Targeting cancer stem cells and their niche: perspectives for future therapeutic targets and strategies. Semin Cancer Biol. 2018;53:139-155. [PMID: 30081228 DOI: 10.1016/j.semcancer.2018.08.002]

MUC1-EGFR crosstalk with IL-6 by activating NF-κB and MAPK pathways to regulate the stemness and paclitaxel-resistance of lung adenocarcinoma

BACKGROUND

The chemotherapy resistance often leads to chemotherapy failure. This study aims to explore the molecular mechanism by which MUC1 regulates paclitaxel resistance in lung adenocarcinoma (LUAD), providing scientific basis for future target selection.

METHODS

The bioinformatics method was used to analyse the mRNA and protein expression characteristics of MUC1 in LUAD. RT-qPCR and ELISA were used to detect the mRNA and protein expression, flow cytometry was used to detect CD133+ cells, and cell viability was detected by CCK-8 assay. The mRNA-seq was performed to analyse the changes in expression profile, GO and KEGG analysis were used to explore the potential biological functions.

RESULTS

MUC1 is highly expressed in LUAD patients and is associated with a higher tumour infiltration. In paclitaxel resistance LUAD cells (A549/TAX cells), the expression of MUC1, EGFR/p-EGFR and IL-6 were higher than that of A549 cells, the proportion of CD133+ cells was significantly increased, and the expression of cancer stem cell (CSCs) transcription factors (NANOG, OCT4 and SOX2) were significantly up-regulated. After knocking down MUC1 in A549/Tax cells, the activity of A549/Tax cells was significantly decreased. Correspondingly, the expression of EGFR, IL-6, OCT4, NANOG, and SOX2 were significantly down-regulated. The mRNA-seq showed that knocking down MUC1 affected the gene expression, DEGs mainly enriched in NF-κB and MAPK signalling pathway.

CONCLUSION

MUC1 was highly expressed in A549/TAX cells, and MUC1-EGFR crosstalk with IL-6 may be due to the activation of NF-κB and MAPK pathways, which promote the enrichment of CSCs and lead to paclitaxel resistance.

Emodin regulated lactate metabolism by inhibiting MCT1 to delay non-small cell lung cancer progression

Lung cancer is one of the most common malignant tumors in the world, with high incidence rate and mortality. Monocarboxylate transporter (MCT) 1 has been found to be widely expressed in various tumors and plays a crucial role in regulating energy metabolism. Emodin, as an important traditional Chinese medicine in China, has been reported to inhibit the progression of lung cancer. However, its potential mechanism has not been fully elucidated. The effects of emodin and MCT1 inhibitor AZD3965 on the proliferation, migration, and invasion of lung cancer cells were detected using cell counting kit-8 (CCK-8) assay, wound-healing assay, and transwell small chamber assay. The content of glucose, lactate, and pyruvate in the cell culture medium was detected using a glucose, lactate, and pyruvate detection kit, and also detected protein expression using western blotting. In addition, to investigate the effects of emodin and AZD3965 on lung cancer in vivo, we constructed nude mice subcutaneous transplant tumor model by subcutaneous injection of lung cancer cells. The results showed that emodin and AZD3965 could inhibit the proliferation, migration, and invasion of lung cancer cells. At the same time, they could inhibit the expression of MCT1 in lung cancer cells and promote the release of lactate, but did not affect the content of glucose and pyruvate. In vivo experiments had shown that emodin and AZD3965 could effectively inhibit the growth of lung cancer and inhibit the expression of MCT1. All in all, our data suggested that emodin inhibited the proliferation, migration, and invasion of lung cancer cells, possibly by inhibiting MCT1, providing important theoretical basis for elucidating the mechanism of emodin in treating lung cancer.

