Regulation Of Cancer Stem Cells Research Articles

Cell scientist to watch – Lena Ho

ABSTRACT Lena Ho studied biochemistry at the University of Wisconsin–Madison, USA, funded by a scholarship from the Singapore Economic Development Board. Lena then joined the lab of Gerald Crabtree at Stanford University for her PhD, where she investigated the function and mechanism of chromatin remodelling proteins in the epigenetic regulation of embryonic, haematopoietic and cancer stem cells. She then moved back to Singapore for a postdoc in Bruno Reversade's lab at the Institute of Medical Biology, A*STAR, where she found that some non-coding RNAs can in fact encode short peptides, exemplified by her discovery of the peptide hormone ELABELA. In 2017, Lena became Assistant Professor at Duke–NUS Medical School and the Institute of Medical Biology, A*STAR, where her Endogenous Peptides lab currently focuses on secreted and mitochondria-localised peptides to uncover new paradigms in cell biology and improve cardiometabolic and immune health.

Abstract 6063: FOXK2 promotes stemness in ovarian cancer by regulating unfolded protein response signaling

Abstract Introduction: Cancer stem cells (CSCs), a rare cell population within tumors that possesses self-renewal and tumor initiation capacity, have been implicated in cancer relapse and resistance to chemotherapy. In ovarian cancer (OC), CSCs are characterized by a high expression of aldehyde dehydrogenase (ALDH). Understanding the regulatory programs promoting stemness could identify new treatments. We identified FOXK2 as a key transcription factor (TF) that promotes stemness in OC. Methods: We generated FOXK2 knockdown OC models by stable transduction of shRNA targeting this TF and measured the population of ALDH+ CSCs, expression of stemness-associated genes, and in vivo tumor initiation capacities. Transcriptomic and ChIP-seq analyses were used to identify key FOXK2 targets. CRISPR-dCas9 genome editing was used to verify the regulatory function of FOXK2. Rescue experiments validated the roles of a newly discovered target gene of FOXK2. Results: Through gene expression analyses in CSCs vs. non-CSCs, we identified FOXK2 as a highly expressed stemness-specific TF in OC. Genetic depletion of FOXK2 diminished stemness features and reduced in vivo tumor initiation capacity. Through ChIP-sequencing we discovered that FOXK2 directly regulates IRE1α (ERN1 gene) expression, a key sensor for the unfolded protein response (UPR). ChIP-sequencing analysis further revealed that FOXK2 binds to an intronic regulatory element of ERN1. Blocking FOXK2 from binding to this enhancer by using a CRISPR/dCas9 diminished IRE1α transcription. At the molecular level, FOXK2-driven upregulation of IRE1α led to alternative XBP1 mRNA splicing and activation of stemness pathways, while genetic or pharmacological blockade of IRE1α inhibited CSCs in OC models. Conclusion: Our data establish a new function for FOXK2 as a key transcriptional regulator of CSCs and a mediator of the UPR, providing insight into potentially targetable new pathways in ovarian CSCs. Citation Format: Yaqi Zhang, Yinu Wang, Guangyuan Zhao, Edward J. Tanner, Mazhar Adli, Daniela E. Matei. FOXK2 promotes stemness in ovarian cancer by regulating unfolded protein response signaling [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 6063.

Abstract 5826: Autophagy regulates cancer stem cell properties in triple negative breast cancer via miR-181a-mediated regulation of ATG5/ATG2B

Abstract Autophagy has a dual role in the maintenance of cancer stem cells (CSCs), but the precise relationship between autophagy and cancer stemness requires further investigation. In this study, it was found that luminal and triple-negative breast cancer require distinct therapeutic approaches because of their different expressions of autophagy flux. We identified that autophagy flux was inhibited in triple-negative breast cancer (TNBC) CSCs. Moreover, miRNA-181a (miR-181a) is upregulated both in TNBC CSCs and patients. ATG5 and ATG2B participate in the early formation of autophagosomes and were revealed as targets of miR-181a. Inhibition of miR-181a expression led to attenuation of TNBC cancer stemness and an increase in autophagy flux. Furthermore, treatment with curcumin led to attenuation of cancer stemness in TNBC CSCs; the expression of ATG5 and ATG2B was enhanced and there was an increase of autophagy flux. These results indicated that ATG5 and ATG2B are involved in the suppression of cancer stemness in TNBC. In summary, autophagy inhibits cancer stemness through the miR-181a-regulated mechanism in TNBC. Promoting tumor-suppressive autophagy using curcumin may be a potential method for the treatment of TNBC. Citation Format: Jong Hoon Park, Jee Won Park, Yesol Kim, Jaehee Jun, Yejin Ahn. Autophagy regulates cancer stem cell properties in triple negative breast cancer via miR-181a-mediated regulation of ATG5/ATG2B [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 5826.

