Abstract 596: eFT508, a potent and highly selective inhibitor of MNK1/2 regulates immune checkpoint and cytokine expression promoting anti-tumor immunity
Authors: Webster Kevin R. , Goel Vikas K. , Staunton Jocelyn , Stumpf Craig R. , Sharma Rajesh , Hung Ivy N. , Parker Gregory S. , Molter Jolene , Chiang Gary G. , Wegerski Christopher J. , Sperry Samuel , Huang Vera , Chen Joan , Thompson Peggy A. , Tran Chinh , Ernst Justin T. , Sprengeler Paul A. , Reich Siegfried H. 
Published: July 2017

Dysregulated translation of messenger RNA (mRNA) plays a role in the pathogenesis of multiple solid tumors and hematological malignancies. MNK1 and MNK2 integrate signals from several oncogenic and immune signaling pathways (including RAS, Toll-like receptors and T cell receptor) by phosphorylating eukaryotic initiation factor 4E (eIF4E) and other key effector proteins including hnRNPA1 and PSF. Phosphorylation of these RNA-binding proteins by MNK1 and MNK2 selectively regulates the stability and translation of a subset of cellular mRNA that control tumor/stromal cell signaling, the tumor microenvironment and immune cell function. eFT508 is a potent and highly selective inhibitor of both MNK1 and MNK2. Ribosome profiling has demonstrated that inhibition of MNK1 and MNK2 by eFT508 selectively regulates the translational efficiency and mRNA stability of a subset of genes that include inflammatory cytokines/chemokines, regulators of stress response, and effectors of anti-tumor immune response. Given the importance of MAPK signaling and translational control to immune cell activation and differentiation, the immunological effect of eFT508 was further evaluated in both normal human immune cells in vitro and immunocompetent syngeneic cancer models in vivo. eFT508 treatment of normal donor T cells has no deleterious effect on αCD3/αCD28 stimulated IL-2 production, T cell proliferation or T cell viability. However, eFT508 selectively down regulates the induction of IL-10 and specific immune checkpoint receptors, including PD-1 and LAG3. Further evaluation of the mechanism of translational regulation has shown LAG3 mRNA contains specific sequence elements in the 5’-untranslated region (UTR) that confer sensitivity to eFT508. In addition, IL-10 mRNA is destabilized upon treatment with eFT508 leading to significant inhibition of IL-10 production in activated T cells. Furthermore, eFT508 treatment results in upregulation of MHC class II molecules on tumor cells, macrophage and dendritic cells through an IL-10/MARCH1 dependent mechanism. The in vivo antitumor effect of eFT508 was assessed in the CT26 BALB/C syngeneic tumor model. CT26 mouse tumor cell proliferation and survival are insensitive to eFT508 in vitro. In vivo, daily oral treatment with 1 mg/kg eFT508 results in significant anti-tumor activity, modulation of tumor infiltrating lymphocytes and establishment of immune memory. In addition, combination of eFT508 with either anti-PD-1 or anti-PD-L1 monoclonal antibodies results in marked efficacy, significantly increasing the percentage of responder animals. eFT508 is currently under evaluation in two phase I/II clinical trials for patients with advanced solid tumors and patients with advanced lymphoma respectively. These findings support further clinical evaluation of eFT508 in combination with checkpoint blockade.

Citation Format: Kevin R. Webster, Vikas K. Goel, Jocelyn Staunton, Craig R. Stumpf, Rajesh Sharma, Ivy N. Hung, Gregory S. Parker, Jolene Molter, Gary G. Chiang, Christopher J. Wegerski, Samuel Sperry, Vera Huang, Joan Chen, Peggy A. Thompson, Chinh Tran, Justin T. Ernst, Paul A. Sprengeler, Siegfried H. Reich. eFT508, a potent and highly selective inhibitor of MNK1/2 regulates immune checkpoint and cytokine expression promoting anti-tumor immunity [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 596. doi:10.1158/1538-7445.AM2017-596