Termed Cancer Stem Cells Research Articles

Extracellular vesicles in non-small cell lung cancer stemness and clinical applications.

Non-small cell lung carcinoma (NSCLC) accounts for 85% of lung cancers, the leading cause of cancer associated deaths in the US and worldwide. Within NSCLC tumors, there is a subpopulation of cancer cells termed cancer stem cells (CSCs) which exhibit stem-like properties that drive NSCLC progression, metastasis, relapse, and therapeutic resistance. Extracellular vesicles (EVs) are membrane-bound nanoparticles secreted by cells that carry vital messages for short- and long-range intercellular communication. Numerous studies have implicated NSCLC CSC-derived EVs in the factors associated with NSCLC lethality. In this review, we have discussed mechanisms of EV-directed cross-talk between CSCs and cells of the tumor microenvironment that promote stemness, tumor progression and metastasis in NSCLC. The mechanistic studies discussed herein have provided insights for developing novel NSCLC diagnostic and prognostic biomarkers and strategies to therapeutically target the NSCLC CSC niche.

TMIC-79. LIPOCALIN-2 MEDIATES CELL-INTRINSIC FUNCTIONS IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) is the most common primary brain tumor with a median survival of 17-20 months. Despite therapeutic treatments including surgery, radiation, chemotherapy, a population of GBM cells, termed cancer stem cells (CSCs) are radio-resistant and chemo-resistant, leading to mortality of the patient. CSCs also have altered metabolic profiles and have an enhanced capacity to scavenge nutrients from their microenvironment, including iron. Lipocalin-2 (LCN2) functions to sequester iron and is traditionally considered an inflammatory marker through its function of limiting iron for bacterial usage; it has also been described to have both a pro and anti-tumorigenic and has context-dependent functions depending on iron status. LCN2 has been shown to be important in brain metastasis, but its role in GBM is still largely unknown. To assess a cell-intrinsic function for LNC2, we added recombinant LCN2 to low LCN2-secreting mouse GBM cell models and observed that proliferation also increased. When we knocked down LCN2 in our higher LCN2 secreting cell lines, we observed that knockdown cells had decreased viability and growth, which was not mediated by apoptosis, but rather, ferroptosis. When these cells were subsequently engrafted into wild-type mice, we observed an increase in survival. This effect was also phenocopied when the cells were implanted into LCN2 knockout mice, suggesting the tumor-intrinsic effect overpowered the global knockout model. Lastly, to investigate how LCN2 plays a role in the GBM microenvironment, we orthotopically implanted syngeneic mouse GBM cells into male and female LCN2 knockout and wild-type mice. We observed no survival difference, further suggesting that LCN2 does not function in an extrinsic manner. Taken together, these data suggest that LCN2 affects proliferation and tumorigenesis, and is another avenue to understanding the complexity of GBM biology. Strategies to reduce LCN2 in GBM may provide a therapeutic target for GBM in the future.

TMIC-82. LIPOCALIN-2 MEDIATES CELL-INTRINSIC AND CELL-EXTRINSIC FUNCTIONS IN GLIOBLASTOMA

Abstract Glioblastoma (GBM) is the most common primary brain tumor with a median survival of 17-20 months. Despite therapeutic treatments including surgery, radiation, chemotherapy, a subset of GBM clones, termed cancer stem cells (CSCs) are radio-resistant and chemo-resistant, leading to mortality of the patient. CSCs also have altered metabolic profiles and have an enhanced capacity to scavenge nutrients from their microenvironment, including iron. Lipocalin-2 (LCN2) functions to sequester iron and is traditionally considered an inflammatory marker through its function of limiting iron for bacterial usage. LCN2 has been described to have both a pro and anti-tumorigenic and has context-dependent functions depending on iron status. LCN2 has been shown to be important in brain metastasis, but its role in GBM is still largely unknown. To investigate how LCN2 plays a role in the GBM microenvironment, we orthotopically implanted syngeneic mouse GBM cells into male and female LCN2 knockout and wild-type mice. Female LCN2 knockout mice succumbed to tumors faster compared to males, revealing another example of sex differences in the tumor microenvironment. To assess a cell-intrinsic function for LNC2, we added recombinant LCN2 to mouse GBM cell lines and saw that proliferation also increased. When we probed for receptor expression in our knockdown cell lines, we saw that the LCN2 canonical receptor, SLC22a17, was upregulated in response. Furthermore, in a subset of slow-cycling cells of CSCs, LCN2 was shown to be up-regulated. Taken together, these data suggest that LCN2 functions in an iron-dependent manner to affect proliferation and sex-specific tumorigenesis. Given the fact that males have more iron than females, it is worth investigating the role of iron in GBM sex difference progression and therapeutic targets.

