Melatonin potentiates the antiproliferative and pro-apoptotic effects of ursolic acid in colon cancer cells by modulating multiple signaling pathways

Ursolic acid (UA), a natural pentacyclic triterpenoid carboxylic acid, is largely distributed in medical herbs and edible plants. Melatonin is an indoleamine compound produced in the pineal gland and also a plant-derived product. Both UA and melatonin have been shown to inhibit cancer cell growth in numerous studies, but they have never been combined altogether as an anticolon cancer treatment. In this study, we investigated whether the association between UA and melatonin leads to an enhanced antiproliferative and pro-apoptotic activities in colon cancer SW480 and LoVo cells. We found that combined treatment with UA and melatonin significantly enhanced inhibition of cell viability and migration, promoted changes in cell morphology and spreading, and increased induction of apoptosis, thereby potentiating the effects of UA alone in colon cancer cells. Moreover, we found that the enhanced effects of UA and melatonin combination are mediated through simultaneous modulation of cytochrome c/caspase, MMP9/COX-2, and p300/NF-B signaling pathways. Combined treatment with UA and melatonin triggered the release of cytochrome c from the mitochondrial intermembrane space into the cytosol, induced cleavage of caspase and PARP proteins, enhanced inhibition of MMP9 and COX-2 expression, promoted p300 and NF-B translocation from cell nuclei to cytoplasm, and abrogated NF-B binding and p300 recruitment to COX-2 promoter in colon cancer cells. These results, therefore, demonstrated that melatonin potentiated the antiproliferative and pro-apoptotic effects of UA in colon cancer cells by modulating multiple signaling pathways and suggest that such a combinational treatment might potentially become an effective way in colon cancer therapy.