Comparative Endocytosis Mechanisms and Anticancer Effect of HPMA copolymer- and PAMAM Dendrimer-MTCP Conjugates for Photodynamic Therapy

Polymer architecture can influence biodistribution and the mode of presentation of bioactive agents to cells. Herein, we examined delivery, loading efficiency and mode of cellular entry of polymer conjugates of the photosensitizer Meso-Tetra (4-Carboxyphenyl) Porphyrine (MTCP) when attached to hyper-branched amine terminated poly(amido amine) (PAMAM) dendrimer or random coil linear N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer containing free amines in the side chains. The in vitro dark cytotoxicity and phototoxicity of MTCP and related conjugates were assessed on mouth epidermal carcinoma (KB) and human adenocarcinoma alveolar basal epithelial (A549) cells. Phototoxicity of polymeric conjugates increased by approximately 100 and 4,000 fold in KB and A549 cells compared with non-conjugated MTCP. The increase in phototoxicity activity was shown to result from increased rate of cellular uptake, whereas, cellular internalization of MTCP was negligible in comparison with the conjugated forms. Our results suggest the superiority of amine-terminated HPMA copolymer vs PAMAM dendrimer under study for delivery of MTCP. Treatment with various pharmacological inhibitors of endocytosis showed that polymer architecture influenced the mechanism of cellular uptake of the conjugated photosensitizer. Results show that polymeric conjugates of MTCP improved solubility, influenced the route and the rate of cellular internalization and drastically enhanced the uptake of the photosensitizer.