MNK Inhibition Research Articles

MNK as a potential pharmacological target for suppressing LPS-induced acute lung injury in mice

Acute lung injury (ALI) or its more severe form, known as acute respiratory distress syndrome (ARDS), is characterized by an initial exudative phase, expression of proinflammatory mediators, activation of inflammatory leukocytes, and impairment of the lung endothelium and epithelium. Despite numerous, novel therapeutic strategies have been developed regarding the pathophysiology of ALI, current treatment is mainly supportive, as specific therapies have not been established in the past few decades. The MAP kinase-interacting kinases (MNK1 and MNK2) are serine threonine kinases which are activated by mitogen-activated protein kinases (MAPKs), regulate protein synthesis by phosphroylating eukaryotic translation initiation factor 4E (eIF4E). Although studies have shown that MAPKs pathway is involved in anti-inflammatory and preventing tissue injury processes, the role of MNKs in ALI has, until now, remained relatively unexplored. Here, we investigated whether partial inhibition of MAPKs pathway by targeting MNKs was effective in the prevention and treatment of ALI. C57BL6 mice were pretreated with MNK1 and MNK2 inhibitor (CGP57380, 30 mg/kg) for 30 min and then challenged with 5 mg/kg LPS for 6 h. The results showed that pretreatment with CGP57380 not only significantly attenuated LPS-induced lung wet/dry ratio, as well as protein content, total cells and neutrophils in bronchoalveolar lavage fluid (BALF), but also decreased the production of pro-inflammatory mediators such as interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-α) and keratinocyte-derived chemoattractant (KC). In addition, CGP57380 was observed to significantly suppress LPS-stimulated phosphorylation of eIF4E and MAPKs in the mouse bone marrow-derived macrophages (BMDMs). The involvement of MNK2 in lung injury was further evident by MNK2 knockout mice. MNK2 deficiency resulted in the attenuated lung histopathological changes, as also reflected by reductions in neutrophil counts, and the less LPS-induced the production of IL-6, TNF-α and KC in mouse BALF. Taken together, these findings demonstrated for the first time that MNK inhibition could effectively reduce the LPS-induced ALI in mice, suggesting a novel and potential application for MNK-based therapy to treat this serious disease.

MNK1 and MNK2 enforce expression of E2F1, FOXM1, and WEE1 to drive soft tissue sarcoma

Soft tissue sarcoma (STS) is a heterogeneous disease that arises from connective tissues. Clinical outcome of patients with advanced tumors especially de-differentiated liposarcoma and uterine leiomyosarcoma remains unsatisfactory, despite intensive treatment regimens including maximal surgical resection, radiation, and chemotherapy. MAP kinase-interacting serine/threonine-protein kinase 1 and 2 (MNK1/2) have been shown to contribute to oncogenic translation via phosphorylation of eukaryotic translation initiation factor 4E (eIF4E). However, little is known about the role of MNK1/2 and their downstream targets in STS. In this study, we show that depletion of either MNK1 or MNK2 suppresses cell viability, anchorage-independent growth, and tumorigenicity of STS cells. We also identify a compelling antiproliferative efficacy of a novel, selective MNK inhibitor ETC-168. Cellular responsiveness of STS cells to ETC-168 correlates positively with that of phosphorylated ribosomal protein S6 (RPS6). Mirroring MNK1/2 silencing, ETC-168 treatment strongly blocks eIF4E phosphorylation and represses expression of sarcoma-driving onco-proteins including E2F1, FOXM1, and WEE1. Moreover, combination of ETC-168 and MCL1 inhibitor S63845 exerts a synergistic antiproliferative activity against STS cells. In summary, our study reveals crucial roles of MNK1/2 and their downstream targets in STS tumorigenesis. Our data encourage further clinical translation of MNK inhibitors for STS treatment.