BIOM-22. BMX EXPRESSION LEVEL IN GLIOBLASTOMA PREDICTS HYPERSENSITIVITY TO IBRUTINIB TREATMENT

Abstract Glioblastoma (GBM) is the most prevalent and aggressive form of primary brain cancer and is notoriously drug and radiation resistant. The tumor recurrence and therapeutic resistance typically seen in GBM are largely driven by a small population of self-renewing, highly tumorigenic cells termed cancer stem cells (CSCs). The stem-cell-like properties of GBM CSCs are promoted, at least in part, by abnormal activation of the Janus kinase/signal transducer and activator of transcription 3 (JAK/STAT3) signaling pathway. This activation can occur through aberrant expression of bone marrow and X-linked (BMX) protein, a non-receptor tyrosine kinase that is upregulated in glioma stem cells and may be targeted by the drug ibrutinib, currently undergoing clinical trials in GBM. In contrast, BMX is not expressed in normal non-cancerous stem cells of the brain. We discovered a striking dissimilarity where a subset of our patient-derived GBM specimens are up to 100-fold more sensitive to ibrutinib than others. We investigated the mechanisms behind this hypersensitivity by analyzing the expression levels of JAK/STAT3 signaling proteins. Here we discovered that the baseline expression value of BMX prior to treatment has a strikingly high predictive value for later later response to ibrutinib, primarily explaining the variation in a specimen’s ibrutinib sensitivity. Furthermore, we found that pediatric GBM tumor models are typically BMX-low and most likely to be hypersensitive to ibrutinib compared to their adult counterparts. Ibrutinib further suppresses GBM and DIPG proliferation in CSC-rich proliferative regions of organoid models. Our data suggest the potential use of BMX as a predictive biomarker of ibrutinib sensitivity, and provide an impetus for mechanistic and preclinical investigation of ibrutinib sensitivity, particularly in pediatric disease.

Abstract 889: NF-κB-mediated mitophagy contributes to the maintenance of cancer stem cells in ovarian cancer

Abstract Tumors contain phenotypically and functionally heterogeneous cancer cells. Among them, a minority of cell subpopulation, termed cancer stem cells (CSCs), which possess the self-renewal capacity and are able to generate the heterogeneous lineage of cancer cells, has been believed to be responsible for the initiation and progression of the tumor. However, it is still unclear how the stemness properties of CSCs are maintained in the tumor. Mitophagy is a process by which damaged mitochondria are cleared via autophagy. The significance of mitophagy in the maintenance of CSC has been investigated in multiple CSC types. Our recent study shows that ovarian CSCs also exhibit enhanced mitophagy, which is mainly attributed to elevated expression of mitophagy receptors BNIP3 and BNIP3L. Downregulation of BNIP3 or BNIP3L significantly diminished mitophagy in ovarian CSCs and compromised their self-renewal capability. Mechanistic investigation further revealed that enhanced NF-κB signaling contributes to the increased expression of BNIP3 and BNIP3L. Inhibition of NF-κB signaling pathway via p65 knockdown or specific inhibitors is able to reduce mitophagy in ovarian CSCs. In summary, our data suggest that selective inhibition of NF-κB is able to deplete CSCs by interfering with mitochondria quality control in these cells and has potential to prevent tumor relapse and metastasis. Citation Format: Na Li, Tejinder Pal, Shurui Cai, Ananya Banerjee, Xuetao Bai, Kousalya Lavudi, Qi-En Wang. NF-κB-mediated mitophagy contributes to the maintenance of cancer stem cells in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 889.

