A cell-based small molecule screening method for identifying inhibitors of epithelial-mesenchymal transition in carcinoma

Can Natural Products Targeting EMT Serve as the Future Anticancer Therapeutics?

Cancer is the leading cause of death and has remained a big challenge for the scientific community. Because of the growing concerns, new therapeutic regimens are highly demanded to decrease the global burden. Despite advancements in chemotherapy, drug resistance is still a major hurdle to successful treatment. The primary challenge should be identifying and developing appropriate therapeutics for cancer patients to improve their survival. Multiple pathways are dysregulated in cancers, including disturbance in cellular metabolism, cell cycle, apoptosis, or epigenetic alterations. Over the last two decades, natural products have been a major research interest due to their therapeutic potential in various ailments. Natural compounds seem to be an alternative option for cancer management. Natural substances derived from plants and marine sources have been shown to have anti-cancer activity in preclinical settings. They might be proved as a sword to kill cancerous cells. The present review attempted to consolidate the available information on natural compounds derived from plants and marine sources and their anti-cancer potential underlying EMT mechanisms.

Protective Effects and Benefits of Olive Oil and Its Extracts on Women's Health

Women and men share similar diseases; however, women have unique issues, including gynecologic diseases and diseases related to menstruation, menopause, and post menopause. In recent decades, scientists paid more attention to natural products and their derivatives because of their good tolerability and effectiveness in disease prevention and treatment. Olive oil is an essential component in the Mediterranean diet, a diet well known for its protective impact on human well-being. Investigation of the active components in olive oil, such as oleuropein and hydroxytyrosol, showed positive effects in various diseases. Their effects have been clarified in many suggested mechanisms and have shown promising results in animal and human studies, especially in breast cancer, ovarian cancer, postmenopausal osteoporosis, and other disorders. This review summarizes the current evidence of the role of olives and olive polyphenols in women's health issues and their potential implications in the treatment and prevention of health problems in women.

Epithelial-Mesenchymal Transition (EMT) as a Therapeutic Target

Metastasis is the spread of cancer cells from the primary tumour to distant sites and organs throughout the body. It is the primary cause of cancer morbidity and mortality, and is estimated to account for 90% of cancer-related deaths. During the initial steps of the metastatic cascade, epithelial cancer cells undergo an epithelial-mesenchymal transition (EMT), and as a result become migratory and invasive mesenchymal-like cells while acquiring cancer stem cell properties and therapy resistance. As EMT is involved in such a broad range of processes associated with malignant transformation, it has become an increasingly interesting target for the development of novel therapeutic strategies. Anti-EMT therapeutic strategies could potentially not only prevent the invasion and dissemination of cancer cells, and as such prevent the formation of metastatic lesions, but also attenuate cancer stemness and increase the effectiveness of more classical chemotherapeutics. In this review, we give an overview about the pros and cons of therapies targeting EMT and discuss some already existing candidate drug targets and high-throughput screening tools to identify novel anti-EMT compounds.

EMT signaling: potential contribution of CRISPR/Cas gene editing

Epithelial to mesenchymal transition (EMT) is a complex plastic and reversible cellular process that has critical roles in diverse physiological and pathological phenomena. EMT is involved in embryonic development, organogenesis and tissue repair, as well as in fibrosis, cancer metastasis and drug resistance. In recent years, the ability to edit the genome using the clustered regularly interspaced palindromic repeats (CRISPR) and associated protein (Cas) system has greatly contributed to identify or validate critical genes in pathway signaling. This review delineates the complex EMT networks and discusses recent studies that have used CRISPR/Cas technology to further advance our understanding of the EMT process.

Targeting codon 158 p53-mutant cancers via the induction of p53 acetylation

Gain of function (GOF) DNA binding domain (DBD) mutations of TP53 upregulate chromatin regulatory genes that promote genome-wide histone methylation and acetylation. Here, we therapeutically exploit the oncogenic GOF mechanisms of p53 codon 158 (Arg¹⁵⁸) mutation, a DBD mutant found to be prevalent in lung carcinomas. Using high throughput compound screening and combination analyses, we uncover that acetylating mutp53^R158G could render cancers susceptible to cisplatin-induced DNA stress. Acetylation of mutp53^R158G alters DNA binding motifs and upregulates TRAIP, a RING domain-containing E3 ubiquitin ligase which dephosphorylates IĸB and impedes nuclear translocation of RelA (p65), thus repressing oncogenic nuclear factor kappa-B (NF-ĸB) signaling and inducing apoptosis. Given that this mechanism of cytotoxic vulnerability appears inapt in p53 wild-type (WT) or other hotspot GOF mutp53 cells, our work provides a therapeutic opportunity specific to Arg¹⁵⁸-mutp53 tumors utilizing a regimen consisting of DNA-damaging agents and mutp53 acetylators, which is currently being pursued clinically.

Codon 158 gain-of-function mutant p53 (158-mutp53) promotes tumourigenesis in lung cancer. Here, the authors show that 158-mutp53 render cancers sensitive to cisplatin and p53 acetylation agents through a mechanism where acetylated mutant p53 upregulates TRAIP and inhibits NF-ĸB signaling.

Recent Advances in Cancer Plasticity: Cellular Mechanisms, Surveillance Strategies, and Therapeutic Optimization

The processes of recurrence and metastasis, through which cancer relapses locally or spreads to distant sites in the body, accounts for more than 90% of cancer-related deaths. At present there are very few treatment options for patients at this stage of their disease. The main obstacle to successfully treat advanced cancer is the cells' ability to change in ways that make them resistant to treatment. Understanding the cellular mechanisms that mediate this cancer cell plasticity may lead to improved patient survival. Epigenetic reprogramming, together with tumor microenvironment, drives such dynamic mechanisms favoring tumor heterogeneity, and cancer cell plasticity. In addition, the development of new approaches that can report on cancer plasticity in their native environment have profound implications for studying cancer biology and monitoring tumor progression. We herein provide an overview of recent advancements in understanding the mechanisms regulating cell plasticity and current strategies for their monitoring and therapy management.

Secondary Metabolites from the Culture of the Marine-derived Fungus Paradendryphiella salina PC 362H and Evaluation of the Anticancer Activity of Its Metabolite Hyalodendrin

High-throughput screening assays have been designed to identify compounds capable of inhibiting phenotypes involved in cancer aggressiveness. However, most studies used commercially available chemical libraries. This prompted us to explore natural products isolated from marine-derived fungi as a new source of molecules. In this study, we established a chemical library from 99 strains corresponding to 45 molecular operational taxonomic units and evaluated their anticancer activity against the MCF7 epithelial cancer cell line and its invasive stem cell-like MCF7-Sh-WISP2 counterpart. We identified the marine fungal Paradendryphiella salina PC 362H strain, isolated from the brown alga Pelvetia caniculata (PC), as one of the most promising fungi which produce active compounds. Further chemical and biological characterizations of the culture of the Paradendryphiella salina PC 362H strain identified (-)-hyalodendrin as the active secondary metabolite responsible for the cytotoxic activity of the crude extract. The antitumor activity of (-)-hyalodendrin was not only limited to the MCF7 cell lines, but also prominent on cancer cells with invasive phenotypes including colorectal cancer cells resistant to chemotherapy. Further investigations showed that treatment of MCF7-Sh-WISP2 cells with (-)-hyalodendrin induced changes in the phosphorylation status of p53 and altered expression of HSP60, HSP70 and PRAS40 proteins. Altogether, our study reveals that this uninvestigated marine fungal crude extract possesses a strong therapeutic potential against tumor cells with aggressive phenotypes and confirms that members of the epidithiodioxopiperazines are interesting fungal toxins with anticancer activities.

