Antiproliferative effect of normal and 13-epi-d-homoestrone and their 3-methyl ethers on human reproductive cancer cell lines

The possibility of the therapeutic use of estrogens emerged following the recognition that certain estradiol analogs, and particularly metabolites (e.g. the A-ring metabolite 2-hydroxyestrone, etc.) inhibit the differentiation of diverse tumor cell lines. Until recently, despite the investigation of numerous synthetic d-ring-substituted estrone derivatives, no analysis had been published on the effects of d-ring expansion of estrone on its tumor-suppressing activity. The aim of the present study was to characterize the antiproliferative effects of normal and 13-epi-d-homoestrone and their 3-methyl ethers (1–4) on human reproductive cancer cell lines.The antitumor activities of the two epimer pairs on HeLa, MCF-7 and Ishikawa cells were determined. Normal d-homoestrone exerted the greatest cytostatic effect on HeLa cells (IC50 = 5.5 μM) and was subjected to further investigations to elucidate its mechanism of action on apoptosis induction. Morphological changes detected by Hoechst 33258–propidium iodide double staining, the cell cycle arrest at phase G2/M and the subsequent increase in the proportion of the subG1 fraction determined by flow cytometric analysis and the significant increase in the activity of caspase-3 confirmed the induction of apoptosis in HeLa cells treated with d-homoestrone. d-Homoestrone was also tested on a non-cancerous human lung fibroblast cell line (MRC-5) to determine its selective toxicity. The concentration in which it inhibited cell proliferation by 50% was at least six times higher for the fibroblast cells than for cervical cancer cells. No significant in vivo estrogenic activity was observed as concerns the uterus weight of gonadectomized rats after a 7-day treatment with normal d-homoestrone.These results led to the conclusion that normal d-homoestrone is a novel antitumor compound with a similar activity on HeLa cells as that of the reference agent cisplatin, but its selectivity toward non-cancerous cells is significantly higher than that of cisplatin. It may be considered to be a basic lead molecule for the preclinical development of potential anticancer agents.

► d-Homoestrone exerted substantial cytostatic effect selectively on HeLa cells.
► Cell cycle arrest and an increase in the apoptotic population were evidenced.
► d-Homoestrone exerted no significant estrogenic activity in gonadectomized rats.