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Improved Radioimmunoimaging of Human Tumor Xenografts by a Mixture of Monoclonal Antibody F(ab')₂ Fragments

The Wistar Institute of Anatomy and Biology, Philadelphia
Division of Nuclear Medicine, Department of Radiology, Hospital of the University of Pennsylvania, Philadelphia

Correspondence: For reprints contact: Dorothee Herlyn, DVM, The Wistar Institute of Anatomy and Biology, 36th St. at Spruce, Philadelphia, PA 19104.

ABSTRACT

F(ab')₂ fragments of monoclonal antibodies (MAbs) GA 73-3 and CO 29.11, with specific binding reactivity in vitro to human tumors of the gastrointestinal tract, were radioiodinated and injected into nude mice bearing human colon carcinoma xenografts. Fragments of both MAbs preferentially localized in tumor tissue compared with normal mouse tissue, as determined by differential tissue counting of radioactivity. The fragments localized specifically only in those tumors to which they bind in vitro and not in unrelated tumors. Radiolabeled fragments of an anti-hepatitis virus MAb did not localize in the tumors. Whole-body scintigraphy demonstrated tumor localization with ¹³¹I-labeled fragments without background subtraction. Best tumor contrast, as quantitated by analyzing digital computer scans, was obtained between Days 2 and 5 after injection. Tumor contrast was significantly enhanced when a mixture of both MAb F(ab')₂ fragments was used. The biologic half-life of the MAb mixture in the tumor was significantly greater than that of either MAb alone, suggesting the use of the MAb mixture in radioimmunotherapy.