Abstract 5933: Biochemical characterization of FGFR2-PPHLN1 and BCR-FGFR1, drivers of epithelial and hematological malignancies

Fibroblast growth factor receptors (FGFRs) are part of the receptor tyrosine kinase (RTK) family and are essential in the activation of various downstream signaling pathways, which are necessary for cell differentiation and proliferation. However, mutation and translocation of FGFRs leads to aberrant activation of signaling, which often results in cancer. This work focuses on the FGFR2-PPHLN1 fusion protein, a driver of intrahepatic cholangiocarcinoma (ICC), and the BCR-FGFR1 fusion protein, a driver of stem cell leukemia/lymphoma (SCLL). Both FGFR2-PPHLN1 and BCR-FGFR1 are poorly characterized, resulting in few therapies and clinical advancements for patients positive for these oncogene-driven neoplasms. Here, we aim to characterize these two FGFR fusion proteins, and analyze therapeutic options to treat these malignancies. Both FGFR2-PPHLN1 and BCR-FGFR1 contain a coiled-coil dimerization domain fused to a constitutively activated kinase provided by either FGFR2 or FGFR1, respectively. This work shows the reliance of these FGFR fusion proteins on the tyrosine kinase activity of the respective FGFR, as kinase dead mutants were not biologically active. Additionally both FGFR2-PPHLN1 and BCR-FGFR1 expressing cells exhibited an over activation of the RAS/MAPK and JAK/STAT pathways, indicating the importance of these pathways in FGFR1-PPHLN1 driven ICC, and BCR-FGFR1 driven SCLL, respectively. Transformed cells expressing FGFR2-PPHLN1 are sensitive to FGFR inhibitor BGJ398. However, this sensitivity is abolished when a kinase activating mutation is introduced with FGFR2(N549K)-PPHLN1. Residue N549 in the FGFR2 kinase domain functions as part of a molecular brake; mutation of this residue disrupts the auto-inhibitory network of hydrogen bonds, leading to increased kinase activation. The loss in sensitivity to BJG398 treatment for cells expressing FGFR2(N549K)-PPHLN1 indicates that BGJ398 treatment alone may be ineffective once secondary mutations are established in the kinase domain. Preliminary data suggests that transformed cells expressing either FGFR2-PPHLN1, or kinase activated FGFR2(N549K)-PPHLN1, may be sensitive to treatment with FGFR inhibitor TAS-120, suggesting that TAS-120 treatment could be beneficial for patients with FGFR2-PPHLN1 driven ICC. Furthermore, we establish BCR-FGFR1 as a client of the Hsp90 chaperone complex. Transformed cells expressing BCR-FGFR1 are sensitive to the Hsp90 inhibitor, Ganetespib, and also respond to combined treatment with Ganetespib and FGFR inhibitor BGJ398, suggesting novel clinical treatment options for patients positive for this fusion. Collectively, we show that the tyrosine kinase activity provided by FGFR2 or FGFR1, respectively is required for the biological activity of these fusion proteins, and we establish novel treatment options for patients with FGFR2-PPHLN1 or BCR-FGFR1 driven malignancies. Citation Format: Malalage Nicole Peiris, Fangda Li, April N. Meyer, Dalida Warda, Daniel J. Donoghue. Biochemical characterization of FGFR2-PPHLN1 and BCR-FGFR1, drivers of epithelial and hematological malignancies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5933.