Preparation of PEG-conjugated fullerene containing Gd3+ ions for photodynamic therapy

A novel photosensitizer with magnetic resonance imaging (MRI) activity was designed from fullerene (C60) for efficient photodynamic therapy (PDT) of tumor. After chemical conjugation of polyethylene glycol (PEG) to C60 (C60-PEG), diethylenetriaminepentaacetic acid (DTPA) was subsequently introduced to the terminal group of PEG to prepare PEG-conjugated C60 (C60-PEG-DTPA). The C60-PEG-DTPA was mixed with gadolinium acetate solution to obtain Gd3+-chelated C60-PEG (C60-PEG-Gd). Following intravenous injection of C60-PEG-Gd into tumor-bearing mice, the PDT anti-tumor effect and the MRI tumor imaging were evaluated. The similar O2
• −generation was observed with or without Gd3+ chelation upon light irradiation. Both of the C60-PEG-Gd and Magnevist® aqueous solutions exhibited a similar MRI activity. When intravenously injected into tumor-bearing mice, the C60-PEG-Gd maintained an enhanced MRI signal at the tumor tissue for a longer time period than Magnevist®. Injection of C60-PEG-Gd plus light irradiation showed significant tumor PDT effect although the effect depended on the timing of light irradiation. The PDT efficacy of C60-PEG-Gd was observed at the time when the tumor accumulation was detected by the enhanced intensity of MRI signal. This therapeutic and diagnostic hybrid system is a promising tool to enhance the PDT efficacy for tumor.