Construction, binding properties, metabolism, and tumor targeting of a single-chain Fv derived from the pancarcinoma monoclonal antibody CC49

CC49 is a "second generation" monoclonal antibody to B72.3, which reacts with the pancarcinoma antigen TAG-72. CC49 has been shown to efficiently target human colon carcinoma xenografts and is currently being evaluated in both diagnostic and therapeutic clinical trials. We describe here th...

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Bibliographic Details
Published in:Cancer research (Chicago, Ill.) Ill.), 1991-12, Vol.51 (23), p.6363-6371
Main Authors: MILENIC, D. E, YOKOTA, T, FILPULA, D. R, FINKELMAN, M. A. J, DODD, S. W, WOOD, J. F, WHITLOW, M, SNOY, P, SCHLOM, J
Format: Article
Language:English
Subjects:
Animals
Antibodies, Monoclonal - metabolism
Biological and medical sciences
Colonic Neoplasms - metabolism
Colonic Neoplasms - therapy
Contrast media. Radiopharmaceuticals
Electrophoresis, Polyacrylamide Gel
Female
Immunoenzyme Techniques
Immunoglobulin Fab Fragments - metabolism
Immunoglobulin G - metabolism
Iodine Radioisotopes - metabolism
Macaca mulatta
Medical sciences
Mice
Mice, Nude
Molecular Weight
Pharmacology. Drug treatments
Radioimmunoassay
Recombinant Proteins - chemical synthesis
Recombinant Proteins - chemistry
Recombinant Proteins - metabolism
Recombinant Proteins - pharmacokinetics
Tissue Distribution
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Summary:CC49 is a "second generation" monoclonal antibody to B72.3, which reacts with the pancarcinoma antigen TAG-72. CC49 has been shown to efficiently target human colon carcinoma xenografts and is currently being evaluated in both diagnostic and therapeutic clinical trials. We describe here the construction and characterization of a recombinant single-chain Fv (sFv) of CC49. The sFv was shown to be a Mr 27,000 homogeneous entity which could be efficiently radiolabeled with 125I or 131I. Comparative direct binding studies and competition radioimmunoassays using CC49 intact IgG, F(ab')2, Fab', and sFv revealed that the monomeric CC49 Fab' and sFv had relative binding affinities 8-fold lower than the dimeric F(ab')2 and intact IgG. Nonetheless, the 131I-labeled sFv was shown to bind biopsies of TAG-72-expressing tumors. Metabolism studies in mice, using radiolabeled CC49 IgG, F(ab')2, Fab', and sFv, demonstrated an extremely rapid plasma and whole body clearance for the sFv. CC49 sFv plasma pharmacokinetic studies in rhesus monkeys also showed a very rapid plasma clearance (T1/2 alpha of 3.9 min and T1/2 beta of 4.2 h). Tumor targeting studies with all four radiolabeled Ig CC49 forms, using the LS-174T human colon carcinoma xenograft model, revealed a much lower percentage injected dose/g tumor binding for the CC49 monomeric sFv and Fab' as compared to the dimeric F(ab')2 and intact IgG. However, tumor:normal tissue ratios (radiolocalization indices) for the sFv were comparable to or greater than those of the other Ig forms. High kidney uptake with 125I-labeled Fab' and F(ab')2 was not seen with 125I-sFv. Gamma scanning studies also showed that 131I-CC49 sFv could efficiently localize tumors. The CC49 sFv may thus have utility in diagnostic and perhaps therapeutic applications for a range of human carcinomas.
ISSN:0008-5472
1538-7445