MAP-ERK Kinase Inhibitors Research Articles

Activation of neurons and satellite glial cells in the DRG produces morphine-induced hyperalgesia.

Activation of neurons and glial cells in the dorsal root ganglion is one of the key mechanisms for the development of hyperalgesia. The aim of the present study was to examine the role of neuroglial activity in the development of opioid-induced hyperalgesia. Male rats were treated with morphine daily for 3days. The resultant phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 in the dorsal root ganglion was analyzed by immunohistochemistry and Western blotting. Pain hypersensitivity was analyzed using behavioral studies. The amount of cytokine expression in the dorsal root ganglion was also analyzed. Repeated morphine treatment induced hyperalgesia and marked induction of phosphorylated ERK1/2 in the neurons and satellite glial cells on day 3. An opioid receptor antagonist, toll like receptor-4 inhibitor, MAP/ERK kinase (MEK) inhibitor and gap junction inhibitor inhibited morphine-induced hyperalgesia and ERK1/2 phosphorylation. Morphine treatment induced alteration of cytokine expression, which was inhibited by the opioid receptor antagonist, toll like receptor-4 inhibitor, MEK inhibitor and gap junction inhibitor. Dexamethasone inhibited morphine-induced hyperalgesia and ERK1/2 phosphorylation after morphine treatment. The peripherally restricted opioid receptor antagonist, methylnaltrexone, inhibited hyperalgesia and ERK1/2 phosphorylation. Morphine activates ERK1/2 in neurons and satellite glial cells in the dorsal root ganglion via the opioid receptor and toll like receptor-4. ERK1/2 phosphorylation is gap junction-dependent and is associated with the alteration of cytokine expression. Inhibition of neuroinflammation by activation of neurons and glia might be a promising target to prevent opioid-induced hyperalgesia.

BRAF Mutant Melanoma Adjusts to BRAF/MEK Inhibitors via Dependence on Increased Antioxidant SOD2 and Increased Reactive Oxygen Species Levels.

B-Rapidly Accelerated Fibrosarcoma (BRAF) mutations are found in about 50% of melanoma patients. Treatment with Food and Drug Administration (FDA)-approved BRAF and MAP/ERK kinase (MEK) inhibitors has improved progression free and overall survival of patients with BRAF mutant melanoma. However, all responders develop resistance typically within 1 year of treatment with these inhibitors. Evidence indicates that reactive oxygen species (ROS) levels are elevated after BRAF pathway inhibition treatment. We aim to decipher the role of mitochondrial antioxidant proteins relative to ROS levels and BRAF pathway inhibitor resistance. We observed BRAF mutant melanoma cells treated with the combination of a MEK inhibitor (trametinib) and a BRAF inhibitor (dabrafenib), exhibited elevated ROS levels, both in in vitro and in vivo melanoma models. We next generated trametinib- and dabrafenib-resistant (TDR) cells and found increased ROS levels after acquisition of resistance. An immunofluorescence experiment showed an increase of DNA damage in TDR cell lines. Furthermore, we observed that TDR cells increased superoxide dismutase 2 (SOD2), an antioxidant, at both mRNA and protein levels, with the upregulation of the transcription factor Nuclear Factor (NF)-κB. Knockdown of SOD2 significantly reduced the growth of BRAF pathway inhibitor-resistant cells. In addition, the results indicate that TDR cells can be re-sensitized to BRAF pathway inhibitors by the ROS scavenger, N-Acetyl Cysteine (NAC). Overall, these data indicate that BRAF pathway inhibitor-resistant cells can compensate for elevated ROS via increased expression of the antioxidant SOD2.

Analysis of NRAS gain in 657 patients with melanoma and evaluation of its sensitivity to a MEK inhibitor

