Background: The signaling network downstream of the human epidermal growth factor receptors ErbB-1 and ErbB-2 have been extensively targeted by cancer therapeutics. Although initially efficacious in a subset of patients, drugs targeting these receptors led invariably to resistance which is often associated with reactivation of the ErbB-3/PI3K-Akt axis. This may be overcome by ErbB-3 ligands that abrogates receptor-mediated signaling.

Methods: the murine MP-RM-1 monoclonal antibody that specifically binds ErbB-3 ectodomain was chimerized by replacing the murine constant regions with the human constant regions and humanized by gratfing Complementarity Determining Regions from the murine into a human antibody framework using a computer assisted molecular modelling. Recombinant genes were placed into the pCDNA3.1 expression vector and transfected into Chinese Hamster Ovary-S cells. Antibodies were screened on the basis of their ability to inhibit Neuregulin-1 (NRG-1)-induced activation of the ErbB-3/PI3K-Akt axis in IR-8 human melanoma cells (Table 1). Four antibody variants, i.e., cMP-RM-1 #1, hMP-RM-1 #6, hMP-RM-1 #10, and hMP-RM-1 #20, were selected and further tested for their ability to promote ErbB-3 downregulation and to inhibit in vitro and in vivo growth of tumor cells.

Results: Four chimeric (c) and sixteen humanized (h) antibody variants were obtained. All variants showed to possess antigen binding affinity comparable to that of their parental antibody. Initial screening identified one chimeric (cMP-RM-1 #1) and three humanized (hMP-RM-1 #6, hMP-RM-1 #10, hMP-RM-1 #20) antibodies as the most effective in inhibiting ErbB-3/Akt phosphorylation and promotion of ErbB-3 downregulation. Further testing revealed the antibodies potently inhibited colony formation ability of tumor cells and halted growth of melanoma and ovarian cancer xenografts in nude mice. Treatment with the antibodies was associated with a decreased ErbB-3 and Akt phosphorylation and ErbB-3 expression in the excised tumor tissue.

Conclusions: This successful production of chimeric/humanized antibodies possessing antitumor activity in vitro and in vivo may provide novel candidates for ErbB-3-targeted therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C58.