Translation Initiation Factor 4E Research Articles

DDR1 promotes metastasis of cervical cancer and downstream phosphorylation signal via binding GRB2

Cervical cancer is a leading cause of cancer-related death among women and its recurrence and metastasis poses challenges to treatment. Discoidin domain receptor 1 (DDR1) was associated with cellular migration and invasion in several types of cancers. However, its function in cervical cancer is still unclear. In this study, we found that DDR1 was significantly more expressed in cervical cancer samples than in normal tissues. SRY-Box transcription factor 2 (SOX2), a known oncogene in cervical cancer, showed a positive correlation with DDR1 and regulated DDR1 transcription, contributing to the elevated expression of DDR1 in cervical cancer. Regarding the function of DDR1 in cervical cancer, the overexpression of DDR1 caused an increase in the migration, invasion, and epithelial-mesenchymal transition (EMT) of cervical cancer cells. In contrast, cervical cancer cells with reduced DDR1 expression exhibited a lower migration rate, fewer invasive cells, and decreased levels of EMT markers. In vivo, mice injected with cervical cancer cells with overexpressed DDR1 showed more pulmonary metastasis and nodule number. Opposite results were found in mice injected with DDR1 silenced cervical cancer cells. Since DDR1 can cause phosphorylation of downstream targets, a phosphorylation omics was employed to reveal the downstream targets of DDR1, including eukaryotic translation initiation factor 4E binding protein 1 and EPH receptor A2. Furthermore, DDR1 bound directly with Src homology 2 domain of growth factor receptor bound protein 2 (GRB2) which mediated the function of DDR1 in the malignant behaviors of cervical cancer and the phosphorylation of downstream targets. In conclusion, DDR1 binds directly to GRB2 and then affects downstream phosphorylation signals, ultimately exacerbating the metastasis of cervical cancer cells. This work sheds light on the mechanism by which DDR1 functions in cervical cancer cells, providing therapeutic strategy for the treatment of cervical cancer.

The Bi-Steric Inhibitor RMC-5552 Reduces mTORC1 Signaling and Growth in Lymphangioleiomyomatosis.

Mutations in the Tuberous Sclerosis Complex (TSC) genes result in the hyperactivation of the mechanistic/mammalian target of rapamycin 1 (mTORC1) growth pathway in mesenchymal pulmonary cells. Rapamycin (SirolimusTM), a naturally occurring macrolide, is the only therapeutic approved for women with lymphangioleiomyomatosis (LAM), a progressive, destructive lung disease caused by TSC gene mutations and mTORC1 hyperactivation. However, on cessation of the drug, lung function decline continues. We demonstrated here that pulmonary LAM cancer stem-like cells (SLS) most highly expressed the eukaryotic translation initiation factor 4E (eIF4E)-dependent translation initiation genes. We also showed that the eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) gene has the lowest expression in these cells, indicating that the 4E-BP1/eIF4E ratio in LAM SLS cells favors unrestrained eIF4E oncogenic mRNA translation. The bi-steric mTORC1-selective compound RMC-5552 prevented growth of LAM-associated fibroblasts (LAFs) and phosphorylation of proteins in the ribosomal protein S6K1/ribosomal protein S6 (S6K1/S6) and 4E-BP1/eIF4E translation mTORC1-driven pathways, whereas rapamycin only blocked the S6K/S6 axis. Rapamycin inhibition of LAF growth was rapidly reversed, but RMC-5552 inhibition was more durable. RMC-5552, through its potential to eradicate LAM cancer SLS cells, may have therapeutic benefit in LAM and other diseases with mTORC1 hyperactivity.

Oncogenic accumulation of cysteine promotes cancer cell proliferation by regulating the translation of D-type cyclins

Malignant cells exhibit a high demand for amino acids to sustain their abnormal proliferation. Particularly, the intracellular accumulation of cysteine is often observed in cancer cells. Previous studies have shown that deprivation of intracellular cysteine in cancer cells results in the accumulation of lipid peroxides in the plasma membrane and induction of ferroptotic cell death, indicating that cysteine plays a critical role in the suppression of ferroptosis. Herein, we found that the oncogenic accumulation of cysteine also contributes to cancer cell proliferation by promoting the cell cycle progression, which is independent of its suppressive effect on ferroptosis. The growth ability of four types of cancer cells, including murine hepatocarcinoma cells, but not of primary hepatocytes, were dependent on the exogenous supply of cysteine. Deprivation of intracellular cysteine in cancer cells induced cell cycle arrest at the G0/G1 phase, accompanied by a decrease in the expression of cyclin D1 and D2 proteins. The cysteine deprivation-induced decrease in D-type cyclin expression was associated with the upregulation of eukaryotic translation initiation factor 4E binding protein (4E-BP1), which represses the translation of cyclin D1 and D2 proteins by binding to eukaryotic translation initiation factor 4E (eIF4E). Similar results were observed in hepatocarcinoma cells treated with erastin, an xCT inhibitor. These findings reveal an unappreciated role of cysteine in regulating the growth of malignant cancer cells and deepen our understanding of the cytotoxic effect of xCT inhibitor to prevent cancer cell proliferation.

