A convenient test system for the identification of CYP4V2 inhibitors

Purpose: Polymorphisms in the gene that codes for the human cytochrome P450 enzyme CYP4V2 are a cause of Bietti crystalline dystrophy (BCD). Therefore, inhibition of CYP4V2 activity may well be a cause of visual disability. However, monitoring the fatty acid hydroxylation reactions catalyzed by this enzyme is tedious and not well suited for inhibitor screening. Methods: We investigated the use of proluciferin compounds as probe substrates for efficient and convenient determination of CYP4V2 activity. Results: Ten proluciferins were tested for conversion by CYP4V2, and eight were found to be substrates of this enzyme. One point inhibitor assays were performed using luciferin 6' 3-furfuryl ether methyl ester (luciferin-3FEME) as the probe substrate and 12 test compounds. As expected, HET0016 had by far the strongest effect, while two other compounds (including osilodrostat) also displayed statistically significant inhibitory potency. The half maximal inhibitory concentration (IC50) for HET0016 was determined to be 179 nM. A recently identified potent inhibitor of human CYP4Z1 was found not to inhibit CYP4V2. To explore the selectivity of this compound between CYP4Z1 and CYP4V2, we developed a homology model of CYP4V2 and conducted docking experiments. Conclusions: We provide the first protocol for a robust and convenient CYP4V2 inhibitor assay that does not depend on fatty acid analysis but can be simply monitored with luminescence. Moreover, we demonstrate additional evidence for the concern that compounds with CYP-inhibitory properties may inhibit CYP4V2 activity and thus, possibly cause visual disability.