Expression of the eukaryotic translation initiation factors 4E and 2alpha in non-Hodgkin's lymphomas

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.

Identification of a First-in-Class Small-Molecule Inhibitor of the EIF4E-RBM38 Complex That Enhances Wild-type TP53 Protein Translation for Tumor Growth Suppression

EIF4E, an mRNA cap-binding protein, is necessary for cap-dependent translation. Overexpression of EIF4E is known to promote cancer development by preferentially translating a group of oncogenic mRNAs. Thus, 4EGI-1, a disruptor of EIF4E-EIF4G1 interaction, was developed to inhibit oncoprotein expression for cancer therapy. Interestingly, RBM38, an RNA-binding protein, interacts with EIF4E on TP53 mRNA, prevents EIF4E from binding to TP53 mRNA cap, and inhibits TP53 expression. Thus, Pep8, an eight amino acid peptide derived from RBM38, was developed to disrupt the EIF4E-RBM38 complex, leading to increased TP53 expression and decreased tumor cell growth. Herein, we have developed a first-in-class small-molecule compound 094, which interacts with EIF4E via the same pocket as does Pep8, dissociates RBM38 from EIF4E, and enhances TP53 translation in RBM38- and EIF4E-dependent manners. Structure-activity relationship studies identified that both the fluorobenzene and ethyl benzamide are necessary for compound 094 to interact with EIF4E. Furthermore, we showed that compound 094 is capable of suppressing three-dimensional tumor spheroid growth in RBM38- and TP53-dependent manners. In addition, we found that compound 094 cooperates with the chemotherapeutic agent doxorubicin and EIF4E inhibitor 4EGI-1 to suppress tumor cell growth. Collectively, we showed that two distinct approaches can be used together to target EIF4E for cancer therapy by enhancing wild-type TP53 expression (094) and by suppressing oncoprotein expression (4EGI-1).

Translational Regulation by eIFs and RNA Modifications in Cancer

Translation is a fundamental process in all living organisms that involves the decoding of genetic information in mRNA by ribosomes and translation factors. The dysregulation of mRNA translation is a common feature of tumorigenesis. Protein expression reflects the total outcome of multiple regulatory mechanisms that change the metabolism of mRNA pathways from synthesis to degradation. Accumulated evidence has clarified the role of an increasing amount of mRNA modifications at each phase of the pathway, resulting in translational output. Translation machinery is directly affected by mRNA modifications, influencing translation initiation, elongation, and termination or altering mRNA abundance and subcellular localization. In this review, we focus on the translation initiation factors associated with cancer as well as several important RNA modifications, for which we describe their association with cancer.

Expression of eIF4E Gene in Glioma and Its Sensitivity to Oxidative Stress

Objective

Increased expression of eIF4E has been observed in various cancers, which makes eIF4E an attractive target of anticancer drugs. This study mainly discussed eIF4E gene expression in glioma and its sensitivity to oxidative stress (OS).

Methods

Relevant data from The Cancer Genome Atlas (TCGA) database regarding eIF4E gene expression and its prognostic significance in glioma samples were analyzed. Additionally, we measured eIF4E at mRNA and protein levels in clinical samples collected between July 2019 and September 2021, as well as glioma cell strains. U251 cells cultured in vitro were treated with OS injury induced by hydrogen peroxide (H₂O₂) and then transfected with si-eIF4E to determine changes in cell multiplication, invasiveness, and migration capacities as well as apoptosis rate. ELISA quantified cell malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) concentrations, and flow cytometry measured reactive oxygen species (ROS) level.

Results

In glioma samples from the TCGA database, eIF4E showed obviously elevated levels in LGG and GBM patients, which was usually associated with adverse patient prognosis (P < 0.05). eIF4E was also upregulated in glioma cell strains than in HBE cells. In comparison with the blank control group, transfection of si-eIF4E statistically suppressed the capacity of U251 cells to proliferate, invade and migrate, and enhance apoptosis rate, while reducing SOD and GSH-Px and increasing MDA and ROS. In addition, H₂O₂ induced the upregulation of eIF4E in U251 cells. H₂O₂ + si-eIF4E exhibited reduced multiplication and number of clone cell formation, invasion, and migration of U251 cells, as well as increased apoptosis rate than H₂O₂ + si-NC group.

Conclusions

eIF4E is highly expressed in glioma. Knocking down eIF4E can effectively inhibit the capacity of U251 to proliferate, invade and migrate, and significantly increase apoptosis. In addition, eIF4E knock-down is able to lower OS reaction under H₂O₂ inducement and enhance U251 cells' sensitivity to OS.

Multifaceted control of mRNA translation machinery in cancer

The mRNA translation machinery is tightly regulated through several, at times overlapping, mechanisms that modulate its efficiency and accuracy. Due to their fast rate of growth and metabolism, cancer cells require an excessive amount of mRNA translation and protein synthesis. However, unfavorable conditions, such as hypoxia, amino acid starvation, and oxidative stress, which are abundant in cancer, as well as many anti-cancer treatments inhibit mRNA translation. Cancer cells adapt to the various internal and environmental stresses by employing specialised transcript-specific translation to survive and gain a proliferative advantage. We will highlight the major signaling pathways and mechanisms of translation that regulate the global or mRNA-specific translation in response to the intra- or extra-cellular signals and stresses that are key components in the process of tumourigenesis.

