Piperine inhibits the proliferation of human prostate cancer cells via induction of cell cycle arrest and autophagy

Piperine, an alkaloid from black and long peppers (Piper nigrum Linn & Piper longum Linn), has been reported to exhibit antitumor activities in vitro and in vivo. To further understand the antitumor mechanism of piperine, we investigated the growth inhibitory effects of piperine on human prostate cancer DU145, PC-3 and LNCaP cells. Piperine treatment resulted in a dose-dependent inhibition of the proliferation of these cell lines. Cell cycle arrest at G0/G1 was induced and cyclin D1 and cyclin A were downregulated upon piperine treatment. Notably, the level of p21Cip1 and p27Kip1 was increased dose-dependently by piperine treatment in both LNCaP and DU145 but not in PC-3 cells, in line with more robust cell cycle arrest in the former two cell lines than the latter one. Although piperine induced low levels of apoptosis, it promoted autophagy as evidenced by the increased level of LC3B-II and the formation of LC3B puncta in LNCaP and PC-3 cells. The piperine-induced autophagic flux was further confirmed by assaying LC3-II accumulation and LC3B puncta formation in the presence of chloroquine, a well-known autophagy inhibitor. Taken together, these results indicated that piperine exhibited anti-proliferative effect in human prostate cancer cells by inducing cell cycle arrest and autophagy.