Isolation, identification, and characterization of cancer stem cells: A review

Contribution of Autophagy to Epithelial Mesenchymal Transition Induction during Cancer Progression

Epithelial Mesenchymal Transition (EMT) is a dedifferentiation process implicated in many physio-pathological conditions including tumor transformation. EMT is regulated by several extracellular mediators and under certain conditions it can be reversible. Autophagy is a conserved catabolic process in which intracellular components such as protein/DNA aggregates and abnormal organelles are degraded in specific lysosomes. In cancer, autophagy plays a controversial role, acting in different conditions as both a tumor suppressor and a tumor-promoting mechanism. Experimental evidence shows that deep interrelations exist between EMT and autophagy-related pathways. Although this interplay has already been analyzed in previous studies, understanding mechanisms and the translational implications of autophagy/EMT need further study. The role of autophagy in EMT is not limited to morphological changes, but activation of autophagy could be important to DNA repair/damage system, cell adhesion molecules, and cell proliferation and differentiation processes. Based on this, both autophagy and EMT and related pathways are now considered as targets for cancer therapy. In this review article, the contribution of autophagy to EMT and progression of cancer is discussed. This article also describes the multiple connections between EMT and autophagy and their implication in cancer treatment.

Metabolomics, Transcriptome and Single-Cell RNA Sequencing Analysis of the Metabolic Heterogeneity between Oral Cancer Stem Cells and Differentiated Cancer Cells

Understanding the distinct metabolic characteristics of cancer stem cells (CSC) may allow us to better cope with the clinical challenges associated with them. In this study, OSCC cell lines (CAL27 and HSC3) and multicellular tumor spheroid (MCTS) models were used to generate CSC-like cells. Quasi-targeted metabolomics and RNA sequencing were used to explore altered metabolites and metabolism-related genes. Pathview was used to display the metabolites and transcriptome data in a KEGG pathway. The single-cell RNA sequencing data of six patients with oral cancer were analyzed to characterize in vivo CSC metabolism. The results showed that 19 metabolites (phosphoethanolamine, carbamoylphosphate, etc.) were upregulated and 109 metabolites (2-aminooctanoic acid, 7-ketocholesterol, etc.) were downregulated in both MCTS cells. Integration pathway analysis revealed altered activity in energy production (glycolysis, citric cycle, fatty acid oxidation), macromolecular synthesis (purine/pyrimidine metabolism, glycerophospholipids metabolism) and redox control (glutathione metabolism). Single-cell RNA sequencing analysis confirmed altered glycolysis, glutathione and glycerophospholipid metabolism in in vivo CSC. We concluded that CSCs are metabolically inactive compared with differentiated cancer cells. Thus, oral CSCs may resist current metabolic-related drugs. Our result may be helpful in developing better therapeutic strategies against CSC.

PGD2/PTGDR2 Signal Affects the Viability, Invasion, Apoptosis, and Stemness of Gastric Cancer Stem Cells and Prevents the Progression of Gastric Cancer

BACKGROUND

Prostaglandin D2 (PGD2) has been shown to restrict the occurrence and development of multiple cancers; nevertheless, its underlying molecular mechanism has not been fully elucidated. The present study investigated the effect of PGD2 on the biological function of the enriched gastric cancer stem cells (GCSCs), as well as its underlying molecular mechanism, to provide a theoretical basis and potential therapeutic drugs for gastric cancer (GC) treatment.

METHODS

The plasma PGD2 levels were detected by Enzyme-linked immunosorbent assay (ELISA). Silencing of lipocalin prostaglandin D synthetases (L-PTGDS) and prostaglandin D2 receptor 2 (PTGDR2) was carried out in GCSCs from SGC-7901 and HGC-27 cell lines. Cell Counting Kit-8, transwell, flow cytometry, and western blotting assays were used to determine cell viability, invasion, apoptosis, and stemness of GCSCs. In vivo xenograft models were used to assess tumor growth.

RESULTS

Clinically, it was found that the plasma PGD2 level decreased significantly in patients with GC. PGD2 suppressed viability, invasion, and stemness and increased the apoptosis of GCSCs. Downregulating L-PTGDS and PTGDR2 promoted viability, invasion, and stemness and reduced the apoptosis of GCSCs. Moreover, the inhibition of GCSCs induced by PGD2 was eliminated by downregulating the expression of PTGDR2. The results of in vivo experiments were consistent with those of in vitro experiments.

CONCLUSION

Our data suggest that PGD2 may be an important marker and potential therapeutic target in the clinical management of GC. L-PTGDS/PTGDR2 may be one of the critical targets for GC therapy. The PGD2/PTGDR2 signal affects the viability, invasion, apoptosis, and stemness of GCSCs and prevents the progression of GC.

Shrinking the battlefield in cancer therapy: Nanotechnology against cancer stem cells

Cancer remains one of the leading causes of mortality worldwide, presenting a significant healthcare challenge owing to the limited efficacy of current treatments. The application of nanotechnology in cancer treatment leverages the unique optical, magnetic, and electrical attributes of nanomaterials to engineer innovative, targeted therapies. Specifically, manipulating nanomaterials allows for enhanced drug loading efficiency, improved bioavailability, and targeted delivery systems, reducing the non-specific cytotoxic effects characteristic of conventional chemotherapies. Furthermore, recent advances in nanotechnology have demonstrated encouraging results in specifically targeting CSCs, a key development considering the role of these cells in disease recurrence and resistance to treatment. Despite these breakthroughs, the clinical approval rates of nano-drugs have not kept pace with research advances, pointing to existing obstacles that must be addressed. In conclusion, nanotechnology presents a novel, powerful tool in the fight against cancer, particularly in targeting the elusive and treatment-resistant CSCs. This comprehensive review delves into the intricacies of nanotherapy, explicitly targeting cancer stem cells, their markers, and associated signaling pathways.

The strategies to cure cancer patients by eradicating cancer stem-like cells

Cancer stem-like cells (CSCs), a subpopulation of cancer cells, possess remarkable capability in proliferation, self-renewal, and differentiation. Their presence is recognized as a crucial factor contributing to tumor progression and metastasis. CSCs have garnered significant attention as a therapeutic focus and an etiologic root of treatment-resistant cells. Increasing evidence indicated that specific biomarkers, aberrant activated pathways, immunosuppressive tumor microenvironment (TME), and immunoevasion are considered the culprits in the occurrence of CSCs and the maintenance of CSCs properties including multi-directional differentiation. Targeting CSC biomarkers, stemness-associated pathways, TME, immunoevasion and inducing CSCs differentiation improve CSCs eradication and, therefore, cancer treatment. This review comprehensively summarized these targeted therapies, along with their current status in clinical trials. By exploring and implementing strategies aimed at eradicating CSCs, researchers aim to improve cancer treatment outcomes and overcome the challenges posed by CSC-mediated therapy resistance.

Connexins in Cancer, the Possible Role of Connexin46 as a Cancer Stem Cell-Determining Protein

Cancer is a widespread and incurable disease caused by genetic mutations, leading to uncontrolled cell proliferation and metastasis. Connexins (Cx) are transmembrane proteins that facilitate intercellular communication via hemichannels and gap junction channels. Among them, Cx46 is found mostly in the eye lens. However, in pathological conditions, Cx46 has been observed in various types of cancers, such as glioblastoma, melanoma, and breast cancer. It has been demonstrated that elevated Cx46 levels in breast cancer contribute to cellular resistance to hypoxia, and it is an enhancer of cancer aggressiveness supporting a pro-tumoral role. Accordingly, Cx46 is associated with an increase in cancer stem cell phenotype. These cells display radio- and chemoresistance, high proliferative abilities, self-renewal, and differentiation capacities. This review aims to consolidate the knowledge of the relationship between Cx46, its role in forming hemichannels and gap junctions, and its connection with cancer and cancer stem cells.

Single Cell Phenotypic Analysis for Cancer Stem Cell Identification by Dual-Isotope ICP-QMS

Single cell phenotypic analysis is significant for clinical diagnosis, treatment, and prognosis of cancer. Accurate differentiation of cancer stem cell (CSC) subpopulations from a large number of cancer cells may become a cancer surveillance tool and provide important implications for the development of new CSC-targeted therapy strategies. Herein, we report a new approach based on dual-isotope inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) for single cell phenotypic analysis. High-throughput single cell sampling was achieved by a spiral channel microfluidic chip for cell focusing and alignment, and single cell analysis was performed with time-resolved ICP-QMS by identifying the highly specific probes. This enables the monitoring of two surface protein markers (EpCAM and MUC1) of three cell types, i.e., HeLa, MCF-7, and HepG2, at single cell level. The analysis of breast cancer stem cells further confirmed its capability in distinguishing rare cell phenotypes. The present study provides promising possibilities for adopting ICP-QMS in biomedical investigations in terms of cell typing, stemness identification of tumor cells, and cell heterogeneity analysis.

