Activation of HGF/c-Met pathway contributes to the reactive oxygen species generation and motility of small cell lung cancer cells

Recording and classifying MET receptor mutations in cancers

Tyrosine kinase inhibitors (TKI) directed against MET have been recently approved to treat advanced non-small cell lung cancer (NSCLC) harbouring activating MET mutations. This success is the consequence of a long characterization of MET mutations in cancers, which we propose to outline in this review. MET, a receptor tyrosine kinase (RTK), displays in a broad panel of cancers many deregulations liable to promote tumour progression. The first MET mutation was discovered in 1997, in hereditary papillary renal cancer (HPRC), providing the first direct link between MET mutations and cancer development. As in other RTKs, these mutations are located in the kinase domain, leading in most cases to ligand-independent MET activation. In 2014, novel MET mutations were identified in several advanced cancers, including lung cancers. These mutations alter splice sites of exon 14, causing in-frame exon 14 skipping and deletion of a regulatory domain. Because these mutations are not located in the kinase domain, they are original and their mode of action has yet to be fully elucidated. Less than five years after the discovery of such mutations, the efficacy of a MET TKI was evidenced in NSCLC patients displaying MET exon 14 skipping. Yet its use led to a resistance mechanism involving acquisition of novel and already characterized MET mutations. Furthermore, novel somatic MET mutations are constantly being discovered. The challenge is no longer to identify them but to characterize them in order to predict their transforming activity and their sensitivity or resistance to MET TKIs, in order to adapt treatment.

Plasma hepatocyte growth factor as a noninvasive biomarker in small cell lung cancer

BACKGROUND

Hepatocyte growth factor (HGF) is a peptide-containing multifunctional cytokine, which is overexpressed and/or activated in multiple malignancies and is reported to be associated with tumor development and inferior survival. At present, the role of HGF in small cell lung cancer (SCLC) has not been fully explored yet.

MATERIALS AND METHODS

The expression of HGF and its value in predicting survival in SCLC were explored from GEO database and in pan-cancer analysis. Furthermore, we detected the expression of HGF using tumor tissue and paired plasma samples from a validation cohort of 71 SCLC patients at our institute. Correlation between tumor and plasma HGF expression and the prognostic values were analyzed.

RESULTS

GEO database analysis revealed that tumor tissue had lower HGF expression than paired normal tissue in SCLC. At our institute, immunohistochemical staining showed negative expression of HGF in tumor tissue of SCLC at our institute (47/47, 100%). The average baseline plasma HGF was 1.28 (range,0.42-4.35) ng/ml. However, plasma HGF was higher in SCLC patients with patients with N3, M1, liver metastasis (LM) and bone metastasis (BM) disease compared with those N0 - 2 (1.25 vs. 1.75 ng/mL, P = 0.000), M0 (1.26 vs. 1.63 ng/mL, P = 0.003), non-LM (1.32 vs. 2.06 ng/mL, P = 0.009), and non-BM (1.35 vs. 1.77 ng/mL, P = 0.047), respectively. Multivariate analysis revealed plasma HGF was an independent predictor for LM and prognostic factor of OS.

CONCLUSION

Our results revealed that plasma HGF rather than tumor HGF exhibited a potential role in predicting metastasis and survival in SCLC. Plasma HGF might be used as a non-invasive detecting and monitoring tool for SCLC.

Orchestrating smart therapeutics to achieve optimal treatment in small cell lung cancer: recent progress and future directions

Small cell lung cancer (SCLC) is a recalcitrant malignancy with elusive mechanism of pathogenesis and dismal prognosis. Over the past decades, platinum-based chemotherapy has been the backbone treatment for SCLC. However, subsequent chemoresistance after initial effectiveness urges researchers to explore novel therapeutic targets of SCLC. Recent years have witnessed significant improvements in targeted therapy in SCLC. New molecular candidates such as Ataxia telangiectasia and RAD3-related protein (ATR), WEE1, checkpoint kinase 1 (CHK1) and poly-ADP-ribose polymerase (PARP) have shown promising therapeutic utility in SCLC. While immune checkpoint inhibitor (ICI) has emerged as an indispensable treatment modality for SCLC, approaches to boost efficacy and reduce toxicity as well as selection of reliable biomarkers for ICI in SCLC have remained elusive and warrants our further investigation. Given the increasing importance of precision medicine in SCLC, optimal subtyping of SCLC using multi-omics have gradually applied into clinical practice, which may identify more drug targets and better tailor treatment strategies to each individual patient. The present review summarizes recent progress and future directions in SCLC. In addition to the emerging new therapeutics, we also focus on the establishment of predictive model for early detection of SCLC. More importantly, we also propose a multi-dimensional model in the prognosis of SCLC to ultimately attain the goal of accurate treatment of SCLC.

Base excision repair accessory factors in senescence avoidance and resistance to treatments

Cancer cells, in which the RAS and PI3K pathways are activated, produce high levels of reactive oxygen species (ROS), which cause oxidative DNA damage and ultimately cellular senescence. This process has been documented in tissue culture, mouse models, and human pre-cancerous lesions. In this context, cellular senescence functions as a tumour suppressor mechanism. Some rare cancer cells, however, manage to adapt to avoid senescence and continue to proliferate. One well-documented mode of adaptation involves increased production of antioxidants often associated with inactivation of the KEAP1 tumour suppressor gene and the resulting upregulation of the NRF2 transcription factor. In this review, we detail an alternative mode of adaptation to oxidative DNA damage induced by ROS: the increased activity of the base excision repair (BER) pathway, achieved through the enhanced expression of BER enzymes and DNA repair accessory factors. These proteins, exemplified here by the CUT domain proteins CUX1, CUX2, and SATB1, stimulate the activity of BER enzymes. The ensued accelerated repair of oxidative DNA damage enables cancer cells to avoid senescence despite high ROS levels. As a by-product of this adaptation, these cancer cells exhibit increased resistance to genotoxic treatments including ionizing radiation, temozolomide, and cisplatin. Moreover, considering the intrinsic error rate associated with DNA repair and translesion synthesis, the elevated number of oxidative DNA lesions caused by high ROS leads to the accumulation of mutations in the cancer cell population, thereby contributing to tumour heterogeneity and eventually to the acquisition of resistance, a major obstacle to clinical treatment.

HGF/c-Met regulates p22phox subunit of the NADPH oxidase complex in primary mouse hepatocytes by transcriptional and post-translational mechanisms

INTRODUCTION AND OBJECTIVES

It is well-known that signaling mediated by the hepatocyte growth factor (HGF) and its receptor c-Met in the liver is involved in the control of cellular redox status and oxidative stress, particularly through its ability to induce hepatoprotective gene expression by activating survival pathways in hepatocytes. It has been reported that HGF can regulate the expression of some members of the NADPH oxidase family in liver cells, particularly the catalytic subunits and p22^phox. In the present work we were focused to characterize the mechanism of regulation of p22^phox by HGF and its receptor c-Met in primary mouse hepatocytes as a key determinant for cellular redox regulation.

MATERIALS AND METHODS

Primary mouse hepatocytes were treated with HGF (50 ng/mL) at different times. cyba expression (gene encoding p22^phox) or protein content were addressed by real time RT-PCR, Western blot or immunofluorescence. Protein interactions were explored by immunoprecipitation and FRET analysis.

RESULTS

Our results provided mechanistic information supporting the transcriptional repression of cyba induced by HGF in a mechanism dependent of NF-κB activity. We identified a post-translational regulation mechanism directed by p22^phox degradation by proteasome 26S, and a second mechanism mediated by p22^phox sequestration by c-Met in plasma membrane.

