Phosphorylated eukaryotic translation initiation factor 4 (eIF4E) is elevated in human cancer tissues

Medicinal chemistry approaches to target the MNK-eIF4E axis in cancer

Aberrant translation of proteins that promote cell proliferation is an essential factor that defines oncogenic processes and cancer. The process for ribosomal translation of proteins from mRNA requires an essential initiation step which is controlled by the protein eIF4E, which binds the RNA 5'-cap and forms the eIF4F complex that subsequently translates protein. Typically, eIF4E is activated by phosphorylation on Ser209 by MNK1 and MNK2 kinases. Substantial work has shown that eIF4E and MNK1/2 are dysregulated in many cancers and this axis has therefore become an active area of interest for developing new cancer therapeutics. This review summarizes and discusses recent work to develop small molecules that target different steps in the MNK-eIF4E axis as potential cancer therapeutics. The aim of this review is to cover the breadth of different molecular approaches being taken and the medicinal chemistry basis for their optimization and testing as new cancer therapeutics.

Mitogen-activated protein kinase-interacting kinase 1 is involved in mTOR-mediated pancreatic exocrine function of bovine pancreatic acinar cells with leucine supply

Leucine improves the exocrine capacity of the cow pancreas, but the mechanism was not revealed clearly. Mitogen-activated protein kinase-interacting kinase 1 (MNK1) is a pancreatic acinar cell-specific stress response kinase that regulates digestive enzyme abundance. We aimed to investigate the MNK1 gene and protein expression profiles among various organs or tissues of dairy cows and to demonstrate the mechanism by which leucine-stimulated MNK1 regulates pancreatic exocrine function. Firstly, the expression profiles of MNK1 protein and gene in the tissues and organs of dairy cows were measured using immunohistochemistry and RT-qPCR methods. Next, an in vitro model of cultured Holstein dairy calf pancreatic acinar cells was used to detect the role of MNK1 during pancreatic enzymes release which is stimulated by leucine. Cells were incubated in culture medium containing L-leucine (0.45 mM) for 180 min, and samples were collected hourly, with the control not containing L-leucine (0 mM). MNK1 was expressed at very high levels in the pancreatic tissue of dairy cows. Leucine supplementation increased the α-amylase level but not lipase level at three time-points (60, 120, and 180 min), and the interaction between treatments and times was significant only for α-amylase. Leucine treatment enhanced (P < 0.05) the phosphorylation of MNK1 and eIF4E. In addition, inhibition of MNK1 decreased leucine-mediated α-amylase and lipase release (P < 0.05) and the phosphorylation of Mnk1 and eIF4E but did not affect (P > 0.05) the phosphorylation of the mTOR signalling pathway factors 4EBP1 and S6K1. In summary, MNK1 is a key regulator of pancreatic exocrine function, which is regulated by leucine in the pancreas of dairy cows.

Using Imidazo[2,1-b][1,3,4]thiadiazol Skeleton to Design and Synthesize Novel MNK Inhibitors

Mitogen-activated protein kinase-interacting protein kinases (MNKs) phosphorylate eukaryotic initiation factor 4E (eIF4E) and regulate the processes of cell proliferation, cell cycle, and migration and invasion of cancer cells. Selectively inhibiting the activity of MNKs could be effective in treating cancers. In this study, we report a series of novel MNK inhibitors with an imidazo[2,1-b][1,3,4]thiadiazol scaffold, from which, compound 18 inhibited the phosphorylation of eIF4E in various cancer cell lines potently. Compound 18 was more potent against MNK2 than MNK1, and decreased the levels of cyclin-B1, cyclin-D3, and MMP-3 in A549 and MDA-MB-231 cells, impaired cell growth and colony formation, arrested the cell cycle in the G0/G1 phase, and inhibited cell migration and the secretion of TNF-α, MCP-1, and IL-8 from A549 cells. It represents a starting compound to design further inhibitors that selectively target MNKs and apply in other diseases.

An optimized MNK1b aptamer, apMNKQ2, and its potential use as a therapeutic agent in breast cancer

Breast cancer is the most commonly diagnosed and leading cause of cancer death among women worldwide. Mitogen-activated protein kinase-interacting kinases (MNKs) promote the expression of several oncogenic proteins and are overexpressed in several types of cancer. In human cells, there are four isoforms of MNKs. The truncated isoform MNK1b, first described in our laboratory, has a higher basal activity and is constitutively active. Aptamers are emerging in recent years as potential therapeutic agents that show significant advantages over drugs of other nature. We have previously obtained and characterized a highly specific aptamer against MNK1b, named apMNK2F, with a dissociation constant in the nanomolar range, which produces significant inhibition of proliferation, migration, and colony formation in breast cancer cells. Furthermore, its sequence analysis predicted two G-quadruplex structures. In this work, we show the optimization process of the aptamer to reduce its size, improving its stability. The obtained aptamer, named apMNKQ2, is able to inhibit proliferation, colony formation, migration, and invasion in breast cancer cells. In murine models of breast cancer, apMNKQ2 has demonstrated its efficacy in reducing tumor volume and the number of metastases. In conclusion, apMNKQ2 could be used as an anti-tumor drug in the future.

Design, Synthesis and Evaluation of Novel Phorbazole C Derivatives as MNK Inhibitors through Virtual High-Throughput Screening

MNKs (mitogen-activated protein kinase-interacting protein kinases) phosphorylate eIF4E at Ser209 to control the translation of certain mRNAs and regulate the process of cell proliferation, cell migration and invasion, etc. Development of MNK inhibitors would be an effective treatment for related diseases. We used the MarineChem3D database to identify hit compounds targeting the protein MNK1 and MNK2 through high-throughput screening. Compounds from the phorbazole family showed good interactions with MNK1, and phorbazole C was selected as our hit compound. By analyzing the binding mode, we designed and synthesized 29 derivatives and evaluated their activity against MNKs, of which, six compounds showed good inhibition to MNKs. We also confirmed three interactions between this kind of compound and MNK1, which are vital for the activity. In conclusion, we report series of novel MNK inhibitors inspired from marine natural products and their relative structure–activity relationship. This will provide important information for further developing MNK inhibitors based on this kind of structure.

Overexpression of p-4EBP1 associates with p-eIF4E and predicts poor prognosis for non-small cell lung cancer patients with resection

Eukaryotic initiation factor 4E (eIF4E) and its phosphorylated form (p-eIF4E) play a crucial role in the protein synthesis, both are under regulation of eIF4E-binding protein 1 (4EBP1) and mitogen-activated protein kinase (MAPK)-interacting kinases (MNKs). This study aims to explore the potential prognostic significance of p-4EBP1 and p-eIF4E in NSCLC patients. The expression of p-4EBP1 and p-eIF4E in NSCLC patients was detected by immunohistochemistry (IHC) staining in tissue microarrays (TMAs) containing 354 NSCLC and 53 non-cancerous lung tissues (Non-CLT). The overexpression percentage of p-4EBP1 and p-eIF4E in lung squamous cell carcinoma (SCC) and adenocarcinoma (ADC) was significantly higher than that of Non-CLT. P-4EBP1 expression in patients with advanced clinical stage was higher than that in early stage. Expression of p-4EBP1 had a positive relationship with p-eIF4E expression both in lung SCC and ADC. NSCLC patients with high expression of p-4EBP1 and p-eIF4E alone or in combination had a lower survival rate than that of other phenotypes. For NSCLC patients, p-4EBP1 is an independent poor prognostic factor as well as clinical stage, LNM and pathological grade. Overexpression of p-4EBP1 and p-eIF4E might be novel prognostic marker for NSCLC, who possesses potential application value for NSCLC targeted therapy.

