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

Discovery of P11-2: A Potent First-in-Class MNK1-Targeting PROTAC Degrader for the Treatment of Cancer

MAPK-interacting kinases (MNKs) are the only known kinases that phosphorylate eIF4E at Ser209, playing a critical role in tumor progression. However, the current MNK inhibitors have been limited due to the deficiency of effectiveness. Herein, we reported the design of the first-in-class MNK1-targeting PROTACs based on the MNK1 inhibitor DS12881479. Among them, P11-2 exhibited robust antitumor activity against MV4-11 cells (IC50 = 45 nM) by efficiently degrading MNK1 (DC50 = 11.92 nM, Dmax > 96%) mediated by the ubiquitin-proteasome system. Notably, P11-2 does not degrade MNK2, which played an important role in maintaining normal function. Moreover, P11-2 significantly suppressed the phosphorylation of eIF4E (IC50 = 22.07 nM), induced apoptosis, and arrested the cell cycle at the G1 phase. In addition, P11-2 exhibited favorable PK profiles and robust antitumor effects in the xenograft model. These findings highlight the potential of P11-2 as a novel therapeutic strategy for targeting the degradation of MNK1.

Thienopyrimidine: A promising scaffold in the development of kinase inhibitors with anticancer activities

Protein kinases represent a highly promising drug target, with over 80 drugs that target about two dozen different protein kinases have been approved by the US FDA, particularly in cancer treatment. Over the past decades, the unique structural characteristics of the thienopyrimidine ring system provide an adaptive platform for designing potent anticancer agents, especially various kinase inhibitors, which has attracted widespread attention. Some of these thienopyrimidines as anticancer kinase inhibitors have already been marketed or are currently undergoing clinical/preclinical studies for the treatment of cancers, such as Olmutinib, Pictilisib, SNS-314, PF-03758309, and Fimepinostat, highlighting the substantial advantages of the thienopyrimidine scaffold in the discovery of anticancer agents. This article reviews the discovery, activity, and structure-activity relationships of antitumor kinase inhibitors based on the thienopyrimidine scaffold, and partially discusses the binding modes between thienopyrimidine derivatives and their kinase targets. By elucidating the application of thienopyrimidine derivatives as anticancer kinase inhibitors, this review aims to provide new perspectives for the development of more effective and novel kinase inhibitors.

Sortase-Mediated Fluorescent Labeling of eIF4E for Investigating Translation Initiation Mechanisms

Translation initiation represents a critical regulatory step in gene expression, orchestrated by the interaction of eukaryotic initiation factor 4E (eIF4E) with the 7-methylguanosine (m7G) cap structure at the 5' end of mRNA. This interaction enables eIF4F, composed of eIF4E, eIF4G, and eIF4A, to recruit the 43S preinitiation complex to the mRNA 5' end. The activity of eIF4E is tightly regulated and often dysregulated in cancer, neurological disorders, and viral infections. To investigate the interactions of human eIF4E with m7G-RNA and eIF4G, we engineered single-cysteine mutants of eIF4E to enable fluorescent dye attachment. However, these mutants presented challenges in purification and exhibited diminished activity. To overcome these issues, we developed a method to fluorescently label eIF4E via sortase-mediated transpeptidation. Our results demonstrate that sortase-labeled eIF4E retains activity comparable to wild-type eIF4E. This approach provides a valuable tool for studying the dynamic mechanisms of translation initiation and its regulation.

eIF4F-mediated dysregulation of mRNA translation in cancer

Messenger RNA (mRNA) translational control plays a pivotal role in regulating cellular proteostasis under physiological and pathological conditions. Dysregulated mRNA translation is pervasive in cancer, in which protein synthesis is elevated to support accelerated cell growth and proliferation. Consequently, targeting the mRNA translation machinery has emerged as a therapeutic strategy to treat cancer. In this Perspective, we summarize the current knowledge of translation dysregulation in cancer, with emphasis on the eukaryotic translation initiation factor 4F complex. We outline recent endeavors to apply this knowledge to develop novel treatment strategies to combat cancer.

Ketamine reverses chronic corticosterone-induced behavioral deficits and hippocampal synaptic dysfunction by regulating eIF4E/BDNF signaling

Major depressive disorder (MDD) is a debilitating illness with a high global burden. While Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, offers rapid-acting antidepressant effects, its mechanism remains incompletely understood. Recent research suggests that dysregulation of mRNA translation via the Eukaryotic initiation factor 4E (eIF4E) pathway might contribute to depression pathophysiology. This study investigates whether Ketamine modulates eIF4E signaling in the hippocampus during its antidepressant action. Herein, adult male mice were exposed to Corticosterone, a well-established model for anxiety and depression, followed by behavioral testing and biochemical analysis. Corticosterone induced depression-like symptoms and disrupted synaptic function, including reduced TrkB/BDNF and eIF4E/MNK1/p-eIF2α/ubiquitin signaling. Ketamine treatment reversed these deficits. Notably, the eIF4E/MNK1 signaling inhibitor, eFT508, blocked Ketamine's antidepressant effect, leading to a return of depression-like phenotype and impaired synaptic signaling. Importantly, these effects were reversed by 7,8-DHF, a BDNF/TrkB signaling agonist. Mice treated with Corticosterone, Ketamine, and eFT508 and subsequently exposed to 7,8-DHF displayed normalized depression-like behaviors and restored synaptic signaling, including increased eIF4E phosphorylation and MNK1 expression. Besides, 7,8-DHF treatment enhanced p-eIF2α levels compared to the eFT508-treated group. These findings suggest that Ketamine exerts its antidepressant action through the regulation of the eIF4E/BDNF signaling pathway in the hippocampus. This study provides novel insights into the molecular mechanisms underlying Ketamine's therapeutic effects and highlights the potential of targeting this pathway for future MDD treatment strategies.

