Abstract P5-05-07: Promestriene effects on estrogen-sensitive breast cancer cell proliferation in vitro

Abstract

Abstract Introduction: Promestriene (3-propyl ethyl, 17B-methyl estradiol) is a synthetic estrogen analogue with potential as a topical treatment for vaginal atrophy caused by estrogen deprivation. Topical Promestriene is minimally absorbed with chronic use and has been reported to significantly improve the symptoms of vaginal atrophy. However, to be considered for use for these symptoms in estrogen responsive post-menopausal breast cancer survivors on an aromatase inhibitor, Promestriene would need to show none of the cyto-proliferative properties of estrogen. Methods: We conducted in vitro testing of estrogen responsive breast cancer cell line MCF-7, T-47D, and BT-474 for dose-dependent, estrogen-like functional responses to Promestriene in both estrogen-rich and estrogen-deprived conditions. As assay controls, cultures treated with Fulvestrant, Testosterone, Progesterone and Estradiol were analyzed in parallel. Analysis: Dose dependent Estrogen-like responses in the cell lines were measured as 1) proliferation using flow cytometric analysis of CSFE fluorescence, 2) estrogen receptor expression by flow cytometry, and 3) GREB 1 RNA expression using TaqMan real time PCR quantitative analysis. All cultures were grown to quiescence in RPMI medium supplemented with 10% fetal calf serum. To induce estrogen deprivation, half of the cultures were then held 3 days in media pre-treated and containing anti-estrogen specific antibodies to sequester any residual estrogen from the culture. Data for each culture treatment were analyzed using linear regression analysis and compared using multifactorial or pairwise analyses to determine the significance of estrogen-like responses relative to the estradiol and untreated controls. Results: In estrogen sufficient cultures, Promestriene exhibited no cell proliferative properties on MCF-7, BT-474, or T47-D tumor cells, even at very high concentrations. However, when estrogen in the media was sequestered and culture allowed to quiesce without estrogen receptor stimulation, low dose Promestriene effects on cell proliferation in MCF-7 estrogen responsive cells were not significantly different from low dose estradiol. Low dose Promestriene (2-10pg/ml), unlike comparable doses of estradiol, did not stimulate GREB1 expression in MCF-7 cells. In contrast, T-47D and BT-474 cell lines proliferated and increased GREB- expression in response Promestriene or Fulvestrant treatments. Conclusions: The potential estrogen-like properties of Promestriene to stimulate the growth of estrogen receptor responsive breast cancer cell lines, especially in estrogen-deprived conditions, suggest caution when prescribed for vaginal atrophy in post-menopausal breast cancer survivors on an aromatase inhibitor. Its ability to activate growth and gene expression in ER- breast cancer cells warrants further study. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-05-07.