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The presence of tumor-infiltrating lymphocytes in triple-negative breast cancers is correlated with improved outcomes. Ras/MAPK pathway activation is associated with significantly lower levels of tumor-infiltrating lymphocytes in triple-negative breast cancers and while MEK inhibition can promote recruitment of tumor-infiltrating lymphocytes to the tumor, here we show that MEK inhibition adversely affects early onset T-cell effector function. We show that α-4-1BB and α-OX-40 T-cell agonist antibodies can rescue the adverse effects of MEK inhibition on T cells in both mouse and human T cells, which results in augmented anti-tumor effects in vivo. This effect is dependent upon increased downstream p38/JNK pathway activation. Taken together, our data suggest that although Ras/MAPK pathway inhibition can increase tumor immunogenicity, the negative impact on T-cell activity is functionally important. This undesirable impact is effectively prevented by combination with T-cell immune agonist immunotherapies resulting in superior therapeutic efficacy.MEK inhibition in breast cancer is associated with increased tumour infiltrating lymphocytes (TILs), however, MAPK activity is required for T cells function. Here the authors show that TILs activity following MEK inhibition can be enhanced by agonist immunotherapy resulting in synergic therapeutic effects.
BACKGROUND - We conducted a prospective trial of BRAF and mitogen-activated protein kinase kinase (MEK) targeted therapy in advanced, operable BRAF mutation-positive melanoma to determine feasibility, tumor response rates, and biomarkers of response and resistance.
STUDY DESIGN - Thirteen patients with locally or regionally advanced BRAF mutation-positive melanoma received dabrafenib 150 mg po bid for 14 days, followed by dabrafenib plus trametinib 2 mg po daily for 14 days before operation. Biopsies and tumor measurements were obtained at baseline and days 14 and 28. Formalin-fixed paraffin embedded specimens were analyzed with hematoxylin and eosin, Ki-67, cleaved caspase-3, CD8, phosphorylated extracellular signal-regulated kinase (ERK), and phosphorylated MEK immunostains.
RESULTS - Therapy was tolerated well, with toxicity ≥ grade 3 in 2 of 13 (15%) patients. All 12 patients receiving >14 days of therapy had substantial reduction in tumor volume (65% at day 14 and 78% at day 28) and underwent resection. After 14 days of dabrafenib therapy, there was a marked reduction in viable melanoma cells and a CD8 T-cell--rich infiltrate. Proliferation of the residual melanoma cells was reduced and apoptosis was increased. The cells continued to express phosphorylated ERK and phosphorylated MEK consistent with incomplete mitogen-activated protein kinase pathway inhibition.
CONCLUSIONS - Preoperative targeted therapy of advanced BRAF-mutant melanoma is feasible, well tolerated, induces brisk tumor responses, and facilitates correlative science. A CD8 T-cell-rich infiltrate indicates a potential immune-mediated mechanism of action. Both proliferation and apoptosis were inhibited, but the mitogen-activated protein kinase pathway remained activated, suggesting intrinsic resistance in a subset of tumor cells. Additional investigation of the anti-tumor immune response during targeted therapy and the mechanisms of intrinsic resistance can yield novel therapeutic strategies.
Copyright © 2015. Published by Elsevier Inc.
PURPOSE - Genetic alterations affecting the MAPK/ERK pathway are common in lung adenocarcinoma (LAD). Early steps of the signaling pathway are most often affected with EGFR, KRAS, and BRAF mutations encompassing more than 70% of all alterations. Somatic mutations in MEK1, located downstream of BRAF, are rare and remain poorly defined as a distinct molecular subset.
EXPERIMENTAL DESIGN - Tumors harboring MEK1 mutations were identified through targeted screening of a large LAD cohort concurrently interrogated for recurrent mutations in MEK1, EGFR, KRAS, BRAF, ERBB2/HER2, NRAS, PIK3CA, and AKT. Additional cases were identified through a search of publically available cancer genomic datasets. Mutations were correlated with patient characteristics and treatment outcomes. Overall survival was compared with stage-matched patients with KRAS- and EGFR-mutant LADs.