A biphenyl inhibitor of eIF4E targeting an internal binding site enables the design of cell-permeable PROTAC-degraders

The eukaryotic translation initiation factor 4E (eIF4E) is the master regulator of cap-dependent protein synthesis. Overexpression of eIF4E is implicated in diseases such as cancer, where dysregulation of oncogenic protein translation is frequently observed. eIF4E has been an attractive target for cancer treatment. Here we report a high-resolution X-ray crystal structure of eIF4E in complex with a novel inhibitor (i4EG-BiP) that targets an internal binding site, in contrast to the previously described inhibitor, 4EGI-1, which binds to the surface. We demonstrate that i4EG-BiP is able to displace the scaffold protein eIF4G and inhibit the proliferation of cancer cells. We provide insights into how i4EG-BiP is able to inhibit cap-dependent translation by increasing the eIF4E-4E-BP1 interaction while diminishing the interaction of eIF4E with eIF4G. Leveraging structural details, we designed proteolysis targeted chimeras (PROTACs) derived from 4EGI-1 and i4EG-BiP and characterized these on biochemical and cellular levels. We were able to design PROTACs capable of binding eIF4E and successfully engaging Cereblon, which targets proteins for proteolysis. However, these initial PROTACs did not successfully stimulate degradation of eIF4E, possibly due to competitive effects from 4E-BP1 binding. Our results highlight challenges of targeted proteasomal degradation of eIF4E that must be addressed by future efforts.

Targeting translation regulators improves cancer therapy

Deregulation of protein synthesis may be involved in multiple aspects of cancer, such as gene expression, signal transduction and drive specific cell biological responses, resulting in promoting cancer growth, invasion and metastasis. Study the molecular mechanisms about translational control may help us to find more effective anti-cancer drugs and develop novel therapeutic opportunities. Recently, the researchers had focused on targeting translational machinery to overcome cancer, and various small molecular inhibitors targeting translation factors or pathways have been tested in clinical trials and exhibited improving outcomes in several cancer types. There is no doubt that an insight into the class of translation regulation protein would provide new target for pharmacologic intervention and further provide opportunities to develop novel anti-tumor therapeutic interventions. In this review, we summarized the developments of translational control in cancer survival and progression et al, and highlighted the therapeutic approach targeted translation regulation to overcome the cancer.

Genome-wide analysis of therapeutic response uncovers molecular pathways governing tamoxifen resistance in ER+ breast cancer

Background

Prioritization of breast cancer patients based on the risk of resistance to tamoxifen plays a significant role in personalized therapeutic planning and improving disease course and outcomes.

Methods

In this work, we demonstrate that a genome-wide pathway-centric computational framework elucidates molecular pathways as markers of tamoxifen resistance in ER+ breast cancer patients. In particular, we associated activity levels of molecular pathways with a wide spectrum of response to tamoxifen, which defined markers of tamoxifen resistance in patients with ER+ breast cancer.

Findings

We identified five biological pathways as markers of tamoxifen failure and demonstrated their ability to predict the risk of tamoxifen resistance in two independent patient cohorts (Test cohort1: log-rank p-value = 0.02, adjusted HR = 3.11; Test cohort2: log-rank p-value = 0.01, adjusted HR = 4.24). We have shown that these pathways are not markers of aggressiveness and outperform known markers of tamoxifen response. Furthermore, for adoption into clinic, we derived a list of pathway read-out genes and their associated scoring system, which assigns a risk of tamoxifen resistance for new incoming patients.

Interpretation

We propose that the identified pathways and their read-out genes can be utilized to prioritize patients who would benefit from tamoxifen treatment and patients at risk of tamoxifen resistance that should be offered alternative regimens.

Funding

This work was supported by the Rutgers SHP Dean's research grant, Rutgers start-up funds, Libyan Ministry of Higher Education and Scientific Research, and Katrina Kehlet Graduate Award from The NJ Chapter of the Healthcare Information Management Systems Society.

Targeted inhibition of mRNA translation initiation factors as a novel therapeutic strategy for mature B-cell neoplasms

Cancer development is frequently associated with dysregulation of mRNA translation to enhance both increased global protein synthesis and translation of specific mRNAs encoding oncoproteins. Thus, targeted inhibition of mRNA translation is viewed as a promising new approach for cancer therapy. In this article we review current progress in investigating dysregulation of mRNA translation initiation in mature B-cell neoplasms, focusing on chronic lymphocytic leukemia, follicular lymphoma and diffuse large B-cell lymphoma. We discuss mechanisms and regulation of mRNA translation, potential pathways by which genetic alterations and the tumor microenvironment alters mRNA translation in malignant B cells, preclinical evaluation of drugs targeted against specific eukaryotic initiation factors and current progress towards clinical development. Overall, inhibition of mRNA translation initiation factors is an exciting and promising area for development of novel targeted anti-tumor drugs.

Translating from cancer to the brain: regulation of protein synthesis by eIF4F

Formation of eukaryotic initiation factor 4F (eIF4F) is widely considered to be the rate-limiting step in cap-dependent translation initiation. Components of eIF4F are often up-regulated in various cancers, and much work has been done to elucidate the role of each of the translation initiation factors in cancer cell growth and survival. In fact, many of the basic mechanisms describing how eIF4F is assembled and how it functions to regulate translation initiation were first investigated in cancer cell lines. These same eIF4F translational control pathways also are relevant for neuronal signaling that underlies long-lasting synaptic plasticity and memory, and in neurological diseases where eIF4F and its upstream regulators are dysregulated. Although eIF4F is important in cancer and for brain function, there is not always a clear path to use the results of studies performed in cancer models to inform one of the roles that the same translation factors have in neuronal signaling. Issues arise when extrapolating from cell lines to tissue, and differences are likely to exist in how eIF4F and its upstream regulatory pathways are expressed in the diverse neuronal subtypes found in the brain. This review focuses on summarizing the role of eIF4F and its accessory proteins in cancer, and how this information has been utilized to investigate neuronal signaling, synaptic function, and animal behavior. Certain aspects of eIF4F regulation are consistent across cancer and neuroscience, whereas some results are more complicated to interpret, likely due to differences in the complexity of the brain, its billions of neurons and synapses, and its diverse cell types.

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.

