Side-population cells in luminal-type breast cancer have tumour-initiating cell properties, and are regulated by HER2 expression and signalling

Co-expression of HIF1A with multi-drug transporters (P-GP, MRP1, and BCRP) in chemoresistant breast, colorectal, and ovarian cancer cells

Therapeutic resistance poses a significant challenge in treating most cancers and often leads to poor clinical outcomes and even treatment failure. One of the primary mechanisms that confer multidrug resistance phenotype to cancer cells is the hyperactivity of certain drug efflux transporters. P-GP, MRP1, and BCRP are the key ABC efflux pumps that collectively extrude a broad spectrum of chemotherapeutic drugs. Besides, HIF1A, a master transcription regulatory protein, is also associated with cancer development and therapeutic resistance. Thereby, this study aimed to delve into the mechanisms of drug resistance, specifically focusing on HIF1A-driven overexpression of ABC transporters. A total of 57 chemoresistant and 57 paired control tissue samples (breast, colorectal, and ovarian) from Bangladeshi cancer patients were analyzed to determine the co-expression level of ABC transporters and HIF1A. Molecular docking was also conducted to evaluate the interactions of HIF1A protein and hypoxia response element (HRE) sequences in the promoter regions transporter genes. This study revealed that HIF1A is significantly overexpressed in chemoresistant tissues, suggesting its pivotal role in chemoresistance mechanisms across malignancies and its potential as a target to overcome therapeutic resistance. The findings from this study also suggest a direct upregulation of ABCB1, ABCC1, and ABCG2 transcription by HIF1A in chemoresistant cancer cells by binding to the HRE sequence in the promoter regions. Thus, inhibition of these interactions of HIF1A appears to be a promising approach to reverse chemoresistance. The findings of this study can serve as a foundation for future research, resolving molecular intricacies to improve treatment outcomes in chemoresistant patients.

Structural regression modelling of peptide based drug delivery vectors for targeted anti-cancer therapy

Drug resistance in cancer poses a serious challenge in finding an effective remedy for cancer patients, because of the multitude of contributing factors influencing this complex phenomenon. One way to counter this problem is using a more targeted and dose-limiting approach for drug delivery, rather than relying on conventional therapies that exhibit multiple pernicious side-effects. Stability and specificity have traditionally been the core issues of peptide-based delivery vectors. In this study, we employed a structural regression modelling approach in the design, synthesis and characterization of a series of peptides that belong to approximately same topological cluster, yet with different electrostatic signatures encoded as a result of their differential positioning of amino acids in a given sequence. The peptides tagged with the fluorophore 5(6)-carboxyfluorescein, showed higher uptake in cancer cells with some of them colocalizing in the lysosomes. The peptides tagged with the anti-cancer drug methotrexate have displayed enhanced cytotoxicity and inducing apoptosis in triple-negative breast cancer cells. They also showed comparable uptake in side-population cells of lung cancer with stem-cell like properties. The most-optimized peptide showed accumulation in the tumor resulting in significant reduction of tumor size, compared to the untreated mice in in-vivo studies. Our results point to the following directives; (i) peptides can be design engineered for targeted delivery (ii) stereochemical engineering of peptide main chain can resist proteolytic enzymes and (iii) cellular penetration of peptides into cancer cells can be modulated by varying their electrostatic signatures.

Generation of Cancer Stem/Initiating Cells by Cell-Cell Fusion

CS/ICs have raised great expectations in cancer research and therapy, as eradication of this key cancer cell type is expected to lead to a complete cure. Unfortunately, the biology of CS/ICs is rather complex, since no common CS/IC marker has yet been identified. Certain surface markers or ALDH1 expression can be used for detection, but some studies indicated that cancer cells exhibit a certain plasticity, so CS/ICs can also arise from non-CS/ICs. Another problem is intratumoral heterogeneity, from which it can be inferred that different CS/IC subclones must be present in the tumor. Cell–cell fusion between cancer cells and normal cells, such as macrophages and stem cells, has been associated with the generation of tumor hybrids that can exhibit novel properties, such as an enhanced metastatic capacity and even CS/IC properties. Moreover, cell–cell fusion is a complex process in which parental chromosomes are mixed and randomly distributed among daughter cells, resulting in multiple, unique tumor hybrids. These, if they have CS/IC properties, may contribute to the heterogeneity of the CS/IC pool. In this review, we will discuss whether cell–cell fusion could also lead to the origin of different CS/ICs that may expand the overall CS/IC pool in a primary tumor.

Novel O-acylated (E)-3-aryl-6,7-dihydrobenzisoxazol-4(5H)-one oximes targeting HSP90-HER2 axis in breast cancer cells

Novel O-acylated (E)-3-aryl-6,7-dihydrobenzisoxazol-4(5H)-one oximes were designed as potential HSP90 inhibitors. A series of the compounds was synthesized by oximation of (E)-3-aryl-6,7-dihydrobenzisoxazol-4(5H)-ones followed by O-acylation with acylamidobenzoic acids. The obtained compounds showed an antiproliferative effect on three breast cancer cell lines (MCF7, MDA-MB-231 and HCC1954). Compound 16s exhibited high antiproliferative potency against HCC1954 breast cancer cells with the IC₅₀ value of 6 µM was selected for in-depth evaluation. Compound 16s did not inhibit the growth of normal epithelial cells. We have demonstrated that the compound 16s can induce apoptosis in cancer cells via inhibition of HSP90 "client" proteins including a key oncogenic receptor, HER2/neu. Described here compounds can be considered for further basic and preclinical investigation as a part of HSP90/HER2-targeted therapies.

Pleiotropic Roles of ABC Transporters in Breast Cancer

Chemotherapeutics are the mainstay treatment for metastatic breast cancers. However, the chemotherapeutic failure caused by multidrug resistance (MDR) remains a pivotal obstacle to effective chemotherapies of breast cancer. Although in vitro evidence suggests that the overexpression of ATP-Binding Cassette (ABC) transporters confers resistance to cytotoxic and molecularly targeted chemotherapies by reducing the intracellular accumulation of active moieties, the clinical trials that target ABCB1 to reverse drug resistance have been disappointing. Nevertheless, studies indicate that ABC transporters may contribute to breast cancer development and metastasis independent of their efflux function. A broader and more clarified understanding of the functions and roles of ABC transporters in breast cancer biology will potentially contribute to stratifying patients for precision regimens and promote the development of novel therapies. Herein, we summarise the current knowledge relating to the mechanisms, functions and regulations of ABC transporters, with a focus on the roles of ABC transporters in breast cancer chemoresistance, progression and metastasis.

Breast Cancer Stem Cells: Biomarkers, Identification and Isolation Methods, Regulating Mechanisms, Cellular Origin, and Beyond

Despite recent advances in diagnosis and treatment, breast cancer (BC) is still a major cause of cancer-related mortality in women. Breast cancer stem cells (BCSCs) are a small but significant subpopulation of heterogeneous breast cancer cells demonstrating strong self-renewal and proliferation properties. Accumulating evidence has proved that BCSCs are the driving force behind BC tumor initiation, progression, metastasis, drug resistance, and recurrence. As a heterogeneous disease, BC contains a full spectrum of different BC subtypes, and different subtypes of BC further exhibit distinct subtypes and proportions of BCSCs, which correspond to different treatment responses and disease-specific outcomes. This review summarized the current knowledge of BCSC biomarkers and their clinical relevance, the methods for the identification and isolation of BCSCs, and the mechanisms regulating BCSCs. We also discussed the cellular origin of BCSCs and the current advances in single-cell lineage tracing and transcriptomics and their potential in identifying the origin and lineage development of BCSCs.