RESULTS - We identified 36 MEK1-mutated cases among 6,024 LAD (0.6%; 95% confidence interval, 0.42-0.85). The majority of patients were smokers (97%, n = 35/36). There was no association with age, sex, race, or stage. The most common mutations were K57N (64%, 23/36) followed by Q56P (19%, 7/36), all mutually exclusive with other driver mutations in the targeted panel. Transversions G:C>T:A were predominant (89%, 31/35), in keeping with smoking-associated DNA damage. Additional less common somatic mutations were identified in the kinase domain, all of which are predicted to converge into a single interaction area based on in silico 3D modeling.
CONCLUSIONS - MEK1 mutations define a distinct subset of lung cancers (∼1%) with potential sensitivity to MEK inhibitors. Mutations are predominantly transversions, in keeping with a strong association with smoking.
©2014 American Association for Cancer Research.
Oxidized phospholipids (oxPLs) generated nonenzymatically display pleiotropic biological actions in inflammation. Their generation by cellular cyclooxygenases (COXs) is currently unknown. To determine whether platelets generate prostaglandin (PG)-containing oxPLs, then characterize their structures and mechanisms of formation, we applied precursor scanning-tandem mass spectrometry to lipid extracts of agonist-activated human platelets. Thrombin, collagen, or ionophore activation stimulated generation of families of PGs comprising PGE₂ and D₂ attached to four phosphatidylethanolamine (PE) phospholipids (16:0p/, 18:1p/, 18:0p/, and 18:0a/). They formed within 2 to 5 min of activation in a calcium, phospholipase C, p38 MAP kinases, MEK1, cPLA₂, and src tyrosine kinase-dependent manner (28.1 ± 2.3 pg/2 × 10⁸ platelets). Unlike free PGs, they remained cell associated, suggesting an autocrine mode of action. Their generation was inhibited by in vivo aspirin supplementation (75 mg/day) or in vitro COX-1 blockade. Inhibitors of fatty acyl reesterification blocked generation significantly, while purified COX-1 was unable to directly oxidize PE in vitro. This indicates that they form in platelets via rapid esterification of COX-1 derived PGE₂/D₂ into PE. In summary, COX-1 in human platelets acutely mediates membrane phospholipid oxidation via formation of PG-esterified PLs in response to pathophysiological agonists.
PURPOSE To assess pharmacodynamic effects and intrinsic and acquired resistance mechanisms of the BRAF inhibitor vemurafenib in BRAF(V600)-mutant melanoma, leading to an understanding of the mechanism of action of vemurafenib and ultimately to optimization of metastatic melanoma therapy. METHODS In the phase II clinical study NP22657 (BRIM-2), patients received oral doses of vemurafenib (960 mg twice per day). Serial biopsies were collected to study changes in mitogen-activated protein kinase (MAPK) signaling, cell-cycle progression, and factors causing intrinsic or acquired resistance by immunohistochemistry, DNA sequencing, or somatic mutation profiling. Results Vemurafenib inhibited MAPK signaling and cell-cycle progression. An association between the decrease in extracellular signal-related kinase (ERK) phosphorylation and objective response was observed in paired biopsies (n = 22; P = .013). Low expression of phosphatase and tensin homolog showed a modest association with lower response. Baseline mutations in MEK1(P124) coexisting with BRAF(V600) were noted in seven of 92 samples; their presence did not preclude objective tumor responses. Acquired resistance to vemurafenib associated with reactivation of MAPK signaling as observed by elevated ERK1/2 phosphorylation levels in progressive lesions and the appearance of secondary NRAS(Q61) mutations or MEK1(Q56P) or MEK1(E203K) mutations. These two activating MEK1 mutations had not previously been observed in vivo in biopsies of progressive melanoma tumors. CONCLUSION Vemurafenib inhibits tumor proliferation and oncogenic BRAF signaling through the MAPK pathway. Acquired resistance results primarily from MAPK reactivation driven by the appearance of secondary mutations in NRAS and MEK1 in subsets of patients. The data suggest that inhibition downstream of BRAF should help to overcome acquired resistance.
