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Radioimmunoimaging of Experimental Thrombi in Dogs Using Technetium-99m-Labeled Monoclonal Antibody Fragments Reactive with Human Platelets

Medical Department, Brookhaven National Laboratory, Upton
SUNY at Stony Brook School of Medicine, Stony Brook, New York
Summa Medical Corporation and Rho-Med Inc., Albuquerque, New Mexico

Correspondence: For reprints contact: P. Som, DVM, Medical Dept., Brookhaven National Laboratory, Upton, NY 11973.

ABSTRACT

Monoclonal antibody 50H.19, which reacts with human platelets, was converted to fragments, pretinned, and made into kits for subsequent radiolabeling with ^99mTc. The antibody, which cross-reacts with dog platelets, was used to evaluate in vitro binding to blood clots and in vivo in experimental thrombi in dogs. After radiolabeling, 97.4 ± 6.4% of the ^99mTc was antibody-associated. The preparations retained immunoreactivity, as determined by: (a) binding studies using whole blood and determining the ratio of cell-to-plasma radioactivity (ratios of 57.6–61.2) and (b) binding of the antibody to clots (clot/serum ratios were 57.2–74.6%). Approximately 50% of the radioactivity was cleared from the blood in 3–6 min and 18–24% was excreted in urine within 3 hr. Experimental thrombi in dogs could be visualized consistently within 2–3 hr postinjection in peripheral veins and arteries, pulmonary arteries, and the right ventricle. In addition, damage to blood vessel intima without visible thrombi could also be detected. This method has the following advantages: short and simple pre-imaging preparation, and rapid visualization of thrombi with no need for blood-pool subtraction or delayed imaging.