In vitro photodynamic therapy in pediatric epithelial liver tumors promoted by hypericin

Limited treatment results in advanced pediatric liver tumors have emphasised the need for alternative treatment approaches in these malignancies. Photodynamic therapy (PDT) has been proposed as promising treatment approach in various malignancies. Hypericin, a naturally occurring substance found in the St. John's Wort, has regularly and successfully been used for visualisation and as photosensitizer in various tumor models. However, there exist no data on the effects of hypericin as photodynamic agent in pediatric malignant epithelial liver tumors. In this study, we investigated the potential role of hypericin for visualization and treatment in hepatoblastoma (HB) and pediatric hepatocellular carcinoma (HCC) cells. Two HB cell lines (HUH6, HepT1) and one HCC cell line (HepG2) were incubated with ascending concentrations of hypericin. Uptake and fluorescending capability were assessed using fluorescence microscopy and FACS. PDT with white light was performed for varying time intervals. Cell viability, cell proliferation and apoptotic rates were assessed using MTT assay, Ki-67 immunocytochemisty and TUNEL test, respectively. The changes within tumor cells under therapy were monitored using standard cytology. Relevant hypericin uptake was observed in all cell lines according to the applied concentrations. Histological analysis revealed no alterations of cell structure in HB and HCC cells after solely hypericin uptake, but severe alterations were found after PDT. Enhancement of the hypericin concentration (up to 12.5 µM) and illumination time of up to 40 min resulted in a decrease of tumor cell viability (HUH6 99.8±2.4%, HepT1 99±2%, HepG2 98.4±1.6%, p<0.05), proliferative activity and complete apoptosis of all cells in all investigated cell lines. These data show that hypericin might be a useful tool for visualisation and as alternative treatment option in HB and HCC.