Sanguinarine inhibits epithelial-mesenchymal transition via targeting HIF-1α/TGF-β feed-forward loop in hepatocellular carcinoma

Epithelial–mesenchymal transition (EMT) plays a crucial role in hepatocellular carcinoma (HCC) progression. Hypoxia and excessive transforming growth factor-β (TGF-β) have been identified as inducers and target for EMT in HCC. Here, we show hypoxia inducible factor-1α (HIF-1α) and TGF-β form a feed-forward loop to induce EMT in HCC cells. Further mechanistic study indicates under both hypoxia and TGF-β stimulation, Smad and PI3K-AKT pathways are activated. We show sanguinarine, a natural benzophenanthridine alkaloid, impairs the proliferation of nine kinds of HCC cell lines and the colony formation of HCC cells. In hypoxic and TGF-β cell models, sanguinarine inhibits HIF-1α signaling and the expression of EMT markers, translocation of Snail and activation of both Smad and PI3K-AKT pathways. Sanguinarine could also inhibit TGF-β-induced cell migration in HCC cells. In vivo studies reveal that the administration of sanguinarine inhibits tumor growth and HIF-1α signaling, inhibits the expression changes of EMT markers as well as Smad and PI3K-AKT pathway proteins. Our findings suggest that sanguinarine is a promising candidate targeting HIF-1α/TGF-β signaling to improve the treatment for HCC patients.

c-Met activation leads to the establishment of a TGFβ-receptor regulatory network in bladder cancer progression

Treatment of muscle-invasive bladder cancer remains a major clinical challenge. Aberrant HGF/c-MET upregulation and activation is frequently observed in bladder cancer correlating with cancer progression and invasion. However, the mechanisms underlying HGF/c-MET-mediated invasion in bladder cancer remains unknown. As part of a negative feedback loop SMAD7 binds to SMURF2 targeting the TGFβ receptor for degradation. Under these conditions, SMAD7 acts as a SMURF2 agonist by disrupting the intramolecular interactions within SMURF2. We demonstrate that HGF stimulates TGFβ signalling through c-SRC-mediated phosphorylation of SMURF2 resulting in loss of SMAD7 binding and enhanced SMURF2 C2-HECT interaction, inhibiting SMURF2 and enhancing TGFβ receptor stabilisation. This upregulation of the TGFβ pathway by HGF leads to TGFβ-mediated EMT and invasion. In vivo we show that TGFβ receptor inhibition prevents bladder cancer invasion. Furthermore, we make a rationale for the use of combinatorial TGFβ and MEK inhibitors for treatment of high-grade non-muscle-invasive bladder cancers.

Immunohistochemical Features of Epithelial-Mesenchymal Transition in Feline Oral Squamous Cell Carcinoma

Feline oral squamous cell carcinoma (FOSCC) is an aggressive malignancy with invasive and metastatic behavior. It is poorly responsive to chemotherapy and radiation. Neoplastic epithelial-mesenchymal transition (EMT) portends highly malignant behavior and enhances resistance to therapy. In transitioning to a more malignant phenotype, carcinoma stem cells undergo transformation mediated by expression of proteins, endowing them with mesenchymal properties advantageous to cell survival. The goal of the current study was to identify proteins associated with EMT in FOSCC. This study documents protein expression patterns in 10 FOSCC biopsies and 3 FOSCC cell lines (SCCF1, SCCF2, SCCF3), compatible with an EMT phenotype. As markers of EMT, P-cadherin, N-cadherin, vimentin, nuclear transcription factors Twist and Snail, hypoxia inducible factor 1α (HIF-1α), programmed death ligand 1, and vascular endothelial growth factor D, as well as E-cadherin, were examined using immunohistochemistry, Western blot, and enzyme-linked immunosorbent assay. P-cadherin, Twist, HIF-1α, and programmed death ligand 1 were commonly expressed in biopsies and cell lines. N-cadherin, classically associated with EMT, was not highly expressed, and E-cadherin was coexpressed along with proteins characteristic of EMT in all specimens. Production of vascular endothelial growth factor A by cell lines, a process regulated by HIF-1α expression, was suppressed by the small-molecule inhibitor dasatinib. These data are consistent with EMT in FOSCC and shed light on cellular changes that could contribute to the aggressive behavior of FOSCC.

Actin cytoskeleton self-organization in single epithelial cells and fibroblasts under isotropic confinement

Actin cytoskeleton self-organization in two cell types, fibroblasts and epitheliocytes, was studied in cells confined to isotropic adhesive islands. In fibroblasts plated onto islands of optimal size, an initially circular actin pattern evolves into a radial pattern of actin bundles that undergo asymmetric chiral swirling before finally producing parallel linear stress fibers. Epitheliocytes, however, did not exhibit succession through all the actin patterns described above. Upon confinement, the actin cytoskeleton in non-keratinocyte epitheliocytes was arrested at the circular stage, while in keratinocytes it progressed as far as the radial pattern but still could not break symmetry. Epithelial–mesenchymal transition pushed actin cytoskeleton development from circular towards radial patterns but remained insufficient to cause chirality. Knockout of cytokeratins also did not promote actin chirality development in keratinocytes. Left–right asymmetric cytoskeleton swirling could, however, be induced in keratinocytes by treatment with small doses of the G-actin sequestering drug, latrunculin A in a transcription-independent manner. Both the nucleus and the cytokeratin network followed the induced chiral swirling. Development of chirality in keratinocytes was controlled by DIAPH1 (mDia1) and VASP, proteins involved in regulation of actin polymerization.

This article has an associated First Person interview with the first author of the paper.

Summary: Epitheliocytes cannot develop the F-actin patterns typically observed in fibroblasts, but can do so after treatments affecting actin polymerization. Regulators of actin polymerization, DIAPH1 and VASP, control this process.

Heterogeneity and Plasticity of Breast Cancer Stem Cells

In the last 20 years, the conventional view of breast cancer as a homogeneous collection of highly proliferating malignant cells was totally replaced by a model of increased complexity, which points out that breast carcinomas are tissues composed of multiple populations of transformed cells. A large diversity of host cells and structural components of the extracellular matrix constitute the mammary tumour microenvironment, which supports its growth and progression, where individual cancer cells evolve with cumulative phenotypic and genetic heterogeneity. Moreover, contributing to this heterogeneity, it has been demonstrated that breast cancers can exhibit a hierarchical organization composed of tumour cells displaying divergent lineage biomarkers and where, at the apex of this hierarchy, some neoplastic cells are able to self-renew and to aberrantly differentiate. Breast cancer stem cells (BCSCs), as they were entitled, not only drive tumourigenesis, but also mediate metastasis and contribute to therapy resistance.Recently, adding more complexity to the system, it has been demonstrated that BCSCs maintain high levels of plasticity, being able to change between mesenchymal-like and epithelial-like states in a process regulated by the tumour microenvironment. These stem cell state transitions play a fundamental role in the process of tumour metastasis, as well as in the resistance to putative therapeutic strategies to target these cells. In this chapter, it will be mainly discussed the emerging knowledge regarding the contribution of BCSCs to tumour heterogeneity, their plasticity, and the role that this plasticity can play in the establishment of distant metastasis. A major focus will also be given to potential clinical implications of these discoveries in breast cancer recurrence and to possible BCSC targeted therapeutics by the use of specific biomarkers.

