Abstract

Photodynamic therapy (PDT) represents a new approach to treatment of a variety of solid malignant tumors in man. Hematoporphyrin-derivative (HpD) in its purified form, dihematoporphyrin ether (DHE) is injected systemically into patients, causing uptake and retention in most malignant tumors for several days (3 to 5). Most normal tissues clear the drug within a few days (1 to 2 days). Exceptions are skin, liver, kidney, and spleen, which retain the drug largely in cells of the reticuloendothelial system. The in situ drag is then activated photochemically (630-nm light generally from an argon- pumped dye laser) by local illumination either from the surface or interstitially by insertion of appropriate light delivery fibers. This can result in a relatively selective destruction of the tumor mass. The activation depth (1/e) of 630-nm light ranges from 2 to 4 mm generally. Tumor necrosis typically occurs to 2 or 3 attenuation depths (5 to 15 mm). The mechanism of tumor retention is unclear but is likely related to the phagocytosis of DHE (which circulates initially at least as a large aggregate) by certain cells in the tumor and possibly by tumor cells themselves. Tumor destruction results from vascular destruction with subsequent tumor-cell death and by direct photochemical effects on the cells or some combination of these. Singlet oxygen found by energy transfer from the porphyrin to endogenous oxygen appears to be a necessary first-formed cytotoxic agent.

© 1984 Optical Society of America