Activated O2^|^bull;^|^minus; and H2O2 Mediated Cell Survival in SU11274-Treated Non-Small-Cell Lung Cancer A549 Cells via c-Met^|^ndash;PI3K^|^ndash;Akt and c-Met^|^ndash;Grb2/SOS^|^ndash;Ras^|^ndash;p38 Pathways

Combination of chemotherapy and c-MET inhibitors has synergistic effects in c-MET overexpressing pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) remains as one of the most lethal malignancies. c-MET is an important oncogenic kinase involved in PDAC progression. We determined the anticancer effect of c-MET inhibitors, crizotinib and cabozantinib, combined with chemotherapeutic agents, doxorubicin, oxaliplatin and gemcitabine, against different PDAC and a lung adenocarcinoma cell line expressing different levels of c-MET. MTT assay was performed to assess cell growth inhibition. Synergistic combinations were evaluated in spheroid cultures, while apoptosis was determined through Hoechst33258 staining. The effect of drug combinations on cell cycle and apoptosis induction was examined by RNase/PI flow cytometric assay. We also evaluated reactive oxygen species (ROS) levels using 2',7'-dichlorofluorescein-diacetate (DCFH-DA) assay to explore the possible mechanisms contributing to synergism. Combination of crizotinib or cabozantinib with doxorubicin exhibited synergistic effects in c-MET overexpressing cells. Conversely, combinations of c-MET inhibitors with other agents were additive or even antagonistic. Combination index (CI) values calculated with Calcusyn software were 0.631-0.730 for crizotinib and 0.542-0.746 for cabozantinib co-administered with doxorubicin. These synergistic combinations showed significant spheroid growth inhibition and apoptosis induction in Suit-2, c-MET dependent PDAC cells. These combinations also significantly increased the number of cells in both apoptotic sub-G1 phase and the G2/M phase compared to single-drug treatment. Increased ROS production seemed to be a possible mechanism underlying synergism. In conclusion, c-MET inhibitors synergize with DNA damaging agent, doxorubicin, in cancer cells with c-MET overexpression, indicating that these combination therapies may be a promising cancer therapeutic strategy.

ASC/inflammasome-independent pyroptosis in ovarian cancer cells through translational augmentation of caspase-1

Canonical pyroptosis is type of programmed cell death depending on active caspase-1, and the inflammasome carries out caspase-1 activation. Here, we showed that docosahexaenoic acid (DHA) induced ovarian cancer cell deaths in caspase-1-dependent manner. DHA increased caspase-1 activity and led to interleukin-1β secretion and gasdermin D cleavage while disulfiram inhibited DHA-induced cell death, suggesting that DHA triggered pyroptosis. Intriguingly, ASC, the molecule recruiting caspase-1 to inflammasome for activation, was dispensable for DHA-induced pyroptosis. Instead, we observed remarkable elevation in caspase-1 abundance concurrent with the activation of caspase-1 in DHA-treated cells. As ectopically overexpressing caspase-1 resulted in robust amount of active caspase-1, we reason that DHA activates caspase-1 and pyroptosis through the generation of excessive amount of caspase-1 protein. Mechanistically, DHA increased caspase-1 by specifically accelerating caspase-1 protein synthesis via the p38MAPK/Mnk1 signaling pathway. We have uncovered an unknown pyroptosis mechanism in which caspase-1-dependent pyroptosis can occur without the participation of ASC/inflammasome.

Protein Kinase Signaling Networks Driven by Oncogenic Gq/11 in Uveal Melanoma Identified by Phosphoproteomic and Bioinformatic Analyses

Metastatic uveal melanoma (UM) patients typically survive only 2 to 3 years because effective therapy does not yet exist. Here, to facilitate the discovery of therapeutic targets in UM, we have identified protein kinase signaling mechanisms elicited by the drivers in 90% of UM tumors: mutant constitutively active G protein α-subunits encoded by GNAQ (Gq) or GNA11 (G11). We used the highly specific Gq/11 inhibitor FR900359 (FR) to elucidate signaling networks that drive proliferation, metabolic reprogramming, and dedifferentiation of UM cells. We determined the effects of FR on the proteome and phosphoproteome of UM cells as indicated by bioinformatic analyses with CausalPath and site-specific gene set enrichment analysis. We found that inhibition of oncogenic Gq/11 caused deactivation of PKC, Erk, and the cyclin-dependent kinases CDK1 and CDK2 that drive proliferation. Inhibition of oncogenic Gq/11 in UM cells with low metastatic risk relieved inhibitory phosphorylation of polycomb-repressive complex subunits that regulate melanocytic redifferentiation. Site-specific gene set enrichment analysis, unsupervised analysis, and functional studies indicated that mTORC1 and 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 2 drive metabolic reprogramming in UM cells. Together, these results identified protein kinase signaling networks driven by oncogenic Gq/11 that regulate critical aspects of UM cell biology and provide targets for therapeutic investigation.

