Characterization of ERK docking domain inhibitors that induce apoptosis by targeting Rsk-1 and caspase-9

Linear motif specificity in signaling through p38α and ERK2 mitogen-activated protein kinases

Mitogen-activated protein kinase (MAPK) cascades are essential for eukaryotic cells to integrate and respond to diverse stimuli. Maintaining specificity in signaling through MAPK networks is key to coupling distinct inputs to appropriate cellular responses. Docking sites-short linear motifs found in MAPK substrates, regulators, and scaffolds-can promote signaling specificity through selective interactions, but how they do so remains unresolved. Here, we screened a proteomic library for sequences interacting with the MAPKs extracellular signal-regulated kinase 2 (ERK2) and p38α, identifying selective and promiscuous docking motifs. Sequences specific for p38α had high net charge and lysine content, and selective binding depended on a pair of acidic residues unique to the p38α docking interface. Finally, we validated a set of full-length proteins harboring docking sites selected in our screens to be authentic MAPK interactors and substrates. This study identifies features that help define MAPK signaling networks and explains how specific docking motifs promote signaling integrity.

Molecular Docking and Simulation-Binding Analysis of Plant Phytochemicals with the Hepatocellular Carcinoma Targets Epidermal Growth Factor Receptor and Caspase-9

Among primary liver cancers, hepatocellular carcinoma (HCC) is one of the most common forms and it has been categorized as the joint-fourth largest reason of cancer-related deaths globally. Different factors such as alcohol abuse, hepatitis B and C, viral infections, and fatty liver diseases are mainly related to the pathogenesis of HCC. In the current study, 1000 total various plant phytochemicals were docked to proteins involved in HCC. The compounds were docked to the active site amino acids of epidermal growth factor receptor and caspase-9 as receptor proteins in order to explore their inhibiting potential. The top five compounds against each receptor protein were explored as potential drug candidates on the basis of their binding affinity and root-mean square deviation values. The top two compounds against each protein were found to be liquoric acid (S-score -9.8 kcal/mol) and madecassic acid (S-score -9.3 kcal/mol) against EGFR, and limonin (S-score -10.5 kcal/mol) and obamegine (S-score -9.3 kcal/mol) against the caspase-9 protein. The selected phytochemicals were further assessed through drug scanning using Lipinski's rule of five to explore their molecular properties and druggability. According to the ADMET analysis, the selected phytochemicals were found to be non-toxic and non-carcinogenic. Finally, the molecular dynamics simulation study revealed that liquoric acid and limonin were stabilized within the binding pockets of EGFR and capase-9, respectively, and stayed firmly bound throughout the simulation. In light of the current findings, the phytochemicals reported in this study, especially liquoric acid and limonin, could be used as potential drugs for the treatment of HCC in the future.

Targeting mitochondrial metabolism for metastatic cancer therapy

Primary tumors evolve metabolic mechanisms favoring glycolysis for adenosine triphosphate (ATP) generation and antioxidant defenses. In contrast, metastatic cells frequently depend on mitochondrial respiration and oxidative phosphorylation (OxPhos). This reliance of metastatic cells on OxPhos can be exploited using drugs that target mitochondrial metabolism. Therefore, therapeutic agents that act via diverse mechanisms, including the activation of signaling pathways that promote the production of reactive oxygen species (ROS) and/or a reduction in antioxidant defenses may elevate oxidative stress and inhibit tumor cell survival. In this review, we will provide (1) a mechanistic analysis of function-selective extracellular signal-regulated kinase-1/2 (ERK1/2) inhibitors that inhibit cancer cells through enhanced ROS, (2) a review of the role of mitochondrial ATP synthase in redox regulation and drug resistance, (3) a rationale for inhibiting ERK signaling and mitochondrial OxPhos toward the therapeutic goal of reducing tumor metastasis and treatment resistance. Recent reports from our laboratories using metastatic melanoma and breast cancer models have shown the preclinical efficacy of novel and rationally designed therapeutic agents that target ERK1/2 signaling and mitochondrial ATP synthase, which modulate ROS events that may prevent or treat metastatic cancer. These findings and those of others suggest that targeting a tumor's metabolic requirements and vulnerabilities may inhibit metastatic pathways and tumor growth. Approaches that exploit the ability of therapeutic agents to alter oxidative balance in tumor cells may be selective for cancer cells and may ultimately have an impact on clinical efficacy and safety. Elucidating the translational potential of metabolic targeting could lead to the discovery of new approaches for treatment of metastatic cancer.

