Combination of EGFR and MEK1/2 inhibitor shows synergistic effects by suppressing EGFR/HER3-dependent AKT activation in human gastric cancer cells

PSMG2-controlled proteasome-autophagy balance mediates the tolerance for MEK-targeted therapy in triple-negative breast cancer

Although the MAPK pathway is aberrantly activated in triple-negative breast cancers (TNBCs), the clinical outcome of MEK-targeted therapy is still poor. Through a genome-wide CRISPR-Cas9 library screening, we find that inhibition of PSMG2 sensitizes TNBC cells BT549 and MB468 to the MEK inhibitor AZD6244. Mechanistically, PSMG2 knockdown impairs proteasome function, which in turn activates autophagy-mediated PDPK1 degradation. The PDPK1 degradation significantly enhances AZD6244-induced tumor cell growth inhibition by interrupting the negative feedback signals toward the AKT pathway. Consistently, co-targeting proteasomes and MEK with inhibitors synergistically suppresses tumor cell growth. The autophagy inhibitor chloroquine partially relieves the PDPK1 degradation and reverses the growth inhibition induced by combinatorial inhibition of MEK and proteasome. The combination regimen with the proteasome inhibitor MG132 plus AZD6244 synergistically inhibits tumor growth in a 4T1 xenograft mouse model. In summary, our study not only unravels the mechanism of MEK inhibitor resistance but also provides a combinatorial therapeutic strategy for TNBC in clinics.

Emerging Neuroblastoma 3D In Vitro Models for Pre-Clinical Assessments

The potential of tumor three-dimensional (3D) in vitro models for the validation of existing or novel anti-cancer therapies has been largely recognized. During the last decade, diverse in vitro 3D cell systems have been proposed as a bridging link between two-dimensional (2D) cell cultures and in vivo animal models, both considered gold standards in pre-clinical settings. The latest awareness about the power of tailored therapies and cell-based therapies in eradicating tumor cells raises the need for versatile 3D cell culture systems through which we might rapidly understand the specificity of promising anti-cancer approaches. Yet, a faithful reproduction of the complex tumor microenvironment is demanding as it implies a suitable organization of several cell types and extracellular matrix components. The proposed 3D tumor models discussed here are expected to offer the required structural complexity while also assuring cost-effectiveness during pre-selection of the most promising therapies. As neuroblastoma is an extremely heterogenous extracranial solid tumor, translation from 2D cultures into innovative 3D in vitro systems is particularly challenging. In recent years, the number of 3D in vitro models mimicking native neuroblastoma tumors has been rapidly increasing. However, in vitro platforms that efficiently sustain patient-derived tumor cell growth, thus allowing comprehensive drug discovery studies on tailored therapies, are still lacking. In this review, the latest neuroblastoma 3D in vitro models are presented and their applicability for a more accurate prediction of therapy outcomes is discussed.

Cetuximab improves AZD6244 antitumor activity in colorectal cancer HT29 cells in vitro and in nude mice by attenuating HER3/Akt pathway activation

The present study investigated the molecular mechanism by which the epidermal growth factor receptor (EGFR) inhibitor cetuximab enhances the antitumor activity of the mitogen-activated protein kinase kinase (MEK) inhibitor AZD6244 in colorectal cancer HT29 cells. HT29 cells were treated with AZD6244 plus cetuximab and then subjected to the following assays: Cell Counting kit-8, BrdU-incorporation, flow cytometric cell cycle distribution and apoptosis analysis, western blot analysis, and nude mouse xenografts. The combination of AZD6244 and cetuximab significantly reduced HT29 cell viability and proliferation compared with AZD6244 alone. The combination treatment reduced the IC₅₀ value from 108.12±10.05 to 28.45±1.92 nM. AZD6244 and cetuximab also induced cell cycle arrest at G1 phase and reduced S phase (88.53% vs. 93.39%, P=0.080; 8.73% vs. 4.24%, P=0.082, respectively). Combination of AZD6244 with cetuximab significantly induced tumor cells apoptosis (14.61% vs. 8.99%, P=0.046). Inhibition of EGFR activity using cetuximab partially abrogated the feedback-activation of phosphorylated receptor tyrosine-protein kinase erB-3 (p-HER3) and p-AKT serine/threonine kinase (AKT), as well as prevented reactivation of p-extracellular regulated kinase (ERK) conferred by AZD6244 treatment. Combination of AZD6244 and cetuximab also inhibited HT29 cell xenograft growth in nude mice and suppressed HER3 and p-AKT levels in xenografts. The EGFR inhibitor cetuximab enhanced the antitumor activity of the MEK inhibitor AZD6244 in colorectal cells in vitro and in vivo. Co-inhibition of MEK and EGFR may be a promising treatment strategy in colorectal cancers.

Synthetic lethal interaction of cetuximab with MEK1/2 inhibition in NRAS-mutant metastatic colorectal cancer

KRAS mutations are an established predictor of lack of response to EGFR-targeted therapies in patients with metastatic colorectal cancer (mCRC). However, little is known about the role of the rarer NRAS mutations as a mechanism of primary resistance to the anti-EGFR monoclonal antibody cetuximab in wild-type KRAS mCRC. Using isogenic mCRC cells with a heterozygous knock-in of the NRAS activating mutation Q61K, we aimed to elucidate the mechanism(s) by which mutant NRAS blocks cetuximab from inhibiting mCRC growth. NRAS^Q61K/+ cells were refractory to cetuximab-induced growth inhibition. Pathway-oriented proteome profiling revealed that cetuximab-unresponsive ERK1/2 phosphorylation was the sole biomarker distinguishing cetuximab-refractory NRAS^Q61K/+ from cetuximab-sensitive NRAS^+/+ cells. We therefore employed four representative MEK1/2 inhibitors (binimetinib, trametinib, selumetinib, and pimasertib) to evaluate the therapeutic value of MEK/ERK signaling in cetuximab-refractory NRAS mutation-induced mCRC. Co-treatment with an ineffective dose of cetuximab augmented, up to more than 1,300-fold, the cytotoxic effects of pimasertib against NRAS^Q61K/+ cells. Simultaneous combination of MEK1/2 inhibitors with cetuximab resulted in extremely high and dose-dependent synthetic lethal effects, which were executed, at least in part, by exacerbated apoptotic cell death. Dynamic monitoring of real-time cell growth rates confirmed that cetuximab synergistically sensitized NRAS^Q61K/+ cellsto MEK1/2 inhibition. Our discovery of a synthetic lethal interaction of cetuximab in combination with MEK1/2 inhibition for the NRAS mutant subgroup of mCRC underscores the importance of therapeutic intervention both in the MEK-ERK and EGFR pathways to achieve maximal therapeutic efficacy against NRAS-mutant mCRC tumors.

