The translation initiation factor eIF4E is an oncogene that is commonly overexpressed in primary breast cancers and metastases. In this article, we report that a pharmacologic inhibitor of eIF4E function, ribavirin, safely and potently suppresses breast tumor formation. Ribavirin administration blocked the growth of primary breast tumors in several murine models and reduced the development of lung metastases in an invasive model. Mechanistically, eIF4E silencing or blockade reduced the invasiveness and metastatic capability of breast cancer cells in a manner associated with decreased activity of matrix metalloproteinase (MMP)-3 and MMP-9. Furthermore, eIF4E silencing or ribavirin treatment suppressed features of epithelial-to-mesenchymal transition, a process crucial for metastasis. Our findings offer a preclinical rationale to explore broadening the clinical evaluation of ribavirin, currently being tested in patients with eIF4E-overexpressing leukemia, as a strategy to treat solid tumors such as metastatic breast cancer. Cancer Res; 75(6); 1102-12. Ó2015 AACR.

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The trimeric GatCAB aminoacyl-tRNA amidotransferases catalyze the amidation of Asp-tRNAAsn and/or Glu-tRNAGln to Asn-tRNAAsn and/or Gln-tRNAGln, respectively, in bacteria and archaea lacking an asparaginyl-tRNA synthetase and/or a glutaminyl-tRNA synthetase. The two misacylated tRNA substrates of these amidotransferases are formed by the action of nondiscriminating aspartyl-tRNA synthetases and glutamyl-tRNA synthetases. We report here that the presence of a physiological concentration of a nondiscriminating aspartyl-tRNA synthetase in the transamidation assay decreases the Km of GatCAB for Asp-tRNAAsn. These conditions, which were practical for the testing of potential inhibitors of GatCAB, also allowed us to discover and characterize two novel inhibitors, aspartycin and glutamycin. These analogues of the 3'-ends of Asp-tRNA and Glu-tRNA, respectively, are competitive inhibitors of the transamidase activity of Helicobacter pylori GatCAB with respect to Asp-tRNAAsn, with Ki values of 134 microM and 105 microM, respectively. Although the 3' end of aspartycin is similar to the 3' end of Asp-tRNAAsn, this analogue was neither phosphorylated nor transamidated by GatCAB. These novel inhibitors could be used as lead compounds for designing new types of antibiotics targeting GatCABs, since the indirect pathway for Asn-tRNAAsn or Gln-tRNAGln synthesis catalyzed by these enzymes is not present in eukaryotes and is essential for the survival of the above-mentioned bacteria.

The microenvironment provides a functional substratum supporting tumour growth. Hyaluronan (HA) is a major component of this structure. While the role of HA in malignancy is well-defined, the mechanisms driving its biosynthesis in cancer are poorly understood. We show that the eukaryotic translation initiation factor eIF4E, an oncoprotein, drives HA biosynthesis. eIF4E stimulates production of enzymes that synthesize the building blocks of HA, UDP-Glucuronic acid and UDP-N-Acetyl-Glucosamine, as well as hyaluronic acid synthase which forms the disaccharide chain. Strikingly, eIF4E inhibition alone repressed HA levels as effectively as directly targeting HA with hyaluronidase. Unusually, HA was retained on the surface of high-eIF4E cells, rather than being extruded into the extracellular space. Surface-associated HA was required for eIF4E’s oncogenic activities suggesting that eIF4E potentiates an oncogenic HA program. These studies provide unique insights into the mechanisms driving HA production and demonstrate that an oncoprotein can co-opt HA biosynthesis to drive malignancy.

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Breast cancer diagnosed within 10 years following childbirth is defined as postpartum breast cancer (PPBC) and is highly metastatic. Interactions between immune cells and other stromal cells within the involuting mammary gland are fundamental in facilitating an aggressive tumor phenotype. The MNK1/2-eIF4E axis promotes translation of pro-metastatic mRNAs in tumor cells, but its role in modulating the function of non-tumor cells in the PPBC microenvironment has not been explored. Here we used a combination of in vivo PPBC models and in vitro assays to study the effects of inactivation of the MNK1/2-eIF4E axis on the pro-tumor function of select cells of the TME. PPBC mice deficient for phospho-eIF4E (eIF4E S209A ) were protected against lung metastasis and exhibited differences in the tumor and lung immune microenvironment compared to wild-type mice. Moreover, expression of fibroblast-derived IL-33, an alarmin known to induce invasion, was repressed upon MNK1/2-eIF4E axis inhibition. Imaging mass cytometry on PPBC and non-PPBC patient samples indicated that human PPBC contains phospho-eIF4E high-expressing tumor cells and CD8 + T cells displaying markers of an activated dysfunctional phenotype. Finally, inhibition of MNK1/2 combined with anti-PD-1 therapy blocked lung metastasis of PPBC. These findings implicate the involvement of the MNK1/2-eIF4E axis during PPBC metastasis and suggest a promising immunomodulatory route to enhance the efficacy of immunotherapy by blocking phospho-eIF4E.