Identification of cell type-specific correlations between ERK activity and cell viability upon treatment with ERK1/2 inhibitors

Increased MAPK signaling is a hallmark of various cancers and is a central regulator of cell survival. Direct ERK1/2 inhibition is considered a promising approach to avoid ERK1/2 reactivation caused by upstream kinases BRAF, MEK1/2, and KRAS, as well as by receptor tyrosine kinase inhibitors, but the dynamics and selectivity of ERK1/2 inhibitors are much less studied compared with BRAF or MEK inhibitors. Using ERK1/2 and downstream kinase ELK1 reporter cell lines of lung cancer (H1299; NRAS^Q61K), colon cancer (HCT-116; KRAS^G13D), neuroblastoma (SH-SY5Y), and leukemia (U937), we examined the relationship between ERK inhibition and drug-induced toxicity for five ERK inhibitors: SCH772984, ravoxertinib, LY3214996, ulixertinib, and VX-11e, as well as one MEK inhibitor, PD0325901. Comparing cell viability and ERK inhibition revealed different ERK dependencies for these cell lines. We identify several drugs, such as SCH772984 and VX-11e, which induce excessive toxicity not directly related to ERK1/2 inhibition in specific cell lines. We also show that PD0325901, LY3214996, and ulixertinib are prone to ERK1/2 reactivation over time. We distinguished two types of ERK1/2 reactivation: the first could be reversed by adding a fresh dose of inhibitors, while the second persists even after additional treatments. We also showed that cells that became resistant to the MEK1/2 inhibitor PD0325901 due to ERK1/2 reactivation remained sensitive to ERK1/2 inhibitor ulixertinib. Our data indicate that correlation of ERK inhibition with drug-induced toxicity in multiple cell lines may help to find more selective and effective ERK1/2 inhibitors.

Development of small molecule extracellular signal-regulated kinases (ERKs) inhibitors for cancer therapy

The mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase 1/2 (ERK1/2) signaling pathway is widely activated by a variety of extracellular stimuli, and its dysregulation is associated with the proliferation, invasion, and migration of cancer cells. ERK1/2 is located at the distal end of this pathway and rarely undergoes mutations, making it an attractive target for anticancer drug development. Currently, an increasing number of ERK1/2 inhibitors have been designed and synthesized for antitumor therapy, among which representative compounds have entered clinical trials. When ERK1/2 signal transduction is eliminated, ERK5 may provide a bypass route to rescue proliferation, and weaken the potency of ERK1/2 inhibitors. Therefore, drug research targeting ERK5 or based on the compensatory mechanism of ERK5 for ERK1/2 opens up a new way for oncotherapy. This review provides an overview of the physiological and biological functions of ERKs, focuses on the structure-activity relationships of small molecule inhibitors targeting ERKs, with a view to providing guidance for future drug design and optimization, and discusses the potential therapeutic strategies to overcome drug resistance.

RAF-Mutant Melanomas Differentially Depend on ERK2 Over ERK1 to Support Aberrant MAPK Pathway Activation and Cell Proliferation

Half of advanced human melanomas are driven by mutant BRAF and dependent on MAPK signaling. Interestingly, the results of three independent genetic screens highlight a dependency of BRAF-mutant melanoma cell lines on BRAF and ERK2, but not ERK1. ERK2 is expressed higher in melanoma compared with other cancer types and higher than ERK1 within melanoma. However, ERK1 and ERK2 are similarly required in primary human melanocytes transformed with mutant BRAF and are expressed at a similar, lower amount compared with established cancer cell lines. ERK1 can compensate for ERK2 loss as seen by expression of ERK1 rescuing the proliferation arrest mediated by ERK2 loss (both by shRNA or inhibition by an ERK inhibitor). ERK2 knockdown, as opposed to ERK1 knockdown, led to more robust suppression of MAPK signaling as seen by RNA-sequencing, qRT-PCR, and Western blot analysis. In addition, treatment with MAPK pathway inhibitors led to gene expression changes that closely resembled those seen upon knockdown of ERK2 but not ERK1. Together, these data demonstrate that ERK2 drives BRAF-mutant melanoma gene expression and proliferation as a function of its higher expression compared with ERK1. Selective inhibition of ERK2 for the treatment of melanomas may spare the toxicity associated with pan-ERK inhibition in normal tissues. IMPLICATIONS: BRAF-mutant melanomas overexpress and depend on ERK2 but not ERK1, suggesting that ERK2-selective inhibition may be toxicity sparing.

Mechanistic Analysis of an Extracellular Signal-Regulated Kinase 2-Interacting Compound that Inhibits Mutant BRAF-Expressing Melanoma Cells by Inducing Oxidative Stress

Constitutively active extracellular signal–regulated kinase (ERK) 1/2 signaling promotes cancer cell proliferation and survival. We previously described a class of compounds containing a 1,1-dioxido-2,5-dihydrothiophen-3-yl 4-benzenesulfonate scaffold that targeted ERK2 substrate docking sites and selectively inhibited ERK1/2-dependent functions, including activator protein-1–mediated transcription and growth of cancer cells containing active ERK1/2 due to mutations in Ras G-proteins or BRAF, Proto-oncogene B-RAF (Rapidly Acclerated Fibrosarcoma) kinase. The current study identified chemical features required for biologic activity and global effects on gene and protein levels in A375 melanoma cells containing mutant BRAF (V600E). Saturation transfer difference-NMR and mass spectrometry analyses revealed interactions between a lead compound (SF-3-030) and ERK2, including the formation of a covalent adduct on cysteine 252 that is located near the docking site for ERK/FXF (DEF) motif for substrate recruitment. Cells treated with SF-3-030 showed rapid changes in immediate early gene levels, including DEF motif–containing ERK1/2 substrates in the Fos family. Analysis of transcriptome and proteome changes showed that the SF-3-030 effects overlapped with ATP-competitive or catalytic site inhibitors of MAPK/ERK Kinase 1/2 (MEK1/2) or ERK1/2. Like other ERK1/2 pathway inhibitors, SF-3-030 induced reactive oxygen species (ROS) and genes associated with oxidative stress, including nuclear factor erythroid 2–related factor 2 (NRF2). Whereas the addition of the ROS inhibitor N-acetyl cysteine reversed SF-3-030–induced ROS and inhibition of A375 cell proliferation, the addition of NRF2 inhibitors has little effect on cell proliferation. These studies provide mechanistic information on a novel chemical scaffold that selectively regulates ERK1/2-targeted transcription factors and inhibits the proliferation of A375 melanoma cells through a ROS-dependent mechanism.