Adaptive responses to mTOR gene targeting in hematopoietic stem cells reveal a proliferative mechanism evasive to mTOR inhibition

The mechanistic target of rapamycin (mTOR) is a central regulator of cell growth and an attractive anticancer target that integrates diverse signals to control cell proliferation. Previous studies using mTOR inhibitors have shown that mTOR targeting suppresses gene expression and cell proliferation. To date, however, mTOR-targeted therapies in cancer have seen limited efficacy, and one key issue is related to the development of evasive resistance. In this manuscript, through the use of a gene targeting mouse model, we have found that inducible deletion of mTOR in hematopoietic stem cells (HSCs) results in a loss of quiescence and increased proliferation. Adaptive to the mTOR loss, mTOR-/- HSCs increase chromatin accessibility and activate global gene expression, contrary to the effects of short-term inhibition by mTOR inhibitors. Mechanistically, such genomic changes are due to a rewiring and adaptive activation of the ERK/MNK/eIF4E signaling pathway that enhances the protein translation of RNA polymerase II, which in turn leads to increased c-Myc gene expression, allowing the HSCs to thrive despite the loss of a functional mTOR pathway. This adaptive mechanism can also be utilized by leukemia cells undergoing long-term mTOR inhibitor treatment to confer resistance to mTOR drug targeting. The resistance can be counteracted by MNK, CDK9, or c-Myc inhibition. These results provide insights into the physiological role of mTOR in mammalian stem cell regulation and implicate a mechanism of evasive resistance in the context of mTOR targeting.

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

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

A Highly Selective MNK Inhibitor Rescues Deficits Associated with Fragile X Syndrome in Mice.

Fragile X syndrome (FXS) is the most common inherited source of intellectual disability in humans. FXS is caused by mutations that trigger epigenetic silencing of the Fmr1 gene. Loss of Fmr1 results in increased activity of the mitogen-activated protein kinase (MAPK) pathway. An important downstream consequence is activation of the mitogen-activated protein kinase interacting protein kinase (MNK). MNK phosphorylates the mRNA cap-binding protein, eukaryotic initiation factor 4E (eIF4E). Excessive phosphorylation of eIF4E has been directly implicated in the cognitive and behavioral deficits associated with FXS. Pharmacological reduction of eIF4E phosphorylation is one potential strategy for FXS treatment. We demonstrate that systemic dosing of a highly specific, orally available MNK inhibitor, eFT508, attenuates numerous deficits associated with loss of Fmr1 in mice. eFT508 resolves a range of phenotypic abnormalities associated with FXS including macroorchidism, aberrant spinogenesis, and alterations in synaptic plasticity. Key behavioral deficits related to anxiety, social interaction, obsessive and repetitive activities, and object recognition are ameliorated by eFT508. Collectively, this work establishes eFT508 as a potential means to reverse deficits associated with FXS.

Preclinical evidence that MNK/eIF4E inhibition by cercosporamide enhances the response to antiangiogenic TKI and mTOR inhibitor in renal cell carcinoma

Eukaryotic translation initiation factor 4E (eIF4E) is deregulated in patients with renal cell carcinoma (RCC) and associated with poor prognosis, and is activated and regulated by Mnk kinases. In this study, we investigated the anti-RCC potential of a unique Mnk inhibitor cercosporamide. We showed that cercosporamide is active against RCC cells via suppressing growth, survival and migration. Combination indices value indicated that the combination of cercosporamide with sunitinib or temsirolimus are synergistic in RCC. In two independent RCC xenograft mouse models, complete tumor growth arrest or reverse was observed throughout the duration of drug treatment in the combination of cercosporamide with sunitinib or temsirolimus groups. Of note, cercosporamide inhibited RCC angiogenesis via negatively regulating a number of RCC endothelial cellular events including morphogenesis, migration, growth and survival. Mechanistically, we found that cercosporamide suppressed pro-angiogenic factors VEGF and HIFα, inhibited EMT and reduced pro-survival and cell cycle proteins; and furthermore this was attributed to cercosporamide’s ability in inhibiting eIF4E. This work demonstrates the anti-RCC activity of cercosporamide through targeting both RCC tumor cells and angiogenesis, and provides the first preclinical proof-of-concept of evidence of Mnk inhibition for RCC treatment.

IL-6 induced upregulation of T-type Ca2+ currents and sensitization of DRG nociceptors is attenuated by MNK inhibition.