Pharmacodynamic and therapeutic pilot studies of single-agent ribavirin in patients with human papillomavirus-related malignancies

OBJECTIVES

Ribavirin inhibits eukaryotic translation initiation factor 4E (eIF4E), thereby decreasing cap-dependent translation. In this two-part study, we assessed the pharmacodynamic effects and therapeutic potential of ribavirin in human papillomavirus (HPV)-related malignancies.

METHODS

In the pharmacodynamic study, ribavirin (400 mg BID for 14 days) was evaluated in 8 patients with HPV-positive localized oropharyngeal carcinoma with phosphorylated-eIF4E (p-eIF4E) ≥ 30%. In the therapeutic study, ribavirin (1400 mg BID in 28-day cycles, continuously dosed) was evaluated in 12 patients with recurrent and/or metastatic HPV-related cancer. Dose interruptions or reductions were allowed according to prespecified criteria. Toxicities were assessed in accordance with National Cancer Institute Common Terminology Criteria for Adverse Events version 4; response was assessed using Response Evaluation Criteria in Solid Tumors version 1.1. Patients remained on study until disease progression or unacceptable toxicity.

RESULTS

Six patients were evaluable in the pharmacodynamic study: 4 had decreased p-eIF4E after 14 days of ribavirin. In the therapeutic study, 12 patients were evaluable for toxicity, and 9 were evaluable for response. Among these, median follow-up was 3.5 months, and best overall response was stable disease in 5 patients and progression of disease in 4 patients. Median progression-free survival was 1.8 months. The most common treatment-related adverse events (grade > 2) were anemia, dyspnea, and hyperbilirubinemia. All patients had anemia (grades 1-3), with 33% having at least 1 dose reduction.

CONCLUSION

Oral ribavirin decreases p-eIF4E levels and is well-tolerated. However, a clear signal of efficacy in patients with recurrent and/or metastatic HPV-related cancers was not observed. (NCT02308241, NCT01268579).

EGPI-1, a novel eIF4E/eIF4G interaction inhibitor, inhibits lung cancer cell growth and angiogenesis through Ras/MNK/ERK/eIF4E signaling pathway

eIF4E plays an important role in regulating tumor growth and angiogenesis, and eIF4E is highly expressed in a variety of lung cancer cell lines. siRNA eIF4E can significantly inhibit the proliferation of lung cancer cells, indicating that inhibition of eIF4E may become a novel anti-tumor target. In the previous study, we synthesized a series of small molecule compounds with the potential to inhibit eIF4E. Among them, the compound EGPI-1 significantly inhibited the proliferation of a variety of lung cancer cells such as A549, NCI-H460, NCI-H1650 and 95D without inhibiting the proliferation of HUVEC cells. Further studies found that EGPI-1 interfered with the eIF4E/eIF4G interaction and inhibited the phosphorylation of eIF4E in NCI-H460 cells. The results of flow cytometry showed that EGPI-1 induced apoptosis and G0/G1 cycle arrest in NCI-H460 cell. Interestingly, we also found that EGPI-1 induced autophagy and DNA damage in NCI-H460 cells. The mechanism results showed that EGPI-1 inhibited the Ras/MNK/ERK/eIF4E signaling pathway. Moreover, EGPI-1 inhibited tube formation of HUVECs, as well as inhibited the neovascularization of CAM, proving the anti-angiogenesis activity of EGPI-1. The NCI-H460 xenograft studies showed that EGPI-1 inhibited tumor growth and angiogenesis in vivo by regulating Ras/MNK/ERK/eIF4E pathway. Our studies proved that eIF4E was a novel target for regulating tumor growth, and the eIF4E/eIF4G interaction inhibitor EGPI-1 was promising to develop into a novel anti-lung cancer drug.

Codon optimality in cancer

A key characteristic of cancer cells is their increased proliferative capacity, which requires elevated levels of protein synthesis. The process of protein synthesis involves the translation of codons within the mRNA coding sequence into a string of amino acids to form a polypeptide chain. As most amino acids are encoded by multiple codons, the nucleotide sequence of a coding region can vary dramatically without altering the polypeptide sequence of the encoded protein. Although mutations that do not alter the final amino acid sequence are often thought of as silent/synonymous, these can still have dramatic effects on protein output. Because each codon has a distinct translation elongation rate and can differentially impact mRNA stability, each codon has a different degree of 'optimality' for protein synthesis. Recent data demonstrates that the codon preference of a transcriptome matches the abundance of tRNAs within the cell and that this supply and demand between tRNAs and mRNAs varies between different cell types. The largest observed distinction is between mRNAs encoding proteins associated with proliferation or differentiation. Nevertheless, precisely how codon optimality and tRNA expression levels regulate cell fate decisions and their role in malignancy is not fully understood. This review describes the current mechanistic understanding on codon optimality, its role in malignancy and discusses the potential to target codon optimality therapeutically in the context of cancer.

Targeting c-Myc to Overcome Acquired Resistance of EGFR Mutant NSCLC Cells to the Third-Generation EGFR Tyrosine Kinase Inhibitor, Osimertinib

Osimertinib (AZD9291 or TAGRISSO) is a promising and approved third-generation EGFR tyrosine kinase inhibitor (TKI) for treating patients with advanced non-small cell lung cancer (NSCLC) harboring EGFR-activating mutations or the resistant T790M mutation. However, the inevitable emergence of acquired resistance limits its long-term efficacy. A fuller understanding of the mechanism of action of osimertinib and its linkage to acquired resistance will enable the development of more efficacious therapeutic strategies. Consequently, we have identified a novel connection between osimertinib or other EGFR-TKIs and c-Myc. Osimertinib rapidly and sustainably decreased c-Myc levels primarily via enhancing protein degradation in EGFR-mutant (EGFRm) NSCLC cell lines and xenograft tumors. c-Myc levels were substantially elevated in different EGFRm NSCLC cell lines with acquired resistance to osimertinib in comparison with their corresponding parental cell lines and could not be reduced any further by osimertinib. Consistently, c-Myc levels were elevated in the majority of EGFRm NSCLC tissues relapsed from EGFR-TKI treatment compared with their corresponding untreated baseline c-Myc levels. Suppression of c-Myc through knockdown or pharmacologic targeting with BET inhibitors restored the response of resistant cell lines to osimertinib. These findings indicate that c-Myc modulation mediates the therapeutic efficacy of osimertinib and the development of osimertinib acquired resistance. Furthermore, they establish c-Myc as a potential therapeutic target and warrant clinical testing of BET inhibition as a potential strategy to overcome acquired resistance to osimertinib or other EGFR inhibitors. SIGNIFICANCE: This study demonstrates a critical role of c-Myc modulation in mediating therapeutic efficacy of osimertinib including osimertinib acquired resistance and suggests targeting c-Myc as a potential strategy to overcome osimertinib acquired resistance.

