Synthesis and characterization of gadolinium-decorated [60]fullerene for tumor imaging and radiation sensitization

Purpose: The excellent contrast of high atomic number (Z) elements compared to soft tissues has advanced their use as contrast agents for computed tomographic imaging and as potential radiation sensitizers. We evaluated whether gadolinium (Gd) could serve as such a theranostic agent for high-resolution magnetic resonance imaging (MRI) due to its paramagnetic properties and radiosensitization due to its high Z. Materials and methods: To improve the relaxivity of Gd, we coupled it to [60]fullerene, an elemental carbon allotropic nanoparticle that seamlessly traverses physiological barriers. By adding serinol, an aliphatic alcohol derived from amino acid serine, we turned [60]fullerene, which is otherwise insoluble in water, into a highly water-soluble derivative and decorated it externally with a payload of chelated gadolinium ions. Results: When [60]fullerene was functionalized in this manner with two gadolinium ions (Gd₂C₆₀), it displayed considerably higher T₁ relaxivity at 4.7 T than the commercially used MRI contrast agent, Magnevist, (18.2 mM⁻¹s⁻¹ vs. 4.7 mM⁻¹s⁻¹). Attempts to increase this even further via decoration of [60]fullerene with 12 gadolinium ions was unsuccessful due to a poor water solubility. However, the current formulation of Gd₂C₆₀ did not result in any appreciable radiosensitization. Conclusion: Our results show a successful generation of a novel contrast agent via decoration of fullerene with two chelated Gd ions. Though this formulation was not successful in generating radiosensitization, other chemical modifications can be further explored to increase radiosensitization potential.