Abstract 1736: Targeting Hsp90-Cdc37 complex overcomes drug resistance in glioma cells harboring FGFR3-TACC3 fusion gene

Abstract

Abstract Glioblastoma is one of the most lethal malignancies with the poorest prognosis among tumors of the central nervous system. Fusion genes are common chromosomal aberrations in many cancers that may give rise to an in-frame fusion protein with oncogenic function. These fusion genes can be used as prognostic markers as well as drug targets in clinical practice. The FGFR3-TACC3 (F3T3) fusion gene was discovered in glioblastoma, with an occurrence rate of up to 8.3% and leading to uncontrolled proliferation and chromosomal instability. Our studies have shown that glioblastoma cells harboring the F3T3 are resistant to the frontline glioblastoma drug Temozolomide (TMZ). Using the Comet assay, we show that TMZ-mediated DNA damage is repaired more rapidly in cells harboring the F3T3 compared to control. Our studies on the mechanism of this drug resistance show that the F3T3 confers an aberrant activation of FGFR and ERK pathways when treated with TMZ. To further explore druggable target(s) to overcome resistance caused by F3T3, we immunoprecipitated (IP) the proteins that interact with F3T3 in U251 glioblastoma cells overexpressing the F3T3 or wildtype FGFR3, followed by LC-MS/MS analyses. Our quantitative proteomic analysis revealed interactions of the F3T3 fusion protein with Hsp90α and Cdc37 proteins. These interactions were further validated by reciprocal IPs followed by Western blotting. Activation of many kinases, such as FGFRs, depends on their interaction with the Hsp90 molecular chaperone system. Hsp90 recruitment is mediated by the co-chaperone adaptor protein Cdc37, which simultaneously binds to both the kinase and Hsp90. To test inhibition of F3T3 association with the Hsp90-Cdc37 complex, we treated U251 cells constitutively expressing F3T3 with the Hsp90 inhibitor Onalespib. We show that Onalespib treatment at 26 nM significantly suppresses the proliferation of F3T3 expressing U251 cells in comparison to micromolar levels of the pan-FGFR inhibitor BGJ398 and PD173074. Our results provide evidence that the F3T3 fusion gene contributes to drug resistance via multiple chemo-resistance pathways. Importantly, our findings establish that F3T3 is an Hsp90 client that shows strong addiction to the Hsp90-Cdc37 complex for cell growth and suggests a novel strategy for targeting F3T3 fusion gene in glioma. Citation Format: Tao Li, Farideh Mehraein-Ghomi, Sanjeev V. Namjoshi, Lynette M. Phillips, Elizabeth A. Ballard, Mary E. Forbes, ping-Chieh Chou, Xuejun Yang, Wei Zhang. Targeting Hsp90-Cdc37 complex overcomes drug resistance in glioma cells harboring FGFR3-TACC3 fusion gene [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 1736.