Synthesis of 7-benzylguanosine cap-analogue conjugates for eIF4E targeted degradation

Eukaryotic translation initiation factor 4E (eIF4E) is a key player in the initiation of cap-dependent translation through recognition of the m⁷GpppX cap at the 5' terminus of coding mRNAs. As eIF4E overexpression has been observed in a number of human diseases, most notably cancer, targeting this oncogenic translation initiation factor has emerged as a promising strategy for the development of novel anti-cancer therapeutics. Toward this end, in the present study, we have rationally designed a series of Bn⁷GxP-based PROTACs for the targeted degradation of eIF4E. Herein we describe our synthetic efforts, in addition to biochemical and cellular characterization of these compounds.

PRMT7 methylates eukaryotic translation initiation factor 2α and regulates its role in stress granule formation

Protein arginine methyltransferases (PRMTs) are a family of enzymes that modify proteins by methylating the guanidino nitrogen atoms of arginine residues to regulate cellular processes such as chromatin remodeling, pre-mRNA splicing, and signal transduction. PRMT7 is the single type III PRMT solely capable of arginine monomethylation. To date, other than histone proteins, there are very few identified substrates of PRMT7. We therefore performed quantitative mass spectrometry experiments to identify PRMT7’s interactome and potential substrates to better characterize the enzyme’s biological function(s) in cells. These experiments revealed that PRMT7 interacts with and can methylate eukaryotic translation initiation factor 2 alpha (eIF2α), in vitro and in breast cancer cells. Furthermore, we uncovered a potential regulatory interplay between eIF2α arginine methylation by PRMT7 and stress-induced phosphorylation status of eIF2α at serine 51. Finally, we demonstrated that PRMT7 is required for eIF2α-dependent stress granule formation in the face of various cellular stresses. Altogether, our findings implicate PRMT7 as a novel mediator of eIF2α-dependent cellular stress response pathways.

A Blood Pact: the Significance and Implications of eIF4E on Lymphocytic Leukemia

Elevated levels of eukaryotic initiation factor 4E (eIF4E) are implicated in neoplasia, with cumulative evidence pointing to its role in the etiopathogenesis of hematological diseases. As a node of convergence for several oncogenic signaling pathways, eIF4E has attracted a great deal of interest from biologists and clinicians whose efforts have been targeting this translation factor and its biological circuits in the battle against leukemia. The role of eIF4E in myeloid leukemia has been ascertained and drugs targeting its functions have found their place in clinical trials. Little is known, however, about the pertinence of eIF4E to the biology of lymphocytic leukemia and a paucity of literature is available in this regard that prospectively evaluates the topic to guide practice in hematological cancer. A comprehensive analysis on the significance of eIF4E translation factor in the clinical picture of leukemia arises, therefore, as a compelling need. This review presents aspects of eIF4E involvement in the realm of the lymphoblastic leukemia status; translational control of immunological function via eIF4E and the state-of-the-art in drugs will also be outlined.

The eIF2-alpha kinase HRI: a potential target beyond the red blood cell

INTRODUCTION

The eIF2α kinase heme-regulated inhibitor (HRI) is one of four well-described kinases that phosphorylate eIF2α in response to various cell stressors, resulting in reduced ternary complex formation and attenuation of mRNA translation. Although HRI is well known for its role as a heme sensor in erythroid progenitors, pharmacologic activation of HRI has been demonstrated to have anti-cancer activity across a wide range of tumor sub-types. Here, the potential of HRI activators as novel cancer therapeutics is explored. Areas covered: We provide an introduction to eIF2 signaling pathways in general, and specifically review data on the eIF2α kinase HRI in erythroid and non-erythroid cells. We review aspects of targeting eIF2 signaling in cancer and highlight promising data using HRI activators against tumor cells. Expert opinion: Pharmacologic activation of HRI inhibits tumor growth as a single agent without appreciable toxicity in vivo. The ability of HRI activators to provide direct and sustained eIF2α phosphorylation without inducing oxidative stress or broad eIF2α kinase activation may be especially advantageous for tolerability. Combination therapy with established therapeutics may further augment anti-cancer activity to overcome disease resistance.

Translational control and the cancer cell response to stress

The evidence for the importance of aberrant translation in cancer cells is overwhelming. Reflecting the wealth of data, there are excellent reviews delineating how ribosomes and initiation factors are linked to cancer [1-3], and the therapeutic strategies being devised to target them [4]. Changes in translational efficiency can engender a malignant phenotype without the need for chromatin reorganization, transcription, splicing and mRNA export [5,6]. Thus, cancer-related modulations of the translational machinery are ideally suited to allow cancer cells to respond to the various stresses encountered along the path of tumorigenesis and organism-wide dissemination [7^•,8,9,10^•]. Emerging findings supporting this notion are the focus of this review.

Role of Eukaryotic Initiation Factors during Cellular Stress and Cancer Progression

Protein synthesis can be segmented into distinct phases comprising mRNA translation initiation, elongation, and termination. Translation initiation is a highly regulated and rate-limiting step of protein synthesis that requires more than 12 eukaryotic initiation factors (eIFs). Extensive evidence shows that the transcriptome and corresponding proteome do not invariably correlate with each other in a variety of contexts. In particular, translation of mRNAs specific to angiogenesis, tumor development, and apoptosis is altered during physiological and pathophysiological stress conditions. In cancer cells, the expression and functions of eIFs are hampered, resulting in the inhibition of global translation and enhancement of translation of subsets of mRNAs by alternative mechanisms. A precise understanding of mechanisms involving eukaryotic initiation factors leading to differential protein expression can help us to design better strategies to diagnose and treat cancer. The high spatial and temporal resolution of translation control can have an immediate effect on the microenvironment of the cell in comparison with changes in transcription. The dysregulation of mRNA translation mechanisms is increasingly being exploited as a target to treat cancer. In this review, we will focus on this context by describing both canonical and noncanonical roles of eIFs, which alter mRNA translation.

