Research progress of MEK1/2 inhibitors and degraders in the treatment of cancer

4-Anilinoquinolinylchalcone derivatives mediate antifibrotic effects through ERK/MRTF-a signaling pathway crosstalk

Quinolones and their analogues are a remarkable group of drugs that have multiple impacts on the human immune system. They are suspected to mediate anti-cancer and anti-inflammatory responses. However, due to their effectiveness in treating a number of significant diseases, such as genitourinary cancer and breast cancer, as well as their antiangiogenic and immunomodulatory qualities, interest in this group of traditional medicines has recently increased. Unfortunately, numerous side effects were observed, such as diarrhea, skin rashes, nausea, vomiting, bleeding, and abnormal liver functions. To overcome these restrictions and to enhance the pharmacological profile, research efforts are focusing on the synthesis and optimization of novel quinolone analogues that lack severe side effects. The present study focuses on the mechanism of action and the signaling pathway involving the 4-anilinoquinolinylchalcone derivative. The objective of the present work was to better understand the mechanism by which anti-fibrosis is mediated by screening 6 synthesized 4-anilinoquinolinylchalcone derivatives for their potential as novel anti-fibrosis therapeutics.

Adjunctive diagnostic tool for histopathological classification of congenital mesoblastic nephroma based in molecular genetic findings

PURPOSE

Congenital mesoblastic nephromas (CMN) are histologically classified into classical, cellular, and mixed subtypes. Most cellular CMNs harbor ETV6-NTRK3 gene fusions, and classic and mixed CMNs harbor EGFR internal tandem duplications (EGFR-ITDs). Classic CMNs are considered benign, whereas recurrent or metastatic diseases occur in the cellular subtypes. Direct identification of mutations is desirable for an accurate diagnosis. However, molecular genetic analyses cannot be performed in a number of histopathology laboratories. This study aimed to investigate a surrogate marker for the accurate histological classification of CMN.

METHODS

Overall, 11 CMN cases diagnosed at our institute were included in this study. Reverse transcription-polymerase chain reaction was performed for the NTRK gene fusion and EGFR-ITDs in all cases. Comprehensive mRNA analysis was performed using the nCounter® Gene Expression Assay. Principal component analysis (PCA) was performed based on the gene expression levels. Immunohistochemical evaluation was conducted for the expression of p-Mek1/2, p-Erk1/2, and EGFR.

RESULTS

PCA revealed differences in mutation patterns between the EGFR-ITDs and NTRK fusion tumor groups. Gene ontology analysis of the highly expressed genes in the EGFR-ITDs tumor group revealed enrichment related to the mitogen-activated protein kinase (MAPK) signaling pathway. p-Mek1/2 and p-Erk1/2 immunoreactivity was significantly increased in the EGFR-ITDs tumor group (p = 0.018 and p = 0.017, respectively). EGFR immunoreactivity is not a useful marker for CMN with EGFR-ITD.

CONCLUSION

p-Mek1/2 and p-Erk1/2 immunoreactivity may be useful markers for EGFR-ITDs. Thus, MEK1/2 inhibitors possess the potential to be used as a targeted therapy for CMN with EGFR-ITDs.

Design and Synthesis of Novel MEK Inhibitors for the Treatment of Solid Tumors

Aberrant activation of the RAS/RAF/MEK/ERK pathway occurs in more than 30% of human cancers. As part of this pathway, MEK1/2 has crucial roles in tumorigenesis, cell proliferation, and inhibition of apoptosis. At present, a number of MEK1/2 inhibitors are approved for the treatment of melanoma. However, MEK1/2 inhibitors have poor single-drug efficacy in the treatment of solid tumors and are prone to drug resistance. A series of compounds containing a diarylamine skeleton and phenylacrylamide (acrylamide) have been designed and synthesized in this paper. The most promising compound M15 showed good inhibitory activity of MEK1 (IC50 = 10.29 nM) and good inhibitory effect on three types of solid tumor cells: MDA-MB-231(IC50 = 2.76 μM), HepG2 (IC50 = 2.57 μM) and A549 (IC50 = 5.40 μM). At the same time, M15 was less toxic to human normal cells (MCF-10A IC50 > 20 μM) and has certain stability of liver microsomes in vitro (human, t1/2 = 27.9 min; rat, t1/2 > 60 min). It can induce apoptosis of MDA-MB-231 cells and slow down their migration. Therefore, compound M15 acts as a novel MEK1/2 inhibitor and may be a promising candidate for solid tumor intervention.

MEK inhibitors in oncology: a patent review and update (2016 - present)

INTRODUCTION

Mitogen-activated protein kinase (MEK) is one of the important components of Ras/Raf/MEK/ERK signaling pathway, transduces signal for cell growth, differentiation, and development. Deregulation of MEK leads to a wide variety of cancer; hence, MEK is considered as potential therapeutic targets for the treatment of cancer. The MEK1/2 inhibitors in combination with other inhibitors showed better therapeutic outcomes in various malignancies including resistant or relapsed or refractory cancer.