CoCl2-mimicked hypoxia induces the assembly of stress granules in trophoblast cells via eIF2α phosphorylation-dependent and -independent pathways.

Hypoxia has been implicated in preeclampsia (PE) pathophysiology. Stress granules (SGs) are present in the placenta of patients with PE. However, the pathways that contribute to SG aggregation in PE remain poorly understood. The objective of the current study is to investigate this issue. We first established an in vitro hypoxia model using human trophoblast cell line HTR-8/SVneo treated with cobalt chloride (CoCl2). CCK8 assay and wound healing assay were conducted to assess the viability and migration of HTR-8/SVneo cells after exposure to CoCl2-mimicked hypoxia. SG component expression in HTR-8/SVneo cells treated with CoCl2 alone, or in combination with indicated siRNAs was evaluated by reverse transcription quantitative PCR (RT-qPCR), western blot and immunofluorescence staining. Our results found CoCl2-mimicked hypoxia inhibits the proliferation and migration of HTR-8/SVneo cells. The treatment of CoCl2 can induce SG assembly in HTR-8/Svneo cells. Mechanistically, both heme-regulated inhibitors (HRI) mediated eukaryotic translation initiation factor (eIF)2α phosphorylation pathway and 4E binding protein 1 (4EBP1) pathway are involved in SG formation under the stress of CoCl2-mimicked hypoxia. Hypoxia-induced SGs in trophoblast cells might contribute to the etiology of PE.

Second-Generation Cap Analogue Prodrugs for Targeting Aberrant Eukaryotic Translation Initiation Factor 4E (eIF4E) Activity in Drug-Resistant Melanoma.

Melanoma is the deadliest form of skin cancer with a 5-year survival rate of less than 20%. While significant strides have been made in the field of kinase-targeted and immune-based therapies for melanoma, the development of resistance to these therapeutic agents has hindered the success of treatment. Drug-resistant melanoma is particularly reliant on enhanced cap-dependent translation to drive the production of oncoproteins that promote growth and survival. The m7GpppX cap-binding protein eukaryotic translation initiation factor 4E (eIF4E) is the rate-limiting factor of cap-dependent translation initiation, and its overexpression in melanoma tumors has been shown to drive resistance to BRAFV600E kinase-targeted inhibitors. These findings point to eIF4E-targeted therapies as a promising strategy to overcome drug resistance in melanoma. Herein, we build upon our previous work of developing cell-permeable cap analogue inhibitors to design second-generation cap analogues that inhibit eIF4E-mediated cap-dependent translation in drug-resistant melanoma cells.

The eukaryotic translation initiation factor eIF4E regulates flowering and circadian rhythm in Arabidopsis.

Translation initiation is a critical, rate-limiting step in protein synthesis. The eukaryotic translation initiation factor 4E (eIF4E) plays an essential role in this process. However, the mechanisms by which eIF4E-dependent translation initiation regulates plant growth and development remain not fully understood. In this study, we found that Arabidopsis eIF4E proteins are distributed in both the nucleus and cytoplasm, with only the cytoplasmic eIF4E being involved in the control of photoperiodic flowering. Genome-wide translation profiling using Ribo-tag sequencing reveals that eIF4E may regulate plant flowering by maintaining the homeostatic translation of components in the photoperiodic flowering pathway. eIF4E not only regulates the translation of flowering genes such as FLOWERING LOCUS T (FT) and FLOWERING LOCUS D (FLD) but also influences the translation of circadian genes like CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and PSEUDO-RESPONSE REGULATOR 9 (PRR9). Consistently, our results show that the eIF4E modulates the rhythmic oscillation of the circadian clock. Together, our study provides mechanistic insights into how the protein translation regulates multiple developmental processes in Arabidopsis, including the circadian clock and photoperiodic flowering.

Remodelling of the translatome controls diet and its impact on tumorigenesis.

