Reactive species responsible for biological actions of photoexcited fullerenes

Fullerene (C-60, C-70, etc.) is an effective photosensitizer and its utiliz ation as a pharmacophore for photo-chemotherapy of tumors has received cons iderable attention. We developed a method to solubilize fullerenes into wat er with poly vinylpyrrolidone (PVP) as a detergent. By using thus prepared aqueous fullerene solutions, we have clarified a series of biological activ ities of fullerene under photoirradiation which include DNA-cleavage, hemol ysis, mutagenicity, cancer-initiation, and cell-toxicity. A newly synthesiz ed C-60 derivative with an acridine moiety as a DNA-chelating function show ed much more effective DNA-cleaving activity in the presence of NADH. Visib le-light irradiation of PVP-solubilized C60 in water in the presence of NAD H as a reductant and molecular oxygen resulted in the formation of O-2.- wh ich was detected by the EPR spin-trapping method. Formation of O-2.- was al so evidenced by the direct observation of a characteristic signal of O-2.- by the use of a low-temperature EPR technique at 77 K. On the other hand, n o formation of O-1(2) was observed by the use of TEMP as a O-1(2) trapping agent. No near-IR luminescence of O-1(2) was also observed in the aqueous C -60/PVP/O-2 system. These results suggest that photoinduced bioactivities o f the PVP-solubilized fullerene are caused not by O-1(2), but by reduced ox ygen species (O-2.-,. OH) which are generated by the electron-transfer reac tion of C-60.- With molecular oxygen.