Spontaneous epithelial-mesenchymal transition and resistance to HER-2-targeted therapies in HER-2-positive luminal breast cancer

Epithelial-Mesenchymal Transition in Cancer: A Focus on Itraconazole, a Hedgehog Inhibitor

Cancer, and the resulting mortality from it, is an ever-increasing concern in global health. Cancer mortality stems from the metastatic progression of the disease, by dissemination of the tumor cells. Epithelial-Mesenchymal Transition, the major hypothesis purported to be the origin of metastasis, confers mesenchymal phenotype to epithelial cells in a variety of contexts, physiological and pathological. EMT in cancer leads to rise of cancer-stem-like cells, drug resistance, relapse, and progression of malignancy. Inhibition of EMT could potentially attenuate the mortality. While novel molecules for inhibiting EMT are underway, repurposing drugs is also being considered as a viable strategy. In this review, Itraconazole is focused upon, as a repurposed molecule to mitigate EMT. Itraconazole is known to inhibit Hedgehog signaling, and light is shed upon the existing evidence, as well as the questions remaining to be answered.

Post-translational modifications in drug resistance

Resistance to antitumor drugs, antimicrobial drugs, and antiviral drugs severely limits treatment effectiveness and cure rate of diseases. Protein post-translational modifications (PTMs) represented by glycosylation, ubiquitination, SUMOylation, acetylation, phosphorylation, palmitoylation, and lactylation are closely related to drug resistance. PTMs are typically achieved by adding sugar chains (glycosylation), small proteins (ubiquitination), lipids (palmitoylation), or functional groups (lactylation) to amino acid residues. These covalent additions are usually the results of signaling cascades and could be reversible, with the triggering mechanisms depending on the type of modifications. PTMs are involved in antitumor drug resistance, not only as inducers of drug resistance but also as targets for reversing drug resistance. Bacteria exhibit multiple PTMs-mediated antimicrobial drug resistance. PTMs allow viral proteins and host cell proteins to form complex interaction networks, inducing complex antiviral drug resistance. This review summarizes the important roles of PTMs in drug resistance, providing new ideas for exploring drug resistance mechanisms, developing new drug targets, and guiding treatment plans.

Proteomic assessment of SKBR3/HER2+ breast cancer cellular response to Lapatinib and investigational Ipatasertib kinase inhibitors

Introduction

Modern cancer treatment strategies aim at achieving cancer remission by using targeted and personalized therapies, as well as harnessing the power of the immune system to recognize and eradicate the cancer cells. To overcome a relatively short-lived response due to resistance to the administered drugs, combination therapies have been pursued.

Objective

The objective of this study was to use high-throughput data generation technologies such as mass spectrometry and proteomics to investigate the broader implications, and to expand the outlook, of such therapeutic approaches. Specifically, we investigated the systems-level response of a breast cancer cell line model to a mixture of kinase inhibitors that has not been adopted yet as a standard therapeutic regime.

Methods

Two critical pathways that sustain the growth and survival of cancer cells, EGFR and PI3K/AKT, were inhibited in SKBR3/HER2+ breast cancer cells with Lapatinib (Tyr kinase inhibitor) and Ipatasertib (Ser/Thr kinase inhibitor), and the landscape of the affected biological processes was investigated with proteomic technologies.

Results

Over 800 proteins matched by three unique peptide sequences were affected by exposing the cells to the drugs. The work corroborated the anti-proliferative activity of Lapatinib and Ipatasertib and uncovered a range of impacted cancer-supportive hallmark processes, among which immune response, adhesion, and migration emerged as particularly relevant to the ability of drugs to effectively suppress the proliferation and dissemination of cancer cells. Changes in the expression of key cancer drivers such as oncogenes, tumor suppressors, EMT and angiogenesis regulators underscored the inhibitory effectiveness of drugs on cancer proliferation. The supplementation of Lapatinib with Ipatasertib further affected additional transcription factors and proteins involved in gene expression, trafficking, DNA repair, and development of multidrug resistance. Furthermore, over fifty of the impacted proteins represent approved or investigational targets in the DrugBank database, which through their protein-protein interaction networks can inform the selection of effective therapeutic partners.

Conclusion

Altogether, the exposure of SKBR3/HER2+ cells to Lapatinib and Ipatasertib kinase inhibitors uncovered a broad plethora of yet untapped opportunities that can be further explored for enhancing the anti-cancer effects of each drug as well as of many other multi-drug therapies that target the EGFR/ERBB2 and PI3K/AKT pathways.

Increased prevalence of hybrid epithelial/mesenchymal state and enhanced phenotypic heterogeneity in basal breast cancer

Intra-tumoral phenotypic heterogeneity promotes tumor relapse and therapeutic resistance and remains an unsolved clinical challenge. Decoding the interconnections among different biological axes of plasticity is crucial to understand the molecular origins of phenotypic heterogeneity. Here, we use multi-modal transcriptomic data-bulk, single-cell, and spatial transcriptomics-from breast cancer cell lines and primary tumor samples, to identify associations between epithelial-mesenchymal transition (EMT) and luminal-basal plasticity-two key processes that enable heterogeneity. We show that luminal breast cancer strongly associates with an epithelial cell state, but basal breast cancer is associated with hybrid epithelial/mesenchymal phenotype(s) and higher phenotypic heterogeneity. Mathematical modeling of core underlying gene regulatory networks representative of the crosstalk between the luminal-basal and epithelial-mesenchymal axes elucidate mechanistic underpinnings of the observed associations from transcriptomic data. Our systems-based approach integrating multi-modal data analysis with mechanism-based modeling offers a predictive framework to characterize intra-tumor heterogeneity and identify interventions to restrict it.

iGenSig-Rx: an integral genomic signature based white-box tool for modeling cancer therapeutic responses using multi-omics data

Multi-omics sequencing is poised to revolutionize clinical care in the coming decade. However, there is a lack of effective and interpretable genome-wide modeling methods for the rational selection of patients for personalized interventions. To address this, we present iGenSig-Rx, an integral genomic signature-based approach, as a transparent tool for modeling therapeutic response using clinical trial datasets. This method adeptly addresses challenges related to cross-dataset modeling by capitalizing on high-dimensional redundant genomic features, analogous to reinforcing building pillars with redundant steel rods. Moreover, it integrates adaptive penalization of feature redundancy on a per-sample basis to prevent score flattening and mitigate overfitting. We then developed a purpose-built R package to implement this method for modeling clinical trial datasets. When applied to genomic datasets for HER2 targeted therapies, iGenSig-Rx model demonstrates consistent and reliable predictive power across four independent clinical trials. More importantly, the iGenSig-Rx model offers the level of transparency much needed for clinical application, allowing for clear explanations as to how the predictions are produced, how the features contribute to the prediction, and what are the key underlying pathways. We anticipate that iGenSig-Rx, as an interpretable class of multi-omics modeling methods, will find broad applications in big-data based precision oncology. The R package is available: https://github.com/wangxlab/iGenSig-Rx .

Grainyhead-like-2, an epithelial master programmer, promotes interferon induction and suppresses breast cancer recurrence

Type-I and -III interferons play a central role in immune rejection of pathogens and tumors, thus promoting immunogenicity and suppressing tumor recurrence. Double strand RNA is an important ligand that stimulates tumor immunity via interferon responses. Differentiation of embryonic stem cells to pluripotent epithelial cells activates the interferon response during development, raising the question of whether epithelial vs. mesenchymal gene signatures in cancer potentially regulate the interferon pathway as well. Here, using genomics and signaling approaches, we show that Grainyhead-like-2 (GRHL2), a master programmer of epithelial cell identity, promotes type-I and -III interferon responses to double-strand RNA. GRHL2 enhanced the activation of IRF3 and relA/NF-kB and the expression of IRF1; a functional GRHL2 binding site in the IFNL1 promoter was also identified. Moreover, time to recurrence in breast cancer correlated positively with GRHL2 protein expression, indicating that GRHL2 is a tumor recurrence suppressor, consistent with its enhancement of interferon responses. These observations demonstrate that epithelial cell identity supports interferon responses in the context of cancer.