PURPOSE - BRAF mutations promote melanoma cell proliferation and survival primarily through activation of MEK. The purpose of this study was to determine the response rate (RR) for the selective, allosteric MEK1/MEK2 inhibitor trametinib (GSK1120212), in patients with metastatic BRAF-mutant melanoma.
PATIENTS AND METHODS - This was an open-label, two-stage, phase II study with two cohorts. Patients with metastatic BRAF-mutant melanoma previously treated with a BRAF inhibitor (cohort A) or treated with chemotherapy and/or immunotherapy (BRAF-inhibitor naive; cohort B) were enrolled. Patients received 2 mg of trametinib orally once daily.
RESULTS - In cohort A (n = 40), there were no confirmed objective responses and 11 patients (28%) with stable disease (SD); the median progression-free survival (PFS) was 1.8 months. In cohort B (n = 57), there was one (2%) complete response, 13 (23%) partial responses (PRs), and 29 patients (51%) with SD (confirmed RR, 25%); the median PFS was 4.0 months. One patient each with BRAF K601E and BRAF V600R had prolonged PR. The most frequent treatment-related adverse events for all patients were skin-related toxicity, nausea, peripheral edema, diarrhea, pruritis, and fatigue. No cutaneous squamous cell carcinoma was observed.
CONCLUSION - Trametinib was well tolerated. Significant clinical activity was observed in BRAF-inhibitor-naive patients previously treated with chemotherapy and/or immunotherapy. Minimal clinical activity was observed as sequential therapy in patients previously treated with a BRAF inhibitor. Together, these data suggest that BRAF-inhibitor resistance mechanisms likely confer resistance to MEK-inhibitor monotherapy. These data support further evaluation of trametinib in BRAF-inhibitor-naive BRAF-mutant melanoma, including rarer forms of BRAF-mutant melanoma.
OBJECTIVE - Dystrophic calcific nodule formation in vitro involves differentiation of aortic valve interstitial cells (AVICs) into a myofibroblast phenotype. Interestingly, inhibition of the kinase MAPK Erk kinase (MEK)1/2 prevents calcific nodule formation despite leading to myofibroblast activation of AVICs, indicating the presence of an additional mechanotransductive component required for calcific nodule morphogenesis. In this study, we assess the role of transforming growth factor β1-induced cadherin-11 expression in calcific nodule formation.
METHODS AND RESULTS - As shown previously, porcine AVICs treated with transforming growth factor β1 before cyclic strain exhibit increased myofibroblast activation and significant calcific nodule formation. In addition to an increase in contractile myofibroblast markers, transforming growth factor β1-treated AVICs exhibit significantly increased expression of cadherin-11. This expression is inhibited by the addition of U0126, a specific MEK1/2 inhibitor. The role of increased cadherin-11 is revealed through a wound assay, which demonstrates increased intercellular tension in transforming growth factor β1-treated AVICs possessing cadherin-11. Furthermore, when small interfering RNA is used to knockdown cadherin-11, calcific nodule formation is abrogated, indicating that robust cell-cell connections are necessary in generating tension for calcific nodule morphogenesis. Finally, we demonstrate enrichment of cadherin-11 in human calcified leaflets.
CONCLUSIONS - These results indicate the necessity of cadherin-11 for dystrophic calcific nodule formation, which proceeds through an Erk1/2-dependent pathway.
