Human IgG2 constant region enhances in vivo stability of anti-tenascin antibody 81C6 compared with its murine parent

• Published in: Clinical cancer research Vol. 4; no. 10; pp. 2495 - 2502
• Main Authors: REIST, C. J, BIGNER, D. D, ZALUTSKY, M. R
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 01-10-1998
• Subjects: Animals; Antibodies, Monoclonal - chemistry; Antibodies, Monoclonal - pharmacokinetics; Antineoplastic agents; Biological and medical sciences; Drug Stability; Humans; Immunoglobulin Constant Regions - chemistry; Immunoglobulin G - chemistry; Immunotherapy; Iodine Radioisotopes; Medical sciences; Mice; Molecular Weight; Pharmacology. Drug treatments; Quality Control; Recombinant Fusion Proteins - chemistry; Tenascin - immunology; Tissue Distribution; Human; Tenascin; Biological fluid; Heterologous system; Stability; Intravenous administration; Rodentia; Molecular hybrid; Monoclonal antibody; IgG2; Malignant tumor; In vitro; In vivo; Tissue; Vertebrata; Mammalia; Glioma; Mouse; Animal; Distribution; Radiopharmaceuticals
• ISSN: 1078-0432; 1557-3265

The in vivo properties of radiolabeled chimeric monoclonal antibodies (mAbs) with human IgG1 and IgG3 constant regions generally
are similar to those of their corresponding murine construct. In contrast, we have observed that chimeric anti-tenascin mAb
81C6, which contains IgG2 constant regions, exhibits significantly higher localization in s.c. D-54 MG xenografts and prolonged
retention in most normal tissues compared with its IgG2b murine parent. The purpose of the present study was to determine
whether substitution of the murine IgG2b constant region domains in mAb 81C6 with those from human IgG2 enhanced the in vivo
stability of the 81C6 mAb. Both mAbs were radioiodinated using Iodogen and administered to athymic mice bearing s.c. D-54
MG human glioma xenografts. The nature of the labeled species present in tumor and normal tissues over a 144-h period was
investigated by trichloroacetic acid precipitation and SDS PAGE. In tumor and most normal tissues, a greater fraction of chimeric
compared with murine 81C6 was present as intact IgG. For example, in tumor at 144 h, the fraction of radioactivity present
as intact IgG was twice as high for chimeric compared with murine 81C6. A substantial fraction of murine but not chimeric
81C6 was present as a Mr 70,000-90,000 molecule, which could represent the generation of Fab/Fc monomers through the reduction
of the interchain disulfide bonds in the murine IgG2b molecule. These results suggest that the higher tumor and normal tissue
levels of chimeric compared with murine 81C6 can be attributed in part to the enhanced in vivo stability of the IgG2 chimeric
mAb. The chimeric construct also was demonstrated to be more stable than murine after incubation with cyst fluid obtained
from glioma resection cavity patients. Chimeric mAbs containing human IgG2 constant region domains could be of particular
value for certain radioimmunotherapeutic applications.