Mitogen-activated Protein Kinase Kinase Inhibitor Research Articles

RAF and MEK Inhibitors in Non-Small Cell Lung Cancer.

Lung cancer, despite recent advancements in survival rates, represents a significant global health burden. Non-small cell lung cancer (NSCLC), the most prevalent type, is driven largely by activating mutations in Kirsten rat sarcoma viral oncogene homologue (KRAS) and receptor tyrosine kinases (RTKs), and less in v-RAF murine sarcoma viral oncogene homolog B (BRAF) and mitogen-activated protein-kinase kinase (MEK), all key components of the RTK-RAS-mitogen-activated protein kinase (MAPK) pathway. Learning from melanoma, the identification of BRAFV600E substitution in NSCLC provided the rationale for the investigation of RAF and MEK inhibition as a therapeutic strategy. The regulatory approval of two RAF-MEK inhibitor combinations, dabrafenib-trametinib, in 2017, and encorafenib-binimetinib, in 2023, signifies a breakthrough for the management of BRAFV600E-mutant NSCLC patients. However, the almost universal emergence of acquired resistance limits their clinical benefit. New RAF and MEK inhibitors, with distinct biochemical characteristics, are in preclinical and clinical development. In this review, we aim to provide valuable insights into the current state of RAF and MEK inhibition in the management of NSCLC, fostering a deeper understanding of the potential impact on patient outcomes.

Pancreatic Cancer Treatment Targeting the HGF/c-MET Pathway: The MEK Inhibitor Trametinib.

Pancreatic cancer is characterized by fibrosis/desmoplasia in the tumor microenvironment, which is primarily mediated by pancreatic stellate cells and cancer-associated fibroblasts. HGF/c-MET signaling, which is instrumental in embryonic development and wound healing, is also implicated for its mitogenic and motogenic properties. In pancreatic cancer, this pathway, along with its downstream signaling pathways, is associated with disease progression, prognosis, metastasis, chemoresistance, and other tumor-related factors. Other features of the microenvironment in pancreatic cancer with the HGF/c-MET pathway include hypoxia, angiogenesis, metastasis, and the urokinase plasminogen activator positive feed-forward loop. All these attributes critically influence the initiation, progression, and metastasis of pancreatic cancer. Therefore, targeting the HGF/c-MET signaling pathway appears promising for the development of innovative drugs for pancreatic cancer treatment. One of the primary downstream effects of c-MET activation is the MAPK/ERK (Ras, Ras/Raf/MEK/ERK) signaling cascade, and MEK (Mitogen-activated protein kinase kinase) inhibitors have demonstrated therapeutic value in RAS-mutant melanoma and lung cancer. Trametinib is a selective MEK1 and MEK2 inhibitor, and it has evolved as a pivotal therapeutic agent targeting the MAPK/ERK pathway in various malignancies, including BRAF-mutated melanoma, non-small cell lung cancer and thyroid cancer. The drug's effectiveness increases when combined with agents like BRAF inhibitors. However, resistance remains a challenge, necessitating ongoing research to counteract the resistance mechanisms. This review offers an in-depth exploration of the HGF/c-MET signaling pathway, trametinib's mechanism, clinical applications, combination strategies, and future directions in the context of pancreatic cancer.

Concurrent targeting of GSK3 and MEK as a therapeutic strategy to treat pancreatic ductal adenocarcinoma.

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies worldwide. However, drug discovery for PDAC treatment has proven complicated, leading to stagnant therapeutic outcomes. Here, we identify Glycogen synthase kinase 3 (GSK3) as a therapeutic target through a whole-body genetic screening utilizing a '4-hit' Drosophila model mimicking the PDAC genotype. Reducing the gene dosage of GSK3 in a whole-body manner or knocking down GSK3 specifically in transformed cells suppressed 4-hit fly lethality, similar to Mitogen-activated protein kinase kinase (MEK), the therapeutic target in PDAC we have recently reported. Consistently, a combination of the GSK3 inhibitor CHIR99021 and the MEK inhibitor trametinib suppressed the phosphorylation of Polo-like kinase 1 (PLK1) as well as the growth of orthotopic human PDAC xenografts in mice. Additionally, reducing PLK1 genetically in 4-hit flies rescued their lethality. Our results reveal a therapeutic vulnerability in PDAC that offers a treatment opportunity for patients by inhibiting multiple targets.