Development of Responsive Nanoparticles for Cancer Therapy

Great efforts are focused on the development of safe nano-carriers for the treatment of cancer in order to overcome some of the typical limitations of conventional therapies [...].

Novel insights into tumorigenesis and prognosis of endometrial cancer through systematic investigation and validation on mitophagy-related signature

In-depth studies on the pathogenesis of endometrial cancer (EC) are critical because of the increasing global incidence of EC. Mitophagy, a mitochondrial quality control process, plays an important role in carcinogenesis and tumor progression. This study aimed to develop a novel mitophagy-based signature to predict the tumorigenesis and prognosis of EC. Data was downloaded from The Cancer Genome Atlas and Gene Expression Omnibus databases, and 29 mitophagy-related genes were downloaded from the Pathway Unification Database. EC patients were classified into two risk groups based on the two-key- gene signature, TOMM40 and MFN1, which were constructed using Cox regression analysis. A better prognosis was noted in the low-risk group. The model was validated for four aspects: clinical features, mutation status, clinical therapeutic response, and immune cell infiltration status. Moreover, according to the contribution to the risk model, TOMM40 was selected for further in vitro experiments. The silencing of TOMM40 inhibited mitochondrial degradation; suppressed cell proliferation; induced cell apoptosis and G1 phase cell cycle arrest; inhibited migration, invasion, and epithelial-mesenchymal transition; and suppressed cell stemness. In conclusion, the mitophagy-related risk score provides a novel perspective for survival and drug selection during the individual treatment of EC patients. TOMM40 serves as an oncogene in EC and promotes tumor progression via a mitophagy-related pathway. Thus, TOMM40 is a potential therapeutic target in EC.

Autologous dendritic cells loaded with antigens from self-renewing autologous tumor cells as patient-specific therapeutic cancer vaccines

A promising personal immunotherapy is autologous dendritic cells (DC) loaded ex vivo with autologous tumor antigens (ATA) derived from self-renewing autologous cancer cells. DC-ATA are suspended in granulocyte-macrophage colony stimulating factor at the time of each subcutaneous injection. Previously, irradiated autologous tumor cell vaccines have produced encouraging results in 150 cancer patients, but the DC-ATA vaccine demonstrated superiority in single-arm and randomized trials in metastatic melanoma. DC-ATA have been injected into more than 200 patients with melanoma, glioblastoma, and ovarian, hepatocellular, and renal cell cancers. Key observations include: [1] greater than 95% success rates for tumor cell cultures and monocyte collection for dendritic cell production; [2] injections are well-tolerated; [3] the immune response is rapid and includes primarily TH1/TH17 cellular responses; [4] efficacy has been suggested by delayed but durable complete tumor regressions in patients with measurable disease, by progression-free survival in glioblastoma, and by overall survival in melanoma.

STAT3 Inhibition Attenuates MYC Expression by Modulating Co-Activator Recruitment and Suppresses Medulloblastoma Tumor Growth by Augmenting Cisplatin Efficacy In Vivo

MB is a common childhood malignancy of the central nervous system, with significant morbidity and mortality. Among the four molecular subgroups, MYC-amplified Group 3 MB is the most aggressive type and has the worst prognosis due to therapy resistance. The present study aimed to investigate the role of activated STAT3 in promoting MB pathogenesis and chemoresistance via inducing the cancer hallmark MYC oncogene. Targeting STAT3 function either by inducible genetic knockdown (KD) or with a clinically relevant small molecule inhibitor reduced tumorigenic attributes in MB cells, including survival, proliferation, anti-apoptosis, migration, stemness and expression of MYC and its targets. STAT3 inhibition attenuates MYC expression by affecting recruitment of histone acetyltransferase p300, thereby reducing enrichment of H3K27 acetylation in the MYC promoter. Concomitantly, it also decreases the occupancy of the bromodomain containing protein-4 (BRD4) and phosphoSer2-RNA Pol II (pSer2-RNAPol II) on MYC, resulting in reduced transcription. Importantly, inhibition of STAT3 signaling significantly attenuated MB tumor growth in subcutaneous and intracranial orthotopic xenografts, increased the sensitivity of MB tumors to cisplatin, and improved the survival of mice bearing high-risk MYC-amplified tumors. Together, the results of our study demonstrate that targeting STAT3 may be a promising adjuvant therapy and chemo-sensitizer to augment treatment efficacy, reduce therapy-related toxicity and improve quality of life in high-risk pediatric patients.

Characterization of bone marrow heterogeneity in NK-AML (M4/M5) based on single-cell RNA sequencing

Normal karyotype acute myeloid leukemia (NK-AML) is a heterogeneous hematological malignancy that contains a minor population of self-renewing leukemia stem cells (LSCs), which complicate efforts to achieve long-term survival. We performed single-cell RNA sequencing to profile 39,288 cells from 6 bone marrow (BM) aspirates including 5 NK-AML (M4/M5) patients and 1 healthy donor. The single-cell transcriptome atlas and gene expression characteristics of each cell population in NK-AML (M4/M5) and healthy BM were obtained. In addition, we identified a distinct LSC-like cluster with possible biomarkers in NK-AML (M4/M5) and verified 6 genes using qRT‒PCR and bioinformatic analyses. In conclusion, we utilized single-cell technologies to provide an atlas of NK-AML (M4/M5) cell heterogeneity, composition, and biomarkers with implications for precision medicine and targeted therapies.

Identification and gene expression profiling of human gonadotrophic pituitary adenoma stem cells

BACKGROUND

Gonadotrophic pituitary adenoma is a major subtype of pituitary adenoma in the sellar region, but it is rarely involved in the hypersecretion of hormones into blood; thus, it is commonly regarded as "non-functioning." Its tumorigenic mechanisms remain unknown. The aim of this study was to identify human gonadotrophic pituitary adenoma stem cells (hPASCs) and explore the underlying gene expression profiles. In addition, the potential candidate genes involved in the invasive properties of pituitary adenoma were examined.

METHODS

The hPASCs from 14 human gonadotrophic pituitary adenoma clinical samples were cultured and verified via immunohistochemistry. Genetic profiling of hPASCs and the matched tumor cells was performed through RNA-sequencing and subjected to enrichment analysis. By aligning the results with public databases, the candidate genes were screened and examined in invasive and non-invasive gonadotrophic pituitary adenomas using Real-time polymerase chain reaction.

RESULTS

The hPASCs were successfully isolated and cultured from gonadotrophic pituitary adenoma in vitro, which were identified as positive for generic stem cell markers (Sox2, Oct4, Nestin and CD133) via immunohistochemical staining. The hPASCs could differentiate into the tumor cells expressing follicle-stimulating hormone in the presence of fetal bovine serum in the culture medium. Through RNA-sequencing, 1352 differentially expressed genes were screened and identified significantly enriched in various gene ontologies and important pathways. The expression levels of ANXA2, PMAIP1, SPRY2, C2CD4A, APOD, FGF14 and FKBP10 were significantly upregulated while FNDC5 and MAP3K4 were downregulated in the invasive gonadotrophic pituitary adenomas compared to the non-invasive ones.

CONCLUSION

Genetic profiling of hPASCs may explain the tumorigenesis and invasiveness of gonadotrophic pituitary adenoma. ANXA2 may serve as a potential therapeutic target for the treatment of gonadotrophic pituitary adenoma.

Sohlh2 Regulates the Stemness and Differentiation of Colon Cancer Stem Cells by Downregulating LncRNA-H19 Transcription

Colon cancer stem cells (CSC) are tumor-initiating cells that drive tumorigenesis and progression through self-renewal and various differentiation potency. Therefore, the identification of factors critical for colon CSC function is vital for the development of therapies. Sohlh2 belongs to the superfamily of bhlh transcription factors and serves as a tumor suppressor in several tumors. The role of Sohlh2 in CSCs remains unknown. Here we demonstrated that Sohlh2 was related to the inhibition of LncRNA-H19/miR-141/β-catenin signaling and led to the consequent suppression of colon CSC stemness and the promotion of colon CSC differentiation in vitro and in vivo. Moreover, Sohlh2 could directly bind to the promoter of LncRNA-H19 and repress its transcription activity. LncRNA-H19 mediated the effects of Sohlh2 on colon CSC stemness and differentiation. Clinically, we observed a significant inverse correlation between Sohlh2 and LncRNA-H19, β-catenin, Lgr5, CD133 expression levels, and positive correlation between Sohlh2 and MUC2, TFF2 expression in colon cancer tissues. Collectively, our findings suggest an important role of the Sohlh2/LncRNA-H19/miR-141/β-catenin pathway in regulating colon CSC stemness and differentiation, suggesting potential therapeutic targets for colon cancer.