Identification and Characterization of Canine Mammary Tumors Stem Cells: A Review

Glands cancers consider the most types of cancers in males or females or both. Many challenges are present in controlling cancers in dogs, the first one is related to populations of tumour cells define as cancer stem cells, cancer cells are resistant to chemotherapy and have the ability to metastasise and returned after successful treatment. Cancer consists of different cells that contain a subtype of cell with stemness characteristics, like high tumourigenicity, the self-renew ability to differentiate and resistance to chemo and radiotherapy. These cells are termed cancer stem cells (CSCs) and are involved in the initiation of tumours, recurrence and metastasis. Canine mammary cell tumours are malignant neoplasms characterized by metastasis and a high infiltration rate. Canine mammary tumours (CMT) occur in female dogs frequently, six to seven (6-7) years old animals ages are more susceptible to the disease, however, it can be diagnosed at 9–11 years of age, which is known as the cancer age, it has the ability to form tumours spheres which are considered a characteristic of stem cells. it is difficult to clarify the histological finding base on Hematoxyline and Eosin stains policy, so biomarkers are recommended like CD44+and CD24- ,also Immunohistochemistry . These tumours are composed of mesenchymal cells and\or myoepithelial cells with proliferative luminal epithelial cells, cartilage, and osseous tissues. Annually around the world, between 200-250 mammary gland tumours out of 100.000 female dogs, 50% were malignant. Surgical removal is the treatment of choice, however, it is ineffective because of the metastasis high rate. It is important to focus on the analysis of CSCs high incidences in dogs (bitches) and CSCs isolation and diagnosis.

Store-Operated Calcium Entry and Its Implications in Cancer Stem Cells.

Tumors are composed by a heterogeneous population of cells. Among them, a sub-population of cells, termed cancer stem cells, exhibit stemness features, such as self-renewal capabilities, disposition to differentiate to a more proliferative state, and chemotherapy resistance, processes that are all mediated by Ca2+. Ca2+ homeostasis is vital for several physiological processes, and alterations in the patterns of expressions of the proteins and molecules that modulate it have recently become a cancer hallmark. Store-operated Ca2+ entry is a major mechanism for Ca2+ entry from the extracellular medium in non-excitable cells that leads to increases in the cytosolic Ca2+ concentration required for several processes, including cancer stem cell properties. Here, we focus on the participation of STIM, Orai, and TRPC proteins, the store-operated Ca2+ entry key components, in cancer stem cell biology and tumorigenesis.

Niclosamide induces miR-148a to inhibit PXR and sensitize colon cancer stem cells to chemotherapy.

SummaryTumor recurrence is often attributed to cancer stem cells (CSCs). We previously demonstrated that down-regulation of Pregnane X Receptor (PXR) decreases the chemoresistance of CSCs and prevents colorectal cancer recurrence. Currently, no PXR inhibitor is usable in clinic. Here, we identify miR-148a as a targetable element upstream of PXR signaling in CSCs, which when over-expressed decreases PXR expression and impairs tumor relapse after chemotherapy in mouse tumor xenografts. We then develop a fluorescent reporter screen for miR-148a activators and identify the anti-helminthic drug niclosamide as an inducer of miR-148a expression. Consequently, niclosamide decreased PXR expression and CSC numbers in colorectal cancer patient-derived cell lines and synergized with chemotherapeutic agents to prevent CSC chemoresistance and tumor recurrence in vivo. Our study suggests that endogenous miRNA inducers is a viable strategy to down-regulate PXR and illuminates niclosamide as a neoadjuvant repurposing strategy to prevent tumor relapse in colon cancer.

Hypoxia induction of SH2D3A triggers malignant progression of lung cancer.

Lung cancer is the most prevalent and aggressive cancer and is one of the leading causes of cancer-related death worldwide. Hypoxia in the tumor microenvironment is associated with poor patient survival and is a crucial characteristic of solid tumors. A subset of tumor cells, termed cancer stem cells (CSCs), with self-renewal and differentiation capabilities simultaneously, are regarded as responsible for cancer tumorigenesis, resistance to therapeutics, and cancer relapse. Recent advances have revealed that hypoxia plays an essential role in CSCs self-replication maintenance. Yet, the underlying mechanisms of hypoxia that trigger the stemness maintenance of CSCs are still poorly understood. Here, we provide evidence showing that SH2D3A expression level was increased in lung cancer and lung CSCs, and high expression of SH2D3A was associated with the overall survival of patients with lung cancer. Mechanistically, HIF-2α, which is a key transcription factor in response to hypoxia directly binds to the SH2D3A promoter and facilitates SH2D3A expression at the transcription level. SH2D3A was found to be functionally important for lung CSC malignant behaviors such as uncontrolled self-replication and proliferation. We demonstrated that pharmacological downregulation of SH2D3A expression by AM966, a small molecule compound, efficiently induces tumor regression in vitro and in vivo. Thus, this study highlights the biological implications of SH2D3A as a novel prognostic marker and therapeutic target in lung cancer in the future.