Targeting Mitochondrial Metabolism to Reverse Radioresistance: An Alternative to Glucose Metabolism

Radiotherapy failure and poor tumor prognosis are primarily attributed to radioresistance. Improving the curative effect of radiotherapy and delaying cancer progression have become difficult problems for clinicians. Glucose metabolism has long been regarded as the main metabolic process by which tumor cells meet their bioenergetic and anabolic needs, with the complex interactions between the mitochondria and tumors being ignored. This misconception was not dispelled until the early 2000s; however, the cellular molecules and signaling pathways involved in radioresistance remain incompletely defined. In addition to being a key metabolic site that regulates tumorigenesis, mitochondria can influence the radiation effects of malignancies by controlling redox reactions, participating in oxidative phosphorylation, producing oncometabolites, and triggering apoptosis. Therefore, the mitochondria are promising targets for the development of novel anticancer drugs. In this review, we summarize the internal relationship and related mechanisms between mitochondrial metabolism and cancer radioresistance, thus exploring the possibility of targeting mitochondrial signaling pathways to reverse radiation insensitivity. We suggest that attention should be paid to the potential value of mitochondria in prolonging the survival of cancer patients.

EGFR and ERK activation resists flavonoid quercetin-induced anticancer activities in human cervical cancer cells in vitro

In the present study, due to the complex and numerous targets of Sarcandrae Herb (also known as Zhong Jie Feng), network pharmacology was performed to analyze its therapeutic effect on 2 cervical cancer cell lines, which could assist with the development of novel therapies. The results suggested that the natural flavonoid quercetin (Que), the effective antitumor ingredient in SH, which is widely present in a variety of plants, may depend on the target, EGFR. Previous studies have shown that EGFR serves a crucial role in the occurrence and development of cervical cancer, but its downstream molecules and regulatory mechanisms remain unknown. The anti-cervical cancer cell properties of Que, which are present in ubiquitous plants, were examined in vitro to identify the association between Que and its underlying pathway using MTT assays, flow cytometry, western blot analysis and Transwell assays. It was found that Que reduced cervical cancer cell viability, promoted G₂/M phase cell cycle arrest and cell apoptosis, as well as inhibited cell migration and invasion. The Tyr1068 phosphorylation site of EGFR and the corresponding ERK target were also examined and the 2 kinases were markedly activated by Que. Furthermore, the EGFR inhibitor, afatinib and the ERK inhibitor, U0126 blocked the increase of EGFR and ERK phosphorylation, and resulted in a notable enhancement of apoptosis and cell cycle arrest. Therefore, to the best of our knowledge, the current results provided the first evidence that EGFR and ERK activation induced by Que could resist Que-induced anticancer activities. On this basis, the present study determined the role of EGFR and the underlying signaling pathways involved in the anti-cervical cancer malignant behavior induced by Que and identified the negative regulatory association.

Pyrvinium pamoate inhibits cell proliferation through ROS-mediated AKT-dependent signaling pathway in colorectal cancer

The use of the anthelmintic drug pyrvinium pamoate (PP) in cancer therapy has been extensively investigated in the last decade. PP has been shown to have an inhibitory effect in colorectal cancer (CRC), but the underlying mechanism remains elusive. We aimed to investigate the antitumor activity and mechanisms of PP in CRC. In the present study, we used CCK-8 assays, colony formation assays, and western blotting to reveal that PP effectively suppressed CRC cell proliferation and the AKT-dependent signaling pathway in a concentration-dependent and time-dependent manner. Flow cytometric analysis and fluorescence microscopy demonstrated that PP increased intracellular reactive oxygen species (ROS) accumulation. We found that the inhibitory effect of PP on cell proliferation and AKT protein expression induced by PP could be partially reversed by N-acetyl-L-cysteine (NAC), an ROS scavenger. In addition, the results also demonstrated that PP inhibited cell migration by modulating epithelial-to-mesenchymal transition (EMT)-related proteins, including E-cadherin and vimentin. In conclusion, our data suggested that PP effectively inhibited cell proliferation through the ROS-mediated AKT-dependent signaling pathway in CRC, further providing evidence for the use of PP as an antitumor agent.

