Signaling networks assembled by oncogenic EGFR and c-Met. Proc Natl Acad Sci U S A. 2008;105:692-697. [PMID: 18180459 DOI: 10.1073/pnas.0707270105]

Anti-tumor activity of WK88-1, a novel geldanamycin derivative, in gefitinib-resistant non-small cell lung cancers with Met amplification

Although epidermal growth factor receptor-tyrosine kinase inhibitors (EGFR-TKIs) have been introduced for the treatment of non-small cell lung cancer (NSCLC), the emergence of secondary T790M mutation in EGFR or amplification of the Met proto-oncogene restrain the clinical success of EGFR-TKIs. Since heat shock protein-90 (Hsp90) stabilizes various oncoproteins including EGFR and c-Met, the inhibition of Hsp90 activity appears as a rational strategy to develop anticancer drugs. Despite preclinical efficacy of geldanamycin-anasamycin (GA)-derivatives containing benzoquinone moiety as Hsp90 inhibitors, the hepatotoxicity of these GA-derivatives restricts their therapeutic benefit. We have prepared WK-88 series of GA-derivatives, which lack the benzoquinone moiety. In this study, we have examined the anticancer effects of WK88-1 in Met-amplified- and gefitinib-resistant (HCC827GR) NSCLC cells and its parental HCC827 cells. Treatment with WK88-1 reduced the cell viability in both HCC827 and HCC827GR cells, which was associated with marked decrease in the constitutive expression of Hsp90 client proteins, such as EGFR, ErbB2, ErbB3, Met and Akt. Moreover, WK88-1 attenuated phosphorylation of these Hsp90 client proteins and reduced the anchorage-independent growth of HCC827GR cells. Administration of WK88-1 did not cause hepatotoxicity in animals and significantly reduced the growth of HCC827GR cells xenograft tumors in nude mice. Our study provides evidence that ErbB3 might be a client for Hsp90 in Met-amplified NSCLCs. In conclusion, we demonstrate that inhibition of Hsp90 dampens the activation of EGFR- or c-Met-mediated survival of Met-amplified NSCLCs and that WK88-1 as a Hsp90 inhibitor alleviates gefitinib resistance in HCC827GR cells.

TGFβ can stimulate the p(38)/β-catenin/PPARγ signaling pathway to promote the EMT, invasion and migration of non-small cell lung cancer (H460 cells)

Signaling pathway(s) responsible for transforming growth factor β (TGFβ)-induced epithelial mesenchymal transition (EMT), invasion and migration of H460 cells (non-small cell lung cancer/NSCLC) was identified in the study. The results showed that TGFβ-induced p(38)/β-catenin/PPARγ signaling pathway played a critical role in the promotion of EMT, invasion and migration of H460 cells. All these pathological outcomes attributed to PPARγ-increased expression of p-EGFR, p-c-MET and Vimentin and the decrease of E-cadherin. Transforming growth factor β and p(38)-induced β-catenin not only stimulated the expression of PPARγ but also physically interacted with it. Blocking the ligand binding domain of PPARγ (with GW9662) could significantly interfere the binding between PPARγ and β-catenin, and interrupt the nuclear infiltration of both factors. These findings suggested that β-catenin was an upstream regulator and a ligand of PPARγ, and the binding between these two molecules was critical for their nuclear infiltration. Transforming growth factor β-induced tumor invasion and migration was also seen in U373 cells (brain glioma, with high inducible PPARγ) in a PPARγ-dependent manner, but not in CH27 cells (squamous NSCLC, with low PPARγ). PPARγ shRNA, GW9662, JW67 and 2,4-diaminoquinazoline were all revealed to have important values in the control of the intrinsic and TGFβ-induced EMT, tumor invasion and migration of H460 cells. The results further suggested that PPARγ and β-catenin may be the potential markers for the early diagnosis and/or treatment of metastatic tumors.

A secreted tyrosine kinase acts in the extracellular environment

Although tyrosine phosphorylation of extracellular proteins has been reported to occur extensively in vivo, no secreted protein tyrosine kinase has been identified. As a result, investigation of the potential role of extracellular tyrosine phosphorylation in physiological and pathological tissue regulation has not been possible. Here, we show that VLK, a putative protein kinase previously shown to be essential in embryonic development, is a secreted protein kinase, with preference for tyrosine, that phosphorylates a broad range of secreted and ER-resident substrate proteins. We find that VLK is rapidly and quantitatively secreted from platelets in response to stimuli and can tyrosine phosphorylate coreleased proteins utilizing endogenous as well as exogenous ATP sources. We propose that discovery of VLK activity provides an explanation for the extensive and conserved pattern of extracellular tyrosine phosphophorylation seen in vivo, and extends the importance of regulated tyrosine phosphorylation into the extracellular environment.

Translational pharmacokinetic-pharmacodynamic modeling for an orally available novel inhibitor of anaplastic lymphoma kinase and c-Ros oncogene 1

An orally available macrocyclic small molecule, PF06463922 [(10R)-7-amino-12-fluoro-2,10,16-trimethyl-15-oxo-10,15,16,17-tetrahydro-2H-8,4-(metheno)pyrazolo[4,3-h][2,5,11]benzoxadiazacyclotetradecine-3-carbonitrile], is a selective inhibitor of anaplastic lymphoma kinase (ALK) and c-Ros oncogene 1 (ROS1). The objectives of the present study were to characterize the pharmacokinetic-pharmacodynamic relationships of PF06463922 between its systemic exposures, pharmacodynamic biomarker (target modulation), and pharmacologic response (antitumor efficacy) in athymic mice implanted with H3122 non-small cell lung carcinomas expressing echinoderm microtubule-associated protein-like 4 (EML4)-ALK mutation (EML4-ALK(L1196M)) and with NIH3T3 cells expressing CD74-ROS1. In these nonclinical tumor models, PF06463922 was orally administered to animals with EML4-ALK(L1196M) and CD74-ROS1 at twice daily doses of 0.3-20 and 0.01-3 mg/kg per dose, respectively. Plasma concentration-time profiles of PF06463922 were adequately described by a one-compartment pharmacokinetic model. Using the model-simulated plasma concentrations, a pharmacodynamic indirect response model with a modulator sufficiently fit the time courses of target modulation (i.e., ALK phosphorylation) in tumors of EML4-ALK(L1196M)-driven models with EC50,in vivo of 36 nM free. A drug-disease model based on an indirect response model reasonably fit individual tumor growth curves in both EML4-ALK(L1196M)- and CD74-ROS1-driven models with the estimated tumor stasis concentrations of 51 and 6.2 nM free, respectively. Thus, the EC60,in vivo (52 nM free) for ALK inhibition roughly corresponded to the tumor stasis concentration in an EML4-ALK(L1196M)-driven model, suggesting that 60% ALK inhibition would be required for tumor stasis. Accordingly, we proposed that the EC60,in vivo for ALK inhibition corresponding to the tumor stasis could be considered a minimum target efficacious concentration of PF06463922 for cancer patients in a phase I trial.

