Star-Shaped Glycopolymers with a Porphyrin Core: Synthesis, Singlet Oxygen Generation, and Photodynamic Therapy

Porphyrin and its derivatives have become the second generation of photosensitizers for photodynamic therapy for cancers. 5,10,15,20-Tetrakis[4-(2-hydroxyethoxy)phenyl]porphyrin photosensitizer was modified into a porphyrin-based ATRP initiator, and it was further used to construct star-shaped glycopolymers bearing galactose residuals by using atom transfer radical polymerization. Four star-shaped glycopolymers were obtained with a porphyrin core bearing four glyco-arms of varying arm lengths. They can be dissolved in water and displayed good light absorption and fluorescent emission due to the presence of porphyrin core. They generated singlet oxygen which may photobleach the indicator 1,3-diphenylisobenzofuran. The galactose-containing polymers show Hep G2 cells (a human liver cancer cell line) affinity which was selected for the toxicity study. These polymers caused lower cell viability in phototoxicity (1 h light irradiation), indicating their effectiveness as photosensitizers. The fluorescence microscopy results are in good agreement with 1O2 generation and the toxicity study, which indicates their effectiveness for potential use in photodynamic therapy. The star polymers with shorter glyco-arms have higher porphyrin content per unit mass, leading more efficient 1O2 generation to cancer cell extermination, while the polymers with longer glyco-arms showed lower toxicity and better lectin recognition and affinity. It is important to balance the photodynamic therapy and cell targeting property for practical applications.