IMPLICATIONS

This study identifies that Sohlh2 directly manipulates LncRNA-H19 transcription and suppresses the β-catenin signaling pathway and the Sohlh2/LncRNA-H19/miR-141/β-catenin signaling pathway plays an essential role in the stemness of colon CSCs.

Oct-4 induces cisplatin resistance and tumor stem cell-like properties in endometrial carcinoma cells

OBJECTIVE

Research has suggested that tumor-initiating tumor stem cells are derived from normal stem cells and that tumor cells undergo progressive de-differentiation to achieve a stem cell-like state. Tumor stem cells are characterized by high proliferation ability, high plasticity, expression of multi-drug resistance proteins, and the ability to seed new tumors. Octamer-binding transcription factor 4 (Oct-4) and its activation targets are overexpressed in the tumor stem cells of various types of tumors, and this expression is associated with the pathogenesis, development, and poor prognosis of tumors. The primary objective of this study was to test if a stably transfected with Oct-4 gene cell line, RL95-2/Oct-4, has the characteristics of tumor stem cells.

MATERIALS AND METHODS

Human endometrial carcinoma cells (RL95-2) were transfected with a plasmid carrying genes for Oct-4 and green fluorescent protein (GFP). The stably transfected cells, RL95-2/Oct-4, were selected using G418 and observed to express the GFP reporter gene under the control of the Oct-4 promoter. GFP expression levels of RL95-2/Oct-4 cells were measured using flow cytometry. The proliferation potential of cells was determined according to cumulative population doubling and colony-formation efficiency. Gene expression was analyzed using reverse transcription-polymerase chain reaction.

RESULTS

RL95-2/Oct-4 cells not only exhibited increased expression of the three most important stem cell genes, Oct-4, Nanog, and Sox2, but also had increased expression of the endometrial tumor stem cell genes CD133 and ALDH1. Furthermore, enhanced expression of these genes in the RL95-2/Oct-4 cells was associated with higher colony-forming ability and growth rate than in parental RL95-2 cells. We also observed that cisplatin induced less cell death in RL95-2/Oct-4 cells than in RL95-2 cells, indicating that RL95-2/Oct-4 cells were more resistant to chemotherapeutic agents.

CONCLUSION

The study findings contribute to investigate the effects of Oct-4 on tumor stem cell origins.

Modulation of Spheroid Forming Capacity and TRAIL Sensitivity by KLF4 and Nanog in Gastric Cancer Cells

The expression of pluripotency factors, and their associations with clinicopathological parameters and drug response have been described in various cancers, including gastric cancer. This study investigated the association of pluripotency factor expression with the clinicopathological characteristics of gastric cancer patients, as well as changes in the expression of these factors upon the stem cell-enriching spheroid culture of gastric cancer cells, regulation of sphere-forming capacity, and response to cisplatin and TRAIL treatments by Nanog and KLF4. Nanog expression was significantly associated with the emergence of a new tumor and a worse prognosis in gastric cancer patients. The expression of the pluripotency factors varied among six gastric cancer cells. KLF4 and Nanog were expressed high in SNU-601, whereas SOX2 was expressed high in SNU-484. The expression of KLF4 and SOX2 was increased upon the spheroid culture of SNU-601 (KLF4/Nanog-high) and SNU-638 (KLF4/Nanog-low). The spheroid culture of them enhanced TRAIL-induced viability reduction, which was accompanied by the upregulation of death receptors, DR4 and DR5. Knockdown and overexpression of Nanog in SNU-601 and SNU-638, respectively, did not affect spheroid-forming capacity, however, its expression was inversely correlated with DR4/DR5 expression and TRAIL sensitivity. In contrast, KLF4 overexpression in SNU-638 increased spheroid formation, susceptibility to cisplatin and TRAIL treatments, and DR4/DR5 expression, while the opposite was found in KLF4-silenced SNU-601. KLF4 is supposed to play a critical role in DR4/DR5 expression and responses to TRAIL and cisplatin, whereas Nanog is only implicated in the former events only. Direct regulation of death receptor expression and TRAIL response by KLF4 and Nanog have not been well documented previously, and the regulatory mechanism behind the process remains to be elucidated.

Regulation of the aryl hydrocarbon receptor in cancer and cancer stem cells of gynecological malignancies: An update on signaling pathways

Gynecological malignancies are a female type of cancers that affects the reproductive system. Cancer metastasis or recurrence mediated by cellular invasiveness occurs at advanced stages of cancer progression. Cancer Stem Cells (CSCs) enrichment in tumors leads to chemoresistance, which results in cancer mortality. Exposure to environmental pollutants such as polycyclic aromatic hydrocarbons is associated with an increased the risk of CSC enrichment in gynecological cancers. One of the important pathways that mediates the metabolism and bioactivation of these environmental chemicals is the transcription factor, aryl hydrocarbon receptor (AhR). The present review explores the molecular mechanisms regulating the crosstalk and interaction of the AhR with cancer-related signaling pathways, such as apoptosis, epithelial-mesenchymal transition, immune checkpoints, and G-protein-coupled receptors in several gynecological malignancies such as ovarian, uterine, endometrial, and cervical cancers. The review also discusses the potential of targeting the AhR pathway as a novel chemotherapy for gynecological cancers.

Establishment and characterization of chemotherapy-enriched sphere-forming cells with stemness phenotypes as a new cell line (BAG50) of gastric carcinoma

Gastric cancer is a malignancy with a high mortality rate worldwide. Cancer stem cells (CSCs) are a small subpopulation of tumor cells that possess the tumor-initiating ability, self-renewal capacity, and high resistance to conventional therapies. Due to the diversity and complexity of human tumors, new cell lines are urgently needed to supply clinically and physiologically relevant cancer models. Here, we report establishing a novel cell line (BAG₅₀) with stemness properties. Chemotherapy-enriched sphere-forming cells with CSC properties isolated from a patient with GC were cultured in a serum-containing medium and passaged for up to 51 passages. The colony-forming ability and tumor-forming capacity of BAG₅₀ cells were evaluated in vitro and in vivo. mRNA upregulation of stemness-related transcriptional factors using real-time PCR as well as expression of CSC markers using flow cytometry was investigated. Finally, STR profiling and chromosome studies were performed. BAG₅₀ cells formed floating spheroid colonies in a serum-free medium. Subcutaneous injection of these cells generated xenograft tumors in nude mice. Pluripotency markers (SOX-2, OCT4, and Cripto-1) in them were upregulated compared with normal gastric cells. The majority of them expressed CSC markers of CD44, CD54, and EpCAM, and stemness marker of oct-4. STR profiling showed a unique DNA fingerprint. Karyotype also demonstrated multiple aneuploidies and chromosomal translocations. We suggested that the highly tumorigenic BAG₅₀ cell line with stem cell-like phenotypes may provide a valuable in vitro tool to support new diagnostic, prognostic, and predictive biomarkers as well as the development of more effective treatment strategies.

Identification of EZH2 as Cancer Stem Cell Marker in Clear Cell Renal Cell Carcinoma and the Anti-Tumor Effect of Epigallocatechin-3-Gallate (EGCG)

Simple Summary

Cancer stem cells (CSCs) refer to a group of undifferentiated heterogeneous tumor cells, defined as capable of self-renewal, differentiation, and may be linked to therapeutic resistance and tumor relapse. The development of novel therapeutic strategies to target CSCs and the identification of typical CSC markers are essential to improve therapy efficacy and prevent tumor relapse. Our study identifies CSC markers in renal cell carcinoma (RCC) and explores a potential treatment strategy and the underlying pharmacological mechanisms.

