Effect of a small-molecule MDM2/MDMX inhibitor on cell cycle arrest and apoptosis in breast cancer cells.

Abstract

e22096 Background: The MDM2 inhibitor which disrupted the MDM2-p53 interaction made little effort on the activation of p53 for breast cancer treatments, due to MDMX over expression. Previously a small molecule inhibitor targeting at MDM2 and MDMX had been successfully synthesized. We tested anti-tumor activity of the small molecule MDM2/MDMX inhibitor, compared with nutlin-3α, a well characterized MDM2 inhibitor, in the wild-type (wt) and mutant (mt) p53 breast cancer cell lines. Methods: Human breast cancer cell lines MCF-7 (wt-p53), ZR-7530 (wt-p53), BT-474 (mt-p53) and MDA-MB-231 (mt-p53) were cultured and treated with the small molecule MDM2/MDMX inhibitor, nutlin-3α or phosphate buffer solution (PBS) for 48 hrs separately. MTT for cell viability, FCM for cell cycle arrest and Annexin V FITC/PI for cell apoptosis were performed. The mechanism of antitumor activity of the small molecule MDM2/MDMX inhibitor was determined by Western-Blot analysis. Results: The inhibitor of MDM2 and MDMX inhibited cell growth and induced cell cycle arrest and apoptosis in mt-p53 breast cancer cells while nutlin-3α cannot. In the breast cancer cells with wt-p53, both of them inhibited cell growth, induced cell cycle arrest and apoptosis, but MDM2/MDMX inhibitor was proven to be more effective. Western Blot revealed that there was higher level of p53 expression in breast cancer cells treated with MDM2/MDMX inhibitor than nutlin-3α. The marked increases in p21, Bax and PUMA expressions were abserved in both wt-p53 and mt-p53 breast cancer cells which indicated that the small molecule MDM2/MDMX inhibitor induced cell apoptosis through p21, Bax and PUMA over expressions. Conclusions: The small molecule MDM2/MDMX inhibitor would be able to suppress cell proliferation, induce cell cycle arrest and apoptosis, activate p53 more effective than nutlin-3α in breast cancer cells, no matter with p53 status. P21, Bax and PUMA were involved in the mechanism of apoptosis induction. The inhibitor of targeting at both MDM2 and MDMX will be a novel treatment for breast cancer p53-independent status in the future.