The dynamic changes in the membranes microviscosity of cancer cells during PDT with photoditazine

The aim of this work was to analyze the viscosity changes in tumor cell membranes in vitro and in vivo after photodynamic therapy (PDT). In vitro studies were carried out on a monolayer culture and 3D spheroids of HeLa Kyoto cells, and an in vivo experiment on a mouse tumor model using the photosensitizer Photoditazine. The microviscosity of tumor cell membranes was assessed by the fluorescence lifetime of the fluorescence molecular rotor BODIPY2 using fluorescence lifetime imaging microscopy FLIM. It was found that PDT causes changes in membrane microviscosity in all studied models. With moderate irradiation, an increase in the microviscosity of membranes in monolayer and spheroids cells is observed. Simillar increase in viscosity was also detected when performing PDT in the “cellular” regime on animal tumors. The opposite tendency was observed with a severe mode of cell irradiation - the microviscosity of the membranes decreased dramatically, which corresponds to a decrease in the microviscosity of tumor cells in vivo under the “vascular” regime of PDT irradiation. These results improve the understanding of the biophysiological mechanisms of PDT in the cellular and vascular regimes and may be useful for the development of new approaches to monitoring its effectiveness.