Breast cancer stem cells expressing different stem cell markers exhibit distinct biological characteristics

Advances in understanding the role and mechanisms of tumor stem cells in HER2-positive breast cancer treatment resistance (Review)

Approximately 15-20% of breast carcinomas exhibit human epidermal growth factor receptor (HER2) protein overexpression. HER2-positive breast cancer (BC) is a heterogeneous and aggressive subtype with poor prognosis and high relapse risk. Although several anti-HER2 drugs have achieved substantial efficacy, certain patients with HER2-positive BC relapse due to drug resistance after a treatment period. There is increasing evidence that BC stem cells (BCSCs) drive therapeutic resistance and a high rate of BC recurrence. BCSCs may regulate cellular self-renewal and differentiation, as well as invasive metastasis and treatment resistance. Efforts to target BCSCs may yield new methods to improve patient outcomes. In the present review, the roles of BCSCs in the occurrence, development and management of BC treatment resistance were summarized; BCSC-targeted strategies for the treatment of HER2-positive BC were also discussed.

Tumour Stem Cells in Breast Cancer

Tumour stem cells (CSCs) are a self-renewing population that plays important roles in tumour initiation, recurrence, and metastasis. Although the medical literature is extensive, problems with CSC identification and cancer therapy remain. This review provides the main mechanisms of CSC action in breast cancer (BC): CSC markers and signalling pathways, heterogeneity, plasticity, and ecological behaviour. The dynamic heterogeneity of CSCs and the dynamic transitions of CSC⁻ non-CSCs and their significance for metastasis are considered.

Astragaloside IV inhibits the progression of liver cancer by modulating macrophage polarization through the TLR4/NF-κB/STAT3 signaling pathway

AIM

The purpose of the present research was to investigate the effect and mechanism of Astragaloside IV (AS-IV) on liver cancer progression in vivo and in vitro. Since M1 macrophages play an essential role in suppressing tumors, while M2 macrophages can accelerate the incidence and progression of tumors by promoting angiogenesis, increasing tumor cell invasion and inhibiting tumor immune response, the effect and mechanism of AS-IV on macrophage polarization and their role in the development of HCC was explored.

METHODS

The effects of different concentrations of AS-IV (0, 50, 80, 100, 120, and 150 μM) on the capacity of hepatocellular carcinoma (HCC) cells to proliferate, migrate, and invade were detected. THP-1 cells were subjected to incubation in PMA for the purpose of stimulating differentiation into M0 macrophages. These macrophages were treated using LPS, IFN-γ, and PMA to produce M1 macrophages or treated using PMA, IL-13, and IL-4 to produce M2 macrophages. HCC cells and M1 or M2 macrophages were co-cultured for 48 hours, then the cell proliferation and migration were measured. The MTT assay was employed to determine cell viability. The capability of the cells to migrate and invade was investigated utilizing the Transwell assay and the wound healing assay. The expression of the M2 macrophage CD206 in macrophages treated with AS-IV was evaluated by flow cytometry. The expression of p-signal transducer and activator of transcription 3 (STAT3), phosphorylated (p)-NF-κB, and toll-like receptor 4 (TLR4) in macrophages was measured after treatment with AS-IV and M2 induction. To verify the function of the TLR4/NF-κB/STAT3 signaling pathway, TLR4 expression was knocked down in M2 macrophages, then the proliferation and migration and the M2 macrophage markers of HCC cells were measured. The effect of AS-IV on HCC in vivo was confirmed by a subcutaneous tumor mouse model. AS-IV was 2 was administered by gavage (0, 40, 80, and 100 mg/kg) for every 3 days. The tumor volume and weight were recorded.

RESULTS

AS-IV suppressed the capacities of HCC cells to proliferate, migrate, and invade in a dose-dependent way. M2 macrophages could promote the proliferative, migratory, and invasive ability of Huh-7 cells, which were suppressed by AS-IV. AS-IV directly attenuated the expression of M2 macrophage markers, indicating that AS-IV can inhibit macrophage M2 polarization. M2 macrophages stimulated the expression of p-STAT3, p-NF-κB, and TLR4, while AS-IV decreased the expression compared to the M2 group, indicating that AS-IV can regulate the TLR4/NF-κB/STAT3 signaling pathway. TLR4 small interfering RNA (siRNA/si) inhibited the proliferation of Huh-7 cells. The tumor volume, as well as weight of mice, was significantly reduced by AS-IV, indicating the antitumor impact of AS-IV in vivo.

CONCLUSION

AS-IV can inhibit the proliferative, invasive, and migratory ability of liver cancer through the suppression of the M2 polarization of macrophages, and the mechanism may involve the TLR4/NF-κB/STAT3 signaling pathway. The present study indicates that AS-IV could be an alternative drug to treat liver cancer, and the polarization of macrophages may be a novel treatment target for HCC.

3D Multicellular Stem-Like Human Breast Tumor Spheroids Enhance Tumorigenicity of Orthotopic Xenografts in Athymic Nude Rat Model

Simple Summary

Breast cancer presents a unique clinical problem because of the variety of cellular subtypes present, including cancer stem cells (CSCs). Breast CSCs can induce the formation of new blood vessels at the site of tumor growth and a develop metastatic phenotype by enhancing a stromal cell response, similar to that of the primary breast cancer. The aim of this study was to investigate breast cancer cells cultured in stromal stem cell factor-supplemented media to generate 3D spheroids that exhibit increased stem-like properties. These 3D stem-like spheroids reproducibly and efficiently established orthotopic breast cancer xenografts in the athymic nude rat. This approach enables a means to develop orthotopic tumors with a stem-like phenotype in a larger athymic rat rodent model of human breast cancer.