Translation initiation complex eIF4F is a therapeutic target for dual mTOR kinase inhibitors in non-Hodgkin lymphoma

Deregulated mRNA translation has been implicated in disease development and in part is controlled by a eukaryotic initiation complex eIF4F (composed of eIF4E, eIF4G and eIF4A). We demonstrate here that the cap bound fraction from lymphoma cells was enriched with eIF4G and eIF4E indicating that lymphoma cells exist in an activated translational state. Moreover, 77% (110/142) of diffuse large B cell lymphoma tumors expressed eIF4E and this was associated with an inferior event free survival. Over-expression of wild-type eIF4E (eIF4E(WT)) but not cap-mutant eIF4E (eIF4E(cap mutant)) increased the activation of the eIF4F complex. Treatment with the active-site dual mTOR inhibitor CC214-1 reduced the level of the eIF4F complex by decreasing the cap bound fraction of eIF4G and increasing the levels of 4E-BP1. CC214-1 inhibited both the cap dependent and global protein translation. CC214-1 inhibited c-Myc, and cyclin D3 translation by decreasing polysomal fractions from lymphoma cells. Inhibition of eIF4E with shRNA further decreased the CC214-1 induced inhibition of the eIF4F complex, c-Myc, cyclin D3 translation, and colony formation. These studies demonstrate that the eIF4F complex is deregulated in aggressive lymphoma and that dual mTOR therapy has therapeutic potential in these patients.

The synergistic inhibition of breast cancer proliferation by combined treatment with 4EGI-1 and MK2206

Cap-dependent translation is a potential cancer-related target (oncotarget) due to its critical role in cancer initiation and progression. 4EGI-1, an inhibitor of eIF4E/eIF4G interaction, was discovered by screening chemical libraries of small molecules. 4EGI-1 inhibits cap-dependent translation initiation by impairing the assembly of the eIF4E/eIF4G complex, and therefore is a potential anti-cancer agent. Here, we report that 4EGI-1 also inhibits mTORC1 signaling independent of its inhibitory role on cap-dependent translation initiation. The inhibition of mTORC1 signaling by 4EGI-1 activates Akt due to both abrogation of the negative feedback loops from mTORC1 to PI3K and activation of mTORC2. We further validated that mTORC2 activity is required for 4EGI-1-mediated Akt activation. The activated Akt counteracted the anticancer effects of 4EGI-1. In support of this model, inhibition of Akt potentiates the antitumor activity of 4EGI-1 both in vitro and in a xenograft mouse model in vivo. Our results suggest that a combination of 4EGI-1and Akt inhibitor is a rational approach for the treatment of cancer.

Antisense oligonucleotide targeting eukaryotic translation initiation factor 4E reduces growth and enhances chemosensitivity of non-small-cell lung cancer cells

Elevated levels of eukaryotic translation initiation factor 4E (eIF4E) enhance translation of many malignancy-related proteins, such as vascular endothelial growth factor (VEGF), c-Myc and osteopontin. In non-small-cell lung cancer (NSCLC), levels of eIF4E are significantly increased compared with normal lung tissue. Here, we used an antisense oligonucleotide (ASO) to inhibit the expression of eIF4E in NSCLC cell lines. eIF4E levels were significantly reduced in a dose-dependent manner in NSCLC cells treated with eIF4E-specific ASO (4EASO) compared with control ASO. Treatment of NSCLC cells with the 4EASO resulted in decreased cap-dependent complex formation, decreased cell proliferation and increased sensitivity to gemcitabine. At the molecular level, repression of eIF4E with ASO resulted in decreased expression of the oncogenic proteins VEGF, c-Myc and osteopontin, whereas expression of β-actin was unaffected. Based on these findings, we conclude that eIF4E-silencing therapy alone or in conjunction with chemotherapy represents a promising approach deserving of further investigation in future NSCLC clinical trials.

Decreased expression of EIF4A1 after preoperative brachytherapy predicts better tumor-specific survival in cervical cancer

OBJECTIVE

The aim of this study is to investigate whether EIF4A1, EIF4E, and EIF4G1 can serve as prognostic markers for patients with cervical cancer receiving preoperative brachytherapy.

MATERIALS AND METHODS

Tissue microarrays composed of 35 normal cervix samples, 87 cervical cancers treated without preoperative therapy, and 50 pairs of cervical cancer tissues collected before and after preoperative brachytherapy were constructed and evaluated for the expression of EIF4A1, EIF4E, and EIF4G using immunohistochemistry. Immunohistochemical staining was scored by the staining intensity and the percentages of tumor cells. The χ test was used to analyze the association between the immunohistochemistry results and clinicopathologic variables. The Kaplan-Meier method was applied to analyze the disease-specific survival.

RESULTS

Overexpression of EIF4A1, EIF4E, and EIF4G1 were detected in 83.9%, 84.7%, and 80.3% of cervical cancers, respectively, all of which were significantly related to advanced International Federation of Gynecology and Obstetrics stage, squamous cell histology, lymph node metastasis, and deep stromal invasion (P < 0.05). The altered expression pattern of EIF4A1 and EIF4E after preoperative brachytherapy was significantly correlated with the cervical cancer response to brachytherapy (P = 0.029 and 0.012, respectively). The decreased expression of EIF4A1 predicted better tumor-specific survival (P = 0.02). The alteration of EIF4A1 was an independent predictor for tumor-specific survival (P = 0.047; hazards ratio, 0.272; 95% confidence interval, 0.076-0.982).

CONCLUSIONS

Overexpression of EIF4A1, EIF4E, and EIF4G1 were acquired malignant phenotypic features of cervical cancer. EIF4A1 might function as a novel prognostic indicator and a potential therapeutic target for cervical cancer.

