Pheophorbide a identified in an Eupatorium perfoliatum extract is a novel lymphatic vascular activator.

The lymphatic vascular system is crucial for maintaining tissue fluid homeostasis and immune surveillance. Promoting lymphatic function represents a new strategy to treat several diseases including lymphedema, chronic inflammation and impaired wound healing. By screening a plant extract library, a petroleum ether extract from the aerial parts of Eupatorium perfoliatum (E. perfoliatum) was found to possess lymphangiogenic properties. With the aid of HPLC activity profiling the active compound was identified as pheophorbide a. Both plant extract and pheophorbide a induced the sprouting and tube formation of human primary lymphatic endothelial cells (LECs). The proliferation of the LECs was increased upon treatment with pheophorbide a but not the E. perfoliatum extract. Treatment with the MEK1/2 inhibitor U0126 reduced the LEC sprouting activity, indicating a potential mechanism of action. These studies suggest that pheophorbide a could represent novel natural therapeutic agent to treat human lymphatic vascular insufficiencies.

Purpurogallin is a novel mitogen-activated protein kinase kinase 1/2 inhibitor that suppresses esophageal squamous cell carcinoma growth in vitro and in vivo.

Purpurogallin is a natural compound that is extracted from nutgalls and oak bark and it possesses antioxidant, anticancer, and anti-inflammatory properties. However, the anticancer capacity of purpurogallin and its molecular target have not been investigated in esophageal squamous cell carcinoma (ESCC). Herein, we report that purpurogallin suppresses ESCC cell growth by directly targeting the mitogen-activated protein kinase kinase 1/2 (MEK1/2) signaling pathway. We found that purpurogallin inhibits anchorage-dependent and -independent ESCC growth. The results of in vitro kinase assays and cell-based assays indicated that purpurogallin also strongly attenuates the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway and also directly binds to and inhibits MEK1 and MEK2 activity. Furthermore, purpurogallin contributed to S and G2 phase cell cycle arrest by reducing cyclin A2 and cyclin B1 expression and also induced apoptosis by activating poly (ADP ribose) polymerase (PARP). Notably, purpurogallin suppressed patient-derived ESCC tumor growth in an in vivo mouse model. These findings indicated that purpurogallin is a novel MEK1/2 inhibitor that could be useful for treating ESCC.

MEK1/2 inhibition by binimetinib is effective as a single agent and potentiates the actions of Venetoclax and ABT-737 under conditions that mimic the chronic lymphocytic leukaemia (CLL) tumour microenvironment.

The survival and proliferation of chronic lymphocytic leukaemia (CLL) cells is driven by multiple signalling pathways, including those mediated by the B cell, Toll-like and chemokine receptors. Many of these pathways converge on the same signalling molecules, including those involved in the Raf-1/MEK/Erk1/2-MAPK pathway. We investigated the effects of the MEK1/2 (also termed MAP2K1/2) inhibitor, binimetinib, against CLL cells cultured under conditions that mimic aspects of the tumour microenvironment. Binimetinib blocked CLL cell survival induced by stroma-conditioned media and phorbol myristylate (PMA). Binimetinib was also significantly more toxic towards CLL cells cultured in the presence of either anti-IgM antibody or stroma-derived factor-1α (SDF-1α) and reduced CLL cell cycle progression and proliferation. Furthermore, binimetinib significantly increased the sensitivity of CLL cells co-cultured with CD40 ligand (CD40L)-expressing fibroblasts to the BH3-mimetics ABT-737 and Venetoclax (ABT-199) via a mechanism involving down-regulation of Mcl-1 (MCL1) activity and Bim (BCL2L11) and Bcl-xL (BCL2L1) expression. Collectively, these data suggest that binimetinib may have both cytotoxic and cytostatic effects on CLL cells by blocking microenvironment-derived signals known to drive survival and proliferation. The combination of binimetinib with a BH3 mimetic may be an effective treatment strategy for CLL, particularly against the proliferative fraction of the disease within the tumour microenvironment.

