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OBJECTIVE - Gastric cancer is the third leading cause of cancer death worldwide and infection by is the strongest risk factor. We have reported increased epidermal growth factor receptor (EGFR) phosphorylation in the -induced human carcinogenesis cascade, and association with DNA damage. Our goal was to determine the role of EGFR activation in gastric carcinogenesis.
DESIGN - We evaluated gefitinib, a specific EGFR inhibitor, in chemoprevention of -induced gastric inflammation and cancer development. Mice with genetically targeted epithelial cell-specific deletion of ( mice) were also used.
RESULTS - In C57BL/6 mice, gefitinib decreased and expression by gastric epithelial cells, myeloperoxidase-positive inflammatory cells in the mucosa and epithelial DNA damage induced by infection. Similar reductions in chemokines, inflammatory cells and DNA damage occurred in infected versus control mice. In -infected transgenic insulin-gastrin (INS-GAS) mice and gerbils, gefitinib treatment markedly reduced dysplasia and carcinoma. Gefitinib blocked ri-induced activation of mitogen-activated protein kinase 1/3 (MAPK1/3) and activator protein 1 in gastric epithelial cells, resulting in inhibition of chemokine synthesis. MAPK1/3 phosphorylation and JUN activation was reduced in gastric tissues from infected wild-type and INS-GAS mice treated with gefitinib and in primary epithelial cells from versus mice. Epithelial EGFR activation persisted in humans and mice after eradication, and gefitinib reduced gastric carcinoma in INS-GAS mice treated with antibiotics.
CONCLUSIONS - These findings suggest that epithelial EGFR inhibition represents a potential strategy to prevent development of gastric carcinoma in -infected individuals.
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PURPOSE - Aberrant activation of EGFR is a hallmark of glioblastoma. However, EGFR inhibitors exhibit at best modest efficacy in glioblastoma. This is in sharp contrast with the observations in EGFR-mutant lung cancer. We examined whether activation of functionally redundant receptor tyrosine kinases (RTKs) conferred resistance to EGFR inhibitors in glioblastoma.
EXPERIMENTAL DESIGN - We collected a panel of patient-derived glioblastoma xenograft (PDX) lines that maintained expression of wild-type or mutant EGFR in serial xenotransplantation and tissue cultures. Using this physiologically relevant platform, we tested the abilities of several RTK ligands to protect glioblastoma cells against an EGFR inhibitor, gefitinib. Based on the screening results, we further developed a combination therapy cotargeting EGFR and insulin receptor (InsR)/insulin-like growth factor 1 receptor (IGF1R).
RESULTS - Insulin and IGF1 induced significant protection against gefitinib in the majority of EGFR-dependent PDX lines with one exception that did not express InsR or IGF1R. Blockade of the InsR/IGF1R pathway synergistically improved sensitivity to gefitinib or dacomitinib. Gefitinib alone effectively attenuated EGFR activities and the downstream MEK/ERK pathway. However, repression of AKT and induction of apoptosis required concurrent inhibition of both EGFR and InsR/IGF1R. A combination of gefitinib and OSI-906, a dual InsR/IGF1R inhibitor, was more effective than either agent alone to treat subcutaneous glioblastoma xenograft tumors.
CONCLUSIONS - Our results suggest that activation of the InsR/IGF1R pathway confers resistance to EGFR inhibitors in EGFR-dependent glioblastoma through AKT regulation. Concurrent blockade of these two pathways holds promise to treat EGFR-dependent glioblastoma.
©2015 American Association for Cancer Research.
PURPOSE - All patients with EGF receptor (EGFR)-mutant lung cancers eventually develop acquired resistance to EGFR tyrosine kinase inhibitors (TKI). Smaller series have identified various mechanisms of resistance, but systematic evaluation of a large number of patients to definitively establish the frequency of various mechanisms has not been conducted.
EXPERIMENTAL DESIGN - Patients with lung adenocarcinomas and acquired resistance to erlotinib or gefitinib enrolled onto a prospective biopsy protocol and underwent a rebiopsy after the development of acquired resistance. Histology was reviewed. Samples underwent genotyping for mutations in EGFR, AKT1, BRAF, ERBB2, KRAS, MEK1, NRAS and PIK3CA, and FISH for MET and HER2.
RESULTS - Adequate tumor samples for molecular analysis were obtained in 155 patients. Ninety-eight had second-site EGFR T790M mutations [63%; 95% confidence interval (CI), 55%-70%] and four had small cell transformation (3%, 95% CI, 0%-6%). MET amplification was seen in 4 of 75 (5%; 95% CI, 1%-13%). HER2 amplification was seen in 3 of 24 (13%; 95% CI, 3%-32%). We did not detect any acquired mutations in PIK3CA, AKT1, BRAF, ERBB2, KRAS, MEK1, or NRAS (0 of 88, 0%; 95% CI, 0%-4%). Overlap among mechanisms of acquired resistance was seen in 4%.