Tumor exosome-based nanoparticles are efficient drug carriers for chemotherapy

Developing biomimetic nanoparticles without loss of the integrity of proteins remains a major challenge in cancer chemotherapy. Here, we develop a biocompatible tumor-cell-exocytosed exosome-biomimetic porous silicon nanoparticles (PSiNPs) as drug carrier for targeted cancer chemotherapy. Exosome-sheathed doxorubicin-loaded PSiNPs (DOX@E-PSiNPs), generated by exocytosis of the endocytosed DOX-loaded PSiNPs from tumor cells, exhibit enhanced tumor accumulation, extravasation from blood vessels and penetration into deep tumor parenchyma following intravenous administration. In addition, DOX@E-PSiNPs, regardless of their origin, possess significant cellular uptake and cytotoxicity in both bulk cancer cells and cancer stem cells (CSCs). These properties endow DOX@E-PSiNPs with great in vivo enrichment in total tumor cells and side population cells with features of CSCs, resulting in anticancer activity and CSCs reduction in subcutaneous, orthotopic and metastatic tumor models. These results provide a proof-of-concept for the use of exosome-biomimetic nanoparticles exocytosed from tumor cells as a promising drug carrier for efficient cancer chemotherapy.

The softness of tumour-cell-derived microparticles regulates their drug-delivery efficiency

Extracellular microparticles (MPs) can function as drug-delivery vehicles for anticancer drugs. Here, we show that the softness of MPs derived from tumour-repopulating cells (TRCs) isolated from three-dimensional fibrin gels enhances the MPs' drug-delivery efficiency. We found that, compared with MPs derived from tumour cells cultured in conventional tissue-culture plastic, TRC-derived MPs intravenously injected in tumour-xenograft-bearing mice showed enhanced accumulation in tumour tissues, enhanced blood-vessel crossing and penetration into tumour parenchyma, and preferential uptake by highly tumorigenic TRCs. We also show that the cytoskeleton-related protein cytospin-A plays a critical role in the regulation of TRC-derived MP softness. The modulation of the mechanical properties of TRC-derived MPs could aid the efficiency of delivery of anticancer drugs.

Assays for functionally defined normal and malignant mammary stem cells

The discovery of rare, heterogeneous self-renewing stem cells with shared developmental and molecular features within epithelial components of mammary gland and breast cancers has provided a conceptual framework to understand cellular composition of these tissues and mechanisms that control their number. These normal mammary epithelial stem cells (MaSCs) and breast cancer stem cells (BCSCs) were identified and analyzed using transplant assays (namely mammary repopulating unit (MRU) assay, mammary tumor-initiating cell (TIC) assay), which reveal their latent ability to regenerate respective normal and malignant epithelial tissues with self-renewing units displaying hierarchical cellular differentiation over multiple generations in recipient mice. "Next-generation" methods using "barcoded" normal and malignant mammary cells, with the help of next-generation sequencing (NGS) technology, have revealed hidden complexity and heterogeneous growth potential of MaSCs and BCSCs. Several single markers or combinations of markers have been reported to prospectively enrich MaSCs and BCSCs. Such markers and the extent to which they enrich for MaSCs and BCSCs activity require a critical appraisal. Also, knowledge of the functional assays and their limitations and harmonious reporting of results is a prerequisite to improve our understanding of MaSCs and BCSCs. This chapter describes evolution of the concept of MaSCs and BCSCs, and specific methodologies to investigate them.

Do Different Stemness Markers Identify Different Pools of Cancer Stem Cells in Malignancies: A Study on ER+ and ER-Breast Cancer Cell Lines

In view of popularity of cancer stem cell (CSC) model all events in evolution of cancer are being explained in that context. Breast cancer is first solid tumor in which CSCs were identified. We aimed to compare stemness profile of two major subtypes [Estrogen receptor positive (ER⁺) and negative (ER^-)] breast cancer using different sets of markers. Expression of CD44/CD24, CK/Vimentin, E-Cadherin/Fibronectin and percentage of side population (SP) was studied in ER⁺ (T47D) and ER^- (MDA-MB-231) cell lines by flow cytometry. Breast CSCs (BCSCs) were sorted using CD44⁺/CD24^-/low expression and SP analysis and cultured. BCSCs were then compared with Non-CSCs (NCSCs) for response to drugs (Paclitaxel and Cisplatin), Ki67 and ER expression. Results showed higher expression of stemness markers (CD44⁺/CD24^-/low, CK⁺/Vimentin⁺ and E-Cadherin^-/Fibrinectin^F+) in MDA-MB-231 cells. Percentage SP representing BCSCs was found to be significantly more in later (3.20 ± 0.002 cf. T47D 1.25% ± 0.0007). BCSCs were found to be more resistant to drugs as compared to NCSCs in both cell lines. ER expression was weak in BCSCs sorted from T47D as compared to NCSCs. Ki67 was expressed in both BCSCs and NCSCs. Differences in expression of stemness markers help to explain aggressive behavior, higher recurrence rate and metastatic potential of MDA-MB-231 cells. However, no correlation amongst different markers used suggests that they may be identifying varied populations of cells in tumor hierarchy. A weak ER expression in BCSCs may be strategy used by BCSCs to escape effect of hormone therapy in ER⁺ breast cancers.

HER2 in stemness and epithelial-mesenchymal plasticity of breast cancer

Breast cancer had been the first non-hematologic malignancy where sub-types based on molecular characterization had entered clinical practice. HER2 over-expression, due to either gene amplification or protein up-regulation, defines one of these sub-types and is clinically exploited by addition of HER2-targeted treatments to the regimens of treatment. Nevertheless, in many occasions HER2-positive cancers are resistant or become refractory to these therapies. Several mechanisms, such as activation of alternative pathways or loss of expression of the receptor in cancer cells, have been proposed as the cause of these therapeutic failures. Cancer stem cells (CSCs, alternatively called tumor-initiating cells) comprise a small percentage of the tumor cells, but are capable of reconstituting and propagating tumors due to their superior intrinsic capacity for regeneration, survival and resistance to therapies. CSCs possess circuits enabling epigenetic plasticity which endow them with the ability to alternate between epithelial and mesenchymal states. This paper will discuss the expression and regulation of HER2 in CSCs of the different sub-types of breast cancer and relationships of the receptor with both the circuits of stemness and epithelial-mesenchymal plasticity. Therapeutic repercussions of the relationship of HER2-initiated signaling with stemness networks will also be proposed.

