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Chemical and Biologic Properties of Isolated Radiolabeled Bleomycin Preparations

Washington Hospital Center and George Washington University, Washington, D.C.
Armed Forces Radiobiology Research Institute, Bethesda, Maryland

Correspondence: For reprints contact: W. C. Eckelman, Nuclear Medicine—Research, George Washington University, Walter Ross Hall, Room 225, 2300 Eye St. N.W., Washington, D.C. 20037.

ABSTRACT

Cobalt-57-bleomycin is a diagnostically useful radiopharmaceutical, but little is known about the nature of its individual fractions in regard to their metal-binding capacity and their in vivo distribution. Bleomycin was separated by high performance liquid chromatography (HPLC) into four major components. These were labeled and the distribution studied in tumor-bearing rats at 2 and 24 hr. In vivo radiochemical purity was also determined. Of the nine HPLC systems studied, Porasil A elated with a mobile phase of 0.3% ammonium formate in methanol gave the best separation of the fractions. These fractions were copper free and retained their biologic activity and purity. An in vitro competitive binding study of ⁵⁷Co-bleomycin with either ⁵⁷Co-human serum albumin (HSA) or ⁵⁷Co-ethylenediaminetetraacetic acid (EDTA) showed the labeled bleomycin to be a strong chelate. The biologic distribution in tumor-bearing rats showed significantly higher concentration in tumors at 2 hr for fractions A₂ and B₂ as compared to the bleomycin mixture. The other fractions, A₁ and demethyl A₂, gave lower tumor concentrations than the bleomycin mixture. The tumor-to-blood ratios for A₂ and B₂ were not significantly different from the bleomycin mixture, suggesting that the concentration of the bleomycin in the tumor was related to blood concentration. Tumor-to-blood ratios of greater than 10:1 at 2 hr were achieved for A₂, B₂, and the mixture; ratios of greater than 31 :1 were achieved at 24 hr for all three. From these data it appears that the major components A₂ and B₂ are the most useful for diagnostic tumor imaging.

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