BackgroundNeuroblastoma rat-sarcoma (NRAS) mutations have been described in Chinese patients with melanoma. However, the status and the clinical significance of NRAS gain have not been investigated on a large scale. MethodsA total of 657 melanoma samples were included in the study. NRAS copy number was examined using the QuantiGene Plex DNA assay. The sensitivities of cell lines and patient-derived xenograft (PDX) models containing NRAS gain to a MAP/ERK kinase (MEK) inhibitor (binimetinib) were also evaluated. ResultsThe overall incidence of NRAS gain was 14.0% (92 of 657). Incidence of NRAS gain in acral, mucosal, chronic sun-induced damage (CSD) and non-CSD melanomas was 12.2%, 15.8%, 9.5% and 19.4%, respectively. NRAS gain was mutually exclusive to NRAS mutations (P = 0.036). The median survival time for melanoma patients with NRAS gain was significantly shorter than that for patients with normal NRAS copy number (P = 0.006). For patients containing NRAS gain, the median survival time for higher copy number (>4 copies) was significantly shorter than those with lower copy number (2–4 copies; P = 0.002). The MEK inhibitor (binimetinib) inhibited the proliferation of melanoma cells and the tumour growth of PDX models with NRAS gain. ConclusionsNRAS gain is frequent in patients with melanoma and may predict a poor prognosis of melanoma. The melanoma cells and PDX models containing NRAS gain are sensitive to MEK inhibitor (binimetinib), indicating that NRAS gain might be a new therapeutic target for melanoma.

Reduced NF1 expression confers resistance to EGFR inhibition in lung cancer.

Activating mutations in the EGF receptor (EGFR) are associated with clinical responsiveness to EGFR tyrosine kinase inhibitors (TKI), such as erlotinib and gefitinib. However, resistance eventually arises, often due to a second EGFR mutation, most commonly T790M. Through a genome-wide siRNA screen in a human lung cancer cell line and analyses of murine mutant EGFR-driven lung adenocarcinomas, we found that erlotinib resistance was associated with reduced expression of neurofibromin, the RAS GTPase-activating protein encoded by the NF1 gene. Erlotinib failed to fully inhibit RAS-ERK signaling when neurofibromin levels were reduced. Treatment of neurofibromin-deficient lung cancers with a MAP-ERK kinase (MEK) inhibitor restored sensitivity to erlotinib. Low levels of NF1 expression were associated with primary and acquired resistance of lung adenocarcinomas to EGFR TKIs in patients. These findings identify a subgroup of patients with EGFR-mutant lung adenocarcinoma who might benefit from combination therapy with EGFR and MEK inhibitors.

Modeling RAS phenotype in colorectal cancer uncovers novel molecular traits of RAS dependency and improves prediction of response to targeted agents in patients.

KRAS wild-type status is an imperfect predictor of sensitivity to anti-EGF receptor (EGFR) monoclonal antibodies in colorectal cancer, motivating efforts to identify novel molecular aberrations driving RAS. This study aimed to build a quantitative readout of RAS pathway activity to (i) uncover molecular surrogates of RAS activity specific to colorectal cancer, (ii) improve the prediction of cetuximab response in patients, and (iii) suggest new treatment strategies. A model of RAS pathway activity was trained in a large colorectal cancer dataset and validated in three independent colorectal cancer patient datasets. Novel molecular traits were inferred from The Cancer Genome Atlas colorectal cancer data. The ability of the RAS model to predict resistance to cetuximab was tested in mouse xenografts and three independent patient cohorts. Drug sensitivity correlations between our model and large cell line compendiums were performed. The performance of the RAS model was remarkably robust across three validation datasets. (i) Our model confirmed the heterogeneity of the RAS phenotype in KRAS wild-type patients, and suggests novel molecular traits driving its phenotype (e.g., MED12 loss, FBXW7 mutation, MAP2K4 mutation). (ii) It improved the prediction of response and progression-free survival (HR, 2.0; P < 0.01) to cetuximab compared with KRAS mutation (xenograft and patient cohorts). (iii) Our model consistently predicted sensitivity to MAP-ERK kinase (MEK) inhibitors (P < 0.01) in two cell panel screens. Modeling the RAS phenotype in colorectal cancer allows for the robust interrogation of RAS pathway activity across cell lines, xenografts, and patient cohorts. It demonstrates clinical utility in predicting response to anti-EGFR agents and MEK inhibitors.