Ilimaquinone Induces Apoptosis and Autophagy in Human Oral Squamous Cell Carcinoma Cells

In this study, the anti-tumor activity of ilimaquinone (IQ), a sesquiterpene quinone isolated from marine sponge Halichondria sp., in oral squamous cell carcinoma (OSCC) cells, was investigated. IQ suppressed the viability of the OSCC cell lines SCC4 and SCC2095 with IC₅₀ values of 7.5 and 8.5 μM, respectively. Flow cytometric analysis demonstrated that IQ induced caspase-dependent apoptosis in SCC4 cells and modulated the expression of several cell growth-related gene products, including Akt, p38, Mcl-1, and p53. Notably, p53 knockdown caused higher resistance to IQ’s anti-tumor activity. In addition, IQ increased reactive oxygen species generation, which was partially reversed by the addition of antioxidants. Furthermore, it triggered autophagy, as evidenced by acidic organelle formation and LC3B-II and Atg5 expression in SCC4 cells. Pretreatment with the autophagy inhibitor 3-methyladenine or chloroquine partially decreased IQ-induced apoptosis, suggesting that IQ induced protective autophagy. In summary, IQ has potential to be used in OSCC therapy.

Role of long noncoding RNA MEG3/miR-378/GRB2 axis in neuronal autophagy and neurological functional impairment in ischemic stroke

Autophagy has been shown to maintain neural system homeostasis during stroke. However, the molecular mechanisms underlying neuronal autophagy in ischemic stroke remain poorly understood. This study aims to investigate the regulatory mechanisms of the pathway consisting of MEG3 (maternally expressed gene 3), microRNA-378 (miR-378), and GRB2 (growth factor receptor-bound protein 2) in neuronal autophagy and neurological functional impairment in ischemic stroke. A mouse model of the middle cerebral artery occluded-induced ischemic stroke and an in vitro model of oxygen-glucose deprivation-induced neuronal injury were developed. To understand the role of the MEG3/miR-378/GRB2 axis in the neuronal regulation, the expression of proteins associated with autophagy in neurons was measured by Western blotting analysis, and neuron death was evaluated using a lactate dehydrogenase leakage rate test. First, it was found that the GRB2 gene, up-regulated in middle cerebral artery occluded-operated mice and oxygen-glucose deprivation-exposed neurons, was a target gene of miR-378. Next, miR-378 inhibited neuronal loss and neurological functional impairment in mice, as well as neuronal autophagy and neuronal death by silencing of GRB2. Confirmatory in vitro experiments showed that MEG3 could specifically bind to miR-378 and subsequently up-regulate the expression of GRB2, which in turn suppressed the activation of Akt/mTOR pathway. Taken together, these findings suggested that miR-378 might protect against neuronal autophagy and neurological functional impairment and proposed that a MEG3/miR-378/GRB2 regulatory axis contributed to better understanding of the pathophysiology of ischemic stroke.

Oleuropein-Induced Apoptosis Is Mediated by Mitochondrial Glyoxalase 2 in NSCLC A549 Cells: A Mechanistic Inside and a Possible Novel Nonenzymatic Role for an Ancient Enzyme

Oleuropein (OP) is a bioactive compound derived from plants of the genus Oleaceae exhibiting antitumor properties in several human cancers, including non-small-cell lung cancer (NSCLC). Recent evidence suggests that OP has proapoptotic effects on NSCLC cells via the mitochondrial apoptotic pathway. However, the exact molecular mechanisms behind the apoptogenic action of OP in NSCLC are still largely unknown. Glyoxalase 2 (Glo2) is an ancient enzyme belonging to the glyoxalase system involved in the detoxification of glycolysis-derived methylglyoxal. However, emerging evidence suggests that Glo2 may have also nonenzymatic roles in some malignant cells. In the present study, we evaluated whether and how Glo2 participated in the proapoptotic effects of OP in NSCLC A549 cells. Our results indicate that OP is able to induce apoptosis in A549 cells through the upregulation of mitochondrial Glo2 (mGlo2), mediated by the superoxide anion and Akt signaling pathway. Moreover, our data shows that the proapoptotic role of mGlo2, observed following OP exposure, occurs via the interaction of mGlo2 with the proapoptotic Bax protein. Conversely, OP does not alter the behavior of nonmalignant human BEAS-2B cells or mGlo2 expression, thus suggesting a specific anticancer role for this bioactive compound in NSCLC. Our data identify a novel pathway through which OP exerts a proapoptotic effect in NSCLC and suggest, for the first time, a novel, nonenzymatic antiapoptotic role for this ancient enzyme in NSCLC.