Oral Cancer Stem Cells: Therapeutic Implications and Challenges.

Head and neck squamous cell carcinoma (HNSCC) is currently one of the 10 most common malignancies worldwide, characterized by a biologically highly diverse group of tumors with non-specific biomarkers and poor prognosis. The incidence rate of HNSCC varies widely throughout the world, with an evident prevalence in developing countries such as those in Southeast Asia and Southern Africa. Tumor relapse and metastasis following traditional treatment remain major clinical problems in oral cancer management. Current evidence suggests that therapeutic resistance and metastasis of cancer are mainly driven by a unique subpopulation of tumor cells, termed cancer stem cells (CSCs), or cancer-initiating cells (CICs), which are characterized by their capacity for self-renewal, maintenance of stemness and increased tumorigenicity. Thus, more understanding of the molecular mechanisms of CSCs and their behavior may help in developing effective therapeutic interventions that inhibit tumor growth and progression. This review provides an overview of the main signaling cascades in CSCs that drive tumor repropagation and metastasis in oral cancer, with a focus on squamous cell carcinoma. Other oral non-SCC tumors, including melanoma and malignant salivary gland tumors, will also be considered. In addition, this review discusses some of the CSC-targeted therapeutic strategies that have been employed to combat disease progression, and the challenges of targeting CSCs, with the aim of improving the clinical outcomes for patients with oral malignancies. Targeting of CSCs in head and neck cancer (HNC) represents a promising approach to improve disease outcome. Some CSC-targeted therapies have already been proven to be successful in pre-clinical studies and they are now being tested in clinical trials, mainly in combination with conventional treatment regimens. However, some studies revealed that CSCs may not be the only players that control disease relapse and progression of HNC. Further, clinical research studying a combination of therapies targeted against head and neck CSCs may provide significant advances.

FTY720 Inhibits Expansion of Breast Cancer Stem Cells via PP2A Activation.

Growing evidence suggests that breast cancer originates from a minor population of cancer cells termed cancer stem cells (CSCs), which can be identified by aldehyde dehydrogenase (ALDH) activity-based flow cytometry analysis. However, novel therapeutic drugs for the eradication of CSCs have not been discovered yet. Recently, drug repositioning, which finds new medical uses from existing drugs, has been expected to facilitate drug discovery. We have previously reported that sphingosine kinase 1 (SphK1) induced proliferation of breast CSCs. In the present study, we focused on the immunosuppressive agent FTY720 (also known as fingolimod or Gilenya), since FTY720 is known to be an inhibitor of SphK1. We found that FTY720 blocked both proliferation of ALDH-positive cells and formation of mammospheres. In addition, we showed that FTY720 reduced the expression of stem cell markers such as Oct3/4, Sox2 and Nanog via upregulation of protein phosphatase 2A (PP2A). These results suggest that FTY720 is an effective drug for breast CSCs in vitro.

Pluripotent Stem Cells: Cancer Study, Therapy, and Vaccination.

IntroductionPluripotent stem cells (PSCs) are promising tools for modern regenerative medicine applications because of their stemness properties, which include unlimited self-renewal and the ability to differentiate into all cell types in the body. Evidence suggests that a rare population of cells within a tumor, termed cancer stem cells (CSCs), exhibit stemness and phenotypic plasticity properties that are primarily responsible for resistance to chemotherapy, radiotherapy, metastasis, cancer development, and tumor relapse. Different therapeutic approaches that target CSCs have been developed for tumor eradication.Results and DiscussionIn this review, we first provide an overview of different viewpoints about the origin of CSCs. Particular attention has been paid to views believe that CSCs are probably appeared through dysregulation of very small embryonic-like stem cells (VSELs) which reside in various tissues as the main candidate for tissue-specific stem cells. The expression of pluripotency markers in these two types of cells can strengthen the validity of this theory. In this regard, we discuss the common properties of CSCs and PSCs, and highlight the potential of PSCs in cancer studies, therapeutic applications, as well as educating the immune system against CSCs.ConclusionIn conclusion, the resemblance of CSCs to PSCs can provide an appropriate source of CSC-specific antigens through cultivation of PSCs which brings to light promising ideas for prophylactic and therapeutic cancer vaccine development.Graphical

The tumor stem cell niche of head and neck - point of intersection with therapeutic potential?

