2-methoxyestradiol is an estrogen receptor agonist that supports tumor growth in murine xenograft models of breast cancer.
OBJECTIVE
2-Methoxyestradiol (2MEO) is being developed as a novel antitumor agent based on its antiangiogenic activity, tumor cell cytotoxicity, and apparent lack of toxicity. However, pharmacologic concentrations of 2MEO bind to estrogen receptors (ER). We have therefore examined the ER activity of 2MEO.


METHODS
Estrogenic actions of 2MEO were evaluated by changes in gene expression of the ER-positive (MCF7) breast tumor cell line and, in vivo, estrogenicity was assessed in breast tumor xenograft models and by measuring endocrine responses in uterus and liver.


RESULTS
In the ER-positive breast tumor cell line (MCF7), microarray experiments revealed that 269 of 279 changes in gene expression common to 2MEO and estradiol were prevented by the ER antagonist, ICI 182,780. Changes in the expression of selected genes and their sensitivity to inhibition by ICI 182,780 were confirmed by quantitative reverse transcription-PCR measurement. Activation of ER in MCF7 cells by 2MEO was further confirmed by stimulation of an estrogen response element-dependent reporter gene that was blocked by ICI 182,780 (1 micromol/L). Doses of 2MEO (15-150 mg/kg) that had no antitumor efficacy in either nu/nu BALB/c or severe combined immunodeficient mice bearing ER-negative MDA-MB-435 tumors had uterotropic and hepatic estrogen-like actions. In female nu/nu BALB/c mice inoculated with the estrogen-dependent MCF7 tumor cells, 2MEO (50 mg/kg/d) supported tumor growth.


CONCLUSIONS
Tumor growth enhancement by 2MEO at doses generating serum levels (100-500 nmol/L) that have estrogenic activity suggests that a conservative approach to the further clinical evaluation of this agent should be adopted and that its evaluation in breast cancer is inappropriate.
Sutherland
Tara E
TE
Department of Pharmacology, University of Melbourne, Parkville, Victoria 3010, Australia.
Schuliga
Michael
M
Harris
Trudi
T
Eckhardt
Bedrich L
BL
Anderson
Robin L
RL
Quan
Lilly
L
Stewart
Alastair G
AG
D000077584:2-Methoxyestradiol; D000818:Animals; D001943:Breast Neoplasms / Q000473:pathology*; D049109:Cell Proliferation; D004195:Disease Models, Animal; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology*; D005260:Female; D020869:Gene Expression Profiling; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D020411:Oligonucleotide Array Sequence Analysis; D011960:Receptors, Estrogen / Q000187:drug effects* / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
D011960:Receptors, Estrogen; D004958:Estradiol; D000077584:2-Methoxyestradiol