Phosphorylation of the 5' cap-binding protein eIF4E by MAPK-interacting kinases (MNK1/2) is important for nociceptor sensitization and the development of chronic pain. IL-6-induced dorsal root ganglion (DRG) nociceptor excitability is attenuated in mice lacking eIF4E phosphorylation, in MNK1/2-/- mice, and by the nonselective MNK1/2 inhibitor cercosporamide. Here, we sought to better understand the neurophysiological mechanisms underlying how IL-6 causes nociceptor excitability via MNK-eIF4E signaling using the highly selective MNK inhibitor eFT508. DRG neurons were cultured from male and female ICR mice, 4-7 wk old. DRG cultures were treated with vehicle, IL-6, eFT508 (pretreat) followed by IL-6, or eFT508 alone. Whole cell patch-clamp recordings were done on small-diameter neurons (20-30 pF) to measure membrane excitability in response to ramp depolarization. IL-6 treatment (1 h) resulted in increased action potential firing compared with vehicle at all ramp intensities, an effect that was blocked by pretreatment with eFT508. Basic membrane properties, including resting membrane potential, input resistance, and rheobase, were similar across groups. Latency to the first action potential in the ramp protocol was lower in the IL-6 group and rescued by eFT508 pretreatment. We also found that the amplitudes of T-type voltage-gated calcium channels (VGCCs) were increased in the DRG following IL-6 treatment, but not in the eFT508 cotreatment group. Our findings are consistent with a model wherein MNK-eIF4E signaling controls the translation of signaling factors that regulate T-type VGCCs in response to IL-6 treatment. Inhibition of MNK with eFT508 disrupts these events, thereby preventing nociceptor hyperexcitability.NEW & NOTEWORTHY In this study, we show that the MNK inhibitor and anti-tumor agent eFT508 (tomivosertib) is effective in attenuating IL-6 induced sensitization of dorsal root ganglion (DRG) nociceptors. Pretreatment with eFT508 in DRG cultures from mice helps mitigate the development of hyperexcitability in response to IL-6. Furthermore, our data reveal that the upregulation of T-type voltage-gated calcium channels following IL-6 application can be blocked by eFT508, implicating the MNK-eIF4E signaling pathway in membrane trafficking of ion channels.

Reciprocal signaling between mTORC1 and MNK2 controls cell growth and oncogenesis.

eIF4E plays key roles in protein synthesis and tumorigenesis. It is phosphorylated by the kinases MNK1 and MNK2. Binding of MNKs to eIF4G enhances their ability to phosphorylate eIF4E. Here, we show that mTORC1, a key regulator of mRNA translation and oncogenesis, directly phosphorylates MNK2 on Ser74. This suppresses MNK2 activity and impairs binding of MNK2 to eIF4G. These effects provide a novel mechanism by which mTORC1 signaling impairs the function of MNK2 and thereby decreases eIF4E phosphorylation. MNK2[S74A] knock-in cells show enhanced phosphorylation of eIF4E and S6K1 (i.e., increased mTORC1 signaling), enlarged cell size, and increased invasive and transformative capacities. MNK2[Ser74] phosphorylation was inversely correlated with disease progression in human prostate tumors. MNK inhibition exerted anti-proliferative effects in prostate cancer cells in vitro. These findings define a novel feedback loop whereby mTORC1 represses MNK2 activity and oncogenic signaling through eIF4E phosphorylation, allowing reciprocal regulation of these two oncogenic pathways.

Nicotinamide-Ponatinib Analogues as Potent Anti-CML and Anti-AML Compounds.

Ponatinib is a multikinase inhibitor that is used to treat chronic myeloid leukemia patients harboring mutated ABL1(T315I) kinase. Due to the potent inhibition of FLT3, RET, and fibroblast growth factor receptors (FGFRs), it is also being evaluated against acute myeloid leukemia (AML), biliary, and lung cancers. The multikinase inhibition profile of ponatinib may also account for its toxicity, thus analogs with improved kinase selectivity or different kinase inhibition profiles could be better tolerated. The introduction of nitrogen into drug compounds can enhance efficacy and drug properties (a concept called “necessary nitrogen”). Here, we introduce additional nitrogen into the benzamide moiety of ponatinib to arrive at nicotinamide analogs. A nicotinamide analogue of ponatinib, HSN748, retains activity against FLT3, ABL1, RET, and PDGFRα/β but loses activity against c-Src and P38α. MNK1 and 2 are key kinases that phosphorylate eIF4E to regulate the protein translation complex. MNK also modulates mTORC1 signaling and contributes to rapamycin resistance. Inhibitors of MNK1 and 2 are being evaluated for anticancer therapy. Ponatinib is not a potent inhibitor of MNK1 or 2, but the nicotinamide analogs are potent inhibitors of MNKs. This illustrates a powerful demonstration of the necessary nitrogen concept to alter both the potency and selectivity of drugs.