Cellular Phenotype Plasticity in Cancer Dormancy and Metastasis

Cancer dormancy is a period of cancer progression in which residual tumor cells exist, but clinically remain asymptomatic for a long time, as well as resistant to conventional chemo- and radiotherapies. Cellular phenotype plasticity represents that cellular phenotype could convert between epithelial cells and cells with mesenchymal traits. Recently, this process has been shown to closely associate with tumor cell proliferation, cancer dormancy and metastasis. In this review, we have described different scenarios of how the transition from epithelial to mesenchymal morphology (EMT) and backwards (MET) are connected with the initiation of dormancy and reactivation of proliferation. These processes are fundamental for cancer cells to invade tissues and metastasize. Recognizing the mechanisms underlying the cellular phenotype plasticity as well as dormancy and targeting them is likely to increase the efficiency of traditional tumor treatment inhibiting tumor metastasis.

Oleuropein inhibits migration ability through suppression of epithelial-mesenchymal transition and synergistically enhances doxorubicin-mediated apoptosis in MCF-7 cells

Distinct metastasis is one of the main causes of breast cancer (BC)-related mortality and epithelial-mesenchymal transition (EMT) is a primary step in metastasis dissemination. On the other hand, doxorubicin (DOX) is an effective chemotherapeutic agent against BC; unfortunately, its clinical use is limited by dose-dependent side effects. Therefore, extensive efforts have been dedicated to suppressing metastasis of BC and also to overcome DOX side effects together with keeping its antitumor efficacy. Studies supported the role of oleuropein (OLEU) in reducing DOX-induced side effects besides its antitumor actions. In this study, the antimigratory effect of OLEU was assessed and real-time PCR (RT-PCR) was used to detect OLEU effect on the expression level of EMT markers, in MCF-7 cells. The cytotoxic effect of OLEU and DOX was assessed by MTT assay, whereas the ratio of apoptosis was investigated by flow cytometry. The results showed that migration ability of MCF-7 cells remarkably decreased in OLEU treated group and RT-PCR results showed that OLEU may exert its antimigratory action by suppressing EMT through downregulation of sirtuin1 (SIRT1). Also, the results indicated that both OLEU and DOX were cytotoxic to MCF-7 cells, whereas DOX-OLEU cotreatment led to additive cytotoxicity and apoptosis rate. This study provides evidence regarding the suppressive role of OLEU on MCF-7 cells migration ability through suppression of EMT, and for the first time, it was proposed that SIRT1 downregulation can be involved in the OLEU antimigratory effect. Also, the findings demonstrated that OLEU can reduce DOX-induced side effects by reducing its effective dose.

The tumour suppressor OPCML promotes AXL inactivation by the phosphatase PTPRG in ovarian cancer

In ovarian cancer, the prometastatic RTK AXL promotes motility, invasion and poor prognosis. Here, we show that reduced survival caused by AXL overexpression can be mitigated by the expression of the GPI-anchored tumour suppressor OPCML Further, we demonstrate that AXL directly interacts with OPCML, preferentially so when AXL is activated by its ligand Gas6. As a consequence, AXL accumulates in cholesterol-rich lipid domains, where OPCML resides. Here, phospho-AXL is brought in proximity to the lipid domain-restricted phosphatase PTPRG, which de-phosphorylates the RTK/ligand complex. This prevents AXL-mediated transactivation of other RTKs (cMET and EGFR), thereby inhibiting sustained phospho-ERK signalling, induction of the EMT transcription factor Slug, cell migration and invasion. From a translational perspective, we show that OPCML enhances the effect of the phase II AXL inhibitor R428 in vitro and in vivo We therefore identify a novel mechanism by which two spatially restricted tumour suppressors, OPCML and PTPRG, coordinate to repress AXL-dependent oncogenic signalling.

Superior efficacy of co-treatment with the dual PI3K/mTOR inhibitor BEZ235 and histone deacetylase inhibitor Trichostatin A against NSCLC

Non-small-cell lung cancer (NSCLC) is the leading cause of cancer-related death worldwide. NSCLC development and progression have recently been correlated with the heightened activation of histone deacetylases (HDACs) and PI3K/Akt signaling pathways. Targeted inhibition of these proteins is promising approach for the development of novel therapeutic strategies to treat patients with advanced NSCLC. For this reason, we combined a dual PI3K and mTOR inhibitor, BEZ235 with the HDAC inhibitor Trichostatin A (TSA), to determine their combined effects on human NSCLC. In this study, we initially discovered that co-treatment with BEZ235 and TSA showed a synergistic effect on inhibition of NSCLC cell proliferation and induction of apoptosis. The combination treatment also synergistically suppressed NSCLC migration, invasion and the NSCLC epithelial-mesenchymal transition (EMT) in vitro. The synergistic effect was also evidenced by declines in xenograft growth and metastasis rates and in ki-67 protein expression in vivo. Together, these results indicated that BEZ235 and TSA combination treatment significantly increased anti-tumor activities compared with BEZ235 and TSA alone, supporting a further evaluation of combination treatment for NSCLC.

Integration of pan-cancer transcriptomics with RPPA proteomics reveals mechanisms of epithelial-mesenchymal transition

Integrating data from multiple regulatory layers across cancer types could elucidate additional mechanisms of oncogenesis. Using antibody-based protein profiling of 736 cancer cell lines, along with matching transcriptomic data, we show that pan-cancer bimodality in the amounts of mRNA, protein, and protein phosphorylation reveals mechanisms related to the epithelial-mesenchymal transition (EMT). Based on the bimodal expression of E-cadherin, we define an EMT signature consisting of 239 genes, many of which were not previously associated with EMT. By querying gene expression signatures collected from cancer cell lines after small-molecule perturbations, we identify enrichment for histone deacetylase (HDAC) inhibitors as inducers of EMT, and kinase inhibitors as mesenchymal-to-epithelial transition (MET) promoters. Causal modeling of protein-based signaling identifies putative drivers of EMT. In conclusion, integrative analysis of pan-cancer proteomic and transcriptomic data reveals key regulatory mechanisms of oncogenic transformation.

Profiling molecular and phenotypic characteristics of large collections of cancer cell lines can be used to identify distinct and common oncogenic pathways across cancer types. So far, most large-scale data obtained from cancer cell lines have been at the genomic, transcriptomic, and phenotypic levels. Recently, high-quality data at the level of cell signaling through protein abundances and phosphorylation sites has become available. By integrating this newly generated protein data with prior transcriptomic data, and by visualizing all cancer cell lines using dimensionality reduction techniques, pan-cancer cell lines are strikingly shown to organize into a gradient of epithelial to mesenchymal types. Interestingly, many of the measured proteins and transcripts display bimodality; the expression of genes, proteins, and protein phosphorylations is either high or low, strongly suggesting that they act as molecular switches. Focusing on further characterizing molecular switches of epithelial-mesenchymal transitions, we identify candidate regulators and small molecules that can induce or reverse such transition, as well as potential causal relationships between proteins. Since the mesenchymal state of tumors is known to be associated with metastasis and later-stage cancer development, better understanding the regulatory mechanisms of epithelial-to-mesenchymal transition can lead to improved targeted therapeutics.

