The CD44+/CD24- phenotype relates to 'triple-negative' state and unfavorable prognosis in breast cancer patients

ALDH1A3 is the switch that determines the balance of ALDH+ and CD24-CD44+ cancer stem cells, EMT-MET, and glucose metabolism in breast cancer

Plasticity is an inherent feature of cancer stem cells (CSCs) and regulates the balance of key processes required at different stages of breast cancer progression, including epithelial-to-mesenchymal transition (EMT) versus mesenchymal-to-epithelial transition (MET), and glycolysis versus oxidative phosphorylation. Understanding the key factors that regulate the switch between these processes could lead to novel therapeutic strategies that limit tumor progression. We found that aldehyde dehydrogenase 1A3 (ALDH1A3) regulates these cancer-promoting processes and the abundance of the two distinct breast CSC populations defined by high ALDH activity and CD24-CD44+ cell surface expression. While ALDH1A3 increases ALDH+ breast cancer cells, it inversely suppresses the CD24-CD44+ population by retinoic acid signaling-mediated gene expression changes. This switch in CSC populations induced by ALDH1A3 was paired with decreased migration but increased invasion and an intermediate EMT phenotype. We also demonstrate that ALDH1A3 increases oxidative phosphorylation and decreases glycolysis and reactive oxygen species (ROS). The effects of ALDH1A3 reduction were countered with the glycolysis inhibitor 2-deoxy-D-glucose (2DG). In cell culture and tumor xenograft models, 2DG suppresses the increase in the CD24-CD44+ population and ROS induced by ALDH1A3 knockdown. Combined inhibition of ALDH1A3 and glycolysis best reduces breast tumor growth and tumor-initiating cells, suggesting that the combination of targeting ALDH1A3 and glycolysis has therapeutic potential for limiting CSCs and tumor progression. Together, these findings identify ALDH1A3 as a key regulator of processes required for breast cancer progression and depletion of ALDH1A3 makes breast cancer cells more susceptible to glycolysis inhibition.

Associations of Early-Life and Adult Anthropometric Measures with the Expression of Stem Cell Markers CD44, CD24, and ALDH1A1 in Women with Benign Breast Biopsies

BACKGROUND

According to the stem cell hypothesis, breast carcinogenesis may be related to the breast stem cell pool size. However, little is known about associations of breast cancer risk factors, such as anthropometric measures, with the expression of stem cell markers in noncancerous breast tissue.

METHODS

The analysis included 414 women with biopsy-confirmed benign breast disease in the Nurses' Health Study and Nurses' Health Study II. Birthweight, weight at age 18, current weight, and current height were reported via self-administered questionnaires. IHC staining of stem cell markers (CD44, CD24, and aldehyde dehydrogenase family 1 member A1) in histopathologically normal epithelial and stromal breast tissue was quantified using an automated computational image analysis system. Linear regression was used to examine the associations of early-life and adult anthropometric measures with log-transformed stem cell marker expression, adjusting for potential confounders.

RESULTS

Birthweight [≥10.0 vs. <5.5 lbs: β (95% confidence interval) = 4.29 (1.02, 7.56); P trend = 0.001 in the stroma] and adult height [≥67.0 vs. <63.0 inch: 0.86 (0.14, 1.58); P trend = 0.02 in the epithelium and stroma combined] were positively associated with CD44 expression. Childhood body fatness was inversely associated (P trend = 0.03) whereas adult height was positively associated with CD24 expression in combined stroma and epithelium (P trend = 0.03).

CONCLUSIONS

Our data suggest that anthropometric measures, such as birthweight, adult height, and childhood body fatness, may be associated with the stem cell expression among women with benign breast disease.

IMPACT

Anthropometric measures, such as birthweight, height, and childhood body fatness, may have long-term impacts on stem cell population in the breast.

Associations of stem cell markers CD44, CD24 and ALDH1A1 with mammographic breast density in women with benign breast biopsies

BACKGROUND

We examined associations of CD44, CD24 and ALDH1A1 breast stem cell markers with mammographic breast density (MBD), a well-established breast cancer (BCa) risk factor.

METHODS

We included 218 cancer-free women with biopsy-confirmed benign breast disease within the Nurses' Health Study (NHS) and NHSII. The data on BCa risk factors were obtained from biennial questionnaires. Immunohistochemistry (IHC) was done on tissue microarrays. For each core, the IHC expression was assessed using a semi-automated platform and expressed as percent of positively stained cells for each marker out of the total cell count. MBD was assessed with computer-assisted techniques. Generalised linear regression was used to examine the associations of each marker with square root-transformed percent density (PD), absolute dense and non-dense areas (NDA), adjusted for BCa risk factors.

RESULTS

Stromal CD44 and ALDH1A1 expression was positively associated with PD (≥ 10% vs. <10% β = 0.56, 95% confidence interval [CI] [0.06; 1.07] and β = 0.81 [0.27; 1.34], respectively) and inversely associated with NDA (β per 10% increase = -0.17 [-0.34; -0.01] and β for ≥10% vs. <10% = -1.17 [-2.07; -0.28], respectively). Epithelial CD24 expression was inversely associated with PD (β per 10% increase = -0.14 [-0.28; -0.01]. Stromal and epithelial CD24 expression was positively associated with NDA (β per 10% increase = 0.35 [0.2 × 10-2; 0.70] and β per 10% increase = 0.34 [0.11; 0.57], respectively).

CONCLUSION

Expression of stem cell markers is associated with MBD.

CD24 negativity reprograms mitochondrial metabolism to PPARα and NF-κB-driven fatty acid β-oxidation in triple-negative breast cancer

CD24 is a well-characterized breast cancer (BC) stem cell (BCSC) marker. Primary breast tumor cells having CD24-negativity together with CD44-positivity is known to maintain high metastatic potential. However, the functional role of CD24 gene in triple-negative BC (TNBC), an aggressive subtype of BC, is not well understood. While the significance of CD24 in regulating immune pathways is well recognized in previous studies, the significance of CD24 low expression in onco-signaling and metabolic rewiring is largely unknown. Using CD24 knock-down and over-expression TNBC models, our in vitro and in vivo analysis suggest that CD24 is a tumor suppressor in metastatic TNBC. Comprehensive in silico gene expression analysis of breast tumors followed by lipidomic and metabolomic analyses of CD24-modulated cells revealed that CD24 negativity induces mitochondrial oxidative phosphorylation and reprograms TNBC metabolism toward the fatty acid beta-oxidation (FAO) pathway. CD24 silencing activates PPARα-mediated regulation of FAO in TNBC cells. Further analysis using reverse-phase protein array and its validation using CD24-modulated TNBC cells and xenograft models nominated CD24-NF-κB-CPT1A signaling pathway as the central regulatory mechanism of CD24-mediated FAO activity. Overall, our study proposes a novel role of CD24 in metabolic reprogramming that can open new avenues for the treatment strategies for patients with metastatic TNBC.

Tyrosine kinase SRC-induced YAP1-KLF5 module regulates cancer stemness and metastasis in triple-negative breast cancer

SRC is the first identified oncogene, and its aberrant activation has been implicated as a driving event in tumor initiation and progression. However, its role in cancer stemness regulation and the underlying regulatory mechanism are still elusive. Here, we identified a YAP1 tyrosine phosphorylation-dependent YAP1-KLF5 oncogenic module, as the key downstream mediator of SRC kinase regulating cancer stemness and metastasis in triple-negative breast cancer (TNBC). SRC was overexpressed in TNBC patient tissues and its expression level was highly correlated with the tumor malignancy. SRC activation induced, while inhibition of SRC kinase reduced the cancer stemness, tumor cell growth and metastasis in vitro and in vivo. Transcriptomic and proteomic analysis revealed that SRC-mediated YAP1 tyrosine phosphorylation induced its interaction with Kruppel-like factor 5 (KLF5) to form a YAP1/TEAD-KLF5 complex in TNBC cells. YAP1-KLF5 association further promoted TEAD-mediated transcriptional program independently of canonical Hippo kinases, which eventually gave rise to the enhanced cancer stemness and metastasis. Disruption of YAP1-KLF5 module in TNBC cells dramatically attenuated the SRC-induced cancer stemness and metastasis in vitro and in vivo. Accordingly, co-upregulations of SRC and YAP1-KLF5 module in TNBC tissues were significantly positively correlated with the tumor malignance. Altogether, our work presents a novel tyrosine phosphorylation-dependent YAP1-KLF5 oncogenic module governing SRC-induced cancer stemness and metastasis in TNBC. Therefore, targeting YAP1/KLF5-mediated transcription may provide a promising strategy for TNBC treatment with SRC aberrantly activation.

