Abstract
Abstract
Castration-resistant prostate cancer (CRPC) express high levels of the anti-apoptotic proteins Bcl-2 and Bcl-xL, resulting in drug resistance and association with poor prognosis. Docetaxel (Doc), an antimitotic drug that is the first-line treatment strategy for CRPC, is known to provide a small survival benefit but patients eventually become resistant to Doc with little hope for survival. It is apparent that Doc chemotherapy alone is not enough to counteract the high levels of Bcl-2/Bcl-xL present in CRPC. ABT-737 is a small molecule that binds to Bcl-2/Bcl-xL with high affinity and disrupts their interaction with pro-apoptotic Bax/Bak, thus enhancing pro-apoptotic signals when combined with other drugs. We investigated whether ABT-737 can increase Doc-mediated apoptosis in CRPC cells. Our results in androgen-dependent LNCaP and CRPC PC3 cell lines indicate that ABT-737 (1 μM) increases Doc (1 nM)-mediated cell death and caspase-dependent apoptosis, as determined by trypan blue exclusion, annexin-FITC/propidium iodide flow cytometry, and Western blot analysis. Our data suggests that Doc's anti-cancer effect results from prolonged cyclin B1/Cdk1 activation and inactivation of Bcl-2/Bcl-xL by phosphorylation, resulting in increased apoptosis. We show a correlation between high phosphorylation (P) of Bcl-2(Ser70)/Bcl-xL(Ser62) and increased apoptosis by Doc and Doc + ABT-737 treatments. Furthermore, the Cdk1 inhibitor purvalanol A blocks Doc + ABT-737-mediated increases in P-Bcl-2/P-Bcl-xL and subsequent apoptotic cell death. Lentivirus pLKO.1 shRNA stable knockdown of Bax but not Bak lowers cell death LNCaP and PC3 cells after treatment with Doc + ABT-737. In contrast to LNCaP and PC3, the CRPC DU145 cell line is null for Bax, expresses high levels of anti-apoptotic Mcl-1, and is more resistant to ABT-737. Retrovirus pBABE stable expression of Bax in DU145 cells restores sensitivity to Doc + ABT-737 compared to the empty vector control cells. We conclude that ABT-737 can sensitize CRPC cells to Doc treatment and may provide an important combination chemotherapy strategy for improving overall survival.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2571. doi:10.1158/1538-7445.AM2011-2571
