[Tumor affinity and DNA interactions of 57Co-bleomycin (author's transl)]

Cobalt-57-bleomycin (BLM) has been proven to be the most stable and useful tumor-diagnostic agent among several radiolabelled BLMs. However, the considerably long half life of 57Co causes troubles in handling and preclude its extensive uses. In our previous work, BLM was proved to form two geometrical isomers, in chelating with Co. In this paper, we compared the tumor affinity of two isomers, to make an improvement of this drug's merit. We investigated biodistribution in tumor-bearing mice and DNA binding properties by fluorescence quenching technique and DNA melting study. A comparison of the data obtained suggests that isomerism affects the tumor affinity of the drug. Both tumor accumulation in tumor-bearing mice and stability of DNA binding of type I isomer were higher than those of type II. If a certain suitable radionuclide is inserted into cold Co-BLM type I isomer, this agent will be a greatly useful tumor-imaging radiopharmaceutical.