CONCLUSION

Our data clearly show that HGF/c-Met exerts regulation of the NADPH oxidase by a wide-range of molecular mechanisms. NADPH oxidase-derived reactive oxygen species regulated by HGF/c-Met represents one of the main mechanisms of signal transduction elicited by this growth factor.

Roles of MET in human cancer

The MET proto-oncogene was first identified in osteosarcoma cells exposed to carcinogens. Although expressed in many normal cells, MET is overexpressed in many human cancers. MET is involved in the initiation and development of various human cancers and mediates proliferation, migration and invasion. Accordingly, MET has been successfully used as a biomarker for diagnosis and prognosis, survival, post-operative recurrence, risk assessment and pathologic grading, as well as a therapeutic target. In addition, recent work indicates that inhibition of MET expression and function has potential clinical benefit. This review summarizes the role, mechanism, and clinical significance of MET in the formation and development of human cancer.

PKCδ mediates mitochondrial ROS generation and oxidation of HSP60 to relieve RKIP inhibition on MAPK pathway for HCC progression

Both protein kinase C (PKC) and reactive oxygen species (ROS) are well-known signaling messengers cross-talking with each other to activate mitogen-activated protein kinases (MAPKs) for progression of hepatocellular carcinoma (HCC). However, the underlying mechanisms are not well elucidated. Especially, whether mitochondrial ROS (mtROS) is involved and how it triggers MAPK signaling are intriguing. In this study, we found mtROS generation and phosphorylation of MAPKs were mediated by PKCδ in HCCs treated with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Heat shock protein 60 (HSP60), one of the chaperones in mitochondria was the major protein oxidized in TPA-treated HCCs. Moreover, depletion of HSP60 or expression of HSP60 cysteine mutant prevented TPA-induced phosphorylation of MAPKs. To delineate how HSP60 mediated MAPK activation, the role of Raf kinase inhibitor protein (RKIP), a negative regulator of MAPK, was investigated. TPA dissociated RKIP from HSP60 in both mitochondria and cytosol, concurrently with translocation of HSP60 and MAPK from mitochondria to cytosol, which was associated with robust phosphorylation of MAPKs in the cytosol. Moreover, TPA induced opposite phenotypical changes of HCCs, G1 cell cycle arrest, and cell migration, which were prevented by mtROS scavengers and depletion of PKCδ and HSP60. Consistently, TPA increased the migration-related genes, hydrogen peroxide inducible clone5, matrix metalloproteinase-1/3, lamininγ2, and suppressed the cell cycle regulator cyclin E1 (CCNE1) via PKCδ/mtROS/HSP60/MAPK-axis. Finally, c-jun and c-fos were required for TPA-induced expression of the migration-related genes and a novel microRNA, miR-6134, was responsible for TPA-induced suppression of CCNE1. In conclusion, PKCδ cross-talked with mtROS to trigger HSP60 oxidation for release of RKIP to activate MAPK, regulating gene expression for migration, and G1 cell cycle arrest in HCC. Targeted therapy aiming at key players like PKCδ, RKIP, and HSP60 is promising for preventing HCC progression.

MET receptor in oncology: From biomarker to therapeutic target

First discovered in the 1984, the MET receptor tyrosine kinase (RTK) and its ligand hepatocyte growth factor or HGF (also known as scatter factor or SF) are implicated as key players in tumor cell migration, proliferation, and invasion in a variety of cancers. This pathway also plays a key role during embryogenesis in the development of muscular and nervous structures. High expression of the MET receptor has been shown to correlate with poor prognosis and resistance to therapy. MET exon 14 splicing variants, initially identified by us in lung cancer, is actionable through various tyrosine kinase inhibitors (TKIs). For this reason, this pathway is of interest as a therapeutic target. In this chapter we will be discussing the history of MET, the genetics of this RTK, and give some background on the receptor biology. Furthermore, we will discuss directed therapeutics, mechanisms of resistance, and the future of MET as a therapeutic target.

Modeling small cell lung cancer (SCLC) biology through deterministic and stochastic mathematical models

Mathematical cancer models are immensely powerful tools that are based in part on the fractal nature of biological structures, such as the geometry of the lung. Cancers of the lung provide an opportune model to develop and apply algorithms that capture changes and disease phenotypes. We reviewed mathematical models that have been developed for biological sciences and applied them in the context of small cell lung cancer (SCLC) growth, mutational heterogeneity, and mechanisms of metastasis. The ultimate goal is to develop the stochastic and deterministic nature of this disease, to link this comprehensive set of tools back to its fractalness and to provide a platform for accurate biomarker development. These techniques may be particularly useful in the context of drug development research, such as combination with existing omics approaches. The integration of these tools will be important to further understand the biology of SCLC and ultimately develop novel therapeutics.

Oxidation of heat shock protein 60 and protein disulfide isomerase activates ERK and migration of human hepatocellular carcinoma HepG2

Hepatocyte growth factor (HGF) and its receptor c-Met were frequently deregulated in hepatocellular carcinoma (HCC). Signaling pathways activated by HGF-c-Met are promising targets for preventing HCC progression. HGF can induce the reactive oxygen species (ROS) signaling for cell adhesion, migration and invasion of tumors including HCC. On the other hand, extracellular signal-regulated kinases (ERK), member of mitogen activated kinase, can be activated by ROS for a lot of cellular processes. As expected, HGF-induced phosphorylation of ERK and progression of HCC cell HepG2 were suppressed by ROS scavengers. By N-(biotinoyl)-N'-(iodoacetyl)-ethylenediamine (BIAM) labeling method, a lot of cysteine (-SH)-containing proteins with M.W. 50-75 kD were decreased in HepG2 treated with HGF or two other ROS generators, 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and phenazine methosulfate. These redox sensitive proteins were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry. Among them, two chaperones, heat shock protein 60 (HSP60) and protein disulfide isomerase (PDI), were found to be the most common redox sensitive proteins in responding to all three agonists. Affinity blot of BIAM-labeled, immunoprecipitated HSP60 and PDI verified that HGF can decrease the cysteine (-SH) containing HSP60 and PDI. On the other hand, HGF and TPA increased cysteinyl glutathione-containing HSP60, consistent with the decrease of cysteine (-SH)-containing HSP60. Moreover, depletion of HSP60 and PDI or expression of dominant negative mutant of HSP60 with alteration of Cys, effectively prevented HGF-induced ERK phosphorylation and HepG2 migration.In conclusion, the redox sensitive HSP60 and PDI are required for HGF-induced ROS signaling and potential targets for preventing HCC progressions.

Extracellular superoxide dismutase inhibits hepatocyte growth factor-mediated breast cancer-fibroblast interactions

We have previously shown tumor suppressive effects of extracellular superoxide dismutase, EcSOD in breast cancer cells. In this study, an RTK signaling array revealed an inhibitory effect of EcSOD on c-Met phosphorylation and its downstream kinase c-Abl in MDA-MB231 cells. Moreover, an extracellular protein array showed that thrombospondin 1 (TSP-1), a scavenger of the c-Met ligand, hepatocyte growth factor (HGF) is significantly up-regulated in EcSOD overexpressing cells (Ec.20). We further determined the effects of EcSOD on HGF/c-Met-mediated cancer-fibroblast interactions by co-culturing normal fibroblasts (RMF) or RMF which overexpresses HGF (RMF-HGF) with MDA-MB231 cells. We observed that while RMF-HGF significantly promoted Matrigel growth of MDA-MB231, overexpression of EcSOD inhibited the HGF-stimulated growth. Similarly, a SOD mimetic, MnTE-2-PyP, inhibited HGF-induced growth and invasion of MDA-MB231. In addition, a long-term heterotypic co-culture study not only showed that Ec.20 cells are resistant to RMF-HGF-induced invasive stimulation but RMF-HGF that were co-cultured with Ec.20 cells showed an attenuated phenotype, suggesting an oxidative-mediated reciprocal interaction between the two cell types. In addition, we demonstrated that RMF-HGF showed an up-regulation of an ROS-generating enzyme, NADPH oxidase 4 (Nox4). Targeting this pro-oxidant significantly suppressed the activated phenotype of RMF-HGF in a collagen contraction assay, suggesting that RMF-HGF contributes to the oxidative tumor microenvironment. We have further shown that scavenging ROS with EcSOD significantly inhibited RMF-HGF-stimulated orthotopic tumor growth of MDA-MB231. This study suggests the loss of EcSOD in breast cancer plays a pivotal role in promoting the HGF/c-Met-mediated cancer-fibroblast interactions.

