Abstract 1906: Mechanisms of resistance to EGFR tyrosine kinase inhibitors involving HER-family ligands and receptors

Abstract

Abstract Known mechanisms of acquired resistance to EGFR tyrosine kinase inhibitor (EGFR-TKI), including the second mutation of EGFR, T790M, MET amplification, and HGF overexpression, explain approximately 60% of cases, but the remaining mechanisms have not been clarified. To investigate novel mechanisms of acquired resistance to EGFR-TKI, we examined HER-family ligands and HER-family receptor status in non-small cell lung carcinoma (NSCLC) cell lines (n=13). Cell lines were divided into two groups with respect to EGFR-TKI sensitivity: highly sensitive (HCC827, PC-9, HCC2935, and HCC4006) and resistant (H1395, H1666, H596, H1437, A549, H226B, H1299, H460, H1792). We examined expression levels of eleven HER-family ligands_EGF, TGFβ, amphiregulin (AREG), betacellulin (BTC), HB-EGF, epigen (EPGN), epiregulin (EREG), and neuregulin (NRG) 1, NRG2, NRG3, and NRG4_in these cell lines. NRG2, NRG4, and EPGN were expressed at 39.5-, 31.4-, and 6.5-fold higher levels, respectively, in EGFR-TKI primary resistant NSCLC cell lines than in highly sensitive cell lines, whereas TGFA, EGF, and AREG were expressed at 0.22-, 0.3-, and 0.34-fold lower levels. Phosphorylation of EGFR was elevated in sensitive cell lines compared to resistant cell lines, but HER2-4 receptors did not evidence a difference in phsophorylation. These results suggest that the EGFR pathway is activated in sensitive cell lines, and HER2-4, which binds to EPGN, EREG, NRG2, and NRG4, might be activated in resistant cell lines. We prepared cell lines HCC827GR and HCC827ER, derived from HCC827, which acquired resistance to gefitinib or erlotinib, respectively. We analyzed HER-family ligands and receptors using these cell lines. Compared to parent cells, EPGN, EREG, HB-EGF, TGFA, NRG1, and AREG were up-regulated in HCC827GR. Phosphorylation status of EGFR, HER2, and HER3 was not altered, but that of HER4 was increased in HCC827GR. In HCC827ER, EGFR binding ligands AREG, BTC, and EGF were down-regulated, while phosphorylation of EGFR, HER2, and HRE3 was decreased. However, NRG2 was remarkably elevated and HER4 and its downstream STAT5 were phosphorylated. These results indicate that HER4 and its binding ligands may contribute to acquired resistance to EGFR-TKI. Considering these results, it is possible that the HER4-STAT5 pathway might be common to primary and acquired resistance to EGFR-TKI. We continue to investigate its significance. 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 1906. doi:1538-7445.AM2012-1906