MNK Inhibition Sensitizes KRAS-Mutant Colorectal Cancer to mTORC1 Inhibition by Reducing eIF4E Phosphorylation and c-MYC Expression

KRAS-mutant colorectal cancers are resistant to therapeutics, presenting a significant problem for ∼40% of cases. Rapalogs, which inhibit mTORC1 and thus protein synthesis, are significantly less potent in KRAS-mutant colorectal cancer. Using Kras-mutant mouse models and mouse- and patient-derived organoids, we demonstrate that KRAS with G12D mutation fundamentally rewires translation to increase both bulk and mRNA-specific translation initiation. This occurs via the MNK/eIF4E pathway culminating in sustained expression of c-MYC. By genetic and small-molecule targeting of this pathway, we acutely sensitize KRASG12D models to rapamycin via suppression of c-MYC. We show that 45% of colorectal cancers have high signaling through mTORC1 and the MNKs, with this signature correlating with a 3.5-year shorter cancer-specific survival in a subset of patients. This work provides a c-MYC-dependent cotargeting strategy with remarkable potency in multiple Kras-mutant mouse models and metastatic human organoids and identifies a patient population that may benefit from its clinical application. SIGNIFICANCE: KRAS mutation and elevated c-MYC are widespread in many tumors but remain predominantly untargetable. We find that mutant KRAS modulates translation, culminating in increased expression of c-MYC. We describe an effective strategy targeting mTORC1 and MNK in KRAS-mutant mouse and human models, pathways that are also commonly co-upregulated in colorectal cancer.This article is highlighted in the In This Issue feature, p. 995.

Inhibiting the MNK1/2-eIF4E axis impairs melanoma phenotype switching and potentiates antitumor immune responses

Melanomas commonly undergo a phenotype switch, from a proliferative to an invasive state. Such tumor cell plasticity contributes to immunotherapy resistance; however, the mechanisms are not completely understood and thus are therapeutically unexploited. Using melanoma mouse models, we demonstrated that blocking the MNK1/2-eIF4E axis inhibited melanoma phenotype switching and sensitized melanoma to anti-PD-1 immunotherapy. We showed that phospho-eIF4E-deficient murine melanomas expressed high levels of melanocytic antigens, with similar results verified in patient melanomas. Mechanistically, we identified phospho-eIF4E-mediated translational control of NGFR, a critical effector of phenotype switching. Genetic ablation of phospho-eIF4E reprogrammed the immunosuppressive microenvironment, exemplified by lowered production of inflammatory factors, decreased PD-L1 expression on dendritic cells and myeloid-derived suppressor cells, and increased CD8+ T cell infiltrates. Finally, dual blockade of the MNK1/2-eIF4E axis and the PD-1/PD-L1 immune checkpoint demonstrated efficacy in multiple melanoma models regardless of their genomic classification. An increase in the presence of intratumoral stem-like TCF1+PD-1+CD8+ T cells, a characteristic essential for durable antitumor immunity, was detected in mice given a MNK1/2 inhibitor and anti-PD-1 therapy. Using MNK1/2 inhibitors to repress phospho-eIF4E thus offers a strategy to inhibit melanoma plasticity and improve response to anti-PD-1 immunotherapy.

Progress in developing MNK inhibitors

The MNKs (mitogen-activated protein kinase-interacting protein kinases) phosphorylate eIF4E (eukaryotic initiation factor 4 E) at serine 209; eIF4E plays an important role in the translation of cytoplasmic mRNAs, all of which possess a 5' 'cap' structure to which eIF4E binds. Elevated levels of eIF4E, p-eIF4E and/or the MNK protein kinases have been found in many types of cancer, including solid tumors and leukemia. MNKs also play a role in metabolic disease. Regulation of the activities of MNKs (MNK1 and MNK2), control the phosphorylation of eIF4E, which in turn has a close relationship with the processes of tumor development, cell migration and invasion, and energy metabolism. MNK knock-out mice display no adverse effects on normal cells or phenotypes suggesting that MNK may be a potentially safe targets for the treatment of various cancers. Several MNK inhibitors or 'degraders' have been identified. Initially, some of the inhibitors were developed from natural products or based on other protein kinase inhibitors which inhibit multiple kinases. Subsequently, more potent and selective inhibitors for MNK1/2 have been designed and synthesized. Currently, three inhibitors (BAY1143269, eFT508 and ETC-206) are in various stages of clinical trials for the treatment of solid cancers or leukemia, either alone or combined with inhibitors of other protein kinase. In this review, we summarize the diverse MNK inhibitors that have been reported in patents and other literature, including those with activities in vitro and/or in vivo.

Downregulation of death receptor 4 is tightly associated with positive response of EGFR mutant lung cancer to EGFR-targeted therapy and improved prognosis

Death receptor 4 (DR4), a cell surface receptor, mediates apoptosis or induces inflammatory cytokine secretion upon binding to its ligand depending on cell contexts. Its prognostic impact in lung cancer and connection between EGFR-targeted therapy and DR4 modulation has not been reported and thus was the focus of this study. Methods: Intracellular protein alterations were measured by Western blotting. Cell surface protein was detected with antibody staining and flow cytometry. mRNA expression was monitored with qRT-PCR. Gene transactivation was analyzed with promoter reporter assay. Drug dynamic effects in vivo were evaluated using xenografts. Gene modulations were achieved with gene overexpression and knockdown. Proteins in human archived tissues were stained with immunohistochemistry. Results: EGFR inhibitors (e.g., osimertinib) decreased DR4 levels only in EGFR mutant NSCLC cells and tumors, being tightly associated with induction of apoptosis. This modulation was lost once cells became resistant to these inhibitors. Increased levels of DR4 were detected in cell lines with acquired osimertinib resistance and in NSCLC tissues relapsed from EGFR-targeted therapy. DR4 knockdown induced apoptosis and augmented apoptosis when combined with osimertinib in both sensitive and resistant cell lines, whereas enforced DR4 expression significantly attenuated osimertinib-induced apoptosis. Mechanistically, osimertinib induced MARCH8-mediated DR4 proteasomal degradation and suppressed MEK/ERK/AP-1-dependent DR4 transcription, resulting in DR4 downregulation. Moreover, we found that DR4 positive expression in human lung adenocarcinoma was significantly associated with poor patient survival. Conclusions: Collectively, we suggest that DR4 downregulation is coupled to therapeutic efficacy of EGFR-targeted therapy and predicts improved prognosis, revealing a previously undiscovered connection between EGFR-targeted therapy and DR4 modulation.

Translation initiation and its relevance in colorectal cancer

Protein synthesis is one of the most essential processes in every kingdom of life, and its dysregulation is a known driving force in cancer development. Multiple signaling pathways converge on the translation initiation machinery, and this plays a crucial role in regulating differential gene expression. In colorectal cancer, dysregulation of initiation results in translational reprogramming, which promotes the selective translation of mRNAs required for many oncogenic processes. The majority of upstream mutations found in colorectal cancer, including alterations in the WNT, MAPK, and PI3K\AKT pathways, have been demonstrated to play a significant role in translational reprogramming. Many translation initiation factors are also known to be dysregulated, resulting in translational reprogramming during tumor initiation and/or maintenance. In this review, we outline the role of translational reprogramming that occurs during colorectal cancer development and progression and highlight some of the most critical factors affecting the etiology of this disease.

eIF4E S209 phosphorylation licenses myc- and stress-driven oncogenesis

To better understand a role of eIF4E S209 in oncogenic translation, we generated EIF4E^S209A/+ heterozygous knockin (4EKI) HCT 116 human colorectal cancer (CRC) cells. 4EKI had little impact on total eIF4E levels, cap binding or global translation, but markedly reduced HCT 116 cell growth in spheroids and mice, and CRC organoid growth. 4EKI strongly inhibited Myc and ATF4 translation, the integrated stress response (ISR)-dependent glutamine metabolic signature, AKT activation and proliferation in vivo. 4EKI inhibited polyposis in Apc^Min/+ mice by suppressing Myc protein and AKT activation. Furthermore, p-eIF4E was highly elevated in CRC precursor lesions in mouse and human. p-eIF4E cooperated with mutant KRAS to promote Myc and ISR-dependent glutamine addiction in various CRC cell lines, characterized by increased cell death, transcriptomic heterogeneity and immune suppression upon deprivation. These findings demonstrate a critical role of eIF4E S209-dependent translation in Myc and stress-driven oncogenesis and as a potential therapeutic vulnerability.

