Abstract 4776: Antitumor activity of pan-HER inhibitors in HER2-positive gastric cancer

Abstract

Abstract Purpose: Molecularly targeted therapy has enabled outstanding advances in cancer treatment. Whereas various anti-HER2 drugs have been developed, trastuzumab is still the only anti-HER2 drug presently available for gastric cancer. Among HER2 targeting drug, afatinib and neratinib inhibit the activation of all HER family protein, and are called pan-HER inhibitors. In this study, we examined the effect of these pan-HER inhibitors to gastric cancer cells. Materials and Methods: We determined the molecular profiles of 12 gastric cancer cell lines. Protein level of HER2 and down-signal pathway molecules were analyzed by Western blotting, and copy number assay or gene expression assay were performed using qPCR. To detect HER2 mutation, we also performed direct-sequence of these cell lines. And next, we examined the antitumor effect of the pan-HER inhibitors afatinib and neratinib in those cell lines, in vitro and in vivo. In addition, we analyzed HER2 alteration in 123 primary gastric cancers resected from Japanese patients to clarify possible candidates with the potential to respond to these drugs. Results: HER2 was amplified in 5 out of 12 gastric cancer cell lines. Gene expression or protein level of HER2 were generally correlated with the copy number of HER2. HER2 mutation was found in one cell line, ECC10, at kinase domain (L755S). In the drug sensitivity analysis, both afatinib and neratinib showed an anti-tumor effect in all the HER2 amplified cell lines both in vitro and in vivo except MKN7 cell line. When the molecular profiles of the cells were compared based on the drug sensitivities, we found that cancer cells with lower mRNA expression levels of IGFBP7, a tumor suppressor gene by inhibiting the activation of IGF-1R, were less sensitive to pan-HER inhibitors. A combination therapy consisting of pan-HER inhibitors and an IGF-1R inhibitor, picropodophyllin, demonstrated a notable synergistic effect. Regarding HER2 alteration in 123 clinical samples, we found 19 cases of HER2 amplification and 3 cases of oncogenic mutations. Conclusion: Afatinib and neratinib are promising therapeutic options for the treatment of HER2-amplified gastric cancer. In addition to HER2 amplification, IGFBP7 might be a biomarker of sensitivity to these drugs, and IGF-1R-targeting therapy can overcome drug insensitiveness in HER2-amplified gastric cancer. Citation Format: Takahiro Yoshioka, Kazuhiko Shien, Yuta Takahashi, Eisuke Kurihara, Kei Namba, Yusuke Ogoshi, Hidejiro Torigoe, Hiroki Sato, Hiromasa Yamamoto, Junichi Soh, Toshiyoshi Fujiwara, Shinichi Toyooka. Antitumor activity of pan-HER inhibitors in HER2-positive gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4776.