Application of hydrogels for targeting cancer stem cells in cancer treatment

Cancer stem cells (CSCs) are a major hindrance to clinical cancer treatment. Owing to their high tumorigenic and metastatic potential, CSCs are vital in malignant tumor initiation, growth, metastasis, and therapeutic resistance, leading to tumorigenesis and recurrence. Compared with normal tumor cells, CSCs express high levels of surface markers (CD44, CD90, CD133, etc.) and activate specific signaling pathways (Wnt/β-catenin, Notch, and Hedgehog). Although Current drug delivery systems (DDS) precisely target CSCs, the heterogeneity and multidrug resistance of CSCs impede CSC isolation and screening. Conversely, hydrogel DDSs exhibit good biocompatibility and high drug delivery efficiency. Hydrogels are three-dimensional (3D) spatial structures for drug encapsulation that facilitate the controlled release of bioactive molecules. Hence, hydrogels can be loaded with drugs to precisely target CSCs. Their 3D structure can also culture non-CSCs and facilitate their transformation into CSCs. for identification and isolation. Given that their elastic modulus and stiffness characteristics reflect those of the cellular microenvironment, hydrogels can simulate extracellular matrix pathways and markers to regulate CSCs, disrupting the equilibrium between CSC and non-CSC transformation. This article reviews the CSC microenvironment, metabolism, signaling pathway, and surface markers. Additionally, we summarize the existing CSC targeting strategies and explore the application of hydrogels for CSC screening and treatment. Finally, we discuss potential advances in CSC research that may lead to curative measures for tumors through targeted and precise attacks on CSCs.

High-Risk Neuroblastoma Challenges and Opportunities for Antibody-Based Cellular Immunotherapy

Immunotherapy has emerged as an attractive option for patients with relapsed or refractory high-risk neuroblastoma (HRNB). Neuroblastoma (NB), a sympathetic nervous system cancer arising from an embryonic neural crest cell, is heterogeneous clinically, with outcomes ranging from an isolated abdominal mass that spontaneously regresses to a widely metastatic disease with cure rates of about 50% despite intensive multimodal treatment. Risk group stratification and stage-adapted therapy to achieve cure with minimal toxicities have accomplished major milestones. Targeted immunotherapeutic approaches including monoclonal antibodies, vaccines, adoptive cellular therapies, their combinations, and their integration into standard of care are attractive therapeutic options, although curative challenges and toxicity concerns remain. In this review, we provide an overview of immune approaches to NB and the tumor microenvironment (TME) within the clinical translational framework. We propose a novel T cell-based therapeutic approach that leverages the unique properties of tumor surface antigens such as ganglioside GD2, incorporating specific monoclonal antibodies and recent advancements in adoptive cell therapy.

Regorafenib synergizes with TAS102 against multiple gastrointestinal cancers and overcomes cancer stemness, trifluridine-induced angiogenesis, ERK1/2 and STAT3 signaling regardless of KRAS or BRAF mutational status

Single-agent TAS102 (trifluridine/tipiracil) and regorafenib are FDA-approved treatments for metastatic colorectal cancer (mCRC). We previously reported that regorafenib combined with a fluoropyrimidine can delay disease progression in clinical case reports of multidrug-resistant mCRC patients. We hypothesized that the combination of TAS102 and regorafenib may be active in CRC and other gastrointestinal (GI) cancers and may in the future provide a treatment option for patients with advanced GI cancer. We investigated the therapeutic effect of TAS102 in combination with regorafenib in preclinical studies employing cell culture, colonosphere assays that enrich for cancer stem cells, and in vivo. TAS102 in combination with regorafenib has synergistic activity against multiple GI cancers in vitro including colorectal and gastric cancer, but not liver cancer cells. TAS102 inhibits colonosphere formation and this effect is potentiated by regorafenib. In vivo anti-tumor effects of TAS102 plus regorafenib appear to be due to anti-proliferative effects, necrosis and angiogenesis inhibition. Growth inhibition by TAS102 plus regorafenib occurs in xenografted tumors regardless of p53, KRAS or BRAF mutations, although more potent tumor suppression was observed with wild-type p53. Regorafenib significantly inhibits TAS102-induced angiogenesis and microvessel density in xenografted tumors, as well inhibits TAS102-induced ERK1/2 activation regardless of RAS or BRAF status in vivo. TAS102 plus regorafenib is a synergistic drug combination in preclinical models of GI cancer, with regorafenib suppressing TAS102-induced increase in microvessel density and p-ERK as contributing mechanisms. The TAS102 plus regorafenib drug combination may be further tested in gastric and other GI cancers.