Concepts and advances in cancer therapeutic vulnerabilities in RAS membrane targeting

For decades oncogenic RAS proteins were considered undruggable due to a lack of accessible binding pockets on the protein surfaces. Seminal early research in RAS biology uncovered the basic paradigm of post-translational isoprenylation of RAS polypeptides, typically with covalent attachment of a farnesyl group, leading to isoprenyl-mediated RAS anchorage at the plasma membrane and signal initiation at those sites. However, the failure of farnesyltransferase inhibitors to translate to the clinic stymied anti-RAS therapy development. Over the past ten years, a more complete picture has emerged of RAS protein maturation, intracellular trafficking, and location, positioning and retention in subdomains at the plasma membrane, with a corresponding expansion in our understanding of how these properties of RAS contribute to signal outputs. Each of these aspects of RAS regulation presents a potential vulnerability in RAS function that may be exploited for therapeutic targeting, and inhibitors have been identified or developed that interfere with RAS for nearly all of them. This review will summarize current understanding of RAS membrane targeting with a focus on highlighting development and outcomes of inhibitors at each step.

MEK inhibitor trametinib does not prevent the growth of anaplastic lymphoma kinase (ALK)-addicted neuroblastomas

Activation of the RAS-RAF-MEK-ERK signaling pathway is implicated in driving the initiation and progression of multiple cancers. Several inhibitors targeting the RAS-MAPK pathway are clinically approved as single- or polyagent therapies for patients with specific types of cancer. One example is the MEK inhibitor trametinib, which is included as a rational polytherapy strategy for treating EML4-ALK-positive, EGFR-activated, or KRAS-mutant lung cancers and neuroblastomas that also contain activating mutations in the RAS-MAPK pathway. In addition, in neuroblastoma, a heterogeneous disease, relapse cases display an increased rate of mutations in ALK, NRAS, and NF1, leading to increased activation of RAS-MAPK signaling. Co-targeting ALK and the RAS-MAPK pathway is an attractive option, because monotherapies have not yet produced effective results in ALK-addicted neuroblastoma patients. We evaluated the response of neuroblastoma cell lines to MEK-ERK pathway inhibition by trametinib. In contrast to RAS-MAPK pathway-mutated neuroblastoma cell lines, ALK-addicted neuroblastoma cells treated with trametinib showed increased activation (inferred by phosphorylation) of the kinases AKT and ERK5. This feedback response was mediated by the mammalian target of rapamycin complex 2-associated protein SIN1, resulting in increased survival and proliferation that depended on AKT signaling. In xenografts in mice, trametinib inhibited the growth of EML4-ALK-positive non-small cell lung cancer and RAS-mutant neuroblastoma but not ALK-addicted neuroblastoma. Thus, our results advise against the seemingly rational option of using MEK inhibitors to treat ALK-addicted neuroblastoma.

AS1041, a Novel Synthesized Derivative of Marine Natural Compound Aspergiolide A, Arrests Cell Cycle, Induces Apoptosis, and Inhibits ERK Activation in K562 Cells

AS1041 is a novel synthesized anthraquinone lactone derivative of marine natural compound aspergiolide A (ASP-A) with new structure skeleton and marked cytotoxicity in cancer cells. To study its cytotoxicity in detail, we evaluated its activity on human K562 chronic myelogenous leukemia cells and investigated the related molecule mechanisms. AS1041 significantly inhibited the proliferation and colony formation of K562 cells. Moreover, AS1041 arrested cell cycle progression at G2/M phase in a concentration-dependent manner, and also caused concentration- and time-dependent induction of apoptosis. In addition, the molecular mechanisms investigation showed that AS1041 did not localize in the cellular nucleus and did not affect topoisomerases I or II. However, AS1041 could inactivate extracellular signal-regulated kinase (ERK) and contribute to AS1041-induced apoptosis. We concluded that AS1041 was cytotoxic to K562 leukemia cells and the cytotoxicity related to the cell cycle arrest, apoptosis induction, and ERK inhibition. These results implied that AS1041 was a novel derivative of ASP-A with significant cytotoxicity to chronic myelogenous leukemia cells and may have therapeutic potential for the treatment of cancer and leukemia.

Targeting Strategies for the Combination Treatment of Cancer Using Drug Delivery Systems

Cancer cells have characteristics of acquired and intrinsic resistances to chemotherapy treatment-due to the hostile tumor microenvironment-that create a significant challenge for effective therapeutic regimens. Multidrug resistance, collateral toxicity to normal cells, and detrimental systemic side effects present significant obstacles, necessitating alternative and safer treatment strategies. Traditional administration of chemotherapeutics has demonstrated minimal success due to the non-specificity of action, uptake and rapid clearance by the immune system, and subsequent metabolic alteration and poor tumor penetration. Nanomedicine can provide a more effective approach to targeting cancer by focusing on the vascular, tissue, and cellular characteristics that are unique to solid tumors. Targeted methods of treatment using nanoparticles can decrease the likelihood of resistant clonal populations of cancerous cells. Dual encapsulation of chemotherapeutic drug allows simultaneous targeting of more than one characteristic of the tumor. Several first-generation, non-targeted nanomedicines have received clinical approval starting with Doxil® in 1995. However, more than two decades later, second-generation or targeted nanomedicines have yet to be approved for treatment despite promising results in pre-clinical studies. This review highlights recent studies using targeted nanoparticles for cancer treatment focusing on approaches that target either the tumor vasculature (referred to as 'vascular targeting'), the tumor microenvironment ('tissue targeting') or the individual cancer cells ('cellular targeting'). Recent studies combining these different targeting methods are also discussed in this review. Finally, this review summarizes some of the reasons for the lack of clinical success in the field of targeted nanomedicines.

MEK inhibitors induce Akt activation and drug resistance by suppressing negative feedback ERK-mediated HER2 phosphorylation at Thr701

Targeting the MEK/ERK pathway has been viewed as a promising strategy for cancer therapy. However, MEK inhibition leads to the compensatory PI3K/AKT activation and thus contributes to the desensitization of cancer cells to MEK inhibitors. The underlying molecular mechanism of this event is not yet understood. In this study, our data showed that the induction of Akt activity by MEK inhibitors was specifically observed in HER2‐positive breast cancer cells. Silence of HER2, or overexpression of HER2 kinase‐dead mutant, prevents the induction of Akt activation in response to MEK inhibition, indicating HER2 as a critical regulator for this event. Furthermore, HER2 Thr701 was demonstrated as a direct phosphorylation target of ERK1/2. Inhibition of this specific phosphorylation prolonged the dimerization of HER2 with EGFR in a clathrin‐dependent manner, leading to the enhanced activation of HER2 and EGFR tyrosine kinase and their downstream Akt pathway. These results suggest that suppression of ERK‐mediated HER2 Thr701 phosphorylation contributes to MEK inhibitor‐induced Akt activation.

