Abstract A43: Increased cyclin A expression is associated with antiprogestin resistance and progesterone receptor isoforms ratio in experimental models of breast cancer

Deregulation of cyclin A expression has been associated with prognosis and tamoxifen responsiveness in breast cancer. We have previously reported an overexpression of cyclin A in two antiprogestin-resistant tumors derived from a hormone-dependent mammary carcinoma induced by medroxyprogesterone acetate (MPA). MPA-induced tumors show high levels of estrogen (ER) and progesterone receptors (PR) and transit through different stages of hormone dependency. Taking into account that antiprogestin-sensitive tumors show higher levels of PR isoform A (PRA) than isoform B (PRB), and that the opposite ratio is observed in the antiprogestin-resistant tumors, we decided to examine the expression of cyclin A in other experimental models containing different PRA/PRB ratios. An increase in cyclin A expression was observed by Western blot (WB) in the acquired antiprogestin-resistant variant C7-2-HIR and in the constitutive resistant C7-HI tumor (1.7 fold and 1.5 fold, respectively) compared to the antiprogestin-responsive tumor C7-2-HI (p Citation Format: Marina Ayre, Melina E. Bilinski, Britta M. Jacobsen, Claudia Lanari, Victoria T. Fabris. Increased cyclin A expression is associated with antiprogestin resistance and progesterone receptor isoforms ratio in experimental models of breast cancer [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr A43.