Abstract 1742: Inhibition of Mer tyrosine kinase with a novel small molecule inhibitor is efficacious in pre-clinical models of non-small cell lung cancer
Authors: Cummings Christopher T. , Davies Kurtis D. , Carrico Jacqueline , DeRyckere Deborah , Zhang Weihe , Wang Xiaodong , Frye Stephen , Earp H. Shelton , Graham Douglas K. 
Published: May 2015

Abstract
Background: Mer tyrosine kinase is frequently overexpressed and activated in non-small cell lung cancer (NSCLC). In addition, genetic inhibition of Mer reduces NSCLC cell growth in vitro and tumor xenograft growth in vivo. In this study, we examined anti-tumor effects mediated by a first-in-class Mer-selective small molecule tyrosine kinase inhibitor (TKI) in pre-clinical models of NSCLC.
Methods: The effects of Mer TKI treatment on activation of Mer and related members of the TAM-family of kinases, Axl and Tyro3, and effects on downstream proliferative and pro-survival signaling pathways were analyzed by immunoblot. In addition, Mer TKI-mediated anti-tumor activity was determined in a panel of NSCLC cell lines using soft-agar and clonogenic assays. Cells were stained with YoPro-1-iodide and propidium iodide dyes and induction of apoptosis was determined using flow cytometry. Finally, a subcutaneous murine xenograft model was employed to determine therapeutic effects in vivo.
Results: The Mer TKI blocked Mer autophosphorylation in numerous cell lines at sub-micromolar concentrations and was highly selective for Mer over Axl and Tyro3. Treatment also inhibited downstream pro-survival signaling through the ERK1/2 and AKT pathways, which resulted in induction of apoptosis. Additionally, treatment reduced colony-forming potential in soft-agar and clonogenic assays by 85% to 99% in a large panel of cell lines. Sensitivity to the Mer TKI was independent of driver oncogene status, as cell lines positive for EGFR mutations, KRAS mutations, and gene fusions all responded to treatment. Interestingly, RNAi mediated knock-down of Axl enhanced sensitivity to Mer TKI treatment in biochemical and functional assays. Finally, in animals treatment decreased tumor progression resulting in a significant decrease in tumor volume.
Conclusions: This Mer TKI is a novel and potent small molecule inhibitor that is selective for Mer over other TAM family kinases in cell-based assays. Treatment with this compound resulted in decreased downstream pro-oncogenic signaling, increased apoptosis, and decreased colony-forming potential in NSCLC cell lines. In addition, treatment was therapeutically effective in murine xenografts. Taken together, these data indicate that Mer inhibition may be an effective strategy for treatment of lung cancer. Sensitivity to the Mer TKI did not depend on driver oncogene status. Development of Mer TKIs for clinical application may therefore provide a molecularly-targeted treatment option for patients without known oncogenic mutations. In addition, Axl inhibition sensitized NSCLC cells to treatment with Mer TKI, suggesting a functional and/or physical interaction between Mer and Axl. In summary, the data presented here validate this Mer TKI as a potential treatment for NSCLC and provide critical data to support its continued development toward clinical application.
Citation Format: Christopher T. Cummings, Kurtis D. Davies, Jacqueline Carrico, Deborah DeRyckere, Weihe Zhang, Xiaodong Wang, Stephen Frye, H. Shelton Earp, Douglas K. Graham. Inhibition of Mer tyrosine kinase with a novel small molecule inhibitor is efficacious in pre-clinical models of non-small cell lung cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1742. doi:10.1158/1538-7445.AM2014-1742