Effects of haematoporphyrin derivative and light in combination with hyperthermia on cells in culture.

Interactions between the photodynamic effect of haematoporphyrin derivative and hyperthermia are reported. Cells labelled with haematoporphyrin derivative and irradiated with red light were sensitized by heat, particularly when the cells were heated after the exposure to light. It is shown that there is a synergistic interaction between the photodynamic effect and hyperthermia (42.5 and 45 degrees C). Hyperthermia-induced inhibition of the repair of photodynamic damage is suggested as a mechanism for the interaction. The possibility that these findings may be advantageous to cancer therapy is discussed.