A MEK inhibitor arrests the cell cycle of human conjunctival fibroblasts and improves the outcome of glaucoma filtration surgery

Better agents are needed to improve glaucoma filtration surgery outcomes compared to current ones. The purpose of this study is to determine whether mitogen-activated protein kinase kinase (MEK) inhibitors can effectively arrest the cell cycle of human conjunctival fibroblasts (HCFs) and inhibit the formation of fibrosis and scarring following glaucoma filtration surgery. A cell counting kit‑8 assay revealed that the MEK inhibitor PD0325901 exhibited concentration-dependent growth inhibition of HCFs. Quantitative PCR, immunocytochemistry, and western blotting demonstrated decreased expression of proliferating cell nuclear antigen (PCNA) and cyclin D1 and increased expression of p27 in HCFs treated with PD0325901. Flow cytometry indicated that PD0325901 arrested the cell cycle of HCFs in the G0/1 phase. The cell-migration assay showed that HCF migration rate was significantly suppressed by PD0325901 exposure. Rabbits were divided into PD0325901-treatment and control groups, and glaucoma filtration surgery was performed. Although intraocular pressure did not differ between PD0325901-treatment and control groups, bleb height was greater in the treatment group. Histopathological evaluation revealed that fibrotic changes were significantly attenuated in the PD0325901-treatment group compared to the control group. In conclusion, the MEK inhibitor impedes HCF proliferation via cell-cycle arrest and may be beneficial for glaucoma filtration surgery by reducing bleb scarring.

Targeting BRAF pathway in low-grade serous ovarian cancer

Targeting BRAF pathway in low-grade serous ovarian cancer

MEK1-ERK1/2 signaling regulates the cardiomyocyte non-sarcomeric actin cytoskeletal network.

During select pathological conditions, the heart can hypertrophy and remodel in either a dilated or concentric ventricular geometry, which is associated with lengthening or widening of cardiomyocytes, respectively. The mitogen-activated protein kinase kinase 1 (MEK1) and extracellular signal-related kinase 1 and 2 (ERK1/2) pathway has been implicated in these differential types of growth such that cardiac overexpression of activated MEK1 causes profound concentric hypertrophy and cardiomyocyte thickening, while genetic ablation of the genes encoding ERK1/2 in the mouse heart causes dilation and cardiomyocyte lengthening. However, the mechanisms by which this kinase signaling pathway controls cardiomyocyte directional growth as well as its downstream effectors are poorly understood. To investigate this, we conducted an unbiased phosphoproteomic screen in cultured neonatal rat ventricular myocytes treated with an activated MEK1 adenovirus, the MEK1 inhibitor U0126, or an eGFP adenovirus control. Bioinformatic analysis identified cytoskeletal-related proteins as the largest subset of differentially phosphorylated proteins. Phos-tag and traditional Western blotting were performed to confirm that many cytoskeletal proteins displayed changes in phosphorylation with manipulations in MEK1-ERK1/2 signaling. From this, we hypothesized that the actin cytoskeleton would be changed in vivo in the mouse heart. Indeed, we found that activated MEK1 transgenic mice and gene-deleted mice lacking ERK1/2 protein had enhanced non-sarcomeric actin expression in cardiomyocytes compared with wild-type control hearts. Consistent with these results, cytoplasmic β- and γ-actin were increased at the subcortical intracellular regions of adult cardiomyocytes. Together, these data suggest that MEK1-ERK1/2 signaling influences the non-sarcomeric cytoskeletal actin network, which may be important for facilitating the growth of cardiomyocytes in length and/or width.NEW & NOTEWORTHY Here, we performed an unbiased analysis of the total phosphoproteome downstream of MEK1-ERK1/2 kinase signaling in cardiomyocytes. Pathway analysis suggested that proteins of the non-sarcomeric cytoskeleton were the most differentially affected. We showed that cytoplasmic β-actin and γ-actin isoforms, regulated by MEK1-ERK1/2, are localized to the subcortical space at both lateral membranes and intercalated discs of adult cardiomyocytes suggesting how MEK1-ERK1/2 signaling might underlie directional growth of adult cardiomyocytes.

Elevated FBXL6 activates both wild-type KRAS and mutant KRASG12D and drives HCC tumorigenesis via the ERK/mTOR/PRELID2/ROS axis in mice