Preventive effects of N-acetyl-l-cysteine against imidacloprid intoxication on Bombyx mori larvae

Imidacloprid, a widely used neonicotinoid insecticide, is toxic to silkworm (Bombyx mori). To explore whether N-acetyl-l-cysteine (NAC) has an effect on preventing silkworm (B. mori) from toxification caused by imidacloprid, we fed the fifth-instar larvae with mulberry leaves dipped in 200 mg/L NAC solution before exposing in imidacloprid, and investigated the silkworm growth, survival rate, feed efficiency, cocoon quality, and the activities of antioxidant enzymes in midgut. The results showed that addition of NAC could significantly increase body weight, survival rate, and feed efficiency of imidacloprid poisoned silkworm larvae (P < 0.05), as well as cocoon mass, cocoon shell mass, and the ratio of cocoon shell (P < 0.05). Furthermore, it could significantly promote the activities of the antioxidant enzymes including superoxide dismutase, catalase, and glutathione peroxide in the midgut of fifth-instar larvae under imidacloprid exposure at the late stage of treatment. In addition, it also could downregulate the malondialdehyde content. The results of our findings proved that the added NAC may have some beneficial effects on protection or restoration of antioxidant balance in imidacloprid exposed larvae.

Reactive Oxygen Species as Intracellular Signaling Molecules in the Cardiovascular System

BACKGROUND

Redox signaling plays an important role in the lives of cells. This signaling not only becomes apparent in pathologies but is also thought to be involved in maintaining physiological homeostasis. Reactive Oxygen Species (ROS) can activate protein kinases: CaMKII, PKG, PKA, ERK, PI3K, Akt, PKC, PDK, JNK, p38. It is unclear whether it is a direct interaction of ROS with these kinases or whether their activation is a consequence of inhibition of phosphatases. ROS have a biphasic effect on the transport of Ca2+ in the cell: on one hand, they activate the sarcoplasmic reticulum Ca2+-ATPase, which can reduce the level of Ca2+ in the cell, and on the other hand, they can inactivate Ca2+-ATPase of the plasma membrane and open the cation channels TRPM2, which promote Ca2+-loading and subsequent apoptosis. ROS inhibit the enzyme PHD2, which leads to the stabilization of HIF-α and the formation of the active transcription factor HIF.

CONCLUSION

Activation of STAT3 and STAT5, induced by cytokines or growth factors, may include activation of NADPH oxidase and enhancement of ROS production. Normal physiological production of ROS under the action of cytokines activates the JAK/STAT while excessive ROS production leads to their inhibition. ROS cause the activation of the transcription factor NF-κB. Physiological levels of ROS control cell proliferation and angiogenesis. ROS signaling is also involved in beneficial adaptations to survive ischemia and hypoxia, while further increases in ROS can trigger programmed cell death by the mechanism of apoptosis or autophagy. ROS formation in the myocardium can be reduced by moderate exercise.

Crosstalk of ROS/RNS and autophagy in silibinin-induced apoptosis of MCF-7 human breast cancer cells in vitro

