Combination of photoactive hypericin and Manumycin A exerts multiple anticancer effects on oxaliplatin-resistant colorectal cells.

The use of natural products as chemotherapeutic agents and tools for manipulation of apoptosis represent an attractive therapeutic concept. In this study, we investigated the anticancer activities of a combination of two natural compounds with different origin, hypericin (plant product) in its photoactive state and Manumycin A (yeast product) and explored the underlying mechanisms of their pro-apoptotic action using an oxaliplatin-resistant variant of human colon adenocarcinoma cell line HT-29-OxR as the experimental model. CCK-8 assay was performed to evaluate the cytotoxicity of the drugs. CalcuSyn software was used to identify the type of interaction between the two agents. BrdU incorporation assay and colony forming assay were performed to study the short- and long-term proliferation of cells. To evaluate the ability of the drug combination to induce apoptosis, PARP p85 fragment was detected using the ELISA method. Changes in apoptosis-related proteins were examined by immunoassays. Our results showed that a synergistic combination of photoactive hypericin and Manumycin A decreased viability, inhibited both short- and long-term cell proliferation, decreased levels of IAPs proteins (cIAP1, cIAP2, XIAP and survivin), induced an apoptotic PARP cleavage associated with decline in procaspase-3 level, promoted phagocytosis of cancer cells, and restored chemosensitivity to oxaliplatin.