Anti-adipogenic effect of epiberberine is mediated by regulation of the Raf/MEK1/2/ERK1/2 and AMPKα/Akt pathways.

It has been reported that alkaloids derived from Coptis chinensis exert anti-adipogenic activity on 3T3-L1 adipocytes by downregulating peroxisome proliferation-activity receptor-γ (PPAR-γ) and CCAAT/enhancer binding protein-α (C/EBP-α). However, the signaling-based mechanism of the inhibitory role of epiberberine in the early stages of 3T3-L1 adipocyte differentiation is uncharacterized. Here, we show that epiberberine had inhibitory effects on adipocyte differentiation and significantly decreased lipid accumulation by downregulating an adipocyte-specific transcription factor, sterol regulatory element-binding protein-1 (SREBP-1). Furthermore, we observed that epiberberine markedly suppressed the differentiation-mediated phosphorylation of components of both the Raf/mitogen-activated protein kinase 1 (MEK1)/extracellular signal-regulated protein kinase 1/2 (ERK1/2) and AMP-activated protein kinase-α1 (AMPKα)/Akt pathways. In addition, gene expression of fatty acid synthase (FAS) was significantly inhibited by treatment with epiberberine during adipogenesis. These results indicate that the anti-adipogenic mechanism of epiberberine is associated with inhibition of phosphorylation of Raf/MEK1/ERK1/2 and AMPKα/Akt, followed by downregulation of the major transcription factors of adipogenesis, such as PPAR-γ, C/EBP-α, and SREBP-1, and FAS. Taken together, this study suggests that the anti-adipogenic effect of epiberberine is mediated by downregulation of the Raf/MEK1/ERK1/2 and AMPKα/Akt pathways during 3T3-L1 adipocyte differentiation. Moreover, the anti-adipogenic effects of epiberberine were not accompanied by modulation of ß-catenin.

Saururus chinensis (Lour.) Baill blocks enterovirus 71 infection by hijacking MEK1-ERK signaling pathway.

The aerial parts of Saururus chinensis (Lour.) Baill are a Chinese herbal medicine used for the treatment of edema and inflammatory diseases. However, the effect of this medicine on enterovirus 71 (EV71) infection has not been explored. Previous studies showed that MEK1-ERK signal pathway was required for efficient replication of EV71 infection and inhibition of this signal pathway has been shown to suppress virus infection. Here we show that the water extract of S. chinensis (Lour.) Baill (SCB) significantly blocks EV71 infection by inhibiting the activation of MEK1-ERK signal pathway with an IC50 of 8.9µg/mL. SCB at 30 and 60 µg/mL blocked EV71-induced cytopathic effect (CPE) and production of infectious virion by 1.9 and 5.1 logs, respectively. Virucidal assay suggested that SCB had no virucidal activity against EV71 and probably exerted its effect by targeting multiple steps in EV71 infection. Knockdown of MEK1 but not MEK2 blocked EV71 replication. And SCB treatment inhibited the activation of MEK1-ERK signal during EV71 infection. Furthermore, we found that rutin at 200 µM, one of the major components of SCB, significantly suppressed EV71 induced CPE and inhibited viral replication in a dose dependent manner. Taken together, SCB inhibited EV71 infection by hijacking MEK1-ERK signal pathway and rutin was the responsible antiviral component of SCB.

MEK 1/2 inhibitors in the treatment of hepatocellular carcinoma.

Sorafenib is the only approved systemic treatment for advanced hepatocellular carcinoma patients and all the recently published randomized controlled trials on new systemic drugs have been unsuccessful. This is likely due to a lack of understanding of tumor progression, molecular drivers, and liver toxicity, as well as flaws in trial design. An important signaling pathway in hepatocarcinogenesis is the MEK cascade involved in various cellular responses, including adaptation and survival. A key role in this cascade is played by MEK, of which MEK 1/2 represent the prototypes and an interesting target for new oncological drugs. This review analyzes recent developments and future perspectives on the role of MEK inhibitors in hepatocellular carcinoma treatment.