Dual Blockade of the PI3K/AKT/mTOR (AZD8055) and RAS/MEK/ERK (AZD6244) Pathways Synergistically Inhibits Rhabdomyosarcoma Cell Growth In Vitro and In Vivo

To provide rationale for using phosphoinositide 3-kinase (PI3K) and/or mitogen-activated protein kinase (MAPK) pathway inhibitors to treat rhabdomyosarcomas, a major cause of pediatric and adolescent cancer deaths. The prevalence of PI3K/MAPK pathway activation in rhabdomyosarcoma clinical samples was assessed using immunohistochemistry. Compensatory signaling and cross-talk between PI3K/MAPK pathways was determined in rhabdomyosarcoma cell lines following p110α short hairpin RNA-mediated depletion. Pharmacologic inhibition of reprogrammed signaling in stable p110α knockdown lines was used to determine the target-inhibition profile inducing maximal growth inhibition. The in vitro and in vivo efficacy of inhibitors of TORC1/2 (AZD8055), MEK (AZD6244), and P13K/mTOR (NVP-BEZ235) was evaluated alone and in pairwise combinations. PI3K pathway activation was seen in 82.5% rhabdomyosarcomas with coactivated MAPK in 36% and 46% of alveolar and embryonal subtypes, respectively. p110α knockdown in cell lines over the short and long term was associated with compensatory expression of other p110 isoforms, activation of the MAPK pathway, and cross-talk to reactivate the PI3K pathway. Combinations of PI3K pathway and MAP-ERK kinase (MEK) inhibitors synergistically inhibited cell growth in vitro. Treatment of RD cells with AZD8055 plus AZD6244 blocked reciprocal pathway activation, as evidenced by reduced AKT/ERK/S6 phosphorylation. In vivo, the synergistic effect on growth and changes in pharmacodynamic biomarkers was recapitulated using the AZD8055/AZD6244 combination but not NVP-BEZ235/AZD6244. Pharmacokinetic analysis provided evidence of drug-drug interaction with both combinations. Dual PI3K/MAPK pathway activation and compensatory signaling in both rhabdomyosarcoma subtypes predict a lack of clinical efficacy for single agents targeting either pathway, supporting a therapeutic strategy combining a TORC1/2 with a MEK inhibitor.

Activation of MAPK Pathways due to DUSP4 Loss Promotes Cancer Stem Cell-like Phenotypes in Basal-like Breast Cancer

Basal-like breast cancer (BLBC) is an aggressive disease that lacks a clinically approved targeted therapy. Traditional chemotherapy is effective in BLBC, but it spares the cancer stem cell (CSC)-like population, which is likely to contribute to cancer recurrence after the initial treatment. Dual specificity phosphatase-4 (DUSP4) is a negative regulator of the mitogen-activated protein kinase (MAPK) pathway that is deficient in highly aggressive BLBCs treated with chemotherapy, leading to aberrant MAPK activation and resistance to taxane-induced apoptosis. Herein, we investigated how DUSP4 regulates the MAP-ERK kinase (MEK) and c-jun-NH2-kinase (JNK) pathways in modifying CSC-like behavior. DUSP4 loss increased mammosphere formation and the expression of the CSC-promoting cytokines interleukin (IL)-6 and IL-8. These effects were caused in part by loss of control of the MEK and JNK pathways and involved downstream activation of the ETS-1 and c-JUN transcription factors. Enforced expression of DUSP4 reduced the CD44(+)/CD24(-) population in multiple BLBC cell lines in a MEK-dependent manner, limiting tumor formation of claudin-low SUM159PT cells in mice. Our findings support the evaluation of MEK and JNK pathway inhibitors as therapeutic agents in BLBC to eliminate the CSC population.

Subtype-Specific MEK-PI3 Kinase Feedback as a Therapeutic Target in Pancreatic Adenocarcinoma

Mutations in the KRAS oncogene are dominant features in pancreatic ductal adenocarcinoma (PDA). Because KRAS itself is considered "undruggable," targeting pathways downstream of KRAS are being explored as a rational therapeutic strategy. We investigated the consequences of MAP-ERK kinase (MEK) inhibition in a large PDA cell line panel. Inhibition of MEK activated phosphoinositide 3-kinase in an EGF receptor (EGFR)-dependent fashion and combinations of MEK and EGFR inhibitors synergistically induced apoptosis. This combinatorial effect was observed in the epithelial but not mesenchymal subtype of PDA. RNA expression analysis revealed predictors of susceptibility to the combination, including E-cadherin, HER3, and the miR200-family of microRNAs, whereas expression of the transcription factor ZEB1 was associated with resistance to the drug combination. Knockdown of HER3 in epithelial-type and ZEB1 in mesenchymal-type PDA cell lines resulted in sensitization to the combination of MEK and EGFR inhibitors. Thus, our findings suggest a new, subtype-specific, and personalized therapeutic strategy for pancreatic cancer.