Probing the binding mechanism of Mnk inhibitors by docking and molecular dynamics simulations

Mitogen-activated protein kinases-interacting kinase 1 and 2 (Mnk1/2) activate the oncogene eukaryotic initiation factor 4E (eIF4E) by phosphorylation. High level of phosphorylated eIF4E is associated with various types of cancers. Inhibition of Mnk prevents eIF4E phosphorylation, making them potential therapeutic targets for cancer. Recently, we have designed and synthesized a series of novel imidazopyridine and imidazopyrazine derivatives that inhibit Mnk1/2 kinases with a potency in the nanomolar to micromolar range. In the current work we model the inhibition of Mnk kinase activity by these inhibitors using various computational approaches. Combining homology modeling, docking, molecular dynamics simulations, and free energy calculations, we find that all compounds bind similarly to the active sites of both kinases with their imidazopyridine and imidazopyrazine cores anchored to the hinge regions of the kinases through hydrogen bonds. In addition, hydrogen bond interactions between the inhibitors and the catalytic Lys78 (Mnk1), Lys113 (Mnk2) and Ser131 (Mnk1), Ser166 (Mnk2) appear to be important for the potency and stability of the bound conformations of the inhibitors. The computed binding free energies (ΔGPred) of these inhibitors are in accord with experimental bioactivity data (pIC50) with correlation coefficients (r(2)) of 0.70 and 0.68 for Mnk1 and Mnk2 respectively. van der Waals energies and entropic effects appear to dominate the binding free energy (ΔGPred) for each Mnk-inhibitor complex studied. The models suggest that the activities of these small molecule inhibitors arise from interactions with multiple residues in the active sites, particularly with the hydrophobic residues.

Translational control by oncogenic signaling pathways

Messenger RNA (mRNA) translation is highly regulated in cells and plays an integral role in the overall process of gene expression. The initiation phase of translation is considered to be the most rate-limiting and is often targeted by oncogenic signaling pathways to promote global protein synthesis and the selective translation of tumor-promoting mRNAs. Translational control is a crucial component of cancer development as it allows cancer cells to adapt to the altered metabolism that is generally associated with the tumor state. The phosphoinositide 3-kinase (PI3K)/Akt and Ras/mitogen-activated protein kinase (MAPK) pathways are strongly implicated in cancer etiology, and they exert their biological effects by modulating both global and specific mRNA translation. In addition to having respective translational targets, these pathways also impinge on the mechanistic/mammalian target of rapamycin (mTOR), which acts as a critical signaling node linking nutrient sensing to the coordinated regulation of cellular metabolism. mTOR is best known as a central regulator of protein synthesis and has been implicated in an increasing number of pathological conditions, including cancer. In this article, we describe the current knowledge on the roles and regulation of mRNA translation by various oncogenic signaling pathways, as well as the relevance of these molecular mechanisms to human malignancies. This article is part of a Special Issue entitled: Translation and cancer.

Celastrol induces unfolded protein response-dependent cell death in head and neck cancer

The survival rate for patients with oral squamous cell carcinoma (OSCC) has not seen marked improvement in recent decades despite enhanced efforts in prevention and the introduction of novel therapies. We have reported that pharmacological exacerbation of the unfolded protein response (UPR) is an effective approach to killing OSCC cells. The UPR is executed via distinct signaling cascades whereby an initial attempt to restore folding homeostasis in the endoplasmic reticulum during stress is complemented by an apoptotic response if the defect cannot be resolved. To identify novel small molecules able to overwhelm the adaptive capacity of the UPR in OSCC cells, we engineered a complementary cell-based assay to screen a broad spectrum of chemical matter. Stably transfected CHO-K1 cells that individually report (luciferase) on the PERK/eIF2α/ATF4/CHOP (apoptotic) or the IRE1/XBP1 (adaptive) UPR pathways, were engineered [1]. The triterpenoids dihydrocelastrol and celastrol were identified as potent inducers of UPR signaling and cell death in a primary screen and confirmed in a panel of OSCC cells and other cancer cell lines. Biochemical and genetic assays using OSCC cells and modified murine embryonic fibroblasts demonstrated that intact PERK-eIF2-ATF4-CHOP signaling is required for pro-apoptotic UPR and OSCC death following celastrol treatment.

Phosphorylated Mnk1 and eIF4E are associated with lymph node metastasis and poor prognosis of nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a head and neck malignant tumor rare throughout most of the world but common in Southeast Asia, especially in Southern China. The phosphorylation of eukaryotic translation initiation factor 4E (eIF4E) by MAP kinase-interacting kinases (Mnk) on Ser-209 promotes cellular proliferation, survival, malignant transformation and metastasis. However, whether the alterations of the expression of p-eIF4E and p-Mnk1 protein are associated with clinicopathologic/prognostic implication for NPC has not been reported. The purposes of the present study are to examine the expression of p-eIF4E and p-Mnk1 protein in NPC and non-cancerous nasopharyngeal epithelial tissues by immunohistochemistry and evaluate the association between the expression of p-eIF4E and p-Mnk1 protein and clinicopathological characteristics of NPC. The results showed that the positive percentage of p-Mnk1 and p-eIF4E proteins expression in NPC (83.5% and 75.4%, respectively) was significantly higher than that in non-cancerous nasopharyngeal epithelium (40.0% and 32.9%, respectively). The positive expression of p-eIF4E and p-Mnk1 in the NPC with cervical lymph node metastasis was significantly higher than those without lymph node metastasis. Additionally, p-eIF4E expression was more pronouncedly increased in metastatic NPC than the matched primary NPC. Increase of p-eIF4E and p-Mnk1 expression was significantly correlated inversely with overall survival. Spearman’s rank correlation test further showed that expression of p-Mnk1 was strongly positive correlated with expression of p-eIF4E in NPC. The expression of p-Mnk1 and p-eIF4E in NPC was proved to be the independent prognostic factors regardless of lymph node metastasis, clinical stages and combination of radiotherapy and chemotherapy, histological type, age and gender by multivariate analysis. Taken together, high expression of p-Mnk1 and p-eIF4E might be novel valuable biomarkers to predict poor prognosis of NPC and therapeutic targets for developing the valid treatment strategies.