High-Content Screening Approaches That Minimize Confounding Factors in RNAi, CRISPR, and Small Molecule Screening

Screening arrayed libraries of reagents, particularly small molecules began as a vehicle for drug discovery, but the in last few years it has become a cornerstone of biological investigation, joining RNAi and CRISPR as methods for elucidating functional relationships that could not be anticipated, and illustrating the mechanisms behind basic and disease biology, and therapeutic resistance. However, these approaches share some common challenges, especially with respect to specificity or selectivity of the reagents as they are scaled to large protein families or the genome. High-content screening (HCS) has emerged as an important complement to screening, mostly the result of a wide array of specific molecular events, such as protein kinase and transcription factor activation, morphological changes associated with stem cell differentiation or the epithelial-mesenchymal transition of cancer cells. Beyond the range of cellular events that can be screened by HCS, image-based screening introduces new processes for differentiating between specific and nonspecific effects on cells. This chapter introduces these complexities and discusses strategies available in image-based screening that can mitigate the challenges they can bring to screening.

Epithelial-to-Mesenchymal Transition: Epigenetic Reprogramming Driving Cellular Plasticity

Epithelial-to-mesenchymal transition (EMT) is a process in which epithelial cells lose their junctions and polarity to gain a motile mesenchymal phenotype. EMT is essential during embryogenesis and adult physiological processes like wound healing, but is aberrantly activated in pathological conditions like fibrosis and cancer. A series of transcription factors (EMT-inducing transcription factor; EMT-TF) regulate the induction of EMT by repressing the transcription of epithelial genes while activating mesenchymal genes through mechanisms still debated. The nuclear interaction of EMT-TFs with larger protein complexes involved in epigenetic genome modulation has attracted recent attention to explain functions of EMT-TFs during reprogramming and cellular differentiation. In this review, we discuss recent advances in understanding the interplay between epigenetic regulators and EMT transcription factors and how these findings could be used to establish new therapeutic approaches to tackle EMT-related diseases.

Novel application of the published kinase inhibitor set to identify therapeutic targets and pathways in triple negative breast cancer subtypes

Triple negative breast cancers (TNBCs) have high recurrence and metastasis rates. Acquisition of a mesenchymal morphology and phenotype in addition to driving migration is a consequential process that promotes metastasis. Although some kinases are known to regulate a mesenchymal phenotype, the role for a substantial portion of the human kinome remains uncharacterized. Here we evaluated the Published Kinase Inhibitor Set (PKIS) and screened a panel of TNBC cell lines to evaluate the compounds’ effects on a mesenchymal phenotype. Our screen identified 36 hits representative of twelve kinase inhibitor chemotypes based on reversal of the mesenchymal cell morphology, which was then prioritized to twelve compounds based on gene expression and migratory behavior analyses. We selected the most active compound and confirmed mesenchymal reversal on transcript and protein levels with qRT-PCR and Western Blot. Finally, we utilized a kinase array to identify candidate kinases responsible for the EMT reversal. This investigation shows the novel application to identify previously unrecognized kinase pathways and targets in acquisition of a mesenchymal TNBC phenotype that warrant further investigation. Future studies will examine specific roles of the kinases in mechanisms responsible for acquisition of the mesenchymal and/or migratory phenotype.

New insights into the role of EMT in tumor immune escape

Novel immunotherapy approaches have provided durable remission in a significant number of cancer patients with cancers previously considered rapidly lethal. Nonetheless, the high degree of nonresponders, and in some cases the emergence of resistance in patients who do initially respond, represents a significant challenge in the field of cancer immunotherapy. These issues prompt much more extensive studies to better understand how cancer cells escape immune surveillance and resist immune attacks. Here, we review the current knowledge of how cellular heterogeneity and plasticity could be involved in shaping the tumor microenvironment (TME) and in controlling antitumor immunity. Indeed, recent findings have led to increased interest in the mechanisms by which cancer cells undergoing epithelial‐mesenchymal transition (EMT), or oscillating within the EMT spectrum, might contribute to immune escape through multiple routes. This includes shaping of the TME and decreased susceptibility to immune effector cells. Although much remains to be learned on the mechanisms at play, cancer cell clones with mesenchymal features emerging from the TME seem to be primed to face immune attacks by specialized killer cells of the immune system, the natural killer cells, and the cytotoxic T lymphocytes. Recent studies investigating patient tumors have suggested EMT as a candidate predictive marker to be explored for immunotherapy outcome. Promising data also exist on the potential utility of targeting these cancer cell populations to at least partly overcome such resistance. Research is now underway which may lead to considerable progress in optimization of treatments.

The EMT spectrum and therapeutic opportunities

Carcinomas are phenotypically arrayed along an epithelial–mesenchymal transition (EMT) spectrum, a developmental program currently exploited to understand the acquisition of drug resistance through a re‐routing of growth factor signaling. This review collates the current approaches employed in developing therapeutics against cancer‐associated EMT, and provides an assessment of their respective strengths and drawbacks. We reflect on the close relationship between EMT and chemoresistance against current targeted therapeutics, with a special focus on the epigenetic mechanisms that link these processes. This prompts the hypothesis that carcinoma‐associated EMT shares a common epigenetic pathway to cellular plasticity as somatic cell reprogramming during tissue repair and regeneration. Indeed, their striking resemblance suggests that EMT in carcinoma is a pathological adaptation of an intrinsic program of cellular plasticity that is crucial to tissue homeostasis. We thus propose a revised approach that targets the epigenetic mechanisms underlying pathogenic EMT to arrest cellular plasticity regardless of upstream cancer‐driving mutations.

A sea urchin in vivo model to evaluate Epithelial-Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is an evolutionarily conserved cellular program, which is a prerequisite for the metastatic cascade in carcinoma progression. Here, we evaluate the EMT process using the sea urchin Paracentrotus lividus embryo. In sea urchin embryos, the earliest EMT event is related to the acquisition of a mesenchymal phenotype by the spiculogenetic primary mesenchyme cells (PMCs) and their migration into the blastocoel. We investigated the effect of inhibiting the epidermal growth factor (EGF) signaling pathway on this process, and we observed that mesenchyme cell differentiation was blocked. In order to extend and validate our studies, we investigated the migratory capability and the level of potential epidermal growth factor receptor (EGFr) targets in a breast cancer cell line after EGF modulation. Altogether, our data highlight the sensitivity of the sea urchin embryo to anti-EMT drugs and pinpoint the sea urchin embryo as a valuable in vivo model system for studying EMT and the screening of anti-EMT candidates.