EGFR phosphorylation of DCBLD2 recruits TRAF6 and stimulates AKT-promoted tumorigenesis

Aberrant activation of EGFR in human cancers promotes tumorigenesis through stimulation of AKT signaling. Here, we determined that the discoidina neuropilin-like membrane protein DCBLD2 is upregulated in clinical specimens of glioblastomas and head and neck cancers (HNCs) and is required for EGFR-stimulated tumorigenesis. In multiple cancer cell lines, EGFR activated phosphorylation of tyrosine 750 (Y750) of DCBLD2, which is located within a recently identified binding motif for TNF receptor-associated factor 6 (TRAF6). Consequently, phosphorylation of DCBLD2 Y750 recruited TRAF6, leading to increased TRAF6 E3 ubiquitin ligase activity and subsequent activation of AKT, thereby enhancing EGFR-driven tumorigenesis. Moreover, evaluation of patient samples of gliomas and HNCs revealed an association among EGFR activation, DCBLD2 phosphorylation, and poor prognoses. Together, our findings uncover a pathway in which DCBLD2 functions as a signal relay for oncogenic EGFR signaling to promote tumorigenesis and suggest DCBLD2 and TRAF6 as potential therapeutic targets for human cancers that are associated with EGFR activation.

Phase I ficlatuzumab monotherapy or with erlotinib for refractory advanced solid tumours and multiple myeloma

BACKGROUND

Ficlatuzumab, a humanised hepatocyte growth factor (HGF) IgG1κ inhibitory monoclonal antibody, was evaluated for recommended phase II dose (RP2D), safety, pharmacokinetics (PKs), antidrug antibody (ADA), pharmacodynamics (PDs) and antitumour activity as monotherapy or combined with erlotinib.

METHODS

Patients with solid tumours received ficlatuzumab 2, 5, 10 or 20 mg kg(-1) intravenously every 2 weeks (q2w). Additional patients were treated at the RP2D erlotinib.

RESULTS

Forty-one patients enrolled at doses ⩽20 mg kg(-1). Common adverse events (AEs) included peripheral oedema, fatigue and nausea. Three patients experienced grade ⩾3 treatment-related hyperkalaemia/hypokalaemia, diarrhoea or fatigue. Best overall response (44%) was stable disease (SD); median duration was 5.5 months (0.4-18.7 months). One patient has been on therapy with SD for >4 years. Pharmacokinetics of ficlatuzumab showed low clearance (0.17-0.26 ml h(-1) kg(-1)), a half-life of 6.8-9.4 days and dose-proportional exposure. Ficlatuzumab/erlotinib had no impact on the PK of either agent. No ADAs were detected. Ficlatuzumab increased serum HGF levels.

CONCLUSIONS

Recommended phase II dose is 20 mg kg(-1) q2w for ficlatuzumab monotherapy or with erlotinib. Preliminary antitumour activity and manageable AEs were observed. Pharmacokinetics were dose-proportional and consistent with other IgG therapeutics. Ficlatuzumab was not immunogenic, and serum HGF was a potential PD marker.

Clinicopathological and prognostic significance of epidermal growth factor receptor overexpression in patients with esophageal adenocarcinoma: a meta-analysis

The prognostic significance of epidermal growth factor receptor (EGFR) overexpression in patients with esophageal adenocarcinoma (EAC) remains controversial. Eligible studies that investigated the association between survival in EAC and the expression status of EGFR were identified by an electronic search of PubMed, EMBASE, and ISI Web of Science. A meta-analysis was performed to clarify the impact of EGFR overexpression on clinicopathological parameters or overall survival (OS) in EAC. A total of seven studies including 1028 patients were subjected to the final analysis. The overall results suggested that overexpression of EGFR was significantly correlated with not only the depth of invasion, lymph node status, and tumors stage of EAC, with a pooled odds ratio of 2.99 (95% confidence interval [CI]: 1.07-8.35; Z = 2.09; P = 0.037), 3.05 (95% CI: 1.77-5.27; Z = 4.00; P < 0.001), and 5.37 (95% CI: 2.49-11.57; Z = 4.29; P < 0.001), respectively, but also the poorer OS with a pooled hazard ratio of 2.20 (95% CI: 1.47-3.31; Z = 3.79; P < 0.001). Overexpression of EGFR correlates with not only the clinicopathological features, but also the worse OS, and it might be useful as a predictive biomarker in clinical practice, yet the clinicopathological and prognostic role of EGFR in EAC still needs further confirmation by well-designed prospective studies.

[Analysis of oncogenic signaling induced by tyrosine kinases in tumors by SILAC-based quantitative proteomic approach]

Protein tyrosine kinases (TK) transmit intracellular signaling induced by many extracellular stimuli resulting in cell growth or adhesion. Deregulation of their activity leads to malignant cell transformation that plays an important role in human cancer. The signaling pathways involved in this oncogenic process are however only partially elucidated. Interestingly, SILAC-based quantitative proteomics allow the identification of the whole spectrum of TK substrates and the dynamic of phosphorylation state involved in oncogenic signaling. For example, this approach has highlighted the unsuspected complexity of the oncogenic signaling induced by the TK Src in colorectal cancer (CRC) cells. In this review, we describe a new SILAC-based technology applied to in vivo models of human tumors engrafted in nude mice. This method revealed significant differences between Src-oncogenic signaling of CRC cells in tumors and in culture. Finally, we discuss the interest of SILAC with recently described in vivo proteomic methods and in cancer, including the analysis of oncogenic signaling in tumor progression and the anti-tumoral activity of TK inhibitors in vivo.

Discoidin domain receptor 2 signaling networks and therapy in lung cancer

Discoidin domain receptor 2 (DDR2) is an atypical receptor tyrosine kinase that binds to and is activated by collagen in the extracellular matrix. Recent exon sequencing studies have identified DDR2 to be mutated with a 3% to 4% incidence in squamous cell cancers of the lung. This article summarizes the current state of knowledge of DDR2 biology and signaling in lung squamous cell cancer. It also explores the context-dependent role of this receptor as both an oncogene and a tumor suppressor in cancer cells. Promising therapeutic opportunities based on existing and novel targeted small molecule inhibitors against DDR2 may provide new strategies for treating lung squamous cell cancer patients.

Systems biology approaches to develop innovative strategies for lung cancer therapy

Lung cancer (LC) is a number one killer of cancer-related death among men and women worldwide. Major advances have been made in the diagnosis, staging and use of surgery for LC, but systemic chemotherapy and radiotherapy alone or in combination with some targeted agents remains the core treatment of advanced LC. Unfortunately, in spite of improved diagnosis, surgical methods and new treatments, mortality is still extremely high among LC patients. To understand the precise functioning of signaling pathways associated with resistance to current treatments in LC, as well as to identify novel treatment regimens, a holistic approach to analyze signaling networks should be applied. Here, we describe systems biology-based approaches to generate biomarkers and novel therapeutic targets in LC, as well as how this may contribute to personalized treatment for this malignancy.

PZR coordinates Shp2 Noonan and LEOPARD syndrome signaling in zebrafish and mice

Noonan syndrome (NS) is an autosomal dominant disorder caused by activating mutations in the PTPN11 gene encoding Shp2, which manifests in congenital heart disease, short stature, and facial dysmorphia. The complexity of Shp2 signaling is exemplified by the observation that LEOPARD syndrome (LS) patients possess inactivating PTPN11 mutations yet exhibit similar symptoms to NS. Here, we identify "protein zero-related" (PZR), a transmembrane glycoprotein that interfaces with the extracellular matrix to promote cell migration, as a major hyper-tyrosyl-phosphorylated protein in mouse and zebrafish models of NS and LS. PZR hyper-tyrosyl phosphorylation is facilitated in a phosphatase-independent manner by enhanced Src recruitment to NS and LS Shp2. In zebrafish, PZR overexpression recapitulated NS and LS phenotypes. PZR was required for zebrafish gastrulation in a manner dependent upon PZR tyrosyl phosphorylation. Hence, we identify PZR as an NS and LS target. Enhanced PZR-mediated membrane recruitment of Shp2 serves as a common mechanism to direct overlapping pathophysiological characteristics of these PTPN11 mutations.