Fasting is associated with a range of health benefits1-6. How fasting signals elicit changes in the proteome to establish metabolic programmes remains poorly understood. Here we show that hepatocytes selectively remodel the translatome while global translation is paradoxically downregulated during fasting7,8. We discover that phosphorylation of eukaryotic translation initiation factor 4E(P-eIF4E) is induced during fasting. We show that P-eIF4E is responsible for controlling the translation of genes involved in lipid catabolism and the production of ketone bodies. Inhibiting P-eIF4E impairs ketogenesis in response to fasting and a ketogenic diet. P-eIF4E regulates those messenger RNAs through a specific translation regulatory element within their 5' untranslated regions (5' UTRs). Our findings reveal a new signalling property of fatty acids, which are elevated during fasting. We found that fatty acids bind and induce AMP-activated protein kinase (AMPK) kinase activity that in turn enhances the phosphorylation of MAP kinase-interacting protein kinase (MNK), the kinase that phosphorylates eIF4E. The AMPK-MNK-eIF4E axis controls ketogenesis, revealing a new lipid-mediated kinase signalling pathway that links ketogenesis to translation control. Certain types of cancer use ketone bodies as an energy source9,10 that may rely on P-eIF4E. Our findings reveal that on a ketogenic diet, treatment with eFT508 (also known as tomivosertib;a P-eIF4E inhibitor) restrains pancreatic tumour growth. Thus, our findings unveil a new fatty acid-induced signalling pathway that activates selective translation, which underlies ketogenesis and provides a tailored diet intervention therapy for cancer.

Selective and effective suppression of pancreatic cancer through MNK inhibition

Objective The study aimed to explore the role of the Wnt/β-catenin signaling pathway in pancreatic cancer progression and chemoresistance, with a focus on identifying specific factors that distinguish between normal and tumor cells, thereby offering potential therapeutic targets. Materials and Methods We analyzed levels of total and phosphorylated eukaryotic translation initiation factor 4E (eIF4E) and β-catenin in pancreatic cancer and normal pancreatic tissues. Functional assays were used to assess the impact of eIF4E phosphorylation on β-catenin signaling, cell proliferation, and chemoresistance, with MNK kinase involvement determined through gene depletion studies. The MNK kinase inhibitor eFT508 was evaluated for its effects on eIF4E phosphorylation, β-catenin activation, and cell viability in both in vitro and in vivo models of pancreatic cancer. Results Both total and phosphorylated eIF4E, along with β-catenin, were significantly elevated in pancreatic cancer tissues compared to normal tissues. Phosphorylation of eIF4E at serine 209 was shown to activate β-catenin signaling, enhance cell proliferation, and contribute to chemoresistance in pancreatic cancer. Importantly, these effects were dependent on MNK kinase activity. Depletion of eIF4E reduced cell viability in both pancreatic cancer and normal cells, while depletion of MNK selectively decreased viability in pancreatic cancer cells. Treatment with eFT508 effectively inhibited eIF4E phosphorylation, suppressed β-catenin activation, and reduced pancreatic cancer cell growth and survival in vitro and in vivo, with minimal impact on normal cells. Conclusions: The MNK-eIF4E-β-catenin axis plays a critical role in pancreatic cancer progression and chemoresistance, distinguishing pancreatic cancer cells from normal cells. Targeting MNK kinases with inhibitors like eFT508 presents a promising therapeutic strategy for pancreatic cancer, with potential for selective efficacy and reduced toxicity.

PPM1G dephosphorylates eIF4E in control of mRNA translation and cell proliferation.

The mRNA 5'cap-binding eukaryotic translation initiation factor 4E (eIF4E) plays a critical role in the control of mRNA translation in health and disease. One mechanism of regulation of eIF4E activity is via phosphorylation of eIF4E by MNK kinases, which promotes the translation of a subset of mRNAs encoding pro-tumorigenic proteins. Work on eIF4E phosphatases has been paltry. Here, we show that PPM1G is the phosphatase that dephosphorylates eIF4E. We describe the eIF4E-binding motif in PPM1G that is similar to 4E-binding proteins (4E-BPs). We demonstrate that PPM1G inhibits cell proliferation by targeting phospho-eIF4E-dependent mRNA translation.

Repression of mRNA translation initiation by GIGYF1 via disrupting the eIF3-eIF4G1 interaction.

Viruses can selectively repress the translation of mRNAs involved in the antiviral response. RNA viruses exploit the Grb10-interacting GYF (glycine-tyrosine-phenylalanine) proteins 2 (GIGYF2) and eukaryotic translation initiation factor 4E (eIF4E) homologous protein 4EHP to selectively repress the translation of transcripts such as Ifnb1, which encodes the antiviral cytokine interferon-β (IFN-β). Herein, we reveal that GIGYF1, a paralog of GIGYF2, robustly represses cellular mRNA translation through a distinct 4EHP-independent mechanism. Upon recruitment to a target mRNA, GIGYF1 binds to subunits of eukaryotic translation initiation factor 3 (eIF3) at the eIF3-eIF4G1 interaction interface. This interaction disrupts the eIF3 binding to eIF4G1, resulting in transcript-specific translational repression. Depletion of GIGYF1 induces a robust immune response by derepressing IFN-β production. Our study highlights a unique mechanism of translational regulation by GIGYF1 that involves sequestering eIF3 and abrogating its binding to eIF4G1. This mechanism has profound implications for the host response to viral infections.