Identification of drugs as single agents or in combination to prevent carcinoma dissemination in a microfluidic 3D environment

Experiments were performed in a modified microfluidic platform recapitulating part of the in vivo tumor microenvironment by co-culturing carcinoma cell aggregates embedded in a three-dimensional (3D) collagen scaffold with human umbilical vein endothelial cells (HUVECs). HUVECs were seeded in one channel of the device to initiate vessel-like structures in vitro prior to introducing the aggregates. The lung adenocarcinoma cell line A549 and the bladder carcinoma cell line T24 were tested. Dose-response assays of four drugs known to interfere with Epithelial Mesenchymal Transition (EMT) signaling pathways were quantified using relative dispersion as a metric of EMT progression. The presence of HUVECs in one channel induces cell dispersal in A549 which then can be inhibited by each of the four drugs. Complete inhibition of T24 aggregate dispersal, however, is not achieved with any single agent, although partial inhibition was observed with 10 μM of the Src inhibitor, AZD-0530. Almost complete inhibition of T24 dispersal in monoculture was achieved only when the four drugs were added in combination, each at 10 μM concentration. Coculture of T24 with HUVECs forfeits the almost-complete inhibition. The enhanced dispersal observed in the presence of HUVECs is a consequence of secretion of growth factors, including HGF and FGF-2, by endothelial cells. This 3D microfluidic co-culture platform provides an in vivo-like surrogate for anti-invasive and anti-metastatic drug screening. It will be particularly useful for defining combination therapies for aggressive tumors such as invasive bladder carcinoma.

Therapeutic Targeting of Epithelial Plasticity Programs: Focus on the Epithelial-Mesenchymal Transition

Mounting data points to epithelial plasticity programs such as the epithelial-mesenchymal transition (EMT) as clinically relevant therapeutic targets for the treatment of malignant tumors. In addition to the widely realized role of EMT in increasing cancer cell invasiveness during cancer metastasis, the EMT has also been implicated in allowing cancer cells to avoid tumor suppressor pathways during early tumorigenesis. In addition, data linking EMT to innate and acquired treatment resistance further points towards the desire to develop pharmacological therapies to target epithelial plasticity in cancer. In this review we organized our discussion on pathways and agents that can be used to target the EMT in cancer into 3 groups: (1) extracellular inducers of EMT, (2) the transcription factors that orchestrate the EMT transcriptome, and (3) the downstream effectors of EMT. We highlight only briefly specific canonical pathways known to be involved in EMT, such as the signal transduction pathways TGFβ, EFGR, and Axl-Gas6. We emphasize in more detail pathways that we believe are emerging novel pathways and therapeutic targets such as epigenetic therapies, glycosylation pathways, and immunotherapy. The heterogeneity of tumors and the dynamic nature of epithelial plasticity in cancer cells make it likely that targeting only 1 EMT-related process will be unsuccessful or only transiently successful. We suggest that with greater understanding of epithelial plasticity regulation, such as with the EMT, a more systematic targeting of multiple EMT regulatory networks will be the best path forward to improve cancer outcomes.

EMT: 2016

The significant parallels between cell plasticity during embryonic development and carcinoma progression have helped us understand the importance of the epithelial-mesenchymal transition (EMT) in human disease. Our expanding knowledge of EMT has led to a clarification of the EMT program as a set of multiple and dynamic transitional states between the epithelial and mesenchymal phenotypes, as opposed to a process involving a single binary decision. EMT and its intermediate states have recently been identified as crucial drivers of organ fibrosis and tumor progression, although there is some need for caution when interpreting its contribution to metastatic colonization. Here, we discuss the current state-of-the-art and latest findings regarding the concept of cellular plasticity and heterogeneity in EMT. We raise some of the questions pending and identify the challenges faced in this fast-moving field.

Pharmacological and immunological targeting of tumor mesenchymalization

Controlling the spread of carcinoma cells to distant organs is the foremost challenge in cancer treatment, as metastatic disease is generally resistant to therapy and is ultimately incurable for the majority of patients. The plasticity of tumor cell phenotype, in which the behaviors and functions of individual tumor cells differ markedly depending upon intrinsic and extrinsic factors, is now known to be a central mechanism in cancer progression. Our expanding knowledge of epithelial and mesenchymal phenotypic states in tumor cells, and the dynamic nature of the transitions between these phenotypes has created new opportunities to intervene to better control the behavior of tumor cells. There are now a variety of innovative pharmacological approaches to preferentially target tumor cells that have acquired mesenchymal features, including cytotoxic agents that directly kill these cells, and inhibitors that block or revert the process of mesenchymalization. Furthermore, novel immunological strategies have been developed to engage the immune system in seeking out and destroying mesenchymalized tumor cells. This review highlights the relevance of phenotypic plasticity in tumor biology, and discusses recently developed pharmacological and immunological means of targeting this phenomenon.

The GAS6-AXL signaling network is a mesenchymal (Mes) molecular subtype-specific therapeutic target for ovarian cancer

Ovarian cancer is a complex disease with heterogeneity among the gene expression molecular subtypes (GEMS) between patients. Patients with tumors of a mesenchymal ("Mes") subtype have a poorer prognosis than patients with tumors of an epithelial ("Epi") subtype. We evaluated GEMS of ovarian cancer patients for molecular signaling profiles and assessed how the differences in these profiles could be leveraged to improve patient clinical outcome. Kinome enrichment analysis identified AXL as a particularly abundant kinase in Mes-subtype tumor tissue and cell lines. In Mes cells, upon activation by its ligand GAS6, AXL coclustered with and transactivated the receptor tyrosine kinases (RTKs) cMET, EGFR, and HER2, producing sustained extracellular signal-regulated kinase (ERK) activation. In Epi-A cells, AXL was less abundant and induced a transient activation of ERK without evidence of RTK transactivation. AXL-RTK crosstalk also stimulated sustained activation of the transcription factor FRA1, which correlated with the induction of the epithelial-mesenchymal transition (EMT)-associated transcription factor SLUG and stimulation of motility exclusively in Mes-subtype cells. The AXL inhibitor R428 attenuated RTK and ERK activation and reduced cell motility in Mes cells in culture and reduced tumor growth in a chick chorioallantoic membrane model. A higher concentration of R428 was needed to inhibit ERK activation and cell motility in Epi-A cells. Silencing AXL in Mes-subtype cells reversed the mesenchymal phenotype in culture and abolished tumor formation in an orthotopic xenograft mouse model. Thus, AXL-targeted therapy may improve clinical outcome for patients with Mes-subtype ovarian cancer.

