Sustained Inhibition of HER3 and EGFR Is Necessary to Induce Regression of HER2-Amplified Gastrointestinal Carcinomas

Abstract

Purpose: Preclinical studies in HER2-amplified gastrointestinal cancer models have shown that cotargeting HER2 with a monoclonal antibody and a small molecule is superior to monotherapy with either inhibitor, but the underlying cooperative mechanisms remain unexplored. We investigated the molecular underpinnings of this synergy to identify key vulnerabilities susceptible to alternative therapeutic opportunities.Experimental Design: The phosphorylation/activation of HER2, HER3, EGFR (HER receptors), and downstream transducers was evaluated in HER2-overexpressing colorectal and gastric cancer cell lines by Western blotting and/or multiplex phosphoproteomics. The in vivo outcome of antibody-mediated HER2 blockade by trastuzumab, reversible HER2 inhibition by lapatinib, and irreversible HER2 inhibition by afatinib was assessed in patient-derived tumorgrafts and cell-line xenografts by monitoring tumor growth curves and by using antibody-based proximity assays.Results: Trastuzumab monotherapy reduced HER3 phosphorylation, with minor consequences on downstream transducers. Lapatinib alone acutely inhibited all HER receptors and effectors but led to delayed rephosphorylation of HER3 and EGFR and partial restoration of ERK and AKT activity. When combined with lapatinib, trastuzumab prevented HER3/EGFR reactivation and caused prolonged inhibition of ERK/AKT. Afatinib alone was also very effective in counteracting the reinstatement of HER3, EGFR, and downstream signaling activation. In vivo, the combination of trastuzumab and lapatinib-or, importantly, monotherapy with afatinib-resulted in overt tumor shrinkage.Conclusions: Only prolonged inhibition of HER3 and EGFR, achievable by dual blockade with trastuzumab and lapatinib or irreversible HER2 inhibition by single-agent afatinib, led to regression of HER2-amplified gastrointestinal carcinomas.

Influence of the HER receptor ligand system on sensitivity to cetuximab and trastuzumab in gastric cancer cell lines

“…These findings are in line with results obtained in breast cancer cells, where sensitive cell lines showed enhanced expression of pHER2 (Y1248) upon trastuzumab therapy (Diermeier et al 2005; Dokmanovic et al 2014). A similar observation was reported for NCI-N87 gastric carcinoma cells, although another publication found no such effect (Leto et al 2015; Yamashita-Kashima et al 2011). …”

Interrogating open issues in cancer precision medicine with patient-derived xenografts

“…Through this effort, several genetic determinants of resistance to EGFR blockade were discovered, including amplifications or mutations in genes encoding druggable kinases 6,7,115,116 . Similarly, more dynamic features such as expression changes in pro-survival genes and the activation of compensatory feedback loops during treatment were identified as mechanisms of tumour adaptation to EGFR family 117,118 or MEK 119 inhibition in colorectal cancer. The flexibility of PDXs also enabled preclinical testing of drug combinations in models displaying some of these resistance traits, with a permutation capability that was clearly beyond the number of testable hypotheses in humans (FIG.…”

Role of ADAM10 in intestinal crypt homeostasis and tumorigenesis

“…Indeed, clinical trails have demonstrated that the combination of trastuzumab (anti-HER2) and lapatinib (HER2/EGFR kinase inhibitor) is beneficial in HER2+ KRAS wild type mCRC patients[127–129]. In breast cancer studies, it has been proposed that the effectiveness of combining trastuzumab and lapatinib treatments relies on the ability of trastuzumab to prevent phosphorylation of HER3, which occurs during prolonged lapatinib treatment due to compensatory HER3 transcriptional upregulation[127–129]. This occurs due to HER2 amplification permitting constitutive HER2 kinase activity and subsequent transactivation of other ErbB receptors particularly HER2/HER3 heterodimers.…”