Abstract

Therapeutic targeting of stem cells needs to be strategically developed to control tumor growth and prevent metastatic burden successfully. Breast cancer presents a unique clinical problem because of the variety of cellular subtypes present, including cancer stem cells (CSCs). The development of 3D stem-like properties of human breast tumor spheroids in stem cell factor conditioned media was investigated in orthotopic xenografts for enhanced tumorgenicity in the athymic nude rat model. MCF-7, ZR-75-1, and MDA-MB-231 breast cancer cell lines were cultured in serum-free, stem cell factor-supplemented medium under non-adherent conditions and passaged to generate 3rd generation spheroids. The spheroids were co-cultured with fetal lung fibroblast (FLF) cells before orthotopic heterotransplantation into the mammary fat pads of athymic nude rats. Excised xenografts were assessed histologically by H&E staining and immunohistochemistry for breast cancer marker (ERB1), proliferation marker (Ki67), mitotic marker (pHH3), hypoxia marker (HIF-2α), CSC markers (CD47, CD44, CD24, and CD133), and vascularization markers (CD31, CD34). Breast cancer cells cultured in stem cell factor supplemented medium generated 3D spheroids exhibited increased stem-like characteristics. The 3D stem-like spheroids co-cultured with FLF as supporting stroma reproducibly and efficiently established orthotopic breast cancer xenografts in the athymic nude rat.

Hopea odorata Extract Can Efficiently Kill Breast Cancer Cells and Cancer Stem-Like Cells in Three-Dimensional Culture More Than in Monolayer Cell Culture

INTRODUCTION

The breast cancer cells with CD44⁺CD24^- phenotype are known to play an important role in tumorigenesis, drug resistance, and cancer recurrence. Breast cancer cells with CD44⁺CD24^- phenotype are cultured in three-dimensional (3D) stereotype showing the recapitulation of tumors in vivo such as cell differentiation, heterogeneity, and microenvironment. Using this 3D model in anti-cancer compound research results in a more accurate reflection than conventional monolayer cell culture. This study aimed to identify the antitumor activity of Hopea odorata methanol extract (HO-MeOH-E) on breast cancer cells and cancer stem-like cells in both models of three-dimensional culture (3D) and monolayer cell culture (2D).

METHODS

HO-MeOH-E was produced from Hopea odorata plant. The VN9 breast cancer cells (VN9) were collected and expanded from the previous study. The breast cancer stem-like cells (VN9CSC) were sorted from the VN9 based on phenotype CD44⁺CD24^-. Both VN9 and VN9CSC were used to culture in monolayer culture (2D) and organoids (3D) before they were used to treat with HO-MeOH-E. Two other anticancer drugs, doxorubicin and tirapazamine, were used as references. The antitumor activities of extracts and drugs were determined via two assays: antiproliferation using the Alamar blue assay and cell cycle assay.

RESULTS

The results showed that HO-MeOH-E was sensitive to both VN9 and VN9CSC in 3D more than 2D culture (IC₅₀ on 3D organoids 144.8 ± 2.172 μg/mL and on 2D 340.2 ± 17.01 μg/mL for VN9CSC (p < 0.001); IC₅₀ on 3D organoids 2055 ± 82.2 μg/mL and on 2D 430.6 ± 8.612 μg/mL for VN9 (p < 0.0001), respectively). HO-MeOH-E inhibits VN9CSC proliferation by blocking S phase and increasing the populations of apoptotic cells; this is consensus to the effect of tirapazamine (TPZ) which is used in hypoxia-activated chemotherapy.

CONCLUSION

Taken these results, HO-MeOH-E has the potential effect in hypoxia-activated chemotherapy specifically on breast cancer stem-like cells with CD44⁺CD24^- phenotype.

Keap1-Nrf2 Pathway Regulates ALDH and Contributes to Radioresistance in Breast Cancer Stem Cells

Tumor recurrence after radiotherapy due to the presence of breast cancer stem cells (BCSCs) is a clinical challenge, and the mechanism remains unclear. Low levels of ROS and enhanced antioxidant defenses are shown to contribute to increasing radioresistance. However, the role of Nrf2-Keap1-Bach1 signaling in the radioresistance of BCSCs remains elusive. Fractionated radiation increased the percentage of the ALDH-expressing subpopulation and their sphere formation ability, promoted mesenchymal-to-epithelial transition and enhanced radioresistance in BCSCs. Radiation activated Nrf2 via Keap1 silencing and enhanced the tumor-initiating capability of BCSCs. Furthermore, knockdown of Nrf2 suppressed ALDH+ population and stem cell markers, reduced radioresistance by decreasing clonogenicity and blocked the tumorigenic ability in immunocompromised mice. An underlying mechanism of Keap1 silencing could be via miR200a, as we observed a significant increase in its expression, and the promoter methylation of Keap1 or GSK-3β did not change. Our data demonstrate that ALDH+ BCSC population contributes to breast tumor radioresistance via the Nrf2-Keap1 pathway, and targeting this cell population with miR200a could be beneficial but warrants detailed studies. Our results support the notion that Nrf2-Keap1 signaling controls mesenchymal-epithelial plasticity, regulates tumor-initiating ability and promotes the radioresistance of BCSCs.