Unveiling the role of PIK3R1 in cancer: A comprehensive review of regulatory signaling and therapeutic implications

Phosphoinositide 3-kinase (PI3K) is responsible for phosphorylating phosphoinositides to generate secondary signaling molecules crucial for regulating various cellular processes, including cell growth, survival, and metabolism. The PI3K is a heterodimeric enzyme complex comprising of a catalytic subunit (p110α, p110β, or p110δ) and a regulatory subunit (p85). The binding of the regulatory subunit, p85, with the catalytic subunit, p110, forms an integral component of the PI3K enzyme. PIK3R1 (phosphoinositide-3-kinase regulatory subunit 1) belongs to class IA of the PI3K family. PIK3R1 exhibits structural complexity due to alternative splicing, giving rise to distinct isoforms, prominently p85α and p55α. While the primary p85α isoform comprises multiple domains, including Src homology 3 (SH3) domains, a Breakpoint Cluster Region Homology (BH) domain, and Src homology 2 (SH2) domains (iSH2 and nSH2), the shorter isoform, p55α, lacks certain domains present in p85α. In this review, we will highlight the intricate regulatory mechanisms governing PI3K signaling along with the impact of PIK3R1 alterations on cellular processes. We will further delve into the clinical significance of PIK3R1 mutations in various cancer types and their implications for prognosis and treatment outcomes. Additionally, we will discuss the evolving landscape of targeted therapies aimed at modulating PI3K-associated pathways. Overall, this review will provide insights into the dynamic interplay of PIK3R1 in cancer, fostering advancements in precision medicine and the development of targeted interventions.

Exploiting Translation Machinery for Cancer Therapy: Translation Factors as Promising Targets

Eukaryotic protein translation has slowly gained the scientific community's attention for its advanced and powerful therapeutic potential. However, recent technical developments in studying ribosomes and global translation have revolutionized our understanding of this complex multistep process. These developments have improved and deepened the current knowledge of mRNA translation, sparking excitement and new possibilities in this field. Translation factors are crucial for maintaining protein synthesis homeostasis. Since actively proliferating cancer cells depend on protein synthesis, dysregulated protein translation is central to tumorigenesis. Translation factors and their abnormal expressions directly affect multiple oncogenes and tumor suppressors. Recently, small molecules have been used to target translation factors, resulting in translation inhibition in a gene-specific manner, opening the door for developing translation inhibitors that can lead to novel chemotherapeutic drugs for treating multiple cancer types caused by dysregulated translation machinery. This review comprehensively summarizes the involvement of translation factors in tumor progression and oncogenesis. Also, it sheds light on the evolution of translation factors as novel drug targets for developing future therapeutic drugs for treating cancer.

MiR-125b targeted regulation of MKNK2 inhibits multiple myeloma proliferation and invasion

BACKGROUND

An increasing number of studies demonstrate that abnormal miRNA expression contributes to the advancement of many tumors. Nonetheless, the potential role of miR-125b in multiple myeloma (MM) remains unknown.

OBJECTIVES

To explore the potential effects and mechanism of miR-125b in MM.

METHODS

Real-time quantitative PCR was used to measure the expression levels of miR-125b and MKNK2 in a variety of MM samples. Colony formation and cell counting Kit-8 (CCK-8) assays were used to assess cell proliferation, the transwell assay was used to evaluate the cell invasion capability, and dual luciferase reporter gene assay and Western blot were used to examine the interaction between miR-125b and MKNK2.

RESULTS

The levels of miR-125b were higher in MM tissue samples, alongside increased expression of MKNK2. There was a negative correlation between MKNK2 and miR-125b expression in MM tissues. MKNK2 was identified as a direct target gene of miR-125b in MM cells. Overexpression of miR-125b suppressed MM cell growth, colony formation, and invasion. In addition, MKNK2 was found to mediate the effects of miR-125b on cell proliferation, colony formation, and invasion in MM.

CONCLUSIONS

miR-125b acts as a suppressive factor in multiple myeloma and can affect the malignant behavior of MM by regulating the expression of MKNK2.

Utilizing non-coding RNA-mediated regulation of ATP binding cassette (ABC) transporters to overcome multidrug resistance to cancer chemotherapy

Multidrug resistance (MDR) is one of the primary factors that produces treatment failure in patients receiving cancer chemotherapy. MDR is a complex multifactorial phenomenon, characterized by a decrease or abrogation of the efficacy of a wide spectrum of anticancer drugs that are structurally and mechanistically distinct. The overexpression of the ATP-binding cassette (ABC) transporters, notably ABCG2 and ABCB1, are one of the primary mediators of MDR in cancer cells, which promotes the efflux of certain chemotherapeutic drugs from cancer cells, thereby decreasing or abolishing their therapeutic efficacy. A number of studies have suggested that non-coding RNAs (ncRNAs), particularly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), play a pivotal role in mediating the upregulation of ABC transporters in certain MDR cancer cells. This review will provide updated information about the induction of ABC transporters due to the aberrant regulation of ncRNAs in cancer cells. We will also discuss the measurement and biological profile of circulating ncRNAs in various body fluids as potential biomarkers for predicting the response of cancer patients to chemotherapy. Sequence variations, such as alternative polyadenylation of mRNA and single nucleotide polymorphism (SNPs) at miRNA target sites, which may indicate the interaction of miRNA-mediated gene regulation with genetic variations to modulate the MDR phenotype, will be reviewed. Finally, we will highlight novel strategies that could be used to modulate ncRNAs and circumvent ABC transporter-mediated MDR.