MET receptor variant R970C favors calpain-dependent generation of a fragment promoting epithelial cell scattering

The receptor tyrosine kinase MET and its ligand, the hepatocyte growth factor, are essential to embryonic development, whereas deregulation of MET signaling is associated with tumorigenesis leading to various cancers, including lung carcinoma. Mutations in the MET kinase domain lead to constitutive kinase activity and are associated with tumorigenesis. In lung cancer, however, some mutations are found in the juxtamembrane domain, and their functional consequences are unknown. Because the juxtamembrane domain of MET is targeted by several proteolytic cleavages, involved in its degradation during cell death or under steady-state conditions, we evaluated the influence of these mutations on the MET proteolytic cleavages. In stably transfected epithelial cells expressing MET, the juxtamembrane mutations R970C, P991S, and T992I were found not to modify the known caspase or presenilin-dependent regulated intramembrane proteolysis. Yet when overexpressed, the R970C variant caused generation of an as yet undescribed 45-kDa fragment (p45 MET). This fragment was found in the confluent lung cancer cell line NCI-H1437 carrying the R970C mutation and at a lesser extent in cell lines expressing WT MET, suggesting that R970C mutation favors this cleavage. Generation of p45 MET required the activity of the calpain proteases, confirming the involvement of proteolysis. Ectopic expression of reconstituted p45 MET in epithelial cell lines favored cell scattering and invasion indicating active role of this fragment in HGF/SF induced responses. Hence, although the juxtamembrane mutations of MET do not affect its known proteolytic cleavages, the R970C MET variant favors calpain dependent proteolytic cleavage in lung cancer cells.

Oxidative stress contributes to hepatocyte growth factor-dependent pro-senescence activity of ovarian cancer cells

The cancer-promoting activity of senescent peritoneal mesothelial cells (HPMCs) has already been well evidenced both in vitro and in vivo. Here we sought to determine if ovarian cancer cells may activate senescence in HPMCs. The study showed that conditioned medium (CM) from ovarian cancer cells (OVCAR-3, SKOV-3, A2780) inhibited growth and promoted the development of senescence phenotype (increased SA-β-Gal, γ-H2A.X, 53BP1, and decreased Cx43) in HPMCs. An analysis of tumors isolated from the peritoneum of patients with ovarian cancer revealed an abundance of senescent HPMCs in proximity to cancerous tissue. The presence of senescent HPMCs was incidental when fragments of peritoneum free from cancer were evaluated. An analysis of the cells' secretome followed by intervention studies with exogenous proteins and neutralizing antibodies revealed hepatocyte growth factor (HGF) as the mediator of the pro-senescence impact of the cancer cells. The activity of cancerous CM and HGF was associated with an induction of mitochondrial oxidative stress. Signaling pathways involved in the senescence of HPMCs elicited by the cancer-derived CM and HGF included p38 MAPK, AKT and NF-κB. HPMCs that senesced prematurely in response to the cancer-derived CM promoted adhesion of ovarian cancer cells, however this effect was effectively prevented by the cell protection against oxidative stress. Collectively, our findings indicate that ovarian cancer cells can elicit HGF-dependent senescence in HPMCs, which may contribute to the formation of a metastatic niche for these cells within the peritoneal cavity.

Genetic Nrf2 Overactivation Inhibits the Deleterious Effects Induced by Hepatocyte-Specific c-met Deletion during the Progression of NASH

We have recently shown that hepatocyte-specific c-met deficiency accelerates the progression of nonalcoholic steatohepatitis in experimental murine models resulting in augmented production of reactive oxygen species and accelerated development of fibrosis. The aim of this study focuses on the elucidation of the underlying cellular mechanisms driven by Nrf2 overactivation in hepatocytes lacking c-met receptor characterized by a severe unbalance between pro-oxidant and antioxidant functions. Control mice (c-met^fx/fx), single c-met knockouts (c-met^Δhepa), and double c-met/Keap1 knockouts (met/Keap1^Δhepa) were then fed a chow or a methionine-choline-deficient (MCD) diet, respectively, for 4 weeks to reproduce the features of nonalcoholic steatohepatitis. Upon MCD feeding, met/Keap1^Δhepa mice displayed increased liver mass albeit decreased triglyceride accumulation. The marked increase of oxidative stress observed in c-met^Δhepa was restored in the double mutants as assessed by 4-HNE immunostaining and by the expression of genes responsible for the generation of free radicals. Moreover, double knockout mice presented a reduced amount of liver-infiltrating cells and the exacerbation of fibrosis progression observed in c-met^Δhepa livers was significantly inhibited in met/Keap1^Δhepa. Therefore, genetic activation of the antioxidant transcription factor Nrf2 improves liver damage and repair in hepatocyte-specific c-met-deficient mice mainly through restoring a balance in the cellular redox homeostasis.

Folate deficient tumor microenvironment promotes epithelial-to-mesenchymal transition and cancer stem-like phenotypes

Clinically, serum level of folate has been negatively correlated to the stage and progression of liver cancer. Nevertheless, the functional consequence of folate deficiency (FD) in malignancy has not been fully investigated. Human hepatocellular carcinoma (HCC) cells (as study model) and other cancer types such as lung and glioma were cultured under folate deficient (FD) and folate complete (FD) conditions. Molecular characterization including intracellular ROS/RNS (reactive oxygen/nitrogen species), viability, colony formation, cancer stem-like cell (CSC) phenotype analyses were performed. In vivo tumorigenesis under FD and FC conditions were also examined. FD induced a significant increase in ROS and RNS, suppressing proliferative ability but inducing metastatic potential. Mesenchymal markers such as Snail, ZEB2, and Vimentin were significantly up-regulated while E-cadherin down-regulated. Importantly, CSC markers such as Oct4, β-catenin, CD133 were induced while PRRX1 decreased under FD condition. Furthermore, FD-conditioned HCC cells showed a decreased miR-22 level, leading to the increased expression of its target genes including HDAC4, ZEB2 and Oct4. Finally, xenograft mouse model demonstrated that FD diet promoted tumorigenesis and metastasis as compared to their FC counterparts. Our data provides rationales for the consideration of folate supplement as a metastasis preventive measure.

Is the Canonical RAF/MEK/ERK Signaling Pathway a Therapeutic Target in SCLC?

