Molecular pharmacodynamics of emixustat in protection against retinal degeneration

Zhang, Jianye; Kiser, Philip D.; Badiee, Mohsen; Palczewska, Grażyna; Dong, Zhiqian; Golczak, Marcin; Tochtrop, Gregory P.; Palczewski, Krzysztof

doi:10.1172/jci80950

Cited by 62 publications

(107 citation statements)

References 69 publications

(109 reference statements)

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“…Already several different families of inhibitors have been identified, each illuminating important aspects of the catalytic mechanism, including retinylamines (28), the non-reti- noid emixustat and its derivatives (6,12), and lipophilic aromatic spin traps (10). In this paper, we show that triacsin C, well known to be a specific inhibitor of long chain ACSLs, is also a potent inhibitor of RPE65 retinol isomerase.…”

Section: Discussionmentioning

confidence: 83%

Inhibition of RPE65 Retinol Isomerase Activity by Inhibitors of Lipid Metabolism

Eroglu

Gentleman

Poliakov

et al. 2016

Journal of Biological Chemistry

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RPE65 is the isomerase catalyzing conversion of all-transretinyl ester (atRE) into 11-cis-retinol in the retinal visual cycle. Crystal structures of RPE65 and site-directed mutagenesis reveal aspects of its catalytic mechanism, especially retinyl moiety isomerization, but other aspects remain to be determined. To investigate potential interactions between RPE65 and lipid metabolism enzymes, HEK293-F cells were transfected with expression vectors for visual cycle proteins and co-transfected with either fatty acyl:CoA ligases (ACSLs) 1, 3, or 6 or the SLC27A family fatty acyl-CoA synthase FATP2/SLCA27A2 to test their effect on isomerase activity. These experiments showed that RPE65 activity was reduced by co-expression of ACSLs or FATP2. Surprisingly, however, in attempting to relieve the ACSL-mediated inhibition, we discovered that triacsin C, an inhibitor of ACSLs, also potently inhibited RPE65 isomerase activity in cellulo. We found triacsin C to be a competitive inhibitor of RPE65 (IC 50 ‫؍‬ 500 nM). We confirmed that triacsin C competes directly with atRE by incubating membranes prepared from chicken RPE65-transfected cells with liposomes containing 0 -1 M atRE. Other inhibitors of ACSLs had modest inhibitory effects compared with triascin C. In conclusion, we have identified an inhibitor of ACSLs as a potent inhibitor of RPE65 that competes with the atRE substrate of RPE65 for binding. Triacsin C, with an alkenyl chain resembling but not identical to either acyl or retinyl chains, may compete with binding of the acyl moiety of atRE via the alkenyl moiety. Its inhibitory effect, however, may reside in its nitrosohydrazone/ triazene moiety.The process of vision begins in the photoreceptor outer segments of the retina with absorption of a photon of light by the 11-cis-retinylidene chromophore ligand of photoreceptor visual pigment opsins, such as rhodopsin. This event photoisomerizes the 11-cis-retinal to the all-trans-isomer, thereby activating the rhodopsin to metarhodopsin and initiating the phototransduction pathway that results in transmission of a signal, via retinal interneurons, for central processing in brain visual centers. Upon completion of the phototransduction cascade processes, the all-trans-retinal releases from its Schiff base linkage following decay of metarhodopsin and is reduced to all-trans-retinol and transported to the retinal pigment epithelium (RPE), 2 a monolayer epithelium apposed to the photoreceptor outer segments. To regenerate the visual pigment, input of 11-cis-retinal is required. This is provided by enzymatic isomerization in the RPE of the esterified all-trans-retinol in a process termed the visual cycle. RPE65 is the key isomerase in the RPE visual cycle that catalyzes the conversion of all-transretinyl ester (atRE) into 11-cis-retinol (1-3). RPE65 is a member of a family of carotenoid oxygenases that has evolved to become a retinol isomerase in the vertebrate retinal visual cycle (4). Recent crystal structures of RPE65 (5-7) and site-directed mutagenesis studies (8, 9) have ...