Functional relevance of a six mesenchymal gene signature in epithelial-mesenchymal transition (EMT) reversal by the triple angiokinase inhibitor, nintedanib (BIBF1120)

Epithelial-mesenchymal transition (EMT), a crucial mechanism in carcinoma progression, describes the process whereby epithelial cells lose their apico-basal polarity and junctional complexes and acquire a mesenchymal-like morphology. Several markers are considered to be authentic indicators of an epithelial or mesenchymal status; however, there is currently no comprehensive or systematic method with which to determine their functional relevance. Previously, we identified a 33-gene EMT signature comprising 25 epithelial and 6 mesenchymal genes that best describe this concept of the EMT spectrum. Here, we designed small-scale siRNA screens targeting these six mesenchymal signature genes (CD99L2, EMP3, ITGA5, SYDE1, VIM, ZEB1) to explore their functional relevance and their roles during EMT reversal by nintedanib (BIBF1120) in a mesenchymal-like SKOV3 ovarian cancer cell line. We found that neither cell proliferation nor cytotoxicity was affected by silencing any of these genes. SKOV3 cells expressing siRNA against mesenchymal genes (ZEB1, EMP3, CD99L2, ITGA5, and SYDE1) showed enhanced colony compaction (reduced inter-nuclear distance). Inductions of E-cadherin expression were only observed in SYDE1- and ZEB1-silenced SKOV3 cells. In addition, only SYDE1-silenced SKOV3 cells showed increased anoikis. Finally, we identified that SYDE1 and ZEB1 were down-regulated in nintedanib-treated SKOV3 cells and SYDE1- and ZEB1-silenced SKOV3 cells showed enhanced nintedanib-induced up-regulation of E-cadherin. Nintedanib-treated SKOV3 cells also showed colony compaction and decreases in EMT scores both in vitro and in vivo. We conclude that SYDE1 and ZEB1 are functionally relevant in EMT reversal. This study thus provides a proof-of-concept for the use of in vitro siRNA screening to explore the EMT-related functions of selected genes and their potential relevance in the discovery of EMT reversing drugs.

Visualizing Epithelial-Mesenchymal Transition Using the Chromobody Technology

The epithelial-mesenchymal transition (EMT) is a complex cellular program involved in the progression of epithelial cancers to a metastatic stage. Along this process, epithelial traits are repressed in favor of a motile mesenchymal phenotype. A detailed characterization and monitoring of EMT-related processes is required for the design of screening strategies needed to develop novel antimetastatic therapies. Overexpression of the canonical EMT biomarker vimentin correlates with increased tumor growth and invasiveness, as well as with reduced patient survival across various epithelial cancers. Moreover, recent findings have demonstrated an active role of vimentin in regulating and reorganizing the cellular architecture toward a migratory and invasive phenotype. However, current studies suffer from a lack of appropriate methods to trace the induction and dynamics of vimentin in cell-based assays. Recently, we have reported a novel intrabody (chromobody)-based approach to study the spatiotemporal organization of endogenous vimentin upon induction of EMT by high-content imaging. In this review, we discuss the relevance of the chromobody technology with regard to the visualization of EMT-related processes in living systems. Cancer Res; 76(19); 5592-6. ©2016 AACR.

A Novel High-Throughput 3D Screening System for EMT Inhibitors: A Pilot Screening Discovered the EMT Inhibitory Activity of CDK2 Inhibitor SU9516

Epithelial-mesenchymal transition (EMT) is a crucial pathological event in cancer, particularly in tumor cell budding and metastasis. Therefore, control of EMT can represent a novel therapeutic strategy in cancer. Here, we introduce an innovative three-dimensional (3D) high-throughput screening (HTS) system that leads to an identification of EMT inhibitors. For the establishment of the novel 3D-HTS system, we chose NanoCulture Plates (NCP) that provided a gel-free micro-patterned scaffold for cells and were independent of other spheroid formation systems using soft-agar. In the NCP-based 3D cell culture system, A549 lung cancer cells migrated, gathered, and then formed multiple spheroids within 7 days. Live cell imaging experiments showed that an established EMT-inducer TGF-β promoted peripheral cells around the core of spheroids to acquire mesenchymal spindle shapes, loss of intercellular adhesion, and migration from the spheroids. Along with such morphological change, EMT-related gene expression signatures were altered, particularly alteration of mRNA levels of ECAD/CDH1, NCAD/CDH2, VIM and ZEB1/TCF8. These EMT-related phenotypic changes were blocked by SB431542, a TGF-βreceptor I (TGFβR1) inhibitor. Inside of the spheroids were highly hypoxic; in contrast, spheroid-derived peripheral migrating cells were normoxic, revealed by visualization and quantification using Hypoxia Probe. Thus, TGF-β-triggered EMT caused spheroid hypoplasia and loss of hypoxia. Spheroid EMT inhibitory (SEMTIN) activity of SB431542 was calculated from fluorescence intensities of the Hypoxia Probe, and then was utilized in a drug screening of EMT-inhibitory small molecule compounds. In a pilot screening, 9 of 1,330 compounds were above the thresholds of the SEMTIN activity and cell viability. Finally, two compounds SB-525334 and SU9516 showed SEMTIN activities in a dose dependent manner. SB-525334 was a known TGFβR1 inhibitor. SU9516 was a cyclin-dependent kinase 2 (CDK2) inhibitor, which we showed also had an EMT-inhibitory activity. The half maximal inhibitory concentration (IC₅₀) of SB-525334 and SU9516 were 0.31 μM and 1.21 μM, respectively, while IC₅₀ of SB431542 was 2.38 μM. Taken together, it was shown that this 3D NCP-based HTS system was useful for screening of EMT-regulatory drugs.

Combinatorial treatment using targeted MEK and SRC inhibitors synergistically abrogates tumor cell growth and induces mesenchymal-epithelial transition in non-small-cell lung carcinoma

Oncogenesis in non-small cell lung cancer (NSCLC) is regulated by a complex signal transduction network. Single-agent targeted therapy fails frequently due to treatment insensitivity and acquired resistance. In this study, we demonstrate that co-inhibition of the MAPK and SRC pathways using a PD0325901 and Saracatinib kinase inhibitor combination can abrogate tumor growth in NSCLC. PD0325901/Saracatinib at 0.25:1 combination was screened against a panel of 28 NSCLC cell lines and 68% of cell lines were found to be sensitive (IC₅₀ < 2 μM) to this combination. In Snail1 positive NSCLC lines, the drug combination complementarily enhanced mesenchymal-epithelial transition (MET), increasing both E-cadherin and Plakoglobin expression, and reducing Snail1, FAK and PXN expression. In addition, the drug combination abrogated cell migration and matrigel invasion. The co-inhibition of MAPK and SRC induced strong G1/G0 cell cycle arrest in the NSCLC lines, inhibited anchorage independent growth and delayed tumor growth in H460 and H358 mouse xenografts. These data provide rationale for further investigating the combination of MAPK and SRC pathway inhibitors in advanced stage NSCLC.

Targeting Epithelial-Mesenchymal Transition (EMT) to Overcome Drug Resistance in Cancer

Epithelial–mesenchymal transition (EMT) is known to play an important role in cancer progression, metastasis and drug resistance. Although there are controversies surrounding the causal relationship between EMT and cancer metastasis, the role of EMT in cancer drug resistance has been increasingly recognized. Numerous EMT-related signaling pathways are involved in drug resistance in cancer cells. Cells undergoing EMT show a feature similar to cancer stem cells (CSCs), such as an increase in drug efflux pumps and anti-apoptotic effects. Therefore, targeting EMT has been considered a novel opportunity to overcome cancer drug resistance. This review describes the mechanism by which EMT contributes to drug resistance in cancer cells and summarizes new advances in research in EMT-associated drug resistance.

