It's a weird issue. On the one hand it seems like C60 can protect against UV damage, on the other hand it seems like it could increase UV damage...
Fullerenes as photosensitizers
Another potential medical application of C60 is related to the photoexcitation of fullerenes. In fact, fullerene can be excited from ground state to 1C60 by photoirradiation. This short-lived species is readily converted to long-lived 3C60 via intersystem crossing. In presence of molecular oxygen, the fullerene can decay from its triplet to ground state, transferring its energy to O2, generating singlet oxygen 1O2, known to be highly cytotoxic species. In addition, the high-energy species 1C60 and 3C60 are excellent acceptors and in the presence of a donor, can undergo a different process, being easily reduced to C60•- by electron transfer. Again, in the presence of oxygen, the fullerene radical anion can transfer one electron, producing a superoxide anion radical O2•- and hydroxyl radical •OH (Yamakoshi et al 2003). The excited fullerene can be reduced under biological conditions in the presence of biological reducing agents eg, guanosin. On the other hand, singlet oxygen and superoxide radical anions are well known reactive species towards DNA (Da Ros et al 2001). This property of fullerenes renders them potential photosensitizers for their use in photodynamic therapy (PDT). Many fullerene conjugates with different functional groups possessing biological affinity to nucleic acids or proteins, are being investigated for anticancer activity. In particular, conjugates of C60 and, acridine or complementary oligonucleotide, which interact with nucleic acids, have been synthesized with the objective of increasing cytotoxicity (An et al 1996; Yamakoshi et al 1996). Cytotoxicity of dendritic C60 monoadduct and malonic acid C60 trisadduct was investigated on Jurkat cells, and upon exposure to UV light, the cell number was found to drop by approximately 19% within two weeks (Rancan et al 2002). Ji et al also studied the biodistribution and tumor uptake of C60(OH)x in five kinds of tumor models by radiotracer 125I-labeled C60(OH)x. (Ji et al 2006).
Iwamoto and Ymakoshi introduced a highly water soluble C60- N vinylpyrrolidine copolymer as agent for photodynamic therapy (Iwamoto and Yamakoshi 2006). C60 was incorporated covalently into poly (vinylpyrrolidone) chain via radical polymerization. This nanoparticle was the most water-soluble fullerene yet reported and aqueous solutions of concentrations even higher than reported for saturated C60 in toluene could be generated with this method.
Liu et al (2007) demonstrated the use of poly ethylene glycol (PEG)-conjugated fullerene containing Gd3+ ions for photodynamic therapy in combination with magnetic resonance imaging (MRI). The authors demonstrate through experimental data that tumor PDT effect was significantly promoted by photosensitizer tumor targetability and MRI activity. C60-PEG-Gd was injected into tumor bearing mice. The MRI activity was introduced into C60-PEG of PDT photosensitizer. The chelate incorporation of Gd3+ ions could convert C60-PEG derivative to a photosensitizer with both the diagnostic and therapeutic functions (Liu et al 2007).
Recently, Mroz et al (2007) investigated the photodynamic activity of fullerenes derivatized with hydrophilic and cationic groups against a range of mouse cancer cell lines. They found that, monocationic fullerene is highly effective photosensitizer for killing cancer cells by rapid induction of apoptosis after illumination.
http://www.ncbi.nlm....les/PMC2676811/