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Section: Discussionmentioning

confidence: 83%

Inhibition of RPE65 Retinol Isomerase Activity by Inhibitors of Lipid Metabolism

Eroglu

Gentleman

Poliakov

et al. 2016

Journal of Biological Chemistry

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“…The terminal aliphatic ring moieties of these molecules, located closest to the active-site entrance, are the most mobile regions of the molecule as evidenced by their higher average atomic displacement parameters and multiple conformations observed in different crystal forms Zhang et al, 2015). The long-range van der Waals interactions formed between this portion of the molecules and residues forming the active-site opening are expected to minimally contribute to the binding affinity of emixustat and MB-001.…”

Section: Identification Of Potential Sites For Emixustatmentioning

confidence: 99%

“…Crystal structures of RPE65 in complex with emixustat and a derivative called MB-001 [(R)-3-Amino-1-(3-((2,6,6-trimethylcyclohex-1-en-1-yl)methoxy)phenyl)propan-1-ol] have revealed molecular interactions governing the binding affinity of these compounds Zhang et al, 2015). We hypothesized that these structures could inform strategies to modify the affinity of emixustat derivatives toward the RPE65 active site with maintenance of retinaldehyde-sequestering activity.…”

Section: Introductionmentioning

confidence: 99%

Rational Tuning of Visual Cycle Modulator Pharmacodynamics

Kiser

Zhang

Badiee

et al. 2017

J Pharmacol Exp Ther

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Modulators of the visual cycle have been developed for treatment of various retinal disorders. These agents were designed to inhibit retinoid isomerase [retinal pigment epithelium-specific 65 kDa protein (RPE65)], the rate-limiting enzyme of the visual cycle, based on the idea that attenuation of visual pigment regeneration could reduce formation of toxic retinal conjugates. Of these agents, certain ones that contain primary amine groups can also reversibly form retinaldehyde Schiff base adducts, which contributes to their retinal protective activity. Direct inhibition of RPE65 as a therapeutic strategy is complicated by adverse effects resulting from slowed chromophore regeneration, whereas effective retinal sequestration can require high drug doses with potential off-target effects. We hypothesized that the RPE65-emixustat crystal structure could help guide the design of retinaldehydesequestering agents with varying degrees of RPE65 inhibitory activity. We found that addition of an isopropyl group to the central phenyl ring of emixustat and related compounds resulted in agents effectively lacking in vitro retinoid isomerase inhibitory activity, whereas substitution of the terminal 6-membered ring with branched moieties capable of stronger RPE65 interaction potentiated inhibition. The isopropyl derivative series produced discernible visual cycle suppression in vivo, albeit much less potently than compounds with a high affinity for the RPE65 active site. These agents were distributed into the retina and formed Schiff base adducts with retinaldehyde. Except for one compound [3-amino-1-(3-isopropyl-5-((2,6,6-trimethylcyclohex-1-en-1-yl)methoxy)phenyl)propan-1-ol (MB-007)], these agents conferred protection against retinal phototoxicity, suggesting that both direct RPE65 inhibition and retinal sequestration are mechanisms of potential therapeutic relevance.

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“…Decreasing levels of all-trans-retinal either with inhibitors of the retinoid cycle such as retinylamine and the retinylamine-derived potent inhibitor, emixustat (Kubota R et al, 2014, Zhang J et al, 2015 or FDA-approved drugs containing amines that sequester accumulated free aldehyde can significantly improve overall retinal health in Abca4 −/− Rdh8 −/− mice, corroborating that all-transretinal is the toxic photo-metabolite.…”

Section: Discussionmentioning

confidence: 85%

Protective Effect of a Locked Retinal Chromophore Analog against Light-Induced Retinal Degeneration

et al. 2018

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Molecular pharmacodynamics of emixustat in protection against retinal degeneration

Cited by 62 publications

References 69 publications

Inhibition of RPE65 Retinol Isomerase Activity by Inhibitors of Lipid Metabolism

Inhibition of RPE65 Retinol Isomerase Activity by Inhibitors of Lipid Metabolism

Rational Tuning of Visual Cycle Modulator Pharmacodynamics

Protective Effect of a Locked Retinal Chromophore Analog against Light-Induced Retinal Degeneration

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