Chemical regulators of epithelial plasticity reveal a nuclear receptor pathway controlling myofibroblast differentiation

Plasticity in epithelial tissues relates to processes of embryonic development, tissue fibrosis and cancer progression. Pharmacological modulation of epithelial transitions during disease progression may thus be clinically useful. Using human keratinocytes and a robotic high-content imaging platform, we screened for chemical compounds that reverse transforming growth factor β (TGF-β)-induced epithelial-mesenchymal transition. In addition to TGF-β receptor kinase inhibitors, we identified small molecule epithelial plasticity modulators including a naturally occurring hydroxysterol agonist of the liver X receptors (LXRs), members of the nuclear receptor transcription factor family. Endogenous and synthetic LXR agonists tested in diverse cell models blocked α-smooth muscle actin expression, myofibroblast differentiation and function. Agonist-dependent LXR activity or LXR overexpression in the absence of ligand counteracted TGF-β-mediated myofibroblast terminal differentiation and collagen contraction. The protective effect of LXR agonists against TGF-β-induced pro-fibrotic activity raises the possibility that anti-lipidogenic therapy may be relevant in fibrotic disorders and advanced cancer.

Targeting Estrogen Receptor Signaling with Fulvestrant Enhances Immune and Chemotherapy-Mediated Cytotoxicity of Human Lung Cancer

PURPOSE

The conversion of tumor cells from an epithelial to a mesenchymal-like phenotype, via a process designated as the epithelial-mesenchymal transition (EMT), is known to mediate tumor resistance to a variety of cell death inducers, including cytotoxic effector immune cells. The goal of this study was to identify and potentially repurpose FDA-approved compounds capable of reducing mesenchymal features of human lung carcinoma cells, which could be used in combination with immunotherapies or chemotherapeutic strategies to improve clinical responses.

EXPERIMENTAL DESIGN

In the current report, we have utilized a quantitative high-throughput screening (qHTS) of a pharmaceutical collection of more than 2,000 compounds to identify clinically approved drugs capable of augmenting the sensitivity of mesenchymal-like, lung cancer cells to immune- and chemotherapy-mediated lysis, both in vitro and in vivo RESULTS: The estrogen receptor antagonist fulvestrant was shown to reduce mesenchymal features of lung carcinoma cells, resulting in tumor sensitization to the cytotoxic effect of antigen-specific T cells, natural killer (NK) effector cells, and chemotherapy both in vivo and in vitro CONCLUSIONS: To our knowledge, this is the first report defining a potential role for estrogenic signaling in promoting tumor resistance to immune-mediated cytotoxicity and chemotherapy in lung cancer. Our data demonstrate a robust association between the acquisition of mesenchymal attributes, therapeutic resistance of lung carcinoma cells, and the expression of estrogen receptor 1 (ESR1), supporting further investigations on the role of estrogen signaling in lung cancer progression via the induction of EMT. Clin Cancer Res; 22(24); 6204-16. ©2016 AACR.

Janus kinases and Src family kinases in the regulation of EGF-induced vimentin expression in MDA-MB-468 breast cancer cells

Epithelial-mesenchymal transition (EMT) is an important process associated with the metastasis of breast cancer cells. Members of the Janus kinases (JAKs) and Src family kinases (SFKs) are implicated in the regulation of an invasive phenotype in various cancer cell types. Using the pharmacological inhibitors JAK Inhibitor I (a pan-JAK inhibitor) and PP2 we investigated the role of the JAKs and SFKs, respectively, in the regulation of EMT markers in the MDA-MB-468 breast cancer cell line model of epidermal growth factor (EGF)-induced EMT. We identified selective inhibition of EGF induction of the mesenchymal marker vimentin by PP2 and JAK Inhibitor I. The effect of JAK Inhibitor I on vimentin protein induction occurred at a concentration lower than that required to significantly inhibit EGF-mediated signal transducer and activator of transcription 3 (STAT3)-phosphorylation, suggesting involvement of a STAT3-independent mechanism of EGF-induced vimentin regulation by JAKs. Despite our identification of a role for the JAK family in EGF-induced vimentin protein expression, siRNA-mediated silencing of each member of the JAK family was unable to phenocopy pharmacological inhibition, indicating potential redundancy among the JAK family members in this pathway. While SFKs and JAKs do not represent global regulators of the EMT phenotype, our findings have identified a role for members of these signaling pathways in the regulation of EGF-induced vimentin expression in the MDA-MB-468 breast cancer cell line.

The development of high-content screening (HCS) technology and its importance to drug discovery

INTRODUCTION

High-content screening (HCS) was introduced about twenty years ago as a promising analytical approach to facilitate some critical aspects of drug discovery. Its application has spread progressively within the pharmaceutical industry and academia to the point that it today represents a fundamental tool in supporting drug discovery and development.

AREAS COVERED

Here, the authors review some of significant progress in the HCS field in terms of biological models and assay readouts. They highlight the importance of high-content screening in drug discovery, as testified by its numerous applications in a variety of therapeutic areas: oncology, infective diseases, cardiovascular and neurodegenerative diseases. They also dissect the role of HCS technology in different phases of the drug discovery pipeline: target identification, primary compound screening, secondary assays, mechanism of action studies and in vitro toxicology.

EXPERT OPINION

Recent advances in cellular assay technologies, such as the introduction of three-dimensional (3D) cultures, induced pluripotent stem cells (iPSCs) and genome editing technologies (e.g., CRISPR/Cas9), have tremendously expanded the potential of high-content assays to contribute to the drug discovery process. Increasingly predictive cellular models and readouts, together with the development of more sophisticated and affordable HCS readers, will further consolidate the role of HCS technology in drug discovery.

Reversible interconversion and maintenance of mammary epithelial cell characteristics by the ligand-regulated EGFR system

Epithelial cell plasticity is controlled by extracellular cues, but the underlying mechanisms remain to be fully understood. Epidermal growth factor (EGF) and amphiregulin (AREG) are high- and low-affinity ligands for EGF receptor (EGFR), respectively. EGFR signaling is known to promote epithelial-mesenchymal transition (EMT) by the activation of ERK and the induction of an EMT transcription factor, ZEB1. Here, we demonstrate that ligand-switching between EGF and AREG at equivalent molarity reversibly interconverts epithelial and mesenchymal-like states of EGFR signal-dependent mammary epithelial cells. The EGF- and AREG-cultured cells also differ in their epithelial characteristics, including the expression of cell surface markers, the mode of migration and the ability for acinus-formation. The ligand-switching between EGF and AREG temporally alters strength of the shared EGFR-ERK signaling. This alteration inverts relative expression levels of ZEB1 and its antagonizing microRNAs, miR-205 and miR-200c, those are critical determinants of the epithelial phenotype. Further, AREG-induced EGFR accumulation on the plasma membrane compensates for the weak association between AREG and EGFR. The EGFR dynamics enables AREG to support proliferation as efficiently as EGF at equivalent molarity and to maintain epithelial characteristics. Our findings reveal a role of EGFR ligands-generated signal strength in the regulation of mammary epithelial cell plasticity.

Epithelial-mesenchymal transition: a new target in anticancer drug discovery

The conversion of cells with an epithelial phenotype into cells with a mesenchymal phenotype, referred to as epithelial-mesenchymal transition, is a critical process for embryonic development that also occurs in adult life, particularly during tumour progression. Tumour cells undergoing epithelial-mesenchymal transition acquire the capacity to disarm the body's antitumour defences, resist apoptosis and anticancer drugs, disseminate throughout the organism, and act as a reservoir that replenishes and expands the tumour cell population. Epithelial-mesenchymal transition is therefore becoming a target of prime interest for anticancer therapy. Here, we discuss the screening and classification of compounds that affect epithelial-mesenchymal transition, highlight some compounds of particular interest, and address issues related to their clinical application.