An increasing amount of evidence suggests the existence of a stem cell-like population in head and neck squamous cell carcinoma (HNSCC). These cells have been termed cancer stem cells (CSC) due to the shared properties with somatic stem cells, such as the ability to self-renew and differentiate. Furthermore, the CSC are thought to be resistant to antineoplastic treatments and are therefore clinically relevant. As with somatic stem cells, CSC are thought to reside in a specialized supportive microenvironment, called the stem cell niche. One possible strategy to target the CSC could be through affecting functions of the stem cell niche.Stromal cell-derived factor-1 (SDF-1) is a multifunctional cytokine, which is secreted by e. g. stromal cells within the niche. SDF-1 is known to be the major regulator of stem cell trafficking between the niche and the peripheral vascular system. Itelicits the chemotactic activity through interaction with atransmembrane receptor CXCR4, expressed by CSC. The SDF-1-CXCR4-axis is thought to play a crucial role in the interaction between CSC and their supportive cells in the tumor niche. A better understanding of these interactions could help in gaining further insight into the pathophysiology of progression/recurrence of malignant diseases and aid in finding new strategies for therapy.Specialized cell culture models are of advantage for deciphering the mechanisms of interaction between CSC and their niche. We anticipate that the recent technological advancements in bioprinting and the development of complex 3D cell culture model systems will contribute to our understanding of these mechanisms and to the establishment of individualized therapies.Here were provide an overview of the current knowledge on the CSC-tumor stem cell niche interactions in HNSCC with a focus on the SDF-1-CXCR4 axis.

Epigenetic regulation of cancer stem cell formation and maintenance.

Cancerous tumours contain a rare subset of cells with stem‐like properties that are termed cancer stem cells (CSCs). CSCs are defined by their ability to divide both symmetrically and asymmetrically, to initiate new tumour growth and to tolerate the foreign niches required for metastatic dissemination. Accumulating evidence suggests that tumours arise from cells with stem‐like properties, the generation of CSCs is therefore likely to be an initiatory event in carcinogenesis. Furthermore, CSCs in established tumours exist in a dynamic and plastic state, with nonstem tumour cells thought to be capable of de‐differentiation to CSCs. The regulation of the CSC state both during tumour initiation and within established tumours is a desirable therapeutic target and is mediated by epigenetic factors. In this review, we will explore the epigenetic parallels between induced pluripotency and the generation of CSCs, and discuss how the epigenetic regulation of CSCs opens up novel opportunities for therapeutic intervention.

Targeting Cancer Stem Cells and Metastasis with Epigenetic Modulation and Anti-HER2 Therapy: Phase I/II Trial of Vorinostat in Combination with Lapatinib

Purpose: Considerable preclinical and clinical data indicate that only a small subset of tumor cells has longterm proliferating capacity. These cells are termed cancer stem cells (CSCs). Failure to eradicate CSCs is hypothesized to be a cause of cancer recurrence after potentially curative therapies. Therefore, approaches that target CSCs have the potential to improve outcomes. We evaluated the combination of vorinostat and lapatinib to target CSCs and metastasis. Experimental Design: We conducted preclinical studies and a phase I/II clinical trial to determine the effects of vorinostat and lapatinib to CSCs. Results: Our preclinical studies demonstrated that vorinostat and lapatinib further reduced CSCs compared to either single agent. Reduction in self-renewal proteins, mammospheres, epithelial-mesenchymal transition (EMT) markers, and cell migration was also observed. Based on these findings, the combination was evaluated in the phase I trial to which a total of 12 patients were enrolled. Dose-limiting toxicity was not observed in phase I, and the recommended phase II dose was vorinostat 400 mg 4 days on 3 days off and lapatinib 1,250 mg daily. In HER2-positive breast cancer patients, the clinical benefit rate was observed in 43% of subjects. Interestingly, patients who remained on vorinostat and lapatinib did not develop any new site of metastasis. Conclusion: The combination of vorinostat and lapatinib is safe and active in HER2-positive breast cancer. Further studies are needed to evaluate this strategy to target CSCs and metastasis.