Proteomic Assessment of SKBR3/HER2+ Breast Cancer Cellular Response to Lapatinib and Investigational Ipatasertib Kinase Inhibitors

Modern cancer treatment approaches aim at achieving cancer remission by using targeted and personalized therapies, as well as harnessing the power of the immune system to recognize and eliminate the cancer cells. To overcome a relatively short-lived response due to the development of resistance to the administered drugs, combination therapies have been pursued, as well. To expand the outlook of combination therapies, the objective of this study was to use high-throughput data generation technologies such as mass spectrometry and proteomics to investigate the response of HER2+ breast cancer cells to a mixture of two kinase inhibitors that has not been adopted yet as a standard treatment regime. The broader landscape of biological processes that are affected by inhibiting two major pathways that sustain the growth and survival of cancer cells, i.e., EGFR and PI3K/AKT, was investigated by treating SKBR3/HER2+ breast cancer cells with Lapatinib or a mixture of Lapatinib/Ipatasertib small molecule drugs. Changes in protein expression and/or activity in response to the drug treatments were assessed by using two complementary quantitative proteomic approaches based on peak area and peptide spectrum match measurements. Over 900 proteins matched by three unique peptide sequences (FDR<0.05) were affected by the exposure of cells to the drugs. The work corroborated the anti-proliferative activity of Lapatinib and Ipatasertib, and, in addition to cell cycle and growth arrest processes enabled the identification of several multi-functional proteins with roles in cancer-supportive hallmark processes. Among these, immune response, adhesion and migration emerged as particularly relevant to the ability to effectively suppress the proliferation and dissemination of cancer cells. The supplementation of Lapatinib with Ipatasertib further affected the expression or activity of additional transcription factors and proteins involved in gene expression, trafficking, DNA repair, and development of multidrug resistance. Furthermore, over fifty of the affected proteins represented approved or investigational targets in the DrugBank database, which through their protein-protein interaction networks can inform the selection of effective therapeutic partners. Altogether, our findings exposed a broad plethora of yet untapped opportunities that can be further explored for enhancing the anti-cancer effects of each drug as well as of many other multi-drug therapies that target the EGFR/ERBB2 and PI3K/AKT pathways. The data are available via ProteomeXchange with identifier PXD051094.

An inflamed tumor cell subpopulation promotes chemotherapy resistance in triple negative breast cancer

Individual cancers are composed of heterogeneous tumor cells with distinct phenotypes and genotypes, with triple negative breast cancers (TNBC) demonstrating the most heterogeneity among breast cancer types. Variability in transcriptional phenotypes could meaningfully limit the efficacy of monotherapies and fuel drug resistance, although to an unknown extent. To determine if transcriptional differences between tumor cells lead to differential drug responses we performed single cell RNA-seq on cell line and PDX models of breast cancer revealing cell subpopulations in states associated with resistance to standard-of-care therapies. We found that TNBC models contained a subpopulation in an inflamed cellular state, often also present in human breast cancer samples. Inflamed cells display evidence of heightened cGAS/STING signaling which we demonstrate is sufficient to cause tumor cell resistance to chemotherapy. Accordingly, inflamed cells were enriched in human tumors taken after neoadjuvant chemotherapy and associated with early recurrence, highlighting the potential for diverse tumor cell states to promote drug resistance.

Update on Epithelial-Mesenchymal Plasticity in Cancer Progression

Epithelial-mesenchymal transition (EMT) is a cellular process by which epithelial cells lose their characteristics and acquire mesenchymal traits to promote cell movement. This program is aberrantly activated in human cancers and endows tumor cells with increased abilities in tumor initiation, cell migration, invasion, metastasis, and therapy resistance. The EMT program in tumors is rarely binary and often leads to a series of gradual or intermediate epithelial-mesenchymal states. Functionally, epithelial-mesenchymal plasticity (EMP) improves the fitness of cancer cells during tumor progression and in response to therapies. Here, we discuss the most recent advances in our understanding of the diverse roles of EMP in tumor initiation, progression, metastasis, and therapy resistance and address major clinical challenges due to EMP-driven phenotypic heterogeneity in cancer. Uncovering novel molecular markers and key regulators of EMP in cancer will aid the development of new therapeutic strategies to prevent cancer recurrence and overcome therapy resistance.

iGenSig-Rx: an integral genomic signature based white-box tool for modeling cancer therapeutic responses using multi-omics data

Multi-omics sequencing is expected to become clinically routine within the next decade and transform clinical care. However, there is a paucity of viable and interpretable genome-wide modeling methods that can facilitate rational selection of patients for tailored intervention. Here we develop an integral genomic signature-based method called iGenSig-Rx as a white-box tool for modeling therapeutic response based on clinical trial datasets with improved cross-dataset applicability and tolerance to sequencing bias. This method leverages high-dimensional redundant genomic features to address the challenges of cross-dataset modeling, a concept similar to the use of redundant steel rods to reinforce the pillars of a building. Using genomic datasets for HER2 targeted therapies, the iGenSig-Rx model demonstrates stable predictive power across four independent clinical trials. More importantly, the iGenSig-Rx model offers the level of transparency much needed for clinical application, allowing for clear explanations as to how the predictions are produced, how the features contribute to the prediction, and what are the key underlying pathways. We expect that iGenSig-Rx as a class of biologically interpretable multi-omics modeling methods will have broad applications in big-data based precision oncology. The R package is available: https://github.com/wangxlab/iGenSig-Rx. NOTE: the Github website will be released upon publication and the R package is available for review through google drive: https://drive.google.com/drive/folders/1KgecmUoon9-h2Dg1rPCyEGFPOp28Ols3?usp=sharing.

Multi-modal transcriptomic analysis unravels enrichment of hybrid epithelial/mesenchymal state and enhanced phenotypic heterogeneity in basal breast cancer

Intra-tumoral phenotypic heterogeneity promotes tumor relapse and therapeutic resistance and remains an unsolved clinical challenge. It manifests along multiple phenotypic axes and decoding the interconnections among these different axes is crucial to understand its molecular origins and to develop novel therapeutic strategies to control it. Here, we use multi-modal transcriptomic data analysis - bulk, single-cell and spatial transcriptomics - from breast cancer cell lines and primary tumor samples, to identify associations between epithelial-mesenchymal transition (EMT) and luminal-basal plasticity - two key processes that enable heterogeneity. We show that luminal breast cancer strongly associates with an epithelial cell state, but basal breast cancer is associated with hybrid epithelial/mesenchymal phenotype(s) and higher phenotypic heterogeneity. These patterns were inherent in methylation profiles, suggesting an epigenetic crosstalk between EMT and lineage plasticity in breast cancer. Mathematical modelling of core underlying gene regulatory networks representative of the crosstalk between the luminal-basal and epithelial-mesenchymal axes recapitulate and thus elucidate mechanistic underpinnings of the observed associations from transcriptomic data. Our systems-based approach integrating multi-modal data analysis with mechanism-based modeling offers a predictive framework to characterize intra-tumor heterogeneity and to identify possible interventions to restrict it.

Role of glycosylation in breast cancer progression and metastasis: implications for miRNA, EMT and multidrug resistance

Breast cancer (BC) is one of the leading causes of death in women, globally. A variety of biological processes results in metastasis, a poorly understood pathological phenomenon, causing a high relapse rate. Glycosylation, microribonucleic acids (miRNAs) and epithelial to mesenchymal transition (EMT), have been shown to regulate this cascade where tumor cells detach from their primary site, enter the circulatory system and colonize distant sites. Integrated proteomics and glycomics approaches have been developed to probe the molecular mechanism regulating such metastasis. In this review, we describe specific aspects of glycosylation and its interrelation with miRNAs, EMT and multidrug resistance during BC progression and metastasis. We explore various approaches that determine the role of proteomes and glycosylation in BC diagnosis, therapy and drug discovery.