Nicotine Synergizes with High-Fat Diet to Induce an Anti-Inflammatory Microenvironment to Promote Breast Tumor Growth

Breast cancer results from a complex interplay of genetics and environment that alters immune and inflammatory systems to promote tumorigenesis. Obesity and cigarette smoking are well-known risk factors associated breast cancer development. Nicotine known to decrease inflammatory signals also modulates immune responses that favor breast cancer development. However, the mechanisms by which nicotine and obesity contribute to breast cancer remain poorly understood. In this study, we examined potential mechanisms by which nicotine (NIC) and high-fat diet (HFD) promote growth of HCC70 and HCC1806 xenografts from African American (AA) triple negative (TN) breast cancer cells. Immunodeficient mice fed on HFD and treated with NIC generated larger HCC70 and HCC1806 tumors when compared to NIC or HFD alone. Increased xenograft growth in the presence of NIC and HFD was accompanied by higher levels of tissue-resident macrophage markers and anti-inflammatory cytokines including IL4, IL13, and IL10. We further validated the involvement of these players by in vitro and ex vivo experiments. We found a proinflammatory milieu with increased expression of IL6 and IL12 in xenografts with HFD. In addition, nicotine or nicotine plus HFD increased a subset of mammary cancer stem cells (MCSCs) and key adipose browning markers CD137 and TMEM26. Interestingly, there was upregulation of stress-induced pp38 MAPK and pERK1/2 in xenografts exposed to HFD alone or nicotine plus HFD. Scratch-wound assay showed marked reduction in proliferation/migration of nicotine and palmitate-treated breast cancer cells with mecamylamine (MEC), a nicotine acetylcholine receptor (nAchR) antagonist. Furthermore, xenograft development in immune-deficient mice, fed HFD plus nicotine, was reduced upon cotreatment with MEC and SB 203580, a pp38MAPK inhibitor. Our study demonstrates the presence of nicotine and HFD in facilitating an anti-inflammatory tumor microenvironment that influences breast tumor growth. This study also shows potential efficacy of combination therapy in obese breast cancer patients who smoke.

Fine-tuning the metabolic rewiring and adaptation of translational machinery during an epithelial-mesenchymal transition in breast cancer cells

ABSTRACT

BACKGROUND

During breast cancer progression, the epithelial to mesenchymal transition has been associated with metastasis and endocrine therapy resistance; however, the underlying mechanisms remain elusive. To gain insight into this process, we studied the transition undergone by MCF7-derived cells, which is driven by the constitutive nuclear expression of a MKL1 variant devoid of the actin-binding domain (MKL1 ΔN200). We characterized the adaptive changes that occur during the MKL1-induced cellular model and focused on regulation of translation machinery and metabolic adaptation.

METHODS

We performed a genome-wide analysis at the transcriptional and translational level using ribosome profiling complemented with RNA-Seq and analyzed the expression of components of the translation machinery and enzymes involved in energy metabolism. NGS data were correlated with metabolomic measurements and quantification of specific mRNAs extracted from polysomes and western blots.

RESULTS

Our results reveal the expression profiles of a luminal to basal-like state in accordance with an epithelial to mesenchymal transition. During the transition, the synthesis of ribosomal proteins and that of many translational factors was upregulated. This overexpression of the translational machinery appears to be regulated at the translational level. Our results indicate an increase of ribosome biogenesis and translation activity. We detected an extensive metabolic rewiring occurring in an already "Warburg-like" context, in which enzyme isoform switches and metabolic shunts indicate a crucial role of HIF-1α along with other master regulatory factors. Furthermore, we detected a decrease in the expression of enzymes involved in ribonucleotide synthesis from the pentose phosphate pathway. During this transition, cells increase in size, downregulate genes associated with proliferation, and strongly upregulate expression of cytoskeletal and extracellular matrix genes.

CONCLUSIONS

Our study reveals multiple regulatory events associated with metabolic and translational machinery adaptation during an epithelial mesenchymal-like transition process. During this major cellular transition, cells achieve a new homeostatic state ensuring their survival. This work shows that ribosome profiling complemented with RNA-Seq is a powerful approach to unveil in-depth global adaptive cellular responses and the interconnection among regulatory circuits, which will be helpful for identification of new therapeutic targets.

Caveolin-1 inhibits breast cancer stem cells via c-Myc-mediated metabolic reprogramming

Breast cancer stem cells (BCSCs) are considered to be the root of breast cancer occurrence and progression. However, the characteristics and regulatory mechanisms of BCSCs metabolism have been poorly revealed, which hinders the development of metabolism-targeted treatment strategies for BCSCs elimination. Herein, we demonstrated that the downregulation of Caveolin-1 (Cav-1) usually occurred in BCSCs and was associated with a metabolic switch from mitochondrial respiration to aerobic glycolysis. Meanwhile, Cav-1 could inhibit the self-renewal capacity and aerobic glycolysis activity of BCSCs. Furthermore, Cav-1 loss was associated with accelerated mammary-ductal hyperplasia and mammary-tumor formation in transgenic mice, which was accompanied by enrichment and enhanced aerobic glycolysis activity of BCSCs. Mechanistically, Cav-1 could promote Von Hippel-Lindau (VHL)-mediated ubiquitination and degradation of c-Myc in BCSCs through the proteasome pathway. Notably, epithelial Cav-1 expression significantly correlated with a better overall survival and delayed onset age of breast cancer patients. Together, our work uncovers the characteristics and regulatory mechanisms of BCSCs metabolism and highlights Cav-1-targeted treatments as a promising strategy for BCSCs elimination.

