Abstract P5-06-03: Truncated ERBB2 Receptors: Diagnostic and Therapeutic Targets

Abstract

Abstract Background: Patients with ERBB2+ breast cancer have aggressive disease and poor prognoses. It is now apparent that many ERBB2+ tumors also express truncated ERBB2 receptors (t-ERBB2s), namely p110 and p95. Increased expression of t-ERBB2s by breast tumors correlates with increased nodal involvement, distant metastasis, and poor clinical outcome in patients. Because t-ERBB2s lack the epitope bound by trastuzumab, expression of high levels of these isoforms may designate patients who would be better treated with alternative anti-ERBB2 therapy such as lapatinib; unfortunately, there is currently no clinical method to distinguish full-length p185- versus t-ERBB2 in patient tumor samples. Materials and Methods: Recombinant forms of p185-, p110- and p95-ERBB2 were constructed using standard cloning techniques and expressed in human mammary epithelial cells (HMLE) via retroviral vector. The expression and subcellular localization of constructs were confirmed by western blot analysis and confocal microscopy. The ability of p185- and t-ERBB2 constructs to transform HMLE cells was evaluated using soft agar assays, and the effects on migration and invasion of these cells were investigated by transwell assays. Finally, the in vivo tumor formation by p185- vs. t-ERBB2 expressing cells was evaluated in immunodeficient mice. Additionally, a novel proximity-based antibody-capture method method to discern full-length versus t-ERBB2 in patient tumor samples was assessed (COPIA). Block tumors and fine-needle aspirates from patient tumor samples were used for quantifying total and phosphorylated ERBB2 receptors. Results and Discussion: Recombinant p185- and t-ERBB2 constructs were stably expressed in HMLE cells, and were correctly targeted to the cell membrane, as shown by confocal immunofluorescence microscopy and immunoblot. Expression of p110 t-ERBB2 increased migration and invasion of HMLE cells compared to p185 ERBB2 (P<0.0001), while p110, p95m and p185 ERBB2s were equally effective at enhancing anchorage-independent growth. In vivo, expression of p110 t-ERBB2 but not other isoforms led to increased tumor formation in mice compared to controls (P<0.005). No apparent phenotypes were elicited by expression of intracellular t-ERBB2 isoforms. Using COPIA testing, t-ERBB2 isoforms were detected in strongly ERBB2- positive tumors (16 of 31 samples, 52%) and were phosphorylated in 10 of 31 (32%). As expected, t-ERBB2s were not detected in ERBB2-negative tumor samples. Truncated ERBB2s, particularly p110, may be major pathogenic drivers in ERBB2+ cancers. These isoforms may accelerate disease progression by promoting invasion and metastasis, and likely mediate resistance to trastuzumab and other therapies. Thus, t-ERBB2s represent attractive novel targets for diagnosis and treatment of ERBB2+ breast cancers. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-06-03.