title: Molecular pharmacodynamics of emixustat in protection against retinal degeneration.
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.
authors.forename: Jianye
authors.initials: J
authors.lastname: Zhang
authors.forename: Philip D
authors.initials: PD
authors.lastname: Kiser
authors.forename: Mohsen
authors.initials: M
authors.lastname: Badiee
authors.forename: Grazyna
authors.initials: G
authors.lastname: Palczewska
authors.forename: Zhiqian
authors.initials: Z
authors.lastname: Dong
authors.forename: Marcin
authors.initials: M
authors.lastname: Golczak
authors.forename: Gregory P
authors.initials: GP
authors.lastname: Tochtrop
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Palczewski
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000172:deficiency / Q000235:genetics; D000429:Alcohol Oxidoreductases / Q000172:deficiency / Q000235:genetics; D000818:Animals; D020134:Catalytic Domain; D002417:Cattle; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D005260:Female; D016166:Free Radical Scavengers / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D008268:Macular Degeneration / Q000188:drug therapy / Q000378:metabolism; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008958:Models, Molecular; D010647:Phenyl Ethers / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D011412:Propanolamines / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D012162:Retinal Degeneration / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D012172:Retinaldehyde / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity; D012545:Schiff Bases / Q000378:metabolism; D013237:Stereoisomerism; D019745:cis-trans-Isomerases / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism; D000099178:Retinoid Isomerohydrolase
chemical_list: D018528:ATP-Binding Cassette Transporters; D000429:Alcohol Oxidoreductases; D004791:Enzyme Inhibitors; D016166:Free Radical Scavengers; D010647:Phenyl Ethers; D011412:Propanolamines; D012172:Retinaldehyde; D012545:Schiff Bases; D019745:cis-trans-Isomerases; D000099178:Retinoid Isomerohydrolase; C512841:Abca4 protein, mouse; C000592692:emixustat; C525880:HSD17B6 protein, mouse