Down-regulation of eIF4GII by miR-520c-3p represses diffuse large B cell lymphoma development

Deregulation of the translational machinery is emerging as a critical contributor to cancer development. The contribution of microRNAs in translational gene control has been established however; the role of microRNAs in disrupting the cap-dependent translation regulation complex has not been previously described. Here, we established that elevated miR-520c-3p represses global translation, cell proliferation and initiates premature senescence in HeLa and DLBCL cells. Moreover, we demonstrate that miR-520c-3p directly targets translation initiation factor, eIF4GII mRNA and negatively regulates eIF4GII protein synthesis. miR-520c-3p overexpression diminishes cells colony formation and reduces tumor growth in a human xenograft mouse model. Consequently, downregulation of eIF4GII by siRNA decreases translation, cell proliferation and ability to form colonies, as well as induces cellular senescence. In vitro and in vivo findings were further validated in patient samples; DLBCL primary cells demonstrated low miR-520c-3p levels with reciprocally up-regulated eIF4GII protein expression. Our results provide evidence that the tumor suppressor effect of miR-520c-3p is mediated through repression of translation while inducing senescence and that eIF4GII is a key effector of this anti-tumor activity.

Control of gene expression on the translational level is critical for proper function of major cellular processes and deregulation of translation can promote cellular transformation. Emerging actors in this post-transcriptional gene regulation are small non-coding RNAs referred to as microRNAs (miRNAs). We established that miR-520c-3p represses tumor growth through the repression of eIF4GII, a major structural component of the translation initiation complex. Since translation of most cellular mRNAs is primarily regulated at the level of initiation, this node is becoming a potential target for therapeutic intervention. Identified in this study, tumor suppressor function of miR-520c-3p is mediated through the inhibition of translational factor eIF4GII, resulting in the repression of global translational machinery and induction of senescence in tumor cells. While aging and senescence has been shown to be associated with reduced translation the linkage between translational deregulation and senescence in malignant cells has not been previously described. Lending further clinical significance to our findings, we were able to demonstrate that primary DLBCL samples had elevated levels of eIF4GII while having reciprocally low miR-520c-3p expression.

Cancer cells exploit eIF4E2-directed synthesis of hypoxia response proteins to drive tumor progression

Human tumors display considerable diversity in their genetic makeup but share common physiologic attributes such as a hypoxic microenvironment that contribute to the malignant phenotype. Hypoxic cells switch from eukaryotic initiation factor 4E (eIF4E) to eIF4E2 cap-dependent translation to synthesize a portion of their proteins. Here, we show that genetically distinct human cancer cells exploit eIF4E2-directed protein synthesis to form cellular masses larger than approximately 0.15 mm, the diffusion limit of oxygen. Cancer cells depleted of eIF4E2 are indistinguishable from control cells under normoxic conditions, but are unable to survive and proliferate in low oxygen conditions. Activation of eIF4E2-directed translation is essential for cancer cells to form a hypoxic tumor core in in vitro spheroids and to form detectable tumors in in vivo xenograft assays. In contrast, the eIF4E-directed protein synthesis pathway alone cannot sustain cellular adaptation to hypoxia in vitro or confer tumorigenic potential in xenograft assays. These data demonstrate that the phenotypic expression of the cancer genome requires translation by the eIF4E2-directed hypoxic protein synthesis machinery.

Targeting eukaryotic translation in mesothelioma cells with an eIF4E-specific antisense oligonucleotide

BACKGROUND

Aberrant cap-dependent translation is implicated in tumorigenesis in multiple tumor types including mesothelioma. In this study, disabling the eIF4F complex by targeting eIF4E with eIF4E-specific antisense oligonucleotide (4EASO) is assessed as a therapy for mesothelioma.

METHODS

Mesothelioma cells were transfected with 4EASO, designed to target eIF4E mRNA, or mismatch-ASO control. Cell survival was measured in mesothelioma treated with 4EASO alone or combined with either gemcitabine or pemetrexed. Levels of eIF4E, ODC, Bcl-2 and β-actin were assessed following treatment. Binding to a synthetic cap-analogue was used to study the strength of eIF4F complex activation following treatment.

RESULTS

eIF4E level and the formation of eIF4F cap-complex decreased in response to 4EASO, but not mismatch control ASO, resulting in cleavage of PARP indicating apoptosis. 4EASO treatment resulted in dose dependent decrease in eIF4E levels, which corresponded to cytotoxicity of mesothelioma cells. 4EASO resulted in decreased levels of eIF4E in non-malignant LP9 cells, but this did not correspond to increased cytotoxicity. Proteins thought to be regulated by cap-dependent translation, Bcl-2 and ODC, were decreased upon treatment with 4EASO. Combination therapy of 4EASO with pemetrexed or gemcitabine further reduced cell number.

CONCLUSION

4EASO is a novel drug that causes apoptosis and selectively reduces eIF4E levels, eIF4F complex formation, and proliferation of mesothelioma cells. eIF4E knockdown results in decreased expression of anti-apoptotic and pro-growth proteins and enhances chemosensitivity.

Eukaryotic translation initiation factors in cancer development and progression

Eukaryotic gene expression is a complicated process primarily regulated at the levels of gene transcription and mRNA translation. The latter involves four main steps: initiation, elongation, termination and recycling. Translation regulation is primarily achieved during initiation which is orchestrated by 12 currently known eukaryotic initiation factors (eIFs). Here, we review the current state of eIF research and present a concise summary of the various eIF subunits. As eIFs turned out to be critically implicated in different oncogenic processes the various eIF members and their contribution to onset and progression of cancer are featured.

Cap-translation inhibitor, 4EGI-1, restores sensitivity to ABT-737 apoptosis through cap-dependent and -independent mechanisms in chronic lymphocytic leukemia

PURPOSE

The lymph node microenvironment promotes resistance to chemotherapy in chronic lymphocytic leukemia (CLL), partly through induction of BCL2 family prosurvival proteins. Currently available inhibitors do not target all BCL2 family prosurvival proteins and their effectiveness is also modified by proapoptotic BCL2 homology domain 3 (BH3) only protein expression. The goal of this study was to evaluate synergy between the eIF4E/eIF4G interaction inhibitor, 4EGI-1, and the BH3 mimetic, ABT-737.