Reliability of CD44, CD24, and ALDH1A1 immunohistochemical staining: Pathologist assessment compared to quantitative image analysis

Background

The data on the expression of stem cell markers CD44, CD24, and ALDH1A1 in the breast tissue of cancer-free women is very limited and no previous studies have explored the agreement between pathologist and computational assessments of these markers. We compared the immunohistochemical (IHC) expression assessment for CD44, CD24, and ALDH1A1 by an expert pathologist with the automated image analysis results and assessed the homogeneity of the markers across multiple cores pertaining to each woman.

Methods

We included 81 cancer-free women (399 cores) with biopsy-confirmed benign breast disease in the Nurses' Health Study (NHS) and NHSII cohorts. IHC was conducted with commercial antibodies [CD44 (Dako, Santa Clara, CA, USA) 1:25 dilution; CD24 (Invitrogen, Waltham, MA, USA) 1:200 dilution and ALDH1A1 (Abcam, Cambridge, United Kingdom) 1:300 dilution]. For each core, the percent positivity was quantified by the pathologist and Definiens Tissue Studio. Correlations between pathologist and computational scores were evaluated with Spearman correlation (for categorical positivity: 0, >0-<1, 1-10, >10-50, and >50%) and sensitivity/specificity (for binary positivity defined with 1 and 10% cut-offs), using the pathologist scores as the gold standard. Expression homogeneity was examined with intra-class correlation (ICC). Analyses were stratified by core [normal terminal duct-lobular units (TDLUs), benign lesions] and tissue type (epithelium, stroma).

Results

Spearman correlation between pathologist and Definiens ranged between 0.40-0.64 for stroma and 0.66-0.68 for epithelium in normal TDLUs cores and between 0.24-0.60 for stroma and 0.61-0.64 for epithelium in benign lesions. For stroma, sensitivity and specificity ranged between 0.92-0.95 and 0.24-0.60, respectively, with 1% cut-off and between 0.43-0.88 and 0.73-0.85, respectively, with 10% cut-off. For epithelium, 10% cut-off resulted in better estimates for both sensitivity and specificity. ICC between the cores was strongest for CD44 for both stroma and epithelium in normal TDLUs cores and benign lesions (range 0.74-0.80). ICC for CD24 and ALDH1A ranged between 0.42-0.63 and 0.44-0.55, respectively.

Conclusion

Our findings show that computational assessments for CD44, CD24, and ALDH1A1 exhibit variable correlations with manual assessment. These findings support the use of computational platforms for IHC evaluation of stem cell markers in large-scale epidemiologic studies. Pilot studies maybe also needed to determine appropriate cut-offs for defining staining positivity.

Role of Cancer Stem-like Cells in the Process of Invasion and Mesenchymal Transformation by a Reconstituted Triple-negative Breast Cancer Cell Population Resistant to p53-induced Apoptosis

We investigated the role of cancer stem cells (CSCs) in a population of triple-negative breast cancer (TNBC) cells that are resistant to apoptosis. A human breast cancer cell population capable of inducing p53 expression with doxycycline (Dox) was created and used as an untreated control (UT). After the addition of Dox to UT for 5 days, the cell population reconstituted with cells showing resistance to apoptosis was named RE. Fluorescence-activated cell sorting (FACS) and immunostaining revealed that after the addition of Dox, the ratio of cells in the S and G2/M phases decreased in UT as apoptosis proceeded, but did not markedly change in apoptosis-resistant RE. CSC-like cells in RE exhibited a cell morphology with a larger ratio of the major/minor axis than UT. FACS showed that RE had a higher proportion of CSC-like cells and contained more CD44+CD24- mesenchymal CSCs than ALDH1A3+ epithelial-like CSCs. In a Matrigel invasion assay, UT was more likely to form a three-dimensional cell population, whereas RE exhibited a planar population, higher migration ability, and the up-regulated expression of epithelial-mesenchymal transition-related genes. These results provide insights into the mechanisms by which TNBC cells acquire treatment resistance at the time of recurrence.

Evaluation of CD44+/CD24- and Aldehyde Dehydrogenase Enzyme Markers in Cancer Stem Cells as Prognostic Indicators for Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) has been extensively studied not just for its aggressive behavior but also to understand its complex molecular nature. This type of heterogeneous tumor shows no expression of estrogen receptor (ER) or progesterone receptor (PR) and does not express the HER2 gene, and often these tumors are high grade with distinct histological groups. The basal-like subtype is most commonly related to the TNBC type of neoplasms; it can be further classified according to Lehmann and Burstein expert’s criteria. TNBC is related to breast stem cell markers such as CD44+/CD24- and high levels of enzyme aldehyde dehydrogenase (ALDH), which have been shown to possess stem cell features that are involved in differentiation, vascular invasion, tumorigenesis, and metastatic potential. CD44+/CD24- and high levels of ALDH have significance as markers as well as indicators of poor prognosis in TNBC. The databases used in this review are PMC, PubMed, and Google Scholar.

Prognosis assessment of CD44+/CD24- in breast cancer patients: a systematic review and meta-analysis

PURPOSE

This meta-analysis investigated the relationships between the CD44⁺/CD24^- phenotype and tumor size, lymph node metastasis, distant metastasis, disease-free survival (DFS), and overall survival (OS) in 8036 postoperative breast cancer patients enrolled in 23 studies.

METHODS

A literature search of PubMed, Medline, Cochrane, Embase, and PMC was conducted to identify eligible studies. The combined odds ratios (ORs) and 95% confidence intervals (95% CIs) were analyzed to evaluate the relationships between the CD44⁺/CD24^- phenotype and the pathological and biological characteristics of breast cancer patients, and the combined hazard ratios (HRs) and 95% CIs were calculated to evaluate the relationships between CD44⁺/CD24^- and DFS and OS of breast cancer patients using Stata12.0 software.

RESULTS

The CD44⁺/CD24^- phenotype were not related to the tumor size (tumor size > 2.0 vs ≤ 2.0 cm, combined OR = 0.98, 95% CI 0.68-1.34, p = 0.792) and did not promote lymph node metastasis (lymph node metastasis vs. no lymph node metastasis, OR = 0.92, 95% CI 0.67-1.27, p = 0.626) and distant metastasis (distant metastasis vs no distant metastasis, combined OR = 3.88, 95% CI 0.93-16.24, p = 0.064). The CD44⁺/CD24^- phenotype was negatively correlated with postoperative DFS (HR = 1.67, 95% CI 1.35-2.07, p < 0.00001) and OS (combined HR = 1.52, 95% CI 1.21-1.91, p = 0.0004).

CONCLUSION

These results suggested expression of the CD44⁺/CD24^- phenotype cannot be used as a reliable indicator of the tumor size, lymph node metastasis, and distant metastasis, however, it can be used be a potential therapeutic targets of DFS, OS in breast cancer patients.

Gene signatures in patients with early breast cancer and relapse despite pathologic complete response

A substantial minority of early breast cancer (EBC) patients relapse despite their tumors achieving pathologic complete response (pCR) after neoadjuvant therapy. We compared gene expression (BC360; nCounter^® platform; NanoString) between primary tumors of patients with post-pCR relapse (N = 14) with: (i) matched recurrent tumors from same patient (intraindividual analysis); and (ii) primary tumors from matched controls with pCR and no relapse (N = 41; interindividual analysis). Intraindividual analysis showed lower estrogen receptor signaling signature expression in recurrent tumors versus primaries (logFC = −0.595; P = 0.022). Recurrent tumors in patients with distant metastases also exhibited reduced expression of immune-related expression parameters. In interindividual analyses, primary tumor major histocompatibility complex class II expression was lower versus controls in patients with any relapse (logFC = −0.819; P = 0.030) or distant relapse (logFC = −1.151; P = 0.013). Primaries with later distant relapse also had greater homologous recombination deficiency than controls (logFC = 0.649; P = 0.026). Although no associations remained statistically significant following adjustment for false discovery rate, our results show that transcriptomic analyses have potential for prognostic value and may help in selecting optimal treatment regimens for EBC at risk of relapse and warrant further investigation.