TSC patient-derived isogenic neural progenitor cells reveal altered early neurodevelopmental phenotypes and rapamycin-induced MNK-eIF4E signaling

BackgroundTuberous sclerosis complex (TSC) is a neurodevelopmental disorder with frequent occurrence of epilepsy, autism spectrum disorder (ASD), intellectual disability (ID), and tumors in multiple organs. The aberrant activation of mTORC1 in TSC has led to treatment with mTORC1 inhibitor rapamycin as a lifelong therapy for tumors, but TSC-associated neurocognitive manifestations remain unaffected by rapamycin.MethodsHere, we generated patient-specific, induced pluripotent stem cells (iPSCs) from a TSC patient with a heterozygous, germline, nonsense mutation in exon 15 of TSC1 and established an isogenic set of heterozygous (Het), null and corrected wildtype (Corr-WT) iPSCs using CRISPR/Cas9-mediated gene editing. We differentiated these iPSCs into neural progenitor cells (NPCs) and examined neurodevelopmental phenotypes, signaling and changes in gene expression by RNA-seq.ResultsDifferentiated NPCs revealed enlarged cell size in TSC1-Het and Null NPCs, consistent with mTORC1 activation. TSC1-Het and Null NPCs also revealed enhanced proliferation and altered neurite outgrowth in a genotype-dependent manner, which was not reversed by rapamycin. Transcriptome analyses of TSC1-NPCs revealed differentially expressed genes that display a genotype-dependent linear response, i.e., genes upregulated/downregulated in Het were further increased/decreased in Null. In particular, genes linked to ASD, epilepsy, and ID were significantly upregulated or downregulated warranting further investigation. In TSC1-Het and Null NPCs, we also observed basal activation of ERK1/2, which was further activated upon rapamycin treatment. Rapamycin also increased MNK1/2-eIF4E signaling in TSC1-deficient NPCs.ConclusionMEK-ERK and MNK-eIF4E pathways regulate protein translation, and our results suggest that aberrant translation distinct in TSC1/2-deficient NPCs could play a role in neurodevelopmental defects. Our data showing upregulation of these signaling pathways by rapamycin support a strategy to combine a MEK or a MNK inhibitor with rapamycin that may be superior for TSC-associated CNS defects. Importantly, our generation of isogenic sets of NPCs from TSC patients provides a valuable platform for translatome and large-scale drug screening studies. Overall, our studies further support the notion that early developmental events such as NPC proliferation and initial process formation, such as neurite number and length that occur prior to neuronal differentiation, represent primary events in neurogenesis critical to disease pathogenesis of neurodevelopmental disorders such as ASD.

P.303 Multidisciplinary approach to mental illness: do inflammation and telomere length form a loop?

Post-translational modulation of eIF4E through phosphorylation by Mnks is highly integral to the pathogenesis of different cancers. Therefore, inhibition of Mnks offers a strategy for cancer treatment. Herein, a series of 2′H-spiro[cyclohexane-1,3′-imidazo[1,5-a]pyridine]-1′,5′-dione derivatives is presented as Mnk inhibitors. Some of them showed sub-micromolar to low nanomolar inhibitory activities against Mnk1/2 with a high level of selectivity for both kinases over CDKs. Biochemical assays revealed that compounds 4c and 4t are non-ATP-competitive inhibitors of Mnks. Lead compound 4t demonstrated a high selectivity for Mnk1/2 over a selection of 51 kinases, and displayed anti-proliferative activities against a panel of cancer cell lines. However, this compound in combination with our in-house CDK4/6 inhibitor 83 did not show a synergistic effect in A2780 ovarian cancer cells, suggesting that caution be exercised in the selection of an agent to be combined with an Mnk inhibitor.

Elevated expression of mcl-1 inhibits apoptosis and predicts poor prognosis in patients with surgically resected non-small cell lung cancer

BackgroundMcl-1, an anti-apoptotic member of bcl-2 family, together with cleaved poly (ADC-ribose) polymerase (c-PARP) can serve as a marker of cell apoptosis. Previously we reported that treatment of Mnk inhibitor CGP57380 resulted in decreased Mcl-1 expression while increased c-PARP expression in non-small cell lung cancer (NSCLC) cells. In this study, we aimed to investigate association between Mcl-1 expression and clinicopathological features of NSCLC, and their correlation between Mcl-1 and both proliferation index (PI) and apoptotic index (AI) in NSCLC patients.MethodsTissue microarrays (TMA) including 350 cases of surgically resected NSCLC were utilize and stained with Mcl-1, Ki-67 and c-PARP antibodies, PI and AI were then evaluated, respectively.ResultsHigher Mcl-1 expression and PI were observed in NSCLC compared with non-cancerous lung tissues (non-CLT), while AI was significantly lower in lung adenocarcinoma (ADC) compared with non-CLT. Additionally, Mcl-1 expression in lung ADC was evidently higher than that of in lung squamous cell carcinoma (SCC). The elevated Mcl-1 expression was associated with PI, and inversely related to AI in NSCLC. NSCLC patients with elevated Mcl-1 expression and high PI, or with high Mcl-1 expression and low AI had remarkably shorter overall survival time than these patients with low Mcl-1 expression.ConclusionsElevated expression of Mcl-1 might be inversely proportional to disease progression of NSCLC patients by promoting cell proliferation and inhibiting apoptosis, and Mcl-1 might serve as novel biomarker of poor prognosis for NSCLC patients.