Abstract

The aim of the study was to develop a new therapeutic strategy to target cancer stem cells (CSCs) in clear cell renal cell carcinoma (ccRCC) and to identify typical CSC markers to improve therapy effectiveness. It was found that the corrected-mRNA expression-based stemness index was upregulated in kidney renal clear cell carcinoma (KIRC) tissues compared to non-tumor tissue and increased with higher tumor stage and grade. EZH2 was identified as a CSC marker and prognosis factor for KIRC patients. The expression of EZH2 was associated with several activated tumor-infiltrating immune cells. High expression of EZH2 was enriched in immune-related pathways, low expression was related to several metabolic pathways. Epigallocatechin-3-gallate (EGCG) was identified as the most potent suppressor of EZH2, was able to inhibit viability, migration, and invasion, and to increase the apoptosis rate of ccRCC CSCs. KIF11, VEGF, and MMP2 were identified as predictive EGCG target genes, suggesting a potential mechanism of how EZH2 might regulate invasiveness and migration. The percentages of FoxP3+ Treg cells in the peripheral blood mononuclear cells of ccRCC patients decreased significantly when cultured with spheres pretreated with EGCG plus sunitinib compared to spheres without treatment. Our findings provide new insights into the treatment options of ccRCC based on targeting CSCs.

Reversal of Epithelial-Mesenchymal Transition and Inhibition of Tumor Stemness of Breast Cancer Cells Through Advanced Combined Chemotherapy

The abnormal activation of the Wnt/β-catenin signaling pathway and epithelial-mesenchymal transition (EMT) in drug-resistant tumor cells and cancer stem cells (CSCs) stimulate tumor metastasis and recurrence. Here, a promising combined chemotherapeutic strategy of salinomycin (SL) and doxorubicin (DOX) with specific inhibition of tumor stemness by a targeted co-delivery nanosystem was developed to overcome this abnormal progression. This strategy could be benefit drugs to effectively penetrate and infiltrate into spheres of 3D-cultured breast cancer stem cells (BCSCs). The expression of the Wnt/β-catenin signaling pathway-related genes (β-catenin, LRP6, LEF1, and TCF12) and target genes (Cyclin D1, Cmyc, and Fibronectin) as well as CSC stemness-related genes (Oct4, Nanog, and Hes1) was downregulated by redox-sensitive co-delivery micelles decorated with oligohyaluronic acid as the active targeting moiety. The changes in EMT-associated gene expression (E-cadherin and Vimentin) in vitro showed that the EMT process was also effectively inverted. This strategy achieved a strong inhibitory effect on solid tumor growth and an effective reduction in the risk of tumor metastasis in 4T1 tumor-bearing mice in vivo and effectively alleviated splenomegaly caused by the malignant tumor. Immunohistochemical staining analysis of E-cadherin, Vimentin, and β-catenin confirmed that the inversion of the EMT was also achieved in solid tumors. These results highlight the potential of SL and DOX combined chemotherapeutic strategy for eliminating breast carcinoma. STATEMENT OF SIGNIFICANCE: Cancer stem cells (CSCs), as an important part of tumor heterogeneity, can survive against conventional chemotherapy and initiate tumorigenesis, recurrence, and metastasis. Moreover, non-CSCs can convert into the CSC state through the abnormal Wnt/β-catenin pathway, which is closely related to the epithelial-mesenchymal transition (EMT) process. Here, redox-degradable binary drug-loaded micelles (PPH/DOX+SL) were designed to target CSCs and overcome drug resistance of breast cancer cells. The combined chemotherapy of salinomycin (SL) and doxorubicin (DOX) reversed drug resistance, while the PPH/DOX+SL micelles enhanced the intracellular accumulation and drug penetration of BCSC spheres. The introduction of SL downregulated the expression of tumor stemness genes and the Wnt/β-catenin pathway-related genes and inverted the EMT process. PPH/DOX+SL continuously inhibited tumor growth and invasion in vivo.

Uncovering the Heterogeneity and Clinical Relevance of Circulating Tumor-Initiating Cells in Hepatocellular Carcinoma Using an Integrated Immunomagnetic-Microfluidic Platform

Circulating tumor-initiating cells (CTICs) with stem cell-like properties play pivotal roles in tumor metastasis and recurrence. However, little is known about the biology and clinical relevance of CTICs in hepatocellular carcinoma (HCC). Here, we investigated the molecular heterogeneity and clinical relevance of CTICs in HCC using a novel integrated immunomagnetic-microfluidic platform (iMAC). We constructed the iMAC and evaluated its ability to detect CTICs using a series of spiked cell experiments. A four-channel microfluidic chip was applied to investigate the composition of CTICs in patients with primary and recurrent HCC utilizing microbeads labeled with one of four stem-related markers: epithelial cell adhesion molecule (EpCAM), CD133, CD90, and CD24. The dynamic changes of these four CTIC subsets were serially monitored during treatment courses. Finally, single-cell RNA profiling was used to reveal the molecular characteristics of the four CTIC subsets. The iMAC platform detected significantly more EpCAM⁺ CTICs in the blood samples from 33 HCC patients than the FDA-approved CellSearch system (0.92 ± 0.94 vs 0.23 ± 0.36, P < 0.001). The number of EpCAM⁺ CTICs (≥0.75/mL) detected by iMAC was a predictor of early recurrence (P = 0.007). The distinct stem-related markers' expression of CTICs could distinguish primary HCC, recurrent HCC, and TACE-resistant HCC. Single-cell transcriptional profiling proved the heterogeneity among individual CTICs and separated the four CTIC subsets into distinct phenotypes. Dissecting the heterogeneity of CTICs using the iMAC represents a novel and informative method for accurate CTIC detection and characterization. This innovative technology will enable more indepth cancer biology research and clinical cancer management than is currently available.

TNF-α-inducing protein of Helicobacter pylori promotes EMT and cancer stem-like cells properties via activation of Wnt/β-catenin signaling pathway in gastric cancer cells

Tumor necrosis factor-α-inducing protein (Tipα) is a newly identified toxin, which promotes the inflammation and carcinogenesis caused by Helicobacter pylori (H. pylori). However, its mechanism of pathogenesis is still unclear. To investigate the carcinogenic mechanisms of Tipα, SGC7901 cells and SGC7901-derived cancer stem-like cells (CSCs) were stimulated by recombinant Tipα protein with or without Wnt/β-catenin signaling inhibitor XAV939. qRT-PCR and Western blotting were employed to detect expression of epithelial-mesenchymal transition (EMT), CSCs markers, and downstream target genes of this signaling pathway. The cell migration ability was measured by wound healing assay and transwell assay. Our results indicated that Tipα promoted CSC properties of SGC7901 spheroids, including increased expression of CSC specific surface markers CD44, Oct4, Nanog, and an increased capacity for self-renewal. Tipα activated Wnt/β-catenin signaling in both SGC7901 cells or CSCs. Furthermore, Tipα induced the EMT and increased the expressions of downstream target genes of this signaling, including c-myc, cyclin D1, and CD44. However, XAV939 pretreatment inhibited Tipα-induced EMT and CSC properties in SGC7901 cells or CSCs. These results suggest that Tipα promotes EMT and CSC-like properties in gastric cancer cells through activation of Wnt/β-catenin signaling pathway, thereby accelerating the progression of gastric cancer.

Photocatalytic Superoxide Radical Generator that Induces Pyroptosis in Cancer Cells

Pyroptosis, a newly characterized form of immunogenic cell death, is attracting increasing attention as a promising approach to cancer immunotherapy. However, biocompatible strategies to activate pyroptosis remain rare. Here, we show that a photocatalytic superoxide radical (O₂^-•) generator, NI-TA, triggers pyroptosis in cancer cells. NI-TA was designed to take advantage of an intramolecular triplet-ground state splitting energy modulation approach. Detailed studies revealed that the pyroptosis triggered by NI-TA under conditions of photoexcitation proceeds through a caspase-3/gasdermin E (GSDME) pathway rather than via canonical processes involving caspase-1/gasdermin-D (GSDMD). NI-TA was found to function via a partial-O₂-recycling mode of action and to trigger cell pyroptosis and provide for effective cancer cell ablation even under conditions of hypoxia (≤2% O₂). In the case of T47D 3D multicellular spheroids, good antitumor efficiency and stemness inhibition are achieved. This work highlights how photocatalytic chemistry may be leveraged to develop effective pyroptosis-inducing agents.