BackgroundKirsten rat sarcoma (KRAS) and mutant KRASG12D have been implicated in human cancers, but it remains unclear whether their activation requires ubiquitination. This study aimed to investigate whether and how F-box and leucine-rich repeat 6 (FBXL6) regulates KRAS and KRASG12D activity in hepatocellular carcinoma (HCC).MethodsWe constructed transgenic mouse strains LC (LSL-Fbxl6KI/+;Alb-Cre, n = 13), KC (LSL-KrasG12D/+;Alb-Cre, n = 10) and KLC (LSL-KrasG12D/+;LSL-Fbxl6KI/+;Alb-Cre, n = 12) mice, and then monitored HCC for 320 d. Multiomics approaches and pharmacological inhibitors were used to determine oncogenic signaling in the context of elevated FBXL6 and KRAS activation. Co‑immunoprecipitation (Co-IP), Western blotting, ubiquitination assay and RAS activity detection assay were employed to investigate the underlying molecular mechanism by which FBXL6 activates KRAS. The pathological relevance of the FBXL6/KRAS/extracellular signal-regulated kinase (ERK)/mammalian target of rapamycin (mTOR)/proteins of relevant evolutionary and lymphoid interest domain 2 (PRELID2) axis was evaluated in 129 paired samples from HCC patients.ResultsFBXL6 is highly expressed in HCC as well as other human cancers (P < 0.001). Interestingly, FBXL6 drives HCC in transgenic mice. Mechanistically, elevated FBXL6 promotes the polyubiquitination of both wild-type KRAS and KRASG12D at lysine 128, leading to the activation of both KRAS and KRASG12D and promoting their binding to the serine/threonine-protein kinase RAF, which is followed by the activation of mitogen-activated protein kinase kinase (MEK)/ERK/mTOR signaling. The oncogenic activity of the MEK/ERK/mTOR axis relies on PRELID2, which induces reactive oxygen species (ROS) generation. Furthermore, hepatic FBXL6 upregulation facilitates KRASG12D to induce more severe hepatocarcinogenesis and lung metastasis via the MEK/ERK/mTOR/PRELID2/ROS axis. Dual inhibition of MEK and mTOR effectively suppresses tumor growth and metastasis in this subtype of cancer in vivo. In clinical samples, FBXL6 expression positively correlates with p-ERK (χ2 = 85.067, P < 0.001), p-mTOR (χ2 = 66.919, P < 0.001) and PRELID2 (χ2 = 20.891, P < 0.001). The Kaplan–Meier survival analyses suggested that HCC patients with high FBXL6/p-ERK levels predicted worse overall survival (log‑rank P < 0.001).ConclusionsFBXL6 activates KRAS or KRASG12D via ubiquitination at the site K128, leading to activation of the ERK/mTOR/PRELID2/ROS axis and tumorigenesis. Dual inhibition of MEK and mTOR effectively protects against FBXL6- and KRASG12D-induced tumorigenesis, providing a potential therapeutic strategy to treat this aggressive subtype of liver cancer.

Leptin-mediated ERK Signaling Pathway Promotes the Transformation of Rat Alveolar Type II Epithelial Cells Induced by Yunnan Tin Mine Dust

Currently, a significant number of miners are involved in mining operations at the Gejiu tin mine in Yunnan. This occupational setting is associated with exposure to dust particles, heavy metals, polycyclic aromatic hydrocarbons, and radioactive radon, thereby significantly elevating the risk of lung cancer. This study aims to investigate the involvement of leptin-mediated extracellular regulated protein kinase (ERK) signaling pathway in the malignant transformation of rat alveolar type II epithelial cells induced by Yunnan tin mine dust. Immortalized rat alveolar cells type II (RLE-6TN) cells were infected with Yunnan tin mine dust at a concentration of 200 μg/mL for nine consecutive generations to establish the infected cell model, which was named R₂₀₀ cells. The cells were cultured normally, named as R cells. The expression of leptin receptor in both cell groups was detected using the Western blot method. The optimal concentration of leptin and mitogen-activated protein kinase kinase (MEK) inhibitor (U0126) on R₂₀₀ cells was determined using the MTT method. Starting from the 20th generation, the cells in the R group were co-cultured with leptin, while the cells in the R₂₀₀ group were co-cultured with the MEK inhibitor U0126. The morphological alterations of the cells in each group were visualized utilizing hematoxylin-eosin staining. Additionally, concanavalin A (ConA) was utilized to detect any morphological differences, and an anchorage-independent growth assay was conducted to assess the malignant transformation of the cells. The changes in the ERK signaling pathway in epithelial cells after the action of leptin were detected using the Western blot method. Both the cells in the R group and R₂₀₀ group express leptin receptor OB-R. Compared to the R₂₀₀ group, the concentration of leptin at 100 ng/mL shows the most significant pro-proliferation effect. The proliferation of R₂₀₀ cells infected with the virus is inhibited by 30 μmol/L U0126, and a statistically significant divergence was seen when compared to the control group (P<0.05). Starting from the 25th generation, the cell morphology of the leptin-induced R₂₀₀ group (R₂₀₀L group) underwent changes, leading to malignant transformation observed at the 30th generation. The characteristics of malignant transformation became evident by the 40th generation in the R₂₀₀L group. In contrast, the other groups showed agglutination of P40 cells, and the speed of cell aggregation increased with an increase in ConA concentration. Notably, the R₂₀₀L group exhibited faster cell aggregation compared to the U0126-induced R₂₀₀ (R₂₀₀LU) group. Additionally, the cells in the R₂₀₀L group were capable of forming clones starting from P30, with a colony formation rate of 2.25‰±0.5‰. However, no clonal colonies were observed in the R₂₀₀LU group and R₂₀₀ group. The expression of phosphorylated extracellular signal-regulated kinase (pERK) was enhanced in cells of the R₂₀₀L group. However, when the cells in the R₂₀₀L group were treated with U0126, a blocking agent, the phosphorylation level of pERK decreased. Leptin can promote the malignant transformation of lung epithelial cells infected by mine dust, and the ERK signaling pathway may be necessary for the transformation of alveolar type II epithelial cells induced by Yunnan tin mine dust.