Reversal of peripheral nerve injury-induced neuropathic pain and cognitive dysfunction via genetic and tomivosertib targeting of MNK.

Neuropathic pain caused by nerve injury presents with severe spontaneous pain and a variety of comorbidities, including deficits in higher executive functions. None of these clinical problems are adequately treated with current analgesics. Targeting of the mitogen-activated protein kinase-interacting kinase (MNK1/2) and its phosphorylation target, the mRNA cap binding protein eIF4E, attenuates many types of nociceptive plasticity induced by inflammatory mediators and chemotherapeutic drugs but inhibiting this pathway does not alter nerve injury-induced mechanical allodynia. We used genetic manipulations and pharmacology to inhibit MNK-eIF4E activity in animals with spared nerve injury, a model of peripheral nerve injury (PNI)-induced neuropathic pain. We assessed the presence of spontaneous pain using conditioned place preference. We also tested performance in a medial prefrontal cortex (mPFC)-dependent rule-shifting task. WT neuropathic animals showed signs of spontaneous pain and were significantly impaired in the rule-shifting task while genetic and pharmacological inhibition of the MNK-eIF4E signaling axis protected against and reversed spontaneous pain and PNI-mediated cognitive impairment. Additionally, pharmacological and genetic inhibition of MNK-eIF4E signaling completely blocked and reversed maladaptive shortening in the length of axon initial segments (AIS) in the mPFC of PNI mice. Surprisingly, these striking positive outcomes on neuropathic pain occurred in the absence of any effect on mechanical allodynia, a standard test for neuropathic pain efficacy. Our results illustrate new testing paradigms for determining preclinical neuropathic pain efficacy and point to the MNK inhibitor tomivosertib (eFT508) as an important drug candidate for neuropathic pain treatment.

Synthesis and evaluation of 2'H-spiro[cyclohexane-1,3'-imidazo[1,5-a]pyridine]-1',5'-dione derivatives as Mnk inhibitors.

Post-translational modulation of eIF4E through phosphorylation by Mnks is highly integral to the pathogenesis of different cancers. Therefore, inhibition of Mnks offers a strategy for cancer treatment. Herein, a series of 2'H-spiro[cyclohexane-1,3'-imidazo[1,5-a]pyridine]-1',5'-dione derivatives is presented as Mnk inhibitors. Some of them showed sub-micromolar to low nanomolar inhibitory activities against Mnk1/2 with a high level of selectivity for both kinases over CDKs. Biochemical assays revealed that compounds 4c and 4t are non-ATP-competitive inhibitors of Mnks. Lead compound 4t demonstrated a high selectivity for Mnk1/2 over a selection of 51 kinases, and displayed anti-proliferative activities against a panel of cancer cell lines. However, this compound in combination with our in-house CDK4/6 inhibitor 83 did not show a synergistic effect in A2780 ovarian cancer cells, suggesting that caution be exercised in the selection of an agent to be combined with an Mnk inhibitor.

Abstract 4142: Physical and functional interactions between MNK and mTOR signaling regulate the activation and differentiation of T cells