EXPERIMENTAL DESIGN

CLL cells were cultured in conditions to mimic the lymph node microenvironment. Protein synthesis and cap-complex formation were determined. Polysome association of mRNAs from BCL2 family survival genes was analyzed by translational profiling. The effects of 4EGI-1 and the BCL2/BCL2L1 antagonist, ABT-737, on CLL cell apoptosis were determined.

RESULTS

Protein synthesis was increased approximately 6-fold by stromal cell/CD154 culture in a phosphoinositide 3-kinase α (PI3Kα)-specific manner and was reduced by 4EGI-1. PI3K inhibitors and 4EGI-1 also reduced cap-complex formation but only 4EGI-1 consistently reduced BCL2L1 and BCL2A1 protein levels. 4EGI-1, but not PI3K inhibitors or rapamycin, induced an endoplasmic reticulum stress response including proapoptotic NOXA and the translation inhibitor phosphorylated eIF2α. 4EGI-1 and ABT-737 synergized to cause apoptosis, independent of levels of prosurvival protein expression in individual patients.

CONCLUSIONS

Overall protein synthesis and cap-complex formation are induced by microenvironment stimuli in CLL. Inhibition of the cap-complex was not sufficient to repress BCL2 family prosurvival expression, but 4EGI-1 inhibited BCL2A1 and BCL2L1 while inducing NOXA through cap-dependent and -independent mechanisms. 4EGI-1 and ABT-737 synergized to produce apoptosis, and these agents may be the basis for a therapeutically useful combination.

Upregulation of the eIF4E signaling pathway contributes to the progression of gastric cancer, and targeting eIF4E by perifosine inhibits cell growth

The increase of eukaryotic translation initiation factor 4E (eIF4E) expression is frequently observed in several types of cancer, making eIF4E an attractive anticancer drug target. However, the role of eIF4E in gastric cancer pathogenesis remains unclear. Perifosine is a bioavailable alkylphospholipid exhibiting antitumor activity in a series of cancer types. In this study, gastric cancer cell lines were selected to explore the role of eIF4E as a potential target for treating human gastric cancer. The expression of total eIF4E (T-eIF4E)and phosphorylated eIF4E (p-eIF4E) in gastric cancer samples was detected by immunohistochemical assay. RNA interference was used to silence eIF4E expression. Sulforhodamine B assay was performed to evaluate tumor cell viability. Colony formation assay was used to examine the effects of eIF4E small interfering RNA (siRNA) or perifosine on colony formation. The mRNA levels of eIF4E were analyzed by qRT-PCR and western blot analysis was carried out to evaluate the expression of Akt and eIF4E. The results showed that increased expression levels of T-eIF4E and p-eIF4E were found in gastric cancer tissues and cells. Reduced eIF4E expression blocked the proliferation of gastric cancer cells. Perifosine downregulated the T-eIF4E and p-eIF4E levels in a dose- and time-dependent manner; it also inhibited the growth of gastric cancer cells. Moreover, this inhibitory effect was significantly enhanced by the combination of eIF4E siRNA and perifosine treatments. Our results indicate that eIF4E gene silencing can inhibit tumor cell growth, and eIF4E can be developed as a promising therapeutic target for gastric cancer.

Tumor suppression by small molecule inhibitors of translation initiation

Translation initiation factors are over-expressed and/or activated in many human cancers and may contribute to their genesis and/or progression. Removal of physiologic restraints on translation initiation causes malignant transformation. Conversely, restoration of physiological restrains on translation initiation reverts malignant phenotypes. Here, we extensively characterize the anti-cancer activity of two small molecule inhibitors of translation initiation: #1181, which targets the eIF2-GTP-Met-tRNA_i ternary complex, and 4EGI-1, which targets the eIF4F complex. In vitro, both molecules inhibit translation initiation, abrogate preferentially translation of mRNAs coding for oncogenic proteins, and inhibit proliferation of human cancer cells. In vivo, both #1181 and 4EGI-1 strongly inhibit growth of human breast and melanoma cancer xenografts without any apparent macroscopic- or microscopic-toxicity. Mechanistically, #1181 phosphorylates eIF2α while 4EGI-1 disrupts eIF4G/eIF4E interaction in the tumors excised from mice treated with these agents. These data indicate that inhibition of translation initiation is a new paradigm in cancer therapy.

Translational control in cancer etiology

The link between perturbations in translational control and cancer etiology is becoming a primary focus in cancer research. It has now been established that genetic alterations in several components of the translational apparatus underlie spontaneous cancers as well as an entire class of inherited syndromes known as "ribosomopathies" associated with increased cancer susceptibility. These discoveries have illuminated the importance of deregulations in translational control to very specific cellular processes that contribute to cancer etiology. In addition, a growing body of evidence supports the view that deregulation of translational control is a common mechanism by which diverse oncogenic pathways promote cellular transformation and tumor development. Indeed, activation of these key oncogenic pathways induces rapid and dramatic translational reprogramming both by increasing overall protein synthesis and by modulating specific mRNA networks. These translational changes promote cellular transformation, impacting almost every phase of tumor development. This paradigm represents a new frontier in the multihit model of cancer formation and offers significant promise for innovative cancer therapies. Current research, in conjunction with cutting edge technologies, will further enable us to explore novel mechanisms of translational control, functionally identify translationally controlled mRNA groups, and unravel their impact on cellular transformation and tumorigenesis.