A phase I dose-escalation study of Selumetinib in combination with Erlotinib or Temsirolimus in patients with advanced solid tumors

Background Combinations of molecularly targeted agents may provide optimal anti-tumor activity and improve clinical outcomes for patients with advanced cancers. Selumetinib (AZD6244, ARRY-142886) is an oral, potent and highly selective, allosteric inhibitor of MEK1/2, a component of the RAS/RAF/MEK/ERK pathway which is constitutively activated in many cancers. We investigated the safety, tolerability, and pharmacokinetics (PK) of selumetinib in combination with molecularly targeted drugs erlotinib or temsirolimus in patients with advanced solid tumors. Methods Two-part study: dose escalation, to determine the maximum tolerated dose (MTD) of selumetinib in combination with erlotinib 100 mg once daily (QD) or temsirolimus 25 mg once weekly, followed by dose expansion at the respective combination MTDs to further investigate safety and anti-tumor effects. Results 48 patients received selumetinib plus erlotinib and 32 patients received selumetinib plus temsirolimus. The MTD with erlotinib 100 mg QD was selumetinib 100 mg QD, with diarrhea being dose limiting. The most common all grade adverse events (AEs): diarrhea, rash, nausea, and fatigue. Four (8.3%) patients had ≥12 weeks stable disease. The MTD with temsirolimus 25 mg once weekly was selumetinib 50 mg twice daily (BID), with mucositis and neutropenia being dose limiting. The most commonly reported AEs: nausea, fatigue, diarrhea, and mucositis. Ten (31.3%) patients had ≥12 weeks stable disease. The combination PK profiles were comparable to previously observed monotherapy profiles. Conclusions MTDs were established for selumetinib in combination with erlotinib or temsirolimus. Overlapping toxicities prevented the escalation of selumetinib to its recommended phase II monotherapy dose of 75 mg BID.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00600496; registered 8 July 2009.

Predicting Drug Combination Index and Simulating the Network-Regulation Dynamics by Mathematical Modeling of Drug-Targeted EGFR-ERK Signaling Pathway

Synergistic drug combinations enable enhanced therapeutics. Their discovery typically involves the measurement and assessment of drug combination index (CI), which can be facilitated by the development and applications of in-silico CI predictive tools. In this work, we developed and tested the ability of a mathematical model of drug-targeted EGFR-ERK pathway in predicting CIs and in analyzing multiple synergistic drug combinations against observations. Our mathematical model was validated against the literature reported signaling, drug response dynamics, and EGFR-MEK drug combination effect. The predicted CIs and combination therapeutic effects of the EGFR-BRaf, BRaf-MEK, FTI-MEK, and FTI-BRaf inhibitor combinations showed consistent synergism. Our results suggest that existing pathway models may be potentially extended for developing drug-targeted pathway models to predict drug combination CI values, isobolograms, and drug-response surfaces as well as to analyze the dynamics of individual and combinations of drugs. With our model, the efficacy of potential drug combinations can be predicted. Our method complements the developed in-silico methods (e.g. the chemogenomic profile and the statistically-inferenced network models) by predicting drug combination effects from the perspectives of pathway dynamics using experimental or validated molecular kinetic constants, thereby facilitating the collective prediction of drug combination effects in diverse ranges of disease systems.

Importance of the type I insulin-like growth factor receptor in HER2, FGFR2 and MET-unamplified gastric cancer with and without Ras pathway activation

Amplification of seven oncogenes: HER2, EGFR, FGFR1, FGFR2, MET, KRAS and IGF1R has been identified in gastric cancer. The first five are targeted therapeutically in patients with HER2-positivity, FGFR2- or MET-amplification but the majority of patients are triple-negative and require alternative strategies. Our aim was to evaluate the importance of the IGF1R tyrosine kinase in triple-negative gastric cancer with and without oncogenic KRAS, BRAF or PI3K3CA mutations. Cell lines and metastatic tumor cells isolated from patients expressed IGF1R, and insulin-like growth factor-1 (IGF-1) activated the PI3-kinase/Akt and Ras/Raf/MAP-kinase pathways. IGF-1 protected triple-negative cells from caspase-dependent apoptosis and anoikis. Protection was mediated via the PI3-kinase/Akt pathway. Remarkably, IGF-1-dependent cell survival was greater in patient samples. IGF-1 stimulated triple-negative gastric cancer cell growth was prevented by IGF1R knockdown and Ras/Raf/MAP-kinase pathway inhibition. The importance of the receptor in cell line and metastatic tumor cell growth in serum-containing medium was demonstrated by knockdown and pharmacological inhibition with figitumumab. The proportions of cells in S-phase and mitotic-phase, and Ras/Raf/MAP-kinase pathway activity, were reduced concomitantly. KRAS-addicted and BRAF-impaired gastric cancer cells were particularly susceptible. In conclusion, IGF1R and the IGF signal transduction pathway merit consideration as potential therapeutic targets in patients with triple-negative gastric cancer.

Phosphoproteomics Reveals MAPK Inhibitors Enhance MET- and EGFR-Driven AKT Signaling in KRAS-Mutant Lung Cancer

Pathway inhibition of the RAS-driven MAPK pathway using small-molecule kinase inhibitors has been a key focus for treating cancers driven by oncogenic RAS, yet significant clinical responses are lacking. Feedback reactivation of ERK driven by drug-induced RAF activity has been suggested as one of the major drug resistance mechanisms, especially in the context of oncogenic RAS. To determine whether additional adaptive resistance mechanisms may coexist, we characterized global phosphoproteomic changes after MEK inhibitor selumetinib (AZD6244) treatment in KRAS-mutant A427 and A549 lung adenocarcinoma cell lines employing mass spectrometry-based phosphoproteomics. We identified 9,075 quantifiable unique phosphosites (corresponding to 3,346 unique phosphoproteins), of which 567 phosphosites were more abundant and 512 phosphosites were less abundant after MEK inhibition. Selumetinib increased phosphorylation of KSR-1, a scaffolding protein required for assembly of MAPK signaling complex, as well as altered phosphorylation of GEF-H1, a novel regulator of KSR-1 and implicated in RAS-driven MAPK activation. Moreover, selumetinib reduced inhibitory serine phosphorylation of MET at Ser985 and potentiated HGF- and EGF-induced AKT phosphorylation. These results were recapitulated by pan-RAF (LY3009120), MEK (GDC0623), and ERK (SCH772984) inhibitors, which are currently under early-phase clinical development against RAS-mutant cancers. Our results highlight the unique adaptive changes in MAPK scaffolding proteins (KSR-1, GEF-H1) and in RTK signaling, leading to enhanced PI3K-AKT signaling when the MAPK pathway is inhibited.

IMPLICATIONS

This study highlights the unique adaptive changes in MAPK scaffolding proteins (KSR-1, GEF-H1) and in RTK signaling, leading to enhanced PI3K/AKT signaling when the MAPK pathway is inhibited. Mol Cancer Res; 14(10); 1019-29. ©2016 AACR.

Drosophila Lung Cancer Models Identify Trametinib plus Statin as Candidate Therapeutic

We have developed a Drosophila lung cancer model by targeting Ras1(G12V)--alone or in combination with PTEN knockdown--to the Drosophila tracheal system. This led to overproliferation of tracheal tissue, formation of tumor-like growths, and animal lethality. Screening a library of FDA-approved drugs identified several that improved overall animal survival. We explored two hits: the MEK inhibitor trametinib and the HMG-CoA reductase inhibitor fluvastatin. Oral administration of these drugs inhibited Ras and PI3K pathway activity, respectively; in addition, fluvastatin inhibited protein prenylation downstream of HMG-CoA reductase to promote survival. Combining drugs led to synergistic suppression of tumor formation and rescue lethality; similar synergy was observed in human A549 lung adenocarcinoma cells. Notably, fluvastatin acted both within transformed cells and also to reduce whole-body trametinib toxicity in flies. Our work supports and provides further context for exploring the potential of combining statins with MAPK inhibitors such as trametinib to improve overall therapeutic index.

