Novel antiproliferative flavonoids induce cell cycle arrest in human prostate cancer cell lines.

Epidemiologic studies have demonstrated an inverse association between flavonoid intake and prostate cancer (PCa) risk. The East Asian diet is very high in flavonoids and, correspondingly, men in China and Japan have the lowest incidence of PCa worldwide. There are thousands of different naturally occurring and synthetic flavonoids. However, only a few have been studied in PCa. Our aim was to identify novel flavonoids with antiproliferative effect in PCa cell lines, as well as determine their effects on cell cycle. We have screened a representative subgroup of 26 flavonoids for antiproliferative effect on the human PCa (LNCaP and PC3), breast cancer (MCF-7), and normal prostate stromal cell lines (PrSC). Using a fluorescence-based cell proliferation assay (Cyquant), we have identified five flavonoids, including the novel compounds 2,2'-dihydroxychalcone and fisetin, with antiproliferative and cell cycle arresting properties in human PCa in vitro. Most of the flavonoids tested exerted antiproliferative effect at lower doses in the PCa cell lines compared to the non-PCa cells. Flow cytometry was used as a means to determine the effects on cell cycle. PC3 cells were arrested in G2/M phase by flavonoids. LNCaP cells demonstrated different cell cycle profiles. Further studies are warranted to determine the molecular mechanism of action of 2,2'-DHC and fisetin in PCa, and to establish their effectiveness in vivo.

Differential mechanisms of bicalutamide-induced apoptosis in prostate cell lines.

Bicalutamide is a non-steroidal antiandrogen used in the treatment of prostate cancer. Although widely accepted as an androgen receptor antagonist, the mechanism by which it induces apoptosis remains unclear. Defining exact pathways by which bicalutamide induces its apoptotic effects would help to advance its clinical applications. We aimed to (a) examine the apoptotic effects of bicalutamide at 24 h and (b) comment on the role of the caspases and calpains in mediating bicalutamide-induced apoptosis in androgen-dependent and androgen-independent cells. PWR-1E, PC-3 and DU-145 cells were treated with bicalutamide and assessed for apoptosis by flow cytometry at 24 h. DU-145 cells were used to compare differences between two different metastatic receptor-negative cells and to verify apoptotic induction at 48 h. To delineate a specific pathway of action for bicalutamide, PC-3 and PWR-1E cells were pretreated with specific inhibitors of caspase-dependent (zVAD-FMK) and caspase-independent pathways (calpain 2 inhibitor). Bicalutamide induced apoptosis in androgen-dependent PWR-1E cells via a caspase-dependent and calpain-independent mechanism. In androgen-independent PC-3 cells, bicalutamide also induced apoptosis by mechanisms that were partially inhibited by pan-caspase inhibition but were partially calpain dependent. Understanding into how bicalutamide exerts its effects in androgen-independent cells will yield further insights into the treatment of hormone-refractory disease.