Enhancement of gefitinib-induced growth inhibition by Marsdenia tenacissima extract in non-small cell lung cancer cells expressing wild or mutant EGFR

BACKGROUND

Non-small cell lung cancer (NSCLC) expressed high levels of epidermal growth factor receptor (EGFR). Gefitinib (Iressa) has demonstrated clinical efficacy in NSCLC patients harboring EGFR mutations or refractory to chemotherapy. However, most of NSCLC patients are with wild type EGFR, and showed limited response to gefitinib. Therefore, to develop new effective therapeutic interventions for NSCLC is still required. Our previous study showed Marsdenia tenacissima extract (MTE) restored gefitinib efficacy in the resistant NSCLC cells, but whether MTE acts in the gefitinib-sensitive NSCLC cells is the same as it in the resistant one is unknown.

METHODS

Dose response curves for gefitinib and MTE were generated for two sensitive NSCLC cell lines with mutant or wild type EGFR status. Three different sequential combinations of MTE and gefitinib on cell growth were evaluated using IC50 and Combination Index approaches. The flow cytometric method was used to detect cell apoptosis and cell cycle profile. The impact of MTE combined with gefitinib on cell molecular network response was studied by Western blotting.

RESULTS

Unlike in the resistant NSCLC cells, our results revealed that low cytotoxic dose of MTE (8 mg/ml) combined gefitinib with three different schedules synergistically or additively enhanced the growth inhibition of gefitinib. Among which, MTE→MTE+gefitinib treatment was the most effective one. MTE markedly prompted cell cycle arrest and apoptosis caused by gefitinib both in EGFR mutant (HCC827) and wild type of NSCLC cells (H292). The Western blotting results showed that MTE→MTE+gefitinib treatment further enhanced the suppression of gefitinib on cell growth and apoptosis pathway such as ERK1/2 and PI3K/Akt/mTOR. This combination also blocked the activation of EGFR and c-Met which have cross-talk with each other. Unlike in gefitinib-resistant NSCLC cells, MTE alone also demonstrated certain unexpected modulation on EGFR related cell signal pathways in the sensitive cells.

CONCLUSION

Our results suggest that MTE is a promising herbal medicine to improve gefitinib efficacy in NSCLC regardless of EGFR status. However, why MTE acted differently between gefitinib-sensitive and -resistant NSCLC cells needs a further research.

Impact of genetic profiles on the efficacy of anti-EGFR antibodies in metastatic colorectal cancer with KRAS mutation

Reports indicate that, even in KRAS-mutated colon cancer, there are subsets of patients who benefit from anti-EGFR monoclonal antibody (MoAb) treatment. The aim of the present study was to identify genetic profiles that contribute to the responsiveness of metastatic colorectal cancer (mCRC) to anti-EGFR MoAb. We retrospectively evaluated the efficacy of anti-EGFR MoAb in mCRC patients with KRAS mutations according to KRAS mutational subtypes, BRAF and PIK3CA mutational status and PTEN and MET expression. Among 21 patients with KRAS-mutant tumors, 8 (38%) harbored p.G13D, 7 (33%) harbored p.G12V, 5 (24%) harbored p.G12D, and 1 (5%) harbored p.G12C mutation. Patients with the p.G13D mutation exhibited a significantly higher disease control rate than patients with other KRAS mutations (P=0.042), and tended to show a longer progression-free survival (PFS) than patients with other KRAS mutations with marginal significance (P=0.074). Patients with loss of PTEN had significantly shorter PFS than those with normal PTEN expression in patients with KRAS mutations (P=0.044). MET overexpression was significantly associated with shorter PFS compared to normal MET expression in patients with KRAS mutations (P=0.016). Our data demonstrated the potential utility of alterations in PTEN and MET expression as predictive markers for response to anti-EGFR MoAbs in mCRC patients with KRAS mutations. In addition, we confirmed the predictive value of the KRAS p.G13D mutation for better response to anti-EGFR therapies in comparison with other KRAS mutations.

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.

Combining affinity proteomics and network context to identify new phosphatase substrates and adapters in growth pathways

Protein phosphorylation homoeostasis is tightly controlled and pathological conditions are caused by subtle alterations of the cell phosphorylation profile. Altered levels of kinase activities have already been associated to specific diseases. Less is known about the impact of phosphatases, the enzymes that down-regulate phosphorylation by removing the phosphate groups. This is partly due to our poor understanding of the phosphatase-substrate network. Much of phosphatase substrate specificity is not based on intrinsic enzyme specificity with the catalytic pocket recognizing the sequence/structure context of the phosphorylated residue. In addition many phosphatase catalytic subunits do not form a stable complex with their substrates. This makes the inference and validation of phosphatase substrates a non-trivial task. Here, we present a novel approach that builds on the observation that much of phosphatase substrate selection is based on the network of physical interactions linking the phosphatase to the substrate. We first used affinity proteomics coupled to quantitative mass spectrometry to saturate the interactome of eight phosphatases whose down regulations was shown to affect the activation of the RAS-PI3K pathway. By integrating information from functional siRNA with protein interaction information, we develop a strategy that aims at inferring phosphatase physiological substrates. Graph analysis is used to identify protein scaffolds that may link the catalytic subunits to their substrates. By this approach we rediscover several previously described phosphatase substrate interactions and characterize two new protein scaffolds that promote the dephosphorylation of PTPN11 and ERK by DUSP18 and DUSP26, respectively.

Reconstructing targetable pathways in lung cancer by integrating diverse omics data

Global 'multi-omics' profiling of cancer cells harbours the potential for characterizing the signalling networks associated with specific oncogenes. Here we profile the transcriptome, proteome and phosphoproteome in a panel of non-small cell lung cancer (NSCLC) cell lines in order to reconstruct targetable networks associated with KRAS dependency. We develop a two-step bioinformatics strategy addressing the challenge of integrating these disparate data sets. We first define an 'abundance-score' combining transcript, protein and phospho-protein abundances to nominate differentially abundant proteins and then use the Prize Collecting Steiner Tree algorithm to identify functional sub-networks. We identify three modules centred on KRAS and MET, LCK and PAK1 and β-Catenin. We validate activation of these proteins in KRAS-dependent (KRAS-Dep) cells and perform functional studies defining LCK as a critical gene for cell proliferation in KRAS-Dep but not KRAS-independent NSCLCs. These results suggest that LCK is a potential druggable target protein in KRAS-Dep lung cancers.

Dynamic reprogramming of signaling upon met inhibition reveals a mechanism of drug resistance in gastric cancer

The Met receptor tyrosine kinase is activated or genetically amplified in some gastric cancers, but resistance to small-molecule inhibitors of Met often emerges in patients. We found that Met abundance correlated with a proliferation marker in patient gastric tumor sections, and gastric cancer cell lines that have MET amplifications depended on Met for proliferation and anchorage-independent growth in culture. Inhibition of Met induced temporal changes in gene expression in the cell lines, initiated by a rapid decrease in the expression of genes encoding transcription factors, followed by those encoding proteins involved in epithelial-mesenchymal transition, and finally those encoding cell cycle-related proteins. In the gastric cancer cell lines, microarray and chromatin immunoprecipitation analysis revealed considerable overlap between genes regulated in response to Met stimulation and those regulated by signal transducer and activator of transcription 3 (STAT3). The activity of STAT3, extracellular signal-regulated kinase (ERK), and the kinase Akt was decreased by Met inhibition, but only inhibitors of STAT3 were as effective as the Met inhibitor in decreasing tumor cell proliferation in culture and in xenografts, suggesting that STAT3 mediates the pro-proliferative program induced by Met. However, the phosphorylation of ERK increased after prolonged Met inhibition in culture, correlating with decreased abundance of the phosphatases DUSP4 and DUSP6, which inhibit ERK. Combined inhibition of Met and the mitogen-activated protein kinase kinase (MEK)-ERK pathway induced greater cell death in cultured gastric cancer cells than did either inhibitor alone. These findings indicate combination therapies that may counteract resistance to Met inhibitors.