AREAS COVERED

A comprehensive patent literature from the year 2016 to May 2024 on MEK inhibitors in oncology, their combination products and structural insights have been reviewed through searching relevant information in PubMed, Scopus, Espacenet, Web of Science, World Intellectual Property Organization and Google Patent databases.

EXPERT OPINION

Overexpression and mutation of MEK have been reported to cause a wide variety of cancers especially resistant cancers. The MEK1/2 inhibitors in combination with other kinase (BRaf/KRas/PI3K) inhibitors showed significant anti-proliferative activity. Other combination of MEK inhibitor with PD-1, DYRK1, EGFR, BTK and/or VEGF inhibitors, etc. showed promising results in many cancers including colorectal, pancreatic, gastrointestinal, solid tumor, breast cancer, melanoma and multiple myeloma, etc. The dual or multi-targeted approaches of these combinations showed better and precise treatment of patients with resistant cancer.

Novel biomarkers and drug correlations of non-canonical WNT signaling in prostate and breast cancer

Prostate cancer (PCa) and breast cancer (BC) present formidable challenges in global cancer-related mortality, necessitating effective management strategies. The present study explores non-canonical Wnt signaling in PCa and BC, aiming to identify biomarkers and assess their clinical and therapeutic implications. Co-expression analyses reveal distinct gene patterns, with five overlapping genes (SULF1, ALG3, IL16, PLXNA2 and RASGFR2) exhibiting divergent expression in both cancers. Clinical relevance investigations demonstrate correlations with TNM stages and biochemical recurrence. Drug correlation analyses unveil potential therapeutic avenues, indicating that Wnt5a and ROR2 expressions are related to MEK inhibitor sensitivity in cancers. Meanwhile, further correlation analyses were conducted between drugs and the other novel non-canonical WNT genes (ALG3, IL16, SULF1, PLXNA2, and RASGRF2). Our findings contribute to understanding non-canonical Wnt signaling, offering insights into cancer progression and potential personalized treatment approaches.

Selumetinib overcomes ITGA2-induced 5-fluorouracil resistance in colorectal cancer

BACKGROUND

Colorectal cancer (CRC) is the third most malignant tumor in the world. 5-fluorouracil (5‑FU) -based chemotherapy is the first-line chemotherapy scheme for CRC, whereas acquired drug resistance poses a huge obstacle to curing CRC patients and the mechanism is still obscure. Therefore, identification of genes associated with 5‑FU chemotherapy and seeking second-line treatment are necessary means to improve survival and prognosis of patients with CRC.

METHODS

The Cancer Therapeutics Response Portal (CTRP) database and Genomics of Drug Sensitivity in Cancer (GDSC) database were used to identify CRC-related genes and potential second-line therapies for 5-FU-resistant CRC. The single-cell RNA sequencing data for CRC tissues were obtained from a GEO dataset. The relationship between ITGA2 and 5-FU-resistant was investigated in vitro and in vivo models.

RESULTS

ACOX1 and ITGA2 were identified as risk biomarkers associated with 5-FU-resistance. We developed a risk signature, consisting of ACOX1 and ITGA2, that was able to distinguish well between 5-FU-resistance and 5-FU-sensitive. The single-cell sequencing data showed that ITGA2 was mainly enriched in malignant cells. ITGA2 was negatively correlated with IC50 values of most small molecule inhibitors, of which selumetinib had the highest negative correlation. Finally, knocking down ITGA2 can make 5-FU-resistant CRC cells sensitive to 5-FU and combining with selumetinib can improve the therapeutic effect of 5-FU resistant cells.

CONCLUSION

In summary, our findings demonstrated the critical role of ITGA2 in enhancing chemotherapy resistance in CRC cells and suggested that selumetinib can restore the sensitivity of chemotherapy-resistant CRC cells to 5-FU by inhibiting ITGA2 expression.

Molecular Dynamics Simulation on the Suppression Mechanism of Phosphorylation to Ser222 by Allosteric Inhibitors Targeting MEK1/2 Kinase

Allosteric inhibitors of mitogen-activated protein kinase 1 (MEK1) reveal distinct interactions with MEK1 activation loop residues. The structural analyses will determine whether, and how, distinct inhibitors suppress the phosphorylation of MEK1 and may guide future therapeutic development. In this study, we explored the suppression mechanism of the phosphorylation process in the presence of MEK allosteric inhibitors, such as selumetinib, trametinib, cobimetinib, and CH5126766, by employing molecular dynamics simulations accompanied by principal component analysis. The simulations of wildtype MEK1 show that Ser222 can come close to γ-phosphate but not Ser218. We have found the conformation where Ser222 is within 5 Å of distance, which makes Ser222 accessible for γ-phosphate. The conformation analysis from the simulations of MEK1 in the presence of allosteric inhibitors reveals that the inhibitor restricts the flexibility of Ser222 through strong interactions with the activation loop, Lys97, and water mediates interactions with amino acids in the vicinity. The results reveal that all the inhibitors act as screeners between the activation loop and Mg-ATP and restricting the flexibility of the activation loop through strong interaction causes the suppression of the phosphorylation process of MEK1. The results conclude that a strong interaction of allosteric inhibitors with the activation loop restricts the movement of Ser222 toward Mg-ATP, which could be the dominant factor for the suppression of phosphorylation in MEK1. This research will provide novel insights to design effective anticancer therapeutics for targeting MEK1 in the future.