Retinoic acid signalling inhibits myogenesis by blocking MYOD translation in pig skeletal muscle cells

Vitamin A is an essential nutrient in animals, playing important roles in animal health. In the pig industry, proper supplementation of vitamin A in the feed can improve pork production performance, while deficiency or excessive intake can lead to growth retardation or disease. However, the specific molecular mechanisms through which vitamin A operates on pig skeletal muscle growth as well as muscle stem cell function remain unexplored. Therefore, in this study, we isolated the pig primary skeletal muscle stem cells (pMuSCs) and treated with retinoic acid (RA), the natural metabolite of vitamin A, and then examined the myogenic capacity of pMuSCs via immunostaining, real-time PCR, CCK8 and western-blot analysis. Unexpectedly, the RA caused a significant decrease in the proliferation and differentiation of pMuSCs. Mechanistically, the RA addition induced the activation of retinoic acid receptor gamma (RARγ), which inhibited the myogenesis through the blockage of protein translation of the master myogenic regulator myogenic differentiation 1 gene (MYOD). Specifically, RARγ inactivate AKT kinase (AKT) signalling and lead to dephosphorylation of eukaryotic translation initiation factor 4E binding protein 1 (eIF4EBP1), which in turn repress the eukaryotic translation initiation factor 4E (eIF4E) complex and block mRNA translation of MYOD. Inhibition of AKT could rescue the myogenic defects of RA-treated pMuSCs. Our findings revealed that retinoid acid signalling inhibits the skeletal muscle stem cell proliferation and differentiation in pigs. Therefore, the vitamin A supplement in the feedstuff should be cautiously optimized to avoid the potential adverse consequences on muscle development associated with the excessive levels of retinoic acid.

Arginine alleviates Clostridium perfringens α toxin-induced intestinal injury in vivo and in vitro via the SLC38A9/mTORC1 pathway.

Clostridium perfringens α toxin is a main virulence factor responsible for gut damage in animals. Arginine is a functional amino acid exhibiting significant immunoregulatory activities. However, the effects and immunoregulatory mechanisms of arginine supplementation on α toxin-induced intestinal injury remain unclear. In vivo, 256 male Arbor Acres chickens were randomly assigned to a 2×2 factorial arrangement, involving diet treatments (with or without 0.3% arginine supplementation) and immunological stress (with or without α toxin challenge). In vitro, IEC-6 cells were treated with or without arginine in the presence or absence of α toxin. Moreover, IEC-6 cells were transfected with siRNA targeting mTOR and SLC38A9 to explore the underlying mechanisms. The results showed that in vivo, arginine supplementation significantly alleviated the α toxin-induced growth performance impairment, decreases in serum immunoglobulin (Ig)A and IgG levels, and intestinal morphology damage. Arginine supplementation also significantly reduced the α toxin-induced increase in jejunal proinflammatory cytokines interleukin (IL)-1β, IL-6 and IL-17 mRNA expression. Clostridium perfringens α toxin significantly decreased jejunal mechanistic target of rapamycin (mTOR) and solute carrier family 38 member 9 (SLC38A9) mRNA expression, while arginine supplementation significantly increased mTOR and SLC38A9 mRNA expression. In vitro, arginine pretreatment mitigated the α toxin-induced decrease in cell viability and the increase in cytotoxicity and apoptosis. Arginine pretreatment also alleviated the α toxin-induced upregulation of mRNA expression of inflammation-related cytokines IL-6, C-X-C motif chemokine ligand (CXCL)10, CXCL11 and transforming growth factor-β (TGF-β), as well as apoptosis-related genes B-cell lymphoma-2 associated X protein (Bax), B-cell lymphoma-2 (Bcl-2), B-cell lymphoma-extra large (Bcl-XL) and cysteinyl aspartate specific proteinase 3 (Caspase-3) and the ratio of Bax to Bcl-2. Arginine pretreatment significantly increased the α toxin-induced decrease in mTOR, SLC38A9, eukaryotic translation initiation factor 4E (eIF4E)-binding protein 1 (4EBP1) and ribosomal protein S6 kinase (S6K) mRNA expression. Knockdown SLC38A9 and mTOR largely abrogated the positive effects of arginine pretreatment on α toxin-induced intracellular changes. Furthermore, SLC38A9 silencing abolished the increased mTOR mRNA expression caused by arginine pretreatment. In conclusion, arginine administration attenuated α toxin-induced intestinal injury in vivo and in vitro, which could be associated with the downregulation of inflammation via regulating SLC38A9/mTORC1 pathway.

