Abstract B38: Trastuzumab-induced recruitment of Csk-homologous kinase (CHK) to ErbB2 receptor is associated with ErbB2-Y1248 phosphorylation and ErbB2 degradation to mediate cell growth inhibition

Abstract

Abstract Trastuzumab is a humanized recombinant monoclonal antibody directed against extracellular region of ErbB2 and used for the treatment of different ErbB2-positive cancers. Based on literature reports and our clinical data from trastuzumab neoadjuvant studies, increased ErbB2-Y1248 phosphorylation is associated with a better response to trastuzumab in patient samples. Also, in trastuzumab-sensitive cell lines (SKBR3 and BT474), increased basal level and trastuzumab-mediated increase in ErbB2-Y1248 phosphorylation was readily detectable compared to trastuzumab-resistant cell line model (JIMT1). The mechanisms of trastuzumab-induced ErbB2-Y1248 phosphorylation and the role of ErbB2-Y1248 phosphorylation in trastuzumab sensitivity/resistance are still incompletely understood. We demonstrate that trastuzumab activates ErbB2 kinase activity in trastuzumab-sensitive cells, which may further contribute to trastuzumab-mediated ErbB2-Y1248 phosphorylation. However, blocking ErbB1/ErbB2 kinase activity with Lapatinib, a small molecule tyrosine kinase inhibitor only partially reduced trastuzumab-mediated ErbB2-Y1248 phosphorylation. This led to the discovery of a previously unappreciated relationship between trastuzumab and Csk-homologous kinase (CHK), a non-receptor tyrosine kinase also known as MATK. We establish that trastuzumab treatment promotes interaction between ErbB2 and CHK in trastuzumab-sensitive but not in trastuzumab-resistant cells despite similar CHK expression levels in both types of cells. Mimicking trastuzumab, CHK overexpression also induces ErbB2-Y1248 phosphorylation, Akt downregulation and cell growth inhibition and further stimulated trastuzumab-mediated reduction in total ErbB2 levels in trastuzumab sensitive cells. Also, CHK overexpression combined with trastuzumab exerts an additive effect on cell growth inhibition in trastuzumab-sensitive but not in trastuzumab-resistant cells. Understanding of the molecular mechanisms of trastuzumab mediated ErbB2 phosphorylation changes may suggest novel therapeutic approaches in the treatment of trastuzumab resistant cancers. Disclaimer: The information presented in this article reflects the views of the authors and does not represent the policy of the U.S. Food and Drug Administration. Citation Format: Milos Dokmanovic, Yun Wu, Yi Shen, Jieqing Chen, Dianne S. Hirsch, Wen Jin Wu. Trastuzumab-induced recruitment of Csk-homologous kinase (CHK) to ErbB2 receptor is associated with ErbB2-Y1248 phosphorylation and ErbB2 degradation to mediate cell growth inhibition. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Drug Sensitivity and Resistance: Improving Cancer Therapy; Jun 18-21, 2014; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(4 Suppl): Abstract nr B38.