The activity of the RAF/MEK/ERK signaling pathway is critical for the proliferation of normal and cancerous cells. Oncogenic mutations driving the development of lung adenocarcinoma often activate this signaling pathway. In contrast, pathway activity levels and their biological roles are not well established in small cell lung cancer (SCLC), a fast-growing neuroendocrine lung cancer subtype. Here we discuss the function of the RAF/MEK/ERK kinase pathway and the mechanisms leading to its activation in SCLC cells. In particular, we argue that activation of this pathway may be beneficial to the survival, proliferation, and spread of SCLC cells in response to multiple stimuli. We also consider evidence that high levels of RAF/MEK/ERK pathway activity may be detrimental to SCLC tumors, including in part by interfering with their neuroendocrine fate. On the basis of these observations, we examined when small molecules targeting kinases in the RAF/MEK/ERK pathway may be useful therapeutically in patients with SCLC, including in combination with other therapeutic agents.

Hepatocyte growth factor/c-met promotes proliferation, suppresses apoptosis, and improves matrix metabolism in rabbit nucleus pulposus cells in vitro

The etiology of intervertebral disc (IVD) degeneration is closely related to apoptosis and extracellular matrix degradation in nucleus pulposus (NP) cells. These defects in NP cells are induced by excessive external stressors such as reactive oxygen species (ROS) and inflammatory cytokines. Recently, hepatocyte growth factor (HGF) has been shown to repair damage in various diseases through anti-apoptotic and anti-inflammatory activity. In this study, we investigated the effects of HGF on NP cell abnormality caused by ROS and inflammatory cytokines by using primary NP cells isolated from rabbit IVD. HGF significantly enhanced the proliferation of NP cells. Apoptosis of NP cells induced by H2 O2 or TNF-α was significantly inhibited by HGF. Induction of mRNA expression of the inflammation mediators cyclooxygenase-2 and matrix metalloproteinase-3 and -9 by TNF-α was significantly suppressed by HGF treatment. Expression of c-Met, a specific receptor for HGF, was confirmed in NP cells and was increased by TNF-α, suggesting that inflammatory cytokines increase sensitivity to HGF. These findings demonstrate that activation of HGF/c-Met signaling suppresses damage caused by ROS and inflammation in NP cells through multiple pathways. We further suggest the clinical potential of HGF for counteracting IVD degradation involved in NP cell abnormalities.

Autism Linked to Increased Oncogene Mutations but Decreased Cancer Rate

Autism spectrum disorder (ASD) is one phenotypic aspect of many monogenic, hereditary cancer syndromes. Pleiotropic effects of cancer genes on the autism phenotype could lead to repurposing of oncology medications to treat this increasingly prevalent neurodevelopmental condition for which there is currently no treatment. To explore this hypothesis we sought to discover whether autistic patients more often have rare coding, single-nucleotide variants within tumor suppressor and oncogenes and whether autistic patients are more often diagnosed with neoplasms. Exome-sequencing data from the ARRA Autism Sequencing Collaboration was compared to that of a control cohort from the Exome Variant Server database revealing that rare, coding variants within oncogenes were enriched for in the ARRA ASD cohort (p<1.0 x 10(-8)). In contrast, variants were not significantly enriched in tumor suppressor genes. Phenotypically, children and adults with ASD exhibited a protective effect against cancer, with a frequency of 1.3% vs. 3.9% (p<0.001), but the protective effect decreased with age. The odds ratio of neoplasm for those with ASD relative to controls was 0.06 (95% CI: 0.02, 0.19; p<0.0001) in the 0 to 14 age group; 0.35 (95% CI: 0.14, 0.87; p = 0.024) in the 15 to 29 age group; 0.41 (95% CI: 0.15, 1.17; p = 0.095) in the 30 to 54 age group; and 0.49 (95% CI: 0.14, 1.74; p = 0.267) in those 55 and older. Both males and females demonstrated the protective effect. These findings suggest that defects in cellular proliferation, and potentially senescence, might influence both autism and neoplasm, and already approved drugs targeting oncogenic pathways might also have therapeutic value for treating autism.

Regulation of the MET oncogene: molecular mechanisms

The MET oncogene is a predictive biomarker and an attractive therapeutic target for various cancers. Its expression is regulated at multiple layers via various mechanisms. It is subject to epigenetic modifications, i.e. DNA methylation and histone acetylation. Hypomethylation and acetylation of the MET gene have been associated with its high expression in some cancers. Multiple transcription factors including Sp1 and Ets-1 govern its transcription. After its transcription, METmRNA is spliced into multiple species in the nucleus before being transported to the cytoplasm where its translation is modulated by at least 30 microRNAs and translation initiation factors, e.g. eIF4E and eIF4B. METmRNA produces a single chain pro-Met protein of 170 kDa which is cleaved into α and β chains. These two chains are bound together through disulfide bonds to form a heterodimer which undergoes either N-linked or O-linked glycosylation in the Golgi apparatus before it is properly localized in the membrane. Upon interactions with its ligand, i.e. hepatocyte growth factor (HGF), the activity of Met kinase is boosted through various phosphorylation mechanisms and the Met signal is relayed to downstream pathways. The phosphorylated Met is then internalized for subsequent degradation or recycle via proteasome, lysosome or endosome pathways. Moreover, the Met expression is subject to autoregulation and activation by other EGFRs and G-protein coupled receptors. Since deregulation of the MET gene leads to cancer and other pathological conditions, a better understanding of the MET regulation is critical for Met-targeted therapeutics.

Blocking c-Met-mediated PARP1 phosphorylation enhances anti-tumor effects of PARP inhibitors

Poly (ADP-ribose) polymerase (PARP) inhibitors have emerged as promising therapeutics for many diseases, including cancer, in clinical trials¹. One PARP inhibitor, olaparib (Lynparza^™, AstraZeneca), was recently approved by the FDA to treat ovarian cancer with BRCA mutations. BRCA1 and BRCA2 play essential roles in repairing DNA double strand breaks, and a deficiency of BRCA proteins sensitizes cancer cells to PARP inhibition^2,3. Here we show that receptor tyrosine kinase c-Met associates with and phosphorylates PARP1 at Tyr907. Phosphorylation of PARP1 Tyr907 increases PARP1 enzymatic activity and reduces binding to a PARP inhibitor, thereby rendering cancer cells resistant to PARP inhibition. Combining c-Met and PARP1 inhibitors synergized to suppress growth of breast cancer cells in vitro and xenograft tumor models. Similar synergistic effects were observed in a lung cancer xenograft tumor model. These results suggest that PARP1 pTyr907 abundance may predict tumor resistance to PARP inhibitors, and that treatment with a combination of c-Met and PARP inhibitors may benefit patients bearing tumors with high c-Met expression who do not respond to PARP inhibition alone.

Met inactivation by S-allylcysteine suppresses the migration and invasion of nasopharyngeal cancer cells induced by hepatocyte growth factor

Purpose

Past studies have reported that S-allylcysteine (SAC) inhibits the migration and invasion of cancer cells through the restoration of E-cadherin, the reduction of matrix metalloproteinase (MMP) and Slug protein expression, and inhibition of the production of reactive oxygen species (ROS). Furthermore, evidence is emerging that shows that ROS induced by radiation could increase Met activation. Following on these reports of SAC and Met, we investigated whether SAC could suppress Met activation.

Materials and Methods

Wound healing, invasion, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium (MTT), soft agar colony forming, western blotting, and gelatin zymography assays were performed in the human nasopharyngeal cancer cell lines HNE1 and HONE1 treated with SAC (0, 10, 20, or 40 mM) and hepatocyte growth factor (HGF).

Results

This study showed that SAC could suppress the migration and invasion of HNE1 and HONE1 cell lines by inhibiting p-Met. An increase of migration and invasion induced by HGF and its decrease in a dose dependent manner by SAC in wound healing and invasion assays was observed. The reduction of p-Met by SAC was positively correlated with p-focal adhesion kinase (p-FAK) and p-extracellular related kinase (p-ERK in both cell lines). SAC reduced Slug, MMP2, and MMP9 involved in migration and invasion with the inhibition of Met-FAK signaling.

