Photodynamic Effect of Polyethylene Glycol–modified Fullerene on Tumor

Abstract

Fullerene (Cm) efficiently generates singlet oxygen when irradiated with light, and thus should have a photodynamic effect on tumors, if it is accumulated in the tumor tissue. To explore tumor targeting of CU, we chemically modified the water–insoluble C60 with polyethylene glycol (PEG), not only to make it soluble in water, but also to enlarge its molecular size. When injected intravenously into mice carrying a tumor mass in the hack sulicutis, the C60–PEG conjugate exhibited higher accumulation and more prolonged retention in the tumor tissue than in normal tissue. The conjugate was excreted without being accumulated in any specific organ. Following intravenous injection of CorPEG conjugate or Photofrin® to tumor–bearing mice, coupled with exposure of the tumor site to visible light, the volume increase of the tumor mass was suppressed and the C60 conjugate exhibited a stronger suppressive effect than Photofrin. Histological examination revealed that conjugate injection plus light irradiation strongly induced tumor necrosis without any damage to the overlying normal skin. The antitumor effect of the conjugate increased with increasing irradiation power and Cm dose, and cures were achieved by treatment with a dose of 424 μg/kg at an irradiation power of 107 J/cm2. These findings indicate that PEG–modified cm is a candidate agent for photodynamic tumor therapy.