Selective insensitivity of ZR-75-1 human breast cancer cells to 2-methoxyestradiol: evidence for type II 17beta-hydroxysteroid dehydrogenase as the underlying cause.
2-Methoxyestradiol (2-MeO-E2), a nonpolar endogenous metabolite of 17beta-estradiol, has strong antiproliferative, apoptotic, and antiangiogenic actions. Among the four human breast cancer cell lines tested (MCF-7, T-47D, ZR-75-1, and MDA-MB-435s), the ZR-75-1 cells were selectively insensitive to the antiproliferative actions of 2-MeO-E2, although these cells had a similar sensitivity as other cell lines to several other anticancer agents (5-fluorouracil, mitomycin C, doxorubicin, colchicine, vinorelbine, and paclitaxel). Mechanistically, this insensitivity is largely attributable to the presence of high levels of a steroid-selective metabolizing enzyme, the type II 17beta-hydroxysteroid dehydrogenase (17beta-HSD), in the ZR-75-1 cells, which rapidly converts 2-MeO-E2 to the inactive 2-methoxyestrone, but this enzyme does not metabolically inactivate other nonsteroidal anticancer agents. The type II 17beta-HSD-mediated conversion of 2-MeO-E2 to 2-methoxyestrone in ZR-75-1 cells followed the first-order kinetics, with a very short half-life (approximately 2 hours). In comparison, the T-47D, MCF-7, and MDA-MB-435s human breast cancer cells, which were highly sensitive to 2-MeO-E2, had very low or undetectable catalytic activity for the conversion of 2-MeO-E2 to 2-methoxyestrone. Reverse transcription-PCR analysis of the mRNA levels of three known oxidative 17beta-HSD isozymes (types II, IV, and VIII) revealed that only the type II isozyme was selectively expressed in the ZR-75-1 cells, whereas the other two isozymes were expressed in all four cell lines. Taken together, our results showed, for the first time, that the high levels of type II 17beta-HSD present in ZR-75-1 cells were largely responsible for the facile conversion of 2-MeO-E2 to 2-methoxyestrone and also for the selective insensitivity to the antiproliferative actions of 2-MeO-E2.
Liu
Zhi-Jian
ZJ
Department of Basic Pharmaceutical Sciences, College of Pharmacy, University of South Carolina, Columbia, South Carolina 29208, USA.
Lee
Won Jun
WJ
Zhu
Bao Ting
BT
D015067:17-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000077584:2-Methoxyestradiol; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000201:enzymology* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D004354:Drug Screening Assays, Antitumor; D004958:Estradiol / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D004960:Estradiol Dehydrogenases; D004967:Estrogens / Q000378:metabolism; D006801:Humans; D006914:Hydroxysteroids / Q000378:metabolism; D007527:Isoenzymes; D007664:Ketosteroids / Q000378:metabolism; D007700:Kinetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013148:Spironolactone / Q000031:analogs & derivatives / Q000494:pharmacology
D004967:Estrogens; D006914:Hydroxysteroids; D007527:Isoenzymes; D007664:Ketosteroids; D013148:Spironolactone; D004958:Estradiol; D000077584:2-Methoxyestradiol; D015067:17-Hydroxysteroid Dehydrogenases; D004960:Estradiol Dehydrogenases; C523763:HSD17B2 protein, human