Modulating multi-functional ERK complexes by covalent targeting of a recruitment site in vivo

Recently, the targeting of ERK with ATP-competitive inhibitors has emerged as a potential clinical strategy to overcome acquired resistance to BRAF and MEK inhibitor combination therapies. In this study, we investigate an alternative strategy of targeting the D-recruitment site (DRS) of ERK. The DRS is a conserved region that lies distal to the active site and mediates ERK-protein interactions. We demonstrate that the small molecule BI-78D3 binds to the DRS of ERK2 and forms a covalent adduct with a conserved cysteine residue (C159) within the pocket and disrupts signaling in vivo. BI-78D3 does not covalently modify p38MAPK, JNK or ERK5. BI-78D3 promotes apoptosis in BRAF inhibitor-naive and resistant melanoma cells containing a BRAF V600E mutation. These studies provide the basis for designing modulators of protein-protein interactions involving ERK, with the potential to impact ERK signaling dynamics and to induce cell cycle arrest and apoptosis in ERK-dependent cancers.

Development of ERK1/2 inhibitors as a therapeutic strategy for tumour with MAPK upstream target mutations

Extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylate a variety of substrates that play key roles in promoting cell survival and proliferation. Many inhibitors, acting on upstream of the ERK pathway, exhibit excellent antitumor activity. However, drug-resistant tumour cells invariably emerge after their use due to the reactivation of ERK1/2 signalling. ERK1/2 inhibitors have shown clinical efficacy as a therapeutic strategy for the treatment of tumours with mitogen-activated protein kinase (MAPK) upstream target mutations. These inhibitors may be effective against cancers with altered MAPK upstream pathway and may be used as a possible strategy to overcome acquired resistance to MAPK inhibitors. In this review, we describe the mechanism and types of ERK1/2 inhibitors, summarise the current development status of small-molecule ERK1/2 inhibitors, including the preclinical data and clinical study progress, and discuss the future research directions for the application of ERK1/2 inhibitors.

Adherence to quality breast cancer survivorship care in four Canadian provinces: a CanIMPACT retrospective cohort study

BACKGROUND

In order to maximize later health, there are established components and guidelines for quality follow-up care of breast cancer survivors. However, adherence to quality follow-up in Canada may not be optimal, and may vary by province. We determined and compared the proportion of patients in each province who received adherent and non-adherent surveillance for recurrence, new cancers and late effects, recommended preventive care, and recommended physician visits for comorbidities.

METHODS

Cohorts consisted of all adult women diagnosed with incident invasive breast cancer between 2007 and 2010/2012 in four Canadian provinces (British Columbia (BC) N = 9338; Manitoba N = 2688; Ontario N = 23,700; Nova Scotia (NS) N = 2735), identified from provincial cancer registries, alive and cancer-free at 30 months post-diagnosis. Their healthcare utilization was determined from one to 5 years post-treatment, using linked administrative databases. Adherence, underuse, and overuse of recommended services were evaluated yearly and compared using descriptive statistics.

RESULTS

In all provinces and follow-up years, the majority of survivors had more than the recommended number of visits to either an oncologist or primary care physician (range 53.8% NS Year 3; 85.8% Ontario Year 4). The proportion of patients with the guideline-recommended number of oncologist visits varied by province (range 29.8% BC Year 5; 74.8% Ontario Year 5), and the proportion of patients with less than the recommended number of specified breast cancer-related visits with either an oncologist or primary care physician ranged from 32.6% (Ontario Year 2) to 84.4% (NS Year 3). Underuse of surveillance breast imaging was identified in NS and BC. The proportion of patients receiving imaging for metastatic disease (not recommended in the guidelines) in BC, Manitoba, and Ontario (not reported in NS) ranged from 20.3% (BC Year 5) to 53.3% (Ontario Year 2). Compliance with recommended physician visits for patients with several chronic conditions was high in Ontario and NS. Preventive care was less than optimal in all provinces with available data.

CONCLUSIONS

Quality of breast cancer survivor follow-up care varies among provinces. Results point to exploration of factors affecting differences, province-specific opportunities for care improvement, and the value of administrative datasets for health system assessment.