Knockdown of Musashi RNA Binding Proteins Decreases Radioresistance but Enhances Cell Motility and Invasion in Triple-Negative Breast Cancer

The therapeutic potential of Musashi (MSI) RNA-binding proteins, important stemness-associated gene expression regulators, remains insufficiently understood in breast cancer. This study identifies the interplay between MSI protein expression, stem cell characteristics, radioresistance, cell invasiveness and migration. MSI-1, MSI-2 and Notch pathway elements were investigated via quantitative polymerase chain reaction (qPCR) in 19 triple-negative breast cancer samples. Measurements were repeated in MDA-MB-231 cells after MSI-1 and -2 siRNA-mediated double knockdown, with further experiments performed after MSI silencing. Flow cytometry helped quantify expression of CD44 and leukemia inhibitory factor receptor (LIFR), changes in apoptosis and cell cycle progression. Proliferation and irradiation-induced effects were assessed using colony formation assays. Radiation-related proteins were investigated via Western blots. Finally, cell invasion assays and digital holographic microscopy for cell migration were performed. MSI proteins showed strong correlations with Notch pathway elements. MSI knockdown resulted in reduction of stem cell marker expression, cell cycle progression and proliferation, while increasing apoptosis. Cells were radiosensitized as radioresistance-conferring proteins were downregulated. However, MSI-silencing-mediated LIFR downregulation resulted in enhanced cell invasion and migration. We conclude that, while MSI knockdown results in several therapeutically desirable consequences, enhanced invasion and migration need to be counteracted before knockdown advantages can be fully exploited.

Breast cancer stem cell RNA-pulsed dendritic cells enhance tumor cell killing by effector T cells

Cancer stem cells (CSCs) underpin the resistance of breast cancer (BC) cells to therapy. Dendritic cell (DC)-based treatment is efficacious and safe, but the efficiency of this technique for targeting CSCs in BC treatment requires further investigation. The present study aimed to investigate the ability of DCs pulsed with breast CSC antigens to activate effector lymphocytes for killing BC cells. CD44⁺/CD24⁻ CSCs were isolated from BCA55-121, an in-house patient-derived BC cell line, and acquisition of stemness properties was confirmed by upregulated expression of OCT4A and a superior proliferative capacity in colony formation assays compared with whole population of BCA55-121 (BCA55-121-WP). DCs were differentiated from monocytes from peripheral blood of healthy donors and pulsed with CSC total RNA. Maturation of the CSC RNA-pulsed DCs was confirmed by increased expression of CD11c, CD40, CD83, CD86 and HLA-DR, as well as reduced CD14 expression compared with monocytes. Total lymphocytes co-cultured with CSC RNA-pulsed DCs were analyzed by flow cytometry for markers including CD3, CD4, CD8, CD16 and CD56. The results revealed that the co-cultures contained mostly cytotoxic CD8+ T lymphocytes followed by CD4+ T lymphocytes and smaller populations of natural killer (NK) and NKT cells. ELISA was used to measure IFN-γ production, and it was revealed that activated CD4⁺ and CD8+ lymphocytes produced more IFN-γ compared with naïve T cells, suggesting that CD8+ T cells were effector T cells. CSC RNA was a more efficient antigen source compared with RNA from mixed BC cells for activating tumor antigen-specific killing by T cells. These CSC-specific effector T cells significantly induced BC cell apoptosis at a 20:1 effector T cell:tumor cell ratio. Of note, the breast CSCs cultures demonstrated resistance to effector T cell killing, which was in part due to increased expression of programmed death ligand 1 in the CSC population. The present study highlights the potential use of CSC RNA for priming DCs in modulating an anticancer immune response against BC.

XIAOPI Formula Inhibits Breast Cancer Stem Cells via Suppressing Tumor-Associated Macrophages/C-X-C Motif Chemokine Ligand 1 Pathway

Macrophages are the most abundant stromal cells associated with the host immune system in multiple malignancies including breast cancer. With proven clinical efficacy and no noticeable adverse effects, XIAOPI formula (XPS) has been approved for breast hyperplasia treatment by the State Food and Drug Administration of China (SFDA) in 2018. The existing knowledge about the anti-breast cancer activities and mechanisms of XPS has been very limited. The present study aimed to investigate whether XPS could exert an anti-breast cancer effect by regulating tumor-associated macrophages (TAMs) in tumor microenvironment. Herein, breast cancer cells and TAMs were co-cultured using the transwell co-culture system to simulate the coexistence of them. XPS could significantly inhibit the proliferation, colony formation, breast cancer stem cells (CSCs) subpopulation, mammosphere formation abilities as well as stemness-related genes expression in both human and mouse breast cancer cells in the co-culture system. Additionally, XPS could suppress M2 phenotype polarization as well as C-X-C motif chemokine ligand 1 (CXCL1) expression and secretion of TAMs. Notably, further mechanistic explorations verified TAMs/CXCL1 as the critical target of XPS in inhibiting breast CSCs self-renewal in the co-culture system as the exogenous CXCL1 administration could abrogate the inhibitory effect of XPS on breast CSCs self-renewal. More importantly, XPS significantly inhibited mammary tumor growth, breast CSCs subpopulation, and TAMs/CXCL1 activity in mouse 4T1-Luc xenografts in vivo without any detectable side effects. Taken together, this study not only uncovers the immunomodulatory mechanism of XPS in treating breast cancer but also sheds novel insights into TAMs/CXCL1 as a potential molecular target for breast CSCs elimination.

