Photosensitizing capabilities of Photofrin® in vascular endothelial cells

The object of the present study was to evaluate the feasibility of photodynamic therapy (PDT) using Photofrin® (porfimer sodium), an United States Food and Drug Administration approved photosensitizer. The in vitro absorption and photosensitizing activities of Photofrin® were evaluated with cultured human microvascular endothelial cells and in vivo activities were evaluated with ductal carcinoma cell stimulated mammary tumor. The viability of microvascular endothelial cells was assessed using rhodamine-phallodin coupled α-tubulin antibody specific for cytoplasmic microtubule and visualized by immunofluorescence microscopy. At the optimal wavelength of 630 nm, the percentage of microvascular endothelial cells killed by variable concentrations of Photofrin® was measured by either live/dead or lactate dehydrogenase-released assays and the in vivo biological activity was assessed by determining the amount of necrosis produced in stimulated mammary tumor. A combination of 3.5 μg/mL Photofrin® and laser light at 630 nm with a power density of 100 mW/cm2 resulted in a 50% cell kill. The lactate dehydrogenase released from microvascular endothelial cells after PDT showed a 50% optical density obtained from each concentration of photosensitizer of 50% cell killing after laser illumination. Stained histology specimens of stimulated mammary tumor demonstrated significant vascular destruction 1 hour after PDT. In conclusion, Photofrin® has the capabilities to destroy microvascular endothelial cells in vitro and vasculature in vivo. However, the degree of absorption and tissue destruction in vasculature in vivo and different anatomical structures should be considered and will be included in our subsequent studies.