RNA-binding protein complex LIN28/MSI2 enhances cancer stem cell-like properties by modulating Hippo-YAP1 signaling and independently of Let-7

The RNA binding protein LIN28 directly modulates the stability and translation of target mRNAs independently of Let-7; however, the key downstream targets of LIN28 in this process are largely unknown. Here, we revealed that Hippo signaling effector YAP1 functioned as a key downstream regulator of LIN28 to modulate the cancer stem cell (CSC)-like properties and tumor progressions in triple negative breast cancer (TNBC). LIN28 was overexpressed in BC tissues and cell lines, and significantly correlated with poorer overall survivals in patients. Ectopic LIN28 expression enhanced, while knockdown of LIN28A inhibited the CSC-like properties, cell growth and invasive phenotypes of TNBC cells in vitro and in vivo. Transcriptome analysis demonstrated LIN28 overexpression significantly induced the expressions of YAP1 downstream genes, while reduced the transcripts of YAP1 upstream kinases, such as MST1/2 and LATS1/2, and knockdown of LIN28A exhibited the opposite effects. Furthermore, constitutive activation of YAP1 in LIN28 knockdown TNBC cells could rescue the cell growth and invasive phenotypes in vitro and in vivo. Mechanistically, instead of the dependence of Let-7, LIN28 recruited RNA binding protein MSI2 in a manner dependent on the LIN28 CSD domain and MSI2 RRM domain, to directly induce the mRNA decay of YAP1 upstream kinases, leading to the inhibition of Hippo pathway and activation of YAP1, which eventually gave rise to increased CSC populations, enhanced tumor cell growth and invasive phenotypes. Accordingly, co-upregulations of LIN28 and MSI2 in TNBC tissues were strongly associated with YAP1 protein level and tumor malignance. Taken together, our findings unravel a novel LIN28/MSI2-YAP1 regulatory axis to induce the CSC-like properties, tumor growth and metastasis, independently of Let-7, which may serve as a potential therapeutic strategy for the treatment of a subset of TNBC with LIN28 overexpression.

The Prostaglandin E2 Pathway and Breast Cancer Stem Cells: Evidence of Increased Signaling and Potential Targeting

Culprits of cancer development, metastasis, and drug resistance, cancer stem cells (CSCs) are characterized by specific markers, active developmental signaling pathways, metabolic plasticity, increased motility, invasiveness, and epithelial-mesenchymal transition. In breast cancer, these cells are often more prominent in aggressive disease, are amplified in drug-resistant tumors, and contribute to recurrence. For breast cancer, two distinct CSC populations exist and are typically defined by CD44+/CD24- cell surface marker expression or increased aldehyde dehydrogenase (ALDH) activity. These CSC populations share many of the same properties but also exhibit signaling pathways that are more active in CD44+/CD24- or ALDH+ populations. Understanding these CSC populations and their shared or specific signaling pathways may lead to the development of novel therapeutic strategies that will improve breast cancer patient outcomes. Herein, we review the current evidence and assess published patient tumor datasets of sorted breast CSC populations for evidence of heightened prostaglandin E2 (PGE₂) signaling and activity in these breast CSC populations. PGE₂ is a biologically active lipid mediator and in cancer PGE₂ promotes tumor progression and poor patient prognosis. Overall, the data suggests that PGE₂ signaling is important in propagating breast CSCs by enhancing inherent tumor-initiating capacities. Development of anti-PGE₂ signaling therapeutics may be beneficial in inhibiting tumor growth and limiting breast CSC populations.

SRC kinase-mediated signaling pathways and targeted therapies in breast cancer

Breast cancer (BC) has been ranked the most common malignant tumor throughout the world and is also a leading cause of cancer-related deaths among women. SRC family kinases (SFKs) belong to the non-receptor tyrosine kinase (nRTK) family, which has eleven members sharing similar structure and function. Among them, SRC is the first identified proto-oncogene in mammalian cells. Oncogenic overexpression or activation of SRC has been revealed to play essential roles in multiple events of BC progression, including tumor initiation, growth, metastasis, drug resistance and stemness regulations. In this review, we will first give an overview of SRC kinase and SRC-relevant functions in various subtypes of BC and then systematically summarize SRC-mediated signaling transductions, with particular emphasis on SRC-mediated substrate phosphorylation in BC. Furthermore, we will discuss the progress of SRC-based targeted therapies in BC and the potential future direction.

Systemic cytology. A novel diagnostic approach for assessment of early systemic disease

Recognition of low grade or asymptomatic systemic diseases suggests prevention of the worst, yet has been proven challenging ever since. Biomarker-based liquid biopsy has emerged in recent years as a practical platform for the assessment of systemic diseases yet, technical realizations were mainly focused on cancer, faced challenges in accuracy at early stage and are lacking provision of sufficient evidence of disease. In particular in cell-based cancer liquid biopsy, obstacles are rarity and heterogeneity of circulating tumor and tumor-associated rare cells. Evidence is mounting about an entire spectrum of distinct circulating rare cell types that denotes the systemic component of a certain physiological state. Therefore, circulating rare cells in combination may arise from yet, also account for systemic diseases, which we denote as multi-rare cell association and involves foremost bone marrow-derived progenitor and stem cells yet, also matured somatic cell types. One would expect immense diagnostic value in the read-out of the so called rare cell population which represents cytological evidence of abnormality. We hypothesize that comprehensive rare cell population profiling as contrasted to the biomarker screening approach may realize the premise of a biopsy as to confirm, characterize, grade, stage or predict a systemic disease. This novel approach represents the "missing link" in diagnostic care of in particular early or residual systemic disease and presumes a steady gain in knowledge about the clinical interpretation of rare cell population profiles thus, expecting the knowledge-driven transformation of cell-based liquid biopsy from suggestion to confirmation. We support our hypothesis by past findings made by others and us and provide insights how to interpret a certain rare cell population profile.

Exploratory comparisons between different anti-mitotics in clinically-used drug combination in triple negative breast cancer

Triple-negative breast cancer (TNBC) constitutes a very aggressive type of breast cancer with few options of cytotoxic chemotherapy available for them. A chemotherapy regimen comprising of doxorubicin hydrochloride and cyclophosphamide, followed by paclitaxel, known as AC-T, is approved for usage as an adjuvant treatment for this type of breast cancer. In this study we aimed to elucidate the role of KIF11 in TNBC progression throughout its inhibition by two synthetic small molecules containing the DHPM core (dihydropyrimidin-2(1H)-ones or -thiones), with the hypothesis that these inhibitors could be an interesting option of antimitotic drug used alone or as adjuvant therapy in association with AC. For this purpose, we evaluated the efficacy of DHPMs used as monotherapy or in combination with doxorubicin and cyclophosphamide, in Balbc-nude mice bearing breast cancer induced by MDA-MB-231, having AC-T as positive control. Our data provide extensive evidence to demonstrate that KIF11 inhibitors showed pronounced antitumor activity, acting in key points of tumorigenesis and cancer progression in in vivo xenograft model of triple negative breast cancer, like down-regulation of KIF11 and ALDH1-A1. Moreover, they didn’t show the classic peripheral neuropathy characterized by impaired mobility, as it is common with paclitaxel use. These results suggest that the use of a MAP inhibitor in breast cancer regimen treatment could be a promising strategy to keep antitumoral activity reducing the side effects.

Angiopoietin-like protein 4 is a chromatin-bound protein that enhances mammosphere formation in vitro and experimental triple-negative breast cancer brain and liver metastases in vivo

INTRODUCTION:

Metastatic progression in triple-negative breast cancer (TNBC) patients occurs primarily because of nuclear reprogramming that includes chromatin remodeling and epigenetic modifications. The existing and most successful chemotherapies available for metastatic TNBC target nuclear proteins or damage DNA. The objectives here are to investigate an undescribed role for the molecular biology of nuclear angiopoietin-like protein 4 (ANGPTL4) and to characterize the effect of ectopic overexpression of ANGPTL4 in the metastatic biology of TNBC.

MATERIALS AND METHODS:

Lentiviral-mediated transduction was used to overexpress ANGPTL4 in the TNBC cell line MD Anderson–metastatic breast cancer 231. The overexpression of ANGPTL4 was confirmed by western blot and ELISA. Subcellular fractionation, western blot, and immunofluorescence microscopy were used to characterize the intracellular localization of ANGPTL4. Mammosphere culture and the anchorage-independent growth assay analyzed the metastatic potential of the cell line. Xenograft assays assessed the effect of ANGPTL4 overexpression on TNBC metastases in vivo.

RESULTS:

The ANGPTL4 overexpressing cell line formed larger mammospheres and anchorage-independent colonies in vitro and developed larger primary tumors, more liver metastases, and brain metastatic outgrowth in vivo in comparison to a cell line that expressed endogenous levels of ANGPTL4. ANGPTL4, aurora kinase A (AURKA), a mitotic kinase, and Tat-interacting protein p60 kDa (Tip60), a lysine acetyltransferase, associated with chromatin in the ANGPTL4 overexpressing cells but not in cells that expressed endogenous levels of ANGPTL4.

