Zotatifin, an eIF4A-Selective Inhibitor, Blocks Tumor Growth in Receptor Tyrosine Kinase Driven Tumors

Targeting eIF4A triggers an interferon response to synergize with chemotherapy and suppress triple-negative breast cancer

Protein synthesis is frequently dysregulated in cancer and selective inhibition of mRNA translation represents an attractive cancer therapy. Here, we show that therapeutically targeting the RNA helicase eIF4A with zotatifin, the first-in-class eIF4A inhibitor, exerts pleiotropic effects on both tumor cells and the tumor immune microenvironment in a diverse cohort of syngeneic triple-negative breast cancer (TNBC) mouse models. Zotatifin not only suppresses tumor cell proliferation but also directly repolarizes macrophages toward an M1-like phenotype and inhibits neutrophil infiltration, which sensitizes tumors to immune checkpoint blockade. Mechanistic studies revealed that zotatifin reprograms the tumor translational landscape, inhibits the translation of Sox4 and Fgfr1, and induces an interferon (IFN) response uniformly across models. The induction of an IFN response is partially due to the inhibition of Sox4 translation by zotatifin. A similar induction of IFN-stimulated genes was observed in breast cancer patient biopsies following zotatifin treatment. Surprisingly, zotatifin significantly synergizes with carboplatin to trigger DNA damage and an even heightened IFN response, resulting in T cell-dependent tumor suppression. These studies identified a vulnerability of eIF4A in TNBC, potential pharmacodynamic biomarkers for zotatifin, and provide a rationale for new combination regimens consisting of zotatifin and chemotherapy or immunotherapy as treatments for TNBC.

MNK, mTOR or eIF4E-selecting the best anti-tumor target for blocking translation initiation

Overexpression of eIF4E is common in patients with various solid tumors and hematologic cancers. As a potential anti-cancer target, eIF4E has attracted extensive attention from researchers. At the same time, mTOR kinases inhibitors and MNK kinases inhibitors, which are directly related to regulation of eIF4E, have been rapidly developed. To explore the optimal anti-cancer targets among MNK, mTOR, and eIF4E, this review provides a detailed classification and description of the anti-cancer activities of promising compounds. In addition, the structures and activities of some dual-target inhibitors are briefly described. By analyzing the different characteristics of the inhibitors, it can be concluded that MNK1/2 and eIF4E/eIF4G interaction inhibitors are superior to mTOR inhibitors. Simultaneous inhibition of MNK and eIF4E/eIF4G interaction may be the most promising anti-cancer method for targeting translation initiation.

Cellular functions of eukaryotic RNA helicases and their links to human diseases

RNA helicases are highly conserved proteins that use nucleoside triphosphates to bind or remodel RNA, RNA-protein complexes or both. RNA helicases are classified into the DEAD-box, DEAH/RHA, Ski2-like, Upf1-like and RIG-I families, and are the largest class of enzymes active in eukaryotic RNA metabolism - virtually all aspects of gene expression and its regulation involve RNA helicases. Mutation and dysregulation of these enzymes have been linked to a multitude of diseases, including cancer and neurological disorders. In this Review, we discuss the regulation and functional mechanisms of RNA helicases and their roles in eukaryotic RNA metabolism, including in transcription regulation, pre-mRNA splicing, ribosome assembly, translation and RNA decay. We highlight intriguing models that link helicase structure, mechanisms of function (such as local strand unwinding, translocation, winching, RNA clamping and displacing RNA-binding proteins) and biological roles, including emerging connections between RNA helicases and cellular condensates formed through liquid-liquid phase separation. We also discuss associations of RNA helicases with human diseases and recent efforts towards the design of small-molecule inhibitors of these pivotal regulators of eukaryotic gene expression.

Lost in translation: a neglected mTOR target for lymphangioleiomyomatosis

Lymphangioleiomyomatosis (LAM) is a cystic lung disease of women resulting from mutations in tuberous sclerosis complex (TSC) genes that suppress the mammalian target of rapamycin complex 1 (mTORC1) pathway. mTORC1 activation enhances a plethora of anabolic cellular functions, mainly via the activation of mRNA translation through stimulation of ribosomal protein S6 kinase (S6K1)/ribosomal protein S6 (S6) and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1)/eukaryotic translation initiation factor 4E (eIF4E). Rapamycin (sirolimus), an allosteric inhibitor of mTORC1, stabilises lung function in many but not all LAM patients and, upon cessation of the drug, disease progression resumes. At clinically tolerable concentrations, rapamycin potently inhibits the ribosomal S6K1/S6 translation ribosome biogenesis and elongation axis, but not the translation 4E-BP1/eIF4E initiation axis. In this mini-review, we propose that inhibition of mTORC1-driven translation initiation is an obvious but underappreciated therapeutic strategy in LAM, TSC and other mTORC1-driven diseases.

