[Preparation and Evaluation of Fullerene Based Nanomedicine]

Fullerenes, large spherical molecules composed solely of carbon atoms, have gathered much attention for practical applications that take advantage of their unique spherical structure, physical properties, and biological activities. For example, fullerene C₆₀ can function as a photosensitizer, an antioxidant, a bioimaging agent, and as a gene or drug carrier. However, the practical use of C₆₀ for these potential biomedical applications has been hampered by the fact that it is only sparingly soluble in water. In this review, we focus on the development of hydrophilic C₆₀ nanoparticles, the surface of which is covered by cyclodextrin (CD), and then evaluate its biological activities. C₆₀/CD nanoparticles were stable under physiological conditions, and even under much harsher conditions. The nanoparticles generate reactive oxygen species (ROS) under visible light irradiation. Efficient photodynamic therapy against tumor growth was achieved by the intravenous injection of C₆₀/CD nanoparticles to tumor bearing mice, followed by photoirradiation. In addition, C₆₀(OH)₁₀, which is regarded as a potential candidate for use in scavenging ROS, was also prepared in the form of water soluble nanoparticles. C₆₀(OH)₁₀/CD nanoparticles protect the liver from injury by the suppression of oxidative stress occurring in the mitochondria, for example, by scavenging ROS such as superoxide anion radicals (O₂^・-), nitric oxide (NO) and peroxynitrite (ONOO^-), which act as critical mediators in liver injuries. C₆₀-based nanoparticles represent a potentially promising material for use in the treatment of cancer and oxidative stress-related diseases, and are promising as well in terms of extensive biological applications.

Mechanochemical Preparation of Stable Sub-100 nm γ-Cyclodextrin:Buckminsterfullerene (C60) Nanoparticles by Electrostatic or Steric Stabilization

Buckminster fullerene (C₆₀ )'s main hurdle to enter the field of biomedicine is its low bioavailability, which results from its extremely low water solubility. A well-known approach to increase the water solubility of C₆₀ is by complexation with γ-cyclodextrins. However, the formed complexes are not stable in time as they rapidly aggregate and eventually precipitate due to attractive intermolecular forces, a common problem in inclusion complexes of cyclodextrins. In this study we attempt to overcome the attractive intermolecular forces between the complexes by designing custom γ-cyclodextrin (γCD)-based supramolecular hosts for C₆₀ that inhibit the aggregation found in native γCD-C₆₀ complexes. The approach entails the introduction of either repulsive electrostatic forces or increased steric hindrance to prevent aggregation, thus enhancing the biomedical application potential of C₆₀ . These modifications have led to new sub-100 nm nanostructures that show long-term stability in solution.

Evaluation of photodynamic activity of C60/2-hydroxypropyl-β-cyclodextrin nanoparticles

The objective of this study is to evaluate the ability of C(60)/2-hydroxypropyl-β-cyclodextrin (HP-β-CyD) naonparticles to generate reactive oxygen species (ROS) and to induce cell toxicity by the photoirradiation. C(60) nanoparticles were prepared by cogrinding with HP-β-CyD for 3 h at 4°C under reduced pressure. The photodynamic activity of C(60)/HP-β-CyD nanoparticles was evaluated by spectroscopic methods, including the electron spin resonance spin-trapping method, and by the cell viability test using Hela cells. C(60)/HP-β-CyD nanoparticles efficiently generated not only superoxide anion radical (O(2)(·-)) and hydroxyl radical (·OH), but also singlet oxygen ((1)O(2)) through photoirradiation. The ROS generation was enhanced by decreasing the mean particle diameter of C(60) nanoparticles, and the particle size smaller than 90 nm showed a high generation of ·OH and (1)O(2). In addition, HP-β-CyD enhanced the generation of (1)O(2), compared with polyvinylpyrrolidone (an effective solubillizer for C(60)), due to partial disposition of C(60) in the hydrophobic CyD cavity. Furthermore, C(60) /HP-β-CyD nanoparticles showed cell toxicity after the light irradiation, but no toxicity was observed without the light irradiation. Therefore, HP-β-CyD is useful for the preparation of stable C(60) nanoparticles with high ROS generation ability, and C(60)/HP-β-CyD nanoparticles are a promising photosensitizer for photodynamic therapy.