The evolving roles of Wnt signaling in stem cell proliferation and differentiation, the development of human diseases, and therapeutic opportunities

The evolutionarily conserved Wnt signaling pathway plays a central role in development and adult tissue homeostasis across species. Wnt proteins are secreted, lipid-modified signaling molecules that activate the canonical (β-catenin dependent) and non-canonical (β-catenin independent) Wnt signaling pathways. Cellular behaviors such as proliferation, differentiation, maturation, and proper body-axis specification are carried out by the canonical pathway, which is the best characterized of the known Wnt signaling paths. Wnt signaling has emerged as an important factor in stem cell biology and is known to affect the self-renewal of stem cells in various tissues. This includes but is not limited to embryonic, hematopoietic, mesenchymal, gut, neural, and epidermal stem cells. Wnt signaling has also been implicated in tumor cells that exhibit stem cell-like properties. Wnt signaling is crucial for bone formation and presents a potential target for the development of therapeutics for bone disorders. Not surprisingly, aberrant Wnt signaling is also associated with a wide variety of diseases, including cancer. Mutations of Wnt pathway members in cancer can lead to unchecked cell proliferation, epithelial-mesenchymal transition, and metastasis. Altogether, advances in the understanding of dysregulated Wnt signaling in disease have paved the way for the development of novel therapeutics that target components of the Wnt pathway. Beginning with a brief overview of the mechanisms of canonical and non-canonical Wnt, this review aims to summarize the current knowledge of Wnt signaling in stem cells, aberrations to the Wnt pathway associated with diseases, and novel therapeutics targeting the Wnt pathway in preclinical and clinical studies.

Initiation of Cancer: The Journey From Mutations in Somatic Cells to Epigenetic Changes in Tissue-resident VSELs

Multiple theories exist to explain cancer initiation, although a consensus on this is crucial for developing effective therapies. 'Somatic mutation theory' suggests that mutations in somatic cells during DNA repair initiates cancer but this concept has several attached paradoxes. Research efforts to identify quiescent cancer stem cells (CSCs) that survive therapy and result in metastasis and recurrence have remained futile. In solid cancers, CSCs are suggested to appear during epithelial-mesenchymal transition by the dedifferentiation and reprogramming of epithelial cells. Pluripotent and quiescent very small embryonic-like stem cells (VSELs) exist in multiple tissues but remain elusive owing to their small size and scarce nature. VSELs are developmentally connected to primordial germ cells, undergo rare, asymmetrical cell divisions and are responsible for the regular turnover of cells to maintain tissue homeostasis throughout life. VSELs are directly vulnerable to extrinsic endocrine insults because they express gonadal and gonadotropin hormone receptors. VSELs undergo epigenetic changes due to endocrine insults and transform into CSCs. CSCs exhibit genomic instability and develop mutations due to errors during DNA replication while undergoing excessive proliferation and clonal expansion to form spheroids. Thus tissue-resident VSELs offer a connection between extrinsic insults and variations in cancer incidence reported in various body tissues. To conclude, cancer is indeed a stem cell disease with mutations occurring as a consequence. In addition to immunotherapy, targeting mutations, and Lgr5 + organoids for developing new therapeutics, targeting CSCs (epigenetically altered VSELs) by improving their niche and epigenetic status could serve as a promising strategy to treat cancer.

Nanomedicine as a multimodal therapeutic paradigm against cancer: on the way forward in advancing precision therapy

Recent years have witnessed dramatic improvements in nanotechnology-based cancer therapeutics, and it continues to evolve from the use of conventional therapies (chemotherapy, surgery, and radiotherapy) to increasingly multi-complex approaches incorporating thermal energy-based tumor ablation (e.g. magnetic hyperthermia and photothermal therapy), dynamic therapy (e.g. photodynamic therapy), gene therapy, sonodynamic therapy (e.g. ultrasound), immunotherapy, and more recently real-time treatment efficacy monitoring (e.g. theranostic MRI-sensitive nanoparticles). Unlike monotherapy, these multimodal therapies (bimodal, i.e., a combination of two therapies, and trimodal, i.e., a combination of more than two therapies) incorporating nanoplatforms have tremendous potential to improve the tumor tissue penetration and retention of therapeutic agents through selective active/passive targeting effects. These combinatorial therapies can correspondingly alleviate drug response against hypoxic/acidic and immunosuppressive tumor microenvironments and promote/induce tumor cell death through various multi-mechanisms such as apoptosis, autophagy, and reactive oxygen-based cytotoxicity, e.g., ferroptosis, etc. These multi-faced approaches such as targeting the tumor vasculature, neoangiogenic vessels, drug-resistant cancer stem cells (CSCs), preventing intra/extravasation to reduce metastatic growth, and modulation of antitumor immune responses work complementary to each other, enhancing treatment efficacy. In this review, we discuss recent advances in different nanotechnology-mediated synergistic/additive combination therapies, emphasizing their underlying mechanisms for improving cancer prognosis and survival outcomes. Additionally, significant challenges such as CSCs, hypoxia, immunosuppression, and distant/local metastasis associated with therapy resistance and tumor recurrences are reviewed. Furthermore, to improve the clinical precision of these multimodal nanoplatforms in cancer treatment, their successful bench-to-clinic translation with controlled and localized drug-release kinetics, maximizing the therapeutic window while addressing safety and regulatory concerns are discussed. As we advance further, exploiting these strategies in clinically more relevant models such as patient-derived xenografts and 3D organoids will pave the way for the application of precision therapy.

Pterostilbene in the treatment of inflammatory and oncological diseases

Pterostilbene (PTS), a naturally occurring analog of resveratrol (RSV), has garnered significant attention due to its potential therapeutic effects in treating inflammatory and oncological diseases. This comprehensive review elucidates the pharmacological properties, mechanisms of action, and therapeutic potential of PTS. Various studies indicate that PTS exhibits anti-inflammatory, antioxidant, and antitumour properties, potentially making it a promising candidate for clinical applications. Its influence on regulatory pathways like NF-κB and PI3K/Akt underscores its diverse strategies in addressing diseases. Additionally, PTS showcases a favorable pharmacokinetic profile with better oral bioavailability compared to other stilbenoids, thus enhancing its therapeutic potential. Given these findings, there is an increased interest in incorporating PTS into treatment regimens for inflammatory and cancer-related conditions. However, more extensive clinical trials are imperative to establish its safety and efficacy in diverse patient populations.

Deregulated transcription factors in the emerging cancer hallmarks

Cancer progression is a multifaceted process that entails several stages and demands the persistent expression or activation of transcription factors (TFs) to facilitate growth and survival. TFs are a cluster of proteins with DNA-binding domains that attach to promoter or enhancer DNA strands to start the transcription of genes by collaborating with RNA polymerase and other supporting proteins. They are generally acknowledged as the major regulatory molecules that coordinate biological homeostasis and the appropriate functioning of cellular components, subsequently contributing to human physiology. TFs proteins are crucial for controlling transcription during the embryonic stage and development, and the stability of different cell types depends on how they function in different cell types. The development and progression of cancer cells and tumors might be triggered by any anomaly in transcription factor function. It has long been acknowledged that cancer development is accompanied by the dysregulated activity of TF alterations which might result in faulty gene expression. Recent studies have suggested that dysregulated transcription factors play a major role in developing various human malignancies by altering and rewiring metabolic processes, modifying the immune response, and triggering oncogenic signaling cascades. This review emphasizes the interplay between TFs involved in metabolic and epigenetic reprogramming, evading immune attacks, cellular senescence, and the maintenance of cancer stemness in cancerous cells. The insights presented herein will facilitate the development of innovative therapeutic modalities to tackle the dysregulated transcription factors underlying cancer.

The Role of Tumor Stem Cells in Colorectal Cancer Drug Resistance

Background: Colorectal cancer is a major cause of mortality among the prevalent malignant tumors of the gastrointestinal tract. Although chemotherapy is a standard treatment for colorectal cancer, its efficacy is limited by chemoresistance. Recent studies have investigated targeting tumor stem cells as a potential new therapeutic approach for addressing chemoresistance in colorectal cancer. Colorectal cancer frequently relapses, with tumor stem cells often representing one of the leading causes of treatment failure. Purpose: Understanding drug resistance in colorectal cancer stem cells is crucial for improving treatment outcomes. By focusing on developing targeted therapies that specifically address drug resistance in colorectal cancer stem cells, there is potential to make significant advancements in the treatment of colorectal cancer.This approach may lead to more effective and lasting outcomes in patients battling colorectal cancer. Research Design: In this review, a comprehensive overview of recent research on colorectal cancer stem cell treatment resistance is presented.Results: Elucidating the key underlying mechanisms. This review also highlights the potential benefits of targeted therapies in overcoming colorectal cancer resistance to treatment. Conclusions: CCSCs are key players in drug resistance of CRC, indicating their potential as targets for effective therapy. Elucidating their role in this process could aid in discovering tailored treatment strategies.The significance of signaling pathways, TME, and miRNA in regulating drug resistance in CCSCs is been highlighted.

Sniping Cancer Stem Cells with Nanomaterials

Cancer stem cells (CSCs) drive tumor initiation, progression, and therapeutic resistance due to their self-renewal and differentiation capabilities. Despite encouraging progress in cancer treatment, conventional approaches often fail to eliminate CSCs, necessitating the development of precise targeted strategies. Recent advances in materials science and nanotechnology have enabled promising CSC-targeted approaches, harnessing the power of tailoring nanomaterials in diverse therapeutic applications. This review provides an update on the current landscape of nanobased precision targeting approaches against CSCs. We elucidate the nuanced application of organic, inorganic, and bioinspired nanomaterials across a spectrum of therapeutic paradigms, encompassing targeted therapy, immunotherapy, and multimodal synergistic therapies. By examining the accomplishments and challenges in this potential field, we aim to inform future efforts to advance nanomaterial-based therapies toward more effective "sniping" of CSCs and tumor clearance.

A niche-mimicking polymer hydrogel-based approach to identify molecular targets for tackling human pancreatic cancer stem cells

BACKGROUND

Pancreatic adenocarcinoma (PAAD) is one of the most fatal human cancers, but effective therapies remain to be established. Cancer stem cells (CSCs) are highly resistant to anti-cancer drugs and a deeper understanding of their microenvironmental niche has been considered important to provide understanding and solutions to cancer eradication. However, as the CSC niche is composed of a wide variety of biological and physicochemical factors, the development of multidisciplinary tools that recapitulate their complex features is indispensable. Synthetic polymers have been studied as attractive biomaterials due to their tunable biofunctionalities, while hydrogelation technique further renders upon them a diversity of physical properties, making them an attractive tool for analysis of the CSC niche.

METHODS

To develop innovative materials that recapitulate the CSC niche in pancreatic cancers, we performed polymer microarray analysis to identify niche-mimicking scaffolds that preferentially supported the growth of CSCs. The niche-mimicking activity of the identified polymers was further optimized by polyethylