The photosensitizer disulfonated aluminum phthalocyanine reduces uptake and alters trafficking of fluid phase endocytosed drugs in vascular endothelial cells—Impact on efficacy of photochemical internalization

Abstract

Targeting cancer vasculature is an emerging field in cancer treatment. Photochemical internalization (PCI) is a drug delivery technology based on photochemical lysis of drug-bearing endocytic vesicles originally designed to target cancer cells. Recent investigations have revealed a lower PCI efficacy in vascular endothelial cells (HUVECs) in vitro than in HT1080 fibrosarcoma cells. This manuscript aims to explore the limiting factor for the PCI effect in HUVECs. Cellular uptake of the photosensitizers AlPcS2a and TPPS2a, and a model compound for macromolecular drugs taken up by fluid phase endocytosis, Alexa488-dextran, was explored by flow cytometry. The uptake of AlPcS2a and TPPS2a was 3.8-fold and 37-fold higher in HUVECs than in HT1080 cells, respectively, while the Alexa488-dextran uptake was 50% lower. AlPcS2a (but not TPPS2a) was shown to reduce Alexa488-dextran uptake in a concentration-dependent manner, resulting in 66% and 33% attenuation of Alexa488-dextran uptake at 20μg/ml AlPcS2a in HUVECs and HT1080 cells respectively. Studies of intracellular localization of Alexa488-dextran and AlPcS2a by confocal microscopy in HUVECs uncovered a concentration-dependent AlPcS2a-induced inhibition of Alexa488-dextran trafficking into AlPcS2a-stained and acidic vesicles. The localization of Alexa488-dextran to AlPcS2a-localizing compartments was reduced by 40% when the AlPcS2a concentration was increased from 5 to 20μg/ml. The treatment dose of AlPcS2a was found to influence on the efficacy of PCI of saporin, but to a lesser extent than expected considering the data from cellular uptake and intracellular trafficking of Alexa488-dextran. The implications of these results for further development of vascular targeting-PCI are discussed.