Study of radioisotope labeled cobalt-bleomycins

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It is known that ^<57>Co-bleomycins have the strong affinity for the malignant tumor. Owing to the long-half life (270 days) of ^<57>Co, ^<57>Co-bleomycins have not been used for the clinical diagnosis. Non-radioactive cobalt binding bleomycins (Co-bleomycins) naturally have the strong affinity for the malignant tumor, too.We intended to label Co-bleomycins with radioisotope (RI) to use for the clinical diagnosis and therapy. Co-bleomycin was easily prepared from bleomycin and cobaltous chloride. As the radioactive reagent for the label, we chose Na^<131>I,^<125>I-Bolton-Hunter reagent and ^<125>I-PIB reagent.A small quantity of Co-bleomycin labeled with ^<125>I-Bolton-Hunter was obtained, and the tumor affinity of this labeled Co-bleomycin was examined by using Ehrlich tumor bearing mice. Unfortunately, the labeled Co-bleomycin had not the affinity for the malignant tumor.An adequate quantity for the animal study of Co-bleomycin labeled with ^<125>I-PIB was not obtained and Na^<131>I … More did not bind to Co-bleomycin.In addition, we intented to label bleomycin with Na^<131>I,^<125>I-Bolton-Hunter reagent and ^<125>I-PIB reagent, respectively. These three lableling reagents were bound to bleomycin with high yield, respectively. The tumor affinity of bleomycin-^<131>I,bleomycin-^<125>I-Bolton-Hunter and bleomycin-^<125>I-PIB was examined by the method described above. These labeled bleomycin had not the affinity for the malignant tumor. To give the tumor affinity to the labeled bleomycin, we attempted to bind cobalt to these three labeled bleomycin. But cobalt did not bind to the labeled bleomycin.From the results mentioned above, it was clarified that RI labeling for Co-bleomycin was very difficult. If RI labeling reagent was bound to the amine of side chain of Co-bleomycin, the biological property of Co-bleomycin would not originate the degeneration in binding the reagent. We undertake to bind RI labeling reagent to the amine of side chain of Co-bleomycin in the next project. Less