Cisplatin-Resistant CD44+ Lung Cancer Cells Are Sensitive to Auger Electrons

Cancer stem cells (CSCs) are resistant to conventional therapy and present a major clinical challenge since they are responsible for the relapse of many cancers, including non-small cell lung cancer (NSCLC). Hence, future successful therapy should also eradicate CSCs. Auger electrons have demonstrated promising therapeutic potential and can induce DNA damage while sparing surrounding cells. Here, we sort primary patient-derived NSCLC cells based on their expression of the CSC-marker CD44 and investigate the effects of cisplatin and a thymidine analog (deoxyuridine) labeled with an Auger electron emitter (125I). We show that the CD44+ populations are more resistant to cisplatin than the CD44− populations. Interestingly, incubation with the thymidine analog 5-[125I]iodo-2′-deoxyuridine ([125I]I-UdR) induces equal DNA damage, G2/M cell cycle arrest, and apoptosis in the CD44− and CD44+ populations. Our results suggest that Auger electron emitters can also eradicate resistant lung cancer CD44+ populations.

Utilizing Carbon Ions to Treat Medulloblastomas that Exhibit Chromothripsis

Purpose of Review

Novel radiation therapies with accelerated charged particles such as protons and carbon ions have shown encouraging results in oncology. We present recent applications as well as benefits and risks associated with their use.

Recent Findings

We discuss the use of carbon ion radiotherapy to treat a specific type of aggressive pediatric brain tumors, namely medulloblastomas with chromothripsis. Potential reasons for the resistance to conventional treatment, such as the presence of cancer stem cells with unique properties, are highlighted. Finally, advantages of particle radiation alone and in combination with other therapies to overcome resistance are featured.

Summary

Provided that future preclinical studies confirm the evidence of high effectiveness, favorable toxicity profiles, and no increased risk of secondary malignancy, carbon ion therapy may offer a promising tool in pediatric (neuro)oncology and beyond.

Insights Into Vascular Anomalies, Cancer, and Fibroproliferative Conditions: The Role of Stem Cells and the Renin-Angiotensin System

Cells exhibiting embryonic stem cell (ESC) characteristics have been demonstrated in vascular anomalies (VAs), cancer, and fibroproliferative conditions, which are commonly managed by plastic surgeons and remain largely unsolved. The efficacy of the mTOR inhibitor sirolimus, and targeted therapies that block the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways in many types of cancer and VAs, further supports the critical role of ESC-like cells in the pathogenesis of these conditions. ESC-like cells in VAs, cancer, and fibroproliferative conditions express components of the renin-angiotensin system (RAS) – a homeostatic endocrine signaling cascade that regulates cells with ESC characteristics. ESC-like cells are influenced by the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways, which directly regulate cellular proliferation and stemness, and interact with the RAS at multiple points. Gain-of-function mutations affecting these pathways have been identified in many types of cancer and VAs, that have been treated with targeted therapies with some success. In cancer, the RAS promotes tumor progression, treatment resistance, recurrence, and metastasis. The RAS modulates cellular invasion, migration, proliferation, and angiogenesis. It also indirectly regulates ESC-like cells via its direct influence on the tissue microenvironment and by its interaction with the immune system. In vitro studies show that RAS inhibition suppresses the hallmarks of cancer in different experimental models. Numerous epidemiological studies show a reduced incidence of cancer and improved survival outcomes in patients taking RAS inhibitors, although some studies have shown no such effect. The discovery of ESC-like cells that express RAS components in infantile hemangioma (IH) underscores the paradigm shift in the understanding of its programmed biologic behavior and accelerated involution induced by β-blockers and angiotensin-converting enzyme inhibitors. The findings of SOX18 inhibition by R-propranolol suggests the possibility of targeting ESC-like cells in IH without β-adrenergic blockade, and its associated side effects. This article provides an overview of the current knowledge of ESC-like cells and the RAS in VAs, cancer, and fibroproliferative conditions. It also highlights new lines of research and potential novel therapeutic approaches for these unsolved problems in plastic surgery, by targeting the ESC-like cells through manipulation of the RAS, its bypass loops and converging signaling pathways using existing low-cost, commonly available, and safe oral medications.

Rapid Isolation of Gastric Adenocarcinoma Cancer Stem Cells as a Target for Autologous Dendritic Cell-Based Immunotherapy

Background

Gastric cancer (GC) is a malignancy cause associated with a high death rate in the world. Cancer stem cells (CSCs) are a rare immortal subpopulation of cells within tumors with characteristics of the ability to self-renew, initiate tumor, and differentiate into defined progenies as well as and high resistance to conventional therapies.

Objectives

Despite the use of surgery and chemotherapy for GC therapy, there are no efficient therapeutic protocols for it to date. Therefore, rapid isolation of CSCs in order to therapeutic targets, especially immunotherapy is very important.

Materials and Methods

Cancerous cell suspension isolated from patients with GC was cultured in the serum-free medium containing EGF, bFGF, LIF, and heparin under non-adherent culture conditions to generate spheres. Expression of mRNA level stemness transcription factors (OCT4, SOX2, SALL4, and Cripto-1), CD44 variable isoforms (CD44s, CD44v3, CD44v6, CD44V8-10) of spheroid-forming single cells compared with gastric normal tissue cells using real time PCR and molecules of CD44, CD54, and EpCAM as gastric CSC markers, and stemness factor Oct4 using flow cytometry, as well as tumorgenicity using subcutaneous injection of sphere-forming cells to nude mice were investigated.

Results

Few cancerous cells isolated from patients with GC were able to generate three-dimensional spheroid colonies in the serum-free medium containing EGF, bFGF, LIF, and heparin under non-adherent culture conditions, and form xenograft tumors in immunodeficient nude mice after subcutaneous injection. Spheroid-forming single cells upregulated stemness transcription factors OCT4, SOX2, SALL4, and Cripto-1 that are associated with pluripotency and self-renewal and CD44 isoforms (CD44s, CD44v3, CD44v6, CD44V8-10) compared with gastric normal tissue cells. Finally, molecules of CD44, CD54, and EpCAM as gastric CSC markers and stemness factor Oct4 were expressed in sphere-forming cells.

Conclusion

We suggested that the sphere formation and tumorigenicity assays are two procedures, leading to the rapid isolation of cancer cells with certain stem-like properties in order to target CSCs using autologous dendritic cell therapy, especially in patients with advanced disease.

Heme Oxygenase-1 Has a Greater Effect on Melanoma Stem Cell Properties Than the Expression of Melanoma-Initiating Cell Markers

Melanoma-initiating cells (MICs) contribute to the tumorigenicity and heterogeneity of melanoma. MICs are identified by surface and functional markers and have been shown to display cancer stem cell (CSC) properties. However, the existence of MICs that follow the hierarchical CSC model has been questioned by studies showing that single unselected melanoma cells are highly tumorigenic in xenotransplantation assays. Herein, we characterize cells expressing MIC markers (CD20, CD24, CD133, Sca-1, ABCB1, ABCB5, ALDH^high) in the B16-F10 murine melanoma cell line. We use flow cytometric phenotyping, single-cell sorting followed by in vitro clonogenic assays, and syngeneic in vivo serial transplantation assays to demonstrate that the expression of MIC markers does not select CSC-like cells in this cell line. Previously, our group showed that heme-degrading enzyme heme oxygenase-1 (HO-1) can be upregulated in melanoma and increase its aggressiveness. Here, we show that HO-1 activity is important for non-adherent growth of melanoma and HO-1 overexpression enhances the vasculogenic mimicry potential, which can be considered protumorigenic activity. However, HO-1 overexpression decreases clone formation in vitro and serial tumor initiation in vivo. Thus, HO-1 plays a dual role in melanoma, improving the progression of growing tumors but reducing the risk of melanoma initiation.

siRNA-induced CD44 knockdown suppresses the proliferation and invasion of colorectal cancer stem cells through inhibiting epithelial-mesenchymal transition

CD44 has shown prognostic values and promising therapeutic potential in multiple human cancers; however, the effects of CD44 silencing on biological behaviors of cancer stem cells (CSCs) have not been fully understood in colorectal cancer. To examine the contribution of siRNA‐induced knockdown of CD44 to the biological features of colorectal CSCs, colorectal CSCs HCT116‐CSCs were generated, and CD44 was knocked down in HCT116‐CSCs using siRNA. The proliferation, migration and invasion of HCT116‐CSCs were measured, and apoptosis and cell‐cycle analyses were performed. The sensitivity of HCT116‐CSCs to oxaliplatin was tested, and xenograft tumor growth assay was performed to examine the role of CD44 in HCT116‐CSCs tumorigenesis in vivo. In addition, the expression of epithelial–mesenchymal transition (EMT) markers E‐cadherin, N‐cadherin and vimentin was quantified. siRNA‐induced knockdown of CD44 was found to inhibit the proliferation, migration and invasion, induce apoptosis, promote cell‐cycle arrest at the G1/G0 phase and increase the sensitivity of HCT116‐CSCs to oxaliplatin in HCT116‐CSCs, and knockdown of CD44 suppressed in vivo tumorigenesis and intrapulmonary metastasis of HCT116‐CSCs. Moreover, silencing CD44 resulted in EMT inhibition. Our findings demonstrate that siRNA‐induced CD44 knockdown suppresses the proliferation, invasion and in vivo tumorigenesis and metastasis of colorectal CSCs by inhibiting EMT.