Enhanced prediction of Src homology 2 (SH2) domain binding potentials using a fluorescence polarization-derived c-Met, c-Kit, ErbB, and androgen receptor interactome

Many human diseases are associated with aberrant regulation of phosphoprotein signaling networks. Src homology 2 (SH2) domains represent the major class of protein domains in metazoans that interact with proteins phosphorylated on the amino acid residue tyrosine. Although current SH2 domain prediction algorithms perform well at predicting the sequences of phosphorylated peptides that are likely to result in the highest possible interaction affinity in the context of random peptide library screens, these algorithms do poorly at predicting the interaction potential of SH2 domains with physiologically derived protein sequences. We employed a high throughput interaction assay system to empirically determine the affinity between 93 human SH2 domains and phosphopeptides abstracted from several receptor tyrosine kinases and signaling proteins. The resulting interaction experiments revealed over 1000 novel peptide-protein interactions and provided a glimpse into the common and specific interaction potentials of c-Met, c-Kit, GAB1, and the human androgen receptor. We used these data to build a permutation-based logistic regression classifier that performed considerably better than existing algorithms for predicting the interaction potential of several SH2 domains.

Celastrol induces apoptosis in gefitinib-resistant non-small cell lung cancer cells via caspases-dependent pathways and Hsp90 client protein degradation

Celastrol, a triterpene extracted from the Chinese herb Tripterygium wilfordii, has been shown to have multiple bioactivities. Although among these activities, its anti-cancer effects have attracted the most attention, the effect of celastrol on gefitinib-resistant non-small cell lung cancer (NSCLC) cells is not clearly known. Here, we examined the potency of celastrol in three different NSCLC cell lines. We explored its treatment mechanism in two gefitinib-resistant NSCLC cell lines (H1650 and H1975). Our data demonstrated that celastrol exerted its apoptotic effect in a dose- and time-dependent manner. Also, the mitochondria membrane potential was gradually lost and the ratio of Bax/Bcl-2 increased after the treatment of celastrol, both of which are indicators of mitochondria membrane integrity. Although the caspases were activated, the treatment with pan-caspase inhibitor could partially inhibit the level of apoptosis. Moreover, the protein level of Hsp90 client proteins, EGFR and AKT, was measured. Interestingly, both client proteins were remarkably down-regulated after the treatment of celastrol. Taken together, our data showed that celastrol may be developed as a promising agent for treating gefitinib-resistant NSCLCs by inducing apoptosis through caspase-dependent pathways and Hsp90 client protein degradation.

A novel lead compound CM-118: antitumor activity and new insight into the molecular mechanism and combination therapy strategy in c-Met- and ALK-dependent cancers

The anaplastic lymphoma kinase (ALK) and the c-Met receptor tyrosine kinase play essential roles in the pathogenesis in multiple human cancers and present emerging targets for cancer treatment. Here, we describe CM-118, a novel lead compound displaying low nanomolar biochemical potency against both ALK and c-Met with selectivity over>90 human kinases. CM-118 potently abrogated hepatocyte growth factor (HGF)-induced c-Met phosphorylation and cell migration, phosphorylation of ALK, EML4-ALK, and ALK resistance mutants in transfected cells. CM-118 inhibited proliferation and/or induced apoptosis in multiple c-Met- and ALK-addicted cancer lines with dose response profile correlating target blockade. We show that the CM-118-induced apoptosis in c-Met-amplified H1993 NSCLC cells involved a rapid suppression of c-Met activity and c-Met-to-EGFR cross-talk, and was profoundly potentiated by EGFR inhibitors as shown by the increased levels of apoptotic proteins cleaved-PARP and Bim as well as reduction of the survival protein Mcl-1. Bim-knockdown or Mcl-1 overexpression each significantly attenuated apoptosis. We also revealed a key role by mTOR in mediating CM-118 action against the EML4-ALK-dependent NSCLC cells. Abrogation of EML4-ALK in H2228 cells profoundly reduced signaling capacity of the rapamycin-sensitive mTOR pathway leading to G 1 cell cycle arrest and mitochondrial hyperpolarization, a metabolic perturbation linked to mTOR inhibition. Depletion of mTOR or mTORC1 inhibited H2228 cell growth, and mTOR inhibitors potentiated CM-118's antitumor activity in vitro and in vivo. Oral administration of CM-118 at a wide range of well tolerated dosages diminished c-Met- and ALK phosphorylation in vivo, and caused tumor regression or growth inhibition in multiple c-Met- and ALK-dependent tumor xenografts in mice. CM-118 exhibits favorable pharmacokinetic and drug metabolism properties hence presents a candidate for clinical evaluation.

Unraveling trastuzumab and lapatinib inefficiency in gastric cancer: Future steps (Review)

The newly developed concept of oncogene addiction provides a rationale for the use of targeted therapies. In sharp contrast to the field of breast cancer treatment, attempts to target human epidermal growth factor receptor 2 (HER2) among gastric cancer (GC) patients have been unsatisfactory. The ToGA trial reported only a modest prolongation of progression-free survival (PFS) with trastuzumab and the subsequent TYTAN and LOGiC trials failed to demonstrate any survival advantage with lapatinib. These results suggest that a response to the molecular-targeted therapies is achieved in only a fraction of the patients; in addition, even responders may experience secondary resistance, with the efficacy of the treatment being decreased or abrogated over a short period of time. Considering the increased recognition of primary or acquired resistance, recent investigations on targeted therapies have been primarily focused on determining in advance the mechanisms that may mediate resistance to treatment and the methods through which such obstacles may be circumvented. The proposed molecules or mechanisms that may be responsible for the development of resistance to single HER2-targeted therapy include a dimerization partner or crosstalk with HER2, such as HER3 and MET, as well as any subsequent activation of their downstream pathways, which exhibit a partial overlap with those of HER2. Furthermore, genetic alterations that stimulate the aberrant activation of the pathways downstream of HER2 may be the underlying mechanisms that restore prosurvival signaling. These mechanisms generate a complex signaling network with a significant potential for signal amplification and diversification. Although in the early stages of description, several compounds have been suggested as next generation treatments for GC, with expectations for their delineating the function of such receptors or molecules, with subsequent contributions of specific survival signaling blockades. This review focuses on the current achievements of anti-HER2 therapies in GC and the plausible mechanisms of resistance to these therapies. Elucidating these mechanisms of resistance may provide valuable information pertinent to the design of future strategies to improve molecular-targeted therapies.

Post-translational modifications of intermediate filament proteins: mechanisms and functions

Intermediate filaments (IFs) are cytoskeletal and nucleoskeletal structures that provide mechanical and stress-coping resilience to cells, contribute to subcellular and tissue-specific biological functions, and facilitate intracellular communication. IFs, including nuclear lamins and those in the cytoplasm (keratins, vimentin, desmin, neurofilaments and glial fibrillary acidic protein, among others), are functionally regulated by post-translational modifications (PTMs). Proteomic advances highlight the enormous complexity and regulatory potential of IF protein PTMs, which include phosphorylation, glycosylation, sumoylation, acetylation and prenylation, with novel modifications becoming increasingly appreciated. Future studies will need to characterize their on-off mechanisms, crosstalk and utility as biomarkers and targets for diseases involving the IF cytoskeleton.