A Novel Class of Common Docking Domain Inhibitors That Prevent ERK2 Activation and Substrate Phosphorylation

Extracellular signal-regulated kinases (ERK1/2) are mitogen-activated protein kinases (MAPKs) that play a pro-tumorigenic role in numerous cancers. ERK1/2 possess two protein-docking sites that are distinct from the active site: the D-recruitment site (DRS) and the F-recruitment site. These docking sites facilitate substrate recognition, intracellular localization, signaling specificity, and protein complex assembly. Targeting these sites on ERK in a therapeutic context may overcome many problems associated with traditional ATP-competitive inhibitors. Here, we identified a new class of inhibitors that target the ERK DRS by screening a synthetic combinatorial library of more than 30 million compounds. The screen detects the competitive displacement of a fluorescent peptide from the DRS of ERK2. The top molecular scaffold from the screen was optimized for structure-activity relationship by positional scanning of different functional groups. This resulted in 10 compounds with similar binding affinities and a shared core structure consisting of a tertiary amine hub with three functionalized cyclic guanidino branches. Compound 2507-1 inhibited ERK2 from phosphorylating a DRS-targeting substrate and prevented the phosphorylation of ERK2 by a constitutively active MEK1 (MAPK/ERK kinase 1) mutant. Interaction between an analogue, 2507-8, and the ERK2 DRS was confirmed by nuclear magnetic resonance and X-ray crystallography. 2507-8 forms critical interactions at the common docking domain residue Asp319 via an arginine-like moiety that is shared by all 10 hits, suggesting a common binding mode. The structural and biochemical insights reported here provide the basis for developing new ERK inhibitors that are not ATP-competitive but instead function by disrupting critical protein-protein interactions.

Targeting ERK beyond the boundaries of the kinase active site in melanoma

Extracellular signal-regulated kinase 1/2 (ERK1/2) constitute a point of convergence for complex signaling events that regulate essential cellular processes, including proliferation and survival. As such, dysregulation of the ERK signaling pathway is prevalent in many cancers. In the case of BRAF-V600E mutant melanoma, ERK inhibition has emerged as a viable clinical approach to abrogate signaling through the ERK pathway, even in cases where MEK and Raf inhibitor treatments fail to induce tumor regression due to resistance mechanisms. Several ERK inhibitors that target the active site of ERK have reached clinical trials, however, many critical ERK interactions occur at other potentially druggable sites on the protein. Here we discuss the role of ERK signaling in cell fate, in driving melanoma, and in resistance mechanisms to current BRAF-V600E melanoma treatments. We explore targeting ERK via a distinct site of protein-protein interaction, known as the D-recruitment site (DRS), as an alternative or supplementary mode of ERK pathway inhibition in BRAF-V600E melanoma. Targeting the DRS with inhibitors in melanoma has the potential to not only disrupt the catalytic apparatus of ERK but also its noncatalytic functions, which have significant impacts on spatiotemporal signaling dynamics and cell fate.

Novel small molecule decreases cell proliferation, migration, clone formation, and gene expression through ERK inhibition in MCF-7 and MDA-MB-231 breast cancer cell lines

The Ras-Raf-MEK1/2-ERK1/2 pathway is an attractive target for the development of anticancer agents because of the high prevalence of ERK activation in human cancers. However, resistance is often developed despite initial clinical response, most likely because of activation of cross-talk pathways. In Research Genetic Cancer Center (RGCC), we are in the process of synthesizing a novel ERK inhibitor, targeting the final stage of the pathway, thus minimizing cross-talk. We have synthesized an intermediate molecule -RGCC416 - and tested its biological activity. MCF-7 and MDA-MB-231 cells were used. Cell viability was measured by crystal violet and cell proliferation by the methyl tetrazolium assay using various compound concentrations. Cell migration and colony formation were determined to assess the ability of invasion and single cancer cell growth, respectively. Expression of genes linked to MAPK/PI3K pathways was determined by PCR. ERK and phospho-ERK levels were determined in both the cytoplasm and the nucleus by western blot. It was found that although the compound did not affect viability, it significantly decreased cell proliferation, migration, and colony formation in both cell lines. In MDA-MB-231, this is possibly through retaining phospho-ERK to the cytoplasm, where it cannot activate cancer-associated genes. There was no difference in ERK levels in MCF-7 cells. This could be because of the different pathways that these cells utilize for survival. We have synthesized a molecule, which could be a promising ERK inhibitor, leading to possible novel treatment options for breast cancer patients.

Protein-Protein Interactions: Emerging Oncotargets in the RAS-ERK Pathway

Given the implication of aberrant RAS-extracellular signal-regulated kinase (ERK) signaling in the development of a large number of tumor types, this route is under intense scrutiny to identify new anticancer drugs. Most avenues in that direction have been primarily focused on the inhibition of the catalytic activity of the kinases that participate in this pathway. Although promising, the efficacy of these therapies is short lived due to undesired toxicity and/or drug resistance problems. As an alternative path, new efforts are now being devoted to the targeting of protein-protein interactions (PPIs) involved in the flow of RAS-ERK signals. Many of these efforts have shown promising results in preclinical models. In this review, we summarize recent progress made in this area.

