Photodynamic effect of polyethylene glycol-modified fullerene on tumor

Fullerene (C-60) 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 C-60, we chemically modified the water-insoluble C-60 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 back subcutis, the C-60-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 C-60-PEG conjugate or Photofrin(R) 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 C-60 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 C-60 dose, and cures were achieved by treatment with a dose of 424 mu g/kg at an irradiation power of 107 J/cm(2). These findings indicate that PEG-modified C-60 is a candidate agent for photodynamic tumor therapy.