Photodynamic effects of haematoporphyrin derivative on synchronized and asynchronous cells of different origin

Phototherapy in the presence of haematoporphyrin derivative has been shown to have a preferential effect on malignant tumours when compared to normal tissue. This communication presents a comparison of the sensitivity to photochemotherapy in vitro of different cell lines. Asynchronous populations of cells were exposed to light in the presence of haematoporphyrin derivative, and found to be inactivated with a comparable efficiency. The lines were of human, Chinese-hamster or mouse origin and had different abilities to form tumours after heterotransplantation into nude mice or transplantation into syngeneic, immunosuppressed mice. Synchronized cells from 4 of the lines showed a similar variation in sensitivity to light throughout the cell cycle. Cells near the middle of interphase showed the highest sensitivity, whilst cells in early G1 were found to be least sensitive towards treatment with haematoporphyrin derivative and light.