CONCLUSIONS:

The ANGPTL4 overexpressing cell line showed in vitro and in vivo activities that suggest that nuclear ANGPTL4, AURKA, and Tip60 may cooperatively modulate TNBC metastases within chromatin-remodeling complexes or DNA-associated machinery.

Anti-Cancer Effects of an Optimised Combination of Ginsenoside Rg3 Epimers on Triple Negative Breast Cancer Models

Key problems of chemotherapies, as the mainstay of treatment for triple-negative breast cancer (TNBC), are toxicity and development of tumour resistance. Using response surface methodology, we previously optimised the combination of epimers of ginsenoside Rg3 (Rg3) for anti-angiogenic action. Here, we show that the optimised combination of 50 µM SRg3 and 25 µM RRg3 (C3), derived from an RSM model of migration of TNBC cell line MDA-MB-231, inhibited migration of MDA-MB-231 and HCC1143, in 2D and 3D migration assays (p < 0.0001). C3 inhibited mammosphere formation efficiency in both cell lines and decreased the CD44⁺ stem cell marker in the mammospheres. Molecular docking predicted that Rg3 epimers had a better binding score with IGF-1R than with EGFR, HER-2 or PDGFR, and predicted an mTOR inhibitory function of Rg3. C3 affected the signalling of AKT in MDA-MB-231 and HCC1143 mammospheres. In a mouse model of metastatic TNBC, an equivalent dose of C3 (23 mg/kg SRg3 + 11 mg/kg RRg3) or an escalated dose of 46 mg/kg SRg3 + 23 mg/kg RRg3 was administered to NSG mice bearing MDA-MB-231-Luc cells. Calliper and IVIS spectrum measurement of the primary and secondary tumour showed that the treatment shrunk the primary tumour and decreased the load of metastasis in mice. In conclusion, this combination of Rg3 epimers showed promising results as a potential treatment option for TNBC patients.

A review of the racial heterogeneity of breast cancer stem cells

Breast Cancer Stem Cells has become the toast of many breast cancer investigators in the past two decades owing to their crucial roles in tumourigenesis, progression, differentiation, survival and chemoresistance. Despite the growing list of research data in this field, racial or ethnic comparison studies on these stem cells remain scanty. This study is a comparative racial analysis of putative breast cancer stem cells. Research articles on the clinicopathological significance of breast cancer stem cells within a period of 17 years (2003-2020) were reviewed across 5 major races (African/Black American, Asian, Caucasian/White, Hispanic/Latino, and American). The associations between the stem cells markers (CD44+/CD24^-/low, BMI1, ALDH1, CD133, and GD2) and clinicopathological and clinical outcomes were analysed. A total of 40 studies were included in this study with 50% Asian, 25% Caucasian, 10% African, 5% American and 2.5% Hispanic/Latino, and 7.5% other mixed races. CD44⁺/CD24^-/low has been associated with TNBC/Basal like phenotype across all races. It is generally associated with poor clinicopathological features such as age, tumour size, lymph node metastasis and lymphovascular invasion. In Asians, CD44⁺/CD24^-/low was associated with DFS and OS but not in Caucasians. ALDH1 was the most studied breast CSC marker (40% of all studies on breast cancer stem cell markers) also associated with poor clinicopathological features including size, age, stage, lymph node metastasis and Nottingham Prognostic Index. ALDH1 was also associated with DFS and OS in Asians but not Caucasians. Racial variations exist in breast cancer stem cell pattern and functions but ill-defined due to multiple factors. Further research is required to better understand the role of breast CSC.

LncRNA PART1 Promotes Proliferation and Migration, Is Associated with Cancer Stem Cells, and Alters the miRNA Landscape in Triple-Negative Breast Cancer

Triple-negative breast cancers (TNBCs) are aggressive, lack targeted therapies and are enriched in cancer stem cells (CSCs). Novel therapies which target CSCs within these tumors would likely lead to improved outcomes for TNBC patients. Long non-coding RNAs (lncRNAs) are potential therapeutic targets for TNBC and CSCs. We demonstrate that lncRNA prostate androgen regulated transcript 1 (PART1) is enriched in TNBCs and in Aldefluor^high CSCs, and is associated with worse outcomes among basal-like breast cancer patients. Although PART1 is androgen inducible in breast cancer cells, analysis of patient tumors indicates its androgen regulation has minimal clinical impact. Knockdown of PART1 in TNBC cell lines and a patient-derived xenograft decreased cell proliferation, migration, tumor growth, and mammosphere formation potential. Transcriptome analyses revealed that the lncRNA affects expression of hundreds of genes (e.g., myosin-Va, MYO5A; zinc fingers and homeoboxes protein 2, ZHX2). MiRNA 4.0 GeneChip and TaqMan assays identified multiple miRNAs that are regulated by cytoplasmic PART1, including miR-190a-3p, miR-937-5p, miR-22-5p, miR-30b-3p, and miR-6870-5p. We confirmed the novel interaction between PART1 and miR-937-5p. In general, miRNAs altered by PART1 were less abundant than PART1, potentially leading to cell line-specific effects in terms miRNA-PART1 interactions and gene regulation. Together, the altered miRNA landscape induced by PART1 explains most of the protein-coding gene regulation changes (e.g., MYO5A) induced by PART1 in TNBC.

Lack of Androgen Receptor Expression Selects for Basal-Like Phenotype and Is a Predictor of Poor Clinical Outcome in Non-Metastatic Triple Negative Breast Cancer

Background: Androgen receptor (AR) has emerged as a significant favorable prognostic indicator in estrogen receptor expressing (ER⁺) breast cancer (BCa); however, its clinical and biological relevance in triple negative breast cancer (TNBC) and association with cancer stem cell (CSC) markers remain ambiguous. Methods: We examined the immunohistochemical expression of AR in a cohort of stage I-III TNBC cases (n = 197) with a long-term clinical follow-up data (mean follow-up = 53.6 months). Significance of AR expression was correlated with prognostic biomarkers including cancer stem cell markers (CD44, CD24, and ALDH1), basal markers (CK5, CK14, and nestin), proliferation marker (ki-67), apoptotic marker (Bcl-2), and COX-2. Expression of CK5 and nestin was used for the categorization of TNBC into basal (TN, CK5⁺, and/or nestin⁺) and non-basal (TN, CK5^-, and/or nestin^-) phenotypes, and Kaplan-Meier curves were used for estimation of overall survival and breast cancer-specific survival (BCSS). Results: AR expression was observed in 18.8% of non-metastatic TNBC tumors. Expression of AR correlated with lower grade (P < 0.001) and conferred a favorable prognostic significance in patients with axillary lymph node metastasis (P = 0.005). Lack of AR expression correlated with expression of CSC phenotype (CD44⁺/CD24^-) (P < 0.001), COX-2 (P = 0.02), basal markers (CK5: P = 0.03), and nestin (P = 0.01). Basal-like phenotype (TN, CK5⁺, and/or nestin⁺) correlated with quadruple-negative breast cancer (QNBC) and showed a significant association with adverse prognostic markers including high proliferation index (P < 0.001), expression of COX-2 (P = 0.009), and CSC phenotype (CD44⁺/CD24^-: P = 0.01). Expression of AR remained an independent prognostic indicator for improved overall survival (P = 0.003), whereas basal-like phenotype was associated with an adverse BCSS (P = 0.013). Conclusions: Assessment of AR and basal markers identified biologically and clinically distinct subgroups of TNBC. Expression of AR defined a low-risk TNBC subgroup associated with improved overall survival, whereas expression of basal markers (CK5 and nestin) identified a high-risk subgroup associated with adverse BCSS. Integration of immunohistochemical analysis of AR and basal biomarkers to the assessment of TNBC tumors is expected to improve the prognostication of an otherwise heterogeneous disease.

The Missing Lnc: The Potential of Targeting Triple-Negative Breast Cancer and Cancer Stem Cells by Inhibiting Long Non-Coding RNAs

Treatment decisions for breast cancer are based on staging and hormone receptor expression and include chemotherapies and endocrine therapy. While effective in many cases, some breast cancers are resistant to therapy, metastasize and recur, leading to eventual death. Higher percentages of tumor-initiating cancer stem cells (CSCs) may contribute to the increased aggressiveness, chemoresistance, and worse outcomes among breast cancer. This may be particularly true in triple-negative breast cancers (TNBCs) which have higher percentages of CSCs and are associated with worse outcomes. In recent years, increasing numbers of long non-coding RNAs (lncRNAs) have been identified as playing an important role in breast cancer progression and some of these have been specifically associated within the CSC populations of breast cancers. LncRNAs are non-protein-coding transcripts greater than 200 nucleotides which can have critical functions in gene expression regulation. The preclinical evidence regarding lncRNA antagonists for the treatment of cancer is promising and therefore, presents a potential novel approach for treating breast cancer and targeting therapy-resistant CSCs within these tumors. Herein, we summarize the lncRNAs that have been identified as functionally relevant in breast CSCs. Furthermore, our review of the literature and analysis of patient datasets has revealed that many of these breast CSC-associated lncRNAs are also enriched in TNBC. Together, this suggests that these lncRNAs may be playing a particularly important role in TNBC. Thus, certain breast cancer-promoting/CSC-associated lncRNAs could be targeted in the treatment of TNBCs and the CSCs within these tumors should be susceptible to anti-lncRNA therapy.

