Production and validation of the pharmacokinetics of a single-chain Fv fragment of the MGR6 antibody for targeting of tumors expressing HER-2 |
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Authors: | Fabio Turatti Delia Mezzanzanica Elena Nardini Elena Luison Lorenzo Maffioli Emilio Bombardieri Claudia de Lalla Silvana Canevari Mariangela Figini |
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Institution: | (1) Unit of Molecular Therapies, Department of Experimental Oncology, Istituto Nazionale per lo Studio e la Cura dei Tumori, Via Venezian 1, 20133 Milan, Italy e-mail: canevari@istitutotumori.mi.it Tel.: +39-02-2390567; Fax: +39-02-2362692, IT;(2) Department of Nuclear Medicine, Istituto Nazionale per lo Studio e la Cura dei Tumori, Via Venezian 1, 20133 Milan, Italy, IT;(3) DIBIT, San Raffaele Scientific Institute, Via Olgettina 58, 20132 Milan, Italy, IT |
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Abstract: | The HER-2 antigen, which is overexpressed in many breast carcinomas, is an ideal target for monoclonal antibodies due to
its low expression in normal tissue and its homogeneous distribution in the tumor mass. We have developed and characterized
the murine MAb MGR6 against HER-2, which is able to inhibit proliferation of tumor cells overexpressing HER-2. On the basis
of these preclinical results, phase I studies in breast carcinoma patients were conducted and radiolocalization data indicated
an antibody half life which directly paralleled that of other whole antibodies and thus resulting in a limited in vivo diagnostic
capacity. To obtain a smaller reagent with possibly improved in vivo properties, a single chain variable fragment (scFv) of
the original MGR6-producing hybridoma was generated by phage display technology. Biologically active MGR6 scFv was purified
rapidly and at high yield by metal affinity chromatography. Competition FACS and ELISA analyses identified an epitope on the
HER-2 extracellular domain that was shared by the scFv and the parental MAb. BIAcore analysis indicated a Koff of 9.3 × 10−4 s−1, similar to that of the intact MGR6 MAb. Distribution and elimination half-lives of MGR6 scFv, calculated from in vivo preclinical
evaluations, were much faster (13 min and 6.2 h, respectively) than previously published results for the intact MAb (mean
t1/2β of 46 h). This represents a theoretical improvement in pharmacokinetics with respect to the parental murine MAb and
points to the potential for utilizing this fragment in redirecting therapeutic agents, such as radioisotopes, to different
human carcinomas overexpressing HER-2.
Received: 10 August 2000 / Accepted: 19 October 2000 |
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Keywords: | Single-chain Fv HER-2 Phage display |
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