Targeting EIF4A triggers an interferon response to synergize with chemotherapy and suppress triple-negative breast cancer

Protein synthesis is frequently dysregulated in cancer and selective inhibition of mRNA translation represents an attractive cancer therapy. Here, we show that therapeutically targeting the RNA helicase eIF4A by Zotatifin, the first-in-class eIF4A inhibitor, exerts pleiotropic effects on both tumor cells and the tumor immune microenvironment in a diverse cohort of syngeneic triple-negative breast cancer (TNBC) mouse models. Zotatifin not only suppresses tumor cell proliferation but also directly repolarizes macrophages towards an M1-like phenotype and inhibits neutrophil infiltration, which sensitizes tumors to immune checkpoint blockade. Mechanistic studies revealed that Zotatifin reprograms the tumor translational landscape, inhibits the translation of Sox4 and Fgfr1, and induces an interferon response uniformly across models. The induction of an interferon response is partially due to the inhibition of Sox4 translation by Zotatifin. A similar induction of interferon-stimulated genes was observed in breast cancer patient biopsies following Zotatifin treatment. Surprisingly, Zotatifin significantly synergizes with carboplatin to trigger DNA damage and an even heightened interferon response resulting in T cell-dependent tumor suppression. These studies identified a vulnerability of eIF4A in TNBC, potential pharmacodynamic biomarkers for Zotatifin, and provide a rationale for new combination regimens comprising Zotatifin and chemotherapy or immunotherapy as treatments for TNBC.

The role of eIF4F-driven mRNA translation in regulating the tumour microenvironment

Cells can rapidly adjust their proteomes in dynamic environments by regulating mRNA translation. There is mounting evidence that dysregulation of mRNA translation supports the survival and adaptation of cancer cells, which has stimulated clinical interest in targeting elements of the translation machinery and, in particular, components of the eukaryotic initiation factor 4F (eIF4F) complex such as eIF4E. However, the effect of targeting mRNA translation on infiltrating immune cells and stromal cells in the tumour microenvironment (TME) has, until recently, remained unexplored. In this Perspective article, we discuss how eIF4F-sensitive mRNA translation controls the phenotypes of key non-transformed cells in the TME, with an emphasis on the underlying therapeutic implications of targeting eIF4F in cancer. As eIF4F-targeting agents are in clinical trials, we propose that a broader understanding of their effect on gene expression in the TME will reveal unappreciated therapeutic vulnerabilities that could be used to improve the efficacy of existing cancer therapies.

Translational Control of Metabolism and Cell Cycle Progression in Hepatocellular Carcinoma

The liver is a metabolic hub characterized by high levels of protein synthesis. Eukaryotic initiation factors, eIFs, control the first phase of translation, initiation. Initiation factors are essential for tumor progression and, since they regulate the translation of specific mRNAs downstream of oncogenic signaling cascades, may be druggable. In this review, we address the issue of whether the massive translational machinery of liver cells contributes to liver pathology and to the progression of hepatocellular carcinoma (HCC); it represents a valuable biomarker and druggable target. First, we observe that the common markers of HCC cells, such as phosphorylated ribosomal protein S6, belong to the ribosomal and translational apparatus. This fact is in agreement with observations that demonstrate a huge amplification of the ribosomal machinery during the progression to HCC. Some translation factors, such as eIF4E and eIF6, are then harnessed by oncogenic signaling. In particular, the action of eIF4E and eIF6 is particularly important in HCC when driven by fatty liver pathologies. Indeed, both eIF4E and eIF6 amplify at the translational level the production and accumulation of fatty acids. As it is evident that abnormal levels of these factors drive cancer, we discuss their therapeutic value.

