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Immunoscintigraphy with 68Ga labeled diabodies

¹ German Cancer Research Center, Heidelberg, Germany; ² Affimed AG, Heidelberg, Germany; ³ Dept Nuclear Medicine, University, Heidelberg, Germany

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Objectives: The development of genetically engineered diabodies which consist of the antibody variable regions held together by a flexible linker, provides small sized ( 50 kD) immunoreactive molecules. These diabodies penetrate rapidly into solid tumors and they are cleared from the circulation within hours. A rapid and gentle technique for labeling those diabodies with 68Ga was developed using isothiocyanate derivatized HBED as a bifunctional chelator. Furthermore, the in vitro and in vivo characteristics will be investigated to evaluate the potential of diabodies for imaging.

Methods: The scFvs were generated by biopanning. The proteins were characterized by flow cytometric experiments on cells and by surface plasmon resonance to determine the binding constants as well as specificity of binding. The best clones were genetically engineered and converted into the diabody format. Labeling is done using HBED-CC. HBED-CC-TFP-ester is coupled to the antibody via lysine residues at room temperature (RT). The complexation reaction is done at pH 5 also at RT.

Results: The generated antibodies revealed binding to antigen expressing cells, while no binding to several haematopoetic cell lines was observed. The following affinity maturation improved the affinity by factor 15 to a Kd of 5 nM. Labeling experiments with [68Ga]HBED-CC showed, that the properties of the recombinant antibodies were nearly not affected by the labeling procedure.

Conclusions: The gentle conditions while labeling with [68Ga]HBED-CC did not affect the affinity of diabodies. The specificity and affinity of the labeled diabodies strongly indicate that these molecules may be well used for imaging.

Research Support: This work was made possible by the Deutsche Krebshilfe e.V.

This Article Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Eder, M. Articles by Eisenhut, M. PubMed Articles by Eder, M. Articles by Eisenhut, M.