Early MEK1/2 inhibition after global cerebral ischemia in rats reduces brain damage and improves outcome by preventing delayed vasoconstrictor receptor upregulation.

BACKGROUND: Global cerebral ischemia following cardiac arrest is associated with increased cerebral vasoconstriction and decreased cerebral blood flow, contributing to delayed neuronal cell death and neurological detriments in affected patients. We hypothesize that upregulation of contractile ETB and 5-HT1B receptors, previously demonstrated in cerebral arteries after experimental global ischemia, are a key mechanism behind insufficient perfusion of the post-ischemic brain, proposing blockade of this receptor upregulation as a novel target for prevention of cerebral hypoperfusion and delayed neuronal cell death after global cerebral ischemia. The aim was to characterize the time-course of receptor upregulation and associated neuronal damage after global ischemia and investigate whether treatment with the MEK1/2 inhibitor U0126 can prevent cerebrovascular receptor upregulation and thereby improve functional outcome after global cerebral ischemia. Incomplete global cerebral ischemia was induced in Wistar rats and the time-course of enhanced contractile responses and the effect of U0126 in cerebral arteries were studied by wire myography and the neuronal cell death by TUNEL. The expression of ETB and 5-HT1B receptors was determined by immunofluorescence. RESULTS: Enhanced vasoconstriction peaked in fore- and midbrain arteries 3 days after ischemia. Neuronal cell death appeared initially in the hippocampus 3 days after ischemia and gradually increased until 7 days post-ischemia. Treatment with U0126 normalised cerebrovascular ETB and 5-HT1B receptor expression and contractile function, reduced hippocampal cell death and improved survival rate compared to vehicle treated animals. CONCLUSIONS: Excessive cerebrovascular expression of contractile ETB and 5-HT1B receptors is a delayed response to global cerebral ischemia peaking 3 days after the insult, which likely contributes to the development of delayed neuronal damage. The enhanced cerebrovascular contractility can be prevented by treatment with the MEK1/2 inhibitor U0126, diminishes neuronal damage and improves survival rate, suggesting MEK1/2 inhibition as a novel strategy for early treatment of neurological consequences following global cerebral ischemia.

Trametinib for the treatment of melanoma.

Advanced melanoma traditionally has had poor prognosis with limited, modestly effective and relatively toxic systemic treatment options like cytotoxic chemotherapy (dacarbazine) and immunomodulating agents (high-dose interleukin-2 and ipilimumab) which have response rates of 6-20%. With the identification of BRAF mutations found to be present in 50% of melanomas and the clinical success of serine/threonine-protein kinase B-raf inhibitors the prognostic landscape of melanoma has changed considerably. Vemurafenib and dabrafenib have been at the forefront of antimelanoma-targeted agents with a tolerable side effect profile and efficacy that compared well with the standard chemotherapy. These characteristics have led to the regulatory approval of both agents for the treatment of melanoma. However, these agents are not curative and have a short life span primarily due to rapidly occurring drug resistance. More recently, mitogen-activated protein kinase kinase (MEK) inhibitors have been found to have strong anticancer activity independently as well as when combined with other agents like B-raf inhibitors due to their activity downstream of RAF. Preclinical data and limited clinical data suggest that MEK inhibitors may be a component of effective therapy for a broad spectrum of cancers with other oncogenic drivers.

A novel MEK1/2 inhibitor induces G1/S cell cycle arrest in human fibrosarcoma cells.

