A Novel Mer Tyrosine Kinase Inhibitor Mediates Increased Cell Killing In Combination With Fgfr Inhibition

Purpose of Study: Although therapies targeting recently identified oncogenic drivers of non-small cell lung cancer (NSCLC) are in clinical use, a significant proportion of patients still lack a molecularly-targeted therapeutic option. Therefore, there is a continued need for development of new therapeutic strategies. We recently demonstrated oncogenic roles for Mer receptor tyrosine kinase in NSCLC. More specifically, we showed aberrant expression of Mer in approximately 70% of NSCLC patient samples compared to normal lung. Additionally, shRNA-mediated Mer inhibition resulted in increased cell death, decreased colony formation in clonogenic assays, increased chemosensitivity, and decreased tumorigenesis in murine xenografts. These data validate Mer as a potential therapeutic target in NSCLC. Fibroblast growth factor receptors (FGFR) are another class of tyrosine kinases that are aberrantly expressed and function to promote tumorigenesis in NSCLC. FGFR inhibition has been validated as a therapeutic strategy in preclinical NSCLC models and several FGFR inhibitors are currently in clinical development for treatment of NSCLC. Although Mer can signal through both the MEK/ERK and PI3K/AKT pathways, in NSCLC Mer signals mainly through PI3K/AKT. Because Mer and FGFR signal primarily through complementary pathways that mediate survival and proliferation (PI3K/AKT and MEK/ERK, respectively), we hypothesized that dual inhibition of FGFR and Mer may provide a therapeutic advantage relative to inhibition of either kinase alone. In this study we investigated the interaction between a novel Mer-selective small molecule tyrosine kinase inhibitor (TKI) and AZD-4547, an FGFR TKI, in NSCLC cell lines. Methods Used: Colo699 (Mer+, FGFR+) and H226 (Mer+, FGFR+) NSCLC cells were cultured for 14 days in soft agar in the presence of Mer TKI and/or AZD-4547, alone or in combination, and colonies were stained and counted. Changes in the activity of downstream signaling pathways, including PI3K/AKT, MEK/ERK, and STAT proteins were evaluated by immunoblotting. Results and Conclusions: In the soft agar assay, Colo699 and H226 colony formation was inhibited in the presence of Mer TKI and AZD-4547, both as single agents and in combination. Importantly, concurrent treatment with Mer TKI and AZD-4547 resulted in a greater decrease in colony-formation relative to either single agent. Immunoblotting revealed increased inhibition of pro-survival signaling in cells treated with both inhibitors relative to the single agents. Taken together, these data suggest that combination therapies targeting Mer kinase and FGFR may be effective for treatment of NSCLC and indicate biochemical mechanisms by which the combination therapy may mediate increased anti-tumor activity. Citation Format: Timothy P. Newton, Christopher T. Cummings, Gregory D. Kirkpatrick, Trista K. Hinz, Deborah DeRyckere, Weihe Zhang, Xiaodong Wang, Stephen Frye, H. Shelton Earp, Lynn Heasley, Douglas K. Graham. A novel Mer tyrosine kinase inhibitor mediates increased cell killing in combination with FGFR inhibition. [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 1736. doi:10.1158/1538-7445.AM2014-1736