Transport and accumulation of PVP-Hypericin in cancer and normal cells characterized by image correlation spectroscopy techniques

PVP-Hypericin (PVP: polyvinylpyrrolidone) is a potent anti-cancer photosensitizer for photodynamic diagnosis (PDD) and therapy (PDT). However, cellular targets and mechanisms involved in the cancer-selectivity of the photosensitizer are not yet fully understood. This paper gives new insights into the differential transport and localization of PVP-Hypericin in cancer and normal cells which are essential to unravel the mechanisms of action and cancer-selectivity. Temporal (TICS) and spatiotemporal (STICS) image correlation spectroscopy are used for the assessment of PVP-Hypericin diffusion and/or velocity in the case of concerted flow in human cervical epithelial HeLa and human lung carcinoma A549 cells, as well as in human primary dendritic cells (DC) and human peripheral blood mononuclear cells (PBMC). Spatiotemporal image cross-correlation spectroscopy (STICCS) based on organelle specific fluorescent labeling is employed to study the accumulation of the photosensitizer in nucleus, mitochondria, early-endosomes and lysosomes of the cells and to assess the dynamics of co-migrating molecules. Whereas STICS and TICS did not show a remarkable difference between the dynamics of PVP-Hypericin in HeLa, A549 and DC cells, a significantly different diffusion rate of the photosensitizer was measured in PBMC. STICCS detected a stationary accumulation of PVP-Hypericin within the nucleus, mitochondria, early endosomes and lysosomes of HeLa and A549 cells. However, significant flow due to the directed motion of the organelles was detected. In contrast, no accumulation in the nucleus and mitochondria of DC and PBMC could be monitored.