Blockade of the ERK pathway has antitumor effects against malignant tumor cells. In this study, we investigated the antitumor activity of JTP-70902, a novel specific MEK inhibitor, against human fibrosarcoma cells in which the ERK pathway is constitutively activated. JTP-70902 was synthesized at Japan Tabacco. Human fibrosarcoma HT1080 cells were cultured. JTP-70902 was added at various concentrations. The number of viable cells was counted employing a trypan blue dye exclusion test. Unsynchronized cells were exposed to JTP-70902 for 24 h. The nuclei were stained with propidium iodide. The DNA content was measured using a FACSCalibur flow cytometer. Protein extraction and Western blot analysis were performed. (1) A dose-dependent inhibition of cell growth was observed at concentrations of 10 nM or more. Forty-eight hours after the treatment, the growth of HT1080 cells was completely inhibited by 200 nM JTP-70902. (2) FACS analysis revealed that a 24-h exposure to JTP-70902 increased the population of G1/S phase cells in a dose-dependent manner. (3) The phosphorylation of ERK was inhibited by JTP-70902. Furthermore, after the treatment with JTP-70902, p21WAF1/CIP1 and p27KIP1 protein expression increased and the phosphorylation of RB was reduced. Our results showed that JTP-70902 inhibits cell growth and induces cell cycle arrest in human Ras mutant fibrosarcoma cells. These results indicate that JTP-70902 might be an attractive compound for molecular-targeting chemotherapy for malignant soft tissue tumors with the activation of the Ras-MEK-ERK pathway.

17-allylamino-17-demethoxygeldanamycin and MEK1/2 inhibitors kill GI tumor cells via Ca2+-dependent suppression of GRP78/BiP and induction of ceramide and reactive oxygen species.

The present studies determine in greater detail the molecular mechanisms upstream of the CD95 death receptor by which geldanamycin heat shock protein 90 inhibitors and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1/2 (MEK1/2) inhibitors interact to kill carcinoma cells. MEK1/2 inhibition enhanced 17-allylamino-17-demethoxygeldanamycin (17AAG) toxicity that was suppressed in cells deleted for mutant active RAS that were nontumorigenic but was magnified in isogenic tumorigenic cells expressing Harvey RAS V12 or Kirsten RAS D13. MEK1/2 inhibitor and 17AAG treatment increased intracellular Ca(2+) levels and reduced GRP78/BiP expression in a Ca(2+)-dependent manner. GRP78/BiP overexpression, however, also suppressed drug-induced intracellular Ca(2+) levels. MEK1/2 inhibitor and 17AAG treatment increased reactive oxygen species (ROS) levels that were blocked by quenching Ca(2+) or overexpression of GRP78/BiP. MEK1/2 inhibitor and 17AAG treatment activated CD95 and inhibition of ceramide synthesis; ROS or Ca(2+) quenching blocked CD95 activation. In SW620 cells that are patient matched to SW480 cells, MEK1/2 inhibitor and 17AAG toxicity was significantly reduced, which correlated with a lack of CD95 activation and lower expression of ceramide synthase 6 (LASS6). Overexpression of LASS6 in SW620 cells enhanced drug-induced CD95 activation and enhanced tumor cell killing. Inhibition of ceramide signaling abolished drug-induced ROS generation but not drug-induced cytosolic Ca(2+) levels. Thus, treatment of tumor cells with MEK1/2 inhibitor and 17AAG induces cytosolic Ca(2+) and loss of GRP78/BiP function, leading to de novo ceramide synthesis pathway activation that plays a key role in ROS generation and CD95 activation.

RDEA119/BAY 869766: a potent, selective, allosteric inhibitor of MEK1/2 for the treatment of cancer.

The RAS-RAF-mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)-ERK pathway provides numerous opportunities for targeted oncology therapeutics. In particular, the MEK enzyme is attractive due to high selectivity for its target ERK and the central role that activated ERK plays in driving cell proliferation. The structural, pharmacologic, and pharmacokinetic properties of RDEA119/BAY 869766, an allosteric MEK inhibitor, are presented. RDEA119/BAY 869766 is selectively bound directly to an allosteric pocket in the MEK1/2 enzymes. This compound is highly efficacious at inhibiting cell proliferation in several tumor cell lines in vitro. In vivo, RDEA119/BAY 869766 exhibits potent activity in xenograft models of melanoma, colon, and epidermal carcinoma. RDEA119/BAY 869766 exhibits complete suppression of ERK phosphorylation at fully efficacious doses in mice. RDEA119/BAY 869766 shows a tissue selectivity that reduces its potential for central nervous system-related side effects. Using pharmacokinetic and pharmacodynamic data, we show that maintaining adequate MEK inhibition throughout the dosing interval is likely more important than achieving high peak levels because greater efficacy was achieved with more frequent but lower dosing. Based on its longer half-life in humans than in mice, RDEA119/BAY 869766 has the potential for use as a once- or twice-daily oral treatment for cancer. RDEA119/BAY 869766, an exquisitely selective, orally available MEK inhibitor, has been selected for clinical development because of its potency and favorable pharmacokinetic profile.