Conclusion

These results suggest that SAC inhibited not only Met activation but also the downstream FAK, Slug, and MMP expression. Finally, SAC may be a potent anticancer compound for nasopharyngeal cancer treated with radiotherapy.

Cancer Associated Fibroblast-Derived Hepatocyte Growth Factor Inhibits the Paclitaxel-Induced Apoptosis of Lung Cancer A549 Cells by Up-Regulating the PI3K/Akt and GRP78 Signaling on a Microfluidic Platform

Tumor stroma and growth factors provide a survival environment to tumor cells and can modulate their chemoresistance by dysregulating several signal pathways. In this study, we fabricated a three-dimensional (3D) microfluidic chip using polydimethylsiloxane (PDMS) to investigate the impact of hepatocyte growth factor (HGF) from cancer-associated fibroblasts (CAF) on the Met/PI3K/AKT activation, glucose regulatory protein (GRP78) expression and the paclitaxel-induced A549 cell apoptosis. With a concentration gradient generator, the assembled chip was able to reconstruct a tumor microenvironment in vitro. We found high levels of HGF in the supernatants of CAF and the CAF matrix from the supernatants of activated HFL1 fibroblasts or HGF enhanced the levels of Met, PI3K and AKT phosphorylation and GRP78 expression in A549 cells cultured in a 3D cell chamber, which was abrogated by anti-HGF. Inhibition of Met attenuated the CAF matrix-enhanced PI3K/AKT phosphorylation and GRP78 expression while inhibition of PI3K reduced GRP78 expression, but not Met phosphorylation in A549 cells. Inhibition of GRP78 failed to modulate the CAF matrix-enhanced Met/PI3K/AKT phosphorylation in A549 cells. Furthermore, inhibition of PI3K or GRP78 enhanced spontaneous and paclitaxel-induced A549 cell apoptosis. Moreover, treatment with the CAF matrix inhibited spontaneous and medium or high dose of paclitaxel-induced A549 cell apoptosis. Inhibition of PI3K or GRP78 attenuated the CAF matrix-mediated inhibition on paclitaxel-induced A549 cell apoptosis. Our data indicated that HGF in the CAF matrix activated the Met/PI3K/AKT and up-regulated GRP78 expression, promoting chemoresistance to paclitaxel-mediated apoptosis in A549 cells. Our findings suggest that the microfluidic system may represent an ideal platform for signaling research and drug screening.

Retrospective Review of MET Gene Mutations

C-MET proto-oncogene is a tyrosine kinase situated on chromosome 7. C-MET and its ligand hepatocyte growth factor/scatter factor (HGF/SF) play a role in proliferation, differentiation and organ development. C-MET genetic aberrations are found associated with driving tumorigenesis. In this retrospective study, we reviewed molecular analysis data gathered from a cancer institute during a two-year period (2010-2012). Upon detection of tumors harboring c-MET mutations, we determined the status of the other mutations tested and evaluated c-MET expression by fluorescent in-situ hybridization (FISH). Our search resulted in identification of 134 c-MET mutations, 44% of which had mutations of at least one of the other genes tested. No c-MET expression aberrancy was detected in this subset by FISH. Survival amongst the patients with surgically resected metastatic colorectal cancers (CRC) was slightly better in those with only a c-MET mutation compared to those with no mutation detected, although the difference was not statistically significant. When c-MET inhibition becomes an integrated part of chemotherapy practice, our observed frequency of co-mutations will be an argument for utilizing c-MET targeted treatment in combination with other targeted drugs and therapeutic strategies. Larger studies can aid to further parse out c-MET prognostic and therapeutic significance.

cMET in NSCLC: Can We Cut off the Head of the Hydra? From the Pathway to the Resistance

In the last decade, the tyrosine kinase receptor cMET, together with its ligand hepatocyte growth factor (HGF), has become a target in non-small cell lung cancer (NSCLC). Signalization via cMET stimulates several oncological processes amongst which are cell motility, invasion and metastasis. It also confers resistance against several currently used targeted therapies, e.g., epidermal growth factor receptor (EGFR) inhibitors. In this review, we will discuss the basic structure of cMET and the most important signaling pathways. We will also look into aberrations in the signaling and the effects thereof in cancer growth, with the focus on NSCLC. Finally, we will discuss the role of cMET as resistance mechanism.

Improved survival of mesenchymal stem cells by macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a critical inflammatory cytokine that was recently associated with progenitor cell survival and potently inhibits apoptosis. We examined the protective effect of MIF on hypoxia/serum deprivation (SD)-induced apoptosis of mesenchymal stem cells (MSCs), as well as the possible mechanisms. MSCs were obtained from rat bone marrow and cultured in vitro. Apoptosis was induced by culturing MSCs under hypoxia/SD conditions for up to 24 h and assessed by flow cytometry. Expression levels of c-Met, Akt, and FOXO3a were detected by Western blotting. CD74 expression was detected by qRT-PCR, Western blot, and immunofluorescence. Oxidative stress under hypoxia/SD was examined by detection of reactive oxygen species (ROS) and activity of superoxide dismutase (SOD) and malondialdehyde (MDA). Hypoxia/SD-induced apoptosis was significantly attenuated by recombinant rat MIF in a concentration-dependent manner. MIF induced CD74-asssociated c-Met activation, which was blocked by knocking down CD74 expression using siRNA. MIF also induced Akt and associated FOXO3a phosphorylation, and this effect was abolished by knocking down either CD74 or Akt. In addition, MIF decreased oxidative stress in MSCs, as shown by decreased ROS and MDA, and increased the activity of SOD. Knockdown of CD74, Akt, or FOXO3a largely attenuated the anti-apoptotic effect of MIF and its ability to protect against oxidative stress. MIF protected MSCs from hypoxia/SD-induced apoptosis by interacting with CD74 to stimulate c-Met, leading to downstream PI3K/Akt-FOXO3a signaling and decreased oxidative stress.

A new hope for precision medicine

The SS1P immunotoxin is combined with immunomodulatory therapy in order to improve its efficacy in human mesothelioma (Hassan et al., this issue).

Role of c-Met/phosphatidylinositol 3-kinase (PI3k)/Akt signaling in hepatocyte growth factor (HGF)-mediated lamellipodia formation, reactive oxygen species (ROS) generation, and motility of lung endothelial cells

Hepatocyte growth factor (HGF) mediated signaling promotes cell proliferation and migration in a variety of cell types and plays a key role in tumorigenesis. As cell migration is important to angiogenesis, we characterized HGF-mediated effects on the formation of lamellipodia, a pre-requisite for migration using human lung microvascular endothelial cells (HLMVECs). HGF, in a dose-dependent manner, induced c-Met phosphorylation (Tyr-1234/1235, Tyr-1349, Ser-985, Tyr-1003, and Tyr-1313), activation of PI3k (phospho-Yp85) and Akt (phospho-Thr-308 and phospho-Ser-473) and potentiated lamellipodia formation and HLMVEC migration. Inhibition of c-Met kinase by SU11274 significantly attenuated c-Met, PI3k, and Akt phosphorylation, suppressed lamellipodia formation and endothelial cell migration. LY294002, an inhibitor of PI3k, abolished HGF-induced PI3k (Tyr-458), and Akt (Thr-308 and Ser-473) phosphorylation and suppressed lamellipodia formation. Furthermore, HGF stimulated p47(phox)/Cortactin/Rac1 translocation to lamellipodia and ROS generation. Moreover, inhibition of c-Met/PI3k/Akt signaling axis and NADPH oxidase attenuated HGF- induced lamellipodia formation, ROS generation and cell migration. Ex vivo experiments with mouse aortic rings revealed a role for c-Met signaling in HGF-induced sprouting and lamellipodia formation. Taken together, these data provide evidence in support of a significant role for HGF-induced c-Met/PI3k/Akt signaling and NADPH oxidase activation in lamellipodia formation and motility of lung endothelial cells.