Introduction: Melanoma is the deadliest form of skin cancer. Melanoma phenotype switching is characterized by reduced expression of melanocyte lineage transcription factor MITF and its downstream targets, leading to increased invasiveness of melanoma cells and resistance to both targeted therapy and immunotherapy, and worse prognosis. In melanoma, MAPK and PI3K pathways ultimately converge upon eukaryotic translation initiation factor 4E (eIF4E) to induce its phosphorylation (p-eIF4E), which is critical for the oncogenicity of eIF4E. Here, we investigate the role of p-eIF4E in melanoma progression and tumor immunity. Methods: We crossed p-eIF4E deficient (eIF4EKI) mice with an inducible melanoma mouse model. We monitored the primary tumor outgrowth, metastasis, and survival of the eIF4EKI mice versus eIF4EWT mice. Melanoma samples were isolated for further investigation. Results: Compared to the eIF4EWT mice, eIF4EKI mice exhibit significantly delayed tumor growth, reduced metastasis, and increased survival. Increased expression of MITF and downstream melanoma antigens were observed in eIF4EKI tumors, suggesting a p-eIF4E-mediated phenotype switching. Cytokine array analysis revealed a novel proinvasive cytokine signature in eIF4EWT melanoma primary culture, further supporting a role of phospho-eIF4E in phenotype switching. The cytokine profiling also revealed a pro-myeloid-derived suppressor cell (MDSC) cytokine signature in the eIF4EWT tumor, indicating a p-eIF4E-linked immunosuppression. In support of the immune suppressive cytokine signature associated with phospho-eIF4E expressing melanomas, immune phenotyping of eIF4EWT melanomas showed a significant increase in MDSCs and less cytotoxic T cells, compared to eIF4EKI melanomas. Finally, pharmacologic inhibition of p-eIF4E in combination with anti-PD-1 immunotherapy results in a synergistic delay in primary tumor outgrowth and reduced metastasis. Conclusions: Here we showed that phosphorylation of eIF4E promotes melanoma phenotype switching, leading to increased invasiveness and reduced expression of tumor-associated antigens. Further, by increasing the secretion of pro-MDSC cytokines, p-eIF4E permits an immunosuppressive microenvironment. Pharmacologic inhibition of p-eIF4E sensitizes melanoma to anti-PD-1 immunotherapy, potentially by increasing melanoma antigen expression and compromising MDSC-mediated immunosuppression. This study provides a novel therapeutic approach for the treatment of melanoma. Citation Format: Fan Huang, Christophe Gonçalves, Qianyu Guo, Joelle Rémy-Sarrazin, Audrey Emond, William Yang, Dany Plourde, Margarita Bartish, Jie Su, Yao Zhan, Marina G. Gimeno, Elie Khoury, Alexandre Benoit, David Dankort, Wilson H. Miller, Sonia V. del Rincón. Phosphorylation of eIF4E promotes phenotype switching and MDSC-mediated immunosuppression in melanoma [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A53.

Diffuse large B-cell lymphoma (DLBCL) accounts for 40% of non-Hodgkin lymphoma, and 30% to 40% of patients will succumb to relapsed/refractory disease (rrDLBCL). Patients with rrDLBCL generally have low long-term survival rates due to a lack of efficient salvage therapies. Small-molecule inhibitors targeting the histone methyltransferase EZH2 represent an emerging group of novel therapeutics that show promising clinical efficacy in patients with rrDLBCL. The mechanisms that control acquired resistance to this class of targeted therapies, however, remain poorly understood. Here, we develop a model of resistance to the EZH2 inhibitor (EZH2i) GSK343 and use RNA-seq data and in vitro investigation to show that GCB (germinal center B-cell)-DLBCL cell lines with acquired drug resistance differentiate toward an ABC (activated B-cell)-DLBCL phenotype. We further observe that the development of resistance to GSK343 is sufficient to induce cross-resistance to other EZH2i. Notably, we identify the immune receptor SLAMF7 as upregulated in EZH2i-resistant cells, using chromatin immunoprecipitation profiling to uncover the changes in chromatin landscape remodeling that permit this altered gene expression. Collectively, our data reveal a previously unreported response to the development of EZH2i resistance in DLBCL, while providing strong rationale for pursuing investigation of dual-targeting of EZH2 and SLAMF7 in rrDLBCL.