Oncogenic PKA signaling increases c-MYC protein expression through multiple targetable mechanisms

Genetic alterations that activate protein kinase A (PKA) are found in many tumor types. Yet, their downstream oncogenic signaling mechanisms are poorly understood. We used global phosphoproteomics and kinase activity profiling to map conserved signaling outputs driven by a range of genetic changes that activate PKA in human cancer. Two signaling networks were identified downstream of PKA: RAS/MAPK components and an Aurora Kinase A (AURKA)/glycogen synthase kinase (GSK3) sub-network with activity toward MYC oncoproteins. Findings were validated in two PKA-dependent cancer models: a novel, patient-derived fibrolamellar carcinoma (FLC) line that expresses a DNAJ-PKAc fusion and a PKA-addicted melanoma model with a mutant type I PKA regulatory subunit. We identify PKA signals that can influence both de novo translation and stability of the proto-oncogene c-MYC. However, the primary mechanism of PKA effects on MYC in our cell models was translation and could be blocked with the eIF4A inhibitor zotatifin. This compound dramatically reduced c-MYC expression and inhibited FLC cell line growth in vitro. Thus, targeting PKA effects on translation is a potential treatment strategy for FLC and other PKA-driven cancers.

eIF4A/PDCD4 Pathway, a Factor for Doxorubicin Chemoresistance in a Triple-Negative Breast Cancer Cell Model

Cells employ several adaptive mechanisms under conditions of accelerated cell division, such as the unfolded protein response (UPR). The UPR is composed of a tripartite signaling system that involves ATF6, PERK, and IRE1, which maintain protein homeostasis (proteostasis). However, deregulation of protein translation initiation could be associated with breast cancer (BC) chemoresistance. Specifically, eukaryotic initiation factor-4A (eIF4A) is involved in the unfolding of the secondary structures of several mRNAs at the 5' untranslated region (5'-UTR), as well as in the regulation of targets involved in chemoresistance. Importantly, the tumor suppressor gene PDCD4 could modulate this process. This regulation might be disrupted in chemoresistant triple negative-BC (TNBC) cells. Therefore, we characterized the effect of doxorubicin (Dox), a commonly used anthracycline medication, on human breast carcinoma MDA-MB-231 cells. Here, we generated and characterized models of Dox chemoresistance, and chemoresistant cells exhibited lower Dox internalization levels followed by alteration of the IRE1 and PERK arms of the UPR and triggering of the antioxidant Nrf2 axis. Critically, chemoresistant cells exhibited PDCD4 downregulation, which coincided with a reduction in eIF4A interaction, suggesting a sophisticated regulation of protein translation. Likewise, Dox-induced chemoresistance was associated with alterations in cellular migration and invasion, which are key cancer hallmarks, coupled with changes in focal adhesion kinase (FAK) activation and secretion of matrix metalloproteinase-9 (MMP-9). Moreover, eIF4A knockdown via siRNA and its overexpression in chemoresistant cells suggested that eIF4A regulates FAK. Pro-atherogenic low-density lipoproteins (LDL) promoted cellular invasion in parental and chemoresistant cells in an MMP-9-dependent manner. Moreover, Dox only inhibited parental cell invasion. Significantly, chemoresistance was modulated by cryptotanshinone (Cry), a natural terpene purified from the roots of Salvia brandegeei. Cry and Dox co-exposure induced chemosensitization, connected with the Cry effect on eIF4A interaction. We further demonstrated the Cry binding capability on eIF4A and in silico assays suggest Cry inhibition on the RNA-processing domain. Therefore, strategic disruption of protein translation initiation is a druggable pathway by natural compounds during chemoresistance in TNBC. However, plasmatic LDL levels should be closely monitored throughout treatment.

Inhibition of coronavirus HCoV-OC43 by targeting the eIF4F complex

The translation initiation complex 4F (eIF4F) is a rate-limiting factor in protein synthesis. Alterations in eIF4F activity are linked to several diseases, including cancer and infectious diseases. To this end, coronaviruses require eIF4F complex activity to produce proteins essential for their life cycle. Efforts to target coronaviruses by abrogating translation have been largely limited to repurposing existing eIF4F complex inhibitors. Here, we report the results of a high throughput screen to identify small molecules that disrupt eIF4F complex formation and inhibit coronavirus RNA and protein levels. Of 338,000 small molecules screened for inhibition of the eIF4F-driven, CAP-dependent translation, we identified SBI-1232 and two structurally related analogs, SBI-5844 and SBI-0498, that inhibit human coronavirus OC43 (HCoV-OC43; OC43) with minimal cell toxicity. Notably, gene expression changes after OC43 infection of Vero E6 or A549 cells were effectively reverted upon treatment with SBI-5844 or SBI-0498. Moreover, SBI-5844 or SBI-0498 treatment effectively impeded the eIF4F complex assembly, with concomitant inhibition of newly synthesized OC43 nucleocapsid protein and OC43 RNA and protein levels. Overall, we identify SBI-5844 and SBI-0498 as small molecules targeting the eIF4F complex that may limit coronavirus transcripts and proteins, thereby representing a basis for developing novel therapeutic modalities against coronaviruses.

