TY - JOUR T1 - <sup>99m</sup>Tc-Labeled Divalent and Tetravalent CC49 Single-Chain Fv’s: Novel Imaging Agents for Rapid In Vivo Localization of Human Colon Carcinoma JF - Journal of Nuclear Medicine JO - J Nucl Med SP - 1519 LP - 1527 VL - 42 IS - 10 AU - Apollina Goel AU - Janina Baranowska-Kortylewicz AU - Steven H. Hinrichs AU - James Wisecarver AU - Gabriela Pavlinkova AU - Sam Augustine AU - David Colcher AU - Barbara J.M. Booth AU - Surinder K. Batra Y1 - 2001/10/01 UR - http://jnm.snmjournals.org/content/42/10/1519.abstract N2 - 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 &gt;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 &lt; 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 %ID/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-background ratio). These reagents, therefore, have the potential for use in clinical imaging studies of cancer in the field of nuclear medicine. ER -