The contribution of estrogen receptor-mediated signaling to cancer progression and metastasis has been well documented. However, much less attention has been given to the role of estrogen metabolism in carcinogenesis. Parent estrogens are metabolized to 2- and 4-hydroxyestrogens (2-OHEs and 4-OHEs) that can retain their estrogenic activity, form reactive quinones that cause DNA damage, or become inactivated primarily by the rate-limiting conjugation enzyme catechol-O-methyltransferase (COMT). The ability of 4-OHEs to induce genomic instability and the malignant transformation of human breast epithelial cells has been reported. Glucuronidation or sulfation of methylated hydroxyestrogens, produced by COMT, increases their solubility and facilitates their excretion via urine or feces. The extent to which catechol estrogens are methylated dictates, in part, their ability to initiate carcinogenesis verses protect against tumor formation. COMT is a ubiquitous polymorphic enzyme that is expressed in humans in both peripheral tissues (soluble, s-COMT) and the central nervous system (membrane-bound). The goal of the present study was to compare the rate at which human wild type (WT) s-COMT and its major polymorphic variant (V108M s-COMT) transfer the methyl group from S-adenosylmethionine to 2-OHE and 4-OHE. This was accomplished by expressing COMT in E. coli, followed by protein purification and steady state Michaelis-Menten kinetics. Production of methylated hydroxyestrogens (2-MeOEs and 4-MeOEs) was quantified using LC-MS/MS methodology. The resulting data indicate that WT s-COMT methylates catechol estrogens more efficiently than V108M s-COMT. In addition, the specificity constant (kcat/KM) of WT s-COMT for methylation of 4-OHE2 was 12-fold greater than that of V108M s-COMT. The kcat/KM of V108M s-COMT was 4-fold greater for 2-OHE2 vs. 4-OHE2. Based on the enhanced catalytic efficiency of WT s-COMT in converting 2-OHEs to 2-MeOEs, 4-OHEs may have greater potential to cause DNA damage. Additional studies are needed to determine if the V108M s-COMT variant contributes to increased risk for cancer. These data provide novel insight into the potential mechanism by which 4-OHEs promote hormone-induced carcinogenesis.

This work was supported by an In Vino Vita Award from Fox Chase Cancer Center.

Citation Format: Daniel D. Krzizike, Margie L. Clapper, Andrew J. Andrews. Specificity of catechol-O-methyltransferase (COMT) for hydroxyestrogens favors 2-OHEs over 4-OHEs [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2345.