Stratification of clear cell renal cell carcinoma by signaling pathway analysis

Investigation of cell signaling pathways in 16 clear cell renal cell carcinomas to identify groups based on commonly shared phosphorylation-driven signaling networks. Using laser capture microdissection and reverse-phase protein arrays, we profiled 75 key nodes spanning signaling pathways important in tumorigenesis. Analysis revealed significantly different (P < 0.05) signaling levels for 27 nodes between two groups of samples, designated A (4 samples; high EGFR, RET, and RASGFR1 levels, converging to activate AKT/mTOR) and B (12 samples; high ERK1/2 and STAT phosphorylation). Group B was further partitioned into groups C (7 samples; elevated expression of LC3B) and D (5 samples; activation of Src and STAT). Network analysis indicated that group A was characterized by signaling pathways related to cell cycle and proliferation, and group B by pathways related to cell death and survival. Homogeneous clear cell renal cell carcinomas could be stratified into at least two major functional groups.

Clinical targeting of mutated and wild-type protein tyrosine kinases in cancer

Clinical therapies for cancer have evolved from toxic, nontargeted agents to manageable, highly targeted therapies. Protein tyrosine kinases are a family of signaling molecules implicated in nearly every cancer type and are the foundation for the development of modern targeted agents. Recent genomic analyses have identified activating mutations, translocations, and amplifications of tyrosine kinases. Selective targeting of these genetically altered tyrosine kinases has resulted in significant clinical advances, including increased patient survival. This indicates that altered protein tyrosine kinases are the main drivers of many different cancers. However, lost during analyses of genetic lesions are the contributions of activated, wild-type kinases on tumor-dependent pathways. New approaches in phosphoproteomic technologies have identified several wild-type tyrosine kinase activation states, suggesting that non-genetically altered kinases can be essential "nodes" for signal transduction. Here, we summarize the evidence supporting the common mechanisms of protein tyrosine kinase activation in cancer and provide a personal perspective on the kinases BCR-ABL and BTK, as well as nonmutated kinase targets in prostate cancer, through our work. We outline the mechanisms of tyrosine kinase activation in the absence of direct mutation and discuss whether non-genetically altered tyrosine kinases or their associated downstream signaling pathways can be effectively targeted.

Overexpression of MET is a new predictive marker for anti-EGFR therapy in metastatic colorectal cancer with wild-type KRAS

Purpose

Since the KRAS mutation is not responsible for all metastatic colorectal cancer (mCRC) patients with resistance to anti-epidermal growth factor receptor (EGFR) monoclonal antibody (MoAb) therapy, new predictive and prognostic factors are actively being sought.

Methods

We retrospectively evaluated the efficacy of anti-EGFR MoAb-based therapies in 91 patients with mCRC according to KRAS, BRAF, and PIK3CA mutational status as well as PTEN and MET expression.

Results

In the patient group with wild-type KRAS, the presence of BRAF mutation or PIK3CA mutations was associated with lower disease control rate (DCR), shorter progression-free survival (PFS), and shorter overall survival. Patients with MET overexpression also showed lower DCR and shorter PFS when compared with patients with normal MET expression. In a separate analysis, 44 patients harboring wild-type KRAS tumors were sorted into subgroups of 25 patients without abnormality in three molecules (BRAF, PIK3CA and MET) and 19 patients with abnormality in at least one of these three molecules. The former group showed significantly higher DCR and longer PFS following anti-EGFR therapy than the latter group.

Conclusions

Our data point to the usefulness of MET overexpression, in addition to BRAF and PIK3CA mutations, as a new predictive marker for responsiveness to anti-EGFR MoAbs in mCRC patients with wild-type KRAS. This study also suggests that application of multiple biomarkers is more effective than the use of a single marker in selecting patients who might benefit from anti-EGFR therapy.

Electronic supplementary material

The online version of this article (doi:10.1007/s00280-014-2401-4) contains supplementary material, which is available to authorized users.

Differential parsing of EGFR endocytic flux among parallel internalization pathways in lung cancer cells with EGFR-activating mutations

Due to the existence of parallel pathways for receptor endocytosis and their complexities, a quantitative understanding of receptor endocytosis in normal and pathological settings requires computational analysis. Here, we develop a mechanistic model of epidermal growth factor receptor (EGFR) endocytosis to determine the relative contributions of three parallel pathways: clathrin-dependent internalization mediated by mitogen-inducible gene 6 (MIG6), an endogenous EGFR kinase inhibitor that links EGFR to endocytic proteins; clathrin-dependent internalization mediated by the ubiquitin ligase CBL, which can be sequestered by the regulatory protein Sprouty2; or alternative pathways that may be non-clathrin mediated. We applied the model to interpret our previous measurements of EGFR endocytosis in lung cancer cells. Interestingly, our results suggest that MIG6 is responsible for at least as much wild-type EGFR internalization as CBL, indicating that a significant fraction of internalizing EGFR may be incapable of driving signaling. Model results also suggest that MIG6's endocytic function is reduced for the kinase-activated and internalization-impaired EGFR mutants found in some lung cancers. Analysis of Sprouty2 knockdown data indicates that Sprouty2 regulates EGFR endocytosis primarily by controlling EGFR expression, rather than by sequestering CBL, and supports the notion that CBL-mediated internalization is impaired for EGFR mutants. We further demonstrate that differences in internalization between wild-type and mutant EGFR cannot explain differences in EGF-mediated EGFR degradation without concomitant changes in EGFR recycling, which we previously quantified. This work provides new quantitative insights into EGFR trafficking in lung cancer and provides a framework for studying parallel endocytosis pathways for other receptors.

HGF signaling regulates Claudin-3 dynamics through its C-terminal tyrosine residues

The hormone HGF regulates morphogenesis and regeneration of multiple organs and increased HGF signaling is strongly associated with metastatic cancer. At the cellular level, one of the distinct effects of HGF is the de-stabilization of cell-cell junctions. Several molecular mechanisms have been shown to be involved that mostly culminate at the E-cadherin adhesion complex. One of the key determinants in HGF-driven morphological changes is the actomyosin cytoskeleton whose organization and physical parameters changes upon stimulation. Here we have investigated how HGF affects the different actomyosin-associated cell-cell junction complexes, Nectin Junctions, Adherens Junctions and Tight Junctions in MDCK cells. We find that components of all complexes stay present at cell-cell contacts until their physical dissociation. We find that at cell-cell junctions, the mobility of Claudin-3, but not that of other cell-cell adhesion receptors, is affected by HGF. This depends on tyrosine residues that likely affect PDZ-domain interactions at the C-terminal tail of Claudin-3, although their phosphorylation is not directly regulated by HGF. Thus we uncovered Claudins as novel targets of HGF signaling at cell-cell junctions.

Mass spectrometry for proteomics-based investigation

Within the past years, we have witnessed a great improvement in mass spectrometry (MS) and proteomics approaches in terms of instrumentation, protein fractionation, and bioinformatics. With the current technology, protein identification alone is no longer sufficient. Both scientists and clinicians want not only to identify proteins but also to identify the protein's posttranslational modifications (PTMs), protein isoforms, protein truncation, protein-protein interaction (PPI), and protein quantitation. Here, we describe the principle of MS and proteomics and strategies to identify proteins, protein's PTMs, protein isoforms, protein truncation, PPIs, and protein quantitation. We also discuss the strengths and weaknesses within this field. Finally, in our concluding remarks we assess the role of mass spectrometry and proteomics in scientific and clinical settings in the near future. This chapter provides an introduction and overview for subsequent chapters that will discuss specific MS proteomic methodologies and their application to specific medical conditions. Other chapters will also touch upon areas that expand beyond proteomics, such as lipidomics and metabolomics.

