Papaya Leaf Extract Slows Growth of Cancer Cell Cultures

Their plan was to examine the effect of an aqueous-extracted papaya leaf fraction on the growth of various tumor cell lines and on the antitumor effect of human lymphocytes. In addition, they attempted to identify the functional molecular weight fraction in the papaya leaf extract. In this study the effect of papaya leaf extract on the proliferative responses of tumor cell lines and human peripheral blood mononuclear cells (PBMC), and cytotoxic activities of PBMC were assessed by the incorporation of radioactive thymidine. Flow cytometric analysis and measurement of caspase-3/7 activities were performed to confirm the induction of apoptosis on tumor cells. Cytokine productions by PBMC were measured by ELISA. Gene profiling of the effect of leaf extract treatment was performed by microarray analysis and real-time RT-PCR.

Results published in the February 17, 2010, issue of the Journal of Ethnopharmacology revealed that papaya leaf extract showed significant growth inhibitory activity on cervix, breast, liver, lung, and pancreas tumor-cell lines. In PBMCs, the production of interleukin-2 (IL-2) and IL-4 was reduced following the addition of leaf extract, whereas that of IL-12p40, IL-12p70, IFN-gamma (interferon-gamma) and TNF-alpha (tumor necrotic factor-alpha) was enhanced without growth inhibition. In addition, cytotoxicity of activated PBMCs was enhanced by the addition of the extract. Moreover, microarray analyses showed that the expression of 23 immunomodulatory genes, classified by gene ontology analysis, was enhanced by the addition of papaya leaf extract.

The investigators identified the active component of the papaya leaf extract, which inhibited tumor cell growth and stimulated anti-tumor effects, to be a fraction with molecular weight less than 1,000. Importantly, the papaya extract did not have any toxic effects on normal cells.

"Based on what I have seen and heard in a clinical setting, nobody who takes this extract experiences demonstrable toxicity; it seems like you could take it for a long time — as long as it is effective,” said contributing author Dr. Nam Dang, professor of hematology and oncology at the University of Florida.

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