Teslenko I, Watson CJW, Chen G, Lazarus P. Inhibition of the aromatase enzyme by exemestane cysteine conjugates.
Mol Pharmacol 2022;
102:MOLPHARM-AR-2022-000545. [PMID:
35953090 PMCID:
PMC9595203 DOI:
10.1124/molpharm.122.000545]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 08/02/2022] [Accepted: 08/05/2022] [Indexed: 11/25/2022] Open
Abstract
Exemestane (EXE) is an aromatase inhibitor used to treat hormone-dependent breast cancer. EXE is extensively metabolized, with unchanged EXE and its active metabolite 17-dihydroexemestane (17-DHE) accounting for 17 and 12%, respectively, of total plasma EXE in vivo The major circulating EXE metabolites are the cysteine conjugates of EXE and 17-DHE, and the 17-DHE glucuronide, which together account for 70% of total plasma EXE in vivo The goal of the present study was to examine the inhibition potential of major metabolites of EXE through inhibition assays using aromatase-overexpressing cells and pooled ovarian tissues. Estrone formation was used as a measure of aromatase activity and was detected and quantified using UPLC-MS. EXE-cys, 17β-DHE, and 17β-DHE-cys all exhibited inhibition of estrone formation at both 1 µM and 10 µM concentrations, with 17β-DHE and EXE-cys showing significant inhibition of estrone formation (63% each) at 10 µM. In contrast, 17β-DHE-Gluc displayed minimal inhibition (5-8%) at both concentrations. In ovarian tissue, EXE-cys and 17β-DHE showed similar patterns of inhibition, with 49% and 47% inhibition, respectively, at 10 µM. The IC50 value for EXE-cys (16 {plus minus} 10 µM) was similar to 17β-DHE (9.2 {plus minus} 2.7 µM) and higher than EXE (1.3 {plus minus} 0.28 µM), and all three compounds showed time-dependent inhibition with IC50 shifts of 13 {plus minus} 10, 5.0 {plus minus} 2.5 and 36 {plus minus} 12-fold, respectively. Given its high circulating levels in patients taking EXE, these results suggest that EXE-cys may contribute to the pharmacologic effect of EXE in vivo Significance Statement The current study is the first to examine the major phase II metabolites of EXE (EXE-cys, 17β-DHE-cys, and 17β-DHE-Gluc) for inhibition potential against the target enzyme, aromatase (CYP19A1). EXE-cys was found to significantly inhibit aromatase in a time dependent manner. Given its high circulating levels in patients taking EXE, this phase II metabolite may play an important role in reducing circulating estrogen levels in vivo.
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