Translation inhibitors induce cell death by multiple mechanisms and Mcl-1 reduction is only a minor contributor

There is significant interest in treating cancers by blocking protein synthesis, to which hematological malignancies seem particularly sensitive. The translation elongation inhibitor homoharringtonine (Omacetaxine mepesuccinate) is undergoing clinical trials for chronic myeloid leukemia, whereas the translation initiation inhibitor silvestrol has shown promise in mouse models of cancer. Precisely how these compounds induce cell death is unclear, but reduction in Mcl-1, a labile pro-survival Bcl-2 family member, has been proposed to constitute the critical event. Moreover, the contribution of translation inhibitors to neutropenia and lymphopenia has not been precisely defined. Herein, we demonstrate that primary B cells and neutrophils are highly sensitive to translation inhibitors, which trigger the Bax/Bak-mediated apoptotic pathway. However, contrary to expectations, reduction of Mcl-1 did not significantly enhance cytotoxicity of these compounds, suggesting that it does not have a principal role and cautions that strong correlations do not always signify causality. On the other hand, the killing of T lymphocytes was less dependent on Bax and Bak, indicating that translation inhibitors can also induce cell death via alternative mechanisms. Indeed, loss of clonogenic survival proved to be independent of the Bax/Bak-mediated apoptosis altogether. Our findings warn of potential toxicity as these translation inhibitors are cytotoxic to many differentiated non-cycling cells.

Targeting Mnks for cancer therapy

Deregulation of protein synthesis is a common event in human cancer and a key player in translational control is eIF4E. Elevated expression levels of eIF4E promote cancer development and progression. Recent findings suggest that eIF4E activity is a key determinant of the PI3K/Akt/mTOR and Ras/Raf/MEK/ERK mediated tumorigenic activity and targeting eIF4E should have a major impact on these pathways in human cancer. The function of eIF4E is modulated through phosphorylation of a conserved serine (Ser209) by Mnk1 and Mnk2 downstream of ERK. While the phosphorylation event is necessary for oncogenic transformation, it seems to be dispensable for normal development. Hence, pharmacologic Mnk inhibitors may provide non-toxic and effective anti-cancer strategy. Strong circumstantial evidence indicates that Mnk inhibition presents attractive therapeutic potential, but the lack of selective Mnk inhibitors has so far confounded pharmacological target validation and clinical development.

Asthma and COPD - The C/EBP Connection

Asthma and chronic obstructive pulmonary disease (COPD) are the two most prominent chronic inflammatory lung diseases with increasing prevalence. Both diseases are associated with mild or severe remodeling of the airways. In this review, we postulate that the pathologies of asthma and COPD may result from inadequate responses and/or a deregulated balance of a group of cell differentiation regulating factors, the CCAAT/Enhancer Binding Proteins (C/EBPs). In addition, we will argue that the exposure to environmental factors, such as house dust mite and cigarette smoke, changes the response of C/EBPs and are different in diseased cells. These novel insights may lead to a better understanding of the etiology of the diseases and may provide new aspects for therapies.

Structure-guided design, synthesis, and evaluation of guanine-derived inhibitors of the eIF4E mRNA-cap interaction

The eukaryotic initiation factor 4E (eIF4E) plays a central role in the initiation of gene translation and subsequent protein synthesis by binding the 5' terminal mRNA cap structure. We designed and synthesized a series of novel compounds that display potent binding affinity against eIF4E despite their lack of a ribose moiety, phosphate, and positive charge as present in m7-GMP. The biochemical activity of compound 33 is 95 nM for eIF4E in an SPA binding assay. More importantly, the compound has an IC(50) of 2.5 μM for inhibiting cap-dependent mRNA translation in a rabbit reticular cell extract assay (RRL-IVT). This series of potent, truncated analogues could serve as a promising new starting point toward the design of neutral eIF4E inhibitors with physicochemical properties suitable for cellular activity assessment.

A review of the association between osteosarcoma metastasis and protein translation

The malignant transformation of mesenchymal cells within the bone leads to the development of osteosarcoma (OS), but the genetic underpinnings of these events are not understood. From a clinical perspective, primary tumour management can be achieved successfully in most patients. However, the development of metastasis to the lungs represents the most common cause of death in OS patients. A clearer understanding of metastasis biology is required to improve cancer mortality and improve outcomes. Modelling the genetics, biology and therapy of OS can be accomplished through research involving a number of species. Most notable is the naturally occurring form of OS that develops in dogs. Through a cross-species and comparative approach important questions can be asked within specific and suitable models to advance our understanding of this disease and its common metastatic outcome. A comparative perspective on the problem of OS metastasis that utilizes a cross-species approach may offer unique opportunities to assist in this prioritization and generate new hypotheses related to this important clinical problem.

Translational control gone awry: a new mechanism of tumorigenesis and novel targets of cancer treatments

Translational control is one of primary regulation mechanisms of gene expression. Eukaryotic translational control mainly occurs at the initiation step, the speed-limiting step, which involves more than ten translation initiation factors [eIFs (eukaryotic initiation factors)]. Changing the level or function of these eIFs results in abnormal translation of specific mRNAs and consequently abnormal growth of cells that leads to human diseases, including cancer. Accumulating evidence from recent studies showed that the expression of many eIFs was associated with malignant transformation, cancer prognosis, as well as gene expression regulation. In the present paper, we perform a critical review of recent advances in understanding the role and mechanism of eIF action in translational control and cancer as well as the possibility of targeting eIFs for therapeutic development.

The cancerous translation apparatus

Deregulations in translational control are critical features of cancer initiation and progression. Activation of key oncogenic pathways promotes rapid and dramatic translational reprogramming, not simply by increasing overall protein synthesis, but also by modulating specific mRNA networks that promote cellular transformation. Additionally, ribosomopathies caused by mutations in ribosome components alter translational regulation leading to specific pathological features, including cancer susceptibility. Exciting advances in our understanding of translational control in cancer have illuminated a striking specificity innate to the translational apparatus. Characterizing this specificity will provide novel insights into how cells normally utilize translational control to modulate gene expression, how it is deregulated in cancer, and how these processes can be targeted to develop new cancer therapies.