Discovery of a Novel ERK Inhibitor with Activity in Models of Acquired Resistance to BRAF and MEK Inhibitors

The high frequency of activating RAS or BRAF mutations in cancer provides strong rationale for targeting the mitogen-activated protein kinase (MAPK) pathway. Selective BRAF and MAP-ERK kinase (MEK) inhibitors have shown clinical efficacy in patients with melanoma. However, the majority of responses are transient, and resistance is often associated with pathway reactivation of the extracellular signal-regulated kinase (ERK) signaling pathway. Here, we describe the identification and characterization of SCH772984, a novel and selective inhibitor of ERK1/2 that displays behaviors of both type I and type II kinase inhibitors. SCH772984 has nanomolar cellular potency in tumor cells with mutations in BRAF, NRAS, or KRAS and induces tumor regressions in xenograft models at tolerated doses. Importantly, SCH772984 effectively inhibited MAPK signaling and cell proliferation in BRAF or MEK inhibitor-resistant models as well as in tumor cells resistant to concurrent treatment with BRAF and MEK inhibitors. These data support the clinical development of ERK inhibitors for tumors refractory to MAPK inhibitors.

Antiproliferative Effects of Continued Mitogen-Activated Protein Kinase Pathway Inhibition following Acquired Resistance to BRAF and/or MEK Inhibition in Melanoma

Inhibitors of the mitogen-activated protein kinases (MAPK), BRAF, and MAP-ERK kinase (MEK) induce tumor regression in the majority of patients with BRAF-mutant metastatic melanoma. The clinical benefit of MAPK inhibitors is restricted by the development of acquired resistance with half of those who benefit having progressed by 6 to 7 months and long-term responders uncommon. There remains no agreed treatment strategy on disease progression in these patients. Without published evidence, fears of accelerated disease progression on inhibitor withdrawal have led to the continuation of drugs beyond formal disease progression. We now show that treatment with MAPK inhibitors beyond disease progression can provide significant clinical benefit, and the withdrawal of these inhibitors led to a marked increase in the rate of disease progression in two patients. We also show that MAPK inhibitors retain partial activity in acquired resistant melanoma by examining drug-resistant clones generated to dabrafenib, trametinib, or the combination of these drugs. All resistant sublines displayed a markedly slower rate of proliferation when exposed to MAPK inhibitors, and this coincided with a reduction in MAPK signaling, decrease in bromodeoxyuridine incorporation, and S-phase inhibition. This cytostatic effect was also associated with diminished levels of cyclin D1 and p-pRb. Two short-term melanoma cultures generated from resistant tumor biopsies also responded to MAPK inhibition, with comparable inhibitory changes in proliferation and MAPK signaling. These data provide a rationale for the continuation of BRAF and MEK inhibitors after disease progression and support the development of clinical trials to examine this strategy.

Coordinate direct input of both KRAS and IGF1 receptor to activation of PI3 kinase in KRAS-mutant lung cancer.

Using a panel of non-small cell lung cancer (NSCLC) lines, we show here that MAP-ERK kinase (MEK) and RAF inhibitors are selectively toxic for the KRAS-mutant genotype, whereas phosphoinositide 3-kinase (PI3K), AKT, and mTOR inhibitors are not. IGF1 receptor (IGF1R) tyrosine kinase inhibitors also show selectivity for KRAS-mutant lung cancer lines. Combinations of IGF1R and MEK inhibitors resulted in strengthened inhibition of KRAS-mutant lines and also showed improved effectiveness in autochthonous mouse models of Kras-induced NSCLC. PI3K pathway activity is dependent on basal IGF1R activity in KRAS-mutant, but not wild-type, lung cancer cell lines. KRAS is needed for both MEK and PI3K pathway activity in KRAS-mutant, but not wild-type, lung cancer cells, whereas acute activation of KRAS causes stimulation of PI3K dependent upon IGF1R kinase activity. Coordinate direct input of both KRAS and IGF1R is thus required to activate PI3K in KRAS-mutant lung cancer cells. It has not yet been possible to target RAS proteins directly, so combined targeting of effect or pathways acting downstream of RAS, including RAF/MEK and PI3K/AKT, has been the most favored approach to the treatment of RAS -mutant cancers. This work sheds light on the ability of RASto activate PI3K through direct interaction, indicating that input is also required from a receptor tyrosinekinase, IGF1R in the case of KRAS -mutant lung cancer. This suggests potential novel combination therapeutic strategies for NSCLC.