Identification and panoramic analysis of drug response-related genes in triple negative breast cancer using as an example NVP-BEZ235

Taking NVP-BEZ235 (BEZ235) as an example to screen drug response-related genes (DRRGs) and explore their potential value in triple-negative breast cancer (TNBC). Through high-throughput technique, multidimensional transcriptome expression data (mRNA, miRNA and lncRNA) of BEZ235-treated and -untreated MDA-MB-468 cell lines were obtained. Combined with transcriptome data of the MDA-MB-468 cells and TCGA-TNBC tissues, differential gene expression analysis and WGCNA were performed to identify DRRGs associated with tumor trait by simulating the drug response microenvironment (DRM) of BEZ235-treated patients. Based on DRRGs, we constructed a ceRNA network and verified the expression levels of three key molecules by RT-qPCR, which not only demonstrated the successful construction of a BEZ235-treated cell line model but also explained the antitumor mechanism of BEZ235. Four molecular subtypes related to the DRM with survival difference were proposed using cluster analysis, namely glycolysis subtype, proliferation depression subtype, immune-suppressed subtype, and immune-activated subtype. A novel prognostic signature consisting of four DRRGs was established by Lasso-Cox analysis, which exhibited outstanding performance in predicting overall survival compared with several excellent reported signatures. The high- and low-risk groups were characterized by enrichment of metabolism-related pathways and immune-related pathways, respectively. Of note, the low-risk group had a better response to immune checkpoint blockade. Besides, pRRophetic analysis found that patients in the low-risk group were more sensitive to methotrexate and cisplation, whereas more resistant to BEZ235, docetaxel and paclitaxel. In conclusion, the DRRGs exemplified by BEZ235 are potential biomarkers for TNBC molecular typing, prognosis prediction and targeted therapy. The novel DRRGs-guided strategy for predicting the subtype, survival and therapy efficacy, might be also applied to more cancers and drugs other than TNBC and BEZ235.

Structural N-glycoproteomics characterization of cell-surface N-glycosylation of MCF-7/ADR cancer stem cells

Breast cancer is responsible for the highest mortality all over the world. Cancer stem cells (CSCs) along with epithelial mesenchymal transition (EMT) are identified as a driver of cancer which are responsible for cancer metastasis and drug resistance. Several signaling pathways are associated with drug resistance. Additionally, glycosyltransferases regulate different types of glycosylation which are involved in drug resistance. To the end, it is urgent to figure out the knowledge on cell-surface altered N-glycosylation and putative markers. Here, differential cell-surface intact N-glycopeptides in adriamycin (ADR)-resistant michigan breast cancer foundation-7 stem cells (MCF-7/ADR CSCs) relative to ADR-sensitive MCF-7 CSCs were analyzed with site- and structure-specific quantitative N-glycoproteomics. The intact N-glycopeptides and differentially expressed intact N-glycopeptides (DEGPs) were determined and quantified via intact N-glycopeptide search engine GPSeeker. Totally, 4777 intact N-glycopeptides were identified and N-glycan sequence structures among 2764 IDs were distinguished from their isomers by structure-diagnostic fragment ions. Among 1717 quantified intact N-glycopeptides, 104 DEGPs were determined (fold change ≥ 1.5 and p value < 0.05). Annotation of protein-protein interaction and biological processes among others of DEGPs were finally carried out; down-regulated intact N-glycopeptide with bisecting GlcNAc from p38-interacting protein and up-regulated intact N-glycopeptide with β1,6-branching N-glycan from integrin beta-5 were found.

Integrin αvβ3 Is a Master Regulator of Resistance to TKI-Induced Ferroptosis in HER2-Positive Breast Cancer

Human epidermal growth factor receptor-2 (HER2)-targeting therapies provide clinical benefits for patients with HER2-positive breast cancer. However, the resistance to monotherapies invariably develops and leads to disease relapse and treatment failure. Previous studies have demonstrated a link between the potency of HER2-targeting tyrosine kinase inhibitors (TKIs) and their ability to induce an iron-dependent form of cell death called ferroptosis. The aim of this study was to understand the mechanisms of resistance to TKI-induced ferroptosis and identify novel approaches to overcome treatment resistance. We used mouse and human HER2-positive models of acquired TKI resistance to demonstrate an intimate link between the resistance to TKIs and to ferroptosis and present the first evidence that the cell adhesion receptor αvβ3 integrin is a critical mediator of resistance to TKI-induced ferroptosis. Our findings indicate that αvβ3 integrin-mediated resistance is associated with the re-wiring of the iron/antioxidant metabolism and persistent activation of AKT signalling. Moreover, using gene manipulation approaches and pharmacological inhibitors, we show that this "αvβ3 integrin addiction" can be targeted to reverse TKI resistance. Collectively, these findings provide critical insights into new therapeutic strategies to improve the treatment of advanced HER2-positive breast cancer patients.

Drug Resistance in Cancers: A Free Pass for Bullying

The cancer burden continues to grow globally, and drug resistance remains a substantial challenge in cancer therapy. It is well established that cancerous cells with clonal dysplasia generate the same carcinogenic lesions. Tumor cells pass on genetic templates to subsequent generations in evolutionary terms and exhibit drug resistance simply by accumulating genetic alterations. However, recent evidence has implied that tumor cells accumulate genetic alterations by progressively adapting. As a result, intratumor heterogeneity (ITH) is generated due to genetically distinct subclonal populations of cells coexisting. The genetic adaptive mechanisms of action of ITH include activating "cellular plasticity", through which tumor cells create a tumor-supportive microenvironment in which they can proliferate and cause increased damage. These highly plastic cells are located in the tumor microenvironment (TME) and undergo extreme changes to resist therapeutic drugs. Accordingly, the underlying mechanisms involved in drug resistance have been re-evaluated. Herein, we will reveal new themes emerging from initial studies of drug resistance and outline the findings regarding drug resistance from the perspective of the TME; the themes include exosomes, metabolic reprogramming, protein glycosylation and autophagy, and the relates studies aim to provide new targets and strategies for reversing drug resistance in cancers.

Inhibiting Cyclin-Dependent Kinase 6 by Taurine: Implications in Anticancer Therapeutics

Cyclin-dependent kinase 6 (CDK6) is linked with a cyclin partner and plays a crucial role in the early stages of cancer development. It is currently a potential drug target for developing therapeutic molecules targeting cancer therapy. Here, we have identified taurine as an inhibitor of CDK6 using combined in silico and experimental studies. We performed various experiments to find the binding affinity of taurine with CDK6. Molecular docking analysis revealed critical residues of CDK6 that are involved in taurine binding. Fluorescence measurement studies showed that taurine binds to CDK6 with a significant binding affinity, with a binding constant of K = 0.7 × 10⁷ M^-1 for the CDK6-taurine complex. Enzyme inhibition assay suggested taurine as a good inhibitor of CDK6 possessing an IC₅₀ value of 4.44 μM. Isothermal titration calorimetry analysis further confirmed a spontaneous binding of taurine with CDK6 and delineated the thermodynamic parameters for the CDK6-taurine system. Altogether, this study established taurine as a CDK6 inhibitor, providing a base for using taurine and its derivatives in CDK6-associated cancer and other diseases.

HER2 Signaling and Breast Cancer Stem Cells: The Bridge behind HER2-Positive Breast Cancer Aggressiveness and Therapy Refractoriness

Simple Summary

Breast cancer (BC) is not a single disease, but a group of different tumors, and altered HER2 expression defines a particularly aggressive subtype. Although HER2 pharmacological inhibition has dramatically improved the prognosis of HER2-positive BC patients, there is still an urgent need for improved knowledge of HER2 biology and mechanisms underlying HER2-driven aggressiveness and drug susceptibility. Emerging data suggest that the clinical efficacy of molecularly targeted therapies is related to their ability to target breast cancer stem cells (BCSCs), a population that is not only self-sustaining and able to differentiate into distinct lineages, but also contributes to tumor growth, aggressiveness, metastasis and treatment resistance. The aim of this review is to provide an overview of how the full-length HER2 receptor, the d16HER2 splice variant and the truncated p95HER2 variants are involved in the regulation and maintenance of BCSCs.

