Technetium-99m labeling and biodistribution of anti-TAC disulfide-stabilized Fv fragment.

T M Yoo, H K Chang, C W Choi, K O Webber, N Le, I S Kim, W C Eckelman, I Pastan, J A Carrasquillo, C H Paik

Department of Nuclear Medicine, Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, Bethesda, Maryland, USA.

Journal of nuclear medicine : official publication, Society of Nuclear Medicine 1997 Feb

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We used a preformed 99mTc chelate approach to label a genetically engineered disulfide-bonded Fv fragment of anti-Tac monoclonal antibody (dsFv). The biodistribution of this 99mTc-labeled dsFv was evaluated in athymic mice with IL-2 alpha-receptor-positive ATAC4 tumor xenografts. Benzoylmercaptoacetyl-triglycine (BzMAG3) was first labeled with 99mTc, and the carboxy group of 99mTc-MAG3 was then activated to the corresponding tetrafluorophenyl ester. This activated ester was purified with a Sep-Pak C18 column and conjugated to dsFv. The resulting 99mTc-MAG3-dsFv was purified with PD-10 size-exclusion chromatography. The immunoreactivity of 99mTc-MAG3-dsFv was 76% +/- 9%. When incubated in serum at 37 degrees C for 24 hr, there was no appreciable dissociation of 99mTc. The mice were co-injected with 125I-dsFv labeled by the Iodo-Gen method as a control. The mice were killed at 15 to 720 min for analysis of biodistribution and radiocatabolites. The tumor uptake of 99mTc-MAG3-dsFv was similar to that of 125I-dsFv. The tumor uptake of 99mTc-MAG3-dsFv was rapid with tumor-to-blood or tumor-to-organ ratio higher than 1 for all organs except the kidneys. The peak tumor value of 5.1% injected dose per gram was obtained at 45 min, and the tumor-to-organ ratios increased steadily over time; a ratio of 15, 11, 7, 95 and 0.10 resulted at 6 hr for blood, liver, stomach, muscle and kidney. The radioactivity was primarily excreted through kidneys. The rapid achievement of high tumor-to-blood and -tissue ratios makes 99mTc-MAG3-dsFv a promising agent for scintigraphic detection of various hematological malignancies that express IL-2 alpha receptors.

Citation

T M Yoo, H K Chang, C W Choi, K O Webber, N Le, I S Kim, W C Eckelman, I Pastan, J A Carrasquillo, C H Paik. Technetium-99m labeling and biodistribution of anti-TAC disulfide-stabilized Fv fragment. Journal of nuclear medicine : official publication, Society of Nuclear Medicine. 1997 Feb;38(2):294-300