Abstract 335: Efficacy of FGFR inhibitors and combination therapies for acquired resistance in FGFR2-fusion cholangiocarcinoma

Background. The fibroblast growth factor receptor(FGFR) signaling pathway is aberrantly activated in approximately 20% of cases of cholangiocarcinoma through various genomic alterations including gene fusions, point mutations, and copy number amplifications. Currently, several FGFR kinase inhibitors are being assessed in clinical trials for patients with FGFR-altered cholangiocarcinoma. Despite evidence of initial responses and disease control, virtually all tumors eventually develop drug resistance. Overcoming acquired drug resistance to FGFR inhibitors has not been comprehensively studied. Methods. Apatient with metastatic cholangiocarcinoma and an activating FGFR2-KIAA1598fusion was enrolled on a Phase 2 clinical trial for the oral FGFR inhibitor, BGJ398. BGJ398 treatment was initially effective with radiographic and tumor marker response; however, after eight months of BGJ398 therapy, the patient developed disease progression. Sequencing of a post-progression liver biopsy revealed a novel secondary mutation (E566A) in the FGFR2 kinase domain, which was absent in the pre-treatment biopsy suggesting that this mutation may be responsible for the resistance to BGJ398. To confirm this, we conducted in vitrostudies to characterize the sensitivity of the FGFR2 secondary mutation to FGFR inhibitors. Results and Conclusions.In vitrocharacterization of the fusion and putative resistance mutationdemonstrated that FGFR2-KIAA1598 WT cells were sensitive to BGJ398 with (IC50value of 10.95 nM) whereas the FGFR2-KIAA1598 E566A cells were resistant (IC50values of 422.4 nM). We investigated additional selective (AZD4547 and JNJ42756493), non-selective (dovtinib and ponatinib), and irreversible (TAS120) FGFR inhibitors. FGFR2-KIAA1598 WT cells were sensitive to AZD4547, JNJ42756493, and TAS120, whereas FGFR2-KIAA1598 E566A cells were resistant to these inhibitors. Interestingly, neither the FGFR2-KIAA1598 WT cells nor the FGFR2-KIAA1598 E566A cells were sensitive to dovitinib, a nonspecific tyrosine kinase inhibitor. Lastly, both populations of cells were equally sensitive to ponatinib, a non-selective FGFR kinase inhibitor. Proteomic analysis by reverse phase protein array (RPPA) revealed upregulation of the mTOR/PI3K/AKT pathway in fusion cells compared to empty controls (FDR: 0.00618), and this expression was further potentiated in FGFR2-KIAA1598 E566A (FDR: 1.96e-19). Furthermore, combination studies with the above FGFR inhibitors and the mTOR inhibitor, INK128, yielded synergistic antitumor effects suggesting that combination therapy may be able to overcome resistance to FGFR inhibitors. Significance. In conclusion, further elucidation of the mechanisms driving resistance to FGFR inhibitors will support the development of next generation FGFR inhibitors as well as combination therapeutic strategies. Citation Format: MelanieA. Krook, Alexandria M. Lenyo, Maxwell J. Wilberding, Hannah D. Barker, Mikayla Dantuono, Hui-Zi Chen, Julie W. Reeser, Michele R. Wing, Jharna Miya, Eric Samorodnitsky, Amy M. Smith, Thuy Dao, Dorrelyn M. Martin, Kristin Dittmar, Kristen K. Ciombor, John L. Hays, Aharon G. Freud, Sameek Roychowdhury. Efficacy of FGFR inhibitors and combination therapies for acquired resistance in FGFR2-fusion cholangiocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 335.