Metabolic Escape Routes of Cancer Stem Cells and Therapeutic Opportunities.

Although improvement in early diagnosis and treatment ameliorated life expectancy of cancer patients, metastatic disease still lacks effective therapeutic approaches. Resistance to anticancer therapies stems from the refractoriness of a subpopulation of cancer cells—termed cancer stem cells (CSCs)—which is endowed with tumor initiation and metastasis formation potential. CSCs are heterogeneous and diverge by phenotypic, functional and metabolic perspectives. Intrinsic as well as extrinsic stimuli dictated by the tumor microenvironment (TME)have critical roles in determining cell metabolic reprogramming from glycolytic toward an oxidative phenotype and vice versa, allowing cancer cells to thrive in adverse milieus. Crosstalk between cancer cells and the surrounding microenvironment occurs through the interchange of metabolites, miRNAs and exosomes that drive cancer cells metabolic adaptation. Herein, we identify the metabolic nodes of CSCs and discuss the latest advances in targeting metabolic demands of both CSCs and stromal cells with the scope of improving current therapies and preventing cancer progression.

Cancer Stem Cell Plasticity - A Deadly Deal.

Intratumoral heterogeneity is a major ongoing challenge in the effective therapeutic targeting of cancer. Accumulating evidence suggests that a fraction of cells within a tumor termed Cancer Stem Cells (CSCs) are primarily responsible for this diversity resulting in therapeutic resistance and metastasis. Adding to this complexity, recent studies have shown that there can be different subpopulations of CSCs with varying biochemical and biophysical traits resulting in varied dissemination and drug-resistance potential. Moreover, cancer cells can exhibit a high level of plasticity or the ability to dynamically switch between CSC and non-CSC states or among different subsets of CSCs. In addition, CSCs also display extensive metabolic plasticity. The molecular mechanisms underlying these different interconnected axes of plasticity has been under extensive investigation and the trans-differentiation process of Epithelial to Mesenchymal transition (EMT) has been identified as a major contributing factor. Besides genetic and epigenetic factors, CSC plasticity is also shaped by non-cell-autonomous effects such as the tumor microenvironment (TME). In this review, we discuss the latest developments in decoding mechanisms and implications of CSC plasticity in tumor progression at biochemical and biophysical levels, and the latest in silico approaches being taken for characterizing cancer cell plasticity. These efforts can help improve existing therapeutic approaches by taking into consideration the contribution of cellular plasticity/heterogeneity in enabling drug resistance.

Cancer stem cell enrichment is associated with enhancement of nicotinamide N-methyltransferase expression.

The cancer stem cell theory states that a subset of tumor cells, termed cancer stem cells (CSCs), has the ability to self-renew and differentiate within the tumors. According to this theory, CSCs would be mainly responsible for tumor initiation, progression, resistance to therapy, recurrence, and metastasis. In this study, a culture system was setup to enrich CSCs from bladder cancer (T24), lung cancer (A549), colorectal cancer (CaCo-2), and osteosarcoma (MG63) cell lines, through sphere formation. Magnetic-activated cell sorting was also used to further increase CSC enrichment. Subsequently, molecular characterization of CSC-enriched cell populations and parental cells was carried out, by exploring the expression levels of stem markers and the enzyme nicotinamide N-methyltransferase (NNMT). Results obtained showed a significant upregulation of stem cell markers in CSC-enriched populations, obtained upon sphere formation, compared with parental counterparts. Moreover, NNMT expression levels were markedly increased in samples enriched with CSCs with respect to control cells. Considering the fundamental role played by CSCs in carcinogenesis, reported data strengthen the hypothesis that sustains a pivotal role of NNMT in cancer growth and metastasis. In addition, these findings could represent an important achievement for the development of new and effective anticancer therapies, based on CSC-associated targets.