The Therapeutic Efficacy and Mechanism of Action of Gnetin C, a Natural Compound from the Melinjo Plant, in a Preclinical Mouse Model of Advanced Prostate Cancer.

The metastasis-associated protein 1/protein kinase B (MTA1/AKT) signaling pathway has been shown to cooperate in promoting prostate tumor growth. Targeted interception strategies by plant-based polyphenols, specifically stilbenes, have shown great promise against MTA1-mediated prostate cancer progression. In this study, we employed a prostate-specific transgenic mouse model with MTA1 overexpression on the background of phosphatase and tensin homolog (Pten) null (R26MTA1; Ptenf/f) and PC3M prostate cancer cells which recapitulate altered molecular pathways in advanced prostate cancer. Mechanistically, the MTA1 knockdown or pharmacological inhibition of MTA1 by gnetin C (dimer resveratrol) in cultured PC3M cells resulted in the marked inactivation of mammalian target of rapamycin (mTOR) signaling. In vivo, mice tolerated a daily intraperitoneal treatment of gnetin C (7 mg/kg bw) for 12 weeks without any sign of toxicity. Treatment with gnetin C markedly reduced cell proliferation and angiogenesis and promoted apoptosis in mice with advanced prostate cancer. Further, in addition to decreasing MTA1 levels in prostate epithelial cells, gnetin C significantly reduced mTOR signaling activity in prostate tissues, including the activity of mTOR-target proteins: p70 ribosomal protein S6 kinase (S6K) and eukaryotic translational initiation factor 4E (elF4E)-binding protein 1 (4EBP1). Collectively, these findings established gnetin C as a new natural compound with anticancer properties against MTA1/AKT/mTOR-activated prostate cancer, with potential as monotherapy and as a possible adjunct to clinically approved mTOR pathway inhibitors in the future.

Abstract 4750: The MNK inhibitor EB1 sensitizes AR-V7 positive castration-resistant prostate cancer to enzalutamide

Abstract Introduction: Resistance to androgen receptor signaling inhibitors (ARSI) like Enzalutamide is frequent in castration resistant prostate cancer (CRPC). The mechanisms driving drug resistance include the overexpression of androgen receptor (AR) and the presence of splice variants like androgen receptor splice variant 7 (AR-V7). Clinical studies (PROPHECY) have demonstrated that AR-V7 positive CRPC patients treated with Enzalutamide show poorer overall survival and thus lack an effective targeted line of treatment. Recently, AR signaling and the regulation of protein translation via the translation initiation factor 4E (eIF4E) and MAPK-interacting kinases (MNKs) have been shown to depend on each other and targeting eIF4E has been proposed to increase the efficacy of ARSI. Objectives: We have recently described EB1 as the first in class non-ATP competitive inhibitor of MNK1/2 (Bou-Petit et al. JMC, 2022) and have now tested its applicability in CRPC. In this work we describe the impact of EB1 on the efficacy of Enzalutamide treatment in CRPC. Methodology: Cell lines 22RV1 and LNCaP-95 were used as AR-V7 positive models of CRPC. Effects of EB1 and Enzalutamide alone and in combination on cell growth were studied through crystal violet assay. Drug combination Index was calculated following Chou-Talalay method using CompuSyn Software. Cell death was studied through propidium iodide (PI) staining. AR transcriptional activity was assessed through RT-qPCR of AR canonical target genes like PSA. A head-to-head study with eFT-508 (Tomivosertib, eFFECTOR Therapeutics, Inc.) as the most advanced Type I MNK inhibitor was performed. Lastly, spheroids obtained through centrifugation in ultra-low attachment plates were used for validating drug interaction in 3D growth and viability studies. Spheroid viability was assessed through PI and Calcein AM staining as well as MTT assay. Results: In vitro results demonstrate strong to moderate synergistic inhibition of cell growth through the induction of cell death by the combination of Enzalutamide and EB1 in AR-V7 positive CRPC cell lines, as well as reduction of AR transcriptional activity (PSA). Drug combination also reduced growth and viability of spheroids, indicating good tumor penetrating properties in 3D models and giving in vitro proof-of-concept for in vivo applications. Furthermore, drug synergy with Enzalutamide could only be observed with EB1 and not with Type-I MNK inhibitors like eFT-508, indicating that MNK1/2 functions beyond its kinase activity might be relevant for cancer progression. Conclusion: Here we demonstrate that the novel MNK inhibitor EB1 shows promising in vitro results, which cannot be obtained with Type-I MNK inhibitors. The combination of EB1 with the standard of care Enzalutamide provide a novel therapeutic opportunity for the treatment of CRPC, particularly in AR-V7 positive patients. Citation Format: Sara García-Ortega, Leticia Suárez-Cabrera, Joan Morote, Olga Méndez, Marta Cano-Galietero, Elena Muro-Blanc, Jose I. Borrell, Anna Santamaria, Santiago Ramón y Cajal, Stefan Hümmer. The MNK inhibitor EB1 sensitizes AR-V7 positive castration-resistant prostate cancer to enzalutamide [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4750.