Abstract

HER2 overexpression/amplification occurs in 15–20% of breast cancers (BCs) and identifies a highly aggressive BC subtype. Recent clinical progress has increased the cure rates of limited-stage HER2-positive BC and significantly prolonged overall survival in patients with advanced disease; however, drug resistance and tumor recurrence remain major concerns. Therefore, there is an urgent need to increase knowledge regarding HER2 biology and implement available treatments. Cancer stem cells (CSCs) represent a subset of malignant cells capable of unlimited self-renewal and differentiation and are mainly considered to contribute to tumor onset, aggressiveness, metastasis, and treatment resistance. Seminal studies have highlighted the key role of altered HER2 signaling in the maintenance/enrichment of breast CSCs (BCSCs) and elucidated its bidirectional communication with stemness-related pathways, such as the Notch and Wingless/β-catenin cascades. d16HER2, a splice variant of full-length HER2 mRNA, has been identified as one of the most oncogenic HER2 isoform significantly implicated in tumorigenesis, epithelial-mesenchymal transition (EMT)/stemness and the response to targeted therapy. In addition, expression of a heterogeneous collection of HER2 truncated carboxy-terminal fragments (CTFs), collectively known as p95HER2, identifies a peculiar subgroup of HER2-positive BC with poor prognosis, with the p95HER2 variants being able to regulate CSC features. This review provides a comprehensive overview of the current evidence regarding HER2-/d16HER2-/p95HER2-positive BCSCs in the context of the signaling pathways governing their properties and describes the future prospects for targeting these components to achieve long-lasting tumor control.

Epigenetic Silencing of HER2 Expression during Epithelial-Mesenchymal Transition Leads to Trastuzumab Resistance in Breast Cancer

HER2 receptor tyrosine kinase (encoded by the ERBB2 gene) is overexpressed in approximately 25% of all breast cancer tumors (HER2-positive breast cancers). Resistance to HER2-targeting therapies is partially due to the loss of HER2 expression in tumor cells during treatment. However, little is known about the exact mechanism of HER2 downregulation in HER2-positive tumor cells. Here, by analyzing publicly available genomic data we investigate the hypothesis that epithelial-mesenchymal transition (EMT) abrogates HER2 expression by epigenetic silencing of the ERBB2 gene as a mechanism of acquired resistance to HER2-targeted therapies. As result, HER2 expression was found to be positively and negatively correlated with the expression of epithelial and mesenchymal phenotype marker genes, respectively. The ERBB2 chromatin of HER2-high epithelial-like breast cancer cells and HER2-low mesenchymal-like cells were found to be open/active and closed/inactive, respectively. Decreased HER2 expression was correlated with increased EMT phenotype, inactivated chromatin and lower response to lapatinib. We also found that induction of EMT in the HER2-positive breast cancer cell line BT474 resulted in downregulated HER2 expression and reduced trastuzumab binding. Our results suggest that ERBB2 gene silencing by epigenetic regulation during EMT may be a mechanism of de novo resistance of HER2-positive breast cancer cells to trastuzumab and lapatinib.

The pan-cancer landscape of crosstalk between epithelial-mesenchymal transition and immune evasion relevant to prognosis and immunotherapy response

An emerging body of evidence has recently recognized the coexistence of epithelial-mesenchymal transition (EMT) and immune response. However, a systems-level view and survey of the interplay between EMT and immune escape program, and their impact on tumor behavior and clinical outcome across various types of cancer is lacking. Here, we performed comprehensive multi-omics analyses to characterize the landscape of crosstalk between EMT and immune evasion and their clinical relevance across 17 types of solid cancer. Our study showed the presence of complex and dynamic immunomodulatory crosstalk between EMT and immune evasion shared by pan-cancer, and the crosstalk was significantly associated with cancer prognosis and immunotherapy response. Integrative quantitative analyses of genomics and immunogenomics revealed that cellular composition of immune infiltrates, non-synonymous mutation burden, chromosomal instability and oncogenic gene alterations are associated with the balance between EMT and immune evasion. Finally, we proposed a scoring model termed EMT-CYT Index (ECI) to quantify the EMT-immunity axis, which was a superior predictor of prognosis and immunotherapy response across different malignancies. By providing a systematic overview of crosstalk between EMT and immune evasion, our study highlights the potential of pan-cancer EMT-immunity crosstalk as a paradigm for dissecting molecular mechanisms underlying cancer progression and guiding more effective and generalized immunotherapy strategies.

Cancer stem cell-targeted therapeutic approaches for overcoming trastuzumab resistance in HER2-positive breast cancer

Application of the anti-HER2 drug trastuzumab has significantly improved the prognosis of patients with the HER2-positive subtype of breast cancer. However, 50% of patients with HER2 amplification relapse due to trastuzumab resistance. Accumulating evidence indicates that breast cancer is driven by a small subset of cancer-initiating cells or breast cancer stem cells (BCSCs), which have the capacity to self-renew and differentiate to regenerate the tumor cell hierarchy. Increasing data suggest that BCSCs are resistant to conventional therapy, including chemotherapy, radiotherapy, and endocrine therapy, which drives distant metastasis and breast cancer relapse. In recent years, the trastuzumab resistance of breast cancer has been closely related to the prevalence of BCSCs. Here, our primary focus is to discuss the role of epithelial-mesenchymal transition (EMT) of BCSCs in the setting of trastuzumab resistance and approaches of reducing or eradicating BCSCs in HER2-positive breast cancer.

5-AZA-dC induces epigenetic changes associated with modified glycosylation of secreted glycoproteins and increased EMT and migration in chemo-sensitive cancer cells

Background

Glycosylation, one of the most fundamental post-translational modifications, is altered in cancer and is subject in part, to epigenetic regulation. As there are many epigenetic-targeted therapies currently in clinical trials for the treatment of a variety of cancers, it is important to understand the impact epi-therapeutics have on glycosylation.

Results

Ovarian and triple negative breast cancer cells were treated with the DNA methyltransferase inhibitor, 5-AZA-2-deoxycytidine (5-AZA-dC). Branching and sialylation were increased on secreted N-glycans from chemo-sensitive/non-metastatic cell lines following treatment with 5-AZA-dC. These changes correlated with increased mRNA expression levels in MGAT5 and ST3GAL4 transcripts in ovarian cancer cell lines. Using siRNA transient knock down of GATA2 and GATA3 transcription factors, we show that these regulate the glycosyltransferases ST3GAL4 and MGAT5, respectively. Moreover, 5-AZA-dC-treated cells displayed an increase in migration, with a greater effect seen in chemo-sensitive cell lines. Western blots showed an increase in apoptotic and senescence (p21) markers in all 5-AZA-dC-treated cells. The alterations seen in N-glycans from secreted glycoproteins in 5-AZA-dC-treated breast and ovarian cancer cells were similar to the N-glycans previously known to potentiate tumour cell survival.

Conclusions

While the FDA has approved epi-therapeutics for some cancer treatments, their global effect is still not fully understood. This study gives insight into the effects that epigenetic alterations have on cancer cell glycosylation, and how this potentially impacts on the overall fate of those cells.