Epithelial-mesenchymal plasticity of breast cancer stem cells: implications for metastasis and therapeutic resistance

Over the past several decades the traditional view of cancer being a homogeneous mass of rapid proliferating malignant cells is being replaced by a model of ever increasing complexity, which points out that cancers are complex tissues composed of multiple cell types. A large variety of immune and other host cells constitute the tumor microenvironment, which supports the growth and progression of the tumor where individual cancer cells evolve with increasing phenotypic and genetic heterogeneity. Furthermore, it has also become clear that, in addition to this cellular and genetic heterogeneity, most tumors exhibit a hierarchical organization composed of tumor cells displaying divergent lineage markers and at the apex of this hierarchy are cells capable of self-renewal. These "cancer stem cells" not only drive tumor growth, but also mediate metastasis and contribute to treatment resistance. Besides displaying remarkable genetic and phenotypic heterogeneity, cancer stem cells maintain plasticity to transition between mesenchymal-like (EMT) and epithelial-like (MET) states in a process regulated by the tumor microenvironment. These stem cell state transitions may play a fundamental role in the process of tumor metastasis. In this review, we will discuss emerging knowledge regarding the plasticity of cancer stem cells and the role that this plasticity plays in tumor metastasis. We also discuss the implications of these findings for the development of cancer stem cell targeted therapeutics.

Computer-assisted quantification of motile and invasive capabilities of cancer cells

High-throughput analysis of cancer cell dissemination and its control by extrinsic and intrinsic cellular factors is hampered by the lack of adequate and efficient analytical tools for quantifying cell motility. Oncology research would greatly benefit from such a methodology that allows to rapidly determine the motile behaviour of cancer cells under different environmental conditions, including inside three-dimensional matrices. We combined automated microscopy imaging of two- and three-dimensional cell cultures with computational image analysis into a single assay platform for studying cell dissemination in high-throughput. We have validated this new approach for medulloblastoma, a metastatic paediatric brain tumour, in combination with the activation of growth factor signalling pathways with established pro-migratory functions. The platform enabled the detection of primary tumour and patient-derived xenograft cell sensitivity to growth factor-dependent motility and dissemination and identified tumour subgroup-specific responses to selected growth factors of excellent diagnostic value.

Epithelial to Mesenchymal Transition in a Clinical Perspective

Tumor growth and metastatic dissemination rely on cellular plasticity. Among the different phenotypes acquired by cancer cells, epithelial to mesenchymal transition (EMT) has been extensively illustrated. Indeed, this transition allows an epithelial polarized cell to acquire a more mesenchymal phenotype with increased mobility and invasiveness. The role of EMT is quite clear during developmental stage. In the neoplastic context in many tumors EMT has been associated with a more aggressive tumor phenotype including local invasion and distant metastasis. EMT allows the cell to invade surrounding tissues and survive in the general circulation and through a stem cell phenotype grown in the host organ. The molecular pathways underlying EMT have also been clearly defined and their description is beyond the scope of this review. Here we will summarize and analyze the attempts made to block EMT in the therapeutic context. Indeed, till today, most of the studies are made in animal models. Few clinical trials are ongoing with no obvious benefits of EMT inhibitors yet. We point out the limitations of EMT targeting such tumor heterogeneity or the dynamics of EMT during disease progression.

Real-time analysis of epithelial-mesenchymal transition using fluorescent single-domain antibodies

Vimentin has become an important biomarker for epithelial-mesenchymal transition (EMT), a highly dynamic cellular process involved in the initiation of metastasis and cancer progression. To date there is no approach available to study endogenous vimentin in a physiological context. Here, we describe the selection and targeted modification of novel single-domain antibodies, so-called nanobodies, to trace vimentin in various cellular assays. Most importantly, we generated vimentin chromobodies by combining the binding moieties of the nanobodies with fluorescent proteins. Following chromobody fluorescence in a cancer-relevant cellular model, we were able for the first time to monitor and quantify dynamic changes of endogenous vimentin upon siRNA-mediated knockdown, induction with TGF-β and modification with Withaferin A by high-content imaging. This versatile approach allows detailed studies of the spatiotemporal organization of vimentin in living cells. It enables the identification of vimentin-modulating compounds, thereby providing the basis to screen for novel therapeutics affecting EMT.

Epithelial-mesenchymal transition and drug resistance in breast cancer (Review)

Breast cancer is the leading cause of cancer death in women worldwide. Insensitivity of tumor cells to drug therapies is an essential reason arousing such high mortality. Epithelial-mesenchymal transition (EMT) is defined by the loss of epithelial characteristics and the acquisition of a mesenchymal phenotype. It is well known that EMT plays an important role in breast cancer progression. Recently, mounting evidence has demonstrated involvement of EMT in antagonizing chemotherapy in breast cancer. Here, we discuss the biological significance and clinical implications of these findings, with an emphasis on novel approaches that effectively target EMT to increase the efficacy of anticancer therapies.

Epithelial-mesenchymal transition in colorectal cancer metastasis: A system review

Tumor metastasis is a multi-step process by which tumor cells disseminate from their primary site and form secondary tumors at a distant site. And metastasis is the major cause of death in the vast majority of cancer patients. However, the mechanisms underlying each step remain obscure. In the past decade, a developmental program epithelial-to-mesenchymal transition (EMT) has been increasingly recognized to play pivotal and intricate roles in promoting carcinoma invasion and metastasis. The EMT process is very complex and controlled by various families of transcriptional regulators through different signaling pathways. In this system review, we focus on the molecular network of the EMT program and its malignant phenotypes associated with metastasis in colorectal cancer (CRC), including cancer stem cells, tumor budding, circulating tumor cells and drug resistance. A better understanding of the molecular regulation of the dynamic EMT program during tumor metastasis will help to provide much-needed therapeutic interventions to target this program when treating metastatic CRC.

MEK Inhibition Overcomes Cisplatin Resistance Conferred by SOS/MAPK Pathway Activation in Squamous Cell Carcinoma

Genomic analyses of squamous cell carcinoma (SCC) have yet to yield significant strategies against pathway activation to improve treatment. Platinum-based chemotherapy remains the mainstay of treatment for SCC of different histotypes either as a single-agent or alongside other chemotherapeutic drugs or radiotherapy; however, resistance inevitably emerges, which limits the duration of treatment response. To elucidate mechanisms that mediate resistance to cisplatin, we compared drug-induced perturbations to gene and protein expression between cisplatin-sensitive and -resistant SCC cells, and identified MAPK-ERK pathway upregulation and activation in drug-resistant cells. ERK-induced resistance appeared to be activated by Son of Sevenless (SOS) upstream, and mediated through Bim degradation downstream. Clinically, elevated p-ERK expression was associated with shorter disease-free survival in patients with locally advanced head and neck SCC treated with concurrent chemoradiation. Inhibition of MEK/ERK, but not that of EGFR or RAF, augmented cisplatin sensitivity in vitro and demonstrated efficacy and tolerability in vivo. Collectively, these findings suggest that inhibition of the activated SOS-MAPK-ERK pathway may augment patient responses to cisplatin treatment.