Induction of mammalian cell transformation and genotoxicity by 2-methoxyestradiol, an endogenous metabolite of estrogen

2-Methoxyestradiol (2-MeOE2) is an endogenous metabolite of 17 beta-estradiol and a proposed inhibitor of tumor growth and angiogenesis. However, 2-MeOE2 is also an inhibitor of microtubule assembly and other microtubule inhibitors, e.g, colcemid and diethylstilbestrol, induce aneuploidy and cell transformation in cultured mammalian cells. To assess the in vitro carcinogenicity and related activity of 2-MeOE2, the abilities of this metabolite to induce cell transformation and genetic effects were studied simultaneously using Syrian hamster embryo (SHE) fibroblasts, Growth of these cells was reduced by treatment with 2-MeOE2 at 0.1-1.0 mu g/ml in a concentration-dependent manner. Treatment of SHE cells with 2-MeOE2 at 0.3 or 1.0 mu g/ml for 2-48 h also resulted in a concentration- and treatment time-related increase in the mitotic index and the percentage of multinucleated cells, Treatment with 2-MeOE2 at 0.1-1.0 mu g/ml for 48 h induced a statistically significant increase in the frequencies of morphological transformation of SHE cells in a concentration-dependent manner. A statistically significant increase in the frequencies of somatic mutations at the Na+/K+ ATPase or hprt locus was also observed in cells treated with 2-MeOE2 for 48 h at 0.1 or 0.3 mu g/ml, respectively. Treatment of SHE cells with 2-MeOE2 at 0.3 or 1.0 mu g/ml for 24 h induced chromosome aberrations, mainly breaks, exchanges and chromosome pulverization, The incidence of chromosome aberrations was not affected by co-treatment with alpha-naphthoflavone, an inhibitor of 2-hydroxylase that inhibits oxidative conversion of 2-MeOE2 to 2-hydroxyestradiol, but the incidence was slightly increased by co-treatment with L-ascorbic acid. Numerical chromosomal changes in the near diploid range and in the tetraploid and near tetraploid ranges were also detected in 2-MeOE2-treated cells. These findings indicate that 2-MeOE2 has cell transforming and genotoxic activities in cultured mammalian cells and potential carcinogenic activity.