Relief of Feedback Inhibition of HER3 Transcription by RAF and MEK Inhibitors Attenuates Their Antitumor Effects in BRAF-Mutant Thyroid Carcinomas

The RAF inhibitor vemurafenib (PLX4032) increases survival in patients with BRAF-mutant metastatic melanoma, but has limited efficacy in patients with colorectal cancers. Thyroid cancer cells are also comparatively refractory to RAF inhibitors. In contrast to melanomas, inhibition of mitogen-activated protein kinase (MAPK) signaling by PLX4032 is transient in thyroid and colorectal cancer cells. The rebound in extracellular signal-regulated kinase (ERK) in thyroid cells is accompanied by increased HER3 signaling caused by induction of ERBB3 (HER3) transcription through decreased promoter occupancy by the transcriptional repressors C-terminal binding protein 1 and 2 and by autocrine secretion of neuregulin-1 (NRG1). The HER kinase inhibitor lapatinib prevents MAPK rebound and sensitizes BRAF-mutant thyroid cancer cells to RAF or MAP-ERK kinase inhibitors. This provides a rationale for combining ERK pathway antagonists with inhibitors of feedback-reactivated HER signaling in this disease. The determinants of primary resistance to MAPK inhibitors vary between cancer types, due to preferential upregulation of specific receptor tyrosine kinases, and the abundance of their respective ligands.

Intermittent Administration of MEK Inhibitor GDC-0973 plus PI3K Inhibitor GDC-0941 Triggers Robust Apoptosis and Tumor Growth Inhibition

Combinations of MAP/ERK kinase (MEK) and phosphoinositide 3-kinase (PI3K) inhibitors have shown promise in preclinical cancer models, leading to the initiation of clinical trials cotargeting these two key cancer signaling pathways. GDC-0973, a novel selective MEK inhibitor, and GDC-0941, a class I PI3K inhibitor, are in early stage clinical trials as both single agents and in combination. The discovery of these selective inhibitors has allowed investigation into the precise effects of combining inhibitors of two major signaling branches downstream of RAS. Here, we investigated multiple biomarkers in the mitogen-activated protein kinase (MAPK) and PI3K pathway to search for points of convergence that explain the increased apoptosis seen in combination. Using washout studies in vitro and alternate dosing schedules in mice, we showed that intermittent inhibition of the PI3K and MAPK pathway is sufficient for efficacy in BRAF and KRAS mutant cancer cells. The combination of GDC-0973 with the PI3K inhibitor GDC-0941 resulted in combination efficacy in vitro and in vivo via induction of biomarkers associated with apoptosis, including Bcl-2 family proapoptotic regulators. Therefore, these data suggest that continuous exposure of MEK and PI3K inhibitors in combination is not required for efficacy in preclinical cancer models and that sustained effects on downstream apoptosis biomarkers can be observed in response to intermittent dosing.

Prevention of Bronchial Hyperplasia by EGFR Pathway Inhibitors in an Organotypic Culture Model

Lung cancer is the leading cause of cancer-related mortality worldwide. Early detection or prevention strategies are urgently needed to increase survival. Hyperplasia is the first morphologic change that occurs in the bronchial epithelium during lung cancer development, followed by squamous metaplasia, dysplasia, carcinoma in situ, and invasive tumor. This study was designed to determine the molecular mechanisms that control bronchial epithelium hyperplasia. Using primary normal human tracheobronchial epithelial (NHTBE) cells cultured by using the 3-dimensional (3D) organotypic method, we found that the epidermal growth factor receptor (EGFR) ligands, EGF, TGF-α, and amphiregulin induced hyperplasia, as determined by cell proliferation and multilayered epithelium formation. We also found that EGF induced increased cyclin D1 expression, which plays a critical role in bronchial hyperplasia; this overexpression was mediated by activating the mitogen-activated protein kinase pathway but not the phosphoinositide 3-kinase/Akt signaling pathway. Erlotinib, an EGFR tyrosine kinase inhibitor, and U0126, a MAP/ERK kinase (MEK) inhibitor, completely inhibited EGF-induced hyperplasia. Furthermore, a promoter analysis revealed that the activator protein-1 transcription factor regulates EGF-induced cyclin D1 overexpression. Activator protein-1 depletion by using siRNA targeting its c-Jun component completely abrogated EGF-induced cyclin D1 expression. In conclusion, we showed that bronchial hyperplasia can be modeled in vitro by using primary NHTBE cells maintained in a 3D organotypic culture. EGFR and MEK inhibitors completely blocked EGF-induced bronchial hyperplasia, suggesting that they have a chemopreventive role.