CONCLUSIONS - This is the largest series reporting mechanisms of acquired resistance to EGFR-TKI therapy. We identified EGFR T790M as the most common mechanism of acquired resistance, whereas MET amplification, HER2 amplification, and small cell histologic transformation occur less frequently. More comprehensive methods to characterize molecular alterations in this setting are needed to improve our understanding of acquired resistance to EGFR-TKIs.
Oncogenic alterations in MET or anaplastic lymphoma kinase (ALK) have been identified in a variety of human cancers. Crizotinib (PF02341066) is a dual MET and ALK inhibitor and approved for the treatment of a subset of non-small cell lung carcinoma and in clinical development for other malignancies. Crizotinib can induce apoptosis in cancer cells, whereas the underlying mechanisms are not well understood. In this study, we found that crizotinib induces apoptosis in colon cancer cells through the BH3-only protein PUMA. In cells with wild-type p53, crizotinib induces rapid induction of PUMA and Bim accompanied by p53 stabilization and DNA damage response. The induction of PUMA and Bim is mediated largely by p53, and deficiency in PUMA or p53, but not Bim, blocks crizotinib-induced apoptosis. Interestingly, MET knockdown led to selective induction of PUMA, but not Bim or p53. Crizotinib also induced PUMA-dependent apoptosis in p53-deficient colon cancer cells and synergized with gefitinib or sorafenib to induce marked apoptosis via PUMA in colon cancer cells. Furthermore, PUMA deficiency suppressed apoptosis and therapeutic responses to crizotinib in xenograft models. These results establish a critical role of PUMA in mediating apoptotic responses of colon cancer cells to crizotinib and suggest that mechanisms of oncogenic addiction to MET/ALK-mediated survival may be cell type-specific. These findings have important implications for future clinical development of crizotinib.
OPINION STATEMENT - Patients whose tumors harbor somatic-activating mutations within the epidermal growth factor receptor (EGFR) gene define a clinically distinct molecular cohort of lung cancers with increased sensitivity to the EGFR tyrosine kinase inhibitors (TKIs), including the "first-generation" reversible inhibitors, erlotinib and gefitinib, and the "second-generation" irreversible inhibitors, afatinib and dacomitinib. Several, large, phase III studies have shown already that patients with EGFR-mutant tumors display radiographic response rates of >60 % and improved progression free survival (PFS) when treated with an EGFR TKI compared with chemotherapy. Unfortunately, despite these initial responses, patients inevitably develop progressive disease, a concept referred to clinically as acquired resistance. Novel strategies are needed to delay or overcome acquired resistance to EGFR TKIs. These strategies include second-generation EGFR inhibitors, rationale combinations of targeted small molecule inhibitors and/or monoclonal antibodies, and addition of traditional cytotoxic chemotherapy to EGFR TKI therapy at the time of progression. Unfortunately, to date, there is no genotype-specific standard of care, and enrollment of patients with acquired resistance to EGFR TKIs into clinical trials specifically addressed at overcoming resistance is paramount to continue to advance the field and to improve outcomes for these patients.
Inhibition of the BRAF(V600E) oncoprotein by the small-molecule drug PLX4032 (vemurafenib) is highly effective in the treatment of melanoma. However, colon cancer patients harbouring the same BRAF(V600E) oncogenic lesion have poor prognosis and show only a very limited response to this drug. To investigate the cause of the limited therapeutic effect of PLX4032 in BRAF(V600E) mutant colon tumours, here we performed an RNA-interference-based genetic screen in human cells to search for kinases whose knockdown synergizes with BRAF(V600E) inhibition. We report that blockade of the epidermal growth factor receptor (EGFR) shows strong synergy with BRAF(V600E) inhibition. We find in multiple BRAF(V600E) mutant colon cancers that inhibition of EGFR by the antibody drug cetuximab or the small-molecule drugs gefitinib or erlotinib is strongly synergistic with BRAF(V600E) inhibition, both in vitro and in vivo. Mechanistically, we find that BRAF(V600E) inhibition causes a rapid feedback activation of EGFR, which supports continued proliferation in the presence of BRAF(V600E) inhibition. Melanoma cells express low levels of EGFR and are therefore not subject to this feedback activation. Consistent with this, we find that ectopic expression of EGFR in melanoma cells is sufficient to cause resistance to PLX4032. Our data suggest that BRAF(V600E) mutant colon cancers (approximately 8-10% of all colon cancers), for which there are currently no targeted treatment options available, might benefit from combination therapy consisting of BRAF and EGFR inhibitors.