Nuclear Factor Erythroid-Derived 2-Like 2-Induced Reductive Stress Favors Self-Renewal of Breast Cancer Stem-Like Cellsviathe FoxO3a-Bmi-1 Axis

Aims: A subpopulation of cancer cells, termed cancer stem cells (CSCs), has stemness properties, such as self-renewal and differentiation, which drive cancer recurrence and tumor resistance. CSCs possess enhanced protection capabilities to maintain reduced intracellular levels of reactive oxygen species (ROS) compared with nonstem-like cancer cells. This study investigated whether reductive stress could regulate self-renewal activity in breast CSCs. Results: We found that manifestation of stemness in breast cancer stem-like cells was associated with an elevated production of reduced glutathione (GSH) maintained by upregulation of glutamate cysteine ligase catalytic subunit (GCLC) and consequently, lowered ROS levels. This was accompanied by upregulation of phospho-AMP-activated protein kinase, FoxO3a, and Bmi-1. Notably, expression of nuclear factor erythroid-derived 2-like 2 (Nrf2) protein was substantially increased in cells undergoing sphere formation. We noticed that expression of Bmi-1 was inhibited after introduction of Nrf2 short interfering RNA into MCF-7 mammosphere cells. Silencing of Nrf2 expression suppressed the xenograft growth of subcutaneously or orthotopically injected human breast cancer cells. Innovation: Association between Nrf2 and self-renewal signaling in CSCs has been reported, but the underlying molecular mechanism remains largely unresolved. This study demonstrates the Nrf2-mediated signaling pathway in maintenance of reductive stress in breast CSCs. Conclusion: Nrf2 overactivation in breast CSCs upregulates GCLC expression and consequently enhances GSH biosynthesis with concurrent reduction in intracellular ROS accumulation, thereby provoking the reductive stress. The consequent upregulation of nuclear FoxO3a and its binding to the promoter of the gene encoding Bmi-1 account for the self-renewal activity of breast cancer stem-like cells and their growth in a xenograft mouse model.

338P - A new insight into tumour immune-evasion: Crosstalk between cancer stem cells and T regulatory cells

BackgroundCancer development is aggravated by a rare population of cells, termed cancer stem cells (CSCs), that uniquely initiates and sustains the disease. Although CSCs can orchestrate the immune systems in favour of tumor, the detailed mechanisms underlying their immunomodulatory effects remain elusive. Recent reports indicate the contribution of exosomes, secreted from various cells, as mediators of cell-to-cell communication and also as a mediator of immune modulation in the tumor microenvironment. MethodsBreast CSCs (bCSCs) were purified from breast cancer cell lines and human breast tumor tissues following which CSC-derived exosomes (CDEs) were isolated. Peripheral blood mononuclear cells were isolated from the blood of healthy donors and breast cancer patients, co-cultured with CDEs, and T regulatory (Treg) cell generation was evaluated. ResultsWe found that bCSCs are able to generate CD4+CD25+FOXP3+ Treg cells having suppressive activity. Our search for the underlying mechanism revealed for the first time that bCSC-secreted exosomes contain FOXP3 protein that uniquely initiates acquisition of Treg characteristics in the infiltrating T lymphocytes. Exosomes from FOXP3-ablated bCSCs failed to augment Treg cell generation indicating the requirement of bCSC-gifted FOXP3 in Treg generation. Interestingly, perturbation of transcription or translation in T naïve cells significantly decreased CDE-augmented FOXP3 level signifying that CDE-FOXP3 utilizes the transcription and translational machineries of T naïve cells to induce Treg cell generation. In fact, exosome-shuttled FOXP3 binds to the CNS2 region of the Foxp3 promoter in T lymphocytes, thus resulting in a sustained expression of FOXP3 and further leading to induction of other genes of Foxp3 interactome, thereby phenotypically converting the T cells to Treg cells. ConclusionsCollectively our data demonstrates that bCSC-shed exosomal FOXP3 plays an important role in procreation of Treg cells within the tumor microenvironment thus leading to tumor-induced immune suppression. Breaching the deadly-liaison between them might be a promising strategy for breast cancer therapy. Legal entity responsible for the studyProf. Tanya Das, Professor, Division of Molecular Medicine, Bose Institute. FundingDepartment of Science and Technology, Govt. of Inda Council of Scientific & Industrial Research (CSIR), Govt. of India. DisclosureAll authors have declared no conflicts of interest.