Prognostic value of hPG80 (circulating progastrin) in IDH-wild type glioblastoma treated with radio-chemotherapy.

2049 Background: hPG80 (circulating progastrin) is a protein secreted by many cancer types, playing a role in tumorigenesis by regulating cancer stem cells, angiogenesis, proliferation/differentiation and decreasing apoptosis. hPG80 is detectable in plasma of cancer patients and previous studies have shown its prognostic role in various cancers. Given the lack of circulating biomarker in glioblastoma, we evaluated the prognostic value of plasma hPG80 in patients with IDH wild type glioblastoma Methods: This multicentric retrospective study included IDHwt glioblastoma patients treated with standard radio-chemotherapy. The ELISA DxPG80.lab kit (Biodena Care, Lausanne, Switzerland) was used to measure hPG80 levels after surgery with a detection threshold of 1 pM in all plasma EDTA samples according to the manufacturer’s instruction. The prognostic impact of hPG80 was evaluated on patient’s progression-free survival (PFS) and overall survival (OS). Results: We included 70 patients (38 males /32 women) with a median age of 64 years (Range 19 - 84). Karnofsky index was > 70% in 52 (91%) of 57 evaluable patients. Tumor biopsy (B), partial resection (PR), complete resection (CR) were performed in 22, 25 and 23 patients respectively. MGMT promotor was methylated in 22 (40%) of the 55 evaluable patients. After surgery, hPG80 was detected in 48 (69%) patients (hPG80+) with a median concentration of 9.52 pM (IQR 5.21 - 21.20). Complete surgery was associated with undetectable levels of hPG80 (52% (CR) vs 28% (PR) vs 14% (B), p = 0.006) and lower concentration if hPG80+ (CR: 5.8 pM [IQR 1.92 - 11.38] vs PR: 12.84 pM [IQR 8.09 - 37.09]; p = 0.04 vs B: 9.86 pM [IQR 4.66 - 21.63]; p = 0.16). With a median follow-up of 39 months (22.4-NR), 86% of patients had progressed and 70% had died. In univariate analysis, hPG80 positivity was associated with PFS (5.6m vs 8.5m, p = 0.053) and OS (14.5 vs 22m, p = 0.04) in hPG80+ vs hPG80- patients respectively. hPG80+ patients with complete surgery had worse median OS than hPG80- patients (14.5 vs 22.0 m; p = 0.051 respectively. Cox proportional hazards model did not fit for covariate analysis. Conclusions: Our findings show that hPG80 could serve as a new circulating prognostic biomarker in IDHwt glioblastoma patients treated with radio-chemotherapy. Further explorations are ongoing in larger cohorts including longitudinal evaluation during the course of the disease.

Knockdown of the stem cell marker Musashi-1 inhibits endometrial cancer growth and sensitizes cells to radiation

BackgroundEndometrial carcinoma is the most common gynecological cancer in Europe. Musashi-1 is known to be a key regulator of endometrial cancer stem cells and a negative prognostic marker. In the present study, we aimed to understand growth and gene expression patterns in endometrial carcinoma after Musashi-1 knockdown in vitro and in vivo. Changes in therapeutic resistance were also assessed.MethodsFirst, we performed analyses to understand Musashi-1 expression patterns using The Cancer Genome Atlas database. We then proceeded to assess effects of small interfering RNA-based Musashi-1 targeting in two endometrial carcinoma cell lines, Ishikawa and KLE. After quantifying baseline changes in cell metabolism, we used MTT tests to assess chemotherapy effects and colony formation assays to understand changes in radioresistance. For mechanistic study, we used quantitative polymerase chain reaction (qPCR) and western blotting of key Musashi-1 target genes and compared results to primary tissue database studies. Finally, xenograft experiments in a mouse model helped understand in vivo effects of Musashi-1 knockdown.ResultsMusashi-1 is aberrantly expressed in primary tumor tissues. In vitro, silencing of Musashi-1 resulted in a strong decline in cell proliferation and radioresistance, while chemoresistance remained unchanged. Loss of Musashi-1 led to downregulation of telomerase, DNA-dependent protein kinase, the Notch pathway and overexpression of cyclin-dependent kinase inhibitor p21, the latter of which we identified as a key mediator of Msi-1 knockdown-related anti-proliferative signaling. In vivo, the anti-proliferative effect was confirmed, with Msi-1 knockdown tumors being about 40% reduced in size.ConclusionsMusashi-1 knockdown resulted in a strong decrease in endometrial cancer proliferation and a loss of radioresistance, suggesting therapeutic potential.