High-Throughput RNA Interference Screen Targeting Synthetic-Lethal Gain-of-Function of Oncogenic Mutant TP53 in Triple-Negative Breast Cancer

TNBC is an aggressive and metastatic subtype of breast cancer in which TP53 mutation occurs frequently and is associated with particularly poor outcome. Mutations in TP53 can disrupt the intrinsic function of the tumor suppressor as well as acquire oncogenic gain-of-function (GOF) activities. However, little is known about its oncogenic GOF mediators and functions. Targeted therapy for TNBC patients is thus one of the most urgent needs in breast cancer therapeutics, and identifying genes that have synthetic lethal interactions with mutant TP53 may be a promising approach. In this chapter, we present procedures on sequential analysis of RNA-seq followed by high-throughput RNA interference screening (HTS-RNAi screening). This approach has been utilized to identify genes with synthetic lethality of mutant TP53, providing a promising strategy for the treatment of mutant TP53 in TNBC and determining its impact on tumorigenesis.

Potential Role of MSC/Cancer Cell Fusion and EMT for Breast Cancer Stem Cell Formation

Solid tumors comprise of maturated cancer cells and self-renewing cancer stem-like cells (CSCs), which are associated with various other nontumorigenic cell populations in the tumor microenvironment. In addition to immune cells, endothelial cells, fibroblasts, and further cell types, mesenchymal stroma/stem-like cells (MSC) represent an important cell population recruited to tumor sites and predominantly interacting with the different cancer cells. Breast cancer models were among the first to reveal distinct properties of CSCs, however, the cellular process(es) through which these cells are generated, maintained, and expanded within neoplastic tissues remains incompletely understood. Here, we discuss several possible scenarios that are not mutually exclusive but may even act synergistically: fusion of cancer cells with MSC to yield hybrid cells and/or the induction of epithelial-mesenchymal transition (EMT) in breast cancer cells by MSC, which can relay signals for retrodifferentiation and eventually, the generation of breast CSCs (BCSCs). In either case, the consequences may be promotion of self-renewal capacity, tumor cell plasticity and heterogeneity, an increase in the cancer cells’ invasive and metastatic potential, and the acquisition of resistance mechanisms towards chemo- or radiotherapy. While specific signaling mechanisms involved in each of these properties remain to be elucidated, the present review article focusses on a potential involvement of cancer cell fusion and EMT in the development of breast cancer stem cells.

The basics of epithelial-mesenchymal transition (EMT): A study from a structure, dynamics, and functional perspective

Epithelial-mesenchymal transition (EMT) is a key step in transdifferentiation process in solid cancer development. Forthcoming evidence suggest that the stratified program transforms polarized, immotile epithelial cells to migratory mesenchymal cells associated with enhancement of breast cancer stemness, metastasis, and drug resistance. It involves primarily several signaling pathways, such as transforming growth factor-β (TGF-β), cadherin, notch, plasminogen activator protein inhibitor, urokinase plasminogen activator, and WNT/beta catenin pathways. However, current understanding on the crosstalk of multisignaling pathways and assemblies of key transcription factors remain to be explored. In this review, we focus on the crosstalk of signal transduction pathways linked to the current therapeutic and drug development strategies. We have also performed the computational modeling on indepth the structure and conformational dynamic studies of regulatory proteins and analyze molecular interactions with their associate factors to understand the complicated process of EMT in breast cancer progression and metastasis. Electrostatic potential surfaces have been analyzed that help in optimization of electrostatic interactions between the protein and its ligand. Therefore, understanding the biological implications underlying the EMT process through molecular biology with biocomputation and structural biology approaches will enable the development of new therapeutic strategies to sensitize tumors to conventional therapy and suppress their metastatic phenotype.

The Flick of a Switch: Conferring Survival Advantage to Breast Cancer Stem Cells Through Metabolic Plasticity

Within heterogeneous tumors, cancer stem cell (CSC) populations exhibit the greatest tumor initiation potential, promote metastasis, and contribute to therapy resistance. For breast cancer specifically, CSCs are identified by CD44^highCD24^low cell surface marker expression and increased aldehyde dehydrogenase activity. In general, bulk breast tumor cells possess altered energetics characterized by aerobic glycolysis. In contrast, breast CSCs appear to have adaptive metabolic plasticity that allows these tumor-initiating cells to switch between glycolysis and oxidative phosphorylation, depending on factors present in the tumor microenvironment (e.g., hypoxia, reactive oxygen species, availability of glucose). In this article, we review the regulatory molecules that may facilitate the metabolic plasticity of breast CSCs. These regulatory factors include epigenetic chromatin modifiers, non-coding RNAs, transcriptional repressors, transcription factors, energy and stress sensors, and metabolic enzymes. Furthermore, breast cancer cells acquire CSC-like characteristics and altered energetics by undergoing epithelial-mesenchymal transition (EMT). This energy costly process is paired with reprogrammed glucose metabolism by epigenetic modifiers that regulate expression of both EMT and other metabolism-regulating genes. The survival advantage imparted to breast CSCs by metabolic plasticity suggests that targeting the factors that mediate the energetic switch should hinder tumorigenesis and lead to improved patient outcomes.

OSM-induced CD44 contributes to breast cancer metastatic potential through cell detachment but not epithelial-mesenchymal transition

Background

Hormone receptor status in human breast cancer cells is a strong indicator of the aggressiveness of a tumor. Triple negative breast cancers (TNBC) are aggressive, difficult to treat, and contribute to high incidences of metastasis by possessing characteristics such as increased tumor cell migration and a large presence of the transmembrane protein, cluster of differentiation 44 (CD44) on the cell membrane. Estrogen receptor-positive (ER+) cells are less aggressive and do not migrate until undergoing an epithelial-mesenchymal transition (EMT).

Methods

The relationship between EMT and CD44 during metastatic events is assessed by observing changes in EMT markers, tumor cell detachment, and migration following cytokine treatment on both parental and CD44 knockdown human breast tumor cells.

Results

ER+ T47D and MCF-7 human breast cancer cells treated with OSM demonstrate increased CD44 expression and CD44 cleavage. Conversely, ER- MDA-MB-231 human breast cancer cells do not show a change in CD44 expression nor undergo EMT in the presence of OSM. In ER+ cells, knockdown expression of CD44 by shRNA did not prevent EMT but did change metastatic processes such as cellular detachment and migration. OSM-induced migration was decreased in both ER+ and ER- cells with shCD44 cells compared to control cells, while the promotion of tumor cell detachment by OSM was decreased in ER+ MCF7-shCD44 cells, as compared to control cells. Interestingly, OSM-induced detachment in ER- MDA-MB-231-shCD44 cells that normally don't detach at significant rates.

Conclusion

OSM promotes both EMT and tumor cell detachment in ER+ breast cancer cells. Yet, CD44 knockdown did not affect OSM-induced EMT in these cells, while independently decreasing OSM-induced cell detachment. These results suggest that regulation of CD44 by OSM is important for at least part of the metastatic cascade in ER+ breast cancer.

Associations of mammographic breast density with breast stem cell marker-defined breast cancer subtypes

PURPOSE

High mammographic breast density is a strong, well-established breast cancer risk factor. Whether stem cells may explain high breast cancer risk in dense breasts is unknown. We investigated the association between breast density and breast cancer risk by the status of stem cell markers CD44, CD24, and ALDH1A1 in the tumor.

METHODS

We included 223 women with primary invasive or in situ breast cancer and 399 age-matched controls from Mayo Clinic Mammography Study. Percent breast density (PD), absolute dense area (DA), and non-dense area (NDA) were assessed using computer-assisted thresholding technique. Immunohistochemical analysis of the markers was performed on tumor tissue microarrays according to a standard protocol. We used polytomous logistic regression to quantify the associations of breast density measures with breast cancer risk across marker-defined tumor subtypes.

