Abstract 1211: Novel detection and characterization of truncated ERBB2 demonstrates potent oncogenicity of the p110 isoform in human mammary epithelial cells
Authors: Ward Toby M. , Iorns Elizabeth , Liu Xinjun , Singh Sharat , Kim Phillip , Jegg Anna , Dean Sonja , Gallas Michelle , Villasboas-Bisneto Jose , Lippman Marc , Landgraf Ralf , Pegram Mark 
Published: June 2012

Abstract
The full-length p185 ERBB2 (HER2) receptor tyrosine kinase is a validated target for breast cancer (BC) therapy. It is now appreciated that a portion of ERBB2+ BC expresses truncated isoforms of the receptor, including the membrane localized forms p95 and p110. Importantly, t-ERBB2s lack the extracellular domain epitope of trastuzumab and act as a resistance mechanism to therapy. Data from transgenic mouse models implicate expression of t-ERBB2s in tumor formation and metastasis. Furthermore, human clinical studies have revealed that expression of t-ERBB2s correlates with poor patient outcome, increased nodal involvement, and increased metastasis.
In this study, we used partially transformed breast epithelial cells (HMLEs) to extend the studies of t-ERBB2 expression in human cells. Stable expression of cDNAs coding for p110 t-ERBB2 led to increased migration (79 cells/ well versus 39, p = 0.04), and invasion (583 cell/ well vs. 290) p = 0.03) of p110 versus p185 expressing HMLE cells, respectively. Importantly, expression of p110 t-ERBB2, but not other isoforms, led to xenograft formation by HMLE cells in NOD/SCID mice (p110, 10 of 12 possible xenografts formed, p185, no xenografts formed).
Accurate clinical profiling of t-ERBB2 expression may aid in selection of ERBB2-targeted therapy. To this end, we used a novel proximity-mediated immunoassay (CoPIA) to detect and quantify t-ERBB2 receptors in patient samples. Analysis of a cohort of 74 primary breast tumors revealed that 52% of breast tumor samples with a high ERBB2-IHC score (3+) contained t-ERBB2, with 32% containing phosphorylated t-ERBB2. In several samples t-ERBB2 accounted for 10-20% of the total ERBB2 receptor population in tumor cells. Finally, fine-needle aspirates of ERBB2+ metastases also revealed expression and phosphorylation of t-ERBB2s.
In addition to its role in prognosis and therapeutic guidance, p110 t-ERBB2 represents an attractive target for therapy. We have generated several mouse monoclonal antibodies targeting the N-termini of p110 t-ERBB2s. Binding of p110 on the surface of living cells was assayed by flow cytometry, and the biological activity of these antibodies is currently being assessed in vitro and in vivo.
Together, these data imply a functional role for the p110 t-ERBB2 isoform in tumorigenesis, invasion, and migration. Furthermore, expression of t-ERBB2 in the majority of IHC 3+ tumor samples reveals a significant incidence of t-ERBB2 in human cancers. Targeting of p110 t-ERBB2 may allow for novel therapeutic intervention in ERBB2+ primary and metastatic breast cancer.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1211. doi:10.1158/1538-7445.AM2011-1211