[Molecular mechanism of erlotinib resistance in epidermal growth factor receptor mutant non-small cell lung cancer cell line H1650]

BACKGROUND

Epidermal growth factor receptor (EGFR) overexpression and mutations were existed in more than 40% of the lung cancer, and it's the one of molecular targets in clinical treatment. But the EGFR tyrosine kinase inhibitors (TKI)-resistance is becoming a challenging clinical problem as following the application of EGFR-TKIs, Gefitinib or Erlotinib. However, the mechanistic explanation for resistance in the some cases is still lacking. Here we researched the resistance mechanism of H1650 cells.

METHODS

Using real-time RT-PCR to analyze the EGFR mRNA expression level in EGFR wild-type non-small cell lung cancer (NSCLC) cells; MTT analysis detected the cytotoxicity for NSCLC cells to Erlotinib; Western blot analysis examined the mutant situations and the downstream signaling protein phosphorylation level in EGFR-mutant NSCLC cells with the treatment of Erlotinib or/and PI3K inhibitor, LY294002.

RESULTS

In the EGFR wild-type NSCLC cells, the expression level of EGFR mRNA varied dramatically and all the cells showed resistant to Erlotinib; In the EGFR-mutant cells, HCC827 and H1650 (the same activating-mutation type), HCC827 cells were Erlotinib-sensitive as well as H1650 demonstrated primary relative resistance. Western blot analysis showed the loss of PTEN and the p-AKT level was not inhibited with the treatment of Erlotinib or/and LY294002 in H1650 cells, while HCC827 cells were no PTEN loss and definitively decrease of p-AKT level.

CONCLUSIONS

EGFR wild-type NSCLC cells were resistant to Erlotinib no matter of how EGFR mRNA expression level. EGFR-activating mutations correlated with responses to Erlotinib. The PTEN loss and activation of AKT signaling pathway contributed to Erlotinib resistance in EGFR-mutant NSCLC cell line H1650.

Assessment, origin, and implementation of breath volatile cancer markers

A new non-invasive and potentially inexpensive frontier in the diagnosis of cancer relies on the detection of volatile organic compounds (VOCs) in exhaled breath samples. Breath can be sampled and analyzed in real-time, leading to fascinating and cost-effective clinical diagnostic procedures. Nevertheless, breath analysis is a very young field of research and faces challenges, mainly because the biochemical mechanisms behind the cancer-related VOCs are largely unknown. In this review, we present a list of 115 validated cancer-related VOCs published in the literature during the past decade, and classify them with respect to their "fat-to-blood" and "blood-to-air" partition coefficients. These partition coefficients provide an estimation of the relative concentrations of VOCs in alveolar breath, in blood and in the fat compartments of the human body. Additionally, we try to clarify controversial issues concerning possible experimental malpractice in the field, and propose ways to translate the basic science results as well as the mechanistic understanding to tools (sensors) that could serve as point-of-care diagnostics of cancer. We end this review with a conclusion and a future perspective.

Heregulin induces resistance to lapatinib-mediated growth inhibition of HER2-amplified cancer cells

Human epidermal growth factor receptor 2 (HER2) amplification occurs in approximately 20% of gastric and gastroesophageal junction cancers in the United States and European Union. Lapatinib, a dual HER2 and epidermal growth factor receptor tyrosine kinase inhibitor, has demonstrated clinical efficacy in HER2-amplified cancer cells. However, several studies have shown that some cytokines can mediate resistance to lapatinib using their receptor tyrosine kinase (RTK) pathways. One of these, Heregulin1 (HRG1), can confer resistance to lapatinib-mediated growth inhibition in HER2-amplified breast cancer cells, but the underlying mechanisms remain unknown. Here, we investigated whether and how HRG1 causes resistance to lapatinib in gastric and gastroesophageal junction cancers in vitro. HER2-amplified gastric and gastroesophageal junction cancer cell lines were highly sensitive to lapatinib. Exposure to HRG1 together with lapatinib rescued cells from lapatinib-induced cell cycle arrest and apoptosis. Downregulation of HER3 with siRNA in the presence of HRG1 re-sensitized HER2-amplified cancer cells to lapatinib. Immunoblotting analysis indicated that HRG1 re-activated HER3 and AKT in the presence of lapatinib, which persisted for at least 72 h. Activation of HER3 and downstream AKT was mediated by residual activity of HER2. HRG1-mediated resistance could be reduced by PI3K/mTOR inhibitors or by complete inhibition of HER2. Thus, we conclude that HRG1 mediates resistance to lapatinib through HER3 and AKT activation, and that this depends on residual HER2 activity. Lapatinib in combination with anti-PI3K therapies or more potent HER2 inhibitors would improve the efficacy and avoid the emergence of resistant cells.

Targeting of Both the c-Met and EGFR Pathways Results in Additive Inhibition of Lung Tumorigenesis in Transgenic Mice

EGFR and c-Met are both overexpressed in lung cancer and initiate similar downstream signaling, which may be redundant. To determine how frequently ligands that initiate signaling of both pathways are found in lung cancer, we analyzed serum for hepatocyte growth factor (HGF), transforming growth factor-alpha, and amphiregulin (AREG) in lung cancer cases and tobacco-exposed controls. HGF and AREG were both significantly elevated in cases compared to controls, suggesting that both HGF/c-Met and AREG/EGFR pathways are frequently active. When both HGF and AREG are present in vitro, downstream signaling to MAPK and Akt in non-small cell lung cancer (NSCLC) cells can only be completely inhibited by targeting both pathways. To test if dual blockade of the pathways could better suppress lung tumorigenesis in an animal model than single blockade, mice transgenic for airway expression of human HGF were treated with inhibitors of both pathways alone and in combination after exposure to a tobacco carcinogen. Mean tumor number in the group using both the HGF neutralizing antibody L2G7 and the EGFR inhibitor gefitinib was significantly lower than with single agents. A higher tumor K-ras mutation rate was observed with L2G7 alone compared to controls, suggesting that agents targeting HGF may be less effective against mutated K-ras lung tumors. This was not observed with combination treatment. A small molecule c-Met inhibitor decreased formation of both K-ras wild-type and mutant tumors and showed additive anti-tumor effects when combined with gefitinib. Dual targeting of c-Met/EGFR may have clinical benefit for lung cancer.

Combining radiotherapy with MEK1/2, STAT5 or STAT6 inhibition reduces survival of head and neck cancer lines

BACKGROUND

Kinases downstream of growth factor receptors have been implicated in radioresistance and are, therefore, attractive targets to improve radiotherapy outcome in head and neck squamous cell carcinoma (HNSCC) patients.

METHODS

An antibody-based array was used to quantify the expression levels of multiple phospho-kinases involved in growth factor signaling in nine untreated or irradiated HNSCC lines. Radiosensitivity was assessed with clonogenic cell survival assays and correlated with the expression levels of the phospho-kinases. Inhibitors of the kinases that were associated with radiosensitivity were tested for their ability to increase radiosensitivity in the 3 most radioresistant HNSCC lines.

RESULTS

The basal expression of phosphorylated Yes, Src and STAT5A, and the expression after radiotherapy of phosphorylated AKT, MSK1/2, Src, Lyn, Fyn, Hck, and STAT6, were correlated with radiosensitivity in the panel of HNSCC lines. In combination with radiotherapy, inhibitors of AKT, p38 and Src Family Kinases (SFK) were variably able to reduce survival, whereas MEK1/2, STAT5 and STAT6 inhibition reduced survival in all cell lines. The combined effect of radiotherapy and the kinase inhibitors on cell survival was mostly additive, although also supra-additive effects were observed for AKT, MEK1/2, p38 and STAT5 inhibition.