RESULTS

Of the 223 cancers in the study, 182 were positive for CD44, 83 for CD24 and 52 for ALDH1A1. Associations of PD were not significantly different across t marker-defined subtypes (51% + vs. 11-25%: OR 2.83, 95% CI 1.49-5.37 for CD44+ vs. OR 1.87, 95% CI 0.47-7.51 for CD44-, p-heterogeneity = 0.66; OR 2.80, 95% CI 1.27-6.18 for CD24+ vs. OR 2.44, 95% CI 1.14-5.22 for CD24-, p-heterogeneity = 0.61; OR 3.04, 95% CI 1.14-8.10 for ALDH1A1+ vs. OR 2.57. 95% CI 1.30-5.08 for ALDH1A1-, p-heterogeneity = 0.94). Positive associations of DA and inverse associations of NDA with breast cancer risk were similar across marker-defined subtypes.

CONCLUSIONS

We found no evidence of differential associations of breast density with breast cancer risk by the status of stem cell markers. Further studies in larger study populations are warranted to confirm these associations.

ALDH1A3-regulated long non-coding RNA NRAD1 is a potential novel target for triple-negative breast tumors and cancer stem cells

To discover novel therapeutic targets for triple-negative breast cancer (TNBC) and cancer stem cells (CSCs), we screened long non-coding RNAs (lncRNAs) most enriched in TNBCs for high expression in CSCs defined by high Aldefluor activity and associated with worse patient outcomes. This led to the identification of non-coding RNA in the aldehyde dehydrogenase 1 A pathway (NRAD1), also known as LINC00284. Targeting NRAD1 in TNBC tumors using antisense oligonucleotides reduced cell survival, tumor growth, and the number of cells with CSC characteristics. Expression of NRAD1 is regulated by an enzyme that causes Aldefluor activity in CSCs, aldehyde dehydrogenase 1A3 (ALDH1A3) and its product retinoic acid. Cellular fractionation revealed that NRAD1 is primarily nuclear localized, which suggested a potential function in gene regulation. This was confirmed by transcriptome profiling and chromatin isolation by RNA purification, followed by sequencing (ChIRP-seq), which demonstrated that NRAD1 has enriched chromatin interactions among the genes it regulates. Gene Ontology enrichment analysis revealed that NRAD1 regulates expression of genes involved in differentiation and catabolic processes. NRAD1 also contributes to gene expression changes induced by ALDH1A3; thereby, the induction of NRAD1 is a novel mechanism through which ALDH1A3 regulates gene expression. Together, these data identify lncRNA NRAD1 as a downstream effector of ALDH1A3, and a target for TNBCs and CSCs, with functions in cell survival and regulation of gene expression.

Carboxypeptidase A4 accumulation is associated with an aggressive phenotype and poor prognosis in triple-negative breast cancer

Using whole transcriptome analysis and a lentiviral short hairpin RNA screening library, carboxypeptidase A4 (CPA4) was identified as a novel marker in breast cancer and a therapeutic target in triple‑negative breast cancer (TNBC) in the present study. Immunohistochemistry was used to evaluate the presence of CPA4, estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2, Ki67, epidermal growth factor receptor, cytokeratin 5/6, aldehyde dehydrogenase 1, cluster of differentiation (CD)44, CD24, claudins, E‑cadherin, vimentin and androgen receptor in 221 cases of breast cancer, including 68 TNBC cases. The effects of CPA4 on the viability and migration ability of TNBC cells were analyzed using RNA interference methods. Increased CPA4 expression, specifically in the cytoplasm of cancer tissue cells, was detected. Furthermore, high CPA4 expression in TNBC cases was associated with low expression of E‑cadherin and with the expression of cancer stem cell markers (high CD44/low CD24). Patients with TNBC and high levels of CPA4 expression had a significantly poorer prognosis compared with those with low CPA4 expression. Notably, viability and migration were reduced, but E‑cadherin expression was upregulated in CPA4‑suppressed TNBC cells. The present data suggested that CPA4 may be a novel inducer for epithelial‑mesenchymal transition, which is characterized by the downregulation of E‑cadherin and mesenchymal phenotypes. To conclude, CPA4 may be a marker for poor prognosis and a promising therapeutic target in TNBC with aggressive phenotypes.

Targeting BCL-xL improves the efficacy of bromodomain and extra-terminal protein inhibitors in triple-negative breast cancer by eliciting the death of senescent cells

Inhibitors of bromodomain and extra-terminal proteins (BETi) suppress oncogenic gene expression and have been shown to be efficacious in many in vitro and murine models of cancer, including triple-negative breast cancer (TNBC), a highly aggressive disease. However, in most cancer models, responses to BETi can be highly variable. We previously reported that TNBC cells either undergo senescence or apoptosis in response to BETi, but the specific mechanisms dictating these two cell fates remain unknown. Using six human TNBC cell lines, we show that the terminal response of TNBC cells to BETi is dictated by the intrinsic expression levels of the anti-apoptotic protein B-cell lymphoma-extra large (BCL-xL). BCL-xL levels were higher in cell lines that senesce in response to BETi compared with lines that primarily die in response to these drugs. Moreover, BCL-xL expression was further reduced in cells that undergo BETi-mediated apoptosis. Forced BCL-xL overexpression in cells that normally undergo apoptosis following BETi treatment shifted them to senescence without affecting the reported mechanism of action of BETi in TNBC, that is, mitotic catastrophe. Most importantly, pharmacological or genetic inhibition of BCL-xL induced apoptosis in response to BETi, and inhibiting BCL-xL, even after BETi-induced senescence had already occurred, still induced cell death. These results indicate that BCL-xL provides a senescent cell death-inducing or senolytic target that may be exploited to improve therapeutic outcomes of TNBC in response to BETi. They also suggest that the basal levels of BCL-xL should be predictive of tumor responses to BETi in current clinical trials.

Targeting Stemness: Implications for Precision Medicine in Breast Cancer

The genomic landscape of breast cancer has been delineated in recent years. Advances in molecular characterization and targeting strategies are making it feasible to integrate clinical, genome-based and phenotype-based diagnostic and therapeutic methods and apply them to individual patient in the era of precision medicine. Cancer stem cells (CSCs) are a subpopulation in the tumor which have the capability of self-renewal and differentiation. Breast CSCs have important clinical implications as they account for tumor initiation, maintenance, metastasis, therapy resistance, and relapse. In this chapter, we will introduce approaches used to characterize breast CSCs, crucial pathways involved in regulating cancer stemness, and implications of breast CSCs in the precision diagnosis and treatment of breast cancer. We will also discuss novel compounds and therapeutic strategies that selectively target breast CSCs. Integration of breast CSC-related molecular diagnosis and targeted therapy into the clinical workflow of precision medicine has the potential to deliver more effective treatment to breast cancer patients.

ERN1 and ALPK1 inhibit differentiation of bi-potential tumor-initiating cells in human breast cancer

Cancers are heterogeneous by nature. While traditional oncology screens commonly use a single endpoint of cell viability, altering the phenotype of tumor-initiating cells may reveal alternative targets that regulate cellular growth by processes other than apoptosis or cell division. We evaluated the impact of knocking down expression of 420 kinases in bi-lineage triple-negative breast cancer (TNBC) cells that express characteristics of both myoepithelial and luminal cells. Knockdown of ERN1 or ALPK1 induces bi-lineage MDA-MB-468 cells to lose the myoepithelial marker keratin 5 but not the luminal markers keratin 8 and GATA3. In addition, these cells exhibit increased β-casein production. These changes are associated with decreased proliferation and clonogenicity in spheroid cultures and anchorage-independent growth assays. Confirmation of these assays was completed in vivo, where ERN1- or ALPK1-deficient TNBC cells are less tumorigenic. Finally, treatment with K252a, a kinase inhibitor active on ERN1, similarly impairs anchorage-independent growth of multiple breast cancer cell lines. This study supports the strategy to identify new molecular targets for types of cancer driven by cells that retain some capacity for normal differentiation to a non-tumorigenic phenotype. ERN1 and ALPK1 are potential targets for therapeutic development.