Graphic abstract

Cyclic Multiplexed-Immunofluorescence (cmIF), a Highly Multiplexed Method for Single-Cell Analysis

Immunotherapy harnesses the power of the adaptive immune system and has revolutionized the field of oncotherapy, as novel therapeutic strategies have been introduced into clinical use. The development of immune checkpoint inhibitors has led to durable control of disease in a subset of advanced cancer patients, such as those with melanoma and non-small cell lung cancer. However, predicting patient responses to therapy remains a major challenge, due to the remarkable genomic, epigenetic, and microenvironmental heterogeneity present in each tumor. Breast cancer (BC) is the most common cancer in women, where hormone receptor-positive (HR+; estrogen receptor and/or progesterone receptor) BC comprises the majority (>50%) and has better prognosis, while a minority (<20%) are triple negative BC (TNBC), which has an aggressive phenotype. There is a clinical need to identify predictors of late recurrence in HR+ BC and predictors of immunotherapy outcomes in advanced TNBC. Tumor-infiltrating lymphocytes (TILs) have recently been shown to predict late recurrence in HR+, counter to the findings that TILs confer good prognosis in TNBC and human epidermal growth factor receptor 2 positive (HER2+) subtypes. Furthermore, the spatial arrangement of TILs also appears to have prognostic value, with dense clusters of immune cells predicting poor prognosis in HR+ and good prognosis in TNBC. Whether TIL clusters in different breast cancer subtypes represent the same or different landscapes of TILs is unknown and may have treatment implications for a significant portion of breast cancer patients. Current histopathological staining technology is not sufficient for characterizing the ensembles of TILs and their spatial patterns, in addition to tumor and microenvironmental heterogeneity. However, recent advances in cyclic immunofluorescence enable differentiation of the subsets based on TILs, tumor heterogeneity, and microenvironment composition between good and poor responders. A computational framework for understanding the importance of the spatial relationships between TILs and tumor cells in cancer tissues, which will allow for quantitative interpretation of cyclic immunostaining, is also under development. This chapter will explore the workflow for a newly developed cyclic multiplexed-immunofluorescence (cmIF) assay, which has been optimized for formalin-fixed. paraffin-embedded tissues and developed to process digital images for quantitative single-cell based spatial analysis of tumor heterogeneity and microenvironment, including immune cell composition.

Mechanisms of tRNA-derived fragments and tRNA halves in cancer treatment resistance

The tRNA-derived fragments (tRFs) and tRNA halves (tiRNAs) are newly discovered noncoding RNAs in recent years. They are derived from specific cleavage of mature and pre-tRNAs and expressed in various cancers. They enhance cell proliferation and metastasis or inhibit cancer progression. Many studies have investigated their roles in the diagnosis, progression, metastasis, and prognosis of various cancers, but the mechanisms through which they are involved in resistance to cancer treatment are unclear. This review outlines the classification of tRFs and tiRNAs and their mechanisms in cancer drug resistance, thus providing new ideas for cancer treatment.

Down-regulation of long non-coding RNA HOTAIR sensitizes breast cancer to trastuzumab

This study aimed to investigate the roles and possible molecular mechanisms of long non-coding RNA HOTAIR in regulating resistance to trastuzumab in breast cancer. Trastuzumab-resistant breast cancer cell line SK-BR-3-TR was assayed for the expression of HOX antisense intergenic RNA (HOTAIR), epithelial-mesenchymal transition (EMT)-related proteins or genes. Methylation levels of TGF- β, PTEN and cyclin-dependent kinase inhibitor 1B (or P27) were determined. In trastuzumab-resistant cell line, the mRNA level of HOTAIR was significantly up-regulated; in addition, the expression of TGF-β, Snail and Vimentin was also up-regulated, E-cadherin was down-regulated while the expression of HER2, PI3K, AKT, mTOR and MAPK in the HER2 receptor pathway and phosphorylation level of HER2 receptor remained unchanged, the methylation levels of the PTEN gene and TGF-β were increased and decreased, respectively. RNA interference downregulated the HOTAIR level and sensitized the cells to trastuzumab. It also resulted in down-regulation of TGF-β, Snail, Vimentin, p-AKT, p-APK and CyclinD1 and up-regulation of E-cadherin, PTEN and P27. Besides, the methylation levels of the PTEN gene and TGF-β were reduced and increased, respectively. Mouse models grafted with SK-BR-3-TR grew faster than with SK-BR-3-TS and siHOTAIR-SK-BR-3-TR.

Controversies around epithelial-mesenchymal plasticity in cancer metastasis

Experimental evidence accumulated over decades has implicated epithelial-mesenchymal plasticity (EMP), which collectively encompasses epithelial-mesenchymal transition and the reverse process of mesenchymal-epithelial transition, in tumour metastasis, cancer stem cell generation and maintenance, and therapeutic resistance. However, the dynamic nature of EMP processes, the apparent need to reverse mesenchymal changes for the development of macrometastases and the likelihood that only minor cancer cell subpopulations exhibit EMP at any one time have made such evidence difficult to accrue in the clinical setting. In this Perspectives article, we outline the existing preclinical and clinical evidence for EMP and reflect on recent controversies, including the failure of initial lineage-tracing experiments to confirm a major role for EMP in dissemination, and discuss accumulating data suggesting that epithelial features and/or a hybrid epithelial-mesenchymal phenotype are important in metastasis. We also highlight strategies to address the complexities of therapeutically targeting the EMP process that give consideration to its spatially and temporally divergent roles in metastasis, with the view that this will yield a potent and broad class of therapeutic agents.

Preclinical Characteristics of the Irreversible Pan-HER Kinase Inhibitor Neratinib Compared with Lapatinib: Implications for the Treatment of HER2-Positive and HER2-Mutated Breast Cancer

An estimated 15–20% of breast cancers overexpress human epidermal growth factor receptor 2 (HER2/ERBB2/neu). Two small-molecule tyrosine kinase inhibitors (TKIs), lapatinib and neratinib, have been approved for the treatment of HER2-positive (HER2+) breast cancer. Lapatinib, a reversible epidermal growth factor receptor (EGFR/ERBB1/HER1) and HER2 TKI, is used for the treatment of advanced HER2+ breast cancer in combination with capecitabine, in combination with trastuzumab in patients with hormone receptor-negative metastatic breast cancer, and in combination with an aromatase inhibitor for the first-line treatment of HER2+ breast cancer. Neratinib, a next-generation, irreversible pan-HER TKI, is used in the US for extended adjuvant treatment of adult patients with early-stage HER2+ breast cancer following 1 year of trastuzumab. In Europe, neratinib is used in the extended adjuvant treatment of adult patients with early-stage hormone receptor-positive HER2+ breast cancer who are less than 1 year from the completion of prior adjuvant trastuzumab-based therapy. Preclinical studies have shown that these agents have distinct properties that may impact their clinical activity. This review describes the preclinical characterization of lapatinib and neratinib, with a focus on the differences between these two agents that may have implications for patient management.

Modeling differentiation-state transitions linked to therapeutic escape in triple-negative breast cancer

Drug resistance in breast cancer cell populations has been shown to arise through phenotypic transition of cancer cells to a drug-tolerant state, for example through epithelial-to-mesenchymal transition or transition to a cancer stem cell state. However, many breast tumors are a heterogeneous mixture of cell types with numerous epigenetic states in addition to stem-like and mesenchymal phenotypes, and the dynamic behavior of this heterogeneous mixture in response to drug treatment is not well-understood. Recently, we showed that plasticity between differentiation states, as identified with intracellular markers such as cytokeratins, is linked to resistance to specific targeted therapeutics. Understanding the dynamics of differentiation-state transitions in this context could facilitate the development of more effective treatments for cancers that exhibit phenotypic heterogeneity and plasticity. In this work, we develop computational models of a drug-treated, phenotypically heterogeneous triple-negative breast cancer (TNBC) cell line to elucidate the feasibility of differentiation-state transition as a mechanism for therapeutic escape in this tumor subtype. Specifically, we use modeling to predict the changes in differentiation-state transitions that underlie specific therapy-induced changes in differentiation-state marker expression that we recently observed in the HCC1143 cell line. We report several statistically significant therapy-induced changes in transition rates between basal, luminal, mesenchymal, and non-basal/non-luminal/non-mesenchymal differentiation states in HCC1143 cell populations. Moreover, we validate model predictions on cell division and cell death empirically, and we test our models on an independent data set. Overall, we demonstrate that changes in differentiation-state transition rates induced by targeted therapy can provoke distinct differentiation-state aggregations of drug-resistant cells, which may be fundamental to the design of improved therapeutic regimens for cancers with phenotypic heterogeneity.