CONCLUSIONS

Kinases of the AKT, MAPK, STAT and SFK pathways correlated with radiosensitivity in a panel of HNSCC lines. Particularly inhibitors against MEK1/2, STAT5 and STAT6 were able to decrease survival in combination with radiotherapy. Hence, inhibitors against these kinases have the potential to improve radiotherapy outcome in HNSCC patients and further research is warranted to confirm this in vivo.

Gastric cancer-molecular and clinical dimensions

Gastric cancer imposes a considerable health burden around the globe despite its declining incidence. The disease is often diagnosed in advanced stages and is associated with a poor prognosis for patients. An in-depth understanding of the molecular underpinnings of gastric cancer has lagged behind many other cancers of similar incidence and morbidity, owing to our limited knowledge of germline susceptibility traits for risk and somatic drivers of progression (to identify novel therapeutic targets). A few germline (PLCE1) and somatic (ERBB2, ERBB3, PTEN, PI3K/AKT/mTOR, FGF, TP53, CDH1 and MET) alterations are emerging and some are being pursued clinically. Novel somatic gene targets (ARID1A, FAT4, MLL and KMT2C) have also been identified and are of interest. Variations in the therapeutic approaches dependent on geographical region are evident for localized gastric cancer-differences that are driven by preferences for the adjuvant strategies and the extent of surgery coupled with philosophical divides. However, greater uniformity in approach has been noted in the metastatic cancer setting, an incurable condition. Having realized only modest successes, momentum is building for carrying out more phase III comparative trials, with some using biomarker-based patient selection strategies. Overall, rapid progress in biotechnology is improving our molecular understanding and can help with new drug discovery. The future prospects are excellent for defining biomarker-based subsets of patients and application of specific therapeutics. However, many challenges remain to be tackled. Here, we review representative molecular and clinical dimensions of gastric cancer.

Gefitinib inhibits invasive phenotype and epithelial-mesenchymal transition in drug-resistant NSCLC cells with MET amplification

Despite the initial response, all patients with epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC) eventually develop acquired resistance to EGFR tyrosine kinase inhibitors (TKIs). The EGFR-T790M secondary mutation is responsible for half of acquired resistance cases, while MET amplification has been associated with acquired resistance in about 5-15% of NSCLCs. Clinical findings indicate the retained addiction of resistant tumors on EGFR signaling. Therefore, we evaluated the molecular mechanisms supporting the therapeutic potential of gefitinib maintenance in the HCC827 GR5 NSCLC cell line harbouring MET amplification as acquired resistance mechanism. We demonstrated that resistant cells can proliferate and survive regardless of the presence of gefitinib, whereas the absence of the drug significantly enhanced cell migration and invasion. Moreover, the continuous exposure to gefitinib prevented the epithelial-mesenchymal transition (EMT) with increased E-cadherin expression and down-regulation of vimentin and N-cadherin. Importantly, the inhibition of cellular migration was correlated with the suppression of EGFR-dependent Src, STAT5 and p38 signaling as assessed by a specific kinase array, western blot analysis and silencing functional studies. On the contrary, the lack of effect of gefitinib on EGFR phosphorylation in the H1975 cells (EGFR-T790M) correlated with the absence of effects on cell migration and invasion. In conclusion, our findings suggest that certain EGFR-mutated patients may still benefit from a second-line therapy including gefitinib based on the specific mechanism underlying tumor cell resistance.

Randomized phase II trial of Onartuzumab in combination with erlotinib in patients with advanced non-small-cell lung cancer

PURPOSE

Increased hepatocyte growth factor/MET signaling is associated with poor prognosis and acquired resistance to epidermal growth factor receptor (EGFR) -targeted drugs in patients with non-small-cell lung cancer (NSCLC). We investigated whether dual inhibition of MET/EGFR results in clinical benefit in patients with NSCLC.

PATIENTS AND METHODS

Patients with recurrent NSCLC were randomly assigned at a ratio of one to one to receive onartuzumab plus erlotinib or placebo plus erlotinib; crossover was allowed at progression. Tumor tissue was required to assess MET status by immunohistochemistry (IHC). Coprimary end points were progression-free survival (PFS) in the intent-to-treat (ITT) and MET-positive (MET IHC diagnostic positive) populations; additional end points included overall survival (OS), objective response rate, and safety.

RESULTS

There was no improvement in PFS or OS in the ITT population (n = 137; PFS hazard ratio [HR], 1.09; P = .69; OS HR, 0.80; P = .34). MET-positive patients (n = 66) treated with erlotinib plus onartuzumab showed improvement in both PFS (HR, .53; P = .04) and OS (HR, .37; P = .002). Conversely, clinical outcomes were worse in MET-negative patients treated with onartuzumab plus erlotinib (n = 62; PFS HR, 1.82; P = .05; OS HR, 1.78; P = .16). MET-positive control patients had worse outcomes versus MET-negative control patients (n = 62; PFS HR, 1.71; P = .06; OS HR, 2.61; P = .004). Incidence of peripheral edema was increased in onartuzumab-treated patients.

CONCLUSION

Onartuzumab plus erlotinib was associated with improved PFS and OS in the MET-positive population. These results combined with the worse outcomes observed in MET-negative patients treated with onartuzumab highlight the importance of diagnostic testing in drug development.

Characterization of the EGFR interactome reveals associated protein complex networks and intracellular receptor dynamics

Growth factor receptor mediated signaling is meanwhile recognized as a complex signaling network, which is initiated by recruiting specific patterns of adaptor proteins to the intracellular domain of epidermal growth factor receptor (EGFR). Approaches to globally identify EGFR-binding proteins are required to elucidate this network. We affinity-purified EGFR with its interacting proteins by coprecipitation from lysates of A431 cells. A total of 183 proteins were repeatedly detected in high-resolution MS measurements. For 15 of these, direct interactions with EGFR were listed in the iRefIndex interaction database, including Grb2, shc-1, SOS1 and 2, STAT 1 and 3, AP2, UBS3B, and ERRFI. The newly developed Cytoscape plugin ModuleGraph allowed retrieving and visualizing 93 well-described protein complexes that contained at least one of the proteins found to interact with EGFR in our experiments. Abundances of 14 proteins were modulated more than twofold upon EGFR activation whereof clathrin-associated adaptor complex AP-2 showed 4.6-fold enrichment. These proteins were further annotated with different cellular compartments. Finally, interactions of AP-2 proteins and the newly discovered interaction of CIP2A could be verified. In conclusion, a powerful technique is presented that allowed identification and quantitative assessment of the EGFR interactome to provide further insight into EGFR signaling.

Gastric cancer-molecular and clinical dimensions

Gastric cancer imposes a considerable health burden around the globe despite its declining incidence. The disease is often diagnosed in advanced stages and is associated with a poor prognosis for patients. An in-depth understanding of the molecular underpinnings of gastric cancer has lagged behind many other cancers of similar incidence and morbidity, owing to our limited knowledge of germline susceptibility traits for risk and somatic drivers of progression (to identify novel therapeutic targets). A few germline (PLCE1) and somatic (ERBB2, ERBB3, PTEN, PI3K/AKT/mTOR, FGF, TP53, CDH1 and MET) alterations are emerging and some are being pursued clinically. Novel somatic gene targets (ARID1A, FAT4, MLL and KMT2C) have also been identified and are of interest. Variations in the therapeutic approaches dependent on geographical region are evident for localized gastric cancer-differences that are driven by preferences for the adjuvant strategies and the extent of surgery coupled with philosophical divides. However, greater uniformity in approach has been noted in the metastatic cancer setting, an incurable condition. Having realized only modest successes, momentum is building for carrying out more phase III comparative trials, with some using biomarker-based patient selection strategies. Overall, rapid progress in biotechnology is improving our molecular understanding and can help with new drug discovery. The future prospects are excellent for defining biomarker-based subsets of patients and application of specific therapeutics. However, many challenges remain to be tackled. Here, we review representative molecular and clinical dimensions of gastric cancer.