Abstract 272: Novel role for eIF4E in homing of acute myeloid leukemia cells

Abstract Acute myeloid leukemia (AML) remains with dismal outcomes, mostly attributed to the inability of therapies to eliminate leukemia stem cells (LSCs) leading to relapse. LSCs home to the bone marrow (BM) niche where they maintain their quiescence state once in contact with mesenchymal stromal cells (MSCs). Therefore, understanding what controls AML-niche interactions could lead to therapeutic approaches that can prevent relapse. First, we implemented a novel 3D in vitro system to mimic human AML-niche interactions. This 3D structure consists of a spheroid formed with BM-MSCs (HS5 cell line), recreating a hypoxic microenvironment. When AML cells (MM6 cell line) are added to the spheroid in a 1:1 proportion, AML cells migrate to the spheroid. After 24 hours, 0.18% of the AML cells home/colonize the spheroid (n=8). Next, we assessed the cell cycle status of AML cells in co-culture with the spheroid and compare to those in liquid culture or placed on a MSC monolayer (2D). We found that cells upon contact with MSCs increased their quiescence, 18.63% G0 in 2D and significantly higher in 3D conditions (25.03%; p=0.0048). It is also important to point out that colonizing cells have a lower proliferate capacity than non-colonizing cells after 7 days of co-culture (p=0.0286). This quiescence feature suggests a stem-like behavior of cells homing to the spheroid. Eukaryotic translation initiation factor 4E (eIF4E) has been found altered in AML. While the capacity of eIF4E to increase cell migration and growth has been shown in solid cancers, the mechanism of eIF4E to accelerate AML progression remains unknown. Thus, we hypothesized that eIF4E may play a role in homing of AML cells to the niche. To this end, we used CRISPR to deplete eIF4E in MM6 cells and found that CRISPR 4E cells have significantly decreased homing capacity to the spheroid compared with control cells (p=0.0065). Importantly, we found a lower percentage of CRISPR 4E cells underwent quiescence after co-culture with MSCs (2D or 3D) (p<0.0001). We corroborated observations using xenograft mice. After 20 hours of intravenous injection, we observed a higher percentage of AML cells in the blood of the mice injected with CRISPR 4E cells compared with control cells (p=0.0286), suggesting that CRISPR 4E cells are not able to effectively exit from peripheral blood to home to their niche. Altogether, we stablished a novel in vitro 3D model that mimics stem cell features of the AML-BM niche. We demonstrated that the depletion of eIF4E in AML cells decreases their homing and prevents them from acquiring niche-induced quiescence. Citation Format: Leandro M. Martinez, Eloisi Caldas Lopes, Mayumi Sugita, Jadwiga Gasiorek, Kata Alilovic, Katherine L. Borden, Monica L. Guzman. Novel role for eIF4E in homing of acute myeloid leukemia cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 272.

Abstract 682: Development of novel eIF4E inhibitors to potently and selectively suppress tumor growth across multiple indications

