Photodynamic Antitumor Activity of Fullerene Modified with Poly(ethylene glycol) with Different Molecular Weights and Terminal Structures.

The objective of this study is to investigate the effect of molecular size and terminal structure of poly(ethylene glycol) (PEG) on the antitumor activity of PEG-modified fullerene (C60). PEG samples with different terminal structures and molecular weights were covalently coupled to C60 and their superoxide anion generation, in vitro or in vivo antitumor activity, and body distribution were assessed for the effect of the photosensitizer, used in photodynamic therapy (PDT), on the tumor. Irrespective of the molecular weight and terminal structure of PEG used, the C60-PEG conjugates exhibited a similar ability of superoxide anion generation and in vitro antitumor activity. On the contrary, a strong suppression of the in vivo tumor growth was observed for the C60-PEG conjugates prepared with methyl-terminated PEG with the highest molecular weight, which showed the longest half-life period in the blood circulation and the highest tumor accumulation among all the conjugates used. It is concluded that the superior tumor targetability of C60-PEG conjugates is one of the keys to enhance the PDT activity.