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play important roles in regulating cell survival and death. Silibinin is a natural polyphenolic flavonoid isolated from milk thistle with anti-tumor activities, but it was found to induce cytoprotective ROS/RNS in human breast cancer MCF-7 cells. Furthermore, treatment with silibinin down-regulates ERα expression in MCF-7 cells, and inducing both autophagy and apoptosis. In this study we explored the relationship between ER-associated pathways and RNS/ROS in MCF-7 cells. We also investigated the molecular mechanisms underlying the reciprocal regulation between ROS/RNS levels and autophagy in the death signaling pathways in silibinin-treated MCF-7 cells. Silibinin (100-300 μmol/L) dose-dependently increased ROS/RNS generation in MCF-7 cells (with high expression of ERα and low expression of ERβ) and MDA-MB-231 cells (with low expression of ERα and high expression of ERβ). Scavenging ROS/RNS significantly enhanced silibinin-induced death of MCF-7 cells, but not MDA-MB231 cells. Pharmacological activation or blockade of ERα in MCF-7 cells significantly enhanced or decreased, respectively, silibinin-induced ROS/RNS generation, whereas activation or block of ERβ had no effect. In silibinin-treated MCF-7 cells, exposure to the ROS/RNS donators decreased the autophagic levels, whereas inhibition of autophagy with 3-MA significantly increased ROS/RNS levels. We further showed that increases in ROS/RNS generation, ERα activation or autophagy down-regulation had protective roles in silibinin-treated MCF-7 cells. Under a condition of ERα activation, scavenging ROS/RNS or stimulating autophagy enhanced the cytotoxicity of silibinin. These results demonstrate the existence of two conflicting pathways in silibinin-induced death of MCF-7 cells: one involves the down-regulation of ERα and thereby augmenting the pro-apoptotic autophagy downstream, leading to cell death; the other involves the up-regulation of pro-survival ROS/RNS; and that the generation of ROS/RNS and autophagy form a negative feedback loop whose balance is regulated by ERα.

Bu-Zhong-Yi-Qi Decoction, the Water Extract of Chinese Traditional Herbal Medicine, Enhances Cisplatin Cytotoxicity in A549/DDP Cells through Induction of Apoptosis and Autophagy

Cisplatin is one of the most active cytotoxic agents for non-small cell lung cancer (NSCLC) treatment. However, the development of cisplatin resistance is common. Bu-Zhong-Yi-Qi decoction (BZYQD), a Chinese traditional herbal medicine, is widely used for the enhancement of antitumor effect in other medications. In this study, we evaluated the effect and drug-resistance reversal mechanism of BZYQD combined with cisplatin on cisplatin-resistant A549/DDP cells. Our results showed that BZYQD exhibited direct cytotoxic and chemosensitizing effects. Cotreatment with BZYQD and cisplatin induced intrinsic apoptotic pathways which were measured by condensed nuclear chromatin, Annexin V/PI apoptosis assay, and apoptosis related proteins expression. In addition, cotreatment with BZYQD and cisplatin also activated autophagy, as indicated by an increase in LC3 puncta, classical autophagosomes and/or autolysosomes, and an accumulation of LC3-II and ATG7 protein. Finally, cotreatment with BZYQD and cisplatin resulted in the generation of ROS and scavenging ROS by NAC almost completely suppressing cell death. These results suggest that cotreatment with BZYQD and cisplatin might reverse cisplatin resistance by inducing ROS accumulation, which activates apoptosis and autophagy by oxidative stress. The combination of BZYQD and cisplatin may represent a novel approach in treatment for NSCLC and thus offer a new target for chemotherapy.

Reactive oxygen species (ROS) and cancer: Role of antioxidative nutraceuticals

Extensive research over the past half a century indicates that reactive oxygen species (ROS) play an important role in cancer. Although low levels of ROS can be beneficial, excessive accumulation can promote cancer. One characteristic of cancer cells that distinguishes them from normal cells is their ability to produce increased numbers of ROS and their increased dependence on an antioxidant defense system. ROS are produced as a byproduct intracellularly by mitochondria and other cellular elements and exogenously by pollutants, tobacco, smoke, drugs, xenobiotics, and radiation. ROS modulate various cell signaling pathways, which are primarily mediated through the transcription factors NF-κB and STAT3, hypoxia-inducible factor-1α, kinases, growth factors, cytokines and other proteins, and enzymes; these pathways have been linked to cellular transformation, inflammation, tumor survival, proliferation, invasion, angiogenesis, and metastasis of cancer. ROS are also associated with epigenetic changes in genes, which is helpful in diagnosing diseases. This review considers the role of ROS in the various stages of cancer development. Finally, we provide evidence that nutraceuticals derived from Mother Nature are highly effective in eliminating cancer cells.

