99mTc-labeled divalent and tetravalent CC49 single-chain Fv's: Novel imaging agents for rapid in vivo localization of human colon carcinoma

A. Goel, J. Baranowska-Kortylewicz, S. H. Hinrichs, J. Wisecarver, G. Pavlinkova, S. Augustine, D. Colcher, B. J.M. Booth, S. K. Batra

Research output: Contribution to journalArticlepeer-review

68 Scopus citations

Abstract

Radioimmunopharmaceutical agents enabling rapid high-resolution imaging, high tumor-to-background ratios, and minimal immunogenicity are being sought for cancer diagnosis and imaging. Genetic engineering techniques have allowed the design of single-chain Fv's (scFv's) of monoclonal antibodies (mAbs) recognizing tumor-associated antigens. These scFv's show good tumor targeting and biodistribution properties in vivo, indicating their potential as imaging agents when labeled with a suitable radionuclide. Methods: Divalent (sc(Fv)2) and tetravalent ([sc(Fv)2]2) scFv's of mAb CC49 were evaluated for radioimmunolocalization of LS-174T colon carcinoma xenografts in athymic mice. scFv's were radiolabeled with 99mTc by way of the bifunctional chelator succinimidyl-6-hydrazinonicotinate hydrochloride using tricine as the transchelator. The immunoreactivity and in vitro stability of the scFv's were analyzed after radiolabeling. Biodistribution and pharmacokinetic studies were performed to determine the tumor-targeting potential of the radiolabeled scFv's. Whole-mouse autoradiography illustrated the possible application of these 99mTc-labeled multivalent scFv's for imaging. Results: The radiolabeling procedure gave ≥95% radiometal incorporation, with a specific activity of >74 MBq/mg scFv. In solid-phase radioimmunoassay, both sc(Fv)2 and [sc(Fv)2]2 exhibited 75%-85% immunoreactivity, with nonspecific binding between 0.8% and 1.2%. Size-exclusion high-performance liquid chromatography showed sc(Fv)2 as a 60-kDa protein and [sc(Fv)2]2 as a 120-kDa protein. Blood clearance studies showed the elimination half-life of 99mTc-labeled sc(Fv)2 as 144 min and that of [sc(Fv)2]2 as 307 min. Whole-body clearance studies confirmed the rapid elimination of scFv's, with half-lives of 184±19 min for sc(Fv)2 and 265±39 min for [sc(Fv)2]2 (P<0.001). At 6 h after administration, the tumor localization was 7.2±0.7 percentage injected dose per gram of tumor (%ID/g) for 99mTc-sc(Fv)2. 99mTc-[sc(Fv)2]2 showed a tumor uptake of 19.1±1.1%lD/g at the same time; the amount of radioactivity in the tumors was 4-fold higher than in the spleen and kidneys and 2-fold higher than in the liver. Macroautoradiography performed at 6 and 16 h after administration clearly detected the tumor with both scFv's. Conclusion: 99mTc-labeled multivalent scFv's show good tumor-targeting characteristics and high radiolocalization indices (tumor-to-back-ground ratio). These reagents, therefore, have the potential for use in clinical imaging studies of cancer in the field of nuclear medicine.

Original languageEnglish (US)
Pages (from-to)1519-1527
Number of pages9
JournalJournal of Nuclear Medicine
Volume42
Issue number10
StatePublished - 2001

Keywords

  • Biodistribution
  • Macroautoradiography
  • Multivalency
  • Single-chain Fv
  • Tc

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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