High-Throughput Miniaturized Synthesis of PROTAC-Like Molecules

The development of miniaturized high-throughput in situ screening platforms capable of handling the entire process of drug synthesis to final screening is essential for advancing drug discovery in the future. In this study, an approach based on combinatorial solid-phase synthesis, enabling the efficient synthesis of libraries of proteolysis targeting chimeras (PROTACs) in an array format is presented. This on-chip platform allows direct biological screening without the need for transfer steps.  UV-induced release of target molecules into individual droplets facilitates further on-chip experimentation. Utilizing a mitogen-activated protein kinase kinases (MEK1/2) degrader as a template, a series of 132 novel PROTAC-like molecules is synthesized using solid-phase Ugi reaction. These compounds are further characterized using various methods, including matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) imaging, while consuming only a few milligrams of starting materials in total. Furthermore, the feasibility of culturing cancer cells on the modified spots and quantifying the effect of MEK suppression is demonstrated. The miniaturized synthesis platform lays a foundation for high-throughput in situ biological screening of potent PROTACs for potential anticancer activity and offers the potential for accelerating the drug discovery process by integrating miniaturized synthesis and biological steps on the same array.

Progress in the development of ERK1/2 inhibitors for treating cancer and other diseases

The extracellular signal-regulated kinases-1 and 2 (ERK1/2) are ubiquitous regulators of many cellular functions, including proliferation, differentiation, migration, and cell death. ERK1/2 regulate cell functions by phosphorylating a diverse collection of protein substrates consisting of other kinases, transcription factors, structural proteins, and other regulatory proteins. ERK1/2 regulation of cell functions is tightly regulated through the balance between activating phosphorylation by upstream kinases and inactivating dephosphorylation by phosphatases. Disruption of homeostatic ERK1/2 regulation caused by elevated extracellular signals or mutations in upstream regulatory proteins leads to the constitutive activation of ERK1/2 signaling and uncontrolled cell proliferation observed in many types of cancer. Many inhibitors of upstream kinase regulators of ERK1/2 have been developed and are part of targeted therapeutic options to treat a variety of cancers. However, the efficacy of these drugs in providing sustained patient responses is limited by the development of acquired resistance often involving re-activation of ERK1/2. As such, recent drug discovery efforts have focused on the direct targeting of ERK1/2. Several ATP competitive ERK1/2 inhibitors have been identified and are being tested in cancer clinical trials. One drug, Ulixertinib (BVD-523), has received FDA approval for use in the Expanded Access Program for patients with no other therapeutic options. This review provides an update on ERK1/2 inhibitors in clinical trials, their successes and limitations, and new academic drug discovery efforts to modulate ERK1/2 signaling for treating cancer and other diseases.

Drug target prediction through deep learning functional representation of gene signatures

Many machine learning applications in bioinformatics currently rely on matching gene identities when analyzing input gene signatures and fail to take advantage of preexisting knowledge about gene functions. To further enable comparative analysis of OMICS datasets, including target deconvolution and mechanism of action studies, we develop an approach that represents gene signatures projected onto their biological functions, instead of their identities, similar to how the word2vec technique works in natural language processing. We develop the Functional Representation of Gene Signatures (FRoGS) approach by training a deep learning model and demonstrate that its application to the Broad Institute's L1000 datasets results in more effective compound-target predictions than models based on gene identities alone. By integrating additional pharmacological activity data sources, FRoGS significantly increases the number of high-quality compound-target predictions relative to existing approaches, many of which are supported by in silico and/or experimental evidence. These results underscore the general utility of FRoGS in machine learning-based bioinformatics applications. Prediction networks pre-equipped with the knowledge of gene functions may help uncover new relationships among gene signatures acquired by large-scale OMICs studies on compounds, cell types, disease models, and patient cohorts.

