Prostate cancer has its highest incidence in the USA and is becoming a major concern in Asian countries.
Bufadienolides are extracts of toxic glands from toads and are used as
anticancer agents, mainly on
leukemia cells. In the present study, the antiproliferative and apoptotic mechanisms of
bufalin and
cinobufagin on
prostate cancer cells were investigated. Proliferation of LNCaP, DU145, and PC3 cells was measured by 3-(4,5-dimethylthiazol-2-yle)-2,5-diphenyltetrazolium
bromide assay and the doubling time (tD) was calculated.
Bufalin and
cinobufagin caused changes in the tD of three
prostate cancer cell lines, which were more significant than that of human mesangial cells. In addition,
bufadienolides induced
prostate cancer cell apoptosis more significantly than that in breast epithelial cell lines.
After treatment, the
caspase-3 activity and
protein expression of
caspase-3, -8, and -9 were elevated. The expression of other apoptotic modulators, including mitochondrial Bax and cytosolic
cytochrome c, were also increased. However, expression of p53 was only enhanced in LNCaP cells. Downregulation of p53 by antisense TP53 restored the cell viability suppressed by bufalienolides. Furthermore, the increased expression of Fas was more significant in DU145 and PC3 cells with mutant p53 than in LNCaP cells. Transfection of Fas
small interfering RNA restored cell viability in the
bufadienolide-treated cells. These results suggest that
bufalin and
cinobufagin suppress cell proliferation and cause apoptosis in
prostate cancer cells via a sequence of apoptotic modulators, including Bax,
cytochrome c, and
caspases. The upstream mediators might be p53 and Fas in
androgen-dependent LNCaP cells and Fas in
androgen-independent DU145 and PC3 cells.