Equiguard suppresses androgen-dependent LNCaP prostate cancer cell proliferation by targeting cell cycle control via down regulation of the retinoblastoma protein Rb and induction of apoptosis via the release of cytochrome c.

Lack of life-prolonging therapies has provided much of the impetus for seeking complementary and alternative management/treatment options by prostate cancer (CaP) patients. Among these, the use of dietary supplements and botanical products has been showing a sustained increase in recent years, owing in part to some encouraging pre-clinical and clinical data shown in a limited number of herbal products. Notably, however, the majority of herbal and dietary supplement products have not been rigorously studied with regard to their efficacy. In vitro mechanistic experiments are considered essential preludes and requisites to more lengthy and costly animal and human studies, in that they may provide relevant insights and scientific basis for effects some of these products purportedly might demonstrate. In vitro studies in our laboratory have shown that a polyherbal supplement, Equiguard, exhibits anti-tumor activity against hormone dependent LNCaP cells cultured in both androgen-proficient (FBS) and -deficient (CS-FBS) conditions. Clinically relevant anti-prostate cancer effects of Equiguard are vividly illustrated by growth suppression and down regulated expression of prostate specific genes, respectively, androgen receptor (AR) and prostate specific antigen (PSA). However, the mechanistic bases contributing to these effects have not been well characterized. This communication describes experiments aimed at further understanding growth arrest elicited by Equiguard in LNCaP cells cultured in FBS and CS-FBS conditions. We have focused on aspects of cell cycle control and induction of apoptosis. Regulation of cell cycle progression by Equiguard was analyzed by examining changes in the expression of Rb and cyclins D/E. Using Western blot analysis, we showed that treatment caused inhibition of Rb phosphorylation, which was accompanied by the reduction of cyclins D/E expression, in both culture conditions. Moreover, cells treated with Equiguard and cultured with FBS-supplemented media showed up-regulation of cyclin-dependent kinase inhibitor Kip1/p27. These results support the interpretation that suppression of Rb phosphorylation mediated the observed growth arrest induced by Equiguard under androgen-proficient condition. In contrast, Equiguard-treated cells cultured in CS-FBS had lowered expression of the Kip1/p27, suggesting that different control mechanisms, possibly evoked by changes in cellular microenvironments, contributed to growth suppression by Equiguard. The growth suppressive effects of Equiguard in both culture conditions were also evaluated with respect to induction of apoptosis. While Equiguard elicited apoptosis was accompanied by an increase in the level of cytosolic cytochrome c, the relative accumulation of cytochrome c in the cytosol was unaffected by culture conditions. These results suggest that the ability to trigger apoptosis as one aspect of the control of cell growth by Equiguard is integrally linked to the release of cytochrome c, by a mechanism largely independent of the presence of androgens.