The Prognosis Performance of a Neutrophil- and Lymphocyte-Associated Gene Mutation Score in a Head and Neck Cancer Cohort

The treatment of head and neck squamous cell carcinomas (HNSCCs) is multimodal, and chemoradiotherapy (CRT) is a critical component. However, the availability of predictive or prognostic markers in patients with HNSCC is limited. Inflammation is a well-documented factor in cancer, and several parameters have been studied, with the neutrophil-to-lymphocyte ratio (NLR) being the most promising. The NLR is the most extensively researched clinical biomarker in various solid tumors, including HNSCC. In our study, we collected clinical and next-generation sequencing (NGS) data with targeted sequencing information from 107 patients with HNSCC who underwent CRT. The difference in the NLR between the good response group and the poor response group was significant, with more patients having a high NLR in the poor response group. We also examined the genetic alterations linked to the NLR and found a total of 41 associated genes across eight common pathways searched from the KEGG database. The overall mutation rate was low, and there was no significant mutation difference between the low- and high-NLR groups. Using a multivariate binomial generalized linear model, we identified three candidate genes (MAP2K2, MAP2K4, and ABL1) that showed significant results and were used to create a gene mutation score (GMS). Using the NLR-GMS category, we noticed that the high-NLR-GMS group had significantly shorter relapse-free survival compared to the intermediate- or low-NLR-GMS groups.

Targeted protein modification as a paradigm shift in drug discovery

Targeted Protein Modification (TPM) is an umbrella term encompassing numerous tools and approaches that use bifunctional agents to induce a desired modification over the POI. The most well-known TPM mechanism is PROTAC-directed protein ubiquitination. PROTAC-based targeted degradation offers several advantages over conventional small-molecule inhibitors, has shifted the drug discovery paradigm, and is acquiring increasing interest as over ten PROTACs have entered clinical trials in the past few years. Targeting the protein of interest for proteasomal degradation by PROTACS was the pioneer of various toolboxes for selective protein degradation. Nowadays, the ever-increasing number of tools and strategies for modulating and modifying the POI has expanded far beyond protein degradation, which phosphorylation and de-phosphorylation of the protein of interest, targeted acetylation, and selective modification of protein O-GlcNAcylation are among them. These novel strategies have opened new avenues for achieving more precise outcomes while remaining feasible and minimizing side effects. This field, however, is still in its infancy and has a long way to precede widespread use and translation into clinical practice. Herein, we investigate the pros and cons of these novel strategies by exploring the latest advancements in this field. Ultimately, we briefly discuss the emerging potential applications of these innovations in cancer therapy, neurodegeneration, viral infections, and autoimmune and inflammatory diseases.

MEK inhibitors in cancer treatment: structural insights, regulation, recent advances and future perspectives

MEK1/2 are critical components of the RAS-RAF-MEK-ERK or MAPK signalling pathway that regulates a variety of cellular functions including proliferation, survival, and differentiation. In 1997, a lung cancer cell line was first found to have a MEK mutation (encoding MEK2P298L). MEK is involved in various human cancers such as non-small cell lung cancer (NSCLC), spurious melanoma, and pancreatic, colorectal, basal, breast, and liver cancer. To date, 4 MEK inhibitors i.e., trametinib, cobimetinib, selumetinib, and binimetinib have been approved by the FDA and several are under clinical trials. In this review, we have highlighted structural insights into the MEK1/2 proteins, such as the αC-helix, catalytic loop, P-loop, F-helix, hydrophobic pocket, and DFG motif. We have also discussed current issues with all FDA-approved MEK inhibitors or drugs under clinical trials and combination therapies to improve the efficacy of clinical drugs. Finally, this study addressed recent developments on synthetic MEK inhibitors (from their discovery in 1997 to 2022), their unique properties, and their relevance to MEK mutant inhibition.

Cutaneous adverse reactions resulting from targeted cancer therapies: histopathologic and clinical findings

Targeted cancer treatments-designed to interfere with specific molecular signals responsible for tumor survival and progression-have shown benefit over conventional chemotherapies but may lead to diverse cutaneous adverse effects. This review highlights clinically significant dermatologic toxicities and their associated histopathologic findings, resulting from various targeted cancer drugs. Case reports and series, clinical trials, reviews, and meta-analyses are included for analysis and summarized herein. Cutaneous side effects resulting from targeted cancer therapies were reported with incidences as high as 90% for certain medications, and reactions are often predictable based on mechanism(s) of action of a given drug. Common and important reaction patterns included: acneiform eruptions, neutrophilic dermatoses, hand-foot skin reaction, secondary cutaneous malignancies, and alopecia. Clinical and histopathologic recognition of these toxicities remains impactful for patient care.

HPIP is an essential scaffolding protein running through the EGFR-RAS-ERK pathway and drives tumorigenesis

The EGFR-RAS-ERK pathway plays a key role in cancer development and progression. However, the integral assembly of EGFR-RAS-ERK signaling complexes from the upstream component EGFR to the downstream component ERK is largely unknown. Here, we show that hematopoietic PBX-interacting protein (HPIP) interacts with all classical components of the EGFR-RAS-ERK pathway and forms at least two complexes with overlapping components. Experiments of HPIP knockout or knockdown and chemical inhibition of HPIP expression showed that HPIP is required for EGFR-RAS-ERK signaling complex formation, EGFR-RAS-ERK signaling activation, and EGFR-RAS-ERK signaling-mediated promotion of aerobic glycolysis as well as cancer cell growth in vitro and in vivo. HPIP expression is correlated with EGFR-RAS-ERK signaling activation and predicts worse clinical outcomes in patients with lung cancer. These results provide insights into EGFR-RAS-ERK signaling complex formation and EGFR-RAS-ERK signaling regulation and suggest that HPIP may be a promising therapeutic target for cancer with dysregulated EGFR-RAS-ERK signaling.

