text":"EY023948"}}EY023948, to M. Golczak); the Department of Veterans Affairs ({"type":"entrez-nucleotide","attrs":{"text":"BX002683","term_id":"26187643","term_text":"BX002683"}}BX002683, to P.D. Kiser); the Foundation Fighting Blindness (to K. Palczewski); and the National Science Foundation (MCB-084480, to G.P. Tochtrop). We thank the staff at the APS NE-CAT beamlines for assistance with diffraction data collection. This work is based on research conducted at the APS on the Northeastern Collaborative Access Team beamlines, which are supported by a grant from the National Institute of General Medical Sciences (P41 GM103403) of the NIH. This research also used resources of the APS, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract DE-AC02-06CH11357. We also thank Yinghua Chen of the Protein Expression Purification and Crystallography Core facility (PEPCC), Department of Physiology and Biophysics, Case Western Reserve University for assistance with circular dichroism (CD) data collection. K. Palczewski is a John H. Hord Professor of Pharmacology.

Acknowledgments

Footnotes

Conflict of interest: K. Palczewski and M. Golczak are co-inventors on US patent 8722669, “Compounds and methods of treating ocular disorders” and US patent 20080275134, “Methods for treatment of retinal degenerative disease,” issued to Case Western Reserve University (CWRU). The values of these patents may be affected by this publication. CWRU may license this technology for commercial development. K. Palczewski is a member of the scientific board of Vision Medicine Inc., which is involved in developing visual cycle modulators. G. Palczewska is an employee of Polgenix Inc. K. Palczewski is the chief scientific officer (CSO) at Polgenix Inc. and an inventor on US patent 7706863, “Methods for assessing a physiological state of a mammalian retina,” and US patent 8346345 B2, “Methods for assessing a physiological state of a mammalian retina,” whose values may be affected by this publication.

Reference information:J Clin Invest. 2015;125(7):2781–2794. doi:10.1172/JCI80950.

Footnotes

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