Differentiation-state plasticity is a targetable resistance mechanism in basal-like breast cancer

Intratumoral heterogeneity in cancers arises from genomic instability and epigenomic plasticity and is associated with resistance to cytotoxic and targeted therapies. We show here that cell-state heterogeneity, defined by differentiation-state marker expression, is high in triple-negative and basal-like breast cancer subtypes, and that drug tolerant persister (DTP) cell populations with altered marker expression emerge during treatment with a wide range of pathway-targeted therapeutic compounds. We show that MEK and PI3K/mTOR inhibitor-driven DTP states arise through distinct cell-state transitions rather than by Darwinian selection of preexisting subpopulations, and that these transitions involve dynamic remodeling of open chromatin architecture. Increased activity of many chromatin modifier enzymes, including BRD4, is observed in DTP cells. Co-treatment with the PI3K/mTOR inhibitor BEZ235 and the BET inhibitor JQ1 prevents changes to the open chromatin architecture, inhibits the acquisition of a DTP state, and results in robust cell death in vitro and xenograft regression in vivo.

Resistance to therapy can be driven by intratumoral heterogeneity. Here, the authors show that drug tolerant persistent cell populations emerge during treatment, and these emergent populations arise through epigenetically mediated cell state transitions rather than sub population selection.

Pan-HER-targeted approach for cancer therapy: Mechanisms, recent advances and clinical prospect

The Human Epidermal Growth Factor Receptor family is composed of 4 structurally related receptor tyrosine kinases that are involved in many human cancers. The efficacy and safety of HER inhibitors have been compared in a wide range of clinical trials, suggesting the superior inhibitory ability of multiple- HER-targeting blockade compared with single receptor antagonists. However, many patients are currently resistant to current therapeutic treatment and novel strategies are warranted to conquer the resistance. Thus, we performed a critical review to summarize the molecular involvement of HER family receptors in tumour progression, recent anti-HER drug development based on clinical trials, and the potential resistance mechanisms of anti-HER therapy.

The Kraken Wakes: induced EMT as a driver of tumour aggression and poor outcome

Epithelial mesenchymal transition (EMT) describes the shift of cells from an epithelial form to a contact independent, migratory, mesenchymal form. In cancer the change is linked to invasion and metastasis. Tumour conditions, including hypoxia, acidosis and a range of treatments can trigger EMT, which is implicated in the subsequent development of resistance to those same treatments. Consequently, the degree to which EMT occurs may underpin the entire course of tumour progression and treatment response in a patient. In this review we look past the protective effect of EMT against the initial treatment, to the role of the mesenchymal state, once triggered, in promoting disease growth, spread and future treatment insensitivity. In patients a correlation was found between the propensity of a treatment to induce EMT and failure of that treatment to provide a survival benefit, implicating EMT induction in accelerated tumour progression after treatment cessation. Looking to the mechanisms driving this detrimental effect; increased proliferation, suppressed apoptosis, stem cell induction, augmented angiogenesis, enhanced metastatic dissemination, and immune tolerance, can all result from treatment-induced EMT and could worsen outcome. Evidence also suggests EMT induction with earlier therapies attenuates benefits of later treatments. Looking beyond epithelial tumours, de-differentiation also has therapy-attenuating effects and reversal thereof may yield similar rewards. A range of potential therapies are in development that may address the diverse mechanisms and molecular control systems involved in EMT-induced accelerated progression. Considering the broad reaching effects of mesenchymal shift identified, successful deployment of such treatments could substantially improve patient outcomes.

Novel cancer stem cell targets during epithelial to mesenchymal transition in PTEN-deficient trastuzumab-resistant breast cancer

Continued use of trastuzumab in PTEN-deficient HER2+ breast cancer induces the epithelial-to-mesenchymal transition (EMT), transforms HER2+ to triple negative breast cancer, and expands breast cancer stem cells (BCSCs). Using cancer cell lines with two distinct states, epithelial and mesenchymal, we identified novel targets during EMT in PTEN-deficient trastuzumab-resistant breast cancer. Differential gene expression and distinct responses to a small molecule in BT474 (HER2+ trastuzumab-sensitive) and the PTEN-deficient trastuzumab-resistant derivative (BT474-PTEN-LTT) provided the selection tools to identify targets during EMT. siRNA knockdown and small molecule inhibition confirmed MEOX1 as one of the critical molecular targets to regulate both BCSCs and mesenchymal-like cell proliferation. MEOX1 was associated with poor survival, lymph node metastasis, and stage of breast cancer patients. These findings suggest that MEOX1 is a clinically relevant novel target in BCSCs and mesenchymal-like cancer cells in PTEN-deficient trastuzumab resistant breast cancer and may serve as target for future drug development.

Identification of novel pathways linking epithelial-to-mesenchymal transition with resistance to HER2-targeted therapy

Resistance to human epidermal growth factor receptor 2 (HER2)-targeted therapies in the treatment of HER2-positive breast cancer is a major clinical problem. To identify pathways linked to resistance, we generated HER2-positive breast cancer cell lines which are resistant to either lapatinib or AZD8931, two pan-HER family kinase inhibitors. Resistance was HER2 independent and was associated with epithelial-to-mesenchymal transition (EMT), resulting in increased proliferation and migration of the resistant cells. Using a global proteomics approach, we identified a novel set of EMT-associated proteins linked to HER2-independent resistance. We demonstrate that a subset of these EMT-associated genes is predictive of prognosis within the ERBB2 subtype of human breast cancers. Furthermore, targeting the EMT-associated kinases Src and Axl potently inhibited proliferation of the resistant cells, and inhibitors to these kinases may provide additional options for the treatment of HER2-independent resistance in tumors.

HER2 in Breast Cancer Stemness: A Negative Feedback Loop towards Trastuzumab Resistance

HER2 receptor tyrosine kinase that is overexpressed in approximately 20% of all breast cancers (BCs) is a poor prognosis factor and a precious target for BC therapy. Trastuzumab is approved by FDA to specifically target HER2 for treating HER2+ BC. However, about 60% of patients with HER2+ breast tumor develop de novo resistance to trastuzumab, partially due to the loss of expression of HER2 extracellular domain on their tumor cells. This is due to shedding/cleavage of HER2 by metalloproteinases (ADAMs and MMPs). HER2 shedding results in the accumulation of intracellular carboxyl-terminal HER2 (p95HER2), which is a common phenomenon in trastuzumab-resistant tumors and is suggested as a predictive marker for trastuzumab resistance. Up-regulation of the metalloproteinases is a poor prognosis factor and is commonly seen in mesenchymal-like cancer stem cells that are risen during epithelial to mesenchymal transition (EMT) of tumor cells. HER2 cleavage during EMT can explain why secondary metastatic tumors with high percentage of mesenchymal-like cancer stem cells are mostly resistant to trastuzumab but still sensitive to lapatinib. Importantly, many studies report HER2 interaction with oncogenic/stemness signaling pathways including TGF-β/Smad, Wnt/β-catenin, Notch, JAK/STAT and Hedgehog. HER2 overexpression promotes EMT and the emergence of cancer stem cell properties in BC. Increased expression and activation of metalloproteinases during EMT leads to proteolytic cleavage and shedding of HER2 receptor, which downregulates HER2 extracellular domain and eventually increases trastuzumab resistance. Here, we review the hypothesis that a negative feedback loop between HER2 and stemness signaling drives resistance of BC to trastuzumab.

Lapatinib resistance in HER2+ cancers: latest findings and new concepts on molecular mechanisms

In the era of new and mostly effective molecular targeted therapies, human epidermal growth factor receptor 2 positive (HER2+) cancers are still intractable diseases. Lapatinib, a dual epidermal growth factor receptor (EGFR) and HER2 tyrosine kinase inhibitor, has greatly improved breast cancer prognosis in recent years after the initial introduction of trastuzumab (Herceptin). However, clinical evidence indicates the existence of both primary unresponsiveness and secondary lapatinib resistance, which leads to the failure of this agent in HER2+ cancer patients. It remains a major clinical challenge to target the oncogenic pathways with drugs having low resistance. Multiple pathways are involved in the occurrence of lapatinib resistance, including the pathways of receptor tyrosine kinase, non-receptor tyrosine kinase, autophagy, apoptosis, microRNA, cancer stem cell, tumor metabolism, cell cycle, and heat shock protein. Moreover, understanding the relationship among these mechanisms may contribute to future tumor combination therapies. Therefore, it is of urgent necessity to elucidate the precise mechanisms of lapatinib resistance and improve the therapeutic use of this agent in clinic. The present review, in the hope of providing further scientific support for molecular targeted therapies in HER2+ cancers, discusses about the latest findings and new concepts on molecular mechanisms underlying lapatinib resistance.