Contribution of miRNAs, tRNAs and tRFs to Aberrant Signaling and Translation Deregulation in Lung Cancer

Simple Summary

The profiles of miRNAs, tRNA-derived fragments and tRNAs from lung cancer biopsy specimens indicate involvement of gene networks that modulate signaling and translation initiation. The current study highlights the important role of several regulatory small non-coding RNAs in aberrant signaling and translation deregulation in lung cancer.

Abstract

Transcriptomics profiles of miRNAs, tRNAs or tRFs are used as biomarkers, after separate examination of several cancer cell lines, blood samples or biopsies. However, the possible contribution of all three profiles on oncogenic signaling and translation as a net regulatory effect, is under investigation. The present analysis of miRNAs and tRFs from lung cancer biopsies indicated putative targets, which belong to gene networks involved in cell proliferation, transcription and translation regulation. In addition, we observed differential expression of specific tRNAs along with several tRNA-related genes with possible involvement in carcinogenesis. Transfection of lung adenocarcinoma cells with two identified tRFs and subsequent NGS analysis indicated gene targets that mediate signaling and translation regulation. Broader analysis of all major signaling and translation factors in several biopsy specimens revealed a crosstalk between the PI3K/AKT and MAPK pathways and downstream activation of eIF4E and eEF2. Subsequent polysome profile analysis and 48S pre-initiation reconstitution experiments showed increased global translation rates and indicated that aberrant expression patterns of translation initiation factors could contribute to elevated protein synthesis. Overall, our results outline the modulatory effects that possibly correlate the expression of important regulatory non-coding RNAs with aberrant signaling and translation deregulation in lung cancer.

Phosphorylation of the mRNA cap-binding protein eIF4E and cancer

Dysregulated protein synthesis is frequently involved in oncogenesis and cancer progression. Translation initiation is thought to be the rate-limiting step in protein synthesis, and the mRNA 5' cap-binding protein eukaryotic translation initiation factor 4E (eIF4E) is a pivotal factor that initiates translation. The activities of eIF4E are regulated at multiple levels, one of which is through its phosphorylation at Serine 209 by the mitogen-activated protein kinase-interacting kinases (MNKs, including MNK1 and MNK2). Benefiting from novel mouse genetic tools and pharmacological MNK inhibitors, our understanding of a role for eIF4E phosphorylation in tumor biology and cancer therapy has greatly evolved in recent years. Importantly, recent studies have found that the level of eIF4E phosphorylation is frequently upregulated in a wide variety of human cancer types, and phosphorylation of eIF4E drives a number of important processes in cancer biology, including cell transformation, proliferation, apoptosis, metastasis and angiogenesis. The MNK-eIF4E axis is being assessed as a therapeutic target either alone or in combination with other therapies in different cancer models. As novel MNK inhibitors are being developed, experimental studies bring new hope to cure human cancers that are not responsive to traditional therapies. Herein we review recent progress on our understanding of a mechanistic role for phosphorylation of eIF4E in cancer biology and therapy.

Impact of Eukaryotic Translation Initiation Factors on Breast Cancer: Still Much to Investigate

Breast carcinoma (BC) remains one of the most serious health problems. It is a heterogeneous entity, and mainly classified according to receptor status for estrogen (ER), progesterone (PR) and egf (HER2/Neu), as well as the proliferation marker ki67. Gene expression in eukaryotes is regulated at the level of both gene transcription and translation, where eukaryotic initiation factors (eIFs) are key regulators of protein biosynthesis. Aberrant translation results in an altered cellular proteome, and this clearly effects cell growth supporting tumorigenesis. The relationship between various eIFs and BC entities, as well as the related regulatory mechanisms, has meanwhile become a focus of scientific interest. Here, we give an overview on the current research state of eIF function, focusing on BC.

Tumor-Derived Exosomal eIF4E as a Biomarker for Survival Prediction in Patients with Non-Small Cell Lung Cancer

Background

The aim of this study was to investigate the expression of tumor-derived exosomal RNA eIF4E (exo-eIF4E) in non-small cell lung cancer (NSCLC) and its correlation with prognosis.

Material/Methods

The Cancer Genome Atlas (TCGA) data was exacted to investigate the role of tissue eIF4E in NSCLC. We enrolled 99 NSCLC patients and 40 healthy volunteers with corresponding serum samples in this study. The levels of exo-eIF4E in the peripheral blood of each group were tested by quantitative polymerase chain reaction (PCR). The chi-squared test and the log-rank test were applied to analyze the correlation between the expression levels of exo-eIF4E and the patients’ clinical-pathological data, including the overall survival.

Results

TCGA data showed that increased eIF4E in NSCLC tissues was associated with late-stage disease (P=0.0497) and inferior overall survival (P=0.017). The expression of exo-eIF4E in the serum of the NSCLC group was significantly higher than that in healthy individuals (P<0.001). Furthermore, advanced TNM stage (P=0.003), distant metastasis (P=0.008), and serum positive cytokeratin fragment 19 (CYFRA21-1) (P=0.023) are more likely present in NSCLC patients with higher exo-eIF4E expression. Moreover, the multivariate combined with univariate analyses verified exo-eIF4E as an independent prognostic factor for shorter overall survival (P=0.01) and progression-free survival (P=0.005). Shorter overall survival (P=0.0005) and inferior progression-free survival (P=0.0017) are more likely present in NSCLC patients with higher exo-eIF4E.

Conclusions

Tumor-derived exo-eIF4E in serum can be a practical tool to predict the prognosis of NSCLC.

The MNK1/2-eIF4E Axis as a Potential Therapeutic Target in Melanoma

: Melanoma is a type of skin cancer that originates in the pigment-producing cells of the body known as melanocytes. Most genetic aberrations in melanoma result in hyperactivation of the mitogen activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways. We and others have shown that a specific protein synthesis pathway known as the MNK1/2-eIF4E axis is often dysregulated in cancer. The MNK1/2-eIF4E axis is a point of convergence for these signaling pathways that are commonly constitutively activated in melanoma. In this review we consider the functional implications of aberrant mRNA translation in melanoma and other malignancies. Moreover, we discuss the consequences of inhibiting the MNK1/2-eIF4E axis on the tumor and tumor-associated cells, and we provide important avenues for the utilization of this treatment modality in combination with other targeted and immune-based therapies. The past decade has seen the increased development of selective inhibitors to block the action of the MNK1/2-eIF4E pathway, which are predicted to be an effective therapy regardless of the melanoma subtype (e.g., cutaneous, acral, and mucosal).