Resistance to cetuximab in EGFR-overexpressing esophageal squamous cell carcinoma xenografts due to FGFR2 amplification and overexpression

Esophageal carcinoma is one of the most virulent malignant diseases and a major cause of cancer-related deaths worldwide. Despite improvements in surgical techniques and perioperative management and surgery combined with chemotherapy and/or radiotherapy, the prognosis of esophageal squamous cell carcinoma (ESCC) at an advanced stage remains poor. ESCC shows a relatively high incidence of EGFR (50% - 70%), and the humanized monoclonal antibody (mAb) cetuximab against EGFR has been undergoing clinical development. However, all responding patients eventually developed acquired resistance to cetuximab. In the current study, we described a cetuximab-sensitive ESCC xeongraft model that developed resistance to cetuximab as a result of FGFR2 gene amplification and overexpression. Inhibition of FGFR2 signaling in this xenograft model restored its sensitivity to cetuximab. The antitumor effect may be induced by inhibition of AKT phosphorylation. These findings suggest that combination therapyincluding cetuximab and FGFR2 inhibition may be a promising strategy to treat ESCC.

Antioxidative properties of 4-methylumbelliferone are related to antibacterial activity in the silkworm (Bombyx mori) digestive tract

Umbelliferones have gained significant attention due to their tumor-inhibitory effects in vitro. This study was undertaken to examine the impact of umbelliferones in an invertebrate model organism, Bombyx mori, to assess the underlying antimicrobial activities via antioxidation in vivo. Oral administration of 4 mM 4-methylumbelliferone (4-MU), a model umbelliferone drug, in B. Mori larvae caused a rapid increase in reactive oxygen species, such as hydrogen peroxide (H2O2) and antimicrobial activity in the digestive tract. In addition, a significant increase in total antioxidant capacity as well as superoxide anion radical-inhibiting activity and reduced glutathione were detected. The antioxidant defense system was activated following induction of H2O2, resulting in a significant rise in catalase (50-66 %) and glutathione peroxidase (175 %) activities, which were helpful in defending digestive tract cells against oxidative injury. These results help in understanding the anticancer mechanism of 4-MU based on its antioxidation in organisms.

Therapeutic targeting of autophagy in cancer. Part I: molecular pathways controlling autophagy

Autophagy is a process in which cells can generate energy and building materials, by degradation of redundant and/or damaged organelles and proteins. Especially during conditions of stress, autophagy helps to maintain homeostasis. In addition, autophagy has been shown to influence malignant transformation and cancer progression. The precise molecular events in autophagy are complex and the core autophagic machinery described to date consists of nearly thirty proteins. Apart from these factors that execute the process of autophagy, several signalling pathways are involved in converting internal and external stimuli into an autophagic response. In this review we provide an overview of the signalling pathways that influence autophagy, particularly in cancer cells. We will illustrate that interference with multiple of these signalling pathways can have significant effects on cancer cell survival.

Combination of BIBW2992 and ARQ 197 is effective against erlotinib-resistant human lung cancer cells with the EGFR T790M mutation

Although the EGFR tyrosine kinase inhibitors (EGFR-TKI) erlotinib and gefitinib have shown marked effects against EGFR-mutated lung cancer, patients acquire resistance by various mechanisms, including the EGFR T790M mutation and Met induction, consequently suffering relapse. Thus, novel agents to overcome EGFR-TKI resistance are urgently needed. We aimed to investigate the inhibitory effects of a combination of BIBW2992 (irreversible EGFR inhibitor)/ARQ 197 (MET inhibitor) on the human lung adenocarcinoma cell line H1975. H1975 cells (harboring a T790M mutation in EGFR) were treated with erlotinib, BIBW2992 or ARQ 197 separately or with combinations of erlotinib/ARQ 197 or BIBW2992/ARQ 197. Cell growth, apoptosis and cell cycle distribution were evaluated by MTT assay, Annexin V/propidium iodide (PI) double staining and flow cytometry, respectively. EGFR, MET, AKT, ERK and the respective phosphorylated counterparts were detected by western blot analysis. Pathway-specific knockdown of MET and/or EGFR kinase signaling was achieved by siRNA interference. H1975 cells displayed EGFR and MET activation, and were resistant to erlotinib. The BIBW2992/ARQ 197 combination significantly inhibited growth, induced cell cycle arrest and apoptosis, and altered the phosphorylation of EGFR, MET, AKT and ERK1/2 in the H1975 cells. Phosphorylation of AKT and ERK1/2, downstream effectors of the EGFR and MET pathways, was not affected by the other tested treatments. Finally, knockdown of MET and/or EGFR in the H1975 cells confirmed the enhanced downstream inhibition of both MET and EGFR pathways. Combination of an irreversible EGFR inhibitor and MET inhibitor is effective in controlling H1975 cells with acquired resistance to erlotinib, by a mechanism involving the downregulation of PI3K/AKT and MEK/ERK signaling pathways.