Prostate cancer (PCa) is the leading cause of cancer related deaths in men. Carica papaya is a popular tropical plant that has been traditionally used for its nutritional and medicinal properties.

We investigated the anti-proliferative responses of papaya leaf juice (LJP) and its various extracts (“biological”- in vitro digested, “physical”- size exclusion, and “chemical”-solvent extraction) on a range of cell lines representing benign hyperplasia, tumorigenic and normal cells of prostate origin.

Time course analysis (by 24h, 48h and 72h) of LJP (1–0.1mg/mL) before and after in vitro digestion, and of molecular weight based fractions of LJP showed anti-proliferative responses. The medium polarity fraction of LJP (0.03–0.003mg/mL) after 72h exposure showed potent growth inhibitory (IC₅₀=0.02–0.07mg/mL) and cytotoxic activities on all prostate cells, with the exception of the normal (RWPE-1 and WPMY-1) cells. Flow cytometry analysis showed S phase cell cycle arrest and apoptosis as a possible mechanism for these activities. Medium polar fraction of LJP also inhibited migration and adhesion of metastatic PC-3 cells.

This is the first report suggesting selective anti-proliferative and anti-metastatic attributes of LJP extract against prostatic diseases, including PCa.