Targeting Protein Synthesis in Colorectal Cancer

Under physiological conditions, protein synthesis controls cell growth and survival and is strictly regulated. Deregulation of protein synthesis is a frequent event in cancer. The majority of mutations found in colorectal cancer (CRC), including alterations in the WNT pathway as well as activation of RAS/MAPK and PI3K/AKT and, subsequently, mTOR signaling, lead to deregulation of the translational machinery. Besides mutations in upstream signaling pathways, deregulation of global protein synthesis occurs through additional mechanisms including altered expression or activity of initiation and elongation factors (e.g., eIF4F, eIF2α/eIF2B, eEF2) as well as upregulation of components involved in ribosome biogenesis and factors that control the adaptation of translation in response to stress (e.g., GCN2). Therefore, influencing mechanisms that control mRNA translation may open a therapeutic window for CRC. Over the last decade, several potential therapeutic strategies targeting these alterations have been investigated and have shown promising results in cell lines, intestinal organoids, and mouse models. Despite these encouraging in vitro results, patients have not clinically benefited from those advances so far. In this review, we outline the mechanisms that lead to deregulated mRNA translation in CRC and highlight recent progress that has been made in developing therapeutic strategies that target these mechanisms for tumor therapy.

Autoantibody profiling identifies predictive biomarkers of response to anti-PD1 therapy in cancer patients

Background: Programmed cell death protein 1 (PD1) inhibitors have revolutionized cancer therapy, yet many patients fail to respond. Thus, the identification of accurate predictive biomarkers of therapy response will improve the clinical benefit of anti-PD1 therapy.

Method: We assessed the baseline serological autoantibody (AAb) profile against ~2300 proteins in 10 samples and ~4600 proteins in 35 samples with alveolar soft part sarcoma (ASPS), non-small-cell lung cancer (NSCLC) and lymphoma using Nucleic Acid Programmable Protein Arrays (NAPPA). 23 selected potential AAb biomarkers were verified using simple, affordable and rapid enzyme linked immune sorbent assay (ELISA) technology with baseline plasma samples from 12 ASPS, 16 NSCLC and 46 lymphoma patients. SIX2 and EIF4E2 AAbs were further validated in independent cohorts of 17 NSCLC and 43 lymphoma patients, respectively, using ELISA. The IgG subtypes in response to therapy were also investigated.

Results: Distinct AAb profiles between ASPS, NSCLC and lymphoma were observed. In ASPS, the production of P53 and PD1 AAbs were significantly increased in non-responders (p=0.037). In NSCLC, the SIX2 AAb was predictive of response with area under the curve (AUC) of 0.87, 0.85 and 0.90 at 3 months, 4.5 months, 6 months evaluation time points, respectively. In the validation cohort, the SIX2 AAb was consistently up-regulated in non-responders (p=0.024). For lymphoma, the EIF4E2 AAb correlated with a favorable response with AUCs of 0.68, 0.70, and 0.70 at 3 months, 4.5 months, and 6 months, respectively. In the validation cohort, the AUCs were 0.74, 0.75 and 0.66 at 3 months, 4.5 months, and 6 months, respectively. The PD1 and PD-L1 IgG2 AAbs were highly produced in ~20% of lymphoma responders. Furthermore, bioinformatics analysis revealed antigen functions of these AAb biomarkers.

Conclusion: This study provides the first evidence that AAb biomarkers selected using high-throughput protein microarrays can predict anti-PD1 therapeutic response and guide anti-PD1 therapy.

Deeping in the Role of the MAP-Kinases Interacting Kinases (MNKs) in Cancer

The mitogen-activated protein kinase (MAPK)-interacting kinases (MNKs) are involved in oncogenic transformation and can promote metastasis and tumor progression. In human cells, there are four MNKs isoforms (MNK1a/b and MNK2a/b), derived from two genes by alternative splicing. These kinases play an important role controlling the expression of specific proteins involved in cell cycle, cell survival and cell motility via eukaryotic initiation factor 4E (eIF4E) regulation, but also through other substrates such as heterogeneous nuclear ribonucleoprotein A1, polypyrimidine tract-binding protein-associated splicing factor and Sprouty 2. In this review, we provide an overview of the role of MNK in human cancers, describing the studies conducted to date to elucidate the mechanism involved in the action of MNKs, as well as the development of MNK inhibitors in different hematological cancers and solid tumors.

Eukaryotic Initiation Factor 4E phosphorylation acts a switch for its binding to 4E-BP1 and mRNA cap assembly

Translational regulation has invited considerable interest consequent of its circumstantial dysregulation during cancer genesis. eIF4E (Eukaryotic Initiation Factor 4E) has been identified as an important factor involved in tumor progression by way of instrumenting the convergence of oncogenic signals for up-regulation of Cap-dependent translation. In the backdrop of dramatic eIF4E over-expression in a large population of human cancers, we suggest that the tumorigenic property of eIF4E is strictly attributed to its phosphorylation state. We provide evidence that while phosphorylated eIF4E fails to be sequestered by 4E-BP1, its dephosphorylated form shows overwhelming binding with 4E-BP1 without any consideration to the state of 4E-BP1 phosphorylation to suggest that eIF4E-4EBP1 binding is governed by eIF4E phosphorylation instead of 4E-BP1. We also show that eIF4E engages in Cap-assembly formation preferably in a phosphorylation-dependent manner to suggest that eIF4E phosphorylation rather than 4E-BP1 regulates its availability for Cap-assembly.

Overexpression of p-Akt, p-mTOR and p-eIF4E proteins associates with metastasis and unfavorable prognosis in non-small cell lung cancer

The Akt (protein kinase B)/mammalian target of rapamycin (mTOR) pathway, which is dysregulated in various cancers, controls the assembly of eukaryotic translation initiation factor 4F (eIF4E) complex. However, whether aberrant expression of phosphorylated Akt (p-Akt), phosphorylated mTOR (p-mTOR) and phosphorylated eIF4E (p-eIF4E) is associated with clinicopathological characteristics in surgically resected non-small cell lung cancer (NSCLC) has been rarely reported. Here, we investigated expression of p-Akt, p-mTOR and p-eIF4E proteins in NSCLC by immunohistochemistry and evaluated their correlation with clinicopathological characteristics and prognostic significance. The results showed that the positive percentage of p-Akt, p-mTOR and p-eIF4E was higher in NSCLC. Additionally, p-mTOR and p-eIF4E was dramatically higher in lung adenocarcinoma (both P<0.05). Most importantly, NSCLC patients with lymph node metastasis had significantly elevated expression of p-Akt, p-mTOR and p-eIF4E (all P<0.05). Positive expression of p-Akt, and any positive expression of p-Akt, p-mTOR and p-eIF4E proteins were positively correlated with clinical stages (both P<0.05). Spearman’s rank correlation test revealed that expression of p-Akt was correlated with p-eIF4E and p-mTOR (r = 0.107, P = 0.047; r = 0.287, P<0.001, respectively). Also, p-eIF4E had positive correlation with p-mTOR (r = 0.265, P<0.001). Furthermore, NSCLC patients with increased expression of p-Akt, p-mTOR and p-eIF4E, and any positive expression of above three proteins had lower overall survival rates (all P<0.05). Multivariate Cox regression analysis further indicated thatp-eIF4E was an independent prognostic factor for NSCLC patients (P = 0.046). Taken together, overexpression of p-Akt, p-mTOR and p-eIF4E proteins is associated with metastasis and poor prognosis of NSCLC patients after surgical resection, and positive expression of p-eIF4E protein may act as an independent unfavorable prognostic biomarker for overall survival of NSCLC patients.

