Photodynamic therapy of fullerene modified with pullulan on hepatoma cells

To design a novel cytospecific photosensitizer for photodynamic antitumor therapy, a fullerene (C(60)) was chemically modified with pullulan which is a water-soluble polysaccharide with a high affinity for asialoglycoprotein receptors. Ethylene diamine was introduced to the terminal aldehyde groups of pullulan by the reductive amination reaction. Pullulan was coupled to C(60) through the terminal amine group. The C(60) end-group conjugated with pullulan was water-soluble and generated superoxide anion upon light irradiation. The C(60)-pullulan conjugates significantly suppressed the in vitro growth of HepG2 hepatoma cells with asialoglycoprotein receptors, while less suppression activity was observed for HeLa cells without the receptors. The conjugates have a high binding affinity for HepG2 cells, in contrast to HeLa cells. When C(60) was conjugated with polyethylene glycol (PEG) with the similar molecular weight in order to compare the in vitro cell binding and antitumor activities with the C(60)-pullulan conjugate, the dependence of cell type on their activities was not observed. Following the intravenous injection of C(60)-pullulan conjugates to mice carrying a subcutaneous mass of HepG2 cells, significant stronger photodynamic effect on tumor was observed than the intravenous injection of C(60)-PEG conjugates and saline. It is concluded that the pullulan conjugation gave C(60) the targetability to HepG2 cells, resulting in enhanced photodynamic tumor therapy effect.