Cancer Biology and Signal Transduction ERK Signal Suppression and Sensitivity to CH5183284/Debio 1347, a Selective FGFR Inhibitor

Drugs that target specific gene alterations have proven beneficial in the treatment of cancer. Because cancer cells have multiple resistance mechanisms, it is important to understand the downstream pathways of the target genes and monitor the pharmacodynamic markers associated with therapeutic efficacy. We performed a transcriptome analysis to characterize the response of various cancer cell lines to a selective fibroblast growth factor receptor (FGFR) inhibitor (CH5183284/Debio 1347), a mitogen-activated protein kinase kinase (MEK) inhibitor, or a phosphoinositide 3-kinase (PI3K) inhibitor. FGFR and MEK inhibition produced similar expression patterns, and the extracellular signal–regulated kinase (ERK) gene signature was altered in several FGFR inhibitor–sensitive cell lines. Consistent with these findings, CH5183284/Debio 1347 suppressed phospho-ERK in every tested FGFR inhibitor–sensitive cell line. Because the mitogen-activated protein kinase (MAPK) pathway functions downstream of FGFR, we searched for a pharmacodynamic marker of FGFR inhibitor efficacy in a collection of cell lines with the ERK signature and identified dual-specificity phosphatase 6 (DUSP6) as a candidate marker. Although a MEK inhibitor suppressed the MAPK pathway, most FGFR inhibitor–sensitive cell lines are insensitive to MEK inhibitors and we found potent feedback activation of several pathways via FGFR. We therefore suggest that FGFR inhibitors exert their effect by suppressing ERK signaling without feedback activation. In addition, DUSP6 may be a pharmacodynamic marker of FGFR inhibitor efficacy in FGFR-addicted cancers.Mol Cancer Ther; 14(12); 2831–9. 2015 AACR. Introduction Several tyrosine kinase-targeting agents have recently been developed. Each of these agents has demonstrable efficacy when used in patient cohorts that are stratified based on the genetic status of their respective molecular targets. The fibroblast growth factor receptors (FGFR) are tyrosine kinases that are constitutively activated in a subset of tumors by genetic alterations such as gene amplification, point mutation, or chromosomal translocation/rearrangement (1, 2). Genetic alterations of FGFR may also be predictive indicators of patient response to FGFR inhibitors (2, 3). For instance, dovitinib, a multitargeted kinase inhibitor that inhibits FGFRs, produced three unconfirmed partial responses in breast cancer harboring FGFR1 gene amplification (4). Although genetic alterations could predict drug efficacy, acquired genetic alterations confer resistance to molecular-targeted drugs. Acquired mutations in target genes or downstream components are major mechanisms of resistance (5–13). Although acquired FGFR mutations have not yet been identified in patients, several FGFR mutations that confer resistance to FGFR inhibitors have been reported (7, 14). Because cancer cells continue to utilize the pathway to which they are originally addicted, they acquire some genetic alterations to reactivate the pathway. Therefore, monitoring of changes in the pathways utilized by cancer cells could be used to predict the efficacy of an inhibitor in tumors. The FGFR family consists of FGFR1, FGFR2, FGFR3, andFGFR4, each of which is bound by a subset of 22 fibroblast growth factor (FGF) ligands. FGFRs are activatedby ligand-dependent or ligandindependent dimerization that leads to intermolecular phosphorylation. FGFR substrate 2 (FRS2) is a key adaptor protein that is phosphorylated by FGFR. Phosphorylated FRS2 recruits several other adaptor proteins and activates the mitogen-associated protein kinase (MAPK) or PI3K/AKT pathways (1). However, the pathway associated with effective FGFR suppression in FGFRaddicted cancers has not yet been identified. Gaining an understanding of the FGFR pathway by studying its function in the presence of FGFR inhibitors will enable identification of candidate pathways utilized by FGFR-addicted cancers and the pharmacodynamic markers of these pathways. In a previous study, we analyzed the signaling pathway of an FGFR fusion kinases, FGFR3-BAIAP2L1 (15). A Rat-2 cell line stably expressing FGFR3-BAIAP2L1 exhibited potent tumorigenic activity. Gene expression analysis revealed strong upregulation of genes downstreamof theMAPKpathway, and upregulation of the MAPKpathwaywas validated byWestern blotting; in contrast, the PI3K/AKT pathwaywas not activated by FGFR3-BAIAP2L1. Therefore, we suggested that MAPK pathway activation is essential to Research Division, Chugai Pharmaceutical Co., Ltd., Kamakura, Kanagawa, Japan. Note: Supplementary data for this article are available at Molecular Cancer Therapeutics Online (http://mct.aacrjournals.org/). Corresponding Author: Yoshito Nakanishi, Research Division, Chugai Pharmaceutical Co. Ltd., 200 Kajiwara, Kamakura, Kanagawa 247-8530, Japan. Phone: 81-467-47-6262; Fax: 81-467-46-5320; E-mail: [email protected] doi: 10.1158/1535-7163.MCT-15-0497 2015 American Association for Cancer Research. Molecular Cancer Therapeutics www.aacrjournals.org 2831 on April 20, 2017. © 2015 American Association for Cancer Research. mct.aacrjournals.org Downloaded from Published OnlineFirst October 5, 2015; DOI: 10.1158/1535-7163.MCT-15-0497