Inhibitory Effect of Polyclonal Antibodies Against HER3 Extracellular Subdomains on Breast Cancer Cell Lines

Differential tumor inhibitory effects induced by HER3 extracellular subdomain-specific mouse monoclonal antibodies

PURPOSE

The therapeutic potential of targeting the human epidermal growth factor receptor-3 (ErbB3/HER3) has long been ignored due to impaired tyrosine kinase function and low expression level in tumor cells compared with EGFR and HER2. Although recent investigations have explored the potential benefit of HER3 targeting and several anti-HER3 agents have been developed, there is still a critical need to design and produce more efficient therapeutics. This study was designed to develop tumor inhibitory monoclonal antibodies (MAbs) against different extracellular subdomains of HER3.

METHODS

Distinct extracellular subdomains of HER3 (D_I+II and D_III+IV) were utilized to produce MAbs by hybridoma technology. Biochemical and functional characteristics of these MAbs were then investigated by various methodologies, including immunoblotting, flow cytometry, cell proliferation, cell signaling, and enzyme-linked immunosorbent assays.

RESULTS

Four anti-D_I+II and six anti-D_III+IV MAbs were obtained, selected based on their ability to bind recombinant full HER3 extracellular domain (ECD). Our data showed that only one anti-D_I+II and four anti-D_III+IV MAbs recognized the native form of HER3 by immunoblotting. Four MAbs recognized the membranous HER3 by flow cytometry leading to induction of different levels of receptor internalization and subsequent degradation. Results of cell proliferation assays using these MAbs indicated that they differentially inhibited proliferation of HER3-expressing cancer cells and showed considerable synergistic effects in combination with trastuzumab. Selected MAb with the highest inhibitory effect significantly inhibited the phosphorylation of AKT and ERK1/2 molecules.

CONCLUSION

Some of the anti-HER3 MAbs produced in this study displayed tumor inhibitory function and may be considered promising candidates for future HER3-targeted cancer therapy.

A novel tumor inhibitory hybridoma monoclonal antibody with dual specificity for HER3 and HER2

BACKGROUND

The human epidermal growth factor receptor (HER/ErbB) family-targeted therapies result in a significant improvement in cancer immunotherapy. Monoclonal antibodies (MAb) against HER2 demonstrated a survival benefit for patients; however, drug resistance unavoidably occurs due to the overexpression of HER3, which leads to treatment failure. Effective inhibition of HER3 besides HER2 is thought to be required to overcome resistance and enhance therapeutic efficacy.

OBJECTIVE

The present study describes the production and characterization of a novel MAb, designated 1G5D2, which acts as a natural bispecific antibody targeting extracellular domains (ECD) of both HER2 and HER3.

METHODS

In this study, 1G5D2 was produced by hybridoma technology against HER3-ECD, and its structural and functional characteristics were studied by various methodologies, including enzyme linked-immunosorbent assays, flow cytometry, immunoblotting, cell signaling, and cell proliferation assays.

RESULTS

1G5D2 specifically binds to both HER2 (subdomain III + IV) and HER3 (subdomain I + II) expressed on tumor cells, and these receptors compete with each other for binding to this MAb. Competition flow cytometry experiments demonstrated that 1G5D2 does not compete with heregulin and recognizes an epitope out of HER3 ligand-binding site. Evaluation of 1G5D2 inhibitory effects in tumor cell lines co-expressing HER2 and HER3 showed that 1G5D2 synergizes with trastuzumab to inhibit both PI3K/AKT and MAPK/ERK pathways and potently downregulates the proliferation of these tumor cells more efficiently than each MAb alone.

CONCLUSION

1G5D2 is the first reported hybridoma antibody, which acts as a natural HER2/HER3 bispecific antibody. It might potentially be a suitable therapeutic candidate for HER2/HER3 overexpressing cancer types.