HER3/ErbB3, an emerging cancer therapeutic target

HER3 is a member of the HER (EGFR/ErbB) receptor family consisting of four closely related type 1 transmembrane receptors (EGFR, HER2, HER3, and HER4). HER receptors are part of a complex signaling network intertwined with the Ras/Raf/MAPK, PI3K/AKT, JAK/STAT, and PKC signaling pathways. Aberrant activation of the HER receptors and downstream signaling molecules tips the balance on cellular events, leading to various types of cancers. Monoclonal antibodies (mAbs) and small molecule inhibitors targeting EGFR and HER2 tyrosine kinase activities exhibit clinical benefits in the treatment of several types of cancers, but their clinical efficacy is limited by the occurrence of drug resistance. HER3 is the preferred dimerization partner of HER2 and it is well established that HER3 plays an important role in drug resistance to EGFR- and HER2-targeting therapies. Since HER3 has limited kinase activity, mAbs are being explored to target HER3 for cancer therapy. Currently, approximately a dozen of anti-HER3 mAbs are at different stages of clinical development. However, the lack of established biomarkers has made it more challenging to stratify cancer patients to whom HER3-targeting therapies can be more effective. In this review, we focus on the validation of HER3 as a cancer drug target, the recent development in biomarker discovery for anti-HER3 therapies, and the progress made in the clinical development of HER3-targeting mAbs.

Epigenetic activation of a cryptic TBC1D16 transcript enhances melanoma progression by targeting EGFR

Metastasis is responsible for most cancer-related deaths, and, among common tumor types, melanoma is one with great potential to metastasize. Here we study the contribution of epigenetic changes to the dissemination process by analyzing the changes that occur at the DNA methylation level between primary cancer cells and metastases. We found a hypomethylation event that reactivates a cryptic transcript of the Rab GTPase activating protein TBC1D16 (TBC1D16-47 kDa; referred to hereafter as TBC1D16-47KD) to be a characteristic feature of the metastatic cascade. This short isoform of TBC1D16 exacerbates melanoma growth and metastasis both in vitro and in vivo. By combining immunoprecipitation and mass spectrometry, we identified RAB5C as a new TBC1D16 target and showed that it regulates EGFR in melanoma cells. We also found that epigenetic reactivation of TBC1D16-47KD is associated with poor clinical outcome in melanoma, while conferring greater sensitivity to BRAF and MEK inhibitors.

Consequences of feedback in signal transduction for targeted therapies

Over the last two decades, many small-molecule inhibitors that target kinase signalling have been developed. More than 20 of these inhibitors are FDA (U.S. Food and Drug Administration)-approved and are now being used in the clinics to treat tumours; even more have entered clinical trials. However, resistance to these inhibitors, either intrinsic to the tumour or acquired during treatment, remains a major problem in targeted therapeutics. One of the mechanisms by which tumours become resistant is the rewiring of the signalling networks via feedback, by which the tumour cells re-activate signalling or activate alternative signalling pathways. In the present article, we review insights from recent quantitative signalling studies combining mathematical modelling and experiments that revealed how feedback rewires MAPK (mitogen-activated protein kinase)/PI3K (phosphoinositide 3-kinase) signalling upon treatment and how that affects drug sensitivity.

MDM4 expression as an indicator of TP53 reactivation by combined targeting of MDM2 and MDM4 in cancer cells without TP53 mutation

MDM2 and MDM4, a structurally related MDM2 homolog, negatively regulates expression and functions of TP53 tumor suppressor gene. To explore the precise expression patterns and function of MDM2 and MDM4 in wild-type (wt) TP53 cancer cells, we analyzed 11 various cancer cell lines with wt TP53. All cell lines exhibited deregulated expression of MDM2 and MDM4, and were divided into two distinct types; the one expressing high levels of MDM4 and another expressing low levels of MDM4. The low MDM4 type expressed higher MDM2 levels than the high MDM4 type. In cells with high MDM4 expression, knockdown of MDM4 or MDM2 reactivated TP53, and simultaneous knockdown of MDM2 and MDM4 synergistically reactivated TP53. In contrast, in cells with low MDM4 expression, knockdown of only MDM2 reactivated TP53. These results suggest that both MDM2 and MDM4 are closely involved in TP53 inactivation in cancer cells with high MDM4 expression, whereas only MDM2, and not MDM4, is a regulator of TP53 in cells with low MDM4 expression. MDM4 expression in wt TP53-tumors is a potential indicator for TP53 reactivation cancer therapy by simultaneous targeting of MDM4 and MDM2. Specific knockdown of MDM2 and MDM4 might be applicable for TP53 restoration therapy.

An increase in integrin-linked kinase non-canonically confers NF-κB-mediated growth advantages to gastric cancer cells by activating ERK1/2

Background

Increased activity or expression of integrin-linked kinase (ILK), which regulates cell adhesion, migration, and proliferation, leads to oncogenesis. We identified the molecular basis for the regulation of ILK and its alternative role in conferring ERK1/2/NF-κB-mediated growth advantages to gastric cancer cells.

Results

Inhibiting ILK with short hairpin RNA or T315, a putative ILK inhibitor, abolished NF-κB-mediated the growth in the human gastric cancer cells AGS, SNU-1, MKN45, and GES-1. ILK stimulated Ras activity to activate the c-Raf/MEK1/2/ERK1/2/ribosomal S6 kinase/inhibitor of κBα/NF-κB signaling by facilitating the formation of the IQ motif-containing GTPase-activating protein 1 (IQGAP1)–Ras complex. Forced enzymatic ILK expression promoted cell growth by facilitating ERK1/2/NF-κB signaling. PI3K activation or decreased PTEN expression prolonged ERK1/2 activation by protecting ILK from proteasome-mediated degradation. C-terminus of heat shock cognate 70 interacting protein, an HSP90-associated E3 ubiquitin ligase, mediated ILK ubiquitination to control PI3K- and HSP90-regulated ILK stabilization and signaling. In addition to cell growth, the identified pathway promoted cell migration and reduced the sensitivity of gastric cancer cells to the anticancer agents 5-fluorouracil and cisplatin. Additionally, exogenous administration of EGF as well as overexpression of EGFR triggered ILK- and IQGAP1-regulated ERK1/2/NF-κB activation, cell growth, and migration.

Conclusion

An increase in ILK non-canonically promotes ERK1/2/NF-κB activation and leads to the growth of gastric cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-014-0069-3) contains supplementary material, which is available to authorized users.

Metastatic tumor evolution and organoid modeling implicate TGFBR2 as a cancer driver in diffuse gastric cancer

Background

Gastric cancer is the second-leading cause of global cancer deaths, with metastatic disease representing the primary cause of mortality. To identify candidate drivers involved in oncogenesis and tumor evolution, we conduct an extensive genome sequencing analysis of metastatic progression in a diffuse gastric cancer. This involves a comparison between a primary tumor from a hereditary diffuse gastric cancer syndrome proband and its recurrence as an ovarian metastasis.