Abstract The role of the PI3K/mTOR and MAPK signaling pathways in regulating T cell activation and differentiation is well established. It has been shown that mTOR acts as a sensor of the T cell metabolic state, coordinating diverse inputs to determine the balance between effector versus memory cell fates. Similarly, the MAPK interacting kinases, MNK1 and MNK2, are key downstream effector kinases that mediate post-transcriptional gene regulation of critical mediators of the T cell response, including immune checkpoint proteins and cytokines, via the phosphorylation of specific RNA binding proteins such as eIF4E and hnRNPA1. eFT508 is a potent and selective inhibitor of both MNK1 and MNK2, which enhances anti-tumor immune responses by decreasing the expression of immune response modulators including PD-1, PD-L1, LAG3, TIM3 and IL-10. Furthermore, eFT508 treatment boosts memory T cell populations while increasing the effectiveness of cytotoxic T lymphocytes. Phosphoproteomic analysis of the effects of eFT508 on early T cell activation identified novel eFT508 sensitive phosphopeptides, including a subset that overlaps with mTOR-dependent phosphorylation sites. In vitro biochemical analysis has shown that eFT508 is not a mTOR kinase inhibitor and that most of these sites are not direct MNK substrates. These results suggest inhibition of MNK by eFT508 can have significant effects on mTOR signaling. Consistent with these findings, we observe a physical association between MNK and mTOR that is disrupted by either eFT508 or the allosteric mTOR inhibitor rapamycin. Our phosphoproteomic analysis also identified novel MNK-dependent phosphorylation sites within the translation initiation factor eIF4G1 that regulate the ability of mTOR to recognize eIF4G1 as a substrate. In addition, phosphorylation of the mTOR target 4EBP1 is decreased upon treatment of T cells with eFT508, although 4EBP1 itself is not a direct substrate of MNK in vitro. These data are consistent with a role for MNK in regulating mRNA translation, not only through phosphorylation of eIF4E, but also by modulating the activity of mTOR toward specific substrates. Given the role of mTOR in controlling memory T cell differentiation, our results provide a potential mechanistic basis to explain the impact of MNK inhibition on T cell differentiation. Ongoing studies are further characterizing the consequences of eFT508 regulation on MNK/mTOR signaling and T cell differentiation. This work significantly expands our current understanding of eFT508’s mechanism of action as well as its ability to promote a prolonged anti-tumor immune response. Citation Format: Craig R. Stumpf, Vikas K. Goel, Rajesh K. Sharma, Gary G. Chiang, Peggy A. Thompson, Kevin R. Webster. Physical and functional interactions between MNK and mTOR signaling regulate the activation and differentiation of T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4142.

Abstract LB-068: Tomivosertib (eFT508), a potent and highly selective inhibitor of MNK1 and MNK2, enhances CAR T cell activity through modulating T cell differentiation

Abstract Chimeric antigen receptor (CAR) T cells have shown great promise in treating hematopoietic malignancies, such as leukemia and non-Hodgkin’s lymphoma. The efficacy and durability of CAR T cell therapy have been correlated with higher levels of T stem cell memory (TSCM) and T central memory (TCM) populations. Accordingly, various strategies to enrich these CAR T cell populations are of intense interest. It is well-established that the PI3K/mTOR pathway plays an important role in T cell activation and differentiation, and perturbations in this pathway can enhance T cell memory populations. Work from our group has demonstrated that MNK modifies mTOR signaling and T cell differentiation. Here, we demonstrate that the MNK1/2 inhibitor tomivosertib can substantially increase TCM and TSCM populations in both primary murine and human T cells. Tomivosertib treatment of murine OT-I T cells biases T cell differentiation towards a TCM (CD8+ CD44+ CD62L+) population upon SIINFEKL peptide stimulation in vitro without adverse effects on T cell proliferation, interferon-γ production or cytotoxic function. Similar effects are seen in vivo, where tomivosertib treatment also enriches the TCM cell pool in a SIINFEKL vaccine-induced OT-I adoptive T cell transfer model, which results in increased persistence as demonstrated by a higher memory-recall T cell response upon re-challenge. Furthermore, addition of tomivosertib during production of human CAR (anti-CD19 scFv-4-1BB-CD3ζ) T cells leads to a significantly increased population of TSCM (CD8+ CD45RO CD45RA+ CD27+ CD95+) cells. Based on these data, the combination of tomivosertib with CD19-directed CAR T cells was assessed in the CD19+ Pfeiffer DLBCL model in vivo. Daily oral administration of tomivosertib in combination with CD19-directed CAR T cells results in improved efficacy in comparison to either monotherapy alone, consistent with tomivosertib promoting and maintaining TSCM populations in vivo. Tomivosertib is currently in multiple Phase II clinical trials as a monotherapy or in combination with checkpoint inhibitors. Citation Format: Vikas K. Goel, Rajesh K. Sharma, Jocelyn Staunton, Craig R. Stumpf, Nathan P. Young, Peggy A. Thompson, Gary G. Chiang, Kevin R. Webster. Tomivosertib (eFT508), a potent and highly selective inhibitor of MNK1 and MNK2, enhances CAR T cell activity through modulating T cell differentiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-068.

