Abstract A53: Phosphorylation of eIF4E promotes phenotype switching and MDSC-mediated immunosuppression in melanoma

Abstract

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.

Controlling TIME: How MNK Kinases Function to Shape Tumor Immunity

“…In support of the immune suppressive cytokine signature associated with phosphorylated eIF4E expression, eIF4E WT melanomas showed a significant increase in MDSCs and fewer cytotoxic CD8 + T-cells, compared to melanomas with phosphorylation-deficient eIF4E [75]. Finally, pharmacologic inhibition of phosphorylated eIF4E reduced MDSC abundance and immunosuppressive function, and synergized with anti-PD-1 immunotherapy to delay tumor growth and metastasis [75]. These data collectively suggest that phosphorylated eIF4E expression in MDSCs is important for their survival and function.…”

“…As a result, understanding how MNK kinases and their substrates function in all the different TIME compartments, including immune cells, is critical and will guide the optimization of these new combination regimens. i) Inhibits transcription and expression of OPN, which is required for M2 phenotype [64,67] ii) Increases stability of Gm-csf mRNAs [69,112] i) Suppresses expression of M2-associated genes (Il10, Arg1, Chil3) [72] ii) Induces expression of M1-associated genes (Nos2, Il6) [72] Myeloid-derived suppressor cells (MDSCs) i) May promote MDSC survival and immunosuppressive phenotype [75] i) OPN can promote MDSC expansion via the STAT3 pathway [64,76] Neutrophils i) Promotes neutrophil survival by upregulating anti-apoptotic proteins (MCL1, BCL2) [21,82] ii) Promotes neutrophil-driven metastasis [21,82] iii) Induces myeloid-neutrophil differentiation in response to G-CSF [82] i) Sustains activation of Src family and downstream pathways ERK1/2 and Akt [83,84] Adaptive immune cells T lymphocytes i) Induces cap-dependent translation of RFLAT-1, which transcribes RANTES mRNAs [86,88] ii) Induces expression of GATA-3 for T H 2 differentiation [88][89][90] iii) Inhibits expression of FOXP3 in CD4 + T-cells [90,91,113] iv) Facilitates B-cell differentiation by inducing CD4 + T-cell production of IL-4 [93] i) Inhibits TNFα translation and expression by binding to TNFα 3 -UTR [4] i) Inhibits expression of IL-2, IFNγ, and Granzyme B [99,100] ii) Inhibits T-cell activation and proliferation by suppressing NFκB, NFAT, and AP-1 [99,101,103] iii) Inhibits formation of memory T-cells through the activity of Akt and FoxO1 [102] IRF8: IFN regulatory factor-8; G-CSF: granulocyte colony-stimulating factor; ...…”

“…Cytokine profiling revealed a pro-MDSC cytokine signature in the eIF4E WT tumor, indicating a phosphorylated eIF4E-linked immunosuppression [75]. In support of the immune suppressive cytokine signature associated with phosphorylated eIF4E expression, eIF4E WT melanomas showed a significant increase in MDSCs and fewer cytotoxic CD8 + T-cells, compared to melanomas with phosphorylation-deficient eIF4E [75]. Finally, pharmacologic inhibition of phosphorylated eIF4E reduced MDSC abundance and immunosuppressive function, and synergized with anti-PD-1 immunotherapy to delay tumor growth and metastasis [75].…”

“…The function of eIF4E in MDSCs has recently been evaluated. Using a preclinical model of melanoma, the authors found that compared to eIF4E WT mice, mice that harbor MNK-resistant, eIF4E S209A exhibited significantly delayed tumor growth, reduced metastasis, and increased survival [75]. Cytokine profiling revealed a pro-MDSC cytokine signature in the eIF4E WT tumor, indicating a phosphorylated eIF4E-linked immunosuppression [75].…”

“…Using a preclinical model of melanoma, the authors found that compared to eIF4E WT mice, mice that harbor MNK-resistant, eIF4E S209A exhibited significantly delayed tumor growth, reduced metastasis, and increased survival [75]. Cytokine profiling revealed a pro-MDSC cytokine signature in the eIF4E WT tumor, indicating a phosphorylated eIF4E-linked immunosuppression [75]. In support of the immune suppressive cytokine signature associated with phosphorylated eIF4E expression, eIF4E WT melanomas showed a significant increase in MDSCs and fewer cytotoxic CD8 + T-cells, compared to melanomas with phosphorylation-deficient eIF4E [75].…”