Enhancement of the effect of 5-aminolevulinic acid-based photodynamic therapy by simultaneous hyperthermia

In the present study, we have investigated a combination of photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA) and simultaneous hyperthermia (HT) on osteosarcoma (HOSM-1) cells, squamous cell carcinoma (KB) cells and fibroblasts (HF), including an assessment of the differences in the sensitivity of these cells to such treatment in vitro. The intracellular accumulation of protoporphyrin IX (PPIX) formed by metabolism of ALA in mitochondria and the influence of the treatment on the mitochondrial membrane potential were evaluated using flow cytometry. The antitumor effects of HT, PDT using ALA (ALA-PDT) and ALA-PDT combined with HT (PDT+HT) were determined by an MTT assay. Western blot analysis of the expression of heat shock protein 60 (Hsp60) and Hsp70 was performed to evaluate the mitochondrial stress caused by each treatment. The intracellular PPIX accumulation in HOSM-1 cells was about 2-fold higher than that in KB cells. An antitumor effect of ALA-PDT and PDT+HT was obtained in each cell line, and indicated a synergistic interaction of the combination therapy in tumor cells. A marked degree of depolarization of the mitochondrial membrane was observed in both tumor cell lines, and there was no marked difference in the degree of depolarization between the cell lines. Marked expression of Hsp60 was observed in HOSM-1 cells treated with PDT+ HT and ALA-PDT, but not in KB cells. Slightly increased expression of Hsp70 was observed for all treatments in both tumor cell lines. These results suggest that the antitumor effect of ALA-PDT therapy against malignant tumor cells is enhanced by simultaneous HT. Furthermore, the differences in sensitivity to these therapies between the two cell types may have occurred because PPIX was not effectively utilized in HOSM-1 cells, compared to its utilization in KB cells.