Combined inhibition of MEK and mammalian target of rapamycin abolishes phosphorylation of cyclin-dependent kinase 4 in glioblastoma cell lines and prevents their proliferation.

The Ras/Raf/MEK/extracellular signal-regulated kinase (ERK) and phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin (mTOR) signaling pathways are aberrantly activated in many tumors, including highly proliferative glioblastomas, but how they are wired with the cell cycle remains imperfectly understood. Inhibitors of MEK/ERK and mTOR pathways are tested as anticancer agents. They are generally considered to induce a G(1) cell cycle arrest through down-regulation of D-type cyclins and up-regulation of p27(kip1). Here, we examined the effect of targeting mTOR by rapamycin and/or MEK by PD184352 in human glioblastoma cell lines. In combination, these drugs cooperatively and potently inhibited the G(1)-S transition and retinoblastoma protein phosphorylation. Their cooperation could not be explained by their partial and differential inhibitory effects on cyclin D1 or D3 but instead by their synergistic inhibition of the activating T172 phosphorylation of cyclin-dependent kinase (CDK) 4. This appeared independent of p27 and unrelated to weak modulations of the CDK-activating kinase activity. The T172 phosphorylation of CDK4 thus appears as a crucial node integrating the activity of both MEK/ERK and mTOR pathways. Combined inhibition of both pathways should be considered as a promising strategy for treatment of tumors harboring a deregulated CDK4 activity.

Targeting the ERK signaling pathway in cancer therapy.

The extracellular signal-regulated kinase (ERK) signaling pathway is a major determinant in the control of diverse cellular processes such as proliferation, survival, differentiation and motility. This pathway is often up-regulated in human tumors and as such represents an attractive target for the development of anticancer drugs. Because of its multiple roles in the acquisition of a complex malignant phenotype, specific blockade of the ERK pathway is expected to result in not only an anti-proliferative effect but also in anti-metastatic and anti-angiogenic effects in tumor cells. Recently potent small-molecule inhibitors targeting the components of the ERK pathway have been developed. Among them, BAY 43-9006 (Raf inhibitor), and PD184352, PD0325901 and ARRY-142886 (MEK1/2 inhibitors) have reached the clinical trial stage. We briefly discuss the possibility that combination of ERK pathway inhibitors (cytostatic agents) and conventional anticancer drugs (cytotoxic agents) provides an excellent basis for the development of new chemotherapeutic strategies against cancer.

Atorvastatin induces T cell anergy via phosphorylation of ERK1.

Modulation of T cell response is a novel property of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors. Previously we reported the benefits of atorvastatin treatment in experimental autoimmune encephalomyelitis, the murine model of the T cell-mediated autoimmune disorder multiple sclerosis, in which a blockade of the T cell cycle by atorvastatin was attributed to an accumulation of the negative regulator p27(Kip1). We show in this report that, in line with the documented role of p27(Kip1) in T cell anergy, treatment with atorvastatin results in a deficient response to a second productive stimulus in human T cells. This effect of atorvastatin was dependent on HMG-CoA reduction and required IL-10 signaling. Importantly, atorvastatin induced an early and sustained phosphorylation of ERK1, but not ERK2, which was crucial for the induction of anergy. On the basis of the therapeutic impact of HMG-CoA reductase inhibitors, the present findings should pave the way for future therapeutic concepts related to tolerance induction in neuroinflammatory disorders such as multiple sclerosis.