Synergistic therapeutic potential of alpelisib in cancers (excluding breast cancer): Preclinical and clinical evidences

The phosphoinositide 3-kinase (PI3K) signaling pathway is well-known for its important role in cancer growth, proliferation and migration. The activation of PI3K pathway is always connected with endocrine resistance and poor prognosis in cancers. Alpelisib, a selective inhibitor of PI3K, has been demonstrated to be effective in combination with endocrine therapy in HR+ PIK3CA-mutated advanced breast cancer in preclinical and clinical trials. Recently, the synergistic effects of alpelisib combined with targeted agents have been widely reported in PIK3CA-mutated cancer cells, such as breast, head and neck squamous cell carcinoma (HNSCC), cervical, liver, pancreatic and lung cancer. However, previous reviews mainly focused on the pharmacological activities of alpelisib in breast cancer. The synergistic therapeutic potential of alpelisib in other cancers has not yet been well reviewed. In this review, an extensive study of related literatures (published until December 20, 2022) regarding the anti-cancer functions and synergistic effects of alpelisib was carried out through the databases. Useful information was extracted. We summarized the preclinical and clinical studies of alpelisib in combination with targeted anti-cancer agents in cancer treatment (excluding breast cancer). The combinations of alpelisib and other targeted agents significantly improved the therapeutic efficacy both in preclinical and clinical studies. Unfortunately, synergistic therapies still could not effectively avoid the possible toxicities and adverse events during treatment. Finally, some prospects for the combination studies in cancer treatment were provided in the paper. Taken together, this review provided valuable information for alpelisib in preclinical and clinical applications.

Discovery of Coumarin-Based MEK1/2 PROTAC Effective in Human Cancer Cells

The RAF/MEK/ERK pathway is a crucial signal path which is closely associated with the proliferation, differentiation, and apoptosis of tumors. MEK1/2 is a key kinase target in the pathway, with ERK1/2 acting as the main substrate of it. Despite the rapid development of MEK1/2 inhibitors, acquired resistance still happens and remains a significant problem. Most of the inhibitors possess a similar diarylamine scaffold. Here we designed and synthesized a series of MEK1/2 degraders based on a coumarin derivative which was a potent non-diarylamine allosteric MEK1/2 inhibitor. P6b among them showed the most potent degradation effect, with DC50 values of 0.3 μM and 0.2 μM in MEK1 and MEK2 degradation, respectively. An antiproliferation assay showed that it more significantly inhibits the growth of A375 cells (IC50= 2.8 μM) compared to A549 cells (IC50 = 27.3 μM). To sum up, we discovered P6b with a non-diarylamine scaffold for the first time as a potent MEK PROTAC effective in human cancer cells.

N-Heterocycle based Degraders (PROTACs) Manifesting Anticancer Efficacy: Recent Advances

Proteolysis Targeting Chimeras (PROTACs) technology has emerged as a promising strategy for the treatment of undruggable therapeutic targets. Researchers have invested a great effort in developing druggable PROTACs; however, the problems associated with PROTACs, including poor solubility, metabolic stability, cell permeability, and pharmacokinetic profile, restrict their clinical utility. Thus, there is a pressing need to expand the size of the armory of PROTACs which will escalate the chances of pinpointing new PROTACs with optimum pharmacokinetic and pharmacodynamics properties. N- heterocycle is a class of organic frameworks that have been widely explored to construct new and novel PROTACs. This review provides an overview of recent efforts of medicinal chemists to develop N-heterocycle-based PROTACs as effective cancer therapeutics. Specifically, the recent endeavors centred on the discovery of PROTACs have been delved into various classes based on the E3 ligase they target (MDM2, IAP, CRBN, and other E3 ligases). Mechanistic insights revealed during the biological assessment of recently furnished Nheterocyclic- based PROTACs constructed via the utilization of ligands for various E3 ligases have been discussed.

Design and Structural Optimization of Orally Bioavailable SOS1 Inhibitors for the Treatment of KRAS-Driven Carcinoma

KRAS mutations (G12C, G12D, etc.) are implicated in the oncogenesis and progression of many refractory cancers. Son of sevenless homolog 1 (SOS1) is a key regulator of KRAS to modulate KRAS from inactive to active states. Herein, we disclosed efficacy-improving tetra-cyclic quinazoline derivatives as an enhanced scaffold for inhibiting the SOS1-KRAS interaction. Compound 37, which conjugated 1-carbonitrile-cyclopropane to tetra-cyclic quinazoline, showed a twofold higher oral drug exposure and 2.5-fold longer half-life than BI-3406 in CD-1 mouse plasma. In a Mia-paca-2 xenograft model, 37 administrated alone inhibited tumor growth by 71%. Preclinical investigations demonstrated that 37 had a limited inhibition of CYP and hERG. Overall, our studies showed that 37 was a promising drug candidate for treatment of KRAS-driven cancer.