STAT3 Mediates Resistance to MEK Inhibitor through MicroRNA miR-17

AZD6244 is a small molecule inhibitor of the MEK (MAP/ERK kinase) pathway currently in clinical trials. However, the mechanisms mediating intrinsic resistance to MEK inhibition are not fully characterized. To define molecular mechanisms of MEK inhibitor resistance, we analyzed responses of 38 lung cancer cell lines following AZD6244 treatment and their genome-wide gene expression profiles and identified a panel of genes correlated with sensitivity or resistance to AZD6244 treatment. In particular, ingenuity pathway analysis revealed that activation of the STAT3 pathway was associated with MEK inhibitor resistance. Inhibition of this pathway by JSI-124, a STAT3-specific small molecule inhibitor, or with STAT3-specific siRNA sensitized lung cancer cells to AZD6244 and induced apoptosis. Moreover, combining a STAT3 inhibitor with AZD6244 induced expression of BIM and PARP cleavage, whereas activation of the STAT3 pathway inhibited BIM expression and elicited resistance to MEK inhibitors. We found that the STAT3-regulated microRNA miR-17 played a critical role in MEK inhibitor resistance, such that miR-17 inhibition sensitized resistant cells to AZD6244 by inducing BIM and PARP cleavage. Together, these results indicated that STAT3-mediated overexpression of miR-17 blocked BIM expression and caused resistance to AZD6244. Our findings suggest novel approaches to overcome resistance to MEK inhibitors by combining AZD6244 with STAT3 or miR-17 inhibitors.

MEK-Independent Survival of B-RAFV600E Melanoma Cells Selected for Resistance to Apoptosis Induced by the RAF Inhibitor PLX4720

To examine mechanisms that determine long-term responses of B-RAF(V600E) melanoma cells to B-RAF inhibitors. B-RAF(V600E) melanoma cells were exposed to the B-RAF inhibitor PLX4720 for prolonged periods to select for cells resistant to apoptosis induced by the inhibitor. The resultant cells were analyzed for activation of extracellular signal regulated kinase (ERK), MAP/ERK kinase (MEK), and Akt, and related signals. Their roles in survival of the cells were also examined. B-RAF(V600E) melanoma cells selected for resistant to PLX4720-induced apoptosis retained the V600E mutation in B-RAF, and proliferated steadily in the presence of the inhibitor, albeit with slow growth rate. These cells displayed high levels of ERK activation, that is, at least in part, independent of the conventional RAF/MEK/ERK pathway, as MEK activation was low and inhibition of MEK did not significantly block activation of ERK. In contrast, extracellular signals appeared involved. This was associated with elevated activation of the phosphoinositide 3-kinase (PI3k)/Akt pathway and could be inhibited by serum starvation and inhibition of PI3k/Akt. Inhibition of MEK did not impact on survival of these cells, whereas serum starvation, inhibition of PI3K/Akt, and inhibition of ERK1/2 reduced their viability. These results indicate that sensitivity to induction of apoptosis may be a major determinant of long-term responses of B-RAF(V600E) melanomas to specific inhibitors and suggest that rebound melanoma growth after initial treatment with the inhibitors may not be responsive to MEK inhibitors, but may be susceptible to inhibition of the PI3k/Akt pathway.