BRCA1 haploinsufficiency cell-autonomously activates RANKL expression and generates denosumab-responsive breast cancer-initiating cells

Denosumab, a monoclonal antibody to the receptor activator of nuclear factor-κB ligand (RANKL), might be a novel preventative therapy for BRCA1-mutation carriers at high risk of developing breast cancer. Beyond its well-recognized bone-targeted activity impeding osteoclastogenesis, denosumab has been proposed to interfere with the cross-talk between RANKL-producing sensor cells and cancer-initiating RANK+ responder cells that reside within premalignant tissues of BRCA1-mutation carriers. We herein tested the alternative but not mutually exclusive hypothesis that BRCA1 deficiency might cell-autonomously activate RANKL expression to generate cellular states with cancer stem cell (CSC)-like properties. Using isogenic pairs of normal-like human breast epithelial cells in which the inactivation of a single BRCA1 allele results in genomic instability, we assessed the impact of BRCA1 haploinsufficiency on the expression status of RANK and RANKL. RANK expression remained unaltered but RANKL was dramatically up-regulated in BRCA1mut/+ haploinsufficient cells relative to isogenic BRCA1+/+ parental cells. Neutralizing RANKL with denosumab significantly abrogated the ability of BRCA1 haploinsufficient cells to survive and proliferate as floating microtumors or "mammospheres" under non-adherent/non-differentiating conditions, an accepted surrogate of the relative proportion and survival of CSCs. Intriguingly, CSC-like states driven by epithelial-to-mesenchymal transition or HER2 overexpression traits responded to some extent to denosumab. We propose that breast epithelium-specific mono-allelic inactivation of BRCA1 might suffice to cell-autonomously generate RANKL-addicted, denosumab-responsive CSC-like states. The convergent addiction to a hyperactive RANKL/RANK axis of CSC-like states from genetically diverse breast cancer subtypes might inaugurate a new era of cancer prevention and treatment based on denosumab as a CSC-targeted agent.

3D Porous Chitosan-Alginate Scaffolds Promote Proliferation and Enrichment of Cancer Stem-Like Cells

Cancer stem cells are increasingly becoming a primary target for new cancer treatment development. The ability to study their transient behavior in vitro will provide the opportunity for high-throughput testing of more effective therapies. We have previously demonstrated the use of 3D porous chitosan-alginate (CA) scaffolds to promote cancer stem-like cell (CSC) proliferation and enrichment in glioblastoma. Here we use 3D porous CA scaffolds to promote cancer stem-like cell enrichment in cell lines from prostate, liver, and breast cancers, and investigate the proliferation, morphology, and gene expressions of cells cultured in CA scaffolds as compared to 2D controls. The 3D CA scaffold cultures for all three cancer types showed reduced proliferation, formation of tumor spheroids, and increased expression of CSC associated mark genes (CD133 and NANOG), as opposed to monolayers. Additionally, we present a putative mechanism for the cancer stem-like cell enrichment on CA scaffolds. This study demonstrates that the cancer stem-like cell enrichment in CA scaffolds is a robust process that is not restricted to particular cancer types.

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.

Breast cancer stem cells: current advances and clinical implications

There is substantial evidence that many cancers, including breast cancer, are driven by a population of cells that display stem cell properties. These cells, termed cancer stem cells (CSCs) or tumor initiating cells, not only drive tumor initiation and growth but also mediate tumor metastasis and therapeutic resistance. In this chapter, we summarize current advances in CSC research with a major focus on breast CSCs (BCSCs). We review the prevailing methods to isolate and characterize BCSCs and recent evidence documenting their cellular origins and phenotypic plasticity that enables them to transition between mesenchymal and epithelial-like states. We describe in vitro and clinical evidence that these cells mediate metastasis and treatment resistance in breast cancer, the development of novel strategies to isolate circulating tumor cells (CTCs) that contain CSCs and the use of patient-derived xenograft (PDX) models in preclinical breast cancer research. Lastly, we highlight several signaling pathways that regulate BCSC self-renewal and describe clinical implications of targeting these cells for breast cancer treatment. The development of strategies to effectively target BCSCs has the potential to significantly improve the outcomes for patients with breast cancer.

Side population cell level in human breast cancer and factors related to disease-free survival

Side population (SP) cells have stem cell-like properties with a capacity for self-renewal and are resistant to chemotherapy and radiotherapy. Therefore the presence of SP cells in human breast cancer probably has prognostic value.

OBJECTIVE

To investigate the characteristics of SP cells and identify the relationship between the SP cells levels and clinico-pathological parameters of the breast tumor and disease-free survival (DFS) in breast cancer patients.

MATERIALS AND METHODS

A total of 122 eligible breast cancer patients were consecutively recruited from January 1, 2006 to December 31, 2007 at Yunnan Tumor Hospital. All eligible subjects received conventional treatment and were followed up for seven years. Predictors of recurrence and/or metastasis and DFS were analyzed using Cox regression analysis. Human breast cancer cells were also obtained from fresh human breast cancer tissue and cultured by the nucleic acid dye Hoechst33342 with Verapami. Flow cytometry (FCM) was employed to isolate the cells of SP and non-SP types.

RESULTS

In this study, SP cells were identified using flow cytometric analysis with Hoechst 33342 dye efflux. Adjusted for age, tumor size, lymph nodal status, histological grade, the Cox model showed a higher risk of recurrence and/or metastasis positively associated with the SP cell level (1.75, 1.02-2.98), as well as with axillary lymph node metastasis (2.99, 1.76-5.09), pathology invasiveness type (1.7, 1.14-2.55), and tumor volume doubling time (TVDT) (1.54, 1.01-2.36).

CONCLUSIONS

The SP cell level is independently associated with tumor progression and clinical outcome after controlling for other pathological factors. The axillary lymph node status, TVDT and the status of non-invasive or invasive tumor independently predict the prognosis of breast cancer.

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.

Downregulation of BCRP and anti-apoptotic proteins by proadifen (SKF-525A) is responsible for the enhanced mitoxantrone accumulation and toxicity in mitoxantrone-resistant human promyelocytic leukemia cells

Multidrug resistance caused by the overexpression of ABC transporter proteins in cancer cells remains a major obstacle limiting chemotherapy efficacy. Drugs inhibiting these transporters have been shown to increase the anti-proliferative properties of chemotherapeutics. As we previously described, proadifen, a P450 monooxygenase inhibitor, might also be able to inhibit some ABC transporters, including breast cancer resistance protein (BCRP). Because mitoxantrone (MTX) is a strong BCRP substrate and is often used in the treatment of leukemia, we investigated the effect of 24 h proadifen pre-treatment on the cytotoxicity of MTX in leukemic cell lines that are sensitive to MTX (HL-60) and MTX-resistant ABCG2-overexpressing subclone (cBCRP). We show for the first time that proadifen is able to enhance the cytotoxic properties of MTX in cBCRP cells, particularly through the inhibition of BCRP expression and activity. This proadifen-MTX synergism was also mediated by the inhibition of various cellular proteins engaged in apoptosis, including Mc-1, Bcl-xL, survivin and activation of procaspase-3. Proadifen also decreased the expression of γH2AX, which is involved in the recruitment of reparation proteins. Moreover, the inhibition of DNA damage repair proteins Ku86 and B23 after proadifen treatment indicate a possible role of proadifen in DNA repair blockage, thus suppressing the reparation rate of MTX-induced DSBs.