Customized synthesis of phosphoprotein bearing phosphoserine or its nonhydrolyzable analog

Studies on the mechanism of protein phosphorylation and therapeutic interventions of its related molecular processes are limited by the difficulty in the production of purpose-built phosphoproteins harboring site-specific phosphorylated amino acids or their nonhydrolyzable analogs. Here we address this limitation by customizing the cell-free protein synthesis (CFPS) machinery via chassis strain selection and orthogonal translation system (OTS) reconfiguration screening. The suited chassis strains and reconfigured OTS combinations with high orthogonality were consequently picked out for individualized phosphoprotein synthesis. Specifically, we synthesized the sfGFP protein and MEK1 protein with site-specific phosphoserine (O-pSer) or its nonhydrolyzable analog, 2-amino-4-phosphonobutyric acid (C-pSer). This study successfully realized building cell-free systems for site-specific incorporation of phosphonate mimics into the target protein. Our work lays the foundation for developing a highly expansible CFPS platform and the streamlined production of user-defined phosphoproteins, which can facilitate research on the physiological mechanism and potential interference tools toward protein phosphorylation.

Small-Molecule PROTACs for Cancer Immunotherapy

Unsatisfactory physicochemical properties of macromolecular drugs seriously hinder their application in tumor immunotherapy. However, these problems can be effectively solved by small-molecule compounds. In the promising field of small-molecule drug development, proteolysis targeting chimera (PROTAC) offers a novel mode of action in the interactions between small molecules and therapeutic targets (mainly proteins). This revolutionary technology has shown considerable impact on several proteins related to tumor survival but is rarely exploited in proteins associated with immuno-oncology up until now. This review attempts to comprehensively summarize the well-studied and less-developed immunological targets available for PROTAC technology, as well as some targets to be explored, aiming to provide more options and opportunities for the development of small-molecule-based tumor immunotherapy. In addition, some novel directions that can magnify and broaden the protein degradation efficiency are mentioned to improve PROTAC design in the future.

Tegaserod Maleate Suppresses the Growth of Gastric Cancer In Vivo and In Vitro by Targeting MEK1/2

Gastric cancer (GC) ranks fifth in global incidence and fourth in mortality. The current treatments for GC include surgery, chemotherapy and radiotherapy. Although treatment strategies for GC have been improved over the last decade, the overall five-year survival rate remains less than 30%. Therefore, there is an urgent need to find novel therapeutic or preventive strategies to increase GC patient survival rates. In the current study, we found that tegaserod maleate, an FDA-approved drug, inhibited the proliferation of gastric cancer cells, bound to MEK1/2 and suppressed MEK1/2 kinase activity. Moreover, tegaserod maleate inhibited the progress of gastric cancer by depending on MEK1/2. Notably, we found that tegaserod maleate suppressed tumor growth in the patient-derived gastric xenograft (PDX) model. We further compared the effect between tegaserod maleate and trametinib, which is a clinical MEK1/2 inhibitor, and confirmed that tegaserod maleate has the same effect as trametinib in inhibiting the growth of GC. Our findings suggest that tegaserod maleate inhibited GC proliferation by targeting MEK1/2.

The overview of Mitogen-activated extracellular signal-regulated kinase (MEK)-based dual inhibitor in the treatment of cancers

Mitogen-activated extracellular signal-regulated kinase 1 and 2 (MEK1/2) are the critical components of the mitogen-activated protein kinase/extracellular signal-regulated kinase 1 and 2 (MAPK/ERK1/2) signaling pathway which is one of the well-characterized kinase cascades regulating cell proliferation, differentiation, growth, metabolism, survival and mobility both in normal and cancer cells. The aberrant activation of MAPK/ERK1/2 pathway is a hallmark of numerous human cancers, therefore targeting the components of this pathway to inhibit its dysregulation is a promising strategy for cancer treatment. Enormous efforts have been done in the development of MEK1/2 inhibitors and encouraging advancements have been made, including four inhibitors approved for clinical use. However, due to the multifactorial property of cancer and rapidly arising drug resistance, the clinical efficacy of these MEK1/2 inhibitors as monotherapy are far from ideal. Several alternative strategies have been developed to improve the limited clinical efficacy, including the dual inhibitor which is a single drug molecule able to simultaneously inhibit two targets. In this review, we first introduced the activation and function of the MAPK/ERK1/2 components and discussed the advantages of MEK1/2-based dual inhibitors compared with the single inhibitors and combination therapy in the treatment of cancers. Then, we overviewed the MEK1/2-based dual inhibitors for the treatment of cancers and highlighted the theoretical basis of concurrent inhibition of MEK1/2 and other targets for development of these dual inhibitors. Besides, the status and results of these dual inhibitors in both preclinical and clinical studies were also the focus of this review.

