Abstract A115: Mechanisms of resistance toward the FGFR inhibitor rogaratinib in preclinical urothelial bladder cancer models
Authors: Jerchel Isabel S , Kamburov Atanas , Zitzmann-Kolbe Sabine , Lesche Ralf , Walter Alexander , Mumberg Dominik , Politz Oliver , Gruenewald Sylvia 
Published: March 2020

Abstract
Introduction: Approximately one in three cases of urothelial bladder carcinoma (UBC) shows high expression of fibroblast growth factor receptor (FGFR) genes, predominantly of FGFR3 and FGFR1. The antitumor activity of the small molecule pan-FGFR-inhibitor rogaratinib (BAY1163877) has been demonstrated in preclinical models1, and the drug is currently being investigated in phase II and III clinical trials. However, clinical experience suggests the emergence of resistance with single-agent therapy. Here, we investigated the changes that occur with long-term FGFR inhibition and the development of resistance in preclinical UBC models, in order to identify possible combination strategies. Methods: We generated 13 resistant cell lines from the rogaratinib-sensitive cell lines JMSU1, RT112, RT4, and SW780, through continuous culture with various, increasing concentrations of rogaratinib. Transcriptomic and proteomic characterization was performed to identify potential therapeutic targets, of which a subset was evaluated using in vitro drug testing. We furthermore generated an in vivo resistant model by repeatedly transplanting JMSU1-derived xenografts. Results: Rogaratinib resistance developed reproducibly in vitro within several months and up to one year. We confirmed the lack of rogaratinib response in proliferation and viability assays. Transcriptomic analysis of resistant cell lines revealed changes in gene expression, with 300 to 2000 differentially expressed genes per sub-line (2-fold, p-adj. = 0.01). Hallmark gene sets such as MYC targets, epithelial-mesenchymal transition, or KRAS signaling were either negatively or positively correlated with resistance, but there was no single pathway change common to all cell lines. Genomic analysis found no mutations of the original driver FGFR genes and only few mutations in other receptor tyrosine kinase (RTK), MAPK, or PI3K signaling pathways. Proteomic analysis revealed activation of other RTKs in the rogaratinib-resistant models compared with the parental, rogaratinib-sensitive cells. These included EGFR, ErbB3, and MET, for which clinically approved inhibitors are available. We tested these as single-agents and in combination with rogaratinib in resistant cell lines to delineate potentially synergistic combinations. The JMSU1 in vivo resistance model confirmed the in vitro observations, where MET was upregulated upon resistance. The best anti-tumor efficacy was achieved with combined FGFR- and MET-inhibition, showing that FGFR signaling can remain a relevant oncogenic driver in addition to other RTKs activated as an escape mechanism. Conclusion: Continuous in vitro culture of cell lines with rogaratinib over several months led to resistance in all four evaluated models. Gene expression was considerably changed in these resistant cell lines, and proteomic analysis revealed activation of several RTKs. While the significance of many gene expression changes still remains to be determined, potent therapeutic targets were identified in several resistant cell lines, which point out opportunities for combination therapy. 1. Grunewald S, Politz O, Bender S, et al. Rogaratinib: A potent and selective pan-FGFR inhibitor with broad antitumor activity in FGFR-overexpressing preclinical cancer models. Int J Cancer. 2019.
Citation Format: Isabel S Jerchel, Atanas Kamburov, Sabine Zitzmann-Kolbe, Ralf Lesche, Alexander Walter, Dominik Mumberg, Oliver Politz, Sylvia Gruenewald. Mechanisms of resistance toward the FGFR inhibitor rogaratinib in preclinical urothelial bladder cancer models [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A115. doi:10.1158/1535-7163.TARG-19-A115