Genetic Interactions of STAT3 and Anticancer Drug Development

Signal transducer and activator of transcription 3 (STAT3) plays critical roles in tumorigenesis and malignant evolution and has been intensively studied as a therapeutic target for cancer. A number of STAT3 inhibitors have been evaluated for their antitumor activity in vitro and in vivo in experimental tumor models and several approved therapeutic agents have been reported to function as STAT3 inhibitors. Nevertheless, most STAT3 inhibitors have yet to be translated to clinical evaluation for cancer treatment, presumably because of pharmacokinetic, efficacy, and safety issues. In fact, a major cause of failure of anticancer drug development is lack of efficacy. Genetic interactions among various cancer-related pathways often provide redundant input from parallel and/or cooperative pathways that drives and maintains survival environments for cancer cells, leading to low efficacy of single-target agents. Exploiting genetic interactions of STAT3 with other cancer-related pathways may provide molecular insight into mechanisms of cancer resistance to pathway-targeted therapies and strategies for development of more effective anticancer agents and treatment regimens. This review focuses on functional regulation of STAT3 activity; possible interactions of the STAT3, RAS, epidermal growth factor receptor, and reduction-oxidation pathways; and molecular mechanisms that modulate therapeutic efficacies of STAT3 inhibitors.

The role of reactive oxygen species and metabolism on cancer cells and their microenvironment

Compelling evidence show that reactive oxygen species (ROS) levels are finely regulated in the cell and can act as "second messengers" in response to diverse stimuli. In tumor epithelial cells, ROS accumulate abnormally and induce signaling cascades that mediate the oncogenic phenotype. In addition to their impact on tumor epithelial cells, ROS also affect the surrounding cells that constitute the tumor microenvironment. Indeed, ROS production increases tumor angiogenesis, drives the onset of inflammation and promotes conversion of fibroblast into myofibroblasts. These cells, initially identified upon wound healing, exhibit similar properties to those observed in fibroblasts associated with aggressive adenocarcinomas. Indeed, analyses of tumors with distinct severity revealed the existence of multiple distinct co-existing subtypes of carcinoma-associated fibroblasts (CAFs), with specific marker protein profiling. Chronic oxidative stress deeply modifies the proportion of these different fibroblast subtypes, further supporting tumor growth and metastatic dissemination. At last, ROS have been implicated in the metabolic reprogramming of both cancer cells and CAFs, allowing an adaptation to oxidative stress that ultimately promotes tumorigenesis and chemoresistance. In this review, we discuss the role of ROS in cancer cells and CAFs and their impact on tumor initiation, progression, and metastasis.

MET and EGFR mutations identified in ALK-rearranged pulmonary adenocarcinoma: molecular analysis of 25 ALK-positive cases

INTRODUCTION

Oncogenic ALK kinase activity associated with ALK gene rearrangement is the target of crizotinib, an ALK inhibitor recently approved by the Food and Drug Administration for the treatment of ALK-rearranged (ALK+) non-small cell lung cancers. ALK+ status is generally thought to be mutually exclusive of epidermal growth factor receptor (EGFR) and KRAS mutations. However, the mutation status of other genes is not widely known in ALK+ tumors. The aim of this study is to survey for mutations involving other genes in 25 ALK+ cases confirmed by fluorescent in situ hybridization.

METHODS

Using the DNA extracted from formalin-fixed paraffin-embedded tumor samples, a MassArray-based Lung Cancer Mutations Screening Panel was performed to test for 179 individual mutations in 10 genes, including EGFR, KRAS, BRAF, ERBB2, JAK2, AKT1, AKT2, KIT, MET and PIK3CA, which have been implicated in lung carcinogenesis and/or considered as potential therapeutic targets.

RESULTS

Five of 25 ALK+ cases showed additional genetic abnormalities, which were verified by gene sequencing. One patient had EGFR del L747-S752. The remaining four mutations were in the MET gene: MET N375S (n = 2) and MET R988C (n = 2). No MET amplification was found by fluorescent in situ hybridization in the four cases with MET mutation. No mutations were detected in the other genes tested.

CONCLUSIONS

In summary, additional mutations were found in 20% of ALK+ cases involving two of the 10 genes tested. Our study highlights that EGFR mutation can be present in ALK+ tumors, though uncommon. Clinical implication of MET mutation in our cases is uncertain and further study is needed.

The role of the c-Met pathway in lung cancer and the potential for targeted therapy

Hepatocyte growth factor receptor (HGFR), the product of the MET gene, plays an important role in normal cellular function and oncogenesis. In cancer, HGFR has been implicated in cellular proliferation, cell survival, invasion, cell motility, metastasis and angiogenesis. Activation of HGFR can occur through binding to its ligand, hepatocyte growth factor (HGF), overexpression/amplification, mutation, and/or decreased degradation. Amplification of HGFR can occur de novo or in resistance to therapy. Mutations of HGFR have been described in the tyrosine kinase domain, juxtamembrane domain, or semaphorin domain in a number of tumors. These mutations appear to have gain of function, and also reflect differential sensitivity to therapeutic inhibition. There have been various drugs developed to target HGFR, including antibodies to HGFR/HGF, small-molecule inhibitors against the tyrosine kinase domain of HGFR and downstream targets. Different HGFR inhibitors are currently in clinical trials in lung cancer and a number of solid tumors. Several phase I trials have already been completed, and two specific trials have been reported combining HGFR with epidermal growth factor receptor (EGFR) inhibition in non-small cell lung cancer. In particular, trials involving MetMAb and ARQ197 (tivantinib) have gained interest. Ultimately, as individualized therapies become a reality for cancers, HGFR will be an important molecular target.

MET phosphorylation predicts poor outcome in small cell lung carcinoma and its inhibition blocks HGF-induced effects in MET mutant cell lines

Background:

Small cell lung carcinoma (SCLC) has poor prognosis and remains orphan from targeted therapy. MET is activated in several tumour types and may be a promising therapeutic target.

Methods:

To evaluate the role of MET in SCLC, MET gene status and protein expression were evaluated in a panel of SCLC cell lines. The MET inhibitor PHA-665752 was used to study effects of pathway inhibition in basal and hepatocyte growth factor (HGF)-stimulated conditions. Immunohistochemistry for MET and p-MET was performed in human SCLC samples and association with outcome was assessed.

Results:

In MET mutant SCLC cells, HGF induced MET phosphorylation, increased proliferation, invasiveness and clonogenic growth. PHA-665752 blocked MET phosphorylation and counteracted HGF-induced effects. In clinical samples, total MET and p-MET overexpression were detected in 54% and 43% SCLC tumours (n=77), respectively. MET phosphorylation was associated with poor median overall survival (132 days) vs p-MET negative cases (287 days)(P<0.001). Phospho-MET retained its prognostic value in a multivariate analysis.

Conclusions:

MET activation resulted in a more aggressive phenotype in MET mutant SCLC cells and its inhibition by PHA-665752 reversed this phenotype. In patients with SCLC, MET activation was associated with worse prognosis, suggesting a role in the adverse clinical behaviour in this disease.

