Antiproliferative effects of isoflavonoids on prostate cancer cells and antitumorigenic effects in xenograft nude mice

Epidemiological studies have suggested that the phytochemical isoflavonoids may be involved in protective effects against prostate cancer. This study investigated the anticancer properties of two biologically active isoflavonoids, genistein and its precursor biochanin A, in two human prostate cancer cell lines LNCaP (androgen-sensitive) and PC-3 (androgen-independent). LNCaP or PC-3 cells cultured in the presence of these isoflavonoids for 48 hours exhibited a dose-dependent decrease in cell viability. The level of apoptosis increased with increasing concentration of the isoflavones in LNCaP cells. In contrast, PC-3 cells were more resistant to induction of apoptosis. The isoflavonoids produced a dose-dependent inhibition of DNA synthesis in both LNCaP and PC-3 with complete inhibition at 37 and 111 μM, respectively. These concentrations were subsequently used to study mechanisms of growth inhibition. In LNCaP, genistein accumulated cells in the G2/M phase, whereas biochanin produced a G1 accumulation.; In PC-3, both isoflavonoids induced a G2/M arrest. Cyclin B protein level was markedly decreased by both phytochemicals in LNCaP, and by biochanin in PC-3. The cell cycle inhibitory protein p21 expression was induced by genistein in both cell lines, whereas biochanin decreased it by 40% in LNCaP. The effects of these plant chemicals on gene expression were investigated using cDNA microarray technology. In both cell lines, genistein and biochanin altered expression of shared and unique genes which are involved in multiple cellular functions, including DNA synthesis, transcription, translation, protein degradation, signal transduction, cell proliferation, and cell adhesion. Lastly, athymic mice were implanted with LNCaP xenografts. In mice treated with biochanin at 400 μg/day for 10 days, mean tumor volume was significantly smaller compared to controls at 3 and 6 weeks, and tumor incidence was 54% compared to 89% in control at 3 weeks. In mice with established tumors, genistein and biochanin treatment slowed the rate of growth compared to controls. In one of two experiments, biochanin significantly decreased the mitotic index in the tumors, whereas in another one genistein increased it. No changes in microvessel density were observed with biochanin treatment. These results indicate that genistein and biochanin have antiproliferative effects both in vitro and in vivo, characterized by shared and distinct mechanisms.