A Novel ERK2 Degrader Z734 Induces Apoptosis of MCF–7 Cells via the HERC3/p53 Signaling Pathway

Breast cancer is one of the leading causes of death worldwide, and synthetic chemicals targeting specific proteins or various molecular pathways for tumor suppression, such as ERK inhibitors and degraders, have been intensively investigated. The targets of ERK participate in the regulation of critical cellular mechanisms and underpin the progression of anticancer therapy. In this study, we identified a novel small molecule, which we named Z734, as a new mitogen–activated protein kinase 1 (ERK2) degrader and demonstrated that Z734 inhibits cell growth by inducing p53–mediated apoptotic pathways in human breast cancer cells. Treatment with Z734 resulted in the inhibition of cancer cell proliferation, colony formation and migration invasion, as well as cancer cell death via apoptosis. In addition, the Co–IP and GST pulldown assays indicated that the HECT and RLD domains containing E3 ubiquitin protein ligase 3 (HERC3) could directly interact with ERK2 through the HECT domain, promoting ERK2 ubiquitination. We also observed a strong link between HERC3 and p53 for the modulation of apoptosis. HERC3 can increase the protein and phosphorylation levels of p53, which further promotes apoptotic activity. In a xenograft mouse model, the effect was obtained in a treatment group that combined Z734 with lapatinib compared with that of the single–treatment groups. In summary, our results indicated that Z734 actively controls the development of breast cancer through apoptosis, and HERC3 may mediate ERK2 and p53 signaling, which offers new potential targets for clinical therapy.

Recent development of BTK-based dual inhibitors in the treatment of cancers

Bruton's tyrosine kinase (BTK) is a promising target in the treatment of various cancers. Despite the early success of BTK inhibitors in the clinic, these single-target drug therapies have limitations in their clinical applications, such as drug resistance. Several alternative strategies have been developed, including the use of dual inhibitors, to maximize the therapeutic potential of anticancer drugs. In this review, we highlight the scientific background and theoretical basis for developing BTK-based dual inhibitors, as well as the status of these agents in preclinical and clinical studies, and discuss further options in this field. We posit that these advances in BTK-based dual inhibitors confirm their feasibility for the treatment of refractory tumors, including those with drug resistance, and provide a framework for future drug design in this field. Accordingly, we anticipate increasingly rapid progress in the development of novel potent dual inhibitors and advanced clinical research on BTK-based dual inhibitors.

Structural effects of morpholine replacement in ZSTK474 on Class I PI3K isoform inhibition: Development of novel MEK/PI3K bifunctional inhibitors

Established roles for PI3K and MAPK signaling pathways in tumorigenesis has prompted extensive research towards the discovery of small-molecule inhibitors as cancer therapeutics. However, significant compensatory regulation exists between these two signaling cascades, leading to redundancy among survival pathways. Consequently, initial clinical trials aimed at either PI3K or MEK inhibition alone have proven ineffective and highlight the need for development of targeted and innovative therapeutic combination strategies. We designed a series of PI3K inhibitor derivatives wherein a single morpholine group of the PI3K inhibitor ZSTK474 was substituted with a variety of 2-aminoethyl functional groups. Analogs with pendant hydroxyl or methoxy groups maintained low nanomolar inhibition towards PI3Kα, PI3Kγ, and PI3Kδ isoforms in contrast to those with pendant amino groups which were significantly less inhibitory. Synthesis of prototype PI3K/MEK bifunctional inhibitors (6r, 6s) was guided by the structure-activity data, where a MEK-targeting inhibitor was tethered directly via a short PEG linker to the triazine core of the PI3K inhibitor analogs. These compounds (6r, 6s) displayed nanomolar inhibition towards PI3Kα, δ, and MEK (IC₅₀ ∼105-350 nM), and low micromolar inhibition for PI3Kβ and PI3Kγ (IC₅₀ ∼1.5-3.9 μM) in enzymatic inhibition assays. Cell viability assays demonstrated superior anti-proliferative activity for 6s over 6r in three tumor-derived cell lines (A375, D54, SET-2), which correlated with inhibition of downstream AKT and ERK1/2 phosphorylation. Compounds 6r and 6s also demonstrated in vivo tolerability with therapeutic efficacy through reduction of kinase activation and amelioration of disease phenotypes in the JAK2V617F mutant myelofibrosis mouse cancer model. Taken together, these results support further structure optimization of 6r and 6s as promising leads for combination therapy in human cancer as a new class of PI3K/MEK bifunctional inhibitors.

VHL-based PROTACs as potential therapeutic agents: Recent progress and perspectives

Proteolysis targeting chimeras (PROTACs), which hijack proteins of interest (POIs) and recruit E3 ligases for target degradation via the ubiquitin-proteasome pathway, are a novel drug discovery paradigm that has been widely used as biological tools and medicinal molecules with the potential of clinical application value. To date, a wide variety of small molecule PROTACs have been developed. Importantly, VHL-based PROTACs have emerged to be a promising approach for proteins, including those non-druggable ones, such as transcriptional factors and scaffold proteins. VHL-based PRTOACs have been developed for the treatment of diseases that are difficult to be dealt with by conventional methods, such as radiotherapy, chemotherapy, and small molecule inhibitors. In this review, the recent advances of VHL-based PRTOACs were summarized, and the chances and challenges associated with this area were also highlighted.