Histone deacetylase inhibitor entinostat in combination with a retinoid downregulates HER2 and reduces the tumor initiating cell population in aromatase inhibitor-resistant breast cancer

Resistance to aromatase inhibitors (AIs) involves increased HER2. One mechanism by which HER2 may mediate resistance is through expansion of the tumor initiating cell (TIC) population. This study investigates whether combining all-trans retinoic acid (ATRA) and histone deacetylase inhibitor entinostat (ENT) can inhibit TICs and HER2 in AI-resistant cells and tumors. Modulation of cell viability and HER2 expression were assessed in AI-resistant cells treated with ATRA + ENT. Letrozole-resistant LTLT-Ca cells treated with ATRA + ENT were assayed for changes in TIC characteristics, such as TIC markers (BCRP, ALDH, and BMI-1), side population (SP), and mammosphere formation. Xenograft tumors of MCF-7Ca cells made resistant to letrozole were treated with ATRA, ATRA + letrozole, ATRA + ENT, or ATRA + ENT + letrozole. Resulting tumors were assayed for changes in TIC characteristics. Patient samples taken pre- and post-AI treatment were analyzed for changes in ERα and HER2 protein expression. Treatment with ATRA + ENT reduced HER2 expression and viability (P < 0.001) in AI-resistant cells, as well as decreased SP (P < 0.0001), mammosphere formation (P < 0.01), and expression of TIC molecular markers (P < 0.01) in LTLT-Ca. A reduction in tumor growth rate was observed in mice treated with ENT + ATRA + letrozole when compared to mice treated with single agents (P < 0.0001) or ENT + ATRA (P = 0.02). Decreased TIC characteristics, including mammosphere formation (P < 0.05), were observed in tumors from the triple combination. An increase in HER2 and downregulation in ERα protein expression was observed in patients upon resistance to AI (P < 0.005). These studies indicate that the combination of ATRA and ENT inhibits the TIC population of AI-resistant cells and may be effective in reducing tumor recurrence.

Loss of microRNA-27b contributes to breast cancer stem cell generation by activating ENPP1

Cancer stem cells (CSCs) have been identified in various types of cancer; however, the mechanisms by which cells acquire CSC properties such as drug resistance and tumour seeding ability are not fully understood. Here, we identified microRNA-27b (miR-27b) as a key regulator for the generation of a side-population in breast cancer cells that showed CSC properties, and also found that the anti-type II diabetes (T2D) drug metformin reduced this side-population via miR-27b-mediated repression of ectonucleotide pyrophosphatase/phosphodiesterase family member 1 (ENPP1), which is involved in T2D development. ENPP1 induced the generation of the side-population via upregulation of the ABCG2 transporter. ENPP1 was also identified as a substrate of the 26S proteasome, the activity of which is downregulated in CSCs. Overall, these results demonstrate that a T2D-associated gene plays an important role in tumour development and that its expression is strictly controlled at the mRNA and protein levels.

MicroRNAs have a role in the acquisition of stem cell-like properties of cancer cells. Here the authors show that microRNA-27b mediates generation of a side-population of breast cancer stem cells, in part by regulating the protein ENPP1, which has been previously linked to the development of diabetes.

Effects of Withania somnifera and Tinospora cordifolia extracts on the side population phenotype of human epithelial cancer cells: toward targeting multidrug resistance in cancer

Recent reports suggest the existence of a subpopulation of stem-like cancer cells, termed as cancer stem cells (CSCs), which bear functional and phenotypic resemblance with the adult, tissue-resident stem cells. Side population (SP) assay based on differential efflux of Hoechst 33342 has been effectively used for the isolation of CSCs. The drug resistance properties of SP cells are typically due to the increased expression of ABC transporters leading to drug efflux. Conventionally used chemotherapeutic drugs may often leads to an enrichment of SP, revealing their inability to target the drug-resistant SP and CSCs. Thus, identification of agents that can reduce the SP phenotype is currently in vogue in cancer therapeutics. Withania somnifera (WS) and Tinospora cordifolia (TC) have been used in Ayurveda for treating various diseases, including cancer. In the current study, we have investigated the effects of ethanolic (ET) extracts of WS and TC on the cancer SP phenotype. Interestingly, we found significant decrease in SP on treatment with TC-ET, but not with WS-ET. The SP-inhibitory TC-ET was further fractionated into petroleum ether (TC-PET), dichloromethane (TC-DCM), and n-butyl alcohol (TC-nBT) fractions using bioactivity-guided fractionation. Our data revealed that TC-PET and TC-DCM, but not TC-nBT, significantly inhibited SP in a dose-dependent manner. Furthermore, flow cytometry-based functional assays revealed that TC-PET and TC-DCM significantly inhibited ABC-B1 and ABC-G2 transporters and sensitized cancer cells toward chemotherapeutic drug-mediated cytotoxicity. Thus, the TC-PET and TC-DCM may harbor phytochemicals with the potential to reverse the drug-resistant phenotype, thus improving the efficacy of cancer chemotherapy.

Huaier aqueous extract inhibits stem-like characteristics of MCF7 breast cancer cells via inactivation of hedgehog pathway

The theory of targeting cancer stem-like cells (CSCs) provides novel strategy for cancer treatment. In the present study, we examined the inhibitory effect of Huaier aqueous extract on eradicating breast cancer stem cells and explored the underlying mechanisms. Our data demonstrated that various concentrations of Huaier extract significantly decreased the viabilities, numbers, and sizes of mammospheres. After incubation with Huaier extract for 24 h, the clonogenicity of MCF7 cell line was obviously impaired, along with less holoclones. In addition, Huaier extract reduced the number of cells expressing CD44+/CD24- and decreased the level of stem cell markers (OCT-4, NESTIN, and NANOG). The hedgehog (Hh), notch, and Wnt/β-catenin pathways were essential stem cell signaling pathways involved in regulating CSC renewal and maintenance. We reported that the inhibitory effect of Huaier extract was partly depended on the inactivation of Hh pathway. These findings provided experimental evidence that Huaier extract was a promising therapeutic drug for eliminating the breast cancer stem cells.

Dynamic and influential interaction of cancer cells with normal epithelial cells in 3D culture

Background

The cancer microenvironment has a strong impact on the growth and dynamics of cancer cells. Conventional 2D culture systems, however, do not reflect in vivo conditions, impeding detailed studies of cancer cell dynamics. This work aims to establish a method to reveal the interaction of cancer and normal epithelial cells using 3D time-lapse.

Methods

GFP-labelled breast cancer cells, MDA-MB-231, were co-cultured with mCherry-labelled non-cancerous epithelial cells, MDCK, in a gel matrix. In the 3D culture, the epithelial cells establish a spherical morphology (epithelial sphere) thus providing cancer cells with accessibility to the basal surface of epithelia, similar to the in vivo condition. Cell movement was monitored using time-lapse analyses. Ultrastructural, immunocytochemical and protein expression analyses were also performed following the time-lapse study.

Results

In contrast to the 2D culture system, whereby most MDA-MB-231 cells exhibit spindle-shaped morphology as single cells, in the 3D culture the MDA-MB-231 cells were found to be single cells or else formed aggregates, both of which were motile. The single MDA-MB-231 cells exhibited both round and spindle shapes, with dynamic changes from one shape to the other, visible within a matter of hours. When co-cultured with epithelial cells, the MDA-MB-231 cells displayed a strong attraction to the epithelial spheres, and proceeded to surround and engulf the epithelial cell mass. The surrounded epithelial cells were eventually destroyed, becoming debris, and were taken into the MDA-MB-231 cells. However, when there was a relatively large population of normal epithelial cells, the MDA-MB-231 cells did not engulf the epithelial spheres effectively, despite repeated contacts. MDA-MB-231 cells co-cultured with a large number of normal epithelial cells showed reduced expression of monocarboxylate transporter-1, suggesting a change in the cell metabolism. A decreased level of gelatin-digesting ability as well as reduced production of matrix metaroproteinase-2 was also observed.

