In vitro and in vivo effects of photodynamic therapy on murine malignant melanoma

Background: The role of photodynamic therapy (PDT) in the treatment of malignant melanoma is not well defined, nor is it known whether the dark melanoma cells absorb the light used in PDT.Methods:In vitro studies: 2×10⁵ B16 murine melanoma cells were incubated with aluminum phthalocyanine (AlpcS₄, 2.5 mg/kg) and were then subjected to photoradiation (50, 100 or 200 J/cm²). Viability was then assessed.In vivo studies: Histology: C57/B1 mice received 2×10⁵ B16 cells subcutaneously and were randomized into study (PDT) and three control groups. AlpcS₄ 2.5 mg/kg was injected intraperitoneally and the mice were exposed to light (100 J/cm²). After 24 hours they were sacrificed and underwent autopsies. Survival: 40 mice were randomized into PDT (40 J/cm²) and control groups and were monitored for 50 days. Tumor growth: 40 mice were randomized into one control and three treatment groups (PDT on day 3, 6, or 12 after injection with B16 cells), and were monitored for 50 days. Temperature: Tumor temperatures before and at the end of PDT were recorded.Results:In vitro studies: PDT caused a decrease in cell viability to 15.5±0.7%, 11.5±2.1%, and 1.5±0.7% (at 50, 100, and 200 J/cm², respectively;P<.001). A significant reduction in thymidine incorporation was noted at all energy levels.In vivo studies: Histology: PDT caused massive tumor necrosis. Survival: PDT prolonged the survival of mice (41±13.4 days) compared to controls (15.8±3.8 days,P<.001). Tumor growth: 31 days after injection with B16 cells, the tumor size was 2.6±0.3 cm in the control group and 1.6±0.2, 0.9±0.3, and 1.0±0.4 cm in the PDT groups (days 3, 6 and 12, respectively;P<.01). Temperature: PDT increased skin temperature to 42.8°C±1.3°C, 45.3°C±3.5°C, and 51.7°C±2.7°C at 40, 60, and 100 J/cm², respectively (P<.01).Conclusions: Photodynamic therapy was found to have significant effects in experimental melanoma in mice. The role of PDT in human melanoma remains to be studied.Presented at the 50th Annual Cancer Symposium of The Society of Surgical Oncology, Chicago, Illinois, March 20–23, 1997.