Preparation and preliminary evaluation of [55Co](II)vancomycin

Co-55 (t1/2=17.53 h) was produced by 150 μA irradiation of a natural nickei target using 15 MeV protons. It was separated from the irradiated target material by two ion exchange chromatography steps with a radiochemical yield of >95% and was used for the preparation of [55Co]vancomycin ([55Co]VAN). Optimization studies were performed using Co-57 due to its longer half-life. Cobalt-57 (t1/2=271.79 d) was produced by irradiation of a natural nickel target with 150 μA current of 22 MeV protons. The 57Co was separated from the irradiated target material using a no-carrier-added method with a radiochemical yield of >97%. Both products were controlled for radionuclide and chemical purity. The solutions of [55Co]VAN were prepared (radiochemical yield >80%) starting with 55Co acetate and vancomycin at room temperature after 30 min. A precise solid phrase extraction (SPE) method was developed using Si Sep-Pak in order to purify/reconstitute the final formulation for animal studies. [55Co]VAN showed a radiochemical purity of more than 99%. The resultant specific activity was about 1.15 TBq/mmol. It is proved that the tracer is stable in the final product and in presence of human serum at 37°C up to 24 h. Biodistribution study of [55Co]VAN in normal rats was undertaken for up to 72 h.