Biological functions of fullerene*

Fullerene (C60) is known to ef®ciently generate singlet oxygen when irradiated with light. In spite of such an unique photodynamic nature, little has been studied on biological functions of C60. This paper describes a tumor-therapeutic trial of C60 based on the photoinduced generation of active oxygen. To achieve preferential accumulation of C60 in the tumor tissue, this water-insoluble drug was chemically conjugated with poly(ethylene glycol) (PEG) not only to make it soluble in water but also to make the molecular size larger. When intravenously injected to tumor-bearing mice, the large-sized, as expected, water-soluble C60PEG conjugate was accumulated to a greater extent and retained for a longer time period in the tumor tissue than in the normal issue. Following intravenous injection of the C60-PEG conjugate, local irradiation of visible light to the tumor site induced tumor necrosis, in contrast to the conjugate injection alone. When the C60 dose was 8.48 mg/mouse, the tumor mass completely disappeared at an irradiation power of 107 J/cm, indicating a high potentiality of the C60-PEG conjugate for photodynamic tumor therapy.