Prostate cancer is the most common invasive malignancy and the second leading cause of cancer-related deaths among males in many Western countries. One approach to control this malignancy is its prevention or slowing its progression through the use of agents present in diet consumed by humans. Pigmented fruits and vegetables have shown to contain many anthocyanins, which contribute to their brilliant color and their strong antioxidant and anti-inflammatory properties. The major anthocyanin present in pigmented fruits and vegetables such as pomegranate, red, blue and purple berries, red and purple grapes, red wine and egg plant is delphinidin. In this study we show that delphinidin through modulations in the cyclin kinase inhibitor-cyclin-cyclin-dependent kinase machinery, results in inhibition of cell growth followed by apoptosis of highly aggressive human prostate carcinoma PC3 cells. Delphinidin (30-300 μM) treatment (48 h) of PC3 cells was found to result in a dose-dependent inhibition of cell growth/cell viability as assessed by trypan blue exclusion and MTT assays. In order to understand the mechanism of growth inhibition of PC3 cells by delphinidin, we studied its effect on critical cell cycle regulatory molecules. Immunoblot analysis revealed that delphinidin treatment (30-300 μM; 48 h) of PC3 cells resulted in significant (i) induction of cyclin kinase inhibitors p21/WAF1 and p27/KIP1; (ii) down-regulation of cyclin E, D1, and D2; and (iii) down-regulation of cyclin-dependent kinase 2, 4, and 6. This delphinidin caused cell growth inhibition was found to be accompanied by induction of apoptosis, as assessed by the cleavage of poly (ADP-ribose) polymerase (PARP), flow cytometry and morphological changes. The induction of apoptosis accompanied a decrease in the levels of antiapoptotic protein Bcl-2 and increase in proapoptotic protein Bax, thus shifting the Bax:Bcl-2 ratio in favor of apoptosis. Delphinidin treatment of PC3 cells was also found to result in significant activation of caspases, as shown by the dose dependent decrease in the protein expression of procaspase-3, -6, -8 and-9 and release of cytochrome c from the mitochondria to the cytosol. This delphinidin-mediated induction of apoptosis was significantly (70-90%) inhibited by the caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp (OMe)-fluoromethylketone (Z-VAD-FMK). These data suggest an essential role of caspases in delphinidin-mediated apoptosis of PC3 cells and involvement of cdk inhibitor-cyclin-cdk machinery during observed cell cycle arrest. It is tempting to suggest that consumption of pigmented fruits and vegetables containing anthocyanins could be an effective strategy to combat prostate cancer.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]