Background: Photodynamic therapy (PDT) has not been reported for human hepatoma, because cancer cells only weakly take up the photosensitizer. Indocyanine green (ICG) is a photosensitizer normally excreted into the bile, and bile excretion is impaired in human hepatomas. We examined whether human hepatoma cell lines preferentially take up the ICG and then assessed the effectiveness of PDT using ICG and near-infrared (NIR) laser.
Methods: HuH-7 and HepG2 human hepatoma cell lines were transplanted subcutaneously into mice. Developing HuH-7 and HepG2 tumors were confirmed that preferentially took up the ICG in 24 h after ICG was administered to mice via tail vein. The HuH-7 tumor showed a high tumor-to-background fluorescence intensity ratio, 255:1, whereas fluorescence intensity of HuH-7 is increased twofold compared to HepG2. HuH-7 cell transplanted mice were divided into three groups: ICG administration only (ICG+NIR-, n = 8), ICG and NIR laser exposure (ICG+NIR+, n = 12), and NIR laser exposure only (ICG-NIR+, n = 5).
Results: Mean tumor volume in the ICG+NIR- and ICG-NIR+ groups increased steadily. In contrast, mean tumor volume in the ICG+NIR+ group did not change between days 0 and 3. Mean tumor volume did not differ significantly between the ICG-NIR+ and ICG-NIR- groups, but was significantly different between the ICG+NIR+ group and both the ICG-NIR+ and ICG+NIR- groups (p < 0.01).
Conclusions: ICG is preferentially taken up by HuH-7 and HepG2 human hepatoma cell line tumors. The tumor-to-background ratio of HuH-7 tumors, in particular, was extremely high. PDT with NIR laser irradiation suppressed HuH-7 human hepatoma cell line tumor growth.