Abstract Despite considerable progress in treating cancer, drug resistance remains the primary hurdle to achieving cures in patients. Tumors often develop resistance through reactivation of the drug-targeted pathway, or activation of alternative parallel pathways, thereby maintaining the original downstream signaling effects. One of the furthest downstream effectors and critical nodes for many oncogenic signaling pathways is eukaryotic translation initiation factor 4E (eIF4E); the main regulator and rate limiting factor for protein synthesis. eIF4E is reactivated by many resistance mechanisms to promote translation of multiple pro-oncogenic factors including Cyclin D1/3, making it an attractive target to potentiate the anti-cancer activity of targeted therapies and to overcome drug resistance. Here, we present the development of novel, potent, and selective eIF4E inhibitors for use in both treatment-naïve and resistance settings across multiple tumor indications. To capitalize on the potential of targeting eIF4E, we developed a series of compounds with unique properties that maintain anti-tumor efficacy while minimizing toxicity. Our novel, selective, and potent oral eIF4E inhibitors (RBX-eIF4Ei) elicit a reversible, dose-dependent cell cycle arrest. Unlike targeting eIF4A, eIF4E inhibition selectively regulates translation of cancer-dependent pathway proteins instead of global protein synthesis, thus reducing on-target toxicity and increasing tolerability. Cellular profiling demonstrates RBX-eIF4Ei are highly selective, nanomolar inhibitors across many tumor types including, NSCLC, CRC, breast, and melanoma. Additionally, RBX-eIF4Ei demonstrate consistent efficacy across both sensitive and resistant cell lines, including intrinsic and acquired resistance models. Combining RBX-eIF4Ei with standard of care targeted therapies produces additive responses in both settings, suggesting its potential anti-neoplastic benefits post progression. In vivo, daily oral monotherapy treatment with RBX-EIF4Ei causes significant tumor growth inhibition across a variety of indications including BRAFmut CRC, BRAFmut melanoma and ER+ breast cancer, with minimal signs of toxicity. Intratumoral concentration of RBX-eIF4Ei correlate with significant tumor cell growth inhibition, as well as reductions in eIF4E target proteins, ODC1 and Cyclin D1. Combination studies with standard of care in both the treatment naïve and resistant settings are ongoing. Collectively, these data support the addition of RBX-eIF4Ei to standard of care in both the naïve and treatment resistance settings across a variety of indications including NSCLC, breast, CRC, and melanoma. IND enabling studies are planned, marking a significant step toward advancing these promising eIF4E inhibitors into clinical development. Citation Format: Matthew B. Friedersdorf, Devon R. Blake, Sarah E. Thompson, Roheeth Pavana, Ramamurty V. Changalvala, Andrew S. Truong, Krista Marran, Abha Bias, Jessica A. Sorrentino. Development of novel eIF4E inhibitors to potently and selectively suppress tumor growth across multiple indications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 682.

Abstract 658: Small molecule allosteric regulators of eIF4E activity target proteomic dysregulation and demonstrate potent antiproliferative activity in multiple myeloma models whilst sparing normal immune cells

Abstract Multiple myeloma is characterized by significant dysregulation of protein translation. The eukaryotic translation initiation factor 4E (eIF4E), a rate determining element of oncogene translation, is highly expressed in multiple myeloma cells compared to normal plasma cells and is associated with enhanced levels of key oncogenic drivers such as MYC. We have developed potent small molecule allosteric regulators of eIF4E activity by aligning medicinal chemistry tools with patient directed pharmacology to optimize and identify orally bioavailable, potent compounds with in vivo activity. To identify sensitive cancer models and markers associated with response to PIC eIF4E regulators, we screened the 302-cell line Eurofins OncoPanel™, followed by gene expression profiling comparing the most and least sensitive cell lines and QIAGEN Ingenuity Pathway Analysis. Consistent with the role of eIF4E, we identified proteomic dysregulation as a marker of sensitivity to PIC eIF4E regulators. In addition, the multiple myeloma cell line MM.1R was amongst the most sensitive cell lines. Proteomic analysis of PIC eIF4E regulator treated MM.1R cells identified significant changes, both increases and decreases, in approximately 8% of the 7800 proteins detected by label free mass spectrometry. QIAGEN Ingenuity Pathway Analysis of significantly altered proteins identified enrichment of proteins involved in the G2/M checkpoint, cell cycle control of chromosomal replication, and DNA repair as well as protein translation, EIF4E regulation and mTOR signaling. PIC eIF4E regulators significantly decreased cell viability of both the steroid sensitive MM.1S and steroid resistant MM.1R multiple myeloma cell lines, which was associated with significantly reduced MYC protein levels. Consistent with earlier reported findings and the mechanistic impacts of PIC eIF4E regulators, reduced MYC expression was associated with a significant decrease in hyper-phosphorylated 4EBP1. In contrast to cancer cells, PIC eIF4E regulator treatment did not affect viability of B, T, NK and plasma cell populations in freshly isolated peripheral blood mononuclear cells (PBMCs) at exposures that cause significant cell death in multiple myeloma cells. Furthermore, CD4+ T-cells isolated from fresh PBMCs demonstrated proliferative responses following stimulation (ImmunoCult™) in the presence of PIC eIF4E regulators. The impact on key oncogenic drivers and potent antiproliferative activity in multiple myeloma models with minimal effects on normal immune cell populations suggests that targeting eIF4E activity with PIC allosteric eIF4E regulators could offer an attractive therapeutic strategy in multiple myeloma. Citation Format: Lisa-Marie Sturla, Xuemei Zhang, Yagmur Kan, Richard Gedrich, Katherine Bowdish, Christopher VanDeusen. Small molecule allosteric regulators of eIF4E activity target proteomic dysregulation and demonstrate potent antiproliferative activity in multiple myeloma models whilst sparing normal immune cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 658.