Conclusions

This culture method is a powerful technique to investigate cancer cell dynamics and cellular changes in response to the microenvironment. The method can be useful for various aspects such as; different combinations of cancer and non-cancer cell types, addressing the organ-specific affinity of cancer cells to host cells, and monitoring the cellular response to anti-cancer drugs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12935-014-0108-6) contains supplementary material, which is available to authorized users.

Essential role of the cancer stem/progenitor cell marker nucleostemin for indole-3-carbinol anti-proliferative responsiveness in human breast cancer cells

BACKGROUND

Nucleostemin is a nucleolus residing GTPase that is considered to be an important cancer stem/progenitor cell marker protein due to its high expression levels in breast cancer stem cells and its role in tumor-initiation of human mammary tumor cells. It has been proposed that nucleostemin may represent a valuable therapeutic target for breast cancer; however, to date evidence supporting the cellular mechanism has not been elucidated.

RESULTS

Expression of exogenous HER2, a member of the EGF receptor gene family, in the human MCF-10AT preneoplastic mammary epithelial cell line formed a new breast cancer cell line, 10AT-Her2, which is highly enriched in cells with stem/progenitor cell-like character. 10AT-Her2 cells display a CD44+/CD24-/low phenotype with high levels of the cancer stem/progenitor cell marker proteins nucleostemin, and active aldehyde dehydrogenase-1. The overall expression pattern of HER2 protein and the stem/progenitor cell marker proteins in the 10AT-Her2 cell population is similar to that of the luminal HER2+ SKBR3 human breast cancer cell line, whereas, both MCF-7 and MDA-MB-231 cells display reduced levels of nucleostemin and no detectable expression of ALDH-1. Importantly, in contrast to the other well-established human breast cancer cell lines, 10AT-Her2 cells efficiently form tumorspheres in suspension cultures and initiate tumor xenograft formation in athymic mice at low cell numbers. Furthermore, 10AT-Her2 cells are highly sensitive to the anti-proliferative apoptotic effects of indole-3-carbinol (I3C), a natural anti-cancer indolecarbinol from cruciferous vegetables of the Brassica genus such as broccoli and cabbage. I3C promotes the interaction of nucleostemin with MDM2 (Murine Double Mutant 2), an inhibitor of the p53 tumor suppressor, and disrupts the MDM2 interaction with p53. I3C also induced nucleostemin to sequester MDM2 in a nucleolus compartment, thereby freeing p53 to mediate its apoptotic activity. siRNA knockdown of nucleostemin functionally documented that nucleostemin is required for I3C to trigger its cellular anti-proliferative responses, inhibit tumorsphere formation, and disrupt MDM2-p53 protein-protein interactions. Furthermore, expression of an I3C-resistant form of elastase, the only known target protein for I3C, prevented I3C anti-proliferative responses in cells and in tumor xenografts in vivo, as well as disrupt the I3C stimulated nucleostemin-MDM2 interactions.

CONCLUSIONS

Our results provide the first evidence that a natural anti-cancer compound mediates its cellular and in vivo tumor anti-proliferative responses by selectively stimulating cellular interactions of the stem/progenitor cell marker nucleostemin with MDM2, which frees p53 to trigger its apoptotic response. Furthermore, our study provides a new mechanistic template that can be potentially exploited for the development of cancer stem/progenitor cell targeted therapeutic strategies.

β-catenin knockdown enhances the effects of fluorouracil in the breast cancer cell line MDA-MB-468

Tumor proliferation, drug resistance and cell stemness are major difficulties that are encountered during breast cancer therapy and are often responsible for disease progression and cancer-related mortality. β-catenin is considered to be an invasion gene in breast cancer. However, how β-catenin regulates breast cancer cell proliferation and stemness remains unclear. In the present study, β-catenin knockdown by small interfering RNA in MDA-MB-468, a highly metastatic breast cancer cell line, inhibited the expression of β-catenin, Oct3/4 (stemness), survivin (anti-apoptosis) and BCRP (drug resistance). Knockdown of β-catenin enhanced the effects of fluorouracil (5-FU) chemotherapy on the proliferation of MDA-MB-468 cells. Thus, these preliminary results indicate that β-catenin knockdown enhanced 5-FU-induced proliferation inhibition in the breast cancer cell line MDA-MB-468, and indicate that combining 5-FU with gene silencing could be an advantageous option for enhancing the curative effect of chemotherapy in breast cancer and other malignancies.

Characterization of side population cells isolated from the colon cancer cell line SW480

Side population (SP) cells may play a crucial role in tumorigenesis and the recurrence of cancer. Many types of cell lines and tissues have demonstrated the presence of SP cells, including colon cancer cell lines. This study aimed to identify cancer stem cells (CSCs) in the SP of the colon cancer cell line SW480. SP cells were isolated by fluorescence-activated cell sorting (FACS), followed by serum-free medium (SFM) culture. The self-renewal, differentiated progeny, clone formation, proliferation, invasion ability, cell cycle, chemosensitivity and tumorigenic properties in SP and non-SP (NSP) cells were investigated through in vitro culture and in vivo serial transplantation. The expression profiles of ATP-binding cassette (ABC) protein transporters and stem cell-related genes were examined by RT-PCR and western blot analysis. The human colon cancer cell lines SW480, Lovo and HCT116 contain 1.1 ± 0.10, 0.93 ± 0.11 and 1.33 ± 0.05% SP cells, respectively. Flow cytometry analysis revealed that SP cells could differentiate into SP and NSP cells. SP cells had a higher proliferation potency and CFE than NSP cells. Compared to NSP cells, SP cells were also more resistant to CDDP and 5-FU, and were more invasive and displayed increased tumorigenic ability. Moreover, SP cells showed higher mRNA and protein expression of ABCG2, MDR1, OCT-4, NANOG, SOX-2, CD44 and CD133. SP cells isolated from human colon cancer cell lines harbor CSC properties that may be related to the invasive potential and therapeutic resistance of colon cancer.

Therapeutic targeting of ERBB2 in breast cancer: understanding resistance in the laboratory and combating it in the clinic

ERBB2 gene amplification occurs in about one quarter of breast carcinomas (BCs) and identifies a distinct clinical subset of BC. The introduction in the clinic of Trastuzumab, a humanized monoclonal antibody (mAb) directed to the ERBB2 extracellular domain, has had a great impact on the therapeutic management of ERBB2+ BC. Yet, not all patients respond to Trastuzumab and resistance develops also among patients that initially benefit from Trastuzumab-based regimens. Pre-clinical studies have discovered several mechanisms through which tumor cells may escape from Trastuzumab-mediated ERBB2 inhibition. These include rewiring of the ErbB signaling network, loss of ERBB2 expression, expression of ERBB2 isoforms refractory to Trastuzumab inhibition, vicarious signaling by non-ErbB tyrosine kinases and constitutive activation of downstream signaling routes, such as the PI3K pathway. While the relative contribution of each of these mechanisms to establishing Trastuzumab resistance in the clinical setting is not fully understood, much attention has been focused on abating resistance by achieving complete blockade of ERBB2-containing dimers. This approach, propelled by the development of novel anti-ERBB2 therapeutics, has led to the recent approval of Lapatinib, Pertuzumab and T-DM1 as additional anti-ERBB2 therapeutics in BC. However, full success is far from being achieved and resistance to ERBB2 targeting remains a relevant problem in the clinical management of BC. Herein, we provide an overview of biological and molecular bases underpinning resistance to ERBB2 therapeutics in BC, discuss outstanding issues in the field of ERBB2 therapeutic targeting and elaborate on future directions of translational research on ERBB2+ breast cancer.