Development of a MEK inhibitor, NFX-179, as a chemoprevention agent for squamous cell carcinoma.

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer. Although cSCC contributes to substantial morbidity and mortality in high-risk individuals, deployment of otherwise effective chemoprevention of cSCC is limited by toxicities. Our systematic computational drug repurposing screen predicted that selumetinib, a MAPK (mitogen-activated protein kinase) kinase inhibitor (MEKi), would reverse transcriptional signatures associated with cSCC development, consistent with our genomic analysis implicating MEK as a chemoprevention target. Although systemic MEKi suppresses the formation of cSCC in mice, systemic MEKi can cause severe adverse effects. Here, we report the development of a metabolically labile MEKi, NFX-179, designed to potently and selectively suppress the MAPK pathway in the skin before rapid metabolism in the systemic circulation. NFX-179 was identified on the basis of its biochemical and cellular potency, selectivity, and rapid metabolism upon systemic absorption. In our ultraviolet-induced cSCC mouse model, topical application of NFX-179 gel reduced the formation of new cSCCs by an average of 60% at doses of 0.1% and greater at 28 days. We further confirmed the localized nature of these effects in an additional split-mouse randomized controlled study where suppression of cSCC was observed only in drug-treated areas. No toxicities were observed. NFX-179 inhibits the growth of human SCC cell lines in a dose-dependent manner, and topical NFX-179 application penetrates human skin and inhibits MAPK signaling in human cSCC explants. Together, our data provide a compelling rationale for using topical MEK inhibition through the application of NFX-179 gel as an effective strategy for cSCC chemoprevention.

Iterative machine learning-based chemical similarity search to identify novel chemical inhibitors

Machine learning-based chemical screening has made substantial progress in recent years. However, these predictions often have low accuracy and high uncertainty when identifying new active chemical scaffolds. Hence, a high proportion of retrieved compounds are not structurally novel. In this study, we proposed a strategy to address this issue by iteratively optimizing an evolutionary chemical binding similarity (ECBS) model using experimental validation data. Various data update and model retraining schemes were tested to efficiently incorporate new experimental data into ECBS models, resulting in a fine-tuned ECBS model with improved accuracy and coverage. To demonstrate the effectiveness of our approach, we identified the novel hit molecules for the mitogen-activated protein kinase kinase 1 (MEK1). These molecules showed sub-micromolar affinity (Kd 0.1–5.3 μM) to MEKs and were distinct from previously-known MEK1 inhibitors. We also determined the binding specificity of different MEK isoforms and proposed potential docking models. Furthermore, using de novo drug design tools, we utilized one of the new MEK inhibitors to generate additional drug-like molecules with improved binding scores. This resulted in the identification of several potential MEK1 inhibitors with better binding affinity scores. Our results demonstrated the potential of this approach for identifying novel hit molecules and optimizing their binding affinities.

Abstract P2023: Mitogen-activated Protein Kinase-directed Modulation Of The Non-sarcomeric Actin Cytoskeleton In Cardiomyocytes