Clinical implications of intratumor heterogeneity: challenges and opportunities

In this review, we highlight the role of intratumoral heterogeneity, focusing on the clinical and biological ramifications this phenomenon poses. Intratumoral heterogeneity arises through complex genetic, epigenetic, and protein modifications that drive phenotypic selection in response to environmental pressures. Functionally, heterogeneity provides tumors with significant adaptability. This ranges from mutual beneficial cooperation between cells, which nurture features such as growth and metastasis, to the narrow escape and survival of clonal cell populations that have adapted to thrive under specific conditions such as hypoxia or chemotherapy. These dynamic intercellular interplays are guided by a Darwinian selection landscape between clonal tumor cell populations and the tumor microenvironment. Understanding the involved drivers and functional consequences of such tumor heterogeneity is challenging but also promises to provide novel insight needed to confront the problem of therapeutic resistance in tumors.

Deciphering the mechanistic effects of eIF4E phosphorylation on mRNA-cap recognition

The mRNA cap-binding oncoprotein "eIF4E" is phosphorylated at residue S209 by Mnk kinases, and is closely associated with tumor development and progression. Despite being well-established, mechanistic details at the molecular level of mRNA recognition by eIF4E due to phosphorylation have not been clearly elucidated. We investigated this through molecular modeling and simulations of the S209 phosphorylated derivative of eIF4E and explored the associated implication on the binding of the different variants of mRNA-cap analogs. A key feature that emerges as a result of eIF4E phosphorylation is a salt-bridge network between the phosphorylated S209 (pS209) and a specific pair of lysine residues (K159 and K162) within the cap-binding interface on eIF4E. This interaction linkage stabilizes the otherwise dynamic C-terminal region of the protein, resulting in the attenuation of the overall plasticity and accessibility of the binding pocket. The pS209-K159 salt-bridge also results in an energetically less favorable environment for the bound mRNA-cap primarily due to electrostatic repulsion between the negative potentials from the phosphates in the cap and those appearing as a result of phosphorylation of S209. These observations collectively imply that the binding of the mRNA-cap will be adversely affected in the phosphorylated derivative of eIF4E. We propose a mechanistic model highlighting the role of eIF4E phosphorylation as a regulatory tool in modulating eIF4E: mRNA-cap recognition and its potential impact on translation initiation.

Discovery of N-Phenyl-4-(1H-pyrrol-3-yl)pyrimidin-2-amine Derivatives as Potent Mnk2 Inhibitors: Design, Synthesis, SAR Analysis, and Evaluation of in vitro Anti-leukaemic Activity

BACKGROUND

Aberrant expression of eukaryotic translation initiation factor 4E (eIF4E) is common in many types of cancer including acute myeloid leukaemia (AML). Phosphorylation of eIF4E by MAPK-interacting kinases (Mnks) is essential for the eIF4E-mediated oncogenic activity. As such, the pharmacological inhibition of Mnks can be an effective strategy for the treatment of cancer.

METHODS

A series of N-phenyl-4-(1H-pyrrol-3-yl)pyrimidin-2-amine derivatives was designed and synthesised. The Mnk inhibitory activity of these derivatives as well as their anti-proliferative activity against MV4-11 AML cells was determined.

RESULTS

These compounds were identified as potent Mnk2 inhibitors. Most of them demonstrated potent anti-proliferative activity against MV4-11 AML cells. The cellular mechanistic studies of the representative inhibitors revealed that they reduced the level of phosphorylated eIF4E and induced apoptosis by down-regulating the anti-apoptotic protein myeloid cell leukaemia 1 (Mcl-1) and by cleaving poly(ADP-ribose)polymerase (PARP). The lead compound 7k possessed desirable pharmacokinetic properties and oral bioavailability.

CONCLUSION

This work proposes that exploration of the structural diversity in the context of Nphenyl- 4-(1H-pyrrol-3-yl)pyrimidin-2-amine would offer potent and selective Mnk inhibitors.

Cancer the'RBP'eutics-RNA-binding proteins as therapeutic targets for cancer

RNA-binding proteins (RBPs) play a critical role in the regulation of various RNA processes, including splicing, cleavage and polyadenylation, transport, translation and degradation of coding RNAs, non-coding RNAs and microRNAs. Recent studies indicate that RBPs not only play an instrumental role in normal cellular processes but have also emerged as major players in the development and spread of cancer. Herein, we review the current knowledge about RNA binding proteins and their role in tumorigenesis as well as the potential to target RBPs for cancer therapeutics.

Translational Control in Cancer

The translation of messenger RNAs (mRNAs) into proteins is a key event in the regulation of gene expression. This is especially true in the cancer setting, as many oncogenes and transforming events are regulated at this level. Cancer-promoting factors that are translationally regulated include cyclins, antiapoptotic factors, proangiogenic factors, regulators of cell metabolism, prometastatic factors, immune modulators, and proteins involved in DNA repair. This review discusses the diverse means by which cancer cells deregulate and reprogram translation, and the resulting oncogenic impacts, providing insights into the complexity of translational control in cancer and its targeting for cancer therapy.

Impact of eIF4E phosphorylation at Ser209 via MNK2a on tumour recurrence after curative surgery in localized clear cell renal cell carcinoma

Background: We investigated the roles of eIF4E phosphorylation (Ser209) in tumour recurrence after curative nephrectomy for localized clear cell renal cell carcinoma (ccRCC).

Methods: Expression of eIF4E, p eIF4E and MNKs (MAPK interacting kinases), was evaluated in surgical specimens obtained from consecutive non metastatic ccRCC patients (n = 290) by immunohistochemistry (IHC), immunoblotting, and qRT PCR at the protein and mRNA levels. In human RCC cell lines, the effects of eIF4E phosphorylation were examined using immunoblotting, proliferation, migration and invasion assays with pharmacological inhibitors (CGP57380 or ETP45835) and specific small interfering (si) RNAs against MNK1/2(a/b).

Results: In postoperative follow-up (median, 7.9 y), 40 patients experienced metastatic recurrence. In multivariate Cox analyses, higher IHC expression of p eIF4E in ccRCC significantly predicted a longer recurrence-free interval. eIF4E is phosphorylated mainly by MNK2a in tumour specimens and cell lines. In 786-O and A-498 cell lines, pharmacological inhibition of MNKs decreased p-eIF4E and increased vimentin and N cadherin but did not influence proliferation. Similarly, MNK2 or MNK2a inhibition with siRNA reduced p-eIF4E and enhanced vimentin translation, cell migration and invasion in the cell lines.

Conclusions: MNK2a-induced eIF4E phosphorylation may suppress metastatic recurrence of ccRCC, partially due to vimentin downregulation at the translational level, consequently leading to inhibition of epithelial–mesenchymal transition.

