Abstract 1334: Chemotherapy regulated microRNA-125/HER2 pathway as a novel therapeutic target for trastuzumab-mediated cellular cytotoxicity in small-cell lung cancer

Abstract

Abstract Small-cell lung cancer (SCLC) accounts for 15% of all lung cancer cases and is a highly lethal disease. For the last several decades, the standard treatment for SCLC has been deadlocked, and new therapeutic strategies are urgently needed. Human epidermal growth factor receptor 2 (HER2) is a member of the HER family and has been reported to be overexpressed in 30% of SCLC cases with poor prognosis. However, the clinical relevance of HER2-targeted therapy for SCLC remains unclear. Here, we firstly identify that cytotoxic drugs induce significant HER2 overexpression through microRNA-125a (miR-125a) and miR-125b downregulation, which in turn act as a novel therapeutic target for trastuzumab-mediated cellular cytotoxicity in SCLC. In this study, we showed that treatment of the HER2-positive SCLC cells, SBC-3 and SBC-5, with cytotoxic drugs induced a significant upregulation of HER2. Cisplatin (CDDP) treatment of SCLC cells resulted in a significant downregulation of miR-125a and miR-125b. We confirmed that miR-125a and miR-125b bound to the 3′-untranslated regions of HER2 mRNA, and that downregulation of miR-125a and miR-125b resulted in upregulation of HER2 in SCLC cells, suggesting a relationship between cytotoxic drug exposure and miR-125/HER2 dysregulation. Furthermore, using a calcein assay we demonstrated a significant synergistic cytotoxic effect of CDDP and trastuzumab that was mediated via antibody-dependent cellular cytotoxicity. Finally, we clearly demonstrated the synergistic anti-tumor effect of these agents in an orthotopic lung cancer model in vivo. Our result offer a novel therapeutic strategy for HER2-positive SCLC by using trastuzumab combined with cytotoxic drugs. Citation Format: Shigehiro Yagishita, Yu Fujita, Yuichi Fujimoto, Fumiyuki Takahashi, Kazuhisa Takahashi, Tomohide Tamura, Fumiaki Koizumi. Chemotherapy regulated microRNA-125/HER2 pathway as a novel therapeutic target for trastuzumab-mediated cellular cytotoxicity in small-cell lung cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1334. doi:10.1158/1538-7445.AM2015-1334