Cancer stem-like cells with increased expression of NY-ESO-1 initiate breast cancer metastasis

Breast cancer stem-like cells (BCSLCs) with a CD44⁺/CD24^−/low phenotype initiate the invasion and metastasis of breast cancer. The expression of New York oesophageal squamous cell carcinoma 1 (NY-ESO-1), one of the most immunogenic cancer-testicular antigens, is largely restricted to cancer and germ cells/placental trophoblasts, with little to no expression in normal adult somatic cells. Currently, few studies have reported the expression or function of NY-ESO-1 in BCSLCs. In the present study, immunohistochemistry indicated enhanced expression levels of NY-ESO-1/CD44 (P<0.01) and decreased expression levels of CD24 (P<0.01) in metastatic breast cancer tissues (MBCT) compared with non-MBCT. Additionally, the co-localization of CD44, CD24 and NY-ESO-1 in tissue samples was determined using immunofluorescence analysis. The results revealed that the expression of NY-ESO-1/CD44/CD24 was associated with breast cancer metastasis. Moreover, Spearman's rank correlation analysis indicated that CD44/CD24 expression was significantly correlated with that of NY-ESO-1. In the present study, mammosphere culture, a valuable method of BCSLC enrichment, was used to enrich MCF-7 and SK-BR-3 BCSLCs; immunofluorescence, western blotting and flow cytometry demonstrated increased expression levels of NY-ESO-1 and CD44, and low expression levels of CD24 in BCSLCs. Furthermore, the cell migration and invasion assays verified that BCSLCs with an increased NY-ESO-1 expression level exhibited greater invasive and migratory capacity compared with parental breast cancer cells. In addition to previously reported findings from the Oncomine database, it was ascertained that CD44⁺/CD24^−/low BCSLCs with an increased level of NY-ESO-1 expression initiated the invasion and metastasis of breast cancer; therefore, NY-ESO-1 may serve as a novel target for metastatic breast cancer immunotherapy.

Identification of new cancer stem cell markers and signaling pathways in HER‑2‑positive breast cancer by transcriptome sequencing

Human epidermal growth factor receptor (HER)‑2‑positive breast cancer accounts for ~25% of all breast cancer cases, has a high propensity for relapse, metastasis and drug resistance, and is associated with a poor prognosis. Therefore, it is necessary to develop more effective therapeutic targets for the treatment of HER‑2‑positive breast cancer. CD44+/CD24‑/low is currently the most commonly used marker for breast cancer stem cells (CSCs), which are considered the main cause of drug resistance, relapse and metastasis. In the present study, the ratio of CD44+/CD24‑/low cells was almost zero in SK‑BR‑3 cells; however, it was >90% in MDA‑MB‑231 cells, as determined by flow cytometry. Since SK‑BR‑3 and MDA‑MB‑231 cells both exhibit a strong propensity for invasion and migration, it was hypothesized that there may be other markers of CSCs in SK‑BR‑3 cells. Therefore, transcriptome sequencing was performed for SK‑BR‑3 and MDA‑MB‑231 cells. It was observed that several leukocyte differentiation antigens and other CSC markers were significantly more highly expressed in SK‑BR‑3 cells. Furthermore, the expression of aldehyde dehydrogenase (ALDH)1A3, CD164 and epithelial cell adhesion molecule (EpCAM) was higher in SK‑BR‑3 cells compared with in other subtypes of breast cell lines, as determined by reverse transcription‑polymerase chain reaction and western blot analysis. In addition, the expression levels of ALDH1A3, ALDH3B2 and EpCAM were higher in HER‑2‑positive breast cancer compared with in paracancerous tissues and other subtypes of breast cancer, as determined by immunohistochemistry. The expression of β‑catenin in the Wnt signaling pathway was lower in SK‑BR‑3 cells compared with in MDA‑MB‑231 cells, which may be used as a prognostic indicator for breast cancer. These findings may help identify novel CSC markers and therapeutic targets for HER‑2‑positive breast cancer.

Hyaluronan-CD44 axis orchestrates cancer stem cell functions

The prominent role of CD44 in tumor cell signaling together with its establishment as a cancer stem cell (CSC) marker for various tumor entities imply a key role for CD44 in CSC functional properties. Hyaluronan, the main ligand of CD44, is a major constituent of CSC niche and, therefore, the hyaluronan-CD44 signaling axis is of functional importance in this special microenvironment. This review aims to provide recent advances in the importance of hyaluronan-CD44 interactions in the acquisition and maintenance of a CSC phenotype. Hyaluronan-CD44 axis has a substantial impact on stemness properties of CSCs and drug resistance through induction of EMT program, oxidative stress resistance, secretion of extracellular vesicles/exosomes and epigenetic control. Potential therapeutic approaches targeting CSCs based on the hyaluronan-CD44 axis are also presented.

Cytotoxic effect of aqueous ethanolic extract of Luffa cylindrica leaves on cancer stem cells CD44+/24- in breast cancer patients with various molecular sub-types using tissue samples in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Luffa cylindrica (L.) M.Roem is a climbing plant its parts have been used as traditional medicine for the treatment of different types of diseases including diarrhea, inflammation, cancer and viral infections. The parts used include fruit, seeds and leaves.

AIM OF THE STUDY

Our study aims to investigate the effect of the aqueous-ethanol extract of Luffa cylindrica leaves on breast cancer stem cells CD44⁺/24^- and other cell sub-populations using clinical samples with different molecular sub-types of breast cancer in vitro.

MATERIALS AND METHODS

Breast tissues were obtained from patients undergoing surgery for the removal of breast tumors after complete clinical and pathological investigations. Tissue samples were processed to cell suspensions and treated with the extract in the tissue culture laboratory. Percentages of cell sub-populations within tumors and viability were measured by flowcytometry using clusters of differentiation as cell markers.

RESULTS

Our results revealed that there were decreases in the total cell viability, CD44⁺/24^- and total CD24⁺ cell sub-populations percentages after treatment with the extract, this may be an important indication of using Luffa leaves extract in the treatment of breast cancer or in combination with the traditional treatments.