Design, synthesis and biological evaluation of MNK-PROTACs.

Mitogen-activated protein kinase (MAPK)-interacting kinases (MNKs) can regulate cellular mRNA translation by controlling the phosphorylation of the eukaryotic translation initiation factor 4E (eIF4E), which plays an important role in tumor initiation, development, and metastasis. Although small-molecule MNK inhibitors have made significant breakthroughs in the treatment of various malignancies, their clinical application can be limited by drug resistance, target selectivity and other factors. The strategy of MNK-PROTACs which selectively degrades MNK kinases provides a new approach for developing small-molecule drugs for related diseases. In this study, DS33059, a small-molecule compound modified based on the ongoing clinical trials drug ETC-206, was chosen as the target protein ligand. A series of novel MNK-PROTACs were designed, synthesized and evaluated biological activity. Several compounds showed good inhibitory activities against MNK1/2. Besides, compounds exhibited moderate to excellent anti-proliferative activity in A549 and TMD-8 cells in vitro. In particular, compound II-5 significantly inhibited A549 (IC50 = 1.79μM) and TMD-8 (IC50 = 1.07μM) cells. The protein degradation assay showed that compound II-5 had good capability to degrade MNK1. The MNK-PROTACs strategy represents a new direction in treating tumors and deserves further exploration.

Recessive resistance against beet chlorosis virus is conferred by the eukaryotic translation initiation factor (iso)4E in Beta vulgaris.

Eukaryotic translation initiation factors (eIFs) are important for mRNA translation but also pivotal for plant-virus interaction. Most of these plant-virus interactions were found between plant eIFs and the viral protein genome-linked (VPg) of potyviruses. In case of lost interaction due to mutation or deletion of eIFs, the viral translation and subsequent replication within its host is negatively affected, resulting in a recessive resistance. Here we report the identification of the Beta vulgaris Bv-eIF(iso)4E as a susceptibility factor towards the VPg-carrying beet chlorosis virus (genus Polerovirus). Using yeast two-hybrid and bimolecular fluorescence complementation assays, the physical interaction between Bv-eIF(iso)4E and the putative BChV-VPg was detected, while the VPg of the closely related beet mild yellowing virus (BMYV) was found to interact with the two isoforms Bv-eIF4E and Bv-eIF(iso)4E. These VPg-eIF interactions within the polerovirus-beet pathosystem were demonstrated to be highly specific, as single mutations within the predicted cap-binding pocket of Bv-eIF(iso)4E resulted in a loss of interaction. To investigate the suitability of eIFs as a resistance resource against beet infecting poleroviruses, B.vulgaris plants were genome edited by CRISPR/Cas9 resulting in knockouts of different eIFs. Asimultaneous knockout of the identified BMYV-interaction partners Bv-eIF4E and Bv-eIF(iso)4E was not achieved, but Bv-eIF(iso)4EKO plants showed a significantly lowered BChV accumulation and decrease in infection rate from 100% to 28.86%, while no influence on BMYV accumulation was observed. Still, these observations support that eIFs are promising candidate genes for polerovirus resistance breeding in sugar beet.

Dual role of GRHL3 in bladder carcinogenesis depending on histological subtypes.

The effect of grainyhead-like transcription factor 3 (GRHL3) on cancer development depends on the cancer subtypes as shown in tumor entities such as colorectal or oral squamous cell carcinomas. Here, we analyzed the subtype-specific role of GRHL3 in bladder carcinogenesis, comparing common urothelial carcinoma (UC) with squamous bladder cancer (sq-BLCA). We examined GRHL3 mRNA and protein expression in cohorts of patient samples, its prognostic role and its functional impact on tumorigeneses in different molecular and histopathological subtypes of bladder cancer. We showed for GRHL3 a reverse expression in squamous and urothelial bladder cancer subtypes. Stably GRHL3-overexpressing EJ28, J82, and SCaBER in vitro models revealed a tumor-suppressive function in squamous and an oncogenic role in the urothelial cancer cells affecting cell and colony growth, and migratory and invasive capacities. Transcriptomic profiling demonstrated highly subtype-specific GRHL3-regulated expression networks coined by the enrichment of genes involved in integrin-mediated pathways. In SCaBER, loss of ras homolog family member A (RHOA) GTPase activity was demonstrated to be associated with co-regulation of eukaryotic translation initiation factor 4E family member 3 (EIF4E3), a potential tumor suppressor gene. Thus, our data provide for the first time a detailed insight into the role of the transcription factor GRHL3 in different histopathological subtypes of bladder cancer.