The chemical composition of bleomycin labelled with 57Co and its distribution and kinetics in the organs of tumour bearing rats were studied. For separating bleomycin, the chromatography on a CM-Sephadex C-25 column with a gradient of ammonium formate was found to be most suitable. It is also possible to use paper chromatography in 10% NH4Cl and thin layer chromatography in 10% ammonium acetate with methyl alcohol 1:1. The fractions obtained by the chromatographic separation were identified as A2, B2 and A1. Labelling with 57Co given rise to a more complicated mixture of labelled compounds, all of them differing chromatographically from the original non-labelled components. Using carrier-free 57Co two main radioactive compounds are formed apparently corresponding to the fractions A2 and B2 containing one atom of Co per molecule. The amount of another two labelled components grows progressively with increasing amount of carrier CoCl2. Since their chromatographic properties are even more different from those of the original compounds, it was concluded that they probably contain two atoms of Co in their molecules. During distribution studies, rapid excretion of labelled bleomycin into the urine and stool was observed. Increased activities were retained in the liver, kidney, intestine and tumour.

131I-labelled antibodies to the fragment E of human fibrin, anti-rat fibrinogen, non-immune rabbit IgG and 67Ga-citrate were used for scintigraphy and distribution studies in experimental tumours in rats. The best visualisation was achieved with 131I-labelled anti-rat fibrinogen antibodies at intervals longer than 48 h after administration. Tumour to tissue ratios found in distribution studies performed formed more than 48 h after administration were higher in most examined tissues when using 131I-labelled antibodies than those obtained with 67Ga-citrate.

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