The influence of non-photodynamic reactions on necrosis formation in PDT treatment

The sizes of tumor necrosis of photosensitized and intact (without the photosensitizer injection) animals were compared under identical regimes of photoirradiation. The results demonstrate that an action spectrum for cellular death following laser treatment is not matched to absorption spectra of photosensitizer. Furthermore, the sizeable damage of tumors (sarcoma M-1 and Pliss lymphosarcoma) were detected on intact rats after laser irradiation. It is consistent with our hypothesis that some non-photodynamic reactions (i.e. the reactions induced by light without the injection of photosensitizer) are activated by light. We believe that non-photodynamic reactions are responsible for the photodestructive effect on intact tumors. According to the theoretical calculations, the localized hyperthermal effect should not be occurred under the experimental PDT conditions, therefore we excluded this phenomenon from consideration. Additional investigations are required to understand the mechanism of necrosis formation.