Ursolic acid overcomes Bcl-2-mediated resistance to apoptosis in prostate cancer cells involving activation of JNK-induced Bcl-2 phosphorylation and degradation.

Androgen-independent prostate cancers express high levels of Bcl-2, and this over-expression of Bcl-2 protects prostate cancer cells from undergoing apoptosis. Ursolic acid (UA) has demonstrated an anti-proliferative effect in various tumor types. The aim of this study is to evaluate the difference between UA-induced apoptosis in androgen-dependent prostate cancer cell line LNCaP cells and androgen-independent prostate cancer cell line LNCaP-AI cells and to reveal the molecular mechanisms underlying the apoptosis. We found that UA treatment in vitro can effectively induce apoptosis in LNCaP and LNCaP-AI cells. UA can overcome Bcl-2-mediated resistance to apoptosis in LNCaP-AI cells. Intrinsic apoptotic pathways can be triggered by UA treatment because c-Jun N-terminal kinase (JNK) is activated and subsequently provokes Bcl-2 phosphorylation and degradation, inducing activation of caspase-9. Although further evaluation is clearly needed, the present results suggest the potential utility of UA as a novel therapeutic agent in advanced prostate cancer.