Abstract 3627: Inhibition of HER family kinase signaling and tumor cell proliferation in non-EGFR and non-HER2 positive cell lines by lapatinib

Abstract

Abstract Deregulation of HER family receptor tyrosine kinases by gene amplification, mutation, protein overexpression or ligand activation promotes oncogenesis. Lapatinib is an oral, selective, potent, dual inhibitor of EGFR and HER2 kinases that is approved in combination with capecitabine for the treatment of patients with advanced or metastatic breast cancer whose tumors overexpress HER2 and who have received prior therapy including an anthracycline, a taxane and trastuzumab. We have identified a panel of tumor cell lines, including breast, colon and melanoma, with normal levels of expression of EGFR, HER2 and low to non-detectable levels of HER4 as determined by RT-PCR and western blotting that are sensitive to cell growth inhibition by lapatinib (IC50s = 90 to 540 nanomolar), but not by trastuzumab (IC50>100 micrograms/mL). High levels of HER3 determined by RT-PCR and western blot, phosphorylated HER3 determined by western blot, and at least one ligand of the HER family determined by RT-PCR are also detected in three cell lines, whereas no mutations of EGFR or HER2 are present. MDA-MB-175VIII, a breast cancer cell line, has a translocation and coamplification of the 8p12 and 11q13 regions and expresses a secreted fusion protein of neuregulin-1 (NRG1), which is a ligand of HER3. HCC2157, a breast cancer cell line, and CHL-1, a melanoma cell line, have high levels of neuregulin-2 (NRG2), another ligand of HER3, and NRG1 RNA, respectively. Sequencing of HER4 genomic DNA in CHL-1 revealed two mutations (2834G>T and 3248C>T) in exons 23 and 27. All three cell lines are also inhibited by an antibody directed against the HER2 dimerization domain. Lapatinib inhibited the phosphorylation of HER2 and HER3, and decreased AKT phosphorylation (Ser 473 and Thr 308) and cyclin D expression in the three cell lines. Small interfering RNA to HER2, HER3 or NRG1, but not EGFR, reduced cell proliferation of CHL-1 cells. NCI-H508, a colon cancer cell line, displayed phosphorylation of EGFR and HER2, but not phosphorylated HER3 and AKT, and had high levels of amphiregulin (AREG) RNA, an EGFR ligand. Lapatinib inhibited the phosphorylation of EGFR and HER2 and decreased ERK phosphorylation in NCI-H508. Small interfering RNA to EGFR or HER2, but not HER3, effectively inhibited cell proliferation of NCI-H508. These results demonstrate that lapatinib can inhibit EGFR and/or HER2 kinase activity and cell proliferation in non-EGFR or non-HER2 amplified or overexpressed tumor cell lines that express a HER ligand in an autocrine manner. Tumors from non-HER2 overexpressing patients who have benefited from lapatinib should be assessed for the expression of HER family kinases, their phosphorylation state and their ligands to determine whether these markers can be used to select patients for future studies. 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 3627.