Objective: To investigate the effects of Ypsilandra thibetica 16 (YB16) extracted from the Ypsilandra thibetica on proliferation and apoptosis of human prostate cancer cells PC-3

and explore its mechanism. Method: PC-3 cells were cultured in vitro and treated with different concentrations of YB16 (0.125~16 μmol·L-1). The effects of YB16 on PC-3 cytotoxicity were detected by (4

5-dimethyl-2-thiazolyl)-2

5-diphenyl-2-H-tetrazolium bromide (MTT) assay

and the cell morphology was observed by phase contrast microscope. Acridine orange (AO) staining and flow cytometry were used to detect the apoptosis of PC-3 cells induced by YB16.Reverse-transcription polymerase chain reaction (RT-PCR) was used to detect the mRNA expression levels of B-cell lymphoma 2 gene (Bcl-2)

B-cell lymphoma 2 gene-xl (Bcl-xl)

Bcl-2 associated X protein (Bax)

and cysteinyl aspartate specific proteinase-3(Caspase-3)of PC-3 cells

and Western blot was used to detect the protein expression levels of Bcl-2

Bcl-xl

Bax and cleaved-Caspase-3. Result: YB16 could significantly inhibit the growth of PC-3 cells in a dose-dependent manner (P<0.05). YB16 could promote PC-3 cells apoptosis

and PC-3 cells had obvious characteristic apoptosis changes in the observation under phase contrast microscope and AO staining. YB16 could reduce the mRNA and protein expression levels of Bcl-2

Bcl-xl

but increase the mRNA and protein expression levels of Bax

Caspase-3 (P<0.05). Conclusion: YB16 can inhibit PC-3 cells proliferation

and induce apoptosis obviously. YB16 has a potential antitumor value

and its mechanism may be associated with promoting Caspase-3 expression.