Neuroprotective effects of genistein on SH-SY5Y cells overexpressing A53T mutant α-synuclein

Genistein, a potent antioxidant compound, protects dopaminergic neurons in a mouse model of Parkinson's disease. However, the mechanism underlying this action remains unknown. This study investigated human SH-SY5Y cells overexpressing the A53T mutant of α-synuclein. Four groups of cells were assayed: a control group (without any treatment), a genistein group (incubated with 20 μM genistein), a rotenone group (treated with 50 μM rotenone), and a rotenone + genistein group (incubated with 20 μM genistein and then treated with 50 μM rotenone). A lactate dehydrogenase release test confirmed the protective effect of genistein, and genistein remarkably reversed mitochondrial oxidative injury caused by rotenone. Western blot assays showed that BCL-2 and Beclin 1 levels were markedly higher in the genistein group than in the rotenone group. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling revealed that genistein inhibited rotenone-induced apoptosis in SH-SY5Y cells. Compared with the control group, the expression of NFE2L2 and HMOX1 was significantly increased in the genistein + rotenone group. However, after treatment with estrogen receptor and NFE2L2 channel blockers (ICI-182780 and ML385, respectively), genistein could not elevate NFE2L2 and HMOX1 expression. ICI-182780 effectively prevented genistein-mediated phosphorylation of NFE2L2 and remarkably suppressed phosphorylation of AKT, a protein downstream of the estrogen receptor. These findings confirm that genistein has neuroprotective effects in a cell model of Parkinson's disease. Genistein can reduce oxidative stress damage and cell apoptosis by activating estrogen receptors and NFE2L2 channels.

Sulforaphane-induced apoptosis involves the type 1 IP3 receptor

In this study we show that anti-tumor effect of sulforaphane (SFN) is partially realized through the type 1 inositol 1,4,5-trisphosphate receptor (IP₃R1). This effect was verified in vitro on three different stable cell lines and also in vivo on the model of nude mice with developed tumors. Early response (6 hours) of A2780 ovarian carcinoma cells to SFN treatment involves generation of mitochondrial ROS and increased transcription of NRF2 and its downstream regulated genes including heme oxygenase 1, NAD(P)H:quinine oxidoreductase 1, and KLF9. Prolonged SFN treatment (24 hours) upregulated expression of NRF2 and IP₃R1. SFN induces a time-dependent phosphorylation wave of HSP27. Use of IP₃R inhibitor Xestospongin C (Xest) attenuates both SFN-induced apoptosis and the level of NRF2 protein expression. In addition, Xest partially attenuates anti-tumor effect of SFN in vivo. SFN-induced apoptosis is completely inhibited by silencing of IP₃R1 gene but only partially blocked by silencing of NRF2; silencing of IP₃R2 and IP₃R3 had no effect on these cells. Xest inhibitor does not significantly modify SFN-induced increase in the rapid activity of ARE and AP1 responsive elements. We found that Xest effectively reverses the SFN-dependent increase of nuclear content and decrease of reticular calcium content. In addition, immunofluorescent staining with IP₃R1 antibody revealed that SFN treatment induces translocation of IP₃R1 to the nucleus. Our results clearly show that IP₃R1 is involved in SFN-induced apoptosis through the depletion of reticular calcium and modulation of transcription factors through nuclear calcium up-regulation.

A high throughput assay to identify substrate-selective inhibitors of the ERK protein kinases

Extracellular signal-regulated kinases 1 and 2 (ERK1/2) phosphorylate a variety of substrates important for survival and proliferation, and their activity is frequently deregulated in tumors. ERK pathway inhibitors have shown clinical efficacy as anti-cancer drugs, but most patients eventually relapse due to reactivation of the pathway. One factor limiting the efficacy of current therapeutics is the difficulty in reaching clinically effective inhibition of the ERK pathway in the absence of on-target toxicities. Here, we describe an assay suitable for high throughput screening to discover substrate selective ERK1/2 inhibitors, which may have a larger therapeutic window than conventional inhibitors. Specifically, we aim to target a substrate-binding pocket within the ERK1/2 catalytic domain outside of the catalytic cleft. The assay uses an AlphaScreen format to detect phosphorylation of a high-efficiency substrate harboring an essential docking site motif. Pilot screening established that the assay is suitably robust for high-throughput screening. Importantly, the assay can be conducted at high ATP concentrations, which we show reduces the discovery of conventional ATP-competitive inhibitors. These studies provide the basis for high-throughput screens to discover new classes of non-conventional ERK1/2 inhibitors.

The D Domain of LRRC4 anchors ERK1/2 in the cytoplasm and competitively inhibits MEK/ERK activation in glioma cells

Background

As a well-characterized key player in various signal transduction networks, extracellular-signal-regulated kinase (ERK1/2) has been widely implicated in the development of many malignancies. We previously found that Leucine-rich repeat containing 4 (LRRC4) was a tumor suppressor and a negative regulator of the ERK/MAPK pathway in glioma tumorigenesis. However, the precise molecular role of LRRC4 in ERK signal transmission is unclear.

Methods

The interaction between LRRC4 and ERK1/2 was assessed by co-immunoprecipitation and GST pull-down assays in vivo and in vitro. We also investigated the interaction of LRRC4 and ERK1/2 and the role of the D domain in ERK activation in glioma cells.