CONCLUSION

Luffa cylindrica has proven to have anticancer activity on three different subtypes of breast cancer including luminal A, luminal B and Her2/neu enriched more over it has cytotoxic effect on both bulk tumor cells as well as cancer stem cells sub population CD44⁺/24^- which possess high tumorigenic potency, these results were confirmed by measuring their viable number after treatment and sphere formation assay results.

LHRH Targeted Chonderosomes of Mitomycin C in Breast Cancer: An In Vitro/ In Vivo Study

BACKGROUND

Mitomycin C (MMC) is an anti-cancer drug used for the treatment of breast cancer with limited therapeutic index, extreme gastric adverse effects and bone marrow suppression. The purpose of the present study was the preparation of a dual-targeted delivery system of MMC for targeting CD44 and LHRH overexpressed receptors of breast cancer.

METHODS

MMC loaded LHRH targeted chonderosome was prepared by precipitation method and was characterized for their physicochemical properties. Cell cycle arrest and cytotoxicity tests were studied on cell lines of MCF-7, MDA-MB231 and 4T1 (as CD44 and LHRH positive cells) and BT-474 cell line (as CD44 negative receptor cells). The in vivo histopathology and antitumor activity of MMC-loaded chonderosomes were compared with free MMC in 4T1 cells inducing breast cancer in Balb-c mice.

RESULTS

MMC loaded LHRH targeted chonderosomes caused 3.3 and 5.5 fold more cytotoxicity on MCF-7 and 4T1 cells than free MMC at concentrations of 100μM and 10μM, respectively. However, on BT-474 cells the difference was insignificant. The cell cycle test showed no change for MMC mechanism of action when it was loaded in chonderosomes compared to free MMC. The in vivo antitumor studies showed that MMC loaded LHRH targeted chonderosomes were 6.5 fold more effective in the reduction of tumor volume than free MMC with the most severe necrosis compared to non-targeted chonderosomes in pathological studies on harvested tumors.

CONCLUSION

The developed MMC loaded LHRH targeted chonderosomes were more effective in tumor growth suppression and may be promising for targeted delivery of MMC in breast cancer.

Screening of acetaminophen-induced alterations in epithelial-to-mesenchymal transition-related expression of microRNAs in a model of stem-like triple-negative breast cancer cells: The possible functional impacts

Current protocols for therapy inefficiently targets triple negative breast cancer and barely eradicate cancer stem cells. Elucidation of the pleiotropic effect of clinically proven therapeutics on cancer cells shed light on novel application of old friends. The pleiotropic effect of acetaminophen (APAP) on breast cancer was previously reported. In a cell model of triple negative breast cancer with stem-like CD44^high/CD24^low phenotype, we screened the impacts of APAP (1 mM, 72 h) on the Epithelial to mesenchymal transition (EMT)-related expression of miRs. APAP significantly overexpressed hsa-miR-130a-3p, 192-5p, 214-3p, 101-3p, 30d-5p, 10a-5p, 99a-5p, 200c-3p, 143-3p, 30b-5p and let-7f-5p showed significant overexpression, but suppressed the expression of hsa-miR-7-5p, 149-3p, 215, 150-5p, 205-5p, 206, 10b-5p, 20b-5p, 145-5p, 26b-5p, 223-3p, 17-5p, 186-5p, 146a-5p and let-7c. It also altered on the expression of selected EMT-related genes, significantly upregulated the expression of KRT19, AKT2, CD24, and TIMP1; but downregulated the expression of MMP2, ALDH1, MMP9, TWIST, NOTCH1, and AKT1. Such shifts in expression profiles increased the population of the cells with CD44^high/CD24^high, and CD44^low/CD24^high phenotypes, significantly reduced the Twist protein and shifted the balance of E-cadherin and Vimentin proteins in favor of differentiation. Treated cells showed a significant reduction of in vitro migration and were significantly chemosensitized to Camptothecin. In conclusion, APAP, at a safe clinical dose, induced a set of targeted alterations in the EMT-related miRs which implicate, even in part, significant mitigation in chemoresistance and in vitro migration. Further studies should also be piloted to elucidate the most crucial miRs and to evaluate its clinical effectiveness.

Breast cancer stem cells: Biology and therapeutic implications

Breast cancer remains to be a dreadful disease even with several advancements in radiation and chemotherapies, owing to the drug resistance and tumor relapse caused by breast cancer stem cells. Cancer stem cells are a minute population of cells of solid tumors which show self-renewal and differentiation properties as well as tumorigenic potential. Several signaling pathways including Notch, Hippo, Wnt and Hedgehog and tumor-stroma exchanges play a critical role in the self-renewal and differentiation of cancer stem cells in breast cancer. Cancer stem cells can grow anchorage-independent manner so they disseminate to different parts of the body to form secondary tumors. Cancer stem cells promote angiogenesis by dedifferentiating to endothelial cells as well as secreting proangiogenic and angiogenic factors. Moreover, multidrug resistance genes and drug efflux transporters expressed in breast cancer stem cells confer resistance to various conventional chemotherapeutic drugs. Indeed, these therapies are recognised to enhance the percent of cancer stem cell population in tumors leading to cancer relapse with increased aggressiveness. Hence, devising the therapeutic interventions to target cancer stem cells would be useful in increasing patients' survival rates. In addition, targeting the self-renewal pathways and tumor-stromal cross-talk helps in eradicating this population. Reversal of the cancer stem cell-mediated drug resistance would increase the sensitivity to various conventional drugs for the effective management of breast cancer. In this review, we have discussed the cancer stem cell origin and their involvement in angiogenesis, metastasis and therapy-resistance. We have also summarized different therapeutic approaches to eradicate the same for the successful treatment of breast cancer.

