Hematoporphyrin derivative photocytotoxicity of human glioblastoma in cell culture

The parameters of hematoporphyrin-derivative (HpD) photocytotoxicity of human glioma cells in cell culture were studied to determine the optimum wavelength and power density of light, to investigate the influence of tissue oxygenation, and to evaluate the role of singlet oxygen and free radicals in producing cell death. Cell survival curves demonstrated a relative killing efficiency of 12:1 for violet compared to red light. Eighty joules of red light were required to produce 100% cell kill at an HpD concentration of 10 μg/ml, a level of HpD that has been quantitated in biopsies from patients receiving HpD photoradiation therapy. No difference in cellular killing efficiency was observed for power densities of red light varying from 10 to 100 mW/cm². Cytotoxicity was directly related to O₂ tension from 12 to 490 torr with a slight but consistent increase in cell kill at O₂ tensions from 7 to 12 torr. Cytotoxicity was effectively quenched by β-carotene, whereas mannitol had no effect, indicating that cytotoxicity is probably mediated via a mechanism involving singlet oxygen. This information may serve as a basis for more effective application of HpD photoradiation therapy and for designing protocols to study the efficacy of such therapy.