Abstract A160: The FGFR axis is a potential radiosensitization target
Authors: Oike Takahiro , Horigome Eisuke , Adachi Akiko , Darwis Narisa Dewi Maulany , Shibata Atsushi , Ohno Tatsuya 
Published: December 2023

Abstract
Background: Establishing methods that sensitize cancers to photons is important for improving the treatment outcome of radiotherapy. Although sequencing has been widely used to identify druggable mutations in various cancers, this strategy have not been used extensively to identify new targets for radiotherapy sensitization. Thus, we performed clinical sequencing of radiotherapy-treated patient samples and investigated whether inhibition of the identified candidate targets resulted in radiosensitization in vitro and in vivo.
Material and Methods: Ninety-eight patients with newly diagnosed and pathologically confirmed cervical cancer who had been treated with definitive radiotherapy were analyzed. DNA was extracted from formalin fixed and paraffin embedded pre-treatment tumor biopsy specimens. The exons of 409 cancer-related genes were sequenced using a next generation sequencer. Identified mutations were analyzed for correlations with clinical outcome. The radiosensitization induced by inhibition of the candidate target was investigated in in vitro clonogenic assays and nude mouse xenograft models using radioresistant cancer cell lines and small molecule inhibitors. The in vitro sensitizer enhancement ratio (SER) was calculated as the ratio of radiation dose required to reduce clonogenic cell survival by 50% without drug to that with drug.
Results: Recurrent mutations were identified in PIK3CA (35.7%), ARID1A (25.5%), NOTCH1 (19.4%), FGFR3 (16.3%), FBXW7 (19.4%), TP53 (13.3%), EP300 (12.2%), and FGFR4 (10.2%). The prevalence of mutations in FGFR family genes combined (24.5%) was almost as high as that for well-studied PIK3CA and ARID1A. Fifty-five percent (21/38) of the identified FGFR mutations were located in the tyrosine kinase domain. Five-year progression-free survival (PFS) rates for FGFR mutation-positive patients (n = 24) were significantly worse than those for FGFR mutation-negative patients (n = 74) (43.9% vs. 68.5%). Multivariate analysis identified FGFR mutations as significant predictors of worse 5 year PFS, independent of clinicopathological variables. To investigate whether the FGFR axis can be targeted by drugs to increase radiosensitization, the radiosensitizing effect of a human-administrable selective pan-FGFR inhibitor LY2874455 was investigated. LY2874455 (at 100 nM) showed a potent in vitro radiosensitizing effect (SER: 1.62, 1.53, and 1.31 for A549, H1299, and H1703 cells, respectively). In A549 xenograft models, the combination of X-rays (10 Gy on day 1) and LY2874455 (3 mg/kg body weight, once daily, on Day 1–7) led to significantly greater suppression of tumor growth than either treatment with X-rays or LY2874455 alone, with no evidence of toxicities. LY2874455 treatment inhibited ERK signaling, the main target of the FGFR axis, both in vitro and in vivo.
Conclusion: These data indicate that targeting the FGFR axis with LY2874455 could potentially be used to sensitize cancers to radiotherapy, which warrants clinical validation.
Citation Format: Takahiro Oike, Eisuke Horigome, Akiko Adachi, Narisa Dewi Maulany Darwis, Atsushi Shibata, Tatsuya Ohno. The FGFR axis is a potential radiosensitization target [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A160.