Metformin and melatonin inhibit DMBA-induced mammary tumorigenesis in rats fed a high-fat diet

The data from in-vitro and in-vivo studies show that both peroral antidiabetic metformin (MF) and pineal hormone melatonin (MT) inhibit the growth of many cancers, including breast cancer. However, most in-vivo studies used standard-type diet with low fat content. Therefore, in this study, we evaluated the chemopreventive effect of MF and MT in an in-vivo model of breast cancer in rats on a high-fat diet (10% of total fat). Mammary carcinogenesis was induced by 7,12-dimethylbenz[a]anthracene (DMBA) in female Sprague-Dawley rats. Chemoprevention with MF (administered in a diet, 0.2%) and MT (administered in tap water, 20 mg/l) was induced 20 days before the carcinogen administration through the termination of the experiment (14 weeks after carcinogen administration). Tumor growth parameters were analyzed together with histopathological examination and immunohistochemical detection of KI67 (proliferation marker), caspase-3, BAX, BCL-2 (apoptosis markers), and CD24 and CD44 (cancer stem cell markers) in mammary tumor samples. The combination of chemopreventive agents decreased tumor incidence by 29%. Cumulative tumor volume was lower in all groups treated with chemoprevention. Histopathology did not show significant changes in high-grade/low-grade tumor ratio. Immunohistochemistry showed increased expression of BAX in the combination group, and caspase-3 expression increased in both MT and combination groups. MT, and particularly the MF and MT combination, inhibited DMBA-induced mammary tumor growth in rats by apoptosis stimulation in cancer cells. Our results indicate that MT supplements in patients treated with MF may have a considerable effect on the incidence of breast cancer.

Nuclear Localization of Cancer Stem Cell Marker CD133 in Triple-Negative Breast Cancer: A Case Report

Aim and background

It has been recently demonstrated that the detection of stem cell niches in triple-negative (TN) breast cancer may provide good prognostic clues for this tumor.

Methods and study design

We investigated the subcellular expression and localization of the cancer stem cell marker CD133 in a TN breast cancer biopsy from a 42-year-old Caucasian woman with a histological diagnosis of high-grade invasive ductal breast carcinoma by immunohistochemistry, flow cytometry and quantitative real-time PCR (qRT-PCR).

Results

We describe for the first time in a TN breast cancer the nuclear mislocalization of CD133, which normally shows membrane localization and more sporadically cytoplasmic localization. We also found this aberrant expression with qRT-PCR analysis but not flow cytometry.

Conclusions

Nuclear localization of CD133 may be an indicator of poor prognosis in TN breast cancer, as it is known that surface molecules, when moving into the nucleus, can act as transcriptional regulators by interfering with molecular pathways directly connected to the proliferation and differentiation of tumor cells.

Intratumor heterogeneity predicts metastasis of triple-negative breast cancer

Even with the identical clinicopathological features, the ability for metastasis is vastly different among triple-negative breast cancer (TNBC) patients. Intratumor heterogeneity (ITH), which is common in breast cancer, may be a key mechanism leading to the tumor progression. In this study, we studied whether a quantitative genetic definition of ITH can predict clinical outcomes in patients with TNBC. We quantified ITH by calculating Shannon index, a measure of diversity in a population, based on Myc, epidermal growth factor receptor/centromeric probe 7 (EGFR/CEP7) and cyclin D1/centromeric probe 11 (CCND1/CEP11) copy number variations (CNVs) in 300 cells at three different locations of a tumor. Among 75 TNBC patients, those who developed metastasis had significantly higher ITH, that is Shannon indices of EGFR/CEP7 and CCND1/CEP11 CNVs. Higher Shannon indices of EGFR/CEP7 and CCND1/CEP11 CNVs were significantly associated with the development of metastasis and were predictive of significantly worse metastasis-free survival (MFS). Regional heterogeneity, defined as the difference in copy numbers of Myc, EGFR or CCND1 at different locations, was found in 52 patients. However, the presence of regional heterogeneity did not correlate with metastasis or MFS. Our findings demonstrate that higher ITH of EGFR/CEP7 and CCND1/CEP11 CNVs is predictive of metastasis and is associated with significantly worse MFS in TNBC patients, suggesting that ITH is a very promising novel prognostic factor in TNBC.

CD44+/CD24- phenotype predicts a poor prognosis in triple-negative breast cancer

Cancer stem cells are enriched in triple-negative breast cancer (TNBC) tumor tissues, which present strong capacities of proliferation and tumorigenicity. The present study detected the distribution of cancer stem cell markers cluster of differentiation (CD)44/CD24 and analyzed the clinical outcomes of different CD44/CD24 phenotypes in patients with TNBC. Multivariate Cox regression analyses were performed with regard to the prognostic value of cancer stem cell markers CD44/CD24, aldehyde dehydrogenase 1 and other baseline clinical characteristics, including tumor size, lymph node involved, adjuvant chemotherapy, Ki-67, breast cancer susceptibility gene 1, cellular tumor antigen p53, vimentin and basal-like status. The multivariate analyses showed that three of these factors, CD44/CD24 phenotype, basal-like status and number of lymph nodes involved, had an impact on overall survival. Furthermore, patients with CD44⁺/CD24^- phenotype, basal-like tumors and ≥4 lymph nodes involved had a significantly worse prognosis. The expression of CD44 and CD24 was detected by double-staining immunohistochemistry, which can locate cancer stem cells individually. Overall, the present results indicated that CD44/CD24 status evaluated by double-staining immunohistochemistry constitutes an independent prognostic factor for TNBC.

KIF11 is required for proliferation and self-renewal of docetaxel resistant triple negative breast cancer cells

Development of chemoresistance remains a major hurdle for triple negative breast cancer treatment. Previous studies suggest that CD44+/CD24- cells, subpopulation of cancer stem cells with self-renewing and tumor-initiating capacities, are partly responsible for chemoresistance and therapeutic failure of triple negative breast cancer. Therefore, novel agents that target cancer stem cells (CSCs) may improve the clinical outcome. KIF11 (kinesin family member 11), overexpressed in many cancer cells, is a molecular motor protein that plays essential role in mitosis. In this study, we assess its role in docetaxel resistant triple negative breast cancer (TNBC). We found that the expression of KIF11 was significantly increased in CD44+/CD24- subpopulation of docetaxel resistant TNBC cells. Knockdown of KIF11 resulted in a significant decrease in the percentage of CSCs and mammosphere formation. KIF11 knockdown also inhibits cell growth and induces cell cycle G2/M arrest followed by cell mitosis and apoptosis. Further docetaxel resistant TNBC xenograft models demonstrated that KIF11 inhibitor exerts growth inhibitory effect in vivo. Of note, we also found that KIF11 was highly expressed in TNBC and its expression was correlated with shorter disease free survival time. All these data indicate that KIF11 is critical for proliferation and self-renewal in TNBC tumor cells in vitro and in vivo, suggesting that KIF11 may be a promising therapeutic target for treating chemoresistant TNBC.

Phytosphingosine exhibits an anti-epithelial-mesenchymal transition function by the inhibition of EGFR signaling in human breast cancer cells

The lack of effective anti-metastatic drugs for the eradication of breast cancer stem cells within tumors, which are often resistant to chemotherapy and radiotherapy, creates a major obstacle during metastatic breast cancer therapy. Although D-ribo-phytosphingosine (PHS) is well known to activate protein kinase (MAPK)-mediated apoptosis, its possible role towards the metastasis signaling mechanisms underlying the epithelial-mesenchymal transition (EMT) remains largely unknown. In this report, we investigate the anti-metastatic potential of the natural sphingolipid PHS for the targeting of breast cancer cells as well as breast stem-like cells in vitro. We showed that PHS led to suppression of migratory potential, spheroid formation, CD44^high/CD24^low subpopulation as well as stem cell- and EMT-associated protein expression in basal type highly malignant breast cancer cell lines. In addition, PHS-based inhibition of EMT was attributable to the downregulation of the EGFR/JAK1/STAT3 signaling axis, as validated by immunoprecipitation assays and breast tumorigenesis mice models. This study demonstrate that PHS can target metastatic tumors with dual specificity (EMT and cancer stem-like cells) and therefore may be serve as a promising candidate for breast cancer treatments.

Tissue-based associations of mammographic breast density with breast stem cell markers

Background

Mammographic breast density is a well-established, strong breast cancer risk factor but the biology underlying this association remains unclear. Breast density may reflect underlying alterations in the size and activity of the breast stem cell pool. We examined, for the first time, associations of CD44, CD24, and aldehyde dehydrogenase family 1 member A1 (ALDH1A1) breast stem cell markers with breast density.

Methods

We included in this study 64 asymptomatic healthy women who previously volunteered for a unique biopsy study of normal breast tissue at the Mayo Clinic (2006-2008). Mammographically identified dense and non-dense areas were confirmed/localized by ultrasound and biopsied. Immunohistochemical analysis of the markers was performed according to a standard protocol and the staining was assessed by a single blinded pathologist. In core biopsy samples retrieved from areas of high vs. low density within the same woman, we compared staining extent and an expression score (the product of staining intensity and extent), using the signed rank test. All tests of statistical significance were two-sided.