Tubulin Isotypes: Emerging Roles in Defining Cancer Stem Cell Niche.

Although the role of microtubule dynamics in cancer progression is well-established, the roles of tubulin isotypes, their cargos and their specific function in the induction and sustenance of cancer stem cells (CSCs) were poorly explored. But emerging reports urge to focus on the transport function of tubulin isotypes in defining orchestrated expression of functionally critical molecules in establishing a stem cell niche, which is the key for CSC regulation. In this review, we summarize the role of specific tubulin isotypes in the transport of functional molecules that regulate metabolic reprogramming, which leads to the induction of CSCs and immune evasion. Recently, the surface expression of GLUT1 and GRP78 as well as voltage-dependent anion channel (VDAC) permeability, regulated by specific isotypes of β-tubulins have been shown to impart CSC properties to cancer cells, by implementing a metabolic reprogramming. Moreover, βIVb tubulin is shown to be critical in modulating EphrinB1signaling to sustain CSCs in oral carcinoma. These tubulin-interacting molecules, Ephrins, GLUT1 and GRP78, are also important regulators of immune evasion, by evoking PD-L1 mediated T-cell suppression. Thus, the recent advances in the field implicate that tubulins play a role in the controlled transport of molecules involved in CSC niche. The indication of tubulin isotypes in the regulation of CSCs offers a strategy to specifically target those tubulin isotypes to eliminate CSCs, rather than the general inhibition of microtubules, which usually leads to therapy resistance.

FOXK2 promotes ovarian cancer stemness by regulating the unfolded protein response pathway.

Understanding the regulatory programs enabling cancer stem cells (CSCs) to self-renew and drive tumorigenicity could identify new treatments. Through comparative chromatin-state and gene expression analyses in ovarian CSCs versus non-CSCs, we identified FOXK2 as a highly expressed stemness-specific transcription factor in ovarian cancer. Its genetic depletion diminished stemness features and reduced tumor initiation capacity. Our mechanistic studies highlight that FOXK2 directly regulated IRE1α (encoded by ERN1) expression, a key sensor for the unfolded protein response (UPR). Chromatin immunoprecipitation and sequencing revealed that FOXK2 bound to an intronic regulatory element of ERN1. Blocking FOXK2 from binding to this enhancer by using a catalytically inactive CRISPR/Cas9 (dCas9) diminished IRE1α transcription. At the molecular level, FOXK2-driven upregulation of IRE1α led to alternative XBP1 splicing and activation of stemness pathways, while genetic or pharmacological blockade of this sensor of the UPR inhibited ovarian CSCs. Collectively, these data establish what we believe is a new function for FOXK2 as a key transcriptional regulator of CSCs and a mediator of the UPR, providing insight into potentially targetable new pathways in CSCs.

Transforming Growth Factor Beta Promotes the Expansion of Cancer Stem Cells <i>via</i> S1PR3 by Ligand-Independent Notch Activation

Growing evidence suggests that cancer originates from cancer stem cells (CSCs), which can be identified by aldehyde dehydrogenase (ALDH) activity-based flow cytometry. However, the regulation of CSC growth is not fully understood. In the present study, we investigated the effects of Transforming Growth Factor-β (TGFβ) in breast CSC expansion. Stimulation with TGFβ increased the ALDH-positive breast CSC population via the phosphorylation of sphingosine kinase 1 (SphK1), a sphingosine-1-phosphate (S1P)-producing enzyme, and subsequent S1P-mediated S1P receptor 3 (S1PR3) activation. These data suggest that TGFβ promotes breast CSC expansion via the ALK5/SphK1/S1P/S1PR3 signaling pathway. Our findings provide new insights into the role of TGFβ in the regulation of CSCs.