Analysis of cellular signaling networks typically involves targeted measurements of phosphorylated protein intermediates. However, phosphoproteomic analyses usually require affinity enrichment of phosphopeptides and can be complicated by artifactual changes in phosphorylation caused by uncontrolled preanalytical variables, particularly in the analysis of tissue specimens. We asked whether changes in protein expression, which are more stable and easily analyzed, could reflect network stimulation and inhibition. We employed this approach to analyze stimulation and inhibition of the epidermal growth factor receptor (EGFR) by EGF and selective EGFR inhibitors. Shotgun analysis of proteomes from proliferating A431 cells, EGF-stimulated cells, and cells co-treated with the EGFR inhibitors cetuximab or gefitinib identified groups of differentially expressed proteins. Comparisons of these protein groups identified 13 proteins whose EGF-induced expression changes were reversed by both EGFR inhibitors. Targeted multiple reaction monitoring analysis verified differential expression of 12 of these proteins, which comprise a candidate EGFR inhibition signature. We then tested these 12 proteins by multiple reaction monitoring analysis in three other models: 1) a comparison of DiFi (EGFR inhibitor-sensitive) and HCT116 (EGFR-insensitive) cell lines, 2) in formalin-fixed, paraffin-embedded mouse xenograft DiFi and HCT116 tumors, and 3) in tissue biopsies from a patient with the gastric hyperproliferative disorder Ménétrier's disease who was treated with cetuximab. Of the proteins in the candidate signature, a core group, including c-Jun, Jagged-1, and Claudin 4, were decreased by EGFR inhibitors in all three models. Although the goal of these studies was not to validate a clinically useful EGFR inhibition signature, the results confirm the hypothesis that clinically used EGFR inhibitors generate characteristic protein expression changes. This work further outlines a prototypical approach to derive and test protein expression signatures for drug action on signaling networks.
Thoracic oncologists traditionally have made treatment decisions based upon tumor histology, distinguishing non-small cell lung cancer (NSCLC) from small cell lung cancer (SCLC). However, recent data has revealed that at least one histological subtype of NSCLC, lung adenocarcinoma comprises multiple molecularly distinct diseases. Lung adenocarcinoma subsets now can be defined by specific 'driver' mutations in genes encoding components of the EGFR signaling pathway. Importantly, these mutations have implications regarding targeted therapy. Here, we focus on EGFR mutant NSCLC-a prime example of a clinically relevant molecular subset of lung cancer, with defined mechanisms of drug sensitivity, primary drug resistance, and acquired resistance to EGFR tyrosine kinase inhibitors. Efforts are now being made to overcome mechanisms of acquired resistance. These findings illustrate how knowledge about the genetic drivers of tumors can lead to rational targeted therapy for individual patients.
PURPOSE - Given the unprecedented efficacy of EGFR tyrosine kinase inhibitors (TKI) in advanced EGFR-mutant lung cancer, adjuvant TKI therapy is an appealing strategy. However, there are conflicting findings regarding the potential benefit of adjuvant EGFR-TKI in patients with lung cancer harboring EGFR mutations. To better understand these results, we studied the natural history of lung cancers which recurred despite adjuvant TKI.
EXPERIMENTAL DESIGN - Patients with recurrent EGFR-mutant lung cancer following adjuvant TKI were identified using an Institutional Review Board-approved mechanism. Recurrent cancer specimens were tested for resistance mutations. Sensitivity to retreatment with EGFR-TKI was evaluated.
RESULTS - Twenty-two patients with cancers harboring an EGFR sensitizing mutation received adjuvant erlotinib or gefitinib for a median of 17 months (range 1-37 months). T790M was more common in cancers which recurred while receiving TKI than in those which recurred after stopping TKI (67% vs. 0%, P = 0.011). Fourteen patients who developed recurrence after stopping EGFR-TKI were retreated, with a median time to progression of 10 months and radiographic response seen in 8 of 11 patients with evaluable disease (73%).
CONCLUSIONS - Recurrence of EGFR-mutant lung cancer after stopping adjuvant TKI should not preclude a trial of TKI retreatment; a phase II trial of erlotinib in this setting is underway. Studies of adjuvant EGFR-TKI will underestimate the potential survival benefit of adjuvant TKI for patients with EGFR-mutant lung cancers if retreatment at recurrence is not given.