Oncogenic Role of ZFAS1 lncRNA in Head and Neck Squamous Cell Carcinomas

Background: Head and neck squamous cell carcinoma (HNSCC) is a heterogeneous disease with high mortality. The identification of specific HNSCC biomarkers will increase treatment efficacy and limit the toxicity of current therapeutic strategies. Long non-coding RNAs (lncRNAs) are promising biomarkers. Accordingly, here we investigate the biological role of ZFAS1 and its potential as a biomarker in HNSCC. Methods: The expression level of ZFAS1 in HNSCC cell lines was analyzed using qRT-PCR. Based on the HNSCC TCGA data, the ZFAS1 expression profile, clinicopathological features, and expression of correlated genes were analyzed in patient tissue samples. The selected genes were classified according to their biological function using the PANTHER tool. The interaction between lncRNA:miRNA and miRNA:mRNA was tested using available online tools. All statistical analyses were accomplished using GraphPad Prism 5. Results: The expression of ZFAS1 was up-regulated in the metastatic FaDu cell line relative to the less aggressive SCC-25 and SCC-040 and dysplastic DOK cell lines. The TCGA data indicated an up-regulation of ZFAS1 in HNSCCs compared to normal tissue samples. The ZFAS1 levels typically differed depending on the cancer stage and T-stage. Patients with a lower expression of ZFAS1 presented a slightly longer disease-free survival and overall survival. The analysis of genes associated with ZFAS1, as well its targets, indicate that they are linked with crucial cellular processes. In the group of patients with low expression of ZFAS1, we detected the up-regulation of suppressors and down-regulation of genes associated with epithelial-to-mesenchymal transition (EMT) process, metastases, and cancer-initiating cells. Moreover, the negative correlation between ZFAS1 and its host gene, ZNFX1, was observed. The analysis of interactions indicated that ZFAS1 has a binding sequence for miR-150-5p. The expression of ZFAS1 and miR-150-5p is negatively correlated in HNSCC patients. miR-150-5p can regulate the 3′UTR of EIF4E mRNA. In the group of patients with high expression of ZFAS1 and low expression of miR-150-5p, we detected an up-regulation of EIF4E. Conclusions: In HNSCC, ZFAS1 displays oncogenic properties, regulates important processes associated with EMT, cancer-initiating cells, and metastases, and might affect patients’ clinical outcomes. ZFAS1 likely regulates the cell phenotype through miR-150-5p and its downstream targets. Following further validation, ZFAS1 might prove a new and valuable biomarker.

Pectolinarigenin Induced Cell Cycle Arrest, Autophagy, and Apoptosis in Gastric Cancer Cell via PI3K/AKT/mTOR Signaling Pathway

Pectolinarigenin (PEC), a natural flavonoid present in Cirsium chanroenicum and in some species of Citrus fruits, has various pharmacological benefits such as anti-inflammatory and anti-cancer activities. In the present study, we investigated the anti-cancer mechanism of PEC induced cell death caused by autophagy and apoptosis in AGS and MKN28 human gastric cancer cells. The PEC treatment significantly inhibited the AGS and MKN28 cell growth in a dose-dependent manner. Further, PEC significantly elevated sub-G1 phase in AGS cells and G2/M phase cell cycle arrest in both AGS and MKN28 cells. Apoptosis was confirmed by Annexin V and Hoechst 33342 fluorescent staining. Moreover, Immunoblotting results revealed that PEC treatment down-regulated the inhibitor of apoptosis protein (IAP) family protein XIAP that leads to the activation of caspase-3 thereby cleavage of PARP (poly-ADP-ribose polymerase) in both AGS and MKN28 cells in a dose-dependent manner. The autophagy-inducing effect was indicated by the increased formation of acidic vesicular organelles (AVOs) and increased protein levels of LC3-II conversion in both AGS and MKN28 cells. PEC shows the down regulation of PI3K/AKT/mTOR pathway which is a major regulator of autophagic and apoptotic cell death in cancer cells that leads to the down-regulation of p-4EBP1, p-p70S6K, and p-eIF4E in PEC treated cells when compared with the untreated cells. In conclusion, PEC treatment might have anti-cancer effect by down-regulation of PI3K/AKT/mTOR pathway leading to G2/M phase cell cycle arrest, autophagic and apoptotic cell death in human gastric cancer cells. Further studies of PEC treatment can support to develop as a potential alternative therapeutic agent for human gastric carcinoma.

Human herpesvirus-encoded kinase induces B cell lymphomas in vivo

Kaposi's sarcoma-associated herpesvirus (KSHV) is a gammaherpesvirus that is the etiological agent of the endothelial cell cancer Kaposi's sarcoma (KS) and 2 B cell lymphoproliferative disorders, primary effusion lymphoma (PEL) and multicentric Castleman's disease (MCD). KSHV ORF36, also known as viral protein kinase (vPK), is a viral serine/threonine kinase. We previously reported that KSHV vPK enhances cell proliferation and mimics cellular S6 kinase to phosphorylate ribosomal protein S6, a protein involved in protein synthesis. We created a mouse model to analyze the function of vPK in vivo. We believe this is the first mouse tumor model of a viral kinase encoded by a pathogenic human virus. We observed increased B cell activation in the vPK transgenic mice compared with normal mice. We also found that, over time, vPK transgenic mice developed a B cell hyperproliferative disorder and/or a high-grade B cell non-Hodgkin lymphoma at a greatly increased incidence compared with littermate controls. This mouse model shows that a viral protein kinase is capable of promoting B cell activation and proliferation as well as augmenting lymphomagenesis in vivo and may therefore contribute to the development of viral cancers.

Increased expression of MNK1b, the spliced isoform of MNK1, predicts poor prognosis and is associated with triple-negative breast cancer

MAP kinase interacting kinases (MNKs) modulate the function of oncogene eukaryotic initiation factor 4E (eIF4E) through phosphorylation, which is necessary for oncogenic transformation. MNK1 gives rise to two mRNAs and thus two MNK1 isoforms, named MNK1a and MNK1b. MNK1b, the splice variant of human MNK1a, is constitutively active and independent of upstream MAP kinases. In this study, we have analyzed the expression of both MNK1 isoforms in 69 breast tumor samples and its association with clinicopathologic/prognostic characteristics of breast cancer. MNK1a and MNK1b expression was significantly increased in tumors relative to the corresponding adjacent normal tissue (p < 0.001). In addition, MNK1b overexpression was found in most of the triple-negative tumors and was associated with a shorter overall and disease-free survival time. Overexpression of MNK1b in MDA-MB-231 cells induced an increase in the expression of the MCL1 antiapoptotic protein and promoted proliferation, invasion and colony formation. In conclusion, a high expression level of MNK1b protein could be used as a marker of poor prognosis in breast cancer patients and it could be a therapeutic target in triple-negative tumors.

CGP57380 enhances efficacy of RAD001 in non-small cell lung cancer through abrogating mTOR inhibition-induced phosphorylation of eIF4E and activating mitochondrial apoptotic pathway

The mammalian target of rapamycin (mTOR) is a potentially important therapeutic target in a broad range of cancer types. mTOR inhibitors such as rapamycin and its analogs (rapalogs) have been proven effective as anticancer agents in non-small cell lung cancer (NSCLC), whereas they strongly enhance phosphorylation of eukaryotic translation initiation factor 4E (eIF4E) and activation of Akt, which cause resistance to mTOR-targeted therapy after an initial response. Rapamycin induces eIF4E phosphorylation by activating MAPK-interacting kinases (Mnks), and therefore targeting Mnk/eIF4E pathway represents a potential therapeutic strategy for the treatment of NSCLC. Here, our results showed that over-expression of p-Mnk1 and p-eIF4E was significantly associated with poor overall survival of NSCLC patients and high expression of p-Mnk1 might act as an independent prognostic biomarker for these patients. Meanwhile, inhibiting Mnk1 expression by Mnk inhibitor (CGP57380) could abrogate rapalogs (RAD001)-induced eIF4E phosphorylation and Akt activation. Furthermore, combination of CGP57380 and RAD001 could induce NSCLC cells apoptosis via activating intrinsic mitochondrial pathway, and exert synergistic antitumor efficacy both in vitro and in vivo. In conclusion, combination of targeting both mTOR and Mnk/eIF4E signaling pathways to enhance effectiveness of mTOR-targeted cancer therapy might be significant innovation for the personalized treatment of NSCLC.

