Mifepristone induces cell growth arrest in SKOV-3 ovarian cancer cells deregulating the pRb/E2F pathway

GOYENECHE, A.A.; CARÓN, R.W.; TELLERIA, C.M

Anaheim, California, USA

Congreso; 96 th Annual Meeting of the American Association of Cancer Research; 2005

American Association of Cancer Research

A major clinical problem in the treatment of ovarian cancer is the intrinsic and acquired resistance to platinum therapy. Therefore, the development of novel strategies for ovarian cancer treatment is of importance. In this work, we set out to explore the effect of the progesterone receptor modulator mifepristone (also known as “RU486”) on proliferation of human ovarian epithelial cancer cells SKOV-3. Cells were first exposed to various doses of mifepristone (5, 10, and 20 mM) for 96 h. Secondly, a time course experiment was conducted by exposing SKOV-3 cells to 20 mM of mifepristone for 1-5 days. Mifepristone inhibited cell proliferation within 24 h of treatment and the inhibition persisted throughout the study. Cell growth suppression was not associated with loss of viability, as evaluated by using a two-color fluorescence cell viability assay. Yet mifepristone, in a dose- and time-dependent manner, suppressed clonogenic survival. The inhibition of SKOV-3 cell growth by mifepristone was confirmed through the decrease in bromodeoxyuridine incorporation in mifepristone-treated cells when compared to cells receiving vehicle alone. Flow cytometric studies of mifepristone-treated cells indicated that the cytostatic effect of the modulator was associated with G1 cell cycle arrest. Further, G1 blockade was accompanied by up-regulation of cyclin-dependent kinase inhibitors p27kip1 and p21waf1/cip1, and decreased  expression of cyclin dependent kinase 2 (cdk-2) protein. Mifepristone also reduced phosphorylation of the retinoblastoma protein (pRb), without changing total pRb levels. Expression of transcription factor E2F needed for the synthesis of S phase regulatory genes was strongly down-regulated by mifepristone, and this was associated with the decrease in expression of E2F regulated genes, such as cdc2 (cdk1) and cyclin A. Overall these results indicate that the contraceptive steroid mifepristone can successfully suppress proliferation of human epithelial SKOV-3 ovarian cancer cells in vitro. The cytostatic effect of mifepristone is associated with G1 cell cycle arrest, deregulation of the pRb/E2F pathway, and loss of clonogenic survival. These preclinical in vitro findings show potential for an effective anti-tumor action of the progesterone receptor modulator mifepristone in vivo. (Supported by NIH Grant 2 P20 RR016479 and funds from the South Dakota Health Research Foundation).