Epigenetic regulation of glycosylation and the impact on chemo-resistance in breast and ovarian cancer

Glycosylation is one of the most fundamental posttranslational modifications in cellular biology and has been shown to be epigenetically regulated. Understanding this process is important as epigenetic therapies such as those using DNA methyltransferase inhibitors are undergoing clinical trials for the treatment of ovarian and breast cancer. Previous work has demonstrated that altered glycosylation patterns are associated with aggressive disease in women presenting with breast and ovarian cancer. Moreover, the tumor microenvironment of hypoxia results in globally altered DNA methylation and is associated with aggressive cancer phenotypes and chemo-resistance, a feature integral to many cancers. There is sparse knowledge on the impact of these therapies on glycosylation. Moreover, little is known about the efficacy of DNA methyltransferase inhibitors in hypoxic tumors. In this review, we interrogate the impact that hypoxia and epigenetic regulation has on cancer cell glycosylation in relation to resultant tumor cell aggressiveness and chemo-resistance.

Cancer stem cell-driven efficacy of trastuzumab (Herceptin): towards a reclassification of clinically HER2-positive breast carcinomas

Clinically HER2+ (cHER2+) breast cancer (BC) can no longer be considered a single BC disease entity in terms of trastuzumab responsiveness. Here we propose a framework for predicting the response of cHER2+ to trastuzumab that integrates the molecular distinctions of intrinsic BC subtypes with recent knowledge on cancer stem cell (CSC) biology. First, we consider that two interchangeable populations of epithelial-like, aldehyde dehydrogenase (ALDH)-expressing and mesenchymal-like, CD44+CD24-/low CSCs can be found in significantly different proportions across all intrinsic BC subtypes. Second, we overlap all the intrinsic subtypes across cHER2+ BC to obtain a continuum of mixed phenotypes in which one extreme exhibits a high identity with ALDH+ CSCs and the other extreme exhibits a high preponderance of CD44+CD24-/low CSCs. The differential enrichment of trastuzumab-responsive ALDH+ CSCs versus trastuzumab-refractory CD44+CD24-/low CSCs can explain both the clinical behavior and the primary efficacy of trastuzumab in each molecular subtype of cHER2+ (i.e., HER2-enriched/cHER2+, luminal A/cHER2+, luminal B/cHER2+, basal/cHER2+, and claudin-low/cHER2+). The intrinsic plasticity determining the epigenetic ability of cHER2+ tumors to switch between epithelial and mesenchymal CSC states will vary across the continuum of mixed phenotypes, thus dictating their intratumoral heterogeneity and, hence, their evolutionary response to trastuzumab. Because CD44+CD24-/low mesenchymal-like CSCs distinctively possess a highly endocytic activity, the otherwise irrelevant HER2 can open the door to a type of "Trojan horse" approach by employing antibody-drug conjugates such as T-DM1, which will allow a rapid and CSC-targeted delivery of cytotoxic drugs to therapeutically manage trastuzumab-unresponsive basal/cHER2+ BC. Contrary to the current dichotomous model used clinically, our model proposes that a reclassification of cHER2+ tumors based on the spectrum of molecular BC subtypes might inform on their CSC-determined sensitivity to trastuzumab, thus providing a better delineation of the predictive value of cHER2+ in BC by incorporating CSCs-driven intra-tumor heterogeneity into clinical decisions.

Expression of breast cancer stem cell markers as predictors of prognosis and response to trastuzumab in HER2-positive breast cancer

Background:

Breast cancer stem cells (BCSCs) have been suggested to have clinical implications for cancer therapeutics because of their proposed role in chemoresistance. The aim of this study was to investigate the impact of BCSC marker expression on clinical outcome and trastuzumab response in human epidermal growth factor receptor 2 (HER2)-positive breast cancer.

Methods:

We analysed the expression of BCSC markers, CD44+/CD24− and aldehyde dehydrogenase 1 (ALDH1), and clinical outcomes in three sets of breast cancer cases: Set 1, 242 HER2-positive primary breast cancers treated by various modalities; Set 2, 447 HER2-positive primary breast cancers treated with surgery and chemotherapy plus adjuvant trastuzumab; Set 3, 112 metastatic HER2-positive breast cancers treated with trastuzumab.

Results:

Expression of CD44+/CD24− and ALDH1 was detected in 30.7% and 10.0%, respectively, of the Set 1 cases, and was associated with hormone receptor negativity. In survival analyses, expression of CD44+/CD24−, but not ALDH1, was found to be an independent prognostic factor for poor disease-free and overall survival in whole patients and also in the subgroup not receiving adjuvant trastuzumab. In Set 2 cases treated with adjuvant trastuzumab, CD44+/CD24− expression was an independent prognostic factor for poor disease-free survival, but not for overall survival; expression of ALDH1 had no impact on disease-free or overall survival. In metastatic disease treated with trastuzumab (Set 3 cases), CD44+/CD24− and ALDH1 expression had no effect on trastuzumab response or survival.

Conclusions:

These results suggest that the CD44+/CD24− phenotype can be used as a prognostic factor for clinical outcome and a predictive factor of trastuzumab response in patients with HER2-positive primary breast cancer.

Enhanced lysis by bispecific oncolytic measles viruses simultaneously using HER2/neu or EpCAM as target receptors

To target oncolytic measles viruses (MV) to tumors, we exploit the binding specificity of designed ankyrin repeat proteins (DARPins). These DARPin-MVs have high tumor selectivity while maintaining excellent oncolytic potency. Stability, small size, and efficacy of DARPins allowed the generation of MVs simultaneously targeted to tumor marker HER2/neu and cancer stem cell (CSC) marker EpCAM. For optimization, the linker connecting both DARPins was varied in flexibility and length. Flexibility had no impact on fusion helper activity whereas length had. MVs with bispecific MV-H are genetically stable and revealed the desired double-target specificity. In vitro, the cytolytic activity of bispecific MVs was superior or comparable to mono-targeted viruses depending on the target cells. In vivo, therapeutic efficacy of the bispecific viruses was validated in an orthotopic ovarian carcinoma model revealing an effective reduction of tumor mass. Finally, the power of bispecific targeting was demonstrated on cocultures of different tumor cells thereby mimicking tumor heterogeneity in vitro, more closely reflecting real tumors. Here, bispecific excelled monospecific viruses in efficacy. DARPin-based targeting domains thus allow the generation of efficacious oncolytic viruses with double specificity, with the potential to handle intratumoral variation of antigen expression and to simultaneously target CSCs and the bulk tumor mass.

Thymus vulgaris (thyme) inhibits proliferation, adhesion, migration, and invasion of human colorectal cancer cells

Colorectal cancer (CRC) remains one of the most common malignancies and a leading cause of cancer-related deaths. Its prognosis remains poor for patients with several grades of this disease. This underscores the need for alternative modalities, such as herbal medicines, to treat this disease. A commonly used plant that appears to be of high medicinal value is Thymus vulgaris L. However, the effects of this plant on the malignant behavior of human CRC cells remains poorly investigated. This study was undertaken to determine the anticancer efficacy of T. vulgaris extract (TVE) in CRC cells. Our results show that TVE inhibits proliferation in a concentration- and time-dependent fashion. This decreased proliferation was concomitant with increased apoptotic cell death as evidenced by increased caspase3/7 activity. Moreover, TVE also decreased adhesion to fibronectin in a concentration-dependent manner. The migratory and invasive capacities of HCT116 cells were significantly inhibited by TVE. Taken together, these data suggest that the TVE inhibits malignant phenotype of colon cancer cells. Therefore, T. vulgaris could have an anticancer effect and that some of its bioactive compounds may prove to be effective treatment modalities for human CRC.