Inhibiting MNK Selectively Targets Cervical Cancer via Suppressing eIF4E-Mediated β-Catenin Activation

Targeting β-catenin has been shown to have great potential therapeutic value in cervical cancer. Because β-catenin is also essential for normal cells, strategies to specifically target cancer will require identification of druggable factors capable of distinguishing β-catenin signaling pathways between cancer and normal cells. Expression of p-eIF4E and p-β-catenin was analyzed in malignant and normal cervical tissues and cells. The effects and its underlying mechanisms of targeting MNK and eukaryotic translation initiation factor 4E (eIF4E) were determined in cervical cancer and normal cells. Inhibiting MNK/eIF4E axis selectively targets cervical cancer without affecting normal cervical cells, via suppressing eIF4E-mediated β-catenin activation. We found that eIF4E phosphorylation was upregulated in cervical cancer cells and tissues but not normal cervical counterparts, and its phosphorylation at Ser 209 activates Wnt/β-catenin signaling, promotes growth and migration in cervical cancer, in an MNK-dependent manner. MNK inhibition via genetic small interfering RNA (siRNA) knockdown or pharmacologic inhibitor effectively decreased phosphorylation of eIF4E and β-catenin, leading to reduced β-catenin activity and transcript levels of Wnt target genes in cervical cancer cells. Consistently, we found that MNK kinase inhibitor is effective in inhibiting proliferation and migration, and inducing apoptosis in cervical cancer but not normal cervical cells. The combination of MNK kinase inhibitor with paclitaxel achieved greater efficacy in cervical cancer cells than paclitaxel alone. Our work identifies MNK-eIF4E axis as a specific and critical regulator of β-catenin activity in cervical cancer but not normal cervical cells, and suggests that targeting MNK is a useful therapeutic strategy in cervical cancer.

A phase II, open label, randomized, noncomparative study of eFT508 (tomivosertib) alone or in combination with avelumab in subjects with relapsed/refractory microsatellite stable colorectal cancer (MSS CRC).

e14145 Background: Dysregulated translation of messenger RNA (mRNA) plays a role in the pathogenesis of solid tumors. Tomivosertib (T), a potent and highly selective small molecule inhibitor of MNK-1 and 2 blocks activation of eIF4E, a key regulator of mRNA translation, selectively regulating translation of a set of mRNAs. Preclinically, T triggers an anti-tumor immune response and enhances responses to checkpoint inhibitors. Avelumab is a fully human checkpoint inhibitor antibody directed against PD-L1. Methods: Part 1: In a 3+3 dose escalation patients (pts) with MSS CRC failing ≥2 prior therapies for metastatic disease received escalating doses of T, administered orally bid, with a fixed dose of 10 mg/kg avelumab q2w. Part 2: Pts were randomized (2:1) to combination therapy at the recommended phase 2 dose (RP2D) from part 1 or T alone. Primary endpoint is objective response rate. All pts have a pretreatment and on treatment biopsy to evaluate target engagement, tumor infiltrating lymphocytes and biomarkers of immune activation. Results: The RP2D for the combination was 200 mg bid T (single agent RP2D) with 10mg/kg avelumab q2w. At this dose level, 1 of 7 pts experienced a dose limiting toxicity being unable to complete the first 28 day cycle due to low grade (1/2) toxicities (nausea, fatigue, myalgia). In part 2, 30 pts were randomized to combination and 15 to monotherapy (25 male, 20 female: mean age 53.9 years, range 32-80 years). The most common adverse events, irrespective of causality were grade 1/2 gastrointestinal (including nausea, vomiting, abdominal pain, constipation and diarrhea) occurring in 77% (n = 23) of the combination and 67% (n = 10) of the monotherapy arm. Toxicities occurring more frequently in the combination arm included diarrhea, constipation, fatigue, myalgia/arthralgia, hypercalcemia and skin rash. Efficacy evaluation is pending from part 2. One pt with confirmed MSS status in part 1 treated at the RP2D achieved a confirmed Partial Response of greater than 8 months. Conclusions: Preliminary data suggest that the combination of T and avelumab has an acceptable safety profile with robust target engagement and demonstrated initial signs of activity. Updated efficacy and biological biopsy data will be presented at the conference. Clinical trial information: NCT03258398.