A conserved rod domain phosphotyrosine that is targeted by the phosphatase PTP1B promotes keratin 8 protein insolubility and filament organization

Post-translational modifications are important functional determinants for intermediate filament (IF) proteins. Phosphorylation of IF proteins regulates filament organization, solubility, and cell-protective functions. Most known IF protein phosphorylation sites are serines localized in the variable "head" and "tail" domain regions. By contrast, little is known about site-specific tyrosine phosphorylation or its implications on IF protein function. We used available proteomic data from large scale studies to narrow down potential phospho-tyrosine sites on the simple epithelial IF protein keratin 8 (K8). Validation of the predicted sites using a pan-phosphotyrosine and a site-specific antibody, which we generated, revealed that the highly conserved Tyr-267 in the K8 "rod" domain was basally phosphorylated. The charge at this site was critically important, as demonstrated by altered filament organization of site-directed mutants, Y267F and Y267D, the latter exhibiting significantly diminished solubility. Pharmacological inhibition of the protein-tyrosine phosphatase PTP1B increased K8 Tyr-267 phosphorylation, decreased solubility, and increased K8 filament bundling, whereas PTP1B overexpression had the opposite effects. Furthermore, there was significant co-localization between K8 and a "substrate-trapping" mutant of PTP1B (D181A). Because K8 Tyr-267 is conserved in many IFs (QYE motif), we tested the effect of the paralogous Tyr in glial fibrillary acidic protein (GFAP), which is mutated in Alexander disease (Y242D). Similar to K8, Y242D GFAP exhibited highly irregular filament organization and diminished solubility. Our results implicate the rod domain QYE motif tyrosine as an important determinant of IF assembly and solubility properties that can be dynamically modulated by phosphorylation.

Complexity of receptor tyrosine kinase signal processing

Our knowledge of molecular mechanisms of receptor tyrosine kinase (RTK) signaling advances with ever-increasing pace. Yet our understanding of how the spatiotemporal dynamics of RTK signaling control specific cellular outcomes has lagged behind. Systems-centered experimental and computational approaches can help reveal how overlapping networks of signal transducers downstream of RTKs orchestrate specific cell-fate decisions. We discuss how RTK network regulatory structures, which involve the immediate posttranslational and delayed transcriptional controls by multiple feed forward and feedback loops together with pathway cross talk, adapt cells to the combinatorial variety of external cues and conditions. This intricate network circuitry endows cells with emerging capabilities for RTK signal processing and decoding. We illustrate how mathematical modeling facilitates our understanding of RTK network behaviors by unraveling specific systems properties, including bistability, oscillations, excitable responses, and generation of intricate landscapes of signaling activities.

Flexibility of the PDZ-binding motif in the micelle-bound form of Jagged-1 cytoplasmic tail

Human Jagged-1, one of the ligands of Notch receptors, is a transmembrane protein composed of a large extracellular region and a 125-residue cytoplasmic tail which bears a C-terminal PDZ recognition motif. To investigate the interaction between Jagged-1 cytoplasmic tail and the inner leaflet of the plasma membrane we determined, by solution NMR, the secondary structure and dynamics of the recombinant protein corresponding to the intracellular region of Jagged-1, J1_tmic, bound to negatively charged lysophospholipid micelles. NMR showed that the PDZ binding motif is preceded by four alpha-helical segments and that, despite the extensive interaction between J1_tmic and the micelle, the PDZ binding motif remains highly flexible. Binding of J1_tmic to negatively charged, but not to zwitterionic vesicles, was confirmed by surface plasmon resonance. To study the PDZ binding region in more detail, we prepared a peptide corresponding to the last 24 residues of Jagged-1, J1C24, and different phosphorylated variants of it. J1C24 displays a marked helical propensity and undergoes a coil-helix transition in the presence of negatively charged, but not zwitterionic, lysophospholipid micelles. Phosphorylation at different positions drastically decreases the helical propensity of the peptides and abolishes the coil-helix transition triggered by lysophospholipid micelles. We propose that phosphorylation of residues upstream of the PDZ binding motif may shift the equilibrium from an ordered, membrane-bound, interfacial form of Jagged-1 C-terminal region to a more disordered form with an increased accessibility of the PDZ recognition motif, thus playing an indirect role in the interaction between Jagged-1 and the PDZ-containing target protein.

Regulation of EGFR trafficking and cell signaling by Sprouty2 and MIG6 in lung cancer cells

The duration and specificity of epidermal growth factor receptor (EGFR) activation and signaling are determinants of cellular decision processes and are tightly regulated by receptor dephosphorylation, internalization and degradation. In addition, regulatory proteins that are upregulated or activated post-transcriptionally upon receptor activation may initiate feedback loops that play crucial roles in spatiotemporal regulation of signaling. We examined the roles of Sprouty2 (SPRY2) and mitogen-inducible gene 6 (MIG6), two feedback regulators of EGFR trafficking and signaling, in lung cancer cells with or without EGFR-activating mutations. These mutations are of interest because they confer unusual cellular sensitivity to EGFR inhibition through a mechanism involving an impairment of EGFR endocytosis. We found that the endocytosis of wild-type and mutant EGFR was promoted by SPRY2 knockdown and antagonized by MIG6 knockdown. SPRY2 knockdown also significantly reduced extracellular signal-regulated kinase (ERK) phosphorylation, EGFR expression, and EGFR recycling. In a cell line expressing mutant EGFR, this effect on ERK led to a marked increase in cell death response to EGFR inhibition. The effects of SPRY2 knockdown on EGFR endocytosis and recycling were primarily the result of the concomitant change in EGFR expression, but this was not true for the observed changes in ERK phosphorylation. Thus, our study demonstrates that SPRY2 and MIG6 are important regulators of wild-type and mutant EGFR trafficking and points to an EGFR expression-independent function of SPRY2 in the regulation of ERK activity that may impact cellular sensitivity to EGFR inhibitors, especially in the context of EGFR mutation.

Regulation of connexin- and pannexin-based channels by post-translational modifications

Connexin (Cx) and pannexin (Panx) proteins form large conductance channels, which function as regulators of communication between neighbouring cells via gap junctions and/or hemichannels. Intercellular communication is essential to coordinate cellular responses in tissues and organs, thereby fulfilling an essential role in the spreading of signalling, survival and death processes. The functional properties of gap junctions and hemichannels are modulated by different physiological and pathophysiological stimuli. At the molecular level, Cxs and Panxs function as multi-protein channel complexes, regulating their channel localisation and activity. In addition to this, gap junctional channels and hemichannels are modulated by different post-translational modifications (PTMs), including phosphorylation, glycosylation, proteolysis, N-acetylation, S-nitrosylation, ubiquitination, lipidation, hydroxylation, methylation and deamidation. These PTMs influence almost all aspects of communicating junctional channels in normal cell biology and pathophysiology. In this review, we will provide a systematic overview of PTMs of communicating junction proteins and discuss their effects on Cx and Panx-channel activity and localisation.