Verdins in photodynamic therapy of squamous cell carcinoma.

Photodynamic therapy (PDT) is a relatively new treatment modality employing photoactive drugs in combination with light to destroy malignant tissue. Porphyrins (ie, hematoporphyrin derivative and dihematoporphyrin ether) have been the most thoroughly investigated photoactive drugs. The primary limitation of the use of porphyrins in PDT is the shallow depth of effective tumor kill. Each photoactive drug is activated maximally by light of a particular wavelength, and longer wavelengths are able to penetrate tissue to a greater depth. Hematoporphyrin derivative and its semipurified form, dihematoporphyrin ether, are activated by light at 630 nm, which penetrates tissue to a maximum of 8 mm. The search for more effective photosensitizers is under way. Verdins, photoactive compounds in the class of chlorins, have recently been synthesized with activating wavelengths near 700 nm. This longer activation wavelength should theoretically allow a greater depth of tumor kill. Verdins have been shown to be effective photosensitizers in a urothelial carcinoma model in rats. In this study, we investigated the effectiveness of these compounds on squamous cell carcinoma in the hamster cheek pouch model.