Pheophorbide a, an active compound isolated from Scutellaria barbata, possesses photodynamic activities by inducing apoptosis in human hepatocellular carcinoma

Abstract

Photodynamic therapy (PDT) is an effective treatment for cancer by inducing apoptosis or necrosis in the target cells. Pheophorbide a (Pa), a chlorophyll derivative, is a photosensitzier which can induce significant anti-proliferative effects in a number of human cancer cell lines. This study investigated the action mechanism of Pa-mediated photodynamic therapy (Pa-PDT) on the human hepatocellular carcinoma, Hep3B cells. Pa-PDT significantly inhibited the growth of Hep3B cells with an IC50 value of 1.5 microM. Intracellular ROS level was increased in Pa-PDT treated cells and the cytotoxic effect could be reversed when ascorbic acid was applied. Pa was found to be localized in the mitochondria and then induced the target cells to undergo apoptosis, which was confirmed by propidium iodide staining and DNA fragmentation assay. Pa-PDT treatment also led to the depolarization of mitochondrial membrane potential (Deltapim) and a release of cytochrome c from mitochondria to the cytosol. The caspase cascade was activated as shown by a significant decrease of procaspase-3 and -9 in Pa-PDT treated cells in a dose-dependent manner. Furthermore, in nude mice model, Pa-PDT treatment could reduce the tumor size by 57% after 14 days treatment.