Plant stress hormones suppress the proliferation and induce apoptosis in human cancer cells

Cellular stressors induce various outcomes including inhibition of cell proliferation and cell death. Sodium salicylate (SA), a plant stress hormone, can suppress the proliferation or cause apoptosis in certain mammalian cancer cells. Plant stress hormones are activators of cellular responses, including cell death, to diverse stress situations in plants. Thus, we hypothesized that plant stress hormones share the ability to adversely affect cancer cells. We found that the plant stress hormone SA suppressed proliferation of lymphoblastic leukemia, prostate, breast and melanoma human cancer cells. Jasmonic acid (JA), a plant stress hormone belonging to the Jasmonate family, induced death in lymphoblastic leukemia cells and caused suppression of cell proliferation in the other human cancer cells mentioned above. Another member of the Jasmonate family, methyl jasmonate (MJ), induced death in each of the cell lines. Plant stress hormones did not affect normal human lymphocytes, in contrast to their strong effect on lymphoblastic leukemia cells. JA and MJ caused apoptotic death, as determined by characteristic nuclear morphology, flow cytometric DNA profile and elevation of caspase-3 activity. Finally, mice bearing EL-4 lymphoma and treated with MJ, survived for significantly (P=0.00953) longer periods of time than untreated mice. These findings suggest that plant stress hormones may potentially be a novel class of anti-cancer drugs.