Integrative molecular and clinical profiling of acral melanoma links focal amplification of 22q11.21 to metastasis

Acral melanoma, the most common melanoma subtype among non-White individuals, is associated with poor prognosis. However, its key molecular drivers remain obscure. Here, we perform integrative genomic and clinical profiling of acral melanomas from 104 patients treated in North America (n = 37) or China (n = 67). We find that recurrent, late-arising focal amplifications of cytoband 22q11.21 are a leading determinant of inferior survival, strongly associated with metastasis, and linked to downregulation of immunomodulatory genes associated with response to immune checkpoint blockade. Unexpectedly, LZTR1 - a known tumor suppressor in other cancers - is a key candidate oncogene in this cytoband. Silencing of LZTR1 in melanoma cell lines causes apoptotic cell death independent of major hotspot mutations or melanoma subtypes. Conversely, overexpression of LZTR1 in normal human melanocytes initiates processes associated with metastasis, including anchorage-independent growth, formation of spheroids, and an increase in MAPK and SRC activities. Our results provide insights into the etiology of acral melanoma and implicate LZTR1 as a key tumor promoter and therapeutic target.

Molecular Docking as a Therapeutic Approach for Targeting Cancer Stem Cell Metabolic Processes

Cancer stem cells (CSCs) are subpopulation of cells which have been demonstrated in a variety of cancer models and involved in cancer initiation, progression, and development. Indeed, CSCs which seem to form a small percentage of tumor cells, display resembling characteristics to natural stem cells such as self-renewal, survival, differentiation, proliferation, and quiescence. Moreover, they have some characteristics that eventually can demonstrate the heterogeneity of cancer cells and tumor progression. On the other hand, another aspect of CSCs that has been recognized as a central concern facing cancer patients is resistance to mainstays of cancer treatment such as chemotherapy and radiation. Owing to these details and the stated stemness capabilities, these immature progenitors of cancerous cells can constantly persist after different therapies and cause tumor regrowth or metastasis. Further, in both normal development and malignancy, cellular metabolism and stemness are intricately linked and CSCs dominant metabolic phenotype changes across tumor entities, patients, and tumor subclones. Hence, CSCs can be determined as one of the factors that correlate to the failure of common therapeutic approaches in cancer treatment. In this context, researchers are searching out new alternative or complementary therapies such as targeted methods to fight against cancer. Molecular docking is one of the computational modeling methods that has a new promise in cancer cell targeting through drug designing and discovering programs. In a simple definition, molecular docking methods are used to determine the metabolic interaction between two molecules and find the best orientation of a ligand to its molecular target with minimal free energy in the formation of a stable complex. As a comprehensive approach, this computational drug design method can be thought more cost-effective and time-saving compare to other conventional methods in cancer treatment. In addition, increasing productivity and quality in pharmaceutical research can be another advantage of this molecular modeling method. Therefore, in recent years, it can be concluded that molecular docking can be considered as one of the novel strategies at the forefront of the cancer battle via targeting cancer stem cell metabolic processes.

Multiple transcriptome analysis of Piwil2-induced cancer stem cells, including piRNAs, mRNAs and miRNAs reveals the mechanism of tumorigenesis and development

BACKGROUND

Cancer stem cells play important roles in the process of tumorigenesis. Our research group obtained cancer stem cell-like cells named Piwil2-iCSCs by reprogramming human preputial fibroblasts (FBs) with the PIWIL2 gene, but the mechanism of Piwil2-iCSCs is still unclear.

METHODS

We sequenced the piRNAs, miRNAs and mRNAs of Piwil2-iCSCs and FBs, and analyzed the differences. Gene Ontology (GO) and, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses and gene set enrichment analysis (GSEA) were performed on the differentially expressed (DE) mRNAs. In addition, we analyzed the variable shear events and fusion genes in the Piwil2-iCSCs. Target gene prediction and functional enrichment analysis were performed for the DE miRNAs.

RESULTS

A total of 1119 DE mRNAs, 220 DE piRNAs, and 440 DE miRNAs were obtained between the Piwil2-iCSCs and FBs. Functional enrichment analysis showed that the genes with upregulated expression were mainly involved in DNA repair, mismatch repair, base excision repair, and nucleotide excision repair. Genes with downregulated expression were mainly involved in the TGF-β receptor signaling pathway, senescence and autophagy in cancer. More frequent shear events occurred in Piwil2-iCSCs and FBs, especially in intron retention (IR) events. We also identified three fusion genes MCM3AP-C21orf58, LRRFIP2-CAV3 and TMEM184B-DMC1. Enrichment analysis of DE miRNAs showed that they were associated with apoptosis, the TGF-β signaling pathway, and the stem cell regulatory signaling pathway. In particular, target gene prediction of the top three miRNAs with upregulated expression showed that they targeted SMAD, GREM1 and other genes to participate in the regulation of TGF-β and other pathways.

CONCLUSION

PIWIL2-induced cancer stem cells have significantly altered levels of miRNAs, piRNAs and mRNAs.TGF-β, autophagy, apoptosis and other pathways may play an important role in stem cell development. The occurrence of alternative splicing and fusion genes may be related to the occurrence of cancer stem cells.

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.

Tumor radioresistance caused by radiation-induced changes of stem-like cell content and sub-lethal damage repair capability

Cancer stem-like cells (CSCs) within solid tumors exhibit radioresistance, leading to recurrence and distant metastasis after radiotherapy. To experimentally study the characteristics of CSCs, radioresistant cell lines were successfully established using fractionated X-ray irradiation. The fundamental characteristics of CSCs in vitro have been previously reported; however, the relationship between CSC and acquired radioresistance remains uncertain. To efficiently study this relationship, we performed both in vitro experiments and theoretical analysis using a cell-killing model. Four types of human oral squamous carcinoma cell lines, non-radioresistant cell lines (SAS and HSC2), and radioresistant cell lines (SAS-R and HSC2-R), were used to measure the surviving fraction after single-dose irradiation, split-dose irradiation, and multi-fractionated irradiation. The SAS-R and HSC2-R cell lines were more positive for one of the CSC marker aldehyde dehydrogenase activity than the corresponding non-radioresistant cell lines. The theoretical model analysis showed that changes in both the experimental-based ALDH (+) fractions and DNA repair efficiency of ALDH (-) fractions (i.e., sub-lethal damage repair) are required to reproduce the measured cell survival data of non-radioresistant and radioresistant cell lines. These results suggest that the enhanced cell recovery in SAS-R and HSC2-R is important when predicting tumor control probability in radiotherapy to require a long dose-delivery time; in other words, intensity-modulated radiation therapy is ideal. This work provides a precise understanding of the mechanism of radioresistance, which is induced after irradiation of cancer cells.

YBX1 Enhances Metastasis and Stemness by Transcriptionally Regulating MUC1 in Lung Adenocarcinoma

Abnormal expression of the transcription factor Y-box-binding protein-1 (YBX1) is associated with the proliferation, migration, aggressiveness, and stem-like properties of various cancers. These characteristics contribute to the tumorigenesis and metastasis of cancer. We found that the expression levels of Mucin-1 (MUC1) and YBX1 were positively correlated in lung adenocarcinoma cells and lung adenocarcinoma tissue. Our retrospective cohort study of 176 lung adenocarcinoma patients after surgery showed that low expression of both YBX1 and MUC1 was an independent predictor of the prognosis and recurrence of lung adenocarcinoma. In lung adenocarcinoma cells, the silencing/overexpression of YBX1 caused a simultaneous change in MUC1, and MUC1 overexpression partially reversed the decreased tumor cell migration, aggressiveness, and stemness caused by YBX1 silencing. Moreover, chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assays proved that MUC1 was the downstream target of YBX1 and that YBX1 bound to the -1480~-1476 position in the promoter region of MUC1 to regulate its transcription. Furthermore, in mouse xenograft models and a lung cancer metastasis model, MUC1, which is downstream of YBX1, partially reversed the decreased number and size of tumors caused by YBX1 silencing. In conclusion, our findings indicated a novel mechanism by which YBX1 promotes the stemness and metastasis of lung adenocarcinoma by targeting MUC1 and provided a combination approach for diagnosis different from traditional single tumor biomarkers to predict patient prognosis and provide clinical treatment targets.

