Photoradiation Therapy of Malignant Tumors; Role of the Laser

Abstract

Photoradiation therapy, in which hematoporphyrin derivative (Hpd) is activated by visible light in situ is being investigated for the control of solid malignant tumors in man |1,2|. This method is based upon the ability of Hpd to first accumulate and be retained in malignant tissue to a greater degree than in some normal tissues |3,4,5|, and then to produce singlet oxygen (¹O₂) when activated by visible light, thus producing a cytotoxic effect |6|. While this latter property, known as a photodynamic effect |7|, is common to a wide range of materials, its combination with tumor localizing ability is guite unigue. Tetraphenylporphine sulfonate appears to possess similar properties to Hpd but suffers the disadvantage of prolonged retention in serum and tissues |8, 9|, thus rendering animals photosensitive for extended periods. This is also a problem with Hpd |1, 2| but is of relatively short duration (approximately 30 days, depending on dose) and can be avoided by preventing sunlight exposure. We have examined many other porphyrins as potential tumor photosensitizers in animals, but none has been found to be as effective as Hpd |10|.