Abstract 2989: BET inhibitors induce Rac1-dependent MNK and eIF4E phosphorylation in cancer cells

Patients with recurrent differentiated thyroid cancers (DTCs) have poor prognosis and suffer from multiple complications from progressive symptomatic disease. Here we show that eukaryotic translation initiation factor 4E (eIF4E), an oncogene that is overexpressed in aggressive thyroid cancers, is required for growth of DTC cells in collagen microenvironment. We show that inhibitors targeting bromodomain and extra-terminal domain (BET) family of proteins also decrease growth of DTC cells in the collagen microenvironment. Unexpectedly, we have found that BET inhibitors induce MNK and eIF4E phosphorylation in cancer cells. Mechanistically, BET inhibitors induce Rac1-mediated cytoskeletal changes and targeting Rac1 blocks these changes as well as MNK and eIF4E phosphorylation. Functionally, we show that MNK inhibitors potentiate the effects of BET inhibitors at suppressing cancer cell proliferation and limiting sphere-forming ability. Together, these results demonstrate crosstalk between BET proteins and the MNK-eIF4E pathway, suggesting that combination therapy with BET and MNK inhibitors has the potential for synergistic inhibition of cancer cells. Citation Format: Thao Pham, Brian T. Decant, Krishan Kumar, Meng Shang, Maria Matsangou, Kazumi Ebine, Hidayatullah G. Munshi. BET inhibitors induce Rac1-dependent MNK and eIF4E phosphorylation in cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2989.