Unfolding RFX1 Mediated Regulation of Cancer Stem Cells

Regulatory factor X1(RFX1) is a unique transcription factor that can act both as an activator and repressor in a context‐dependent manner. In most of the cases, it has been shown to exert an inhibitory action on its targets. It belongs to the evolutionarily conserved RFX (Regulatory Factor binding to the X‐box) family of transcription factors consisting of eight homologs (RFX1‐8) in humans. RFX1 is seen down‐regulated in many cancers and is speculated to have a critical role in regulating stem cell properties. Cancer stem cells are major hurdles in cancer therapy as they are capable of repopulating a tumor after treatment. We aim to understand the regulation of cancer stemness by RFX1 in human teratocarcinomal (NTERA‐2) cancer stem like cells.We have chosen NTERA2 cl.D1 (NT2) embryonic carcinoma cells since they are the malignant counterparts of embryonic stem cells and are pluripotent in nature, making them an ideal candidate to be used as a cancer stem cell model. The cells were differentiated using DISC (Days in suspension culture) method to obtain differentiated populations (NT2D). Using real time analysis, the expression of RFX1 was evaluated in proliferating (NT2P) and differentiating (NT2D) cell populations. A significant increase in RFX1 expression was observed in NT2D cells compared to NT2P cells. For further validation, the same was done in stem cell population enriched using Abcg2 promoter where the stem (GFP+ve) and non‐stem (GFP‐ve) cell populations were sorted out by FACS. Further RFX1 expression was perturbed in NTERA cells, and the assessment of cardinal properties of CSCs, such as clonogenicity/self‐renewal properties, proliferation potential, and migration/invasive properties in vitro,revealed that RFX1 plays a significant role in cancer stemness. Therefore, understanding the regulation of cancer stemness by RFX1 will allow us to formulate better diagnostic and therapeutic approaches to address chemoresistant cancers.

Targeting Epigenetic Modifiers of Tumor Plasticity and Cancer Stem Cell Behavior.

Tumor heterogeneity poses one of the greatest challenges to a successful treatment of cancer. Tumor cell populations consist of different subpopulations that have distinct phenotypic and genotypic profiles. Such variability poses a challenge in successfully targeting all tumor subpopulations at the same time. Relapse after treatment has been previously explained using the cancer stem cell model and the clonal evolution model. Cancer stem cells are an important subpopulation of tumor cells that regulate tumor plasticity and determine therapeutic resistance. Tumor plasticity is controlled by genetic and epigenetic changes of crucial genes involved in cancer cell survival, growth and metastasis. Targeting epigenetic modulators associated with cancer stem cell survival can unlock a promising therapeutic approach in completely eradicating cancer. Here, we review various factors governing epigenetic dysregulation of cancer stem cells ranging from the role of epigenetic mediators such as histone and DNA methyltransferases, histone deacetylases, histone methyltransferases to various signaling pathways associated with cancer stem cell regulation. We also discuss current treatment regimens targeting these factors and other promising inhibitors in clinical trials.

Parathyroid Hormone-Related Protein Inhibition Blocks Triple-Negative Breast Cancer Expansion in Bone Through Epithelial to Mesenchymal Transition Reversal.

ABSTRACTParathyroid hormone‐related protein (PTHrP) plays a major role in skeletal metastasis but its action mechanism has not been fully defined. We previously demonstrated the crucial importance of PTHrP in promoting mammary tumor initiation, growth, and metastasis in a mouse model with a mammary epithelium‐targeted Pthlh gene ablation. We demonstrate here a novel mechanism for bone invasion involving PTHrP induction of epithelial to mesenchymal transition (EMT) and cancer stem cells (CSCs) regulation. Clustered regularly interspaced short palindromic repeats (CRISPR)‐mediated Pthlh gene ablation was used to study EMT markers, phenotype, and invasiveness in two triple‐negative breast cancer (TNBC) cell types (established MDA‐MB‐231 and patient‐derived PT‐TNBC cells). In vitro, Pthlh ablation in TNBC cells reduced EMT markers, mammosphere‐forming ability, and CD44high/CD24low cells ratio. In vivo, cells were injected intratibially into athymic nude mice, and therapeutic treatment with our anti‐PTHrP blocking antibody was started 2 weeks after skeletal tumors were established. In vivo, compared to control, lytic bone lesion from Pthlh ‐ablated cells decreased significantly over 2 weeks by 27% for MDA‐MB‐231 and by 75% for PT‐TNBC‐injected mice (p < 0.001). Micro‐CT (μCT) analyses also showed that antibody therapy reduced bone lytic volume loss by 52% and 48% for non‐ablated MDA‐MB‐231 and PT‐TNBC, respectively (p < 0.05). Antibody therapy reduced skeletal tumor burden by 45% and 87% for non‐ablated MDA‐MB‐231 and PT‐TNBC, respectively (p < 0.002) and caused a significant decrease of CSC/EMT markers ALDH1, vimentin, and Slug, and an increase in E‐cadherin in bone lesions. We conclude that PTHrP is a targetable EMT molecular driver and suggest that its pharmacological blockade can provide a potential therapeutic approach against established TNBC‐derived skeletal lesions. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