Expression of HER-2 in rectal cancers treated with preoperative radiotherapy: a potential biomarker predictive of metastasis

BACKGROUND

Evidence suggests HER-2 overexpression may be predictive of prognosis in colorectal cancer patients, though this remains controversial.

OBJECTIVES

This study was performed to assess the prognostic value of HER-2 expression in locally advanced rectal cancer patients after preoperative radiotherapy.

PATIENTS AND METHODS

HER-2 expression was evaluated based on immunohistochemical (IHC) staining of resected specimens from 142 mid-to-low rectal cancer patients. Fluorescence in situ hybridization (FISH) was performed to confirm HER-2 overexpression in samples with an IHC score of 2+. Tumor regression grading (TRG) of the primary tumors was determined semiquantitatively using a tumor regression grading scheme advocated in the AJCC Cancer Staging Manual 7 edition.

RESULTS

When the total staining intensity was evaluated, 106 samples (74.6%) showed barely-perceptible positivity (0-1+; HER-2--negative), 15 samples (10.6%) showed moderate positivity (2+) and 21 samples (14.8%) showed strong positivity (3+, HER-2 positive). FISH confirmed that 2 cases showing moderate HER-2 positivity (2+) overexpressed HER2. There was no significant difference between the HER-2 positive and -negative groups with respect to age, gender, TRG, TNM stage, downstaging status, lymphovascular invasion or tumor differentiation. A significant correlation was found between HER-2 overexpression and the incidence of distant metastasis (p = 0.005). Subgroup analysis revealed this correlation was not significant (p = 0.247) in the radiation-insensitive (TRG0-2) subgroup, whereas a significant correlation (p = 0.026) between HER-2 overexpression and distant metastasis was found in the radiation-resistant (TRG3) subgroup. Multivariate analysis identified ypN stage (OR = 0.473, p = 0.002)and overexpression of HER-2 (OR = 3.704, p = 0.008) as independent risk factors for distant metastasis. There was no correlation between HER-2 overexpression and disease-free survival or overall survival among the study population.

LIMITATIONS

We reported that HER-2 overexpression was correlated with distant metastasis in rectal cancer patients, especially in the radiation-insensitive group. However, there are certain limitations. First, this study was limited due to the fact that the number of rectal patients enrolled was only 142, which is relatively small. Second, HER-2 expression was measured by IHC with a positive ratio around 15%, which is fairly high according to the literature. Also, we collected the tissue samples preoperatively. It would be interesting to know the HER-2 expression levels pre- and postradiotherapy, as well as their correlation with local recurrence or distant metastasis. Finally, in rectal cancer patients, there is little information published on HER-2 and its role in tumor progression and metastasis. Therefore, we are pursuing the regulatory molecule underlined.

CONCLUSIONS

HER-2 is overexpressed in around 15% of rectal cancer patients who receive neoadjuvant radiotherapy. Moreover, HER-2 overexpression could be a predictive biomarker of distant metastasis in rectal cancer patients after preoperative radiotherapy, especially patients showing a poor response to neoadjuvant radiotherapy.

Loss of WISP2/CCN5 in estrogen-dependent MCF7 human breast cancer cells promotes a stem-like cell phenotype

It has been proposed that the epithelial-mesenchymal transition (EMT) in mammary epithelial cells and breast cancer cells generates stem cell features. WISP2 (Wnt-1-induced signaling protein-2) plays an important role in maintenance of the differentiated phenotype of estrogen receptor-positive breast cancer cells and loss of WISP2 is associated with EMT. We now report that loss of WISP2 in MCF7 breast cancer cells can also promote the emergence of a cancer stem-like cell phenotype characterized by high expression of CD44, increased aldehyde dehydrogenase activity and mammosphere formation. Higher levels of the stem cell markers Nanog and Oct3/4 were observed in those mammospheres. In addition we show that low-cell inoculums are capable of tumor formation in the mammary fat pad of immunodeficient mice. Gene expression analysis show an enrichment of markers linked to stem cell function such as SOX9 and IGFBP7 which is linked to TGF-β inducible, SMAD3-dependent transcription. Taken together, our data demonstrate that WISP2 loss promotes both EMT and the stem-like cell phenotype.

Ovarian cancer stem cell-specific gene expression profiling and targeted drug prescreening

Cancer stem cells, with unlimited self-renewal potential and other stem cell characteristics, occur in several types of cancer, including ovarian cancer (OvC). Although CSCs can cause tumor initiation, malignant proliferation, relapse and multi-drug resistance, ways to eliminate them remain unknown. In the present study, we compared ovarian cancer stem cell (OVCSC) expression profiles in normal ovarian surface epithelium and ovarian cells from patients with advanced disease to identify key pathways and specific molecular signatures involved in OVC progression and to prescreen candidate small-molecule compounds with anti-OVCSC activity. Comparison of genome-wide expression profiles of OvC stemness groups with non-stemness controls revealed 6495, 1347 and 509 differentially expressed genes in SDC, SP1 and SP2 groups, respectively, with a cut-off of fold-change set at >1.5 and P<0.05. NAB1 and NPIPL1 were commonly upregulated whereas PROS1, GREB1, KLF9 and MTUS1 were commonly downregulated in all 3 groups. Most differentially expressed genes consistently clustered with molecular functions such as protein receptor binding, kinase activity and chemo-repellent activity. These genes regulate cellular components such as centrosome, plasma membrane receptors, and basal lamina, and may participate in biological processes such as cell cycle regulation, chemoresistance and stemness induction. Key Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways such as ECM receptor, ErbB signaling, endocytosis and adherens junction pathways were enriched. Gene co-expression extrapolation screening by the Connectivity Map revealed several small-molecule compounds (such as SC-560, disulfiram, thapsigargin, esculetin and cinchonine) with potential anti-OVCSC properties targeting OVCSC signature genes. We identified several key CSC features and specific regulation networks in OVCSCs and predicted several small molecules with potential anti-OVCSC pharmacological properties, which may aid the development of OVCSC-specific drugs.

Newly-derived neuroblastoma cell lines propagated in serum-free media recapitulate the genotype and phenotype of primary neuroblastoma tumours

Recently protocols have been devised for the culturing of cell lines from fresh tumours under serum-free conditions in defined neural stem cell medium. These cells, frequently called tumour initiating cells (TICs) closely retained characteristics of the tumours of origin. We report the isolation of eight newly-derived neuroblastoma TICs from six primary neuroblastoma tumours and two bone marrow metastases. The primary tumours from which these TICs were generated have previously been fully typed by whole genome sequencing (WGS). Array comparative genomic hybridisation (aCGH) analysis showed that TIC lines retained essential characteristics of the primary tumours and exhibited typical neuroblastoma chromosomal aberrations such as MYCN amplification, gain of chromosome 17q and deletion of 1p36. Protein analysis showed expression for neuroblastoma markers MYCN, NCAM, CHGA, DBH and TH while haematopoietic markers CD19 and CD11b were absent. We analysed the growth characteristics and confirmed tumour-forming potential using sphere-forming assays, subcutaneous and orthotopic injection of these cells into immune-compromised mice. Affymetrix mRNA expression profiling of TIC line xenografts showed an expression pattern more closely mimicking primary tumours compared to xenografts from classical cell lines. This establishes that these neuroblastoma TICs cultured under serum-free conditions are relevant and useful neuroblastoma tumour models.