Acquired resistance to EGF receptor (EGFR) tyrosine kinase inhibitors (TKIs) is inevitable in metastatic EGFR-mutant lung cancers. Here, we modeled disease progression using EGFR-mutant human tumor cell lines. Although five of six models displayed alterations already found in humans, one harbored an unexpected secondary NRAS Q61K mutation; resistant cells were sensitive to concurrent EGFR and MEK inhibition but to neither alone. Prompted by this finding and because RAS/RAF/MEK mutations are known mediators of acquired resistance in other solid tumors (colon cancers, gastrointestinal stromal tumors, and melanomas) responsive to targeted therapies, we analyzed the frequency of secondary KRAS/NRAS/BRAF/MEK1 gene mutations in the largest collection to date of lung cancers with acquired resistance to EGFR TKIs. No recurrent NRAS, KRAS, or MEK1 mutations were found in 212, 195, or 146 patient samples, respectively, but 2 of 195 (1%) were found to have mutations in BRAF (G469A and V600E). Ectopic expression of mutant NRAS or BRAF in drug-sensitive EGFR-mutant cells conferred resistance to EGFR TKIs that was overcome by addition of a MEK inhibitor. Collectively, these positive and negative results provide deeper insight into mechanisms of acquired resistance to EGFR TKIs in lung cancer and inform ongoing clinical trials designed to overcome resistance. In the context of emerging knowledge about mechanisms of acquired resistance to targeted therapies in various cancers, our data highlight the notion that, even though solid tumors share common signaling cascades, mediators of acquired resistance must be elucidated for each disease separately in the context of treatment.
UNLABELLED - BRAF inhibitors (BRAFi) induce antitumor responses in nearly 60% of patients with advanced V600E/KBRAF melanomas. Somatic activating MEK1 mutations are thought to be rare in melanomas, but their potential concurrence with V600E/KBRAF may be selected for by BRAFi. We sequenced MEK1/2 exon 3 in melanomas at baseline and upon disease progression. Of 31 baseline V600E/KBRAF melanomas, 5 (16%) carried concurrent somatic BRAF/MEK1 activating mutations. Three of 5 patients with BRAF/MEK1 double-mutant baseline melanomas showed objective tumor responses, consistent with the overall 60% frequency. No MEK1 mutation was found in disease progression melanomas, except when it was already identified at baseline. MEK1-mutant expression in V600E/KBRAF melanoma cell lines resulted in no significant alterations in p-ERK1/2 levels or growth-inhibitory sensitivities to BRAFi, MEK1/2 inhibitor (MEKi), or their combination. Thus, activating MEK1 exon 3 mutations identified herein and concurrent with V600E/KBRAF do not cause BRAFi resistance in melanoma.
SIGNIFICANCE - As BRAF inhibitors gain widespread use for treatment of advanced melanoma, biomarkers for drug sensitivity or resistance are urgently needed. We identify here concurrent activating mutations in BRAF and MEK1 in melanomas and show that the presence of a downstream mutation in MEK1 does not necessarily make BRAF–mutant melanomas resistant to BRAF inhibitors.
© 2012 AACR.
The development of acquired drug resistance hampers the long-term success of B-RAF inhibitor therapy for melanoma patients. Here we show (V600E)B-RAF copy-number gain as a mechanism of acquired B-RAF inhibitor resistance in 4 out of 20 (20%) patients treated with B-RAF inhibitor. In cell lines, (V600E)B-RAF overexpression and knockdown conferred B-RAF inhibitor resistance and sensitivity, respectively. In (V600E)B-RAF amplification-driven (versus mutant N-RAS-driven) B-RAF inhibitor resistance, extracellular signal-regulated kinase reactivation is saturable, with higher doses of vemurafenib down-regulating phosho-extracellular signal-regulated kinase and re-sensitizing melanoma cells to B-RAF inhibitor. These two mechanisms of extracellular signal-regulated kinase reactivation are sensitive to the MEK1/2 inhibitor AZD6244/selumetinib or its combination with the B-RAF inhibitor vemurafenib. In contrast to mutant N-RAS-mediated (V600E)B-RAF bypass, which is sensitive to C-RAF knockdown, (V600E)B-RAF amplification-mediated resistance functions largely independently of C-RAF. Thus, alternative clinical strategies may potentially overcome distinct modes of extracellular signal-regulated kinase reactivation underlying acquired B-RAF inhibitor resistance in melanoma.