Evaluation of NCAM and c-Kit as hepatic progenitor cell markers for intrahepatic cholangiocarcinomas

BACKGROUND

Intrahepatic cholangiocarcinomas (ICCs) are primary liver malignancies and are the second most common type of malignancy after hepatocellular carcinoma. ICCs are heterogeneous in clinical features, genotype, and biological behavior, suggesting that ICCs can initiate in different cell lineages.

AIM

We investigated intrahepatic cholangiocarcinoma RBE cell lines for the markers neural cell adhesion molecule (NCAM) and c-Kit, which possess hepatic progenitor cells properties.

METHODS

NCAM + c-Kit + cells were tested for hepatic progenitor cell properties including proliferation ability, colony formation, spheroid formation, and invasiveness in NOD/SCID mice. The Agilent Whole Human Genome Microarray Kit was used to evaluate differences in gene expression related to stem cell signaling pathways between NCAM + c-Kit + and NCAM-c-Kit- subset cells. Microarray results were further confirmed by real-time RT-PCR.

RESULTS

NCAM + c-Kit + cells showed hepatic progenitor cell-like traits including the abilities to self-renew and differentiate and tumorigenicity in NOD/SCID mice. Differences were observed in the expression of 421 genes related to stem cell signaling pathways (fc ≥ 2 or fc ≤ 0.5), among which 231 genes were upregulated and 190 genes were downregulated.

CONCLUSION

NCAM + c-Kit + subset cells in RBE may have properties of hepatic progenitor cells. NCAM combined with c-Kit may be a valuable marker for isolating and purifying ICC stem/progenitor cells.

Cancer stem cell in breast cancer therapeutic resistance

Development of therapeutic resistance and metastasis is a major challenge with current breast cancer (BC) therapy. Mounting evidence suggests that a subpopulation of cancer stem cells (CSCs) contribute to the cancer therapeutic resistance and metastasis, leading to the recurrence and death in patients. Breast cancer stem cells (BCSCs) are not only a consequence of mutations that overactivate the self-renewal ability of normal stem cells or committed progenitors but also a result of the de-differentiation of cancer cells induced by somatic mutations or microenvironmental components under treatment. Eradication of BCSCs may bring hope and relief to patients whose lives are threatened by recurrent BCs. Therefore, a better understanding of the generation, regulatory mechanisms, and identification of CSCs in BC therapeutic resistance and metastasis will be imperative for developing BCSC-targeted strategies. Here we summarize the latest studies about cell surface markers and signalling pathways that sustain the stemness of BCSC and discuss the associations of mechanisms behind these traits with phenotype and behavior changes in BCSCs. More importantly, their implications for future study are also evaluated and potential BCSC-targeted strategies are proposed to break through the limitation of current therapies.

Limited utility of tissue micro-arrays in detecting intra-tumoral heterogeneity in stem cell characteristics and tumor progression markers in breast cancer

Background

Intra-tumoral heterogeneity has been recently addressed in different types of cancer, including breast cancer. A concept describing the origin of intra-tumoral heterogeneity is the cancer stem-cell hypothesis, proposing the existence of cancer stem cells that can self-renew limitlessly and therefore lead to tumor progression. Clonal evolution in accumulated single cell genomic alterations is a further possible explanation in carcinogenesis. In this study, we addressed the question whether intra-tumoral heterogeneity can be reliably detected in tissue-micro-arrays in breast cancer by comparing expression levels of conventional predictive/prognostic tumor markers, tumor progression markers and stem cell markers between central and peripheral tumor areas.

Methods

We analyzed immunohistochemical expression and/or gene amplification status of conventional prognostic tumor markers (ER, PR, HER2, CK5/6), tumor progression markers (PTEN, PIK3CA, p53, Ki-67) and stem cell markers (mTOR, SOX2, SOX9, SOX10, SLUG, CD44, CD24, TWIST) in 372 tissue-micro-array samples from 72 breast cancer patients. Expression levels were compared between central and peripheral tumor tissue areas and were correlated to histopathological grading. 15 selected cases additionally underwent RNA sequencing for transcriptome analysis.

Results

No significant difference in any of the analyzed between central and peripheral tumor areas was seen with any of the analyzed methods/or results that showed difference. Except mTOR, PIK3CA and SOX9 (nuclear) protein expression, all markers correlated significantly (p < 0.05) with histopathological grading both in central and peripheral areas.

Conclusion

Our results suggest that intra-tumoral heterogeneity of stem-cell and tumor-progression markers cannot be reliably addressed in tissue-micro-array samples in breast cancer. However, most markers correlated strongly with histopathological grading confirming prognostic information as expression profiles were independent on the site of the biopsy was taken.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1495-6) contains supplementary material, which is available to authorized users.

Bridging the divide: preclinical research discrepancies between triple-negative breast cancer cell lines and patient tumors

Triple-negative breast cancer (TNBC) is the most refractory subtype of breast cancer and disproportionately accounts for the majority of breast cancer related deaths. Effective treatment of this disease remains an unmet medical need. Over the past several decades, TNBC cell lines have been used as the foundation for drug development and disease modeling. However, ever-mounting research demonstrates striking differences between cell lines and clinical TNBC tumors, disconnecting bench research and actual clinical responses. In this review, we discuss the limitations of cell lines and the importance of using patients' tumors for translational research, and highlight the usage of patient-derived xenograft (PDXs) models that have emerged as a clinically relevant platform for preclinical studies. PDX tumors possess tumor heterogeneity with similar cellular, molecular, genetic and epigenetic properties akin to those found within patients' tumors. Moreover, PDX and clinical tumors possess abnormal vasculature with higher blood vessel permeability, a feature that is not always demonstrated in in vivo cell line xenografts. Development of clinically relevant, novel drug-nanoparticles capable of accumulating in PDX tumors through the enhanced permeability and retention effect in tumor vasculature may lead to new and effective TNBC treatments.

