Induction of apoptosis by Hypericin through activation of caspase-3 in human carcinoma cells

Potent photosensitizer Hypericin (HY), is a lipid soluble perylquinone deri vative of the genus Hypericum and has a strong photodynamic effect on tumor s and viruses. However, the mechanisms of tumor cell death induced by this compound is still unclear. Furthermore, there are no reports on mechanisms in cell apoptosis induced by perylquinones in human nasopharyngeal carcinom a (NPC) and other mucosal cells. We studied the photodynamic effects of HY compound in poorly differentiated (CNE2) and moderately differentiated (TW0 -1) human NPC cells as well as human mucosal colon (CCL-220.1) and bladder (SD) cells. Using these cell lines we investigated few hall marks of apopto tic commitments in a drug and light dose dependent manner. Tumor cells phot oactivated with HY showed cell size shrinkage and an increase in the sub-di ploid DNA content. A loss of membrane phospholipid asymmetry associated wit h apoptosis was induced in all tumor cell lines as evidenced by the externa lization of phosphatidylserine. Under apoptotic conditions, Western blot an alysis of poly (ADP-ribose) polymerase, a caspase substrate, showed the cla ssical cleavage pattern (116-85 kDa) associated with apoptosis in PDT-treat ed cell lysates. In addition, 85 kDa cleaved product was blocked by using t etrapeptide caspase inhibitors such as DEVD-CHO or z-VAD-fmk. These results demonstrate that tumor cell death induced by photoactivated HY is mediated by caspase proteases. This study also identifies that CNE2, CCL-220.1 (col on) and SD (bladder) cell lines are more sensitive than TW0-1 cell line to PDT using perylquinone HY.