Serum N-glycan analysis in breast cancer patients--Relation to tumour biology and clinical outcome

Glycosylation and related processes play important roles in cancer development and progression, including metastasis. Several studies have shown that N-glycans have potential diagnostic value as cancer serum biomarkers. We have explored the significance of the abundance of particular serum N-glycan structures as important features of breast tumour biology by studying the serum glycome and tumour transcriptome (mRNA and miRNA) of 104 breast cancer patients. Integration of these types of molecular data allows us to study the relationship between serum glycans and transcripts representing functional pathways, such as metabolic pathways or DNA damage response. We identified tri antennary trigalactosylated trisialylated glycans in serum as being associated with lower levels of tumour transcripts involved in focal adhesion and integrin-mediated cell adhesion. These glycan structures were also linked to poor prognosis in patients with ER negative tumours. High abundance of simple monoantennary glycan structures were associated with increased survival, particularly in the basal-like subgroup. The presence of circulating tumour cells was found to be significantly associated with several serum glycome structures like bi and triantennary, di- and trigalactosylated, di- and trisialylated. The link between tumour miRNA expression levels and N-glycan production is also examined.

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.

Soluble factors regulated by epithelial-mesenchymal transition mediate tumour angiogenesis and myeloid cell recruitment

Epithelial-mesenchymal transition (EMT) programmes provide cancer cells with invasive and survival capacities that might favour metastatic dissemination. Whilst signalling cascades triggering EMT have been extensively studied, the impact of EMT on the crosstalk between tumour cells and the tumour microenvironment remains elusive. We aimed to identify EMT-regulated soluble factors that facilitate the recruitment of host cells in the tumour. Our findings indicate that EMT phenotypes relate to the induction of a panel of secreted mediators, namely IL-8, IL-6, sICAM-1, PAI-1 and GM-CSF, and implicate the EMT-transcription factor Snail as a regulator of this process. We further show that EMT-derived soluble factors are pro-angiogenic in vivo (in the mouse ear sponge assay), ex vivo (in the rat aortic ring assay) and in vitro (in a chemotaxis assay). Additionally, conditioned medium from EMT-positive cells stimulates the recruitment of myeloid cells. In a bank of 40 triple-negative breast cancers, tumours presenting features of EMT were significantly more angiogenic and infiltrated by a higher quantity of myeloid cells compared to tumours with little or no EMT. Taken together, our results show that EMT programmes trigger the expression of soluble mediators in cancer cells that stimulate angiogenesis and recruit myeloid cells in vivo, which might in turn favour cancer spread.

Exploring mechanisms of acquired resistance to HER2 (human epidermal growth factor receptor 2)-targeted therapies in breast cancer

HER2 (human epidermal growth factor receptor 2)-targeted therapy in breast cancer is one of the earliest and arguably most successful examples of the modern class of targeted drugs. Initially identified in the 1980s, the observation that HER2 acts as an independent predictor of poor prognosis in the 20% of breast cancer cases carrying a gene amplification or protein overexpression cemented its place at the forefront of research in this field. The outlook for patients with HER2-positive breast cancer has been revolutionized by the introduction of HER2-targeted agents, such as trastuzumab and lapatinib, yet resistance is frequently encountered and multiple different resistance mechanisms have been identified. We have explored resistance to a novel pan-HER inhibitor, AZD8931, and we examine mechanisms of resistance common to trastuzumab, lapatinib and AZD8931, and discuss the current problems associated with translating the wealth of pre-clinical data into clinical benefit.

The role of adipose-derived stem cells in breast cancer progression and metastasis

Conventional breast cancer extirpation involves resection of parts of or the whole gland, resulting in asymmetry and disfiguration. Given the unsatisfactory aesthetic outcomes, patients often desire postmastectomy reconstructive procedures. Autologous fat grafting has been proposed for reconstructive purposes for decades to restore form and anatomy after mastectomy. Fat has the inherent advantage of being autologous tissue and the most natural-appearing filler, but given its inconsistent engraftment and retention rates, it lacks reliability. Implementation of autologous fat grafts with cellular adjuncts, such as multipotent adipose-derived stem cells (ADSCs), has shown promising results. However, it is pertinent and critical to question whether these cells could promote any residual tumor cells to proliferate, differentiate, or metastasize or even induce de novo carcinogenesis. Thus far, preclinical and clinical study findings are discordant. A trend towards potential promotion of both breast cancer growth and invasion by ADSCs found in basic science studies was indeed not confirmed in clinical trials. Whether experimental findings eventually correlate with or will be predictive of clinical outcomes remains unclear. Herein, we aimed to concisely review current experimental findings on the interaction of mesenchymal stem cells and breast cancer, mainly focusing on ADSCs as a promising tool for regenerative medicine, and discuss the implications in clinical translation.

Inhibitory effects of proton beam irradiation on integrin expression and signaling pathway in human colon carcinoma HT29 cells

Proton radiotherapy has been established as a highly effective modality used in the local control of tumor growth. Although proton radiotherapy is used worldwide to treat several types of cancer clinically with great success due to superior targeting and energy deposition, the detailed regulatory mechanisms underlying the functions of proton radiation are not yet well understood. Accordingly, in the present study, to assess the effects of proton beam on integrin-mediated signaling pathways, we investigated the expression of integrins related to tumor progression and integrin trafficking, and key molecules related to cell adhesion, as well as examining phosphorylation of signaling molecules involved in integrin-mediated signaling pathways. Proton beam irradiation inhibited the increase in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced integrin β1 protein expression and the gene expression of members of the integrin family, such as α5β1, α6β4, αvβ3, and αvβ6 in human colorectal adenocarcinoma HT-29 cells. Simultaneously, the gene expression of cell adhesion molecules, such as FAK and CDH1, and integrin trafficking regulators, such as RAB4, RAB11, and HAX1, was decreased by proton beam irradiation. Moreover, proton beam irradiation decreased the phosphorylation of key molecules involved in integrin signaling, such as FAK, Src, and p130Cas, as well as PKC and MAPK, which are known as promoters of cell migration, while increased the phosphorylation of AMPK and the gene expression of Rab IP4 involved in the inhibition of cell adhesion and cell spreading. Taken together, our findings suggest that proton beam irradiation can inhibit metastatic potential, including cell adhesion and migration, by modulating the gene expression of molecules involved in integrin trafficking and integrin-mediated signaling, which are necessary for tumor progression.

MiR-200c suppresses TGF-β signaling and counteracts trastuzumab resistance and metastasis by targeting ZNF217 and ZEB1 in breast cancer

Resistance to trastuzumab and concomitantly distal metastasis are leading causes of mortality in HER2-positive breast cancers, the molecular basis of which remains largely unknown. Here, we generated trastuzumab-resistant breast cancer cells with increased tumorigenicity and invasiveness compared with parental cells, and observed robust epithelial-mesenchymal transition (EMT) and consistently elevated TGF-β signaling in these cells. MiR-200c, which was the most significantly downregulated miRNA in trastuzumab-resistant cells, restored trastuzumab sensitivity and suppressed invasion of breast cancer cells by concurrently targeting ZNF217, a transcriptional activator of TGF-β, and ZEB1, a known mediator of TGF-β signaling. Given the reported backward inhibition of miR-200c by ZEB1, ZNF217 also exerts a feedback suppression of miR-200c via TGF-β/ZEB1 signaling. Restoration of miR-200c, silencing of ZEB1 or ZNF217 or blockade of TGF-β signaling increased trastuzumab sensitivity and suppressed invasiveness of breast cancer cells. Therefore, our study unraveled nested regulatory circuits of miR-200c/ZEB1 and miR-200c/ZNF217/TGF-β/ZEB1 in synergistically promoting trastuzumab resistance and metastasis of breast cancer cells. These findings provide novel insights into the common role of EMT and related molecular machinery in mediating the malignant phenotypes of breast cancers.