Structure of mitogen-activated protein kinase kinase 1 in the DFG-out conformation

Eukaryotic protein kinases contain an Asp-Phe-Gly (DFG) motif, the conformation of which is involved in controlling the catalytic activity, at the N-terminus of the activation segment. The motif can be switched between active-state (DFG-in) and inactive-state (DFG-out) conformations: however, the mechanism of conformational change is poorly understood, partly because there are few reports of the DFG-out conformation. Here, a novel crystal structure of nonphosphorylated human mitogen-activated protein kinase kinase 1 (MEK1; amino acids 38-381) complexed with ATP-γS is reported in which MEK1 adopts the DFG-out conformation. The crystal structure revealed that the structural elements (the αC helix and HRD motif) surrounding the active site are involved in the formation/stabilization of the DFG-out conformation. The ATP-γS molecule was bound to the canonical ATP-binding site in a different binding mode that has never been found in previously determined crystal structures of MEK1. This novel ATP-γS binding mode provides a starting point for the design of high-affinity inhibitors of nonphosphorylated inactive MEK1 that adopts the DFG-out conformation.

Small-Molecule Inhibitors and Degraders Targeting KRAS-Driven Cancers

Drug resistance continues to be a major problem associated with cancer treatment. One of the primary causes of anticancer drug resistance is the frequently mutated RAS gene. In particular, considerable efforts have been made to treat KRAS-induced cancers by directly and indirectly controlling the activity of KRAS. However, the RAS protein is still one of the most prominent targets for drugs in cancer treatment. Recently, novel targeted protein degradation (TPD) strategies, such as proteolysis-targeting chimeras, have been developed to render "undruggable" targets druggable and overcome drug resistance and mutation problems. In this study, we discuss small-molecule inhibitors, TPD-based small-molecule chemicals for targeting RAS pathway proteins, and their potential applications for treating KRAS-mutant cancers. Novel TPD strategies are expected to serve as promising therapeutic methods for treating tumor patients with KRAS mutations.

Rational Design, Optimization, and Biological Evaluation of Novel MEK4 Inhibitors against Pancreatic Adenocarcinoma

Growth, division, and development of healthy cells relies on efficient response to environmental survival cues. The conserved mitogen-activated protein kinase (MAPK) family of pathways interface extracellular stimuli to intracellular processes for this purpose. Within these pathways, the MEK family has been identified as a target of interest due to its clinical relevance. Particularly, MEK4 has drawn recent attention for its indications in pancreatic and prostate cancers. Here, we report two potent MEK4 inhibitors demonstrating significant reduction of phospho-JNK and antiproliferative properties against pancreatic cancer cell lines. Furthermore, molecular inhibition of MEK4 pathway activates the MEK1/2 pathway, with the combination of MEK1/2 and MEK4 inhibitors demonstrating synergistic effects against pancreatic cancer cells. Our inhibitors provided insight into the crosstalk between MAPK pathways and new tools for elucidating the roles of MEK4 in disease states, findings which will pave the way for better understanding of the MAPK pathways and development of additional probes.

Diverse landscape of dermatologic toxicities from small-molecule inhibitor cancer therapy

BACKGROUND

Advances in molecular biology and genetics have contributed to breakthrough treatments directed at specific pathways associated with the development of cancer. Small-molecule inhibitors (Nibs) aimed at a variety of cellular pathways have been efficacious; however, they are associated with significant dermatologic toxicities.

METHODS

We conducted a comprehensive review of dermatologic toxicities associated with Nibs categorized into the following five groups: (a) mitogen-activated protein kinase; (b) growth factor/multi-tyrosine kinase; (c) cell division/DNA repair; (d) signaling associated with myeloproliferative neoplasms; and (e) other signaling pathways. Prospective phase I, II, or III clinical trials, retrospective literature reviews, systematic reviews/meta-analyses, and case reviews/reports were included for analysis.

RESULTS

Dermatologic toxicities reviewed were associated with every class of Nibs and ranged from mild to severe or life-threatening adverse skin reactions. Inflammatory reactions manifesting as maculopapular, papulopustular/acneiform, and eczematous lesions were frequent types of dermatologic toxicities seen with Nibs. Squamous cell carcinoma with keratoacanthoma-like features was associated with a subset of Nibs. Substantial overlap in dermatologic toxicities was found between Nibs.

CONCLUSIONS

Dermatologic toxicities from Nibs are diverse and may overlap between classes of Nibs. Recognition of the various types of toxicities from Nibs is critical for patient care in the era of "oncodermatology/dermatopathology."