Photodynamic effect of hematoporphyrin derivative as a function of optical spectrum and incident energy density

Tumor cell killing effect of hematoporphyrin derivative (HPD) and light was studied in culture to determine the dependence of this effect on treatment variables. Particular attention has been given to the spectral characteristics of the light and the absorption properties of hematoporphyrin. A human tumor cell line was treated using HPD and three broad bands of light ranging from the short- to the long-wavelength end of the visible spectrum. Cell killing was assessed by trypan blue exclusion. A transformed mouse embryo cell line was treated in a similar manner, and its reproductive efficiency was determined following treatment. Results of both studies are consistent with the hypothesis that the photocytotoxic action of HPD plus light is directly proportional to the number of light quanta absorbed by the HPD in each cell. For thin layers of cells, such as in situ carcinoma, it appears that short-wavelength radiation falling in the porphyrin Soret band around 400 nm may have from 12 to 30 times the killing power as does red light.