Results

Both the primary tumor and ovarian metastasis have common biallelic loss-of-function of both the CDH1 and TP53 tumor suppressors, indicating a common genetic origin. While the primary tumor exhibits amplification of the Fibroblast growth factor receptor 2 (FGFR2) gene, the metastasis notably lacks FGFR2 amplification but rather possesses unique biallelic alterations of Transforming growth factor-beta receptor 2 (TGFBR2), indicating the divergent in vivo evolution of a TGFBR2-mutant metastatic clonal population in this patient. As TGFBR2 mutations have not previously been functionally validated in gastric cancer, we modeled the metastatic potential of TGFBR2 loss in a murine three-dimensional primary gastric organoid culture. The Tgfbr2 shRNA knockdown within Cdh1^-/-; Tp53^-/- organoids generates invasion in vitro and robust metastatic tumorigenicity in vivo, confirming Tgfbr2 metastasis suppressor activity.

Conclusions

We document the metastatic differentiation and genetic heterogeneity of diffuse gastric cancer and reveal the potential metastatic role of TGFBR2 loss-of-function. In support of this study, we apply a murine primary organoid culture method capable of recapitulating in vivo metastatic gastric cancer. Overall, we describe an integrated approach to identify and functionally validate putative cancer drivers involved in metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0428-9) contains supplementary material, which is available to authorized users.

Discovery of novel AKT inhibitors with enhanced anti-tumor effects in combination with the MEK inhibitor

Tumor cells upregulate many cell signaling pathways, with AKT being one of the key kinases to be activated in a variety of malignancies. GSK2110183 and GSK2141795 are orally bioavailable, potent inhibitors of the AKT kinases that have progressed to human clinical studies. Both compounds are selective, ATP-competitive inhibitors of AKT 1, 2 and 3. Cells treated with either compound show decreased phosphorylation of several substrates downstream of AKT. Both compounds have desirable pharmaceutical properties and daily oral dosing results in a sustained inhibition of AKT activity as well as inhibition of tumor growth in several mouse tumor models of various histologic origins. Improved kinase selectivity was associated with reduced effects on glucose homeostasis as compared to previously reported ATP-competitive AKT kinase inhibitors. In a diverse cell line proliferation screen, AKT inhibitors showed increased potency in cell lines with an activated AKT pathway (via PI3K/PTEN mutation or loss) while cell lines with activating mutations in the MAPK pathway (KRAS/BRAF) were less sensitive to AKT inhibition. Further investigation in mouse models of KRAS driven pancreatic cancer confirmed that combining the AKT inhibitor, GSK2141795 with a MEK inhibitor (GSK2110212; trametinib) resulted in an enhanced anti-tumor effect accompanied with greater reduction in phospho-S6 levels. Taken together these results support clinical evaluation of the AKT inhibitors in cancer, especially in combination with MEK inhibitor.

Novel synthetic oleanane triterpenoid AMR-MeOAc inhibits K-Ras through ERK, Akt and survivin in pancreatic cancer cells

K-Ras activating mutations are a major problem that drives aggressive tumor growth and metastasis in pancreatic cancer. Currently, there are no effective targeted therapies for this genetically defined subset of cancers harboring oncogenic K-Ras mutations that confer drug resistance, aggressive tumor growth, metastasis and poor clinical outcome. We identified a novel synthetic oleanane triterpenoid compound designated AMR-MeOAc that effectively kills K-Ras mutant pancreatic cancer HPAF-II cells. The cytotoxic effects correlated with apoptosis induction, as was evidenced by increase of apoptosis cells upon the treatment of AMR-MeOAc in HPAF-II cells. Our studies revealed that AMR-MeOAc treatment inhibits cancer associated survival gene survivin. Moreover, AMR-MeOAc also led to down regulation of Akt, ERK1/2 and survivin protein levels. Our results indicate that AMR-MeOAc or its active analogs could be a novel class of anticancer agents against K-Ras driven human pancreatic cancer.

ERK1/2 blockade prevents epithelial-mesenchymal transition in lung cancer cells and promotes their sensitivity to EGFR inhibition

Overcoming cellular mechanisms of de novo and acquired resistance to drug therapy remains a central challenge in the clinical management of many cancers, including non-small cell lung cancer (NSCLC). Although much work has linked the epithelial-mesenchymal transition (EMT) in cancer cells to the emergence of drug resistance, it is less clear where tractable routes may exist to reverse or inhibit EMT as a strategy for drug sensitization. Here, we demonstrate that extracellular signal-regulated kinase (ERK) 1/2 (mitogen-activated protein kinase 3/1, MAPK3/1) signaling plays a key role in directing the mesenchymal character of NSCLC cells and that blocking ERK signaling is sufficient to heighten therapeutic responses to EGF receptor (EGFR) inhibitors. MEK1/2 (MAPKK1/2) inhibition promoted an epithelial phenotype in NSCLC cells, preventing induction of EMT by exogenous TGF-β. Moreover, in cells exhibiting de novo or acquired resistance to the EGFR inhibitor gefitinib, MEK inhibition enhanced the sensitivity to gefitinib and slowed cell migration. These effects only occurred, however, if MEK was inhibited for a period sufficient to trigger changes in EMT marker expression. Consistent with these findings, changes in EMT phenotypes and markers were also induced by the expression of mutant KRAS in a MEK-dependent manner. Our results suggest that prolonged exposure to MEK or ERK inhibitors may not only restrain EMT but also overcome naïve or acquired resistance of NSCLC to EGFR-targeted therapy in the clinic.

Claudin-3 overexpression increases the malignant potential of colorectal cancer cells: roles of ERK1/2 and PI3K-Akt as modulators of EGFR signaling

The altered expressions of claudin proteins have been reported during the tumorigenesis of colorectal cancer. However, the molecular mechanisms that regulate these events in this cancer type are poorly understood. Here, we report that epidermal growth factor (EGF) increases the expression of claudin-3 in human colorectal adenocarcinoma HT-29 cells. This increase was related to increased cell migration and the formation of anchorage-dependent and anchorage-independent colonies. We further showed that the ERK1/2 and PI3K-Akt pathways were involved in the regulation of these effects because specific pharmacological inhibition blocked these events. Genetic manipulation of claudin-1 and claudin-3 in HT-29 cells showed that the overexpression of claudin-1 resulted in decreased cell migration; however, migration was not altered in cells that overexpressed claudin-3. Furthermore, the overexpression of claudin-3, but not that of claudin-1, increased the tight junction-related paracellular flux of macromolecules. Additionally, an increased formation of anchorage-dependent and anchorage-independent colonies were observed in cells that overexpressed claudin-3, while no such changes were observed when claudin-1 was overexpressed. Finally, claudin-3 silencing alone despite induce increase proliferation, and the formation of anchoragedependent and -independent colonies, it was able to prevent the EGF-induced increased malignant potential. In conclusion, our results show a novel role for claudin-3 overexpression in promoting the malignant potential of colorectal cancer cells, which is potentially regulated by the EGF-activated ERK1/2 and PI3K-Akt pathways.