Characterization of a stem-like subpopulation in basal-like ductal carcinoma in situ (DCIS) lesions

Previously, we found that basal-like ductal carcinoma in situ (DCIS) contains cancer stem-like cells. Here, we characterize stem-like subpopulations in a model of basal-like DCIS and identify subpopulations of CD49f+/CD24- stem-like cells that possess aldehyde dehydrogenase 1 activity. We found that these cells show enhanced migration potential compared with non-stem DCIS cells. We also found that the chemopreventive agent sulforaphane can target these DCIS stem-like cells, reduce aldehyde dehydrogenase 1 (ALDH1) expression, and decrease mammosphere and progenitor colony formation. Furthermore, we characterized exosomal trafficking of microRNAs in DCIS and found that several microRNAs (miRs) including miR-140, miR-29a, and miR-21 are differentially expressed in exosomes from DCIS stem-like cells. We found that SFN treatment could reprogram DCIS stem-like cells as evidenced by significant changes in exosomal secretion more closely resembling that of non-stem cancer cells. Finally, we demonstrated that exosomal secretion of miR-140 might impact signaling in nearby breast cancer cells.

Predicting degree of benefit from adjuvant trastuzumab in NSABP trial B-31

BACKGROUND

National Surgical Adjuvant Breast and Bowel Project (NSABP) trial B-31 suggested the efficacy of adjuvant trastuzumab, even in HER2-negative breast cancer. This finding prompted us to develop a predictive model for degree of benefit from trastuzumab using archived tumor blocks from B-31.

METHODS

Case subjects with tumor blocks were randomly divided into discovery (n = 588) and confirmation cohorts (n = 991). A predictive model was built from the discovery cohort through gene expression profiling of 462 genes with nCounter assay. A predefined cut point for the predictive model was tested in the confirmation cohort. Gene-by-treatment interaction was tested with Cox models, and correlations between variables were assessed with Spearman correlation. Principal component analysis was performed on the final set of selected genes. All statistical tests were two-sided.

RESULTS

Eight predictive genes associated with HER2 (ERBB2, c17orf37, GRB7) or ER (ESR1, NAT1, GATA3, CA12, IGF1R) were selected for model building. Three-dimensional subset treatment effect pattern plot using two principal components of these genes was used to identify a subset with no benefit from trastuzumab, characterized by intermediate-level ERBB2 and high-level ESR1 mRNA expression. In the confirmation set, the predefined cut points for this model classified patients into three subsets with differential benefit from trastuzumab with hazard ratios of 1.58 (95% confidence interval [CI] = 0.67 to 3.69; P = .29; n = 100), 0.60 (95% CI = 0.41 to 0.89; P = .01; n = 449), and 0.28 (95% CI = 0.20 to 0.41; P < .001; n = 442; P(interaction) between the model and trastuzumab < .001).

CONCLUSIONS

We developed a gene expression-based predictive model for degree of benefit from trastuzumab and demonstrated that HER2-negative tumors belong to the moderate benefit group, thus providing justification for testing trastuzumab in HER2-negative patients (NSABP B-47).

Neuregulin autocrine signaling promotes self-renewal of breast tumor-initiating cells by triggering HER2/HER3 activation

Currently, only patients with HER2-positive tumors are candidates for HER2-targeted therapies. However, recent clinical observations suggest that the survival of patients with HER2-low breast cancers, who lack HER2 amplification, may benefit from adjuvant therapy that targets HER2. In this study, we explored a mechanism through which these benefits may be obtained. Prompted by the hypothesis that HER2/HER3 signaling in breast tumor-initiating cells (TIC) promotes self-renewal and survival, we obtained evidence that neuregulin 1 (NRG1) produced by TICs promotes their proliferation and self-renewal in HER2-low tumors, including in triple-negative breast tumors. Pharmacologic inhibition of EGFR, HER2, or both receptors reduced breast TIC survival and self-renewal in vitro and in vivo and increased TIC sensitivity to ionizing radiation. Through a tissue microarray analysis, we found that NRG1 expression and associated HER2 activation occurred in a subset of HER2-low breast cancers. Our results offer an explanation for why HER2 inhibition blocks the growth of HER2-low breast tumors. Moreover, they argue that dual inhibition of EGFR and HER2 may offer a useful therapeutic strategy to target TICs in these tumors. In generating a mechanistic rationale to apply HER2-targeting therapies in patients with HER2-low tumors, this work shows why these therapies could benefit a considerably larger number of patients with breast cancer than they currently reach.

Epithelial-to-mesenchymal transition: what is the impact on breast cancer stem cells and drug resistance

There is increasing interest in cancer stem cells (CSCs) and their role in cancer progression. Recently, CSCs have been identified in brain, skin, and intestinal tumors and it has been suggested that these CSCs are responsible for tumor growth and metastasis. In breast cancer fatality is often due to the development of metastatic disease (MBC). Almost 30% of early breast cancer patients eventually develop MBC and in 90% of these multi-drug resistance (MDR) occurs. This could be attributed to the presence of breast cancer stem cells (BCSCs). Epithelial-to-mesenchymal transition (EMT) is a process known to contribute to metastasis in cancer and it is mainly characterized by loss of E-cadherin expression. The TGF-β signaling pathway has an established role in promoting EMT by down-regulating E-cadherin via a number of transcription factors, such as Twist, Snail and Slug. EMT has also been reported to produce cells with stem cell-like properties. Definition of the exact molecular mechanisms that are involved in the generation of stem cells through EMT could lead to the identification of new potential therapeutic targets and enable the development of more efficient strategies for particular patient groups. In this review we discuss what is known about the relationship between EMT, BCSCs and MDR.

Identification of cancer stem-like side population cells in purified primary cultured human laryngeal squamous cell carcinoma epithelia

Cancer stem-like side population (SP) cells have been identified in many solid tumors; however, most of these investigations are performed using established cancer cell lines. Cancer cells in tumor tissue containing fibroblasts and many other types of cells are much more complex than any cancer cell line. Although SP cells were identified in the laryngeal squamous cell carcinoma (LSCC) cell line Hep-2 in our pilot study, it is unknown whether the LSCC tissue contains SP cells. In this study, LSCC cells (LSCCs) were primary cultured and purified from a surgically resected LSCC specimen derived from a well-differentiated epiglottic neoplasm of a Chinese male. This was followed by the verification of epithelium-specific characteristics, such as ultrastructure and biomarkers. A distinct SP subpopulation (4.45±1.07%) was isolated by Hoechst 33342 efflux analysis from cultured LSCCs by using a flow cytometer. Cancer stem cell (CSC)-associated assays, including expression of self-renewal and CSC marker genes, proliferation, differentiation, spheroid formation, chemotherapy resistance, and tumorigenicity were then conducted between SP and non-SP (NSP) LSCCs. In vitro and in vivo assays revealed that SP cells manifested preferential expression of self-renewal and CSC marker genes, higher capacity for proliferation, differentiation, and spheroid formation; enhanced resistance to chemotherapy; and greater xenograft tumorigenicity in immunodeficient mice compared with NSP cells. These findings suggest that the primary cultured and purified LSCCs contain cancer stem-like SP cells, which may serve as a valuable model for CSC research in LSCC.

