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

Co-55 (t_1/2=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 (t_1/2=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.