Revisiting potential value of antitumor drugs in the treatment of COVID-19

Since an outbreak started in China in 2019, coronavirus disease 2019 (COVID-19) has rapidly become a worldwide epidemic with high contagiousness and caused mass mortalities of infected cases around the world. Currently, available treatments for COVID-19, including supportive care, respiratory support and antiviral therapy, have shown limited efficacy. Thus, more effective therapeutic modalities are highly warranted. Drug repurposing, as an efficient strategy to explore a potential broader scope of the application of approved drugs beyond their original indications, accelerates the process of discovering safe and effective agents for a given disease. Since the outbreak of COVID-19 pandemic, drug repurposing strategy has been widely used to discover potential antiviral agents, and some of these drugs have advanced into clinical trials. Antitumor drugs compromise a vast variety of compounds and exhibit extensive mechanism of action, showing promising properties in drug repurposing. In this review, we revisit the potential value of antitumor drugs in the treatment of COVID-19 and systematically discuss their possible underlying mechanisms of the antiviral actions.

eIF4A1 Inhibitor Suppresses Hyperactive mTOR-Associated Tumors by Inducing Necroptosis and G2/M Arrest

Aberrantly activated mechanistic target of rapamycin (mTOR) signaling pathway stimulates translation initiation/protein synthesis and eventually causes tumors. Targeting these processes thus holds potential for treating mTOR-associated diseases. We tested the potential of eFT226, a sequence-selective inhibitor of eIF4A-mediated translation, in the treatment of mTOR hyperactive cells caused by the deletion of tuberous sclerosis complex 1/2 (TSC1/2) or phosphatase and TENsin homology (PTEN). eFT226 preferentially inhibited the proliferation of Tsc2- and Pten-deficient cells by inducing necroptosis and G2/M phase arrest. In addition, eFT226 blocked the development of TSC2-deficient tumors. The translation initiation inhibitor is thus a promising regimen for the treatment of hyperactive mTOR-mediated tumors.

Protein synthesis control in cancer: selectivity and therapeutic targeting

Translational control of mRNAs is a point of convergence for many oncogenic signals through which cancer cells tune protein expression in tumorigenesis. Cancer cells rely on translational control to appropriately adapt to limited resources while maintaining cell growth and survival, which creates a selective therapeutic window compared to non-transformed cells. In this review, we first discuss how cancer cells modulate the translational machinery to rapidly and selectively synthesize proteins in response to internal oncogenic demands and external factors in the tumor microenvironment. We highlight the clinical potential of compounds that target different translation factors as anti-cancer therapies. Next, we detail how RNA sequence and structural elements interface with the translational machinery and RNA-binding proteins to coordinate the translation of specific pro-survival and pro-growth programs. Finally, we provide an overview of the current and emerging technologies that can be used to illuminate the mechanisms of selective translational control in cancer cells as well as within the microenvironment.

Translational Control of COVID-19 and Its Therapeutic Implication

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of COVID-19, which has broken out worldwide for more than two years. However, due to limited treatment, new cases of infection are still rising. Therefore, there is an urgent need to understand the basic molecular biology of SARS-CoV-2 to control this virus. SARS-CoV-2 replication and spread depend on the recruitment of host ribosomes to translate viral messenger RNA (mRNA). To ensure the translation of their own mRNAs, the SARS-CoV-2 has developed multiple strategies to globally inhibit the translation of host mRNAs and block the cellular innate immune response. This review provides a comprehensive picture of recent advancements in our understanding of the molecular basis and complexity of SARS-CoV-2 protein translation. Specifically, we summarize how this viral infection inhibits host mRNA translation to better utilize translation elements for translation of its own mRNA. Finally, we discuss the potential of translational components as targets for therapeutic interventions.