Non-small cell lung cancers (NSCLC) that have developed resistance to EGF receptor (EGFR) tyrosine kinase inhibitor (TKI), including gefitinib and erlotinib, are clinically linked to an epithelial-to-mesenchymal transition (EMT) phenotype. Here, we examined whether modulating EMT maintains the responsiveness of EGFR-mutated NSCLCs to EGFR TKI therapy. Using human NSCLC cell lines harboring mutated EGFR and a transgenic mouse model of lung cancer driven by mutant EGFR (EGFR-Del19-T790M), we demonstrate that EGFR inhibition induces TGFb secretion followed by SMAD pathway activation, an event that promotes EMT. Chronic exposure of EGFR-mutated NSCLC cells to TGFb was sufficient to induce EMT and resistance to EGFR TKI treatment. Furthermore, NSCLC HCC4006 cells with acquired resistance to gefitinib were characterized by a mesenchymal phenotype and displayed a higher prevalence of the EGFR T790M mutated allele. Notably, combined inhibition of EGFR and the TGFb receptor in HCC4006 cells prevented EMT but was not sufficient to prevent acquired gefitinib resistance because of an increased emergence of the EGFR T790M allele compared with cells treated with gefitinib alone. Conversely, another independent NSCLC cell line, PC9, reproducibly developed EGFR T790M mutations as the primary mechanism underlying EGFR TKI resistance, even though the prevalence of the mutant allele was lower than that in HCC4006 cells. Thus, our findings underscore heterogeneity within NSCLC cells lines harboring EGFR kinase domain mutations that give rise to divergent resistance mechanisms in response to treatment and anticipate the complexity of EMT suppression as a therapeutic strategy. Cancer Res; 75(20); 4372-83. Ó2015 AACR.

Although EGFR mutant-selective TKIs are clinically effective, acquired resistance can occur by reactivating ERK. We show using in vitro models of acquired EGFR TKI resistance with a mesenchymal phenotype that CXCR7, an atypical GPCR, activates the MAPK-ERK pathway via β-arrestin. Depletion of CXCR7 inhibited the MAPK pathway, significantly attenuated EGFR TKI resistance and resulted in mesenchymal to epithelial transition. CXCR7 overexpression was essential in reactivation of ERK1/2 for the generation of EGFR TKI resistant persister cells. Many NSCLC patients harboring an EGFR kinase domain mutation, who progressed on EGFR inhibitors, demonstrated increased CXCR7 expression. These data suggest that CXCR7 inhibition could considerably delay and prevent the emergence of acquired EGFR TKI resistance in EGFR mutant NSCLC.Becker et al.

Oxidative stress generated by diabetes plays a key role in the development of diabetic retinopathy (DR), a common diabetic complication. DR remains asymptomatic until it reaches advanced stages, which complicate its treatment. Although it is known that good metabolic control is essential for preventing DR, knowledge of the disease is incomplete and an effective treatment with no side effects is lacking. Pterostilbene (Pter), a natural stilbene with good antioxidant activity, has proved to beneficially affect different pathologies, including diabetes. Therefore, our study aimed to analyse the protective and/or therapeutic capacity of Pter against oxidant damage by characterising early retinal alterations induced by hyperglycaemia, and its possible mechanism of action in a rabbit model of type 1 diabetes mellitus. Pter reduced lipid and protein oxidative damage, and recovered redox status and the main activities of antioxidant enzymes. Moreover, the redox regulation by Pter was associated with activation of the PI3K/AKT/GSK3β/NRF2 pathway. Our results show that Pter is a powerful protective agent that may delay early DR development.

◥Progression on therapy in non-small cell lung carcinoma (NSCLC) is often evaluated radiographically, however, imagebased evaluation of said therapies may not distinguish disease progression due to intrinsic tumor drug resistance or inefficient tumor penetration of the drugs. Here we report that the inhibition of mutated EGFR promotes the secretion of a potent vasoconstrictor, endothelin-1 (EDN1), which continues to increase as the cells become resistant with a mesenchymal phenotype. As EDN1 and its receptor (EDNR) is linked to cancer progression, EDNRantagonists have been evaluated in several clinical trials with disappointing results. These trials were based on a hypothesis that the EDN1-EDNR axis activates the MAPK-ERK signaling pathway that is vital to the cancer cell survival; the trials were not designed to evaluate the impact of tumor-derived EDN1 in modifying tumor microenvironment or contributing to drug resistance. Ectopic overexpression of EDN1 in cells with mutated EGFR resulted in poor drug delivery and retarded growth in vivo but not in vitro. Intratumoral injection of recombinant EDN significantly reduced blood flow and subsequent gefitinib accumulation in xenografted EGFRmutant tumors. Furthermore, depletion of EDN1 or the use of endothelin receptor inhibitors bosentan and ambrisentan improved drug penetration into tumors and restored blood flow in tumorassociated vasculature. Correlatively, these results describe a simplistic endogenous yet previously unrealized resistance mechanism inherent to a subset of EGFR-mutant NSCLC to attenuate tyrosine kinase inhibitor delivery to the tumors by limiting drug-carrying blood flow and the drug concentration in tumors.Significance: EDNR antagonists can be repurposed to improve drug delivery in VEGFA-secreting tumors, which normally respond to TKI treatment by secreting EDN1, promoting vasoconstriction, and limiting blood and drug delivery.