Autophagy regulates the cancer stem cell phenotype of head and neck squamous cell carcinoma through the noncanonical FOXO3/SOX2 axis

Autophagy is an essential catabolic process that orchestrates cellular homeostasis and plays dual roles in tumor promotion and suppression. However, the mechanism by which autophagy affects the self-renewal of cancer stem cells (CSCs) remains unclear. In this study, we investigated whether autophagy activation contributes to CSC properties of head and neck squamous cell carcinoma (HNSCC). The results showed that the autophagy level and CSC properties of HNSCC cells were elevated in response to several adverse conditions, including treatment with cisplatin, starvation, and hypoxia. Pretreatment with autophagy inhibitors, such as 3-MA and chloroquine, diminished the CSC properties acquired under adverse conditions. In addition, the isolated CSCs were endowed with stronger autophagic activity than non-CSCs, and the CSC properties were dampened when autophagy was inhibited either by 3-MA, chloroquine, or Beclin1 knockdown. Notably, the tumor-initiating activity of CSCs was decreased upon knocking down Beclin1. Further study revealed that FOXO3, a substrate for autophagy, was enriched in the nucleus of cells with lower autophagy levels. Nuclear FOXO3 directly bound to the promoter region of SOX2 and negatively regulated its transcriptional activity. Overexpression of FOXO3 decreased the expression of SOX2 and thereby impaired the CSC phenotype both in vitro and in vivo. Taken together, our findings suggest that the activation of autophagy is essential for the acquisition of CSC properties in adverse conditions and the self-renewal of CSCs. We clarify the role of autophagy in regulating the CSC phenotype and demonstrate that the noncanonical FOXO3/SOX2 axis is the intrinsic regulatory mechanism.

Repurposing of Anticancer Stem Cell Drugs in Brain Tumors

Brain tumors in adults may be infrequent when compared with other cancer etiologies, but they remain one of the deadliest with bleak survival rates. Current treatment modalities encompass surgical resection, chemotherapy, and radiotherapy. However, increasing resistance rates are being witnessed, and this has been attributed, in part, to cancer stem cells (CSCs). CSCs are a subpopulation of cancer cells that reside within the tumor bulk and have the capacity for self-renewal and can differentiate and proliferate into multiple cell lineages. Studying those CSCs enables an increasing understanding of carcinogenesis, and targeting CSCs may overcome existing treatment resistance. One approach to weaponize new drugs is to target these CSCs through drug repurposing which entails using drugs, which are Food and Drug Administration-approved and safe for one defined disease, for a new indication. This approach serves to save both time and money that would otherwise be spent in designing a totally new therapy. In this review, we will illustrate drug repurposing strategies that have been used in brain tumors and then further elaborate on how these approaches, specifically those that target the resident CSCs, can help take the field of drug repurposing to a new level.

The Role of the Renin-Angiotensin System in the Cancer Stem Cell Niche

Cancer stem cells (CSCs) drive metastasis, treatment resistance, and tumor recurrence. CSCs reside within a niche, an anatomically distinct site within the tumor microenvironment (TME) that consists of malignant and non-malignant cells, including immune cells. The renin-angiotensin system (RAS), a critical regulator of stem cells and key developmental processes, plays a vital role in the TME. Non-malignant cells within the CSC niche and stem cell signaling pathways such as the Wnt, Hedgehog, and Notch pathways influence CSCs. Components of the RAS and cathepsins B and D that constitute bypass loops of the RAS are expressed on CSCs in many cancer types. There is extensive in vitro and in vivo evidence showing that RAS inhibition reduces tumor growth, cell proliferation, invasion, and metastasis. However, there is inconsistent epidemiological data on the effect of RAS inhibitors on cancer incidence and survival outcomes, attributed to different patient characteristics and methodologies used between studies. Further mechanistic studies are warranted to investigate the precise effects of the RAS on CSCs directly and/or the CSC niche. Targeting the RAS, its bypass loops, and convergent signaling pathways participating in the TME and other key stem cell pathways that regulate CSCs may be a novel approach to cancer treatment.

Potential Role of GST-π in Lung Cancer Stem Cell Cisplatin Resistance

Background

Cancer stem cells (CSCs) are responsible for tumorigenesis, chemoresistance, and metastasis. Chemoresistance is a major challenge in the management of lung cancer. Glutathione-sulphur-transferase-π (GST-π) plays an important role in the origin and development of various types of cancer by regulating the cellular redox balance. Recent investigations have demonstrated that GST-π is associated with the chemoresistance of lung CSCs (LCSCs). However, the mechanism of GST-π in lung cancer, particularly in LCSCs, remains unclear. The present study is aimed at exploring the potential role of GST-π in stemness and cisplatin (DDP) resistance of LCSCs. Materials and methods. In the present study, lung cancer cell spheres were established using the A549 cell line, which according to our previous research, was confirmed to exhibit characteristics of stem cells. Next, GST-π protein expression, apoptosis percentage, and intracellular reactive oxygen species (ROS) concentration in A549 adherent cells and A549 cell spheres were analyzed by western blotting and flow cytometry, respectively. Finally, DDP resistance, ROS concentration, and GST-π expression in LCSCs were analyzed following the interference with GST-π using DL-buthionine-(S,R)-sulphoximine and N-acetylcysteine.

Results

The results revealed that GST-π was highly expressed in A549 cell spheres compared with A549 adherent cells and was associated with a decreased intracellular ROS concentration (both P < 0.05). Regulating GST-π protein expression could alter DDP resistance of LCSCs by influencing ROS.

Conclusion

These results suggested that GST-π may be important for LCSC drug resistance by downregulating ROS levels. These findings may contribute to the development of new adjuvant therapeutic strategies for lung cancer.

Connexin46 Expression Enhances Cancer Stem Cell and Epithelial-to-Mesenchymal Transition Characteristics of Human Breast Cancer MCF-7 Cells

Connexins (Cxs) are a family of proteins that form two different types of ion channels: hemichannels and gap junction channels. These channels participate in cellular communication, enabling them to share information and act as a synchronized syncytium. This cellular communication has been considered a strong tumor suppressor, but it is now recognized that some type of Cxs can be pro-tumorigenic. For example, Cx46 expression is increased in human breast cancer samples and correlates with cancer stem cell (CSC) characteristics in human glioma. Thus, we explored whether Cx46 and glioma cells, can set up CSC and epithelial-to-mesenchymal transition (EMT) properties in a breast cancer cell line. To this end, we transfected MCF-7 cells with Cx46 attached to a green fluorescent protein (Cx46GFP), and we determined how its expression orchestrates both the gene-expression and functional changes associated with CSC and EMT. We observed that Cx46GFP increased Sox2, Nanog, and OCT4 mRNA levels associated with a high capacity to form monoclonal colonies and tumorspheres. Similarly, Cx46GFP increased the mRNA levels of n-cadherin, Vimentin, Snail and Zeb1 to a higher migratory and invasive capacity. Furthermore, Cx46GFP transfected in MCF-7 cells induced the release of higher amounts of VEGF, which promoted angiogenesis in HUVEC cells. We demonstrated for the first time that Cx46 modulates CSC and EMT properties in breast cancer cells and thus could be relevant in the design of future cancer therapies.

Cancer stem cells and strategies for targeted drug delivery

Cancer stem cells (CSCs) are a small proportion of cancer cells with high tumorigenic activity, self-renewal ability, and multilineage differentiation potential. Standard anti-tumor therapies including conventional chemotherapy, radiation therapy, and molecularly targeted therapies are not effective against CSCs, and often lead to enrichment of CSCs that can result in tumor relapse. Therefore, it is hypothesized that targeting CSCs is key to increasing the efficacy of cancer therapies. In this review, CSC properties including CSC markers, their role in tumor growth, invasiveness, metastasis, and drug resistance, as well as CSC microenvironment are discussed. Further, CSC-targeted strategies including the use of targeted drug delivery systems are examined.

