Free Radical Scavenging and Photodynamic Functions of Micelle-like Hydrophilic Hexa(sulfobutyl)fullerene (FC₄S)

Abstract

Biological applications of water-soluble hexa(sulfobutyl)fullerene (FC ₄ S) are reviewed. It was synthesized in a yield of 80–85% by the treatment of C ₆₀ in dimethoxyethane (DME) with sodium naphthalide (10 equiv.) at 25 °C, followed by reacting the resulting hexa-anionic fullerene intermediates with an excess of 1,4-butane sultone (15 equiv.). FC ₄ S showed an enhanced superoxide radical (O ₂ ^−.) scavenging activity and suppression efficiency against the superoxide-induced ferricytochrome c reduction under physiologic conditions, as compared with those of fullerenols at a dose level of 100 μ m. For example, a profound suppression efficiency of 60 and 96% was detected at a dose level of 50 and 100 μ m, respectively. Aggregation behaviors of FC ₄ S molecules in aqueous solution were investigated using SAXS (small-angle X-ray scattering) and SANS (small-angle neutron scattering) techniques. We concluded that the aggregation size and shape of FC ₄ S nanoparticles with the radius of gyration,R _g of 18.9–19.1 Å remain relatively unchanged with the variation of concentration in the concentration range of 0.35–26.0 mM. The phenomena were correlated to a high total surface area of nanoparticles and interfacial accessability of fullerene cages to reactive oxygen radical species.

The ICR mice implanted with sarcoma 180 tumor cells on the subcuticle skin area were utilized as an animal model. Upon administration of FC ₄ S (15 mg/kg) by intraperitoneal injection and the photodynamic therapeutic (PDT) treatment on the tumor-bearing mouse using argon laser irradiation at 514.5 nm with the total light dose of 100 J/cm ², the tumor size was found to decrease largely to only roughly 10% of the tumor control at 30 days after laser irradiation. These data substantiated the effectiveness of FC ₄ S in reducing the growth of tumor in vivo and demonstrate the potential use of it as a sensitizing agent in the photodynamic therapy for tumor and cancer-related diseases. Good photostability of FC ₄ S in aqueous solution was revealed in several experiments. Acute and subacute toxicity studies of FC ₄ S were investigated by administering the substrate by either a single dose intravenous injection (i.v.) at 100 mg/kg or a single dose intraperitoneal injection (i.p.) at 500 mg/kg and intraperitoneal injection (i.p.) with 12-repeated daily doses of 0.6–60 mg/kg, respectively.