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Date M, Fukuchi K, Namiki Y, Okumura A, Morita S, Takahashi H, Ohura K. Therapeutic effect of photodynamic therapy using PAD-S31 and diode laser on human liver cancer cells. Liver International 2004: DOI: 10.1111/j.1478-3231.2004.0902.x. © Blackwell Munksgaard 2004 Photodynamic therapy (PDT) is an effective local cancer treatment which a photosensitizer is administered and the tumor is irradiated with light. We examined the effect of PDT using PAD-S31 as the photosensitizer, and the 670 nm diode laser on human hepatocellular carcinomas (HCCs). Huh-7, HepG2 and Hep3B cell lines were used in the all experiments. Cell viability was determined by a modified MTT assay. Two methods were used for the determination of apoptosis: terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick-end labeling assay and detection of fragmented mono- and oligo-nucleosomes by enzyme-linked immunosorbent assay. The caspase activity was measured by fluorometric assay. Cytochrome c in cytosolic fraction was determined using a human cytochrome c immunoassay. Xenografts of human oral HCC cells were generated in KSN S1c nude mice. In vitro PDT showed excellent cytotoxicity that was a function of laser energy, drug concentration and time to the hepatoma cell lines. The combined use of PAD-S31 and laser irradiation showed excellent anti-tumor activity without severe side-effect against human hepatoma xenografts in nude mice. PDT-mediated cell death occurred predominantly by apoptosis in vitro and in vivo. Furthermore, this treatment initiates early cytochrome c release, followed by late caspase-3 and -9 activation. Our study demonstrates that PDT using PAD-S31 and the diode laser induces apoptosis that is mediated by cytochrome c release and caspase activation in human liver cancer cell lines. It is expected that this therapy will be clinically useful for the treatment of patients with HCC. [ABSTRACT FROM AUTHOR]