MiRNAs as Modulators of Cholesterol in Breast Cancer Stem Cells: An Approach to Overcome Drug Resistance in Cancer.

It has been postulated that a small number of Cancer Stem Cells (CSCs) buried in tumour mass drive cancer growth and impart cancer drug resistance. However, their eradication has not been achieved so far as the mechanistic understanding of CSCs' role in cancer development and growth is limited. The cholesterol accumulation and efflux processes have been shown to play an important role in maintaining cell's integrity and its sensitivity towards drugs, as altered cholesterol pathways contribute to cancer drug resistance. Emerging pieces of evidence have indicated miRNAs as regulators of CSCs, and also as regulators of cholesterol pathways in cancer cells, but a link between the two has not been fully established so far. In this review, we have collated key signalling pathways and published evidence emphasising the involvement of miRNAs and cholesterol in CSCs related drug resistance. Additionally, we have used bioinformatics analysis to identify miRNAs that may modulate cholesterol pathways in CSCs at a molecular level to contribute to cancer drug resistance. Our results show that two miRNAs (hsa-miR-34a-5p and hsa-miR-373-3p) interact and bind to two known Breast CSC markers (CD44 and CD24) and mediate the expression of several cholesterol-related genes (INSIG2, APOL2, CYP51A1, HDLB, and DHCR7). Furthermore, survival analysis of the breast cancer patients' gene expression data revealed that higher expression of these genes is associated with poor disease-free survival. We, therefore, propose that targeting these two miRNAs could possibly provide a way to alter cell's response to drugs via modulating cholesterol pathways in CSCs.

CANCER STEM CELLS: THE GREATEST MENACE IN CONQUERING CANCER MANAGEMENT

Cancer stem cells (CSCs) also known as tumor initiating cells, are pluripotent and self-renewing subpopulation of cancer cells. This subpopulation is heterogeneous in nature which includes quiescent population and a proliferative population. Since CSCs were first identified in leukemia, their importance in chemoresistance, radioresistance, metastasis and recurrence were explored in detail through many studies. Different transcription factors like OCT4, SOX2, NANOG, KLF4, and c-Myc, as well as many signaling pathways like Wnt, Notch, NF-κB, Hedgehog and JAK/STAT are important regulators of CSCs. In addition different cells of tumor microenvironment, hypoxic condition, extracellular matrix and many miRNAs also regulate CSCs. This review summarizes model of CSC, properties and characterization CSC, and factors that regulate CSC. Figure 1 - Graphical abstract

NOX4 regulates TGFβ-induced proliferation and self-renewal in glioblastoma stem cells.

Glioblastoma (GBM) is the most aggressive and common glioma subtype, with a median survival of 15 months after diagnosis. Current treatments have limited therapeutic efficacy; thus, more effective approaches are needed. The glioblastoma tumoural mass is characterised by a small cellular subpopulation – glioblastoma stem cells (GSCs) – that has been held responsible for glioblastoma initiation, cell invasion, proliferation, relapse and resistance to chemo‐ and radiotherapy. Targeted therapies against GSCs are crucial, as is understanding the molecular mechanisms that govern the GSCs. Transforming growth factor β (TGFβ) signalling and reactive oxygen species (ROS) production are known to govern and regulate cancer stem cell biology. Among the differentially expressed genes regulated by TGFβ in a transcriptomic analysis of two different patient‐derived GSCs, we found NADPH oxidase 4 (NOX4) as one of the top upregulated genes. Interestingly, when patient tissues were analysed, NOX4 expression was found to be higher in GSCs versus differentiated cells. A functional analysis of the role of NOX4 downstream of TGFβ in several patient‐derived GSCs showed that TGFβ does indeed induce NOX4 expression and increases ROS production in a NOX4‐dependent manner. NOX4 downstream of TGFβ regulates GSC proliferation, and NOX4 expression is necessary for TGFβ‐induced expression of stem cell markers and of the transcription factor nuclear factor erythroid 2‐related factor 2 (NRF2), which in turn controls the cell’s antioxidant and metabolic responses. Interestingly, overexpression of NOX4 recapitulates the effects induced by TGFβ in GSCs: enhanced proliferation, stemness and NRF2 expression. In conclusion, this work functionally establishes NOX4 as a key mediator of GSC biology.