Vertical Targeting of the Phosphatidylinositol-3 Kinase Pathway as a Strategy for Treating Melanoma

Melanoma is relatively resistant to chemotherapy; improved targeting of molecules critical for cell proliferation and survival are needed. Phosphatidylinositol-3 kinase (PI3K) is an important target in melanoma; however, activity of PI3K inhibitors (PI3KI) is limited. Our purpose was to assess mTOR as a cotarget for PI3K. Using a method of quantitative immunofluorescence to measure mTOR expression in a large melanoma cohort, we studied associations with PI3K subunits, p85 and p110α. We assessed addition of the mTOR inhibitor rapamycin to 2 PI3KIs, NVP-BKM120 and LY294002. We studied in vitro activity of a novel dual PI3K/mTOR inhibitor NVP-BEZ235 and activity of the combination of NVP-BEZ235 and the MAP/ERK kinase (MEK) inhibitor AZD6244. Strong coexpression of mTOR and p110α was observed (ρ = 0.658; P < 0.0001). Less coexpression was seen with p85 (ρ = 0.239; P < 0.0001). Strong synergism was shown between rapamycin and both PI3KIs. Activity of both PI3KIs was similarly enhanced with all rapamycin concentrations used. The dual PI3K/mTOR inhibitor effectively inhibited viability in 23 melanoma cell lines (IC(50) values in the nanomolar range), regardless of B-Raf mutation status, with resultant reduction in clonogenicity and downregulation of pAkt and pP70S6K. Synergism was seen when combining NVP-BEZ235 and AZD6244, with resultant increases in poly(ADP-ribose) polymerase and caspase-2 cleavage. mTOR and p110α are coexpressed in melanoma. Rapamycin concentrations as low as 1 nmol/L enhance activity of PI3KIs. The dual PI3K/mTOR inhibitor NVP-BEZ235 is highly active in melanoma cells in vitro, suggesting that concurrent PI3K and mTOR targeting in melanoma warrants further investigation, both alone and in combination with MEK inhibitors.

Combination of EGFR and MEK1/2 inhibitor shows synergistic effects by suppressing EGFR/HER3-dependent AKT activation in human gastric cancer cells

EGFR tyrosine kinase inhibitors have shown promising efficacy in the treatment of tumors with EGFR mutations and amplifications. However, tyrosine kinase inhibitors have also proven ineffective against most tumors with EGFR wild-type (WT) alleles. Although some genetic changes, including the KRAS mutation, have been shown to confer resistance to tyrosine kinase inhibitors, novel strategies for the treatment of cancer patients with tumors harboring EGFR WT alleles have yet to be thoroughly delineated. The principal objective of this study was to improve our current understanding of drug interactions between EGFR and MAP/ERK kinase (MEK) inhibitors in an effort to gain insight into a novel therapeutic strategy against EGFR WT tumors. Using a panel of human EGFR WT gastric cancer cell lines, we showed that gastric cancer cells harboring the KRAS mutation were selectively sensitive to MEK inhibition as compared with those cells harboring KRAS and PI3K mutations and KRAS WT alleles. However, all cell lines were found to be resistant to EGFR inhibition. The results from Western blots and phosphoprotein arrays showed that, in MEK inhibitor resistant cell lines, AKT was activated through the EGFR/HER3/PI3K pathway following AZD6244 (ARRY-142886) treatment. Blockade of this feedback mechanism through the targeting of MEK and EGFR resulted in detectable synergistic effects in some cell lines in vitro and in vivo. Our results provide the basis for a rational combination strategy against human EGFR WT gastric cancers, predicated on the understanding of cross-talk between the MEK and EGFR pathways.

Inhibition of PI3K and MEK: It Is All about Combinations and Biomarkers

A small molecule inhibitor of MAP/ERK kinase (MEK) was effective against human breast cancer cells with a basal-like gene expression signature. Antitumor activity was limited by both feedback upregulation of phosphatidylinositol-3 kinase (PI3K)/AKT upon inhibition of MEK as well as loss of the phosphatase PTEN. Therefore, MEK inhibitors should preferably be investigated in combination with PI3K inhibitors in basal-like breast cancers.

2-Alkylamino- and alkoxy-substituted 2-amino-1,3,4-oxadiazoles—O-Alkyl benzohydroxamate esters replacements retain the desired inhibition and selectivity against MEK (MAP ERK kinase)

This paper reports a second generation MEK inhibitor. The previously reported potent and efficacious MEK inhibitor, PD-184352 (CI-1040), contains an integral hydroxamate moiety. This compound suffered from less than ideal solubility and metabolic stability. An oxadiazole moiety behaves as a bioisostere for the hydroxamate group, leading to a more metabolically stable and efficacious MEK inhibitor.