Molecular profiles of EGFR, K-ras, c-met, and FGFR in pulmonary pleomorphic carcinoma, a rare lung malignancy

BACKGROUND

Pulmonary pleomorphic carcinoma (PPC) is a rare type of lung cancer characterized by the poor response to conventional chemotherapy and subsequent disappointing outcomes. Therefore, it is paramount to delineate the molecular characteristics of this disease entity.

METHODS

In this study, we retrospectively examined the surgical specimens of 61 patients who underwent lung surgery. Mutational or gene amplification statuses of epidermal growth factor receptor (EGFR), k-ras, c-kit, c-met, and fibroblast growth factor receptor (FGFR) were examined using genomic DNA sequencing, real-time PCR and/or fluorescence in situ hybridization (FISH).

RESULTS

The median age was 61 years, and 50 patients were men and 11 were women. In the histologic review of epithelial component, adenocarcinoma were in 44 cases (72%), squamous cell carcinoma in 15 (25%) and large cell carcinoma in 2 patients (3%). Overall, 30 cases (49%) had any molecular alterations. Nine patients (15%) possessed EGFR deletion in exon 19 (n = 8) or L858R mutations in exon 21 (n = 1), while 3 other cases having atypical EGFR mutations. Six patients (9.8%) had k-ras mutations in exon 12, and 3 had c-kit mutations. High gene copy number of c-met was found in 11 patients (18.0%) and that of FGFR was in 6 patients (9.8%). No significant relationships were identified among the occurrence and type of mutations and patient survival or any other clinicopathological variables.

CONCLUSIONS

Given the diverse repertoire of mutational profiles observed in PPC samples, clinical trials based on accurate cancer-genotyping should be considered as a legitimate treatment scheme for this rare disease entity in the future.

Cooperative signaling for angiogenesis and neovascularization by VEGF and HGF following islet transplantation

BACKGROUND

Delayed angiogenesis remains a significant challenge to the survival of transplanted islets. In this study, using a murine model of subcutaneous islet transplantation with matrigel basement membrane matrix, we determined the role of the proangiogenic growth factors in enhancing the islet engraftment.

METHODS

BALB/c islets were transplanted subcutaneously in growth factor reduced (GFR) or growth factor supplemented (GFS) matrigel into diabetic severe combined immunodeficient mice. GFS matrigel was prepared by supplementing GFR with proangiogenic factors, vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF). The functioning grafts were harvested at 15 days and vessel formation was analyzed histopathologically.

RESULTS

Our results demonstrate that suboptimal (250) islet equivalents in GFS-VEGF+HGF were able to restore normoglycemia, whereas those transplanted in GFR failed to reverse diabetes. Histopathology of the GFS-VEGF+HGF graft revealed 12±3 blood vessels per field, whereas GFR, GFS-VEGF, and GFS-HGF grafts had only 3±1, 6±2, and 4±1 blood vessels, respectively. Insulin staining demonstrated increased number of islets in matrigel supplemented with VEGF and HGF. Protein and mRNA analysis demonstrated enhanced intercellular adhesion molecule and vascular cell adhesion molecule within the islets when supplemented with both VEGF+HGF suggesting stable blood vessel formation. Transcription factors focal adhesion kinase phosphorylation and extracellular signal-regulated kinase1/2 phosphorylation were also increased (8-fold and 4.6-fold, respectively) when both the growth factors were present. There was weak expression of transcription factors when VEGF or HGF were supplemented alone.

CONCLUSION

We conclude that proangiogenic growth factors, VEGF and HGF, synergistically enhance angiogenesis after islet transplantation leading to stable engraftment.

Metastasis: cancer cell's escape from oxidative stress

According to a "canonical" view, reactive oxygen species (ROS) positively contribute, in different ways, to carcinogenesis and to malignant progression of tumor cells: they drive genomic damage and genetic instability, transduce, as signaling intermediates, mitogenic and survival inputs by growth factor receptors and adhesion molecules, promote cell motility and shape the tumor microenvironment by inducing inflammation/repair and angiogenesis. Chemopreventive and tumor-inhibitory effects of endogenous, diet-derived or supplemented antioxidants largely support this notion. However, emerging lines of evidence indicates that tumor cells also need to defend themselves from oxidative damage in order to survive and successfully spread at distance. This "heresy" has recently received important impulse from studies on the role of antioxidant capacity in cancer stem cells self-renewal and resistance to therapy; additionally, the transforming activity of some oncogenes has been unexpectedly linked to their capacity to maintain elevated intracellular levels of reduced glutathione (GSH), the principal redox buffer. These studies underline the importance of cellular antioxidant capacity in metastasis, as the result of a complex cell program involving enhanced motility and a profound change in energy metabolism. The glycolytic switch (Warburg effect) observed in malignant tissues is triggered by mitochondrial oxidative damage and/or activation of redox-sensitive transcription factors, and results in an increase of cell resistance to oxidants. On the other hand, cytoskeleton rearrangement underlying cell motile and tumor-aggressive behavior use ROS as intermediates and are therefore facilitated by oxidative stress. Along this line of speculation, we suggest that metastasis represents an integrated strategy for cancer cells to avoid oxidative damage and escape excess ROS in the primary tumor site, explaning why redox signaling pathways are often up-regulated in malignancy and metastasis.

The MET axis as a therapeutic target

The MET receptor tyrosine kinase and its ligand hepatocyte growth factor (HGF) have been implicated in transformation of a variety of malignancies. Chronic or dysregulated activation of the MET/HGF pathway may lead to increased cell growth, invasion, angiogenesis, and metastasis, reduced apoptosis, altered cytoskeletal functions and other biological changes. It has been suggested that ligand activated MET stimulation can be sufficient for a transforming phenotype. In addition, amplification and activation mutations (germline and/or somatic) within the tyrosine kinase domain, juxtamembrane domain, or semaphorin domain have been identified for MET. MET gain-of-function mutations lead to either deregulated or prolonged tyrosine kinase activity, which are instrumental to its transforming activity. A number of therapeutic strategies targeting ligand-dependent activation or the kinase domain have been employed to inhibit MET. The different structural requirements for activation of signaling events and biological functions regulated by MET will be summarized. Therapeutic targets and current pre-clinical and clinical approaches will be described. Targeting the HGF/MET pathway, alone or in combination with standard therapies, is likely to improve present therapies in MET-dependent malignancies.

Role of c-Met in cancer: emphasis on lung cancer

Lung cancer remains the leading cause of cancer death. It is often diagnosed at late stages and is treated systemically with cytotoxic chemotherapy, which is generally ineffective. Research efforts have focused on developing therapies targeted to growth factor receptor pathways, such as epidermal growth factor receptor (EGFR), but the results from clinical trials overall show very small improvements in survival. Research on signaling pathways dysregulated in lung cancer is ongoing, including investigation of the hepatocyte growth factor receptor (HGFR) or c-Met. Protein tyrosine kinases, such as EGFR and c-Met, are a family of oncogenes that regulate important cellular processes, such as differentiation, proliferation, cell cycle, motility, and apoptosis. Hepatocyte growth factor (HGF), a ligand for c-Met, is secreted by mesodermal cells during development. It produces multiple effects upon binding to its receptor (HGFR/c-Met) and regulates proliferation, motility, mitogenesis, and morphogenesis. Studies in cell lines isolated from various tumors show that several intracellular pathways participate in c-Met signaling, including growth factor receptor-bound protein 2 (Grb2), mitogen-activated protein (MAP) kinase, phosphoinositol 3-kinase (PI3K), and phospholipase C-gamma (PLC-gamma). c-Met is overexpressed in many tumors. However, overexpression may not be sufficient to cause increased activity; the receptor needs to be activated. In some cases, the kinases are constitutively active due to mutations in the gene. The cytoskeletal protein paxillin also appears to be activated along with c-Met. Correlative studies from patient tissue samples and cell lines have rendered the same information, indicating that the signaling pathways dysregulated are complex and interdependent. Mutations in human c-Met have been exogenously expressed in Caenorhabditis elegans, which can serve as a model for determining the role of gene mutations in a whole organism. Several inhibitors of c-Met/HGF binding are in development, including some in phase I trials. Their effectiveness in improving cancer outcomes will be determined in the near future.