Regulation of cancer stem cell activity by thyroid hormone receptor β.

Increasing numbers of cancer stem cell markers have been recently identified. It is not known, however, whether a member of the nuclear receptor superfamily, thyroid hormone receptor β (TRβ), can function to regulate cancer stem cell (CSC) activity. Using anaplastic thyroid cancer cells (ATC) as a model, we highlight the role of TRβ in CSC activity. ATC is one of the most aggressive solid cancers in humans and is resistant to currently available therapeutics. Recent studies provide evidence that CSC activity underlies aggressiveness and therapeutic resistance of ATC. Here we show that TRβ inhibits CSC activity by suppressing tumor-sphere formation of human ATC cells and their tumor-initiating capacity. TRβ suppresses the expression of CSC regulators, including ALDH, KLF2, SOX2, b-catenin, and ABCG2, in ATC cell-induced xenograft tumors. Single-cell transcriptomic analysis shows that TRβ reduces CSC population in ATC-induced xenograft tumors. Analysis of The Cancer Genome Atlas (TCGA) database demonstrates that the inhibition of CSC capacity by TRβ contributes to favorable clinical outcomes in human cancer. Our studies show that TRβ is a newly identified transcription regulator that acts to suppress CSC activity and that TRβ could be considered as a molecular target for therapeutic intervention of ATC.

Cell-based immunotherapy of glioblastoma multiforme.

Glioblastoma multiforme (GBM) is the most aggressive and lethal primary glial brain tumor. It has an unfavorable prognosis and relatively ineffective treatment protocols, with the median survival of patients being ~15 months. Tumor resistance to treatment is associated with its cancer stem cells (CSCs). At present, there is no medication or technologies that have the ability to completely eradicate CSCs, and immunotherapy (IT) is only able to prolong the patient's life. The present review aimed to investigate systemic solutions for issues associated with immunosuppression, such as ineffective IT and the creation of optimal conditions for CSCs to fulfill their lethal potential. The present review also investigated the main methods involved in local immunosuppression treatment, and highlighted the associated disadvantages. In addition, novel treatment options and targets for the elimination and regulation of CSCs with adaptive and active IT are discussed. Antagonists of TGF-β inhibitors, immune checkpoints and other targeted medication are also summarized. The role of normal hematopoietic stem cells (HSCs) in the mechanisms underlying systemic immune suppression development in cases of GBM is analyzed, and the potential reprogramming of HSCs during their interaction with cancer cells is discussed. Moreover, the present review emphasizes the importance of the aforementioned interactions in the development of immune tolerance and the inactivation of the immune system in neoplastic processes. The possibility of solving the problem of systemic immunosuppression during transplantation of donor HSCs is discussed.

The Roles of Noncoding RNAs in the Development of Osteosarcoma Stem Cells and Potential Therapeutic Targets.

Osteosarcoma (OS) is the common bone tumor in children and adolescents. Because of chemotherapy resistance, the OS patients have a poor prognosis. The one reason of chemotherapeutic resistance is the development of cancer stem cells (CSCs). CSCs represent a small portion of tumor cells with the capacity of self-renewal and multipotency, which are associated with tumor initiation, metastasis, recurrence and drug resistance. Recently, noncoding RNAs (ncRNAs) have been reported to critically regulate CSCs. Therefore, in this review article, we described the role of ncRNAs, especially miRNAs, lncRNAs and circRNAs, in regulating CSCs development and potential mechanisms. Specifically, we discussed the role of multiple miRNAs in targeting CSCs, including miR-26a, miR-29b, miR-34a, miR-133a, miR-143, miR-335, miR-382, miR-499a, miR-1247, and let-7days. Moreover, we highlighted the functions of lncRNAs in regulating CSCs in OS, such as B4GALT1-AS1, DANCR, DLX6-AS1, FER1L4, HIF2PUT, LINK-A, MALAT1, SOX2-OT, and THOR. Due to the critical roles of ncRNAs in regulation of OS CSCs, targeting ncRNAs might be a novel strategy for eliminating CSCs for OS therapy.

