Abstract 4567: Multiplex assay in FFPE tissues to simultaneously quantify the human EGF receptor (HER1-4) family proteins

Abstract

Abstract The human EGF receptor family (HER's) consists of two clinically validated drug targets (EGFR (HER1) and HER2), and two receptors (HER3 and HER4) which are the subject of intensive preclinical and early clinical investigation. Although drugs inhibiting both EGFR and HER2 show significant antitumor activity in the clinic, the acquisition of resistance is a hallmark of these and other targeted therapies. In the case of both targets, one of the emerging resistance mechanisms is the co-expression of other members of the EGFR superfamily. It was recently shown that HER2 co-expression mediates resistance in EGFR inhibitor (cetuximab) treated head and neck cancer (Sci Transl Med 7(3)99). Similarly, much attention has been paid to HER3 both as a bona fide drug target as well as a resistance mechanism (Oncogene 27, 3944). Finally, HER4, though less well studied may play a role in drug response (Breast Cancer Research 11:R50). We have previously build HER1 and HER2 specific SRM assays. HER3 is usually expressed at much lower levels than EGFR and HER2 (often <10%). Yet, receptor crosstalk and heterodimerization can allow even very low levels of HER3 to exert a large impact on drug response. According to one report (Cancer Epidemiol Biomarkers Prev. 19(4):982), IHC analysis of HER3 may be inadequate to properly quantitate HER3 expression in FFPE tumor tissues. This antibody inadequacy may be a result of high sequence homology/identity between HER3 and other HER family members. Due to the critical need to accurately quantitate this receptor, we have used a mass spectrometric approach to develop a specific and quantitative SRM assay for HER3 from FFPE tumor tissue. These preclinical studies are being extended by assessing the expression levels of the complete HER family in two cohorts of clinical tumor tissue which had been treated with HER family antagonists. First, we measured HER3 expression in a set of neoadjuvant gefitinib treated NSCLC tumors. In this cohort, 12/15 tumor showed low but measurable levels of HER3 expression, ranging from 50-100 amol/ug tumor tissue. In a second tissue set, we measured HER3 expression in a cohort of advanced (Stage III-IV) breast cancer tissues which had undergone post resection adjuvant treatment with trastuzumab. These breast cancer samples demonstrated a higher level of expression of HER3, ranging from 50 - 250amol/ug tumor tissue, and 15/18 tumors were HER3 positive. In both studies, the relationship between HER family expression and response to either gefitinib or trastuzumab is currently under study. Analysis of HER4 in these cohorts is ongoing. It is critically important to understand mechanisms of resistance in patients undergoing targeted therapies, and Liquid Tissue-SRM promises to be a platform which can deliver extremely high sensitivity, absolute specificity as well as multiplexing capabilities to assess the four HER family targets in unison. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4567. doi:1538-7445.AM2012-4567