A better understating of the mechanisms by which cardiomyocytes grow in different directions could open up new therapeutic avenues for hypertrophic and dilated cardiomyopathies, diseases that include the widening and lengthening of cardiomyocytes, respectively. Mitogen-activated protein kinase kinase 1 (MEK1) and extracellular signal-related kinases 1/2 (ERK1/2) are known to control this directional growth of cardiomyocytes, such that activated MEK1 causes concentric hypertrophy and cardiomyocyte widening, while genetic ablation of ERK1/2 proteins causes dilation and cardiomyocyte lengthening. To determine how these proteins may control this directional growth response, we conducted a phosphoproteomic screen using neonatal rat ventricular myocytes (NRVMs) treated with activated MEK1 adenovirus, U0126 MEK1 inhibitor, or control GFP adenovirus. The resulting data pinpointed over 2700 sites on 324 proteins as changing their phosphorylation status with modulation of this signaling cascade. Gene ontology analysis found that cytoskeletal-associated proteins were the largest subset of proteins with phosphorylation changes. Traditional and PhosTag western blots verified that many of these cytoskeletal proteins change expression as well as their phosphorylation status in NRVMs. In vivo experiments showed that cytoplasmic actin expression was upregulated in MEK1 transgenic or ERK1/2 gene-deleted hearts. Furthermore, MEK1 transgenic adult cardiomyocytes had enhanced cytoplasmic actin at lateral membranes. Palladin, an actin nucleating protein, changed both phosphorylation status and isoform expression in response to modulation of MEK1-ERK1/2 signaling. Adeno-associated viruses were used to overexpress different palladin isoforms. Immunostaining for these proteins showed that localization of palladin isoforms moved from the subcortical compartment to the sarcomere, suggesting these isoforms preferentially associate with either cytoskeletal or sarcomeric actin. Future studies will further examine the signaling roles that cytoplasmic actin may play in healthy and diseased cardiomyocytes and delineate preferential binding of actin associated proteins between cytoplasmic and sarcomeric actin in cardiomyocytes.

Dupilumab for the treatment of dermatologic adverse events associated with MEK and EGFR inhibitors.

3143 Background: Mitogen activated protein kinase kinase inhibitors (MEKi) and epidermal growth factor receptor inhibitors (EGFRi) are targeted therapies used in the treatment of various cancers. Dermatologic adverse events (dAEs) are common with these medications. Dupilumab, a human monoclonal antibody that targets IL-4, is an FDA approved therapy for the treatment of atopic dermatitis. It has also shown utility in the treatment of many other skin disorders, including toxicities associated with anticancer therapies. In our study, we aim to evaluate the efficacy and safety of dupilumab for the treatment of MEKi/EGFRi associated dAEs. Methods: Patients who received dupilumab for the treatment of a dAE attributed to MEKi or EGFRi from 3/1/2017 to 10/1/2022 were identified at Memorial Sloan Kettering Cancer Center. Severity of dAEs was graded at baseline and follow up using Common Terminology Criteria for Adverse Events (CTCAE) v5.0. Patient response to dupilumab was categorized into complete response (CR) (reduction to grade 0), partial response (PR) (reduction to grade 1), or no response (NR) (including change from grade 3/2 to grade ≥ 2). Results: A total of 17 patients (median age 62 years [5 – 87], 58.8% female) who received dupilumab for MEKi (70.6%) or EGFRi (29.4%) related dAEs were identified. Two patients on MEKi were also on concomitant BRAF inhibitors. Patients were white (88.2%), black (5.9%), and Asian (5.9%) and were all undergoing treatment for solid tumors. All dAEs had an eczematous phenotype; 16 were grade 2 (88.2%) and one (5.9%) was grade 3. The median time from dAE development to initiation of dupilumab was 121 days (5 – 1330). Following treatment, 15 patients (88.2%) experienced improvement, with 46.7% and 53.3% achieving CR and PR, respectively. Patients were on dupilumab for a median of 89 days (0-2556), with CR and PR patients exhibiting initial documented response after a median of 30 days (6 – 173). The median CTCAE grade decreased from 2 to 1, and the number of patients on topical and systemic steroids following addition of dupilumab decreased from 17 (100%) to 7 (41.2%) and 5 (29.4%) to 1 (5.9%), respectively. As a result of intolerable anti-cancer therapy-associated dAEs, 4 patients (all on MEKi) initially discontinued their antineoplastics. Three patients (75%) were successfully rechallenged with their original MEKi, while 1 (25%) was switched to another MEKi without subsequent dAE recurrence. No patients reported adverse events to dupilumab treatment. Conclusions: Patients may experience eczematous eruptions while undergoing treatment with MEKi or EGFRi. Dupilumab may be a safe and effective steroid sparing therapeutic option for the management of these dAEs.

Combination Treatment Targeting mTOR and MAPK Pathways Has Synergistic Activity in Multiple Myeloma

Multiple myeloma (MM) is an incurable, malignant B cell disorder characterized by frequent relapses and a poor prognosis. Thus, new therapeutic approaches are warranted. The phosphatidylinositol-3-kinase (PI3K) pathway plays a key role in many critical cellular processes, including cell proliferation and survival. Activated PI3K/AKT (protein kinases B)/mTOR (mammalian target of rapamycin) signaling has been identified in MM primary patient samples and cell lines. In this study, the efficacy of PI3K and mTOR inhibitors in various MM cell lines representing three different prognostic subtypes was tested. Whereas MM cell lines were rather resistant to PI3K inhibition, treatment with the mTOR inhibitor temsirolimus decreases the phosphorylation of key molecules in the PI3K pathway in MM cell lines, leading to G0/G1 cell cycle arrest and thus reduced proliferation. Strikingly, the efficacy of temsirolimus was amplified by combining the treatment with the Mitogen-activated protein kinase kinase (MEK) inhibitor trametinib. Our findings provide a scientific rationale for the simultaneous inhibition of mTOR and MEK as a novel strategy for the treatment of MM.