Abstract ES13-1: Targeting EZH2 functions

Abstract Anaplasia, or loss of mature specialized features, is a characteristic of malignant cells. Thus, it is not surprising that deregulation of proteins that govern cell type identity may lead to cancer. EZH2, a Polycomb group protein which regulates transcriptional memory in normal cells through H3K27 trimethylation, is overexpressed in breast cancer compared to normal breast, and is a tissue-based biomarker of survival in patients with breast cancer. EZH2 enhances breast cancer initiation and progression, making it a desirable therapeutic target with several inhibitors already in clinical trials. While the main mechanism of EZH2 oncogenic function has been ascribed to trimethylation of H3K27, mounting evidence supports that EZH2 also functions through non-canonical H3K27me3-independent mechanisms, especially in triple negative breast carcinomas (TNBC). These include transcriptional activation through direct binding to the NOTCH1 promoter to regulate cancer stem cells, and EZH2 phosphorylation at specific sites to either reduce affinity for histone H3 and/or increase binding to nonhistone proteins to promote metastasis. This body of work highlights the importance of blocking EZH2 H3K27me3-dependent as well as non-canonical functions in TNBC to improve outcomes. In this Educational Session, I will discuss current insights into EZH2 oncogenic mechanisms in TNBC including metaplastic carcinomas, an aggressive and chemoresistant TNBC subtype. We will also discuss how the discovery of novel EZH2 mechanisms may set the stage for the development of previously unconsidered therapeutic opportunities. Citation Format: CG Kleer. Targeting EZH2 functions [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr ES13-1.

Lipid metabolism of cancer stem cells.

Cancer stem cells (CSCs), also termed cancer-initiating cells, are a special subset of cells with high self-replicating and self-renewing abilities that can differentiate into various cell types under certain conditions. A number of studies have demonstrated that CSCs have distinct metabolic properties. The reprogramming of energy metabolism enables CSCs to meet the needs of self-renewal and stemness maintenance. Increasing evidence supports the view that alterations in lipid metabolism, including an increase in fatty acid (FA) uptake, de novo lipogenesis, formation of lipid droplets and mitochondrial FA oxidation, are involved in CSC regulation. In the present review, the metabolic characteristics of CSCs, particularly in lipid metabolism, were summarized. In addition, the potential mechanisms of CSC lipid metabolism in treatment resistance were discussed. Given their significance in cancer biology, targeting CSC metabolism may serve an important role in future cancer treatment.

DOT1L Is a Novel Cancer Stem Cell Target for Triple-Negative Breast Cancer.

Although chemotherapies kill most cancer cells, stem cell-enriched survivors seed metastasis, particularly in triple-negative breast cancers (TNBC). TNBCs arise from and are enriched for tumor stem cells. Here, we tested if inhibition of DOT1L, an epigenetic regulator of normal tissue stem/progenitor populations, would target TNBC stem cells. Effects of DOT1L inhibition by EPZ-5676 on stem cell properties were tested in three TNBC lines and four patient-derived xenograft (PDX) models and in isolated cancer stem cell (CSC)-enriched ALDH1+ and ALDH1- populations. RNA sequencing compared DOT1L regulated pathways in ALDH1+ and ALDH1- cells. To test if EPZ-5676 decreases CSC in vivo, limiting dilution assays of EPZ-5676/vehicle pretreated ALDH1+ and ALDH1- cells were performed. Tumor latency, growth, and metastasis were evaluated. Antitumor activity was also tested in TNBC PDX and PDX-derived organoids. ALDH1+ TNBC cells exhibit higher DOT1L and H3K79me2 than ALDH1-. DOT1L maintains MYC expression and self-renewal in ALDH1+ cells. Global profiling revealed that DOT1L governs oxidative phosphorylation, cMyc targets, DNA damage response, and WNT activation in ALDH1+ but not in ALDH1- cells. EPZ-5676 reduced tumorspheres and ALDH1+ cells in vitro and decreased tumor-initiating stem cells and metastasis in xenografts generated from ALDH1+ but not ALDH1- populations in vivo. EPZ-5676 significantly reduced growth in vivo of one of two TNBC PDX tested and decreased clonogenic 3D growth of two other PDX-derived organoid cultures. DOT1L emerges as a key CSC regulator in TNBC. Present data support further clinical investigation of DOT1L inhibitors to target stem cell-enriched TNBC.