Results

A total of 64, 28, and 10 women were available for CD44, CD24, and ALDH1A1 staining, respectively. For all three markers, we found higher levels of staining extent in dense as compared to non-dense tissue, though for CD24 and ALDH1A1 the difference did not reach statistical significance (CD44, 6.3% vs. 2.0%, p < 0.001; CD24, 8.0% vs. 5.6%, p = 0.10; and ALDH1A1, 0.5% vs. 0.3%, p = 0.12). The expression score for CD44 was significantly greater in dense as compared to non-dense tissue (9.8 vs.3.0, p < 0.001).

Conclusions

Our findings suggest an increased presence and/or activity of stem cells in dense as compared to non-dense breast tissue.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0889-3) contains supplementary material, which is available to authorized users.

Stathmin1 expression is associated with aggressive phenotypes and cancer stem cell marker expression in breast cancer patients

Stathmin1 (STMN1) regulates progression in various cancers. The present study aimed to determine the relationship between STMN1 expression and several cancer-related markers in breast cancer. Using immunohistochemistry, we evaluated STMN1, estrogen receptor, progesterone receptor, human epidermal growth factor receptor 2, Ki-67, epidermal growth factor receptor (EGFR), CK5/6, CD44, CD24, aldehyde dehydrogenase 1, E-cadherin, epithelial cell adhesion molecule, and vimentin in 237 breast cancer patients and the clinical significance of STMN1. STMN1 expression was evaluated in 51 breast cancer cell lines, and the prognostic value of STMN1 was calculated. Higher STMN1 expression was detected in cancer tissues and was predominantly localized in the cytoplasm. High STMN1 expression was associated with the triple negative subtype, nuclear grade progression, high expression of Ki-67, EGFR, CK5/6, E-cadherin and high CD44/low CD24. According to gene expression-based outcome for breast cancer online and the Kaplan-Meier plotter, STMN1 expression was higher in basal-type cell lines than in luminal-type cell lines, and overall survival and post-progression survival in the high STMN1 expression breast cancer patients were shorter than in low STMN1 expression patients. High STMN1 expression is a possible marker of breast cancer aggressiveness in association with proliferation, phenotype and cancer stem cell type.

Cancer stem cell marker glycosylation: Nature, function and significance

Glycans are essential for the maintenance of normal biological function, with alterations in glycan expression being a hallmark of cancer. Cancer stem cells (CSCs) are a subset of cells within a tumour capable of self-renewal, cellular differentiation and resistances to conventional therapies. As is the case with stem cells, marker proteins present on the cell surface are frequently used to identify and enrich CSCs, with the expression of these markers statistical correlating with the likelihood of cancer recurrence and overall patient survival. As such CSC markers are of high clinical relevance. The majority of markers currently used to identify CSC populations are glycoproteins, and although the diverse biological roles for many of these markers are known, the nature and function of the glycan moiety on these glycoproteins remains to be fully elucidated. This mini-review summarises our current knowledge regarding the types and extent of CSC marker glycosylation, and the various roles that these glycans play in CSC biology, including in mediating cell adhesion, metastasis, evading apoptosis, tear shear resistance, tumour growth, maintaining pluripotency, self-renewal, trafficking, maintaining stability, maintaining enzymatic activity and aiding epithelial mesenchymal transitioning. Given that CSCs markers have multiple diverse biological functions, and are potentially of significant diagnostic and therapeutic benefit the search for new markers that are uniquely expressed on CSCs is vital to selectively target/identify this subset of cancer cells. As such we have also outlined how high-throughput lectin microarrays can be used to successfully profile the glycosylation status of CSC and to identify glyco-markers unique to CSCs.

Stemness-Related Markers in Cancer

Cancer stem cells (CSCs), with their self-renewal ability and multilineage differentiation potential, are a critical subpopulation of tumor cells that can drive tumor initiation, growth, and resistance to therapy. Like embryonic and adult stem cells, CSCs express markers that are not expressed in normal somatic cells and are thus thought to contribute towards a 'stemness' phenotype. This review summarizes the current knowledge of stemness-related markers in human cancers, with a particular focus on important transcription factors, protein surface markers and signaling pathways.

Caspase14 expression is associated with triple negative phenotypes and cancer stem cell marker expression in breast cancer patients

BACKGROUND AND OBJECTIVES

The Caspase14 (CASP14) was reported that the low expression of CASP14 in ovarian cancer and colon cancer was associated with cancer progression, on the other hand, that the CASP14 expression in breast cancer was higher than that of non-cancerous tissues. The purpose of this study is to determine the clinical significance of CASP14 in breast cancer.

METHODS

We performed immunohistochemistry for CASP14, ER, PgR, HER2, Ki67, EGFR, CK5/6, CD44, CD24, ALDH1, claudins, and androgen receptor in 222 breast cancer patients including 55 TNBC cases, and evaluated the relationship of CASP14, above-mentioned markers, and prognosis. Using public microarray database of breast cancer, the prognostic value of CASP14 was calculated.

RESULTS

High CASP14 expression was significantly associated with TNBC subtype (P = 0.015), nuclear grade (P = 0.006), Ki67, EGFR (P < 0.001, P = 0.016), ALDH1, CD44 and CD24 (P < 0.001, P < 0.001, P = 0.001) in 222 breast cancer cases, and the high expression of claudin1 (P = 0.017), and androgen receptor (P = 0.002) in TNBC cases was related to the high CASP14. According to the public database, survival in the high CASP14 breast cancer patients was shorter than low CASP14 patients.

CONCLUSIONS

High CASP14 expression is a marker of breast cancer aggressiveness in association with proliferation, TNBC phenotype, and cancer stemness.

Clinicopathological and prognostic value of CD24 expression in breast cancer: a meta-analysis

BACKGROUND

A number of studies have been conducted to explore the relationship between CD24 expression and the prognosis of breast cancer; however, the results remain inconsistent. Therefore, we performed this meta-analysis to clarify the impact of CD24 expression on clinicopathological features and prognosis of breast cancer.

METHODS

A comprehensive literature search for relevant studies was performed, and statistical analysis was conducted using Stata software.

RESULTS

Twenty studies, including 5,179 cases, were included in this meta-analysis. The pooled analysis indicated that CD24 expression was associated with lymph node invasion (odds ratio [OR] = 0.68, for negative vs. positive, 95% confidence interval [95% CI], 0.53-0.87, p = 0.002) and TNM stage (OR = 0.63, for I + II vs. III + IV, 95% CI, 0.49-0.81, p<0.001). The prognosis analysis also suggested CD24 overexpression indicated a poorer 5-year overall survival (OS) rate (relative risk ratio [RR] = 0.93, 95% CI, 0.86-0.99, p = 0.03) and 5-year disease-free survival (DFS) rate (RR = 0.90, 95% CI, 0.83-0.98, p = 0.02). However, CD24 expression had no correlation with tumor size, tumor grade, distance metastasis, estrogen receptor (ER) status, progesterone receptor (PR) status, or HER2 status.

CONCLUSIONS

Our results suggest that higher CD24 expression is significantly associated with lower OS rate, lower DFS rate and some clinicopathological factors such as lymph node invasion and TNM stage. This meta-analysis suggested that CD24 is an efficient prognostic factor in breast cancer.

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.

H19/let-7/LIN28 reciprocal negative regulatory circuit promotes breast cancer stem cell maintenance

Long noncoding RNA-H19 (H19), an imprinted oncofetal gene, has a central role in carcinogenesis. Hitherto, the mechanism by which H19 regulates cancer stem cells, remains elusive. Here we show that breast cancer stem cells (BCSCs) express high levels of H19, and ectopic overexpression of H19 significantly promotes breast cancer cell clonogenicity, migration and mammosphere-forming ability. Conversely, silencing of H19 represses these BCSC properties. In concordance, knockdown of H19 markedly inhibits tumor growth and suppresses tumorigenesis in nude mice. Mechanistically, we found that H19 functions as a competing endogenous RNA to sponge miRNA let-7, leading to an increase in expression of a let-7 target, the core pluripotency factor LIN28, which is enriched in BCSC populations and breast patient samples. Intriguingly, this gain of LIN28 expression can also feedback to reverse the H19 loss-mediated suppression of BCSC properties. Our data also reveal that LIN28 blocks mature let-7 production and, thereby, de-represses H19 expression in breast cancer cells. Appropriately, H19 and LIN28 expression exhibits strong correlations in primary breast carcinomas. Collectively, these findings reveal that lncRNA H19, miRNA let-7 and transcriptional factor LIN28 form a double-negative feedback loop, which has a critical role in the maintenance of BCSCs. Consequently, disrupting this pathway provides a novel therapeutic strategy for breast cancer.