Abstract 1632: MDM2 inhibitor alrizomadlin (APG-115) promotes antitumor activity of mitogen-activated protein kinase (MAPK) inhibitors in uveal melanoma

Abstract Uveal melanoma (UM) is the commonest primary intraocular malignancy, yet its molecular pathogenesis is poorly understood. Most UM cases have activating mutations in genes encoding G protein subunits alpha Q or 11, leading to activation of downstream effectors. These include protein kinase C, mitogen-activated protein kinases (MAPK1/3; also termed extracellular signal-regulated kinase 2/1 [ERK2⁄ERK1], respectively), and yes-associated protein, suggesting a rationale for therapeutically targeting these related pathways. Genetic analyses show that TP53 is infrequently mutated in UM, but associated pathways may be functionally inactivated. Ubiquitination-mediated degradation of p53 activates MAPK signaling, such that, active p53 may promote suppression of MAPK signaling. Alrizomadlin (APG-115) is a small molecule targeting p53/MDM2 that is in clinical development for solid and hematologic cancers. This study evaluated the antitumor effect of alrizomadlin, alone or combined with other targeted therapies, in preclinical models of UM. In cell-based antiproliferation assays of many UM cell lines, alrizomadlin exerted moderate growth inhibitory effects (IC50 = 0.151-1.857μM). When combined with inhibitors against mitogen-activated protein kinase kinase (MEK) [trametinib and selumetinib], mammalian target of rapamycin (mTOR) [rapamycin], focal adhesion kinase (FAK) [defactinib and Ascentage’s APG-2449, which targets FAK/ALK/ROS1], and MEK/rapidly accelerated fibrosarcoma [RAF] [VS-6766], alrizomadlin demonstrated enhanced antiproliferative activity. In a UM xenograft model (MP41), alrizomadlin showed dose-dependent antitumor activity when administered at 25, 50, and 100 mg/kg, with tumor growth inhibition (TGI) rates of 24.8%, 38%, and 39.1%, respectively. In this model, synergistic antitumor effects were observed when alrizomadlin was combined with selumetinib or APG-2449, with TGI rates of 65.4% and 47.5%, respectively. Mechanistically, alrizomadlin likely increased p53, MDM2, and downstream p21 in MP41 cells. Importantly, alrizomadlin inhibited ERK phosphorylation and enhanced selumetinib inhibition in a dose- and time-dependent manner. Prior studies indicated that FAK can suppress p53 by enhancing MDM2-dependent p53 ubiquitination. In this study, APG-2449 showed dose-dependent inhibition of FAK phosphorylation and upregulation of p53. Alrizomadlin also inhibited phosphorylation of FAK and downstream ERK. Therefore, the combination of alrizomadlin and APG-2449 was synergistic. Combining MEK and FAK inhibitors also markedly augmented caspase-3 and poly (ADP-ribose) polymerase 1 (PARP-1) cleavage (apoptosis hallmarks) and enhanced observed antitumor effects. In conclusion, our results demonstrate the potential utility of combining alrizomadlin with MAPK pathway inhibitors to treat patients with UM. Citation Format: Guangfeng Wang, Eric Liang, Ping Min, Dajun Yang, Yifan Zhai. MDM2 inhibitor alrizomadlin (APG-115) promotes antitumor activity of mitogen-activated protein kinase (MAPK) inhibitors in uveal melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1632.

Combining SOS1 and MEK Inhibitors in a Murine Model of Plexiform Neurofibroma Results in Tumor Shrinkage.