Results

Here, we showed that LRRC4 and ERK1/2 interact via the D domain and CD domain, respectively. Following EGF stimuli, the D domain of LRRC4 anchors ERK1/2 in the cytoplasm and abrogates ERK1/2 activation and nuclear translocation. In glioblastoma cells, ectopic LRRC4 expression competitively inhibited the interaction of endogenous mitogen-activated protein kinase (MEK) and ERK1/2. Mutation of the D domain decreased the LRRC4-mediated inhibition of MAPK signaling and its anti-proliferation and anti-invasion roles.

Conclusions

Our results demonstrated that the D domain of LRRC4 anchors ERK1/2 in the cytoplasm and competitively inhibits MEK/ERK activation in glioma cells. These findings identify a new mechanism underlying glioblastoma progression and suggest a novel therapeutic strategy by restoring the activity of LRRC4 to decrease MAPK cascade activation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-016-0355-1) contains supplementary material, which is available to authorized users.

Computational design, chemical synthesis, and biological evaluation of a novel ERK inhibitor (BL-EI001) with apoptosis-inducing mechanisms in breast cancer

Extracellular signal-regulated kinase1/2 (ERK1/2) plays a crucial role in the resistance of apoptosis in carcinogenesis; however, its targeted small-molecule inhibitors still remain to be discovered. Thus, in this study, we computationally and experimentally screened a series of small-molecule inhibitors targeting ERK toward different types of human breast cancer cells. Subsequently, we synthesized some candidate ERK inhibitors, identified a novel ERK inhibitor (BL-EI001) with anti-proliferative activities, and analyzed the BL-EI001/ERK complex. Moreover, we found that BL-EI001 induced breast cancer cell apoptosis via mitochondrial pathway but independent on Ras/Raf/MEK pathway. In addition, we carried out proteomics analyses for exploring some possible BL-EI001-induced apoptotic pathways, and further found that BL-EI001-induced apoptosis affected ERK phosphorylation in breast cancer. Further, we found that BL-EI001 bear anti-tumor activities without remarkable toxicities, and also induced mitochondrial apoptosis by targeting ERK in vivo. Taken together, these results demonstrate that in silico design and experimental discovery of a synthesized small-molecule ERK inhibitor (BL-EI001) as a potential novel apoptosis-inducing drug in the treatment of breast cancer.

Small-molecule inhibitors of ERK-mediated immediate early gene expression and proliferation of melanoma cells expressing mutated BRaf

Constitutive activation of the extracellular-signal-regulated kinases 1 and 2 (ERK1/2) are central to regulating the proliferation and survival of many cancer cells. The current inhibitors of ERK1/2 target ATP binding or the catalytic site and are therefore limited in their utility for elucidating the complex biological roles of ERK1/2 through its phosphorylation and regulation of over 100 substrate proteins. To overcome this limitation, a combination of computational and experimental methods was used to identify low-molecular-mass inhibitors that are intended to target ERK1/2 substrate-docking domains and selectively interfere with ERK1/2 regulation of substrate proteins. In the present study, we report the identification and characterization of compounds with a thienyl benzenesulfonate scaffold that were designed to inhibit ERK1/2 substrates containing an F-site or DEF (docking site for ERK, FXF) motif. Experimental evidence shows the compounds inhibit the expression of F-site containing immediate early genes (IEGs) of the Fos family, including c-Fos and Fra1, and transcriptional regulation of the activator protein-1 (AP-1) complex. Moreover, this class of compounds selectively induces apoptosis in melanoma cells containing mutated BRaf and constitutively active ERK1/2 signalling, including melanoma cells that are inherently resistant to clinically relevant kinase inhibitors. These findings represent the identification and initial characterization of a novel class of compounds that inhibit ERK1/2 signalling functions and their potential utility for elucidating ERK1/2 and other signalling events that control the growth and survival of cancer cells containing elevated ERK1/2 activity.

Structural modifications of (Z)-3-(2-aminoethyl)-5-(4-ethoxybenzylidene)thiazolidine-2,4-dione that improve selectivity for inhibiting the proliferation of melanoma cells containing active ERK signaling

We herein report on the pharmacophore determination of the ERK docking domain inhibitor (Z)-3-(2-aminoethyl)-5-(4-ethoxybenzylidene)thiazolidine-2,4-dione, which has led to the discovery of compounds with greater selectivities for inhibiting the proliferation of melanoma cells containing active ERK signaling.

Cooperativity of CD44 and CD49d in leukemia cell homing, migration, and survival offers a means for therapeutic attack

