Anti-HER3 Domain 1 and 3 Antibodies Reduce Tumor Growth by Hindering HER2/HER3 Dimerization and AKT-Induced MDM2, XIAP, and FoxO1 Phosphorylation

Abstract

Blockade of the human epidermal growth factor receptor 3 (HER3) and of the downstream phosphatidylinositide 3-kinase (PI3K)/AKT pathway is a prerequisite for overcoming drug resistance and to develop novel treatments for cancers that are not eligible for the currently approved targeted therapies. To this end, we generated specific antibodies (Abs) against domain 1 (D1) and domain 3 (D3) of HER3 that recognize epitopes that do not overlap with the neuregulin-binding site. The fully human H4B-121 Ab and the mouse monoclonal Abs 16D3-C1 and 9F7-F11 inhibited tumor growth in nude mice xenografted with epidermoid, pancreatic, or triple-negative breast cancer cells. The combination of one anti-HER3 Ab and trastuzumab improved tumor growth inhibition in mice xenografted with HER2(low) cancer cell lines, for which trastuzumab alone shows no or moderate efficiency. Ab-induced disruption of tumor growth was associated with G1 cell cycle arrest, proliferation inhibition, and apoptosis of cancer cells. Anti-HER3 Abs blocked HER2/HER3 heterodimerization and HER3 phosphorylation at the cell membrane, leading to inhibition of phosphorylation of the downstream AKT targets murine double minute 2, X-linked inhibitor of apoptosis, and forkhead box O1. This study demonstrates that anti-HER3 D1 and D3 Abs could represent a new option for immunotherapy of pancreatic and triple-negative breast cancers.

Antiproliferative Effect of Lapatinib in HER2-Positive and HER2-Negative/HER3-High Breast Cancer: Results of the Presurgical Randomized MAPLE Trial (CRUK E/06/039)

“…HER3 has a docking site for the p85 subunit of PI3K and acts as the preferred heterodimerization partner for HER2. HER2-HER3 heterodimers are increasingly identified as key drivers of the PI3K cell survival pathway (23)(24)(25)(26). Activation of HER3 and downstream PI3K has been shown to predict resistance to trastuzumab but sensitivity to lapatinib in vitro (27).…”

Combining Anti-ERBB3 Antibodies Specific for Domain I and Domain III Enhances the Anti-Tumor Activity over the Individual Monoclonal Antibodies

“…In fact, the interaction between dI and HRGβ is increased at pH 5.5 as compared to neutral pH. Consistent with this model, Lazrek et al recently described dI-binding anti-ERBB3 antibodies capable of blocking HRG-induced phosphorylation of Akt [16]. However, its ability to enhance the activity of ERBB2-targeted agents suggests its binding impacts the balance between activating and inhibitory mechanisms dictating ERBB3 activity.…”

“…Blockade of ERBB3-dependent signaling in combination with ERBB2 blockade has been shown to improve cell growth inhibition [16]. As compared to either agent alone the combination of the A5/F4 oligoclonal plus trastuzumab at an empirically determined fixed ratio (200∶1) synergistically improves cell growth inhibition at the 50% effect level in all three cell lines tested (Figure 5).…”

Examination of HER3 targeting in cancer using monoclonal antibodies

“…The EC 50 of our mAb for IgB3 binding ranged between 0.21 nM (XC252) and 16.8 nM (NG140). Next, we compared mAb ability to bind to the native form of the receptor using FACS and NIH/3T3-R2R3 cells, which co-overexpress ectopic HER2 and HER3 (25) (Fig. 1 B and C).…”