Abstract 2091: PRN1371, an irreversible, covalent inhibitor of FGFR1-4 exhibits sustained pathway inhibition in cancer cell lines

Introduction: Multiple human cancers harbor alterations in FGFRs that drive tumor growth, including mutations, translocations and amplifications. PRN1371 is an irreversible, covalent FGFR1-4 inhibitor that exhibits highly selective and sustained inhibition of FGFR which extends well beyond circulating drug concentrations in preclinical models. The duration of inhibition of the FGFR signaling pathway is dependent on protein turnover of FGFR, which may vary depending on the type of FGFR alteration. Thus, we set out to investigate whether the duration of target inhibition differs across cancer cell lines of various lineages harboring different FGFR alterations, including fusions and mutations. Furthermore, as FGFR inhibitors exhibit hyperphosphatemia via on-target pharmacology, we also investigated the duration of target inhibition in primary renal epithelial cells which are wild-type for FGFR. Materials and Methods: Cancer cell lines from several lineages harboring different FGFR alterations were treated with increasing concentrations of PRN1371 in vitro for 1 hour, before washing out the compound. Cells were harvested at various time-points post-washout, protein lysates were generated and assessed for modulation of the downstream signaling pathway by western blot analysis. Results: Dose-dependent inhibition of phospho-ERK was observed in the cancer cell lines tested in response to compound treatment for 1 hour in vitro. Dose dependent partial or full rebound of phospho-ERK back to baseline levels were detected in cancer cell lines after a prolonged period post-washout. In contrast, full rebound of phospho-ERK was observed at 1 hour post washout in response to a non-covalent inhibitor. Studies are on-going to assess duration of pathway inhibition in the primary renal proximal epithelial cells. Conclusions: PRN1371 is a potent, highly selective irreversible inhibitor exhibiting sustained inhibition of FGFR signaling across cancer cell lines harboring different FGFR alterations. The duration of inhibition of the downstream signaling was comparable across cancer cell lines harboring different FGFR alterations, including mutations, fusions and amplification of FGFR and was prolonged when compared to a non-covalent inhibitor. A Phase 1 clinical trial of PRN1371 for the treatment of solid tumors harboring FGFR alterations is ongoing (NCT02608125). Citation Format: Eleni Venetsanakos, Yan Xing, Natalie Loewenstein, J. Michael Bradshaw, Dane Karr, Jacob LaStant, Philip Nunn, Jin Shu, Abha Bommireddi, Jens Oliver Funk, David M. Goldstein, Stefani Wolff, Ken A. Brameld, Steven G. Gourlay. PRN1371, an irreversible, covalent inhibitor of FGFR1-4 exhibits sustained pathway inhibition in cancer cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2091. doi:10.1158/1538-7445.AM2017-2091