Fluorescence imaging during photodynamic therapy of experimental tumors inmice sensitized with disulfonated aluminum phthalocyanine

A fluorescence imaging system was used to monitor the emission of disulfona ted aluminum phthalocyanine (AlS2Pc) during the photodynamic therapy (PDT) of murine tumors. Cells of the MS-2 fibrosarcoma were injected in mice in t wo compartments in order to cause the development of tumors in different ho st tissues. Two drug doses and two uptake times were considered. Moreover, the fluorescence of the AlS2Pc was excited using two wavelengths on the opp osite sides of the absorption peak to detect a possible change in the absor ption spectrum of the sensitizer induced by the PDT, In the tumors, the tre atment induces a variation of the fluorescence intensity: in some mice a mi ld photobleaching takes place, in others a fluorescence enhancement occurs. Which effect predominates depends on the experimental conditions, even tho ugh a large spread of data was found amongst nice of the same group. In all mice, independently of the drug dose, uptake time or tumor compartment, a marked increase in the fluorescence signal takes place at the borders of th e irradiated area, To quantify this effect we evaluated the ratio between t he fluorescence intensities in the peritumoral area and in the tumor itself . This ratio increases monotonically during the PDT, showing a different be havior with the two excitation wavelengths, This indicates that the AlS2Pc absorption spectrum shifts toward shorter wavelengths as a result of the ir radiation.