Network quantification of EGFR signaling unveils potential for targeted combination therapy

The epidermal growth factor receptor (EGFR) signaling network is activated in most solid tumors, and small-molecule drugs targeting this network are increasingly available. However, often only specific combinations of inhibitors are effective. Therefore, the prediction of potent combinatorial treatments is a major challenge in targeted cancer therapy. In this study, we demonstrate how a model-based evaluation of signaling data can assist in finding the most suitable treatment combination. We generated a perturbation data set by monitoring the response of RAS/PI3K signaling to combined stimulations and inhibitions in a panel of colorectal cancer cell lines, which we analyzed using mathematical models. We detected that a negative feedback involving EGFR mediates strong cross talk from ERK to AKT. Consequently, when inhibiting MAPK, AKT activity is increased in an EGFR-dependent manner. Using the model, we predict that in contrast to single inhibition, combined inactivation of MEK and EGFR could inactivate both endpoints of RAS, ERK and AKT. We further could demonstrate that this combination blocked cell growth in BRAF- as well as KRAS-mutated tumor cells, which we confirmed using a xenograft model.

MEK inhibitors as a chemotherapeutic intervention in multiple myeloma

The Ras/Raf/MEK/extracellular signal regulated kinase (ERK) (Ras/mitogen-activated protein kinases (MAPK)) signal transduction pathway is a crucial mediator of many fundamental biological processes, including cellular proliferation, survival, angiogenesis and migration. Aberrant signalling through the Ras/MAPK cascade is common in a wide array of malignancies, including multiple myeloma (MM), making it an appealing candidate for the development of novel targeted therapies. In this review, we explore our current understanding of the Ras/MAPK pathway and its role in MM. Additionally, we summarise the current status of small molecule inhibitors of MEK under clinical evaluation, and discuss future approaches required to optimise their use.

OPB-31121, a novel small molecular inhibitor, disrupts the JAK2/STAT3 pathway and exhibits an antitumor activity in gastric cancer cells

We investigated the mechanisms of action and antitumor effects of OPB-31121, a novel STAT3 inhibitor, in gastric cancer cells. OPB-31121 downregulated JAK2 and gp130 expression and inhibited JAK2 phosphorylation which leads to inhibition of STAT3 phosphorylation. OPB-31121 inhibited constitutively activated and IL-6-induced JAK/STAT signaling pathway. OPB-31121 decreased cell proliferation in both gastric cancer cells and in a xenograft model, induced the apoptosis of gastric cancer cells, inhibited the expression of antiapoptotic proteins, and showed synergism with 5-fluorouracil and cisplatin. Taken together, our study suggests that STAT3 inhibition with OPB-31121 can be tested in patients with gastric cancer.

Exploiting MEK inhibitor-mediated activation of ERα for therapeutic intervention in ER-positive ovarian carcinoma

While the clinical benefit of MEK inhibitor (MEKi)-based therapy is well established in Raf mutant malignancies, its utility as a suppressor of hyperactive MAPK signaling in the absence of mutated Raf or Ras, is an area of ongoing research. MAPK activation is associated with loss of ERα expression and hormonal resistance in numerous malignancies. Herein, we demonstrate that MEKi induces a feedback response that results in ERα overexpression, phosphorylation and transcriptional activation of ER-regulated genes. Mechanistically, MEKi-mediated ERα overexpression is largely independent of erbB2 and AKT feedback activation, but is ERK-dependent. We subsequently exploit this phenomenon therapeutically by combining the ER-antagonist, fulvestrant with MEKi. This results in synergistic suppression of tumor growth, in vitro and potentiation of single agent activity in vivo in nude mice bearing xenografts. Thus, we demonstrate that exploiting adaptive feedback after MEKi can be used to sensitize ERα-positive tumors to hormonal therapy, and propose that this strategy may have broader clinical utility in ERα-positive ovarian carcinoma.

EGFR/TGFα and TGFβ/CTGF Signaling in Neuroendocrine Neoplasia: Theoretical Therapeutic Targets

Neuroendocrine neoplasms (NENs) are a heterogeneous family of malignancies whose proliferation is partially dependent on growth factors secreted by the microenvironment and the tumor itself. Growth factors which were demonstrated to be important in experimental models of NENs include EGF (epidermal growth factor), TGF (transforming growth factor) α, TGFβ and CTGF (connective tissue growth factor). EGF and TGFα bind to the EGF receptor to stimulate an intact RAS/RAF/MAPK pathway, leading to the transcription of genes associated with cell proliferation, invasion and metastasis. Theoretically, TGFα stimulation can be inhibited at several points of the MAPK pathway, but success is limited to NEN models and is not evident in the clinical setting. TGFβ1 stimulates TGFβ receptors (TGFβRI and TGFβRII) resulting in inhibition of neuroendocrine cell growth through SMAD-mediated activation of the growth inhibitor P21(WAF1/CIP1). Although some NENs are inhibited by TGFβ1, paradoxical growth is seen in experimental models of gastric and small intestinal (SI) NENs. Therapeutic targeting of TGFβ1 in NENs is therefore complicated by uncertainty of the effect of TGFβ1 secretion on the direction of proliferative regulation. CTGF expression is associated with more malignant clinical phenotypes in a variety of cancers, including NENs. CTGF promotes growth in gastric and SI-NEN models, and is implicated as a mediator of local and distant fibrosis caused by NENs of enterochromaffin cell origin. CTGF inhibitors are available, but their anti-proliferative effect has not been tested in NENs. In summary, growth factors are essential for NEN proliferation, and although interventions targeting these proteins are effective in experimental models, only limited clinical efficacy has been identified.

Antitumor activity of saracatinib (AZD0530), a c-Src/Abl kinase inhibitor, alone or in combination with chemotherapeutic agents in gastric cancer

Src is a nonreceptor tyrosine kinase involved in the cross-talk and mediation of many signaling pathways that promote cell proliferation, adhesion, invasion, migration, and tumorigenesis. Increased Src activity has been reported in many types of human cancer, including gastric cancer. Therefore, this factor has been identified as a promising therapeutic target for cancer treatments, and targeting Src in gastric cancer is predicted to have potent effects. We evaluated the antitumor effect of a c-Src/Abl kinase inhibitor, saracatinib (AZD0530), alone or combined with chemotherapeutic agents in gastric cancer cell lines and a NCI-N87 xenograft model. Among 10 gastric cancer cell lines, saracatinib specifically inhibited the growth and migration/invasion of SNU216 and NCI-N87 cells. Saracatinib blocked the Src/FAK, HER family, and oncogenic signaling pathways, and it induced G(1) arrest and apoptosis in SNU216 and NCI-N87 cells. Apoptosis required induction of the proapoptotic BCL2 family member Bim. Knockdown of Bim using siRNA decreased apoptosis induced by treatment with saracatinib, suggesting that Bim has an important role in saracatinib-induced apoptosis. Saracatinib enhanced the effects of lapatinib, an EGFR/HER2 dual inhibitor, in SNU216 and NCI-N87 cells. Furthermore, combined treatment with saracatinib and 5-fluorouracil (5-FU) or cisplatin exerted synergistic effects in both saracatinib-sensitive and saracatinib-resistant cells. Consistent with our in vitro findings, cotreatment with saracatinib and 5-FU resulted in enhanced antitumor activity in the NCI-N87 xenografts. These data indicate that the inhibition of Src kinase activity by saracatinib alone or in combination with other agents can be a strategy to target gastric cancer.