Individuals with neurofibromatosis type 1 develop rat sarcoma virus (RAS)-mitogen-activated protein kinase-mitogen-activated and extracellular signal-regulated kinase (RAS-MAPK-MEK)-driven nerve tumors called neurofibromas. Although MEK inhibitors transiently reduce volumes of most plexiform neurofibromas in mouse models and in neurofibromatosis type 1 (NF1) patients, therapies that increase the efficacy of MEK inhibitors are needed. BI-3406 is a small molecule that prevents Son of Sevenless (SOS)1 interaction with Kirsten rat sarcoma viral oncoprotein (KRAS)-GDP, interfering with the RAS-MAPK cascade upstream of MEK. Single agent SOS1 inhibition had no significant effect in the DhhCre;Nf1 fl/fl mouse model of plexiform neurofibroma, but pharmacokinetics (PK)-driven combination of selumetinib with BI-3406 significantly improved tumor parameters. Tumor volumes and neurofibroma cell proliferation, reduced by MEK inhibition, were further reduced by the combination. Neurofibromas are rich in ionized calcium binding adaptor molecule 1 (Iba1)+ macrophages; combination treatment resulted in small and round macrophages, with altered cytokine expression indicative of altered activation. The significant effects of MEK inhibitor plus SOS1 inhibition in this preclinical study suggest potential clinical benefit of dual targeting of the RAS-MAPK pathway in neurofibromas. SIGNIFICANCE STATEMENT: Interfering with the RAS-mitogen-activated protein kinase (RAS-MAPK) cascade upstream of mitogen activated protein kinase kinase (MEK), together with MEK inhibition, augment effects of MEK inhibition on neurofibroma volume and tumor macrophages in a preclinical model system. This study emphasizes the critical role of the RAS-MAPK pathway in controlling tumor cell proliferation and the tumor microenvironment in benign neurofibromas.

Mitogen-Activated Pathway Kinase Inhibitor-Associated Retinopathy: Do Features Differ with Upstream versus Downstream Inhibition?

Introduction: Many cancers have derangement of the mitogen-activated pathway kinase (MAPK), making this pathway blockade a therapeutic target. However, inhibitors of MAPK can result in adverse effects including retinopathy. This study compares clinical and morphological characteristics of serous retinal disturbances in patients taking agents with variable inhibition of MAPK: either direct interference of mitogen-activated protein kinase kinase (MEK) or extracellular signal-regulated kinase (ERK) inhibitors or with indirect inhibition via interference with FGFR signaling. Methods: This retrospective observational study of prospectively collected pooled data is from a single tertiary oncology referral center. Of 339 patients receiving MAPK inhibitors (171, 107, and 61 on FGFR, MEK, and ERK inhibitors, respectively) for treatment of metastatic cancer, this study included 128 eyes of 65 patients with evidence of retinopathy confirmed by optical coherence tomography (OCT). The main outcome was characteristics of treatment-emergent choroid/retinal OCT abnormalities as compared to baseline OCT. Results: In all patients on one of three drug classes (FGFRi, MEKi, ERKi), the retinopathy manifested as subretinal fluid foci that were bilateral, fovea involving, and reversible without intervention. There were notable differences between the three classes of drugs: the proportion of patients with retinopathy, number of fluid foci per eye, proportion of eyes with intraretinal edema, and the proportion of symptomatic patients was least for the upstream target (FGFR inhibitors) and greatest for the downstream targets (MEK or ERK inhibitors). Conclusion: This study shows MAPK pathway inhibitors may cause subretinal fluid foci with unique clinical and morphological characteristics depending on the target (FGFR, MEK, or ERK) implicated. Retinopathy is more common, more symptomatic, and more severe (more fluid foci, more expansive fluid configurations) the further downstream the MAPK pathway is inhibited.

MEK/ERK activation plays a decisive role in Zika virus morphogenesis and release.

Brazil has experienced an increase in outbreaks caused by flaviviruses. The high incidence of dengue fever, the morbidity of Zika in children, and the high mortality of yellow fever have affected millions in recent years. Deciphering host-virus interactions is important for treating viral infections, and the mitogen-activated protein kinases (MAPK) are an interesting target because of their role in flavivirus replication. In particular, mitogen-activated protein kinase kinase (MEK), which targets extracellular-signal-regulated kinase (ERK), is necessary for dengue and yellow fever infections. In this study, we evaluated the role of the MEK/ERK pathway and the effect of the MEK inhibitor trametinib on the Asian ZIKV strain PE243 and the prototype African ZIKV strain MR766, addressing genome replication, morphogenesis, and viral release. ZIKV infection stimulated ERK phosphorylation in Vero cells at 12 and 18hours postinfection (hpi). Trametinib showed sustained antiviral activity, inhibiting both ZIKV strains for at least four days, and electron microscopy showed probable inhibition of ZIKV morphogenesis. ZIKV PE243 can complete one cycle in Vero cells in 14hours; genome replication was detected around 8hpi, intracellular viral particles at 12hpi, and extracellular progeny at 14hpi. Treatments at 6-hour intervals showed that trametinib inhibited late stages of viral replication, and the titration of intra- or extracellular virions showed that the treatment especially affected viral morphogenesis and release. Thus, ZIKV stimulated ERK phosphorylation during viral morphogenesis and release, which correlated with trametinib inhibiting both the signaling pathway and viral replication.

Protein phosphatase 6 regulates trametinib sensitivity, a mitogen-activated protein kinase kinase (MEK) inhibitor, by regulating MEK1/2-ERK1/2 signaling in canine melanoma cells.

