Fluence rate effects on photodynamic therapy of B16 pigmented melanoma

In vivo experiments were performed to evaluate the effect of fluence rate on the efficiency of Zn(II)-2,3 naphthalocyanine (ZnNc) photosensitization of B16 pigmented melanoma subcutaneously transplanted in C57B1/6 mice. The tumour was irradiated with 774 nm light at 24 h after an injection of liposome--which incorporated ZnNc (0.5 mg kg-1 b.w.). A total light dose of 360 J cm-2 was delivered at fluence rates of 260, 320, 380, 440 and 500 mW cm-2. Separate groups of mice utilized to monitor tumour temperature changes during irradiation without or after anaesthesia. Tumour response was determined by measuring the mean tumour diameter of the treated towards the untreated animals for a period of 21 days following PDT, as well as the percentage of cured animals. The most promising result (40% complete tumour response) was obtained with anaesthetized mice following 380 mW cm-2. Higher dose rates (440 and 500 mW cm-2) led to less promising results for both anaesthetized and non anaesthetized mice. These results outline the potential of PDT with longer wavelengths for the treatment of highly pigmented tumour tissues. The optimal fluence rate for tumour treatment should be chosen in order to avoid inflammatory effects (tissue swelling) and oxygen suppression with sublethal injury to the tumour cells.