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Molecular Modeling and Preclinical Evaluation of the Humanized NR-LU-13 Antibody¹

Departments of Molecular Biology [S. S. G., S. C. G., D. M. S.], Pharmacology [D. B. A., J. M. R., B. B.], and Pathobiology [R. T. L], NeoRx Corporation, Seattle, Washington 98119, and Department of Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom [S. S., A. H., J. P., A. R. R.]

A mouse-human chimeric monoclonal antibody (chNR-LU-13), specific for the EGP40 pancarcinoma antigen, was humanized through three-dimensional molecular modeling. Humanization of the chNR-LU-13 antibody is expected to enhance its use for patients undergoing immunotherapy. On the basis of the observed amino acid sequence identity, chNR-LU-13 complementary determining regions (CDRs) of the V_L and V_H regions were grafted onto the human anti-DNA-associated idiotype immunoglobulin clone, R3.5H5G'CL. Ten amino acids residues within the humanized framework were back-mutated to their corresponding chNR-LU-13 sequence, because they were predicted to disrupt the canonical classification of the CDRs or were within 5 Å of a CDR. Synthesis of the V_L and V_H regions was accomplished by recursive PCR, and the dual-chain expression vector p451.C4 was positioned under control of the CMV^P+E. We observed by competitive ELISA that the recombinant humanized NR-LU-13 (huNR-LU-13) IgG1 antibody exhibited an indistinguishable immunoreactivity profile when compared with the murine monoclonal antibody (muNR-LU-10). The huNR-LU-13 antibody was effective in mediating both antibody-dependent cellular cytotoxicity and complement-mediated cytotoxicity when assayed against either the breast carcinoma cell line, MCF-7, or the colon adenocarcinoma cell line, SW1222. Biodistribution studies using i.v. coinjected ¹³¹I-muNR-LU-10 and ¹²⁵I-huNR-LU-13 confirmed that the huNR-LU-13 specifically targets to the tumor in athymic BALB/c mice bearing the SW1222 human tumor xenograft. Humanization of the chNR-LU-13 antibody is expected to eliminate an undesired human anti-mouse antibody response, allowing for repeated i.v. administration into humans.

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