PAX5 is expressed in small-cell lung cancer and positively regulates c-Met transcription

PAX5 is a nuclear transcription factor required for B cell development, and its expression was evaluated in upper aerodigestive malignancies and pancreatic cancer by immunoblotting. The PAX5 protein expression was relatively strong in small-cell lung cancer (SCLC, 11/12); however, its expression was not detected in non-SCLC (NSCLC, n=13), mesothelioma (n=7), pancreatic (n=6), esophageal (n=6) and head and neck cancer cell lines (n=12). In comparison, PAX8 and PAX3 expressions were absent or non-detectable in SCLC cell lines; however, PAX8 was expressed in most of the tested NSCLC cell lines (13/13) and also frequently in all the other cell lines. We also detected frequent expressions of PAX2 and PAX9 protein in the various cell lines. Utilizing neuroendocrine tumor samples, we found that the frequency as well as the average intensity of the expression of PAX5 increased from pulmonary carcinoid (9%, moderate and strong PAX5 expression, n=44), to large-cell neuroendocrine carcinoma (LCNC, 27%, n=11) to SCLC (33%, n=76). FISH analysis revealed no translocations of the PAX5 gene, but polyploidy in some SCLC tumor tissues (6/37). We determined that PAX5 could regulate the transcription of c-Met using luciferase-coupled reporter and chromatin immunoprecipitation analysis. In addition, the phospho-c-Met (active form) and PAX5 were both localized to the same intra-nuclear compartment in hepatocyte growth factor treated SCLC cells and interacted with each other. Finally, we determined the therapeutic translational potential of PAX5 using PAX5 knockdown SCLC cells in conjunction with Topoisomerase 1 (SN38) and c-Met (SU11274) inhibitors. Loss of endogenous PAX5 significantly decreased the viability of SCLC cells, especially when combined with SN38 or SU11274, and maximum effect was seen when both inhibitors were used. Therefore, we propose that PAX5 could be an important regulator of c-Met transcription and a potential target for therapy in SCLC.

YC-1 induces heat shock protein 70 expression and prevents oxidized LDL-mediated apoptosis in vascular smooth muscle cells

Heat shock protein 70 (hsp70) functioning as molecular chaperon in physiological conditions is induced under stress environment, which affords a defensive mechanism for cells to escape cellular damage. Hence, it is a critical issue to develop a nontoxic hsp70-inducing compound against cellular death. The present study was conducted to evaluate whether 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl-indazol (YC-1) can effectively induce hsp70 expression and protect vascular smooth muscle cells (VSMCs) against oxidized low-density lipoprotein-induced cytotoxicity. We showed that YC-1 enhanced hsp70 expression in VSMCs through a concentration- and time-dependent manner with maximum expression at 18 and 24 h without involving the cyclic guanosine monophosphate and reactive oxygen species signal in the pathway. Furthermore, we did not observe significant cytotoxicity after YC-1 treatment through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, lactic dehydrogenase, and fluorescence activating cell sorting scan assays. We demonstrated that the nuclear level of heat shock transcription factor 1 increased at 2 h after YC-1 treatment, and hsp70 expression was directed by the up-regulation of hsp70 mRNA, which peaked at 6 h and was followed by a decline. Hence, translocation of heat shock transcription factor 1 and increased level of hsp70 mRNA would account for Hsp70 expression. Finally, we found that YC-1 protects VSMCs from oxidized low-density lipoprotein-inducing apoptosis. According to our observations, YC-1 would be an effectively pharmacological hsp70 inducer that can be used as a cytoprotective agent in vascular diseases.

Flavonoids as RTK inhibitors and potential anticancer agents

Tyrosine kinase receptors (RTKs) play a crucial role in the regulation of the cell division cycle. Currently more than 50 RTKs divided into several subfamilies have been described. The inhibition of these enzymes has emerged as an important research-area. Compounds able to inhibit the activity of these enzymes are expected to display antiproliferative properties. Flavonoids are representative of various small molecules acting as RTK inhibitors. These naturally occurring compounds are able to bind to the ATP-binding site of several kinases. The most plausible current hypothesis explaining the action of these substances on kinases is that the chromenone moiety of the flavonoid acts as a mimetic of the adenine moiety of ATP, the receptor co-factor. In this review, we report recent results on the activity of natural and synthetic derivatives of flavonoids as inhibitors of RTKs. Mechanistic aspects, the therapeutic usefulness, and the potential clinical use are discussed.

Hepatocyte growth factor improves viability after H2O2-induced toxicity in bile duct epithelial cells

Intracellular defence mechanisms against oxidative stress may play an important role in the progression of liver diseases, including cholangiopathies. The multifunctional anti-apoptotic hepatocyte growth factor (HGF) has been suggested to have antioxidant functions. The effect of HGF upon cell viability, the generation of ROS, the expression of genes that play a role in ROS defence, and the activation of caspase-3 were measured in bile duct epithelial (BDE) cells in the presence or absence of H(2)O(2). HGF reduced H(2)O(2)-induced loss of viability, diminished H(2)O(2)-mediated ROS generation and abrogated H(2)O(2)-triggered changes in GSH/GSSG ratio. Furthermore, HGF increased the gene-expression of gamma-glutamylcysteine synthetase (GCLC) and glutathione reductase (GSR), while no effect was seen upon the gene-expression of superoxide dismutase 1 (SOD1), catalase (CAT), glutathione peroxidase (GPX1), and glutathione synthetase (GSR). Finally, HGF diminished the proteolytical activation of the key mediator of apoptosis (caspase-3) after H(2)O(2) exposure. Together, HGF may improve viability in bile duct epithelia cells after H(2)O(2) induced toxicity by proliferation, strengthening the intrinsic antioxidant defences, and/or by an attenuation of apoptosis. These in vitro results support the evaluation of HGF as antioxidative factor in hepatobiliary pathologies.

Paxillin is a target for somatic mutations in lung cancer: implications for cell growth and invasion

Lung cancer is characterized by abnormal cell growth and invasion, and the actin cytoskeleton plays a major role in these processes. The focal adhesion protein paxillin is a target of a number of oncogenes involved in key signal transduction and important in cell motility and migration. In lung cancer tissues, we have found that paxillin was highly expressed (compared with normal lung), amplified (12.1%, 8 of 66) and correlated with increased MET and epidermal growth factor receptor (EGFR) gene copy numbers, or mutated (somatic mutation rate of 9.4%, 18 of 191). Paxillin mutations (19 of 21) were clustered between LD motifs 1 and 2 and the LIM domains. The most frequent point mutation (A127T) enhanced lung cancer cell growth, colony formation, focal adhesion formation, and colocalized with Bcl-2 in vitro. Gene silencing from RNA interference of mutant paxillin led to reduction of cell viability. A murine in vivo xenograft model of A127T paxillin showed an increase in tumor growth, cell proliferation, and invasion. These results establish an important role for paxillin in lung cancer.