Melanoma is a highly aggressive and metastatic cancer occurring in both humans and dogs. Canine melanoma accounts for a significant proportion of neoplastic diseases in dogs, and despite standard treatments, overall survival rates remain low. Protein phosphatase 6 (PP6), an evolutionarily conserved serine/threonine protein phosphatase, regulates various biological processes. Additionally, the loss of PP6 function reportedly leads to the development of melanoma in humans. However, there are no reports regarding the role of PP6 in canine cancer cells. We, therefore, conducted a study investigating the role of PP6 in canine melanoma by using four canine melanoma cell lines: CMec1, CMM, KMeC and LMeC. PP6 knockdown increased phosphorylation levels of mitogen-activated protein kinase kinase 1/2 (MEK1/2) and extracellular signal-regulated kinase 1/2 (ERK1/2) but not Akt. Furthermore, PP6 knockdown decreased sensitivity to trametinib, a MEK inhibitor, but did not alter sensitivity to Akt inhibitor. These findings suggest that PP6 may function as a tumor suppressor in canine melanoma and modulate the response to trametinib treatment. Understanding the role of PP6 in canine melanoma could lead to the development of more effective treatment strategies for this aggressive disease.

Neuronal differentiation drives the antitumor activity of mitogen-activated protein kinase kinase (MEK) inhibition in glioblastoma.

Epidermal growth factor receptor (EGFR) amplification is found in nearly 40%-50% of glioblastoma cases. Several EGFR inhibitors have been tested in glioblastoma but have failed to demonstrate long-term therapeutic benefit, presumably because of acquired resistance. Targeting EGFR downstream signaling with mitogen-activated protein kinase kinase 1 and 2 (MEK1/2) inhibitors would be a more effective approach to glioblastoma treatment. We tested the therapeutic potential of MEK1/2 inhibitors in glioblastoma using 3D cultures of glioma stem-like cells (GSCs) and mouse models of glioblastoma. Several MEK inhibitors were screened in an unbiased high-throughput platform using GSCs. Cell death was evaluated using flow cytometry and Western blotting (WB) analysis. RNA-seq, real-time quantitative polymerase chain reaction, immunofluorescence, and WB analysis were used to identify and validate neuronal differentiation. Unbiased screening of multiple MEK inhibitors in GSCs showed antiproliferative and apoptotic cell death in sensitive cell lines. An RNA-seq analysis of cells treated with trametinib, a potent MEK inhibitor, revealed upregulation of neurogenesis and neuronal differentiation genes, such as achaete-scute homolog 1 (ASCL1), delta-like 3 (DLL3), and neurogenic differentiation 4 (NeuroD4). We validated the neuronal differentiation phenotypes in vitro and in vivo using selected differentiation markers (β-III-tubulin, ASCL1, DLL3, and NeuroD4). Oral treatment with trametinib in an orthotopic GSC xenograft model significantly improved animal survival, with 25%-30% of mice being long-term survivors. Our findings demonstrated that MEK1/2 inhibition promotes neuronal differentiation in glioblastoma, a potential additional mechanism of action of MEK1/2 inhibitors. Thus, MEK inhibitors could be efficacious in glioblastoma patients with activated EGFR/MAPK signaling.

DDI2 promotes tumor metastasis and resists antineoplastic drugs-induced apoptosis in colorectal cancer.

The normal colorectal mucosa undergoes precancerous lesions that can develop over time into colorectal cancer (CRC). In the stage of precancerous lesions, DNA replication stress may lead to genome instability. We have performed whole-exome sequencing on genomic DNA obtained from three cases of CRC tissues and identified a novel frameshift mutation of DNA damage inducible 1 homolog 2 gene (DDI2, c. 854 del T). To date, there is no direct evidence that DDI2 is involved in the carcinogenesis of CRC. In this study, we demonstrated that DDI2 is upregulated in the early stage of CRC based on clinical samples and public databases. We also found that 5FU, a standard chemotherapeutic agent for CRC treatment, increased DDI2 mRNA levels in a dose-dependent manner. Depression of DDI2 inhibited CRC cell proliferation, migration and invasion both in vitro and in vivo. Transcriptome sequencing revealed that DDI2 was involved in the mitogen-activated protein kinase (MAPK) pathway. Furthermore, DDI2 resists a MAPK kinase (MEK) inhibitor (trametinib) and a PolyADP-ribose polymerase 1 (PARP1) inhibitor (talazoparib) induced apoptosis in CRC cells. Thus, our results indicate that DDI2 may play a vital role in the carcinogenesis of CRC and could serve as a promising therapeutic target for CRC.