Cyclotron Production of High-Specific Activity 55Co and In Vivo Evaluation of the Stability of 55Co Metal-Chelate-Peptide Complexes.

This work describes the production of high-specific activity Co-55 and the evaluation of the stability of Co-55-metal-chelate-peptide complexes in vivo. Co-55 was produced via the 58 Ni(p, alpha) Co-55 reaction and purified using anion exchange chromatography with an average recovery of 92% and an average specific activity of 1.96 GBq/mu mol. Co-55-DO3A and Co-55-NO2A peptide complexes were radiolabeled at 3.7 MBq/mu g and injected into HCT-116 tumor xenografted mice. Positron emission tomography (PET) and biodistribution studies were performed at 24 and 48 hours postinjection and compared to those of (CoCl2)-Co-55. Both Co-55-metal-chelate complexes demonstrated good in vivo stability by reducing the radiotracers' uptake in the liver by sixfold at 24 hours with similar to 1% ID/g and at 48 hours with similar to 0.5% ID/g and reducing uptake in the heart by fourfold at 24 hours with similar to 0.7% ID/g and sevenfold at 48 hours with similar to 0.35% ID/g. These results support the use of Co-55 as a promising new radiotracer for PET imaging of cancer and other diseases.