MNK1 inhibitor CGP57380 overcomes mTOR inhibitor-induced activation of eIF4E: the mechanism of synergic killing of human T-ALL cells

Although the treatment of adult T-cell acute lymphoblastic leukemia (T-ALL) has been significantly improved, the heterogeneous genetic landscape of the disease often causes relapse. Aberrant activation of mammalian target of rapamycin (mTOR) pathway in T-ALL is responsible for treatment failure and relapse, suggesting that mTOR inhibition may represents a new therapeutic strategy. In this study, we investigated whether the mTOR complex 1 (mTORC1) inhibitor everolimus could be used as a therapeutic agent against human T-ALL. We showed that rapamycin and its analog RAD001 (everolimus) exerted only mild inhibition on the viability of Jurkat, CEM and Molt-4 cell lines (for everolimus the maximum inhibition was <40% at 100 nM), but greatly enhanced the phosphorylation of eIF4E, a downstream substrate of MAPK-interacting kinase (MNK) that was involved in promoting cell survival. Furthermore, we demonstrated in Jurkat cells that mTOR inhibitor-induced eIF4E phosphorylation was independent of insulin-like growth factor-1/insulin-like growth factor-1 receptor axis, but was secondary to mTOR inhibition. Then we examined the antileukemia effects of CGP57380, a MNK1 inhibitor, and we found that CGP57380 (4-16 μM) dose-dependently suppressed the expression of both phosphor-MNK1 and phosphor-eIF4E, thereby inhibiting downstream targets such as c-Myc and survivin in T-ALL cells. Importantly, CGP57380 produced a synergistic growth inhibitory effect with everolimus in T-ALL cells, and treatment with this targeted therapy overcame everolimus-induced eIF4E phosphorylation. In conclusion, our results suggest that dual-targeting of mTOR and MNK1/eIF4E signaling pathways may represent a novel therapeutic strategy for the treatment of human T-ALL.

Abstract 3855: Inhibition of MNK by eFT508 reprograms T-cell signaling to promote an antitumor immune response

Abstract Mitogen-activated protein (MAP) kinase signaling cascades play a vital role in T-cell activation upon antigen recognition. MNK1 and MNK2 are important downstream effector kinases in the MAPK pathway that largely function in regulating the expression of important signaling molecules, including cytokines and immune checkpoint receptors. MNKs are primarily thought to regulate the expression of select mRNAs, predominantly via post-transcriptional mechanisms involving the phosphorylation of the eukaryotic translation initiation factor eIF4E as well as the RNA binding proteins hnRNPA1 and PSF. eFT508 is a potent and highly selective inhibitor of MNK1 and MNK2 that has been shown to promote antitumor immunity by decreasing the expression of immunosuppressive molecules, such as immune checkpoint receptors. In order to identify key T-cell components that are regulated by MNK phosphorylation and may mediate the effects of eFT508 treatment, we performed an unbiased phosphoproteomic analysis of T cells during the early stages of T-cell receptor-mediated stimulation with and without eFT508 treatment. Primary human T cells were pretreated with eFT508 for two hours prior to stimulation with αCD3/αCD28 for an additional 30 minutes. Protein samples were then prepared for multiplexed phosphoproteomic analysis by mass spectrometry. Consistent with previous proteomic studies using stimulated T cells, a number of phosphopeptides associated with T-cell receptor signaling, among other cellular activities, were detected. Moreover, treatment with eFT508 specifically blocked the phosphorylation of distinct phosphosites on select proteins. The phosphoproteins modulated by eFT508 treatment are involved in important T-cell signaling pathways, cell proliferation and differentiation programs, stress responses, and post-transcriptional and translational gene regulation. Furthermore, there was enrichment for specific sequences surrounding the phosphorylation site in eFT508-sensitive peptides, highlighting a potential mechanism mediating MNK target recognition. Confirmation of MNK-mediated phosphorylation of novel substrates is being conducted in vitro by biochemical analysis of direct phosphorylation of potential substrates by MNK1 or MNK2 and in cellular lysates treated with eFT508 by Western blot analysis using phosphosite-specific antibodies. These findings have significantly expanded our understanding of cell signaling through MNK1 and MNK2 and will help to illuminate potential regulatory programs through which inhibition of MNKs by eFT508 can modulate antitumor immunity. Citation Format: Craig R. Stumpf, Joan Chen, Vikas K. Goel, Gregory S. Parker, Gary G. Chiang, Peggy A. Thompson, Kevin R. Webster. Inhibition of MNK by eFT508 reprograms T-cell signaling to promote an antitumor immune response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3855.