Abstract LB-66: Quantitative assessment of HER/erbB receptor protein expression and activation status in FFPE tumor samples identifies an activated HER1 signature in squamous cell carcinomas of the head and neck

Abstract

Abstract The oncogenesis and maintenance of several solid tumor types appears dependent on HER1/erbB1 activation status through several mechanisms including gene mutations, gene amplification/overexpression, and ligand availability. However, it has been difficult to correlate HER1 protein levels or activation status in squamous cell carcinoma of the head and neck (SCCHN) to the 10-30% targeted-drug response rates due to the lack of robust, sensitive, and quantitative assays in formalin-fixed, paraffin embedded (FFPE) tumor tissues. Toward the goal of having improved predictive assays for anti-EGFR based therapy we used the novel VeraTagTM technology to develop sensitive and quantitative assays to measure the total HER1, HER2, and HER3 protein levels and the activated forms represented by HER1-HER1 homodimers, phosphorylated HER1, and HER1-HER2 heterodimers in SCCHN and other head and neck (H&N) FFPE tumor tissues. In addition, a VeraTag assay for the receptor tyrosine kinase c-Met, which may also contribute to poor SCCHN prognosis and to resistance to HER1 inhibitors, was used to quantitatively measure protein levels. Utilizing macrodissected samples, similar HER1 protein levels above isotype control background (ITC) were measured by VeraTag assay in >90% of both SCCHN (S/B median=27-fold; mean=34-fold) and other H&N tumors (S/B median=24-fold; mean=25-fold). In SCCHN samples, HER1 VeraTag protein measurements significantly correlated with HER1 protein as measured by IHC (Spearman's r =0.587, p=0.0083, n=19), HER1 DNA levels as measured by FISH (r =0.688, p=0.0016, n=19), and HER1 mRNA levels measured by qPCR (r =-0.649, p=0.0036, n=18). HER2 and HER3 VeraTag protein levels were generally low, with approximately half of the SCCHN tumors having below detectable levels. HER3 VeraTag protein levels correlated with HER3 mRNA (qPCR) levels (r =-0.574, p=0.016) whereas the HER2 protein and mRNA (qPCR) measurements did not significantly correlate. Active HER1 was notable in approximately 50% of SCCHN tumors as measured by a signal to background (S/B) >2- to 3-fold for HER1-HER1 homodimers, or HER1 phosphotyrosine (pY) (pY1173 and pan-pY), or HER1-HER2 heterodimers. Although the distribution of HER1 protein expression levels was similar between the SCCHN and other H&N tumors (unpaired t-test p=0.413); the SCCHN tumors had dramatically greater HER1 activation as seen with increased relative levels of HER1-HER1 homodimers (p=0.0055) and HER1pY1173 (p=0.0036). The SCCHN tumor set could be divided into several subgroups based on signatures characterized by HER1 VeraTag protein levels, activation profile, and c-Met protein levels. Two notable signatures include tumors having medium to high HER1 protein levels/active HER1 with co-expression of either relatively low or high c-Met levels, represented by 2/19 and 5/19 tumors, respectively. The association of these signatures with prognosis and targeted drug responses will be evaluated in future studies with clinical samples. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-66.