2-Methoxyestradiol blocks cell-cycle progression at G(2)/M phase and inhibits growth of human prostate cancer cells

2-Methoxyestradiol (2-ME), an endogenous metabolite of 17 beta -estradiol, is present in human blood and urine. Here we show for the first time that 2 -ME significantly inhibited the growth of normal prostate epithelial cells and androgen-dependent LNCaP and an drogen-independent DU145 prostate cance r cells, This growth Inhibition was accompanied by a twofold increase in th e G(2)/M Population, with a concomitant decrease in the G(1) population, as shown by cell-cycle analysis. 2-ME treatment affected the cell-cycle progr ession of prostate cancer cells specifically by blocking cells In the G(2) phase. Immunoblot analysis of the key cell-cycle regulatory proteins In the G(2)/M phase showed a 14-fold increase In the expression of p21 and an eig htfold increase in the expression of p34 cell division cycle 2 (cdc2). We a lso found an accumulation of phosphorylated cdc2 after 2-ME treatment. Furt hermore, Wee I kinase was detectable after 2-ME treatment. 2-ME treatment a lso led to an increase In the activity of caspase-3, followed by apoptosis, as shown by terminal deoxynucleotidyl transferase-mediated deoxyuridine 5- triphosphate-biotin nick end-labeling and fluorescein isothiocyanate-poly(A DP-ribose) polymerase assay. Estrogen receptor levels did not change after treatment with 2-ME. Examination of the signaling pathways that mediate 2-M E-induced apoptosis showed reduction in the level of p53 expression and its DNA-binding activity. Given the fact that p53 mutations are common in pati ents with metastatic prostate cancer, our finding that 2-ME-mediated growth inhibition of human prostate cancer cells occurred in a p53-independent ma nner has considerable clinical significance. These findings, combined with the limited toxicity of 2-ME, may have significant implications for alterna tive treatment of advanced prostate cancer. (C) 2001 Wiley-Liss, Inc.