A CD44 blockade drives leukemic cells into differentiation and apoptosis by dislodging from the osteogenic niche. Because anti-CD49d also supports hematopoietic stem cell mobilization, we sought to determine the therapeutic efficacy of a joint CD49d/CD44 blockade. To unravel the underlying mechanism, the CD49d(-) EL4 lymphoma was transfected with CD49d or point-mutated CD49d, prohibiting phosphorylation and FAK binding; additionally, a CD44(-) Jurkat subline was transfected with murine CD44, CD44 with a point mutation in the ezrin binding site, or with cytoplasmic tail-truncated CD44. Parental and transfected EL4 and Jurkat cells were evaluated for adhesion, migration, and apoptosis susceptibility in vitro and in vivo. Ligand-binding and Ab-blocking studies revealed CD44-CD49d cooperation in vitro and in vivo in adhesion, migration, and apoptosis resistance. The cooperation depends on ligand-induced proximity such that both CD44 and CD49d get access to src, FAK, and paxillin and via lck to the MAPK pathway, with the latter also supporting antiapoptotic molecule liberation. Accordingly, synergisms were only seen in leukemia cells expressing wild-type CD44 and CD49d. Anti-CD44 together with anti-CD49d efficiently dislodged EL4-CD49d/Jurkat-CD44 in bone marrow and spleen. Dislodging was accompanied by increased apoptosis susceptibility that strengthened low-dose chemotherapy, the combined treatment most strongly interfering with metastatic settlement and being partly curative. Ab treatment also promoted NK and Ab-dependent cellular cytotoxicity activation, which affected leukemia cells independent of CD44/CD49d tail mutations. Thus, mostly owing to a blockade of joint signaling, anti-CD44 and anti-CD49d hamper leukemic cell settlement and break apoptosis resistance, which strongly supports low-dose chemotherapy.

P90RSK and Nrf2 Activation via MEK1/2-ERK1/2 Pathways Mediated by Notoginsenoside R2 to Prevent 6-Hydroxydopamine-Induced Apoptotic Death in SH-SY5Y Cells

6-Hydroxydopamine (6-OHDA) is known to contribute to neuronal death in Parkinson's disease. In this study, we found that the preincubation of SH-SY5Y cells for 24 h with 20  μ M notoginsenoside R2 (NGR2), which is a newly isolated notoginsenoside from Panax notoginseng, showed neuroprotective effects against 6-OHDA-induced oxidative stress and apoptosis. NGR2 incubation successively resulted in the activation of P90RSK, inactivation of BAD, and inhibition of 6-OHDA-induced mitochondrial membrane depolarization, thus preventing the mitochondrial apoptosis pathway. NGR2 incubation also led to the activation of Nrf2 and subsequent activity enhancement of phase II detoxifying enzymes, thus suppressing 6-OHDA-induced oxidative stress, and these effects could be removed by Nrf2 siRNA. We also found that the upstream activators of P90RSK and Nrf2 were the MEK1/2-ERK1/2 pathways but not the JNK, P38, or PI3K/Akt pathways. Interestingly, NGR2 incubation could also activate MEK1/2 and ERK1/2. Most importantly, NGR2-mediated P90RSK and Nrf2 activation, respective downstream target activation, and neuroprotection were reversed by the genetic silencing of MEK1/2 and ERK1/2 by using siRNA and PD98059 application. These results suggested that the neuroprotection elicited by NGR2 against 6-OHDA-induced neurotoxicity was associated with NGR2-mediated P90RSK and Nrf2 activation through MEK1/2-ERK1/2 pathways.

MicroRNA-193b enhances tumor progression via down regulation of neurofibromin 1

Despite improvements in therapeutic approaches for head and neck squamous cell carcinomas (HNSCC), clinical outcome has remained disappointing, with 5-year overall survival rates hovering around 40-50%, underscoring an urgent need to better understand the biological bases of this disease. We chose to address this challenge by studying the role of micro-RNAs (miRNAs) in HNSCC. MiR-193b was identified as an over-expressed miRNA from global miRNA profiling studies previously conducted in our lab, and confirmed in HNSCC cell lines. In vitro knockdown of miR-193b in FaDu cancer cells substantially reduced cell proliferation, migration and invasion, along with suppressed tumour formation in vivo. By integrating in silico prediction algorithms with in vitro experimental mRNA profilings, plus mRNA expression data of clinical specimens, neurofibromin 1 (NF1) was identified to be a target of miR-193b. Concordantly, miR-193b knockdown decreased NF1 transcript and protein levels significantly. Luciferase reporter assays confirmed the direct interaction of miR-193b with NF1. Moreover, p-ERK, a downstream target of NF1 was also suppressed after miR-193b knockdown. FaDu cells treated with a p-ERK inhibitor (U0126) phenocopied the reduced cell proliferation, migration and invasion observed with miR-193b knockdown. Finally, HNSCC patients whose tumours expressed high levels of miR-193b experienced a lower disease-free survival compared to patients with low miR-193b expression. Our findings identified miR-193b as a potentially novel prognostic marker in HNSCC that drives tumour progression via down-regulating NF1, in turn leading to activation of ERK, resulting in proliferation, migration, invasion, and tumour formation.

Approaches to Ras signaling modulation and treatment of Ras-dependent disorders: a patent review (2007--present)

INTRODUCTION

Ras proteins are small GTPases molecular switches that cycle through two alternative conformational states, a GDP-bound inactive state and a GTP-bound active state. In the active state, Ras proteins interact with and modulate the activity of several downstream effectors regulating key cellular processes including proliferation, differentiation, survival, senescence, migration and metabolism. Activating mutations of RAS genes and of genes encoding Ras signaling members have a great incidence in proliferative disorders, such as cancer, immune and inflammatory diseases and developmental syndromes. Therefore, Ras and Ras signaling represent important clinical targets for the design and development of pharmaceutically active agents, including anticancer agents.