4EGI-1 induces apoptosis and enhances radiotherapy sensitivity in nasopharyngeal carcinoma cells via DR5 induction on 4E-BP1 dephosphorylation

The eIF4F complex regulated by a various group of eIF4E-binding proteins (4E-BPs) can initial the protein synthesis. Small molecule compound 4EGI-1, an inhibitor of the cap-dependent translation initiation through disturbing the interaction between eIF4E and eIF4G which are main elements of the eIF4E complex, has been reported to suppress cell proliferation by inducing apoptosis in many types of cancer. And death receptor 5 (DR5) is a major component in the extrinsic apoptotic pathway. However, the correlation among 4EGI-1, DR5 and 4E-BPs have not been discovered in NPC now. Therefore, we intend to find out the effect of 4EGI-1 on the apoptosis process of NPC and the relationship among 4EGI-1, DR5 and 4E-BPs. Our results revealed a significant down regulation of DR5 expression in NPC tissues, which inversely correlated with lymph node metastasis status and clinical stages. Depressed DR5 expression was an independent biomarker for poor prognosis in NPC, and elevated DR5 expression showed longer overall survival time in 174 NPC patients. Besides, 4EGI-1 induced apoptosis in NPC cells through the DR5-caspase-8 axis on 4E-BP1 and eIF4E dephosphorylation exerting positive influence on their anti-tumor activities. The induction of DR5 also sensitized NPC cells to radiotherapy, and the SER was 1.195. These results establish the death receptor pathway as a novel anticancer mechanism of eIF4E/eIF4G interaction inhibitor in NPC.

MNK1/2 inhibition limits oncogenicity and metastasis of KIT-mutant melanoma

Melanoma can be stratified into unique subtypes based on distinct pathologies. The acral/mucosal melanoma subtype is characterized by aberrant and constitutive activation of the proto-oncogene receptor tyrosine kinase C-KIT, which drives tumorigenesis. Treatment of these melanoma patients with C-KIT inhibitors has proven challenging, prompting us to investigate the downstream effectors of the C-KIT receptor. We determined that C-KIT stimulates MAP kinase-interacting serine/threonine kinases 1 and 2 (MNK1/2), which phosphorylate eukaryotic translation initiation factor 4E (eIF4E) and render it oncogenic. Depletion of MNK1/2 in melanoma cells with oncogenic C-KIT inhibited cell migration and mRNA translation of the transcriptional repressor SNAI1 and the cell cycle gene CCNE1. This suggested that blocking MNK1/2 activity may inhibit tumor progression, at least in part, by blocking translation initiation of mRNAs encoding cell migration proteins. Moreover, we developed an MNK1/2 inhibitor (SEL201), and found that SEL201-treated KIT-mutant melanoma cells had lower oncogenicity and reduced metastatic ability. Clinically, tumors from melanoma patients harboring KIT mutations displayed a marked increase in MNK1 and phospho-eIF4E. Thus, our studies indicate that blocking MNK1/2 exerts potent antimelanoma effects and support blocking MNK1/2 as a potential strategy to treat patients positive for KIT mutations.

MAP kinase-interacting serine/threonine kinase 2 promotes proliferation, metastasis, and predicts poor prognosis in non-small cell lung cancer

We hypothesized that MAP kinase-interacting serine/threonine kinase 2 (MNK2) may contribute to non-small cell lung cancer (NSCLC) development, and serve as a new therapeutic target. Immunohistochemical staining evaluated the correlation between MNK2 expression and clinicopathological features in 367 NSCLC cancer tissues. We determined the effects of MNK2 silencing in NSCLC cell lines in vitro and in vivo. RT-PCR and western blotting was used to examine the impact of MNK2 on ERK and AKT pathways. MNK2 was overexpressed in NSCLC cell lines and tumor tissues. Patients with MNK2 overexpression had lower OS rates (P < 0.001). High expression of MNK2 was correlated with lymph node metastasis (P = 0.008). MNK2 functioned as an independent prognostic factor for poor survival in patients with NSCLC (P = 0.003). MNK2 down-regulation inhibited proliferation, migration and invasion in vitro (P < 0.001), and reduced tumor growth and invasion in nude mice (P < 0.05). MNK2 enhanced phosphorylation of eIF4E, a downstream target of ERK and AKT pathways, which promoted NSCLC proliferation and invasion. We conclude that MNK2 overexpression in NSCLC is associated with proliferation, migration, invasion, and lower survival rates in patients via the phosphorylated eIF4E-mediated signaling pathway.

Eukaryotic translation initiation factors and cancer

Recent technological advancements have shown tremendous mechanistic accomplishments in our understanding of the mechanism of messenger RNA translation in eukaryotic cells. Eukaryotic messenger RNA translation is very complex process that includes four phases (initiation, elongation, termination, and ribosome recycling) and diverse mechanisms involving protein and non-protein molecules. Translation regulation is principally achieved during initiation step of translation, which is organized by multiple eukaryotic translation initiation factors. Eukaryotic translation initiation factor proteins help in stabilizing the formation of the functional ribosome around the start codon and provide regulatory mechanisms in translation initiation. Dysregulated messenger RNA translation is a common feature of tumorigenesis. Various oncogenic and tumor suppressive genes affect/are affected by the translation machinery, making the components of the translation apparatus promising therapeutic targets for the novel anticancer drug. This review provides details on the role of eukaryotic translation initiation factors in messenger RNA translation initiation, their contribution to onset and progression of tumor, and how dysregulated eukaryotic translation initiation factors can be used as a target to treat carcinogenesis.

Targeting EIF4F complex in non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) accounts for about 85–90% of lung cancer cases, which represents the leading cause of cancer-related death in the world. The majority of lung cancer patients doesn't respond well to conventional chemo-/radio-therapeutic regimens and have a poor prognosis. The recent introduction of targeted therapy and immunotherapy gives new hopes to NSCLC patients, but their outcome/prognosis is far from satisfactory. The translation initiation EIF4F complex has been shown to play important roles in cancer progression, but its functional role and therapeutic effect in lung cancers especially NSCLC remain largely unknown. In this current review, we summarize recent findings regarding the role of EIF4F complex in NSCLC progression and targeted therapy potentials. We also discuss the unanswered questions and future directions in this field.

BAY 1143269, a novel MNK1 inhibitor, targets oncogenic protein expression and shows potent anti-tumor activity

The initiation of mRNA translation has received increasing attention as an attractive target for cancer treatment in the recent years. The oncogenic eukaryotic translation initiation factor 4E (eIF4E) is the major substrate of MAP kinase-interacting kinase 1 (MNK1), and it is located at the junction of the cancer-associated PI3K and MAPK pathways. The fact that MNK1 is linked to cell transformation and tumorigenesis renders the kinase a promising target for cancer therapy. We identified a novel small molecule MNK1 inhibitor, BAY 1143269, by high-throughput screening and lead optimization. In kinase assays, BAY 1143269 showed potent and selective inhibition of MNK1. By targeting MNK1 activity, BAY 1143269 strongly regulated downstream factors involved in cell cycle regulation, apoptosis, immune response and epithelial-mesenchymal transition in vitro or in vivo. In addition, BAY 1143269 demonstrated strong efficacy in monotherapy in cell line and patient-derived non-small cell lung cancer xenograft models as well as delayed tumor regrowth in combination treatment with standard of care chemotherapeutics. In summary, the inhibition of MNK1 activity with a highly potent and selective inhibitor BAY 1143269 may provide an innovative approach for anti-cancer therapy.