Peperotetraphin inhibits the proliferation of human prostate cancer cells via induction of cell cycle arrest and apoptosis

Peperotetraphin (methyl rel-(1R,2S,3S)-2,3-bis (7-methoxy-1,3-benzodioxol-5-yl) cyclobutanecarboxylate) was a novel cyclobutane-type norlignan, which was iso- lated from the whole plant of Peperomia tetraphylla .I n this study, we explored its anti-tumor effect and the molecular mechanism in human prostate cancer PC-3 cell lines. Firstly, cell viability was evaluated by Cell Counting Kit (CCK-8) assay. The PC-3 cells were treated with increasing concentrations of peperotetraphin for 24, 48 and 72 h, respectively. The results showed that peperotetraphin inhibited the growth of PC-3 cell in a dose- and time- dependent manner. Next, the cell cycle distributions were analyzed by flow cytometric analysis (FCM), and the data suggested that peperotetraphin could significantly induce cell cycle arrested at the G1-S phase transition. Then, the cell apoptosis was detected by the terminal deoxynucleo- tidyl transferase-mediated dUTP nick end labeling (TUN- EL) and annexin V-FITC/PI dual staining analysis, the data confirmed apoptosis-inducing activity of peperotetraphin and the apoptosis rates increased from 3.9 to 32.3 % when treated with increasing concentrations of peperotetraphin from 0 to 50 lM. The expression levels of apoptosis-reg- ulating protein caspase-3, Bax and Bcl-2 were also ana- lyzed by Western blot analysis. The results showed that the expression levels of Bax and the activity of caspase-3 were upregulated, whereas the expression levels of Bcl-2 were downregulated compared with those of the control. These findings demonstrated that peperotetraphin exhibited effective cell growth inhibition by inducing cancer to undergo G1 phase arrest and apoptosis. The results sug- gested that peperotetraphin might have potential as che- moprevention or anti-tumor agent to prostatic cancer.