Abstract 4833: Activation of ERBB2 signaling causes resistance to the EGFR-directed therapeutics antibody cetuximab

Abstract

Abstract <Background> The epidermal growth factor receptor directed antibody, cetuximab (Cmab), is an effective therapy for patients (pts) with colorectal cancer (CRC) particularly with KRAS and BRAF wild type. Treatment in all pts is limited eventually by the development of acquired resistance but little is known about the underlying mechanism. <Methods> We established 3 Cmab resistant cell lines HCC827CR, GEOCR and A431CR through the exposure to increasing concentration of Cmab. In order to determine why these cell lines were resistant to Cmab we performed genome wide copy number analyses and analysis of ERBB family ligands. We analyzed the growth of Cmab sensitive and resistant cells in vitro and in vivo. Furthermore, we obtained clinical specimens from colon cancer pts treated with Cmab based therapy. Specimens obtained prior to therapy and at the time of Cmab resistance were evaluated. <Result> Genome-wide copy number analysis detected the localized genomic amplification in HCC 827CR, which was identified as ERBB2 and confirmed using FISH. Amplification of ERBB2 was also detected in the GEO CR cells. ERBB2 inhibition, with either trastuzumab or lapatinib, restored the Cmab sensitivity in those cell lines. In drug sensitive cell lines, Cmab effectively inhibited growth and ERK1/2 signaling both of which were inhibited in presence of ERBB2 amplification. In contrast, despite detecting ERBB2 activation in the A431 CR cells we did not identify ERBB2 amplification. Instead we detected increased levels of the ERBB3 ligand heregulin. The disruption of ERBB2/ERBB3 herterodimerization using pertuzumab restored Cmab sensitivity in A431CR in vitro and in vivo. CRC patients with ERBB2 amplification (n=13) treated with Cmab based therapy survived significantly shorter than pts without ERBB2 amplification (n=220) (The median OS 89 vs 149 days, p=0.0013; log-rank test). We also identified evidence of ERBB2 amplification at the time of acquired drug resistance using either tumor biopsies or by analyzing serum HER2 extracellular domain (ECD). We further analyzed plasma heregulin from CRC patients and the concentrations ranged widely (Median, 1622 pg/ml; range 0-18,045 pg/ml). Pts who achieved response to Cmab therapy (n=16) had significantly lower heregulin concentration than pts without response (n=49) (Mean, 1,050 vs 3,601 pg/ml, p<0.001; unpaired t test). In addition we identified a significant increase in plasma heregulin levels obtained at the time of clinic cetuximab resistance compared to pre-treatment specimens (p=0.0313). <Conclusion> We identify activation of ERBB2 signaling, either through ERBB2 amplification or through heregulin upregulation, as a mechanism of both de novo and acquired cetuximab resistance. These results suggest that ERBB2 inhibitors, in combination with Cmab, may represent a rational therapeutic strategy in Cmab-resistant cancers. 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 4833. doi:1538-7445.AM2012-4833