Abstract 1863: Using a cell based model system to characterize CYP17A1 genetic variants

Abstract

Abstract Androgen and estrogen steroid hormones are potent growth stimuli for both prostate and breast cancer. Cytochrome P450 17A1 (CYP17A1), a P450 monooxygenase, is required for the synthesis of these hormones and is the target of abiraterone, a drug approved for the treatment of castration-resistant prostate cancer. CYP17A1 catalyzes the 17α hydroxylation of the C21 steroids pregnenolone and progesterone and has a lyase activity that cleaves the C17-20 bond to produce the sex steroid precursors, dehydroepiandrosterone (DHEA) and androstenedione. We identified twelve nonsynonymous single nucleotide polymorphisms (SNPs) in CYP17A1 and hypothesized that the resultant amino acid changes might alter hydroxylase and lyase activity and thereby impact steroid hormone synthesis. This hypothesis was examined by transiently transfecting HEK293T cells, with either wild-type or polymorphic CYP17A1 constructs. Cells were treated for 3 hours with tritiated ([3H]) progesterone and the production of hydroxylated (OH) metabolites analyzed by HPLC. In cells transfected with wild-type CYP17A1, 8.11% and 55.5% of the [3H]-progesterone was recovered as 16-OH progesterone, and 17-OH progesterone, respectively. Using the ratio of 17-OH progesterone to 16-OH progesterone as a quantitative measure of CYP17A1 enzyme activity, wild-type CYP17A1 yields a ratio of 6.9+/- 0.05. In contrast, the SNP (rs200063521) which causes an aspartic acid to histidine amino acid change at residue 216, results in a 2.2 fold decrease in 16OH-progesterone synthesis compared to wild-type suggesting altered hydroxylase function. CYP17A1 protein expression, as determined by western blot analysis, suggests that a glycine to arginine conversion at residue 162 (rs141821705) results in decreased protein levels. Studies to further characterize the CYP17A1 variants are underway. This work could lead to a better understanding of the role of CYP17A1 SNPs in cancer progression and response to CYP17A1 targeted therapies. Citation Format: Cameron P. Capper, Jiayan Liu, Lauren McIntosh, José M. Larios, Michael D. Johnson, Paul F. Hollenberg, Richard J. Auchus, James M. Rae. Using a cell based model system to characterize CYP17A1 genetic variants. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1863. doi:10.1158/1538-7445.AM2015-1863