NRP1-positive lung cancer cells possess tumor-initiating properties

Tumor-initiating cells possess the capacity for self-renewal and to create heterogeneous cell lineages within a tumor. Therefore, the identification and isolation of cancer stem cells is an essential step in the analysis of their biology. The aim of the present study was to determine whether the cell surface protein neuropilin 1 (NRP1) can be used as a biomarker of stem-like cells in lung cancer tumors. For this purpose, NRP1-negative (NRP1-) and NRP1-positive (NRP1+) cell subpopulations from two lung cancer cell lines were sorted by flow cytometry. The NRP1+ cell subpopulation showed an increased expression of pluripotency markers OCT-4, Bmi-1 and NANOG, as well as higher cell migration, clonogenic and self-renewal capacities. NRP1 gene knockdown resulted not only in a decreased expression of stemness markers but also in a decrease in the clonogenic, cell migration and self-renewal potential. In addition, the NRP1+ cell subpopulation exhibited dysregulated expression of epithelial-to-mesenchymal transition-associated genes, including the ΔNp63 isoform protein, a previously reported characteristic of cancer stem cells. Notably, a genome-wide expression analysis of NRP1-knockdown cells revealed a potential new NRP1 pathway involving OLFML3 and genes associated with mitochondrial function. In conclusion, we demonstrated that NRP1+ lung cancer cells have tumor-initiating properties. NRP1 could be a useful biomarker for tumor-initiating cells in lung cancer tumors.

Anti-cancer stem cell activity of a hedgehog inhibitor GANT61 in estrogen receptor-positive breast cancer cells

Estradiol (E2) increases not only the cell growth but also the cancer stem cell (CSC) proportion in estrogen receptor (ER)‐positive breast cancer cells. It has been suggested that the non‐canonical hedgehog (Hh) pathway activated by E2 plays an important role in the regulation of CSC proportion in ER‐positive breast cancer cells. We studied anti‐CSC activity of a non‐canonical Hh inhibitor GANT61 in ER‐positive breast cancer cells. Effects of GANT61 on the cell growth, cell cycle progression, apoptosis and CSC proportion were investigated in four ER‐positive breast cancer cell lines. CSC proportion was measured using either the mammosphere assay or CD44/CD24 assay. Expression levels of pivotal molecules in the Hh pathway were measured. Combined effects of GANT61 with antiestrogens on the anti‐cell growth and anti‐CSC activities were investigated. E2 significantly increased the cell growth and CSC proportion in all ER‐positive cell lines. E2 increased the expression levels of glioma‐associated oncogene (GLI) 1 and/or GLI2. GANT61 decreased the cell growth in association with a G1‐S cell cycle retardation and increased apoptosis. GANT61 decreased the E2‐induced CSC proportion measured by the mammosphere assay in all cell lines. Antiestrogens also decreased the E2‐induced cell growth and CSC proportion. Combined treatments of GANT61 with antiestrogens additively enhanced anti‐cell growth and/or anti‐CSC activities in some ER‐positive cell lines. In conclusion, the non‐canonical Hh inhibitor GANT61 inhibited not only the cell growth but also the CSC proportion increased by E2 in ER‐positive breast cancer cells. GANT61 enhanced anti‐cell growth and/or anti‐CSC activities of antiestrogens in ER‐positive cell lines.

Genetic profiling of putative breast cancer stem cells from malignant pleural effusions

A common symptom during late stage breast cancer disease is pleural effusion, which is related to poor prognosis. Malignant cells can be detected in pleural effusions indicating metastatic spread from the primary tumor site. Pleural effusions have been shown to be a useful source for studying metastasis and for isolating cells with putative cancer stem cell (CSC) properties. For the present study, pleural effusion aspirates from 17 metastatic breast cancer patients were processed to propagate CSCs in vitro. Patient-derived aspirates were cultured under sphere forming conditions and isolated primary cultures were further sorted for cancer stem cell subpopulations ALDH1⁺ and CD44⁺CD24^-/low. Additionally, sphere forming efficiency of CSC and non-CSC subpopulations was determined. In order to genetically characterize the different tumor subpopulations, DNA was isolated from pleural effusions before and after cell sorting, and compared with corresponding DNA copy number profiles from primary tumors or bone metastasis using low-coverage whole genome sequencing (SCNA-seq). In general, unsorted cells had a higher potential to form spheres when compared to CSC subpopulations. In most cases, cell sorting did not yield sufficient cells for copy number analysis. A total of five from nine analyzed unsorted pleura samples (55%) showed aberrant copy number profiles similar to the respective primary tumor. However, most sorted subpopulations showed a balanced profile indicating an insufficient amount of tumor cells and low sensitivity of the sequencing method. Finally, we were able to establish a long term cell culture from one pleural effusion sample, which was characterized in detail. In conclusion, we confirm that pleural effusions are a suitable source for enrichment of putative CSC. However, sequencing based molecular characterization is impeded due to insufficient sensitivity along with a high number of normal contaminating cells, which are masking genetic alterations of rare cancer (stem) cells.