Photocytotoxicity in vivo of haematoporphyrin derivative components.

Phototoxicity of haematoporphyrin derivative (HPD) and some of its component porphyrins was assayed using Lewis Lung Carcinoma transplanted in C57BL mice. Skin photosensitivity was assessed by measuring percentage increase in footpad thickness after exposure to light. HPD and its aggregate fraction photosensitised the skin, was active in tumour destruction and caused fluorescence in the tumour while the non-aggregate fraction and pure haematoporphyrin were inactive, both in treatment of tumours and in sensitising the skin. The commercial product, Photofrin II was also photoactive and protoporphyrin was slightly active. It is concluded that the therapeutic activity of HPD is associated entirely with the aggregate fraction and compounds effective in tumour phototherapy also sensitise the skin.