AREAS COVERED

The authors summarize methods available to down-regulate the Ras pathway and review recent patents covering Ras signaling modulators, as well as methods designed to kill specifically cancer cells bearing activated RAS oncogene.

EXPERT OPINION

Targeted therapy approach based on direct targeting of molecules specifically altered in Ras-dependent diseases is pursued with molecules that down-regulate expression or inhibit the biological function of mutant Ras or Ras signaling members. The low success rate in a clinical setting of molecules targeting activated members of the Ras pathway may require development of novel approaches, including combined and synthetic lethal therapies.

A critical role for protein tyrosine phosphatase nonreceptor type 5 in determining individual susceptibility to develop stress-related cognitive and morphological changes

While stressful life events confer increased risk for the development of psychopathology, most individuals experiencing adversity maintain normal psychological functioning, suggesting that individual differences may influence the susceptibility to develop stress-related psychiatric disorders. However, little is known about what determines this difference between individuals at the molecular level. In the present study, we identify that protein tyrosine phosphatase nonreceptor type 5 (PTPN5) (also known as STEP) is a critical determinant of differences in individual susceptibility to develop stress-related cognitive and morphological changes in rats. Our data demonstrate that ablation of PTPN5 expression delays physiological recovery from stress and augments the development of stress-related cognitive and morphological changes, whereas overexpression of a constitutively active variant of PTPN5 enhances the individual's resilience to stress. Our data also reveal that reduced PTPN5 expression prolongs the duration of extracellular signal-regulated kinase activation, leading to an elevation of Ca(V)1.2 channel expression and a recovery delay of K(V)4.2 channels from inactivation, which in turn heightens neuronal vulnerability to glutamate toxicity. Moreover, intraperitoneal injections of L-type Ca(2+) channel blocker nifedipine after stress resulted in a significantly lower rate for developing stress-related cognitive and morphological changes seen in PTPN5 knockdown rats. Together, these results identify a novel role for PTPN5 in mediating the development of stress-related cognitive and morphological changes and suggest that people with PTPN5 deficiency may have a greater susceptibility to capture the deleterious effects of stress.

Computational insights for the discovery of non-ATP competitive inhibitors of MAP kinases

Due to their role in cellular signaling mitogen activated protein (MAP) kinases represent targets of pharmaceutical interest. However, the majority of known MAP kinase inhibitors compete with cellular ATP and target an ATP binding pocket that is highly conserved in the 500 plus representatives of the human protein kinase family. Here we review progress toward the development of non-ATP competitive MAP kinase inhibitors for the extracellular signal regulated kinases (ERK1/2), the c-jun N-terminal kinases (JNK1/2/3) and the p38 MAPKs (α, β, γ, and δ). Special emphasis is placed on the role of computational methods in the drug discovery process for MAP kinases. Topics include recent advances in X-ray crystallography theory that improve the MAP kinase structures essential to structurebased drug discovery, the use of molecular dynamics to understand the conformational heterogeneity of the activation loop and inhibitors discovered by virtual screening. The impact of an advanced polarizable force field such as AMOEBA used in conjunction with sophisticated kinetic and thermodynamic simulation methods is also discussed.

ERK1/2 MAP kinases: structure, function, and regulation

ERK1 and ERK2 are related protein-serine/threonine kinases that participate in the Ras-Raf-MEK-ERK signal transduction cascade. This cascade participates in the regulation of a large variety of processes including cell adhesion, cell cycle progression, cell migration, cell survival, differentiation, metabolism, proliferation, and transcription. MEK1/2 catalyze the phosphorylation of human ERK1/2 at Tyr204/187 and then Thr202/185. The phosphorylation of both tyrosine and threonine is required for enzyme activation. Whereas the Raf kinase and MEK families have narrow substrate specificity, ERK1/2 catalyze the phosphorylation of hundreds of cytoplasmic and nuclear substrates including regulatory molecules and transcription factors. ERK1/2 are proline-directed kinases that preferentially catalyze the phosphorylation of substrates containing a Pro-Xxx-Ser/Thr-Pro sequence. Besides this primary structure requirement, many ERK1/2 substrates possess a D-docking site, an F-docking site, or both. A variety of scaffold proteins including KSR1/2, IQGAP1, MP1, β-Arrestin1/2 participate in the regulation of the ERK1/2 MAP kinase cascade. The regulatory dephosphorylation of ERK1/2 is mediated by protein-tyrosine specific phosphatases, protein-serine/threonine phosphatases, and dual specificity phosphatases. The combination of kinases and phosphatases make the overall process reversible. The ERK1/2 catalyzed phosphorylation of nuclear transcription factors including those of Ets, Elk, and c-Fos represents an important function and requires the translocation of ERK1/2 into the nucleus by active and passive processes involving the nuclear pore. These transcription factors participate in the immediate early gene response. The activity of the Ras-Raf-MEK-ERK cascade is increased in about one-third of all human cancers, and inhibition of components of this cascade by targeted inhibitors represents an important anti-tumor strategy. Thus far, however, only inhibition of mutant B-Raf (Val600Glu) has been found to be therapeutically efficacious.