K-RAS mutant pancreatic tumors show higher sensitivity to MEK than to PI3K inhibition in vivo

Activating K-RAS mutations occur at a frequency of 90% in pancreatic cancer, and to date no therapies exist targeting this oncogene. K-RAS signals via downstream effector pathways such as the MAPK and the PI3K signaling pathways, and much effort has been focused on developing drugs targeting components of these pathways. To better understand the requirements for K-RAS and its downstream signaling pathways MAPK and PI3K in pancreatic tumor maintenance, we established an inducible K-RAS knock down system that allowed us to ablate K-RAS in established tumors. Knock down of K-RAS resulted in impaired tumor growth in all pancreatic xenograft models tested, demonstrating that K-RAS expression is indeed required for tumor maintenance of K-RAS mutant pancreatic tumors. We further examined signaling downstream of K-RAS, and detected a robust reduction of pERK levels upon K-RAS knock down. In contrast, no effect on pAKT levels could be observed due to almost undetectable basal expression levels. To investigate the requirement of the MAPK and the PI3K pathways on tumor maintenance, three selected pancreatic xenograft models were tested for their response to MEK or PI3K inhibition. Tumors of all three models regressed upon MEK inhibition, but showed less pronounced response to PI3K inhibition. The effect of MEK inhibition on pancreatic xenografts could be enhanced further by combined application of a PI3K inhibitor. These data provide further rationale for testing combinations of MEK and PI3K inhibitors in clinical trials comprising a patient population with pancreatic cancer harboring mutations in K-RAS.

ERBB3 (HER3) is a key sensor in the regulation of ERBB-mediated signaling in both low and high ERBB2 (HER2) expressing cancer cells

Aberrant expression and activation of EGFR and ERBB2 (HER2) have been successfully targeted for cancer therapeutics. Recent evidence from both basic and clinical studies suggests that ERBB3 (HER3) serves as a key activator of downstream signaling through dimerization with other ERBB proteins and plays a critical role in the widespread clinical resistance to EGFR and HER2 targeting cancer therapies. As a result, HER3 is actively pursued as an antibody therapeutic target for cancer. Ligand binding is thought to be a prerequisite for dimerization of HER3 with other ERBB proteins, which results in phosphorylation of its c-terminal tyrosine residues and activation of downstream AKT and MAPK signaling pathways. In this study, we report that an anti-HER2 monoclonal antibody (HER2Mab), which blocks HER2 dimerization with HER3, induces HER3 dimerization with EGFR in both low and high HER2 expressing cancer cells. Treatment of the low HER2 expressing MCF7 cancer cells with HER2Mab promoted cell proliferation and migration in the absence of HER3 ligand stimulation. Follow-up studies revealed that HER2Mab-induced HER3 signaling via EGFR/HER3 dimerization and activation of downstream AKT signaling pathways. These results suggest that equilibrium of dimerization among the ERBB proteins can be perturbed by HER2Mab and HER3 plays a key role in sensing the perturbation.

Activity of the MEK inhibitor selumetinib (AZD6244; ARRY-142886) in nasopharyngeal cancer cell lines

This study evaluated the preclinical activity of selumetinib (AZD6244, ARRY-142866), an inhibitor of the mitogen-activated protein kinase kinase (MAPKK or MEK1/2) in 6 nasopharyngeal cancer (NPC) cell lines. Selumetinib could achieve up to 90 % inhibition of cell growth with the respective IC(50) values in NPC cell lines as follow: HK1 = 0.04 μM, HK1-LMP1(B95.8) = 0.17 μM, HONE-1-EBV = 0.46 μM, HONE-1 = 1.79 μM, CNE-2 = 2.20 μM and C666-1 > 10 μM. The drug-sensitive cell lines HK1, HK1-LMP1(B95.8) and HONE-1-EBV have higher basal expression of phosphorylated (pi)-MAPK than the less sensitive cell lines. BRAF mutations were not detected in all 6 cell lines. Re-introduction of the EBV genome into HONE-1 cells, generating the HONE-1-EBV cell line, seemed to result in elevated expression of pi-MAPK and sensitivity to selumetinib when compared with the parental HONE-1 cells. At a concentration of 0.5 μM and 5 μM, selumetinib induced apoptosis (as indicated by cleaved PARP expression and caspase 3 induction), and G(0)/G(1) cycle arrest in HONE-1-EBV and HK1-LMP1(B95.8) cells. The combination of selumetinib (at IC(25) concentration) and the EGFR tyrosine kinase inhibitor, gefitinib (at concentrations of 0.1, 3 and 9 μM) resulted in synergistic growth inhibition in HK1-LMP1(B95.8) cells. The combination of selumetinib (at IC(25) concentration) and cisplatin (at concentrations of 0.1, 0.4, 0.8 and 2 μM) resulted in synergistic growth inhibition in HONE-1 and HONE-1-EBV cells. This result suggests that selumetinib alone or in combination with gefitinib or cisplatin maybe a promising strategy against NPC. Further studies are warranted.

MEK inhibition leads to PI3K/AKT activation by relieving a negative feedback on ERBB receptors

The phosphoinositide 3-kinase (PI3K)/AKT and RAF/MEK/ERK signaling pathways are activated in a wide range of human cancers. In many cases, concomitant inhibition of both pathways is necessary to block proliferation and induce cell death and tumor shrinkage. Several feedback systems have been described in which inhibition of one intracellular pathway leads to activation of a parallel signaling pathway, thereby decreasing the effectiveness of single-agent targeted therapies. In this study, we describe a feedback mechanism in which MEK inhibition leads to activation of PI3K/AKT signaling in EGFR and HER2-driven cancers. We found that MEK inhibitor-induced activation of PI3K/AKT resulted from hyperactivation of ERBB3 as a result of the loss of an inhibitory threonine phosphorylation in the conserved juxtamembrane domains of EGFR and HER2. Mutation of this amino acid led to increased ERBB receptor activation and upregulation of the ERBB3/PI3K/AKT signaling pathway, which was no longer responsive to MEK inhibition. Taken together, these results elucidate an important, dominant feedback network regulating central oncogenic pathways in human cancer.

