Boldine Activates Intrinsic Apoptotic Pathway in DU-145 Androgen-Independent Prostate Cancer Cell Line

Abstract

Prostate cancer is one of the most common forms of cancer in men and continues to be a problem in the developed world. The treatment approaches for androgen-independent prostate cancer are unsatisfactory and the survival of those patients remains poor. Thus, there is a strong demand to develop novel therapeutic agents to treat and prevent this advanced malignancy. The present study evaluated the effect of boldine (2,9-dihydroxy-1,10-dimethoxy-aporphine), an aporphine alkaloid occurs abundantly in the leaves of Boldo (Peumus boldus Molina), on growth and cell death of DU-145 androgen-independent prostate cancer cell line. The cell viability was measured by MTT test and LDH release was used to quantify necrosis cell death. Genomic DNA, caspase-3 activity, expression of cleaved caspase-9, Hsp70, Bcl-2 and Bax proteins were analyzed in order to study the apoptotic process. The results showed that boldine was able to reduce cell viability in the range of 60-240 mM concentrations, and suggest this aporphine alkaloid induces cell death by intrinsic apoptotic pathway that probably involves the down-regulation of heat shock protein 70 (Hsp70). In fact, an increase of caspase-3 enzyme activity and Bax protein expression, in conjunction with the more pronounced decrease in Bcl-2 occurred in DU-145 cells treated with boldine at 60-120 mM concentrations. In addition, caspase-9 was shown to be observably activated. Moreover, boldine such as quercetin, a well-known Hsp70 protein inhibitor, induced a reduction of Hsp70 expression. The hypothesis of apoptosis induction in our experimental conditions was reinforced by a high DNA fragmentation at 60-120 µM concentrations, not correlated to LDH release. The present findings, starting point for further investigation, suggest that boldine structure might be used to design novel derivatives for the developing of potential new drugs for advanced prostate cancer therapy.