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Iodinated Bleomycin: An Unsatisfactory Radiopharmaceutical for Tumor Localization

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 Street N.W., Washington, D.C. 20037.

ABSTRACT

Cobalt-57-bleomycin is a clinically useful tumor-localizing agent, but attempts to label bleomycin (BLEO) with other radionuclides have been made because of the long physical half-life of ⁵⁷Co. As an alternative labeling approach, we iodinated BLEO both directly on the imidazole ring and indirectly by reaction with N-succinimidyl 3-(4-hydroxy, 3-iodophenyl) propionate. Directly iodinated BLEO retained anti-bacterial activity, but in tumor-bearing rats it showed a lower tumor-to-blood ratio (2.3) at 2 hr than did ⁵⁷Co-BLEO (11.8). The antibacterial activity of the indirectly labeled BLEO was markedly reduced and this material showed a tumor-to-blood ratio of 0.55 at 2 hr. The radioiodinated bleomycins are not suitable substitutes for ⁵⁷Co-BLEO as tumor-imaging radiopharmaceuticals.