Sorafenib and Mek inhibition is synergistic in medullary thyroid carcinoma in vitro

Clinical trials using kinase inhibitors have demonstrated transient partial responses and disease control in patients with progressive medullary thyroid cancer (MTC). The goal of this study was to identify potential combinatorial strategies to improve on these results using sorafenib, a multikinase inhibitor with activity in MTC, as a base compound to explore signaling that might predict synergystic interactions. Two human MTC cell lines, TT and MZ-CRC-1, which harbor endogenous C634W or M918T RET mutations, respectively, were exposed to sorafenib, everolimus, and AZD6244 alone and in combination. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide (MTT) and poly (ADP-ribose) polymerase (PARP) cleavage assays were performed to measure cell survival and apoptosis. Western blots were performed to confirm activity of the compounds and to determine possible mechanisms of resistance and predictors of synergy. As a solitary agent, sorafenib was the most active compound on MTT assay. Western blots confirmed that sorafenib, everolimus, and AZD6244 inhibited their anticipated targets. At concentrations below its IC(50), sorafenib-treated TT and MZ-CRC-1 cells demonstrated transient inhibition and then re-activation of Erk over 6 h. In concordance, synergistic effects were only identified using sorafenib in combination with the Mek inhibitor AZD6244 (P<0.001 for each cell line). Cells treated with everolimus demonstrated activation of Akt and Ret via TORC2 complex-dependent and TORC2 complex-independent mechanisms respectively. Everolimus was neither additive nor syngergistic in combination with sorafenib or AZD6244. In conclusion, sorafenib combined with a Mek inhibitor demonstrated synergy in MTC cells in vitro. Mechanisms of resistance to everolimus in MTC cells likely involved TORC2-dependent and TORC2-independent pathways.

Targeted therapies for gastric cancer: current status

Gastric cancer represents one of the most common cancers internationally. Unfortunately the majority of patients still present at an advanced stage, and despite advances in diagnostic and treatment strategies, outcomes still remain poor with high mortality rates despite a decline in incidence. Whilst the utility of classical chemotherapy agents has been explored thoroughly (and continues to be investigated, alone or in various combinations), advances have been slow and the efficacy of these agents has reached a plateau. As such, the focus of recent study has shifted toward developing a greater understanding of the molecular biology of carcinogenesis and the cancer cell phenotype, and, in turn, the development of rationally designed drugs that target molecular aberrancies in signal transduction pathways specific to gastric cancer. These targets include circulating growth and angiogenic factors, cell surface receptors, and other molecules that comprise downstream intracellular signalling pathways, including receptor tyrosine kinases. Therapeutic advances in this area significantly lag behind other solid organ malignancies such as breast and colorectal cancer. This article reviews the role of targeted therapies in gastric cancer, including rationale and mechanism of action, current and emerging data, as single-agent therapy or in combination regimens. A recently published randomized phaseIII trial supporting the use of trastuzumab, an anti-human epidermal growth factor receptor 2 (HER2)/neu monoclonal antibody, in a selected population of patients is discussed. Therapies that have been evaluated in phase II trials are also reviewed, as well as promising new therapies currently being investigated in preclinical or phase I studies. There is optimism that targeted therapies, whether as single-agent therapy or in combination with traditional therapies, including chemotherapy, radiotherapy and surgery, may yet have an impact on improvement of the overall prognosis of gastric cancer.

Sunitinib synergizes the antitumor effect of cisplatin via modulation of ERCC1 expression in models of gastric cancer

We evaluated the effects of sunitinib monotherapy and in combination with cisplatin in human gastric cancer cell lines. Sunitinib showed antiproliferative effect in gastric cancer cells line with high PDGFRA expression. Knockdown of PDGFRA showed that sunitinib sensitivity was correlated with the basal expression of PDGFRA. Synergistic growth inhibitory activity in combination with cisplatin was identified. We further explored how sunitinib potentiated the activity of cisplatin. We found that sunitinib treatment resulted in the down-regulation of ERCC1 expression via the modulation of PDGFRA expression in gastric cancer cells. The effect was verified via SNU484 xenograft model. Our data support the rationale of clinical trial using sunitinib in combination of cisplatin in gastric cancer.

Deciphering the role of forkhead transcription factors in cancer therapy

Forkhead O transcription factors (FOXO) are critical for the regulation of cell cycle arrest, cell death, and DNA damage repair. Inactivation of FOXO proteins may be associated with tumorigenesis, including breast cancer, prostate cancer, glioblastoma, rhabdomyosarcoma, and leukemia. Accumulated evidence shows that activation of oncogenic pathways such as phosphoinositide-3-kinase/AKT/IKK or RAS/mitogen-activated protein kinase suppresses FOXO transcriptional activity through the phosphorylation of FOXOs at different sites that ultimately leads to nuclear exclusion and degradation of FOXOs. In addition, posttranslational modifications of FOXOs such as acetylation, methylation and ubiquitination also contribute to modulating FOXO3a functions. Several anti-cancer drugs like paclitaxel, imatinib, and doxorubicin activate FOXO3a by counteracting those oncogenic pathways which restrain FOXOs functions. In this review, we will illustrate the regulation of FOXOs and reveal potential therapeutics that target FOXOs for cancer treatment.

Down-regulation of mitogen-inducible gene 6, a negative regulator of EGFR, enhances resistance to MEK inhibition in KRAS mutant cancer cells

Previously, we found that KRAS mutant cancer cells showed variable response to AZD6244, a MEK inhibitor through differential activation of EGFR/AKT. To investigate its mechanism, we performed cDNA microarray using four KRAS mutant cancer cells. We found that treatment with AZD6244 reduced the expression of mitogen-inducible gene 6 (MIG6), a negative feedback regulator for EGFR, in AZD6244-resistant cells, while activity of EGFR and AKT was increased in these cells. Reconstitution or knockdown of MIG6 expression affected cancer cell responses to AZD6244. Treatment with a combination of EGFR inhibitor and AZD6244 inhibited cell proliferation synergistically without activation of AKT in AZD6244-resistant cells. Our study provides a mechanism of differential response to MEK inhibition in KRAS mutant cancer.

Deep sequencing of gastric carcinoma reveals somatic mutations relevant to personalized medicine

BACKGROUND

Globally, gastric cancer is the second most common cause of cancer-related death, with the majority of the health burden borne by economically less-developed countries.

METHODS

Here, we report a genetic characterization of 50 gastric adenocarcinoma samples, using affymetrix SNP arrays and Illumina mRNA expression arrays as well as Illumina sequencing of the coding regions of 384 genes belonging to various pathways known to be altered in other cancers.

RESULTS

Genetic alterations were observed in the WNT, Hedgehog, cell cycle, DNA damage and epithelial-to-mesenchymal-transition pathways.

CONCLUSIONS

The data suggests targeted therapies approved or in clinical development for gastric carcinoma would be of benefit to ~22% of the patients studied. In addition, the novel mutations detected here, are likely to influence clinical response and suggest new targets for drug discovery.

Role of epidermal growth factor receptor inhibitors in the treatment of gastric carcinoma

Gastric cancer is one of the most common digestive system malignancies. Traditional chemoradiotherapy has modest efficacy in the treatment of gastric cancer. The epidermal growth factor receptor (EGFR) signal transduction pathway plays an important role in tumor proliferation, angiogenesis, invasion, and migration. EGFR inhibitors have been and are being developed to treat gastric carcinoma. In this paper, we review the role of EGFR inhibitors in the treatment of gastric carcinoma.