Deep-Red/Near-Infrared Turn-On Fluorescence Probes for Aldehyde Dehydrogenase 1A1 in Cancer Stem Cells

Accumulating evidence supports that cancer stem cells (CSCs) are responsible for cancer proliferation, metastasis, and therapy resistance; therefore, an effective strategy to identify and isolate CSCs is required urgently. Because of their low invasiveness and high signal/noise ratio, "turn-on" fluorescence probes working in the deep-red/near-infrared (DR/NIR) region are one of the most attractive yet undeveloped tools for CSC detection. Herein, we report DR/NIR turn-on fluorescence probes, CS5-A and CS7-A, targeted to aldehyde dehydrogenase 1A1 as an intracellular CSC marker. In contrast to the conventional "always-on" green-fluorescent ALDEFLUOR, we succeeded in generating high-contrast (signal/noise ratio > 8.3) and wash-free in vitro CSC imaging with the DR probe C5S-A. This probe can facilitate CSC isolation with minimal contamination by autofluorescence from other tissues through fluorescence-activated cell sorting. Furthermore, the NIR absorbance/emission and turn-on properties of C7S-A allow simple and rapid CSC detection in vivo within 15 min.

Microgel Single-Cell Culture Arrays on a Microfluidic Chip for Selective Expansion and Recovery of Colorectal Cancer Stem Cells

Cancer stem cells (CSCs) are rare and lack definite biomarkers, necessitating new methods for a robust expansion. Here, we developed a microfluidic single-cell culture (SCC) approach for expanding and recovering colorectal CSCs from both cell lines and tumor tissues. By incorporating alginate hydrogels with droplet microfluidics, a high-density microgel array can be formed on a microfluidic chip that allows for single-cell encapsulation and nonadhesive culture. The SCC approach takes advantage of the self-renewal property of stem cells, as only the CSCs can survive in the SCC and form tumorspheres. Consecutive imaging confirmed the formation of single-cell-derived tumorspheres, mainly from a population of small-sized cells. Through on-chip decapsulation of the alginate microgel, ∼6000 live cells can be recovered in a single run, which is sufficient for most biological assays. The recovered cells were verified to have the genetic and phenotypic characteristics of CSCs. Furthermore, multiple CSC-specific targets were identified by comparing the transcriptomics of the CSCs with the primary cancer cells. To summarize, the microgel SCC array offers a label-free approach to obtain sufficient quantities of CSCs and thus is potentially useful for understanding cancer biology and developing personalized CSC-targeting therapies.

MicroRNA‑8063 targets heterogeneous nuclear ribonucleoprotein AB to inhibit the self‑renewal of colorectal cancer stem cells via the Wnt/β‑catenin pathway

The presence of cancer stem cells (CSCs) is a major cause of therapeutic failure in a variety of cancer types, including colorectal cancer (CRC). However, the underlying mechanisms that regulate the self-renewal of colorectal cancer stem cells (CRCSCs) remain unclear. Our previous study utilized CRCSCs and their parent cells; through gene microarray screening and bioinformatics analysis, we hypothesized that microRNA (miR)-8063 may bind to, and regulate the expression of, heterogeneous nuclear ribonucleoprotein AB (hnRNPAB) to facilitate the regulation of CRCSC self-renewal. The aim of the present study was to confirm this conjecture through relevant experiments. The results indicated that compared with that in parent cells, miR-8063 expression was significantly downregulated in CRCSCs, while hnRNPAB expression was increased. Furthermore, hnRNPAB was identified as a direct target of miR-8063 using a dual-Luciferase assay. Overexpression of hnRNPAB promoted the acquisition of CSC characteristics in CRC cells (increased colony formation ability, enhanced tumorigenicity, and upregulated expression of CSC markers), as well as the upregulation of key proteins (Wnt3a, Wnt5a and β-catenin) in the Wnt/β-catenin signaling pathway. Similarly, after silencing miR-8063 in CRC cells, the characteristics of CSC were altered, and the expression of hnRNPAB protein was promoted. However, post overexpression of miR-8063 in CRCSCs, the self-renewal ability of CSCs was weakened with the downregulation of hnRNPAB protein, Wnt3a, Wnt5a and β-catenin. These results suggest that as a tumor suppressor, miR-8063 is involved in regulating the self-renewal of CRCSCs, where loss of miR-8063 expression weakens its inhibition on hnRNPAB, which leads to the activation of Wnt/β-catenin signaling to promote the self-renewal of CRCSCs.

FOXD1 promotes EMT and cell stemness of oral squamous cell carcinoma by transcriptional activation of SNAI2

Background

Epithelial-mesenchymal transition (EMT) and cell stemness are implicated in the initiation and progression of oral squamous cell carcinoma (OSCC). Revealing the intrinsic regulatory mechanism may provide effective therapeutic targets for OSCC.

Results

In this study, we found that Forkhead box D1 (FOXD1) was upregulated in OSCC compared with normal samples. Patients with a higher FOXD1 expression had a poorer overall survival and disease-free survival. Immunohistochemical staining results showed that FOXD1 expression was related to the clinical stage and relapse status of OSCC patients. When FOXD1 expression was knocked down in CAL27 and SCC25 cells, the migration, invasion, colony formation, sphere formation, and proliferation abilities decreased. Moreover, EMT and stemness-related markers changed remarkably, which indicated that the EMT process and cell stemness were inhibited. Conversely, overexpression of FOXD1 promoted EMT and cell stemness. Further study demonstrated that FOXD1 could bind to the promoter region and activate the transcription of SNAI2. In turn, the elevated SNAI2 affected EMT and cell stemness. An in vivo study showed that FOXD1-overexpressing CAL27 cells possessed a stronger tumorigenic ability.

Conclusions

Our findings revealed a novel mechanism in regulating EMT and cell stemness and proposed FOXD1 as a potential marker for the diagnosis and treatment of OSCC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00671-9.

Epigenetic modulators for brain cancer stem cells: Implications for anticancer treatment

Primary malignant brain tumors are a major cause of morbidity and mortality in both adults and children, with a dismal prognosis despite multimodal therapeutic approaches. In the last years, a specific subpopulation of cells within the tumor bulk, named cancer stem cells (CSCs) or tumor-initiating cells, have been identified in brain tumors as responsible for cancer growth and disease progression. Stemness features of tumor cells strongly affect treatment response, leading to the escape from conventional therapeutic approaches and subsequently causing tumor relapse. Recent research efforts have focused at identifying new therapeutic strategies capable of specifically targeting CSCs in cancers by taking into consideration their complex nature. Aberrant epigenetic machinery plays a key role in the genesis and progression of brain tumors as well as inducing CSC reprogramming and preserving CSC characteristics. Thus, reverting the cancer epigenome can be considered a promising therapeutic strategy. Three main epigenetic mechanisms have been described: DNA methylation, histone modifications, and non-coding RNA, particularly microRNAs. Each of these mechanisms has been proven to be targetable by chemical compounds, known as epigenetic-based drugs or epidrugs, that specifically target epigenetic marks. We review here recent advances in the study of epigenetic modulators promoting and sustaining brain tumor stem-like cells. We focus on their potential role in cancer therapy.

Cancer Stem-Like Phenotype of Mitochondria Dysfunctional Hep3B Hepatocellular Carcinoma Cell Line

Mitochondria are major organelles that play various roles in cells, and mitochondrial dysfunction is the main cause of numerous diseases. Mitochondrial dysfunction also occurs in many cancer cells, and these changes are known to affect malignancy. The mitochondria of normal embryonic stem cells (ESCs) exist in an undifferentiated state and do not function properly. We hypothesized that mitochondrial dysfunction in cancer cells caused by the depletion of mitochondrial DNA might be similar to the mitochondrial state of ESCs. We generated mitochondria dysfunctional (ρ0) cells from the Hep3B hepatocellular carcinoma cell line and tested whether these ρ0 cells show cancer stem-like properties, such as self-renewal, chemotherapy resistance, and angiogenesis. Compared with Hep3B cells, the characteristics of each cancer stem-like cell were increased in Hep3B/ρ0 cells. The Hep3B/ρ0 cells formed a continuous and large sphere from a single cell. Additionally, the Hep3B/ρ0 cells showed resistance to the anticancer drug doxorubicin because of the increased expression of ATP-binding cassette Subfamily B Member 1. The Hep3B/ρ0 conditioned medium induced more and thicker blood vessels and increased the mobility and invasiveness of the blood vessel cells. Therefore, our data suggest that mitochondrial dysfunction can transform cancer cells into cancer stem-like cells.