HER2 drives luminal breast cancer stem cells in the absence of HER2 amplification: implications for efficacy of adjuvant trastuzumab

Although current breast cancer treatment guidelines limit the use of HER2-blocking agents to tumors with HER2 gene amplification, recent retrospective analyses suggest that a wider group of patients may benefit from this therapy. Using breast cancer cell lines, mouse xenograft models and matched human primary and metastatic tissues, we show that HER2 is selectively expressed in and regulates self-renewal of the cancer stem cell (CSC) population in estrogen receptor-positive (ER(+)), HER2(-) luminal breast cancers. Although trastuzumab had no effects on the growth of established luminal breast cancer mouse xenografts, administration after tumor inoculation blocked subsequent tumor growth. HER2 expression is increased in luminal tumors grown in mouse bone xenografts, as well as in bone metastases from patients with breast cancer as compared with matched primary tumors. Furthermore, this increase in HER2 protein expression was not due to gene amplification but rather was mediated by receptor activator of NF-κB (RANK)-ligand in the bone microenvironment. These studies suggest that the clinical efficacy of adjuvant trastuzumab may relate to the ability of this agent to target the CSC population in a process that does not require HER2 gene amplification. Furthermore, these studies support a CSC model in which maximal clinical benefit is achieved when CSC targeting agents are administered in the adjuvant setting. Cancer Res; 73(5); 1635-46. ©2012 AACR.

FOXA1 represses the molecular phenotype of basal breast cancer cells

Breast cancer is a heterogeneous disease that comprises multiple subtypes. Luminal subtype tumors confer a more favorable patient prognosis, which is, in part, attributed to estrogen receptor (ER)-α positivity and antihormone responsiveness. Expression of the forkhead box transcription factor, FOXA1, similarly correlates with the luminal subtype and patient survival, but is also present in a subset of ER-negative tumors. FOXA1 is also consistently expressed in luminal breast cancer cell lines even in the absence of ER. In contrast, breast cancer cell lines representing the basal subtype do not express FOXA1. To delineate an ER-independent role for FOXA1 in maintaining the luminal phenotype, and hence a more favorable prognosis, we performed expression microarray analyses on FOXA1-positive and ER-positive (MCF7, T47D), or FOXA1-positive and ER-negative (MDA-MB-453, SKBR3) luminal cell lines in the presence or absence of transient FOXA1 silencing. This resulted in three FOXA1 transcriptomes: (1) a luminal signature (consistent across cell lines), (2) an ER-positive signature (restricted to MCF7 and T47D) and (3) an ER-negative signature (restricted to MDA-MB-453 and SKBR3). Gene set enrichment analyses revealed FOXA1 silencing causes a partial transcriptome shift from luminal to basal gene expression signatures. FOXA1 binds to a subset of both luminal and basal genes within luminal breast cancer cells, and loss of FOXA1 increases enhancer RNA transcription for a representative basal gene (CD58). These data suggest FOXA1 directly represses a subset of basal signature genes. Functionally, FOXA1 silencing increases migration and invasion of luminal cancer cells, both of which are characteristics of basal subtype cells. We conclude FOXA1 controls plasticity between basal and luminal breast cancer cells, not only by inducing luminal genes but also by repressing the basal phenotype, and thus aggressiveness. Although it has been proposed that FOXA1-targeting agents may be useful for treating luminal tumors, these data suggest that this approach may promote transitions toward more aggressive cancers.

Ovarian cancer stem cells: working towards the root of stemness

Despite medical advances made over the past decade, ovarian cancer remains one of the more lethal gynecologic cancers in the United States. While current therapeutic strategies are relatively effective, there is a high incidence of recurrent chemoresistant disease. This has been attributed, in part, to a regenerative tumor cell sub-population that has acquired stem cell properties which allows these cells to escape standard chemotherapeutics and drive recurrent disease. To date, a number of laboratories have identified these cancer stem cell (CSC) sub-populations in ovarian cancer cell lines, tumors or ascites and the collective findings suggest ovarian CSCs are likely to be as heterogeneous as the disease itself. Moreover, the multiple ovarian histophenotypes and possible sites of disease origin together with the potential for differential hierarchal contributions of multiple CSCs populations represent significant challenges to the identification, functional characterization and therapeutic targeting of ovarian CSC. This review will highlight the markers and methodology currently used to identify and isolate these cells. We will discuss some of the underlying ovarian CSC biology, the signaling pathways implicated in their survival, replication and differentiation and potential therapeutic targeting strategies.

The importance of HER2 signaling in the tumor-initiating cell population in aromatase inhibitor-resistant breast cancer

Aromatase inhibitors (AIs) are an effective therapy in treating estrogen receptor-positive breast cancer. Nonetheless, a significant percentage of patients either do not respond or become resistant to AIs. Decreased dependence on ER-signaling and increased dependence on growth factor receptor signaling pathways, particularly human epidermal growth factor receptor 2 (EGFR2/HER2), have been implicated in AI resistance. However, the role of growth factor signaling remains unclear. This current study investigates the possibility that signaling either through HER2 alone or through interplay between epidermal growth factor receptor 1 (EGFR/HER1) and HER2 mediates AI resistance by increasing the tumor initiating cell (TIC) subpopulation in AI-resistant cells via regulation of stem cell markers, such as breast cancer resistance protein (BCRP). TICs and BCRP are both known to be involved in drug resistance. Results from in vitro analyses of AI-resistant versus AI-sensitive cells and HER2-versus HER2+ cells, as well as from in vivo xenograft tumors, indicate that (1) AI-resistant cells overexpress both HER2 and BCRP and exhibit increased TIC characteristics compared to AI-sensitive cells; (2) inhibition of HER2 and/or BCRP decrease TIC characteristics in letrozole-resistant cells; and (3) HER2 and its dimerization partner EGFR/HER1 are involved in the regulation of BCRP. Overall, these results suggest that reducing or eliminating the TIC subpopulation with agents that target BCRP, HER2, EGFR/HER1, and/or their downstream kinase pathways could be effective in preventing and/or treating acquired AI resistance.

Asperjinone, a nor-neolignan, and terrein, a suppressor of ABCG2-expressing breast cancer cells, from thermophilic Aspergillus terreus

Breast cancer cells express ABCG2 transporters, which mediate multidrug resistance. Discovering a novel compound that can suppress ABCG2 expression and restore drug sensitivity could be the key to improving breast cancer therapeutics. In the current work, one new nor-neolignan, asperjinone (1), as well as 12 other known compounds, was isolated from Aspergillus terreus. The structure of the new isolate was determined by spectroscopic methods. Among these isolates, terrein (2) displayed strong cytotoxicity against breast cancer MCF-7 cells. Treatment with terrein (2) significantly suppressed growth of ABCG2-expressing breast cancer cells. This suppressive effect was achieved by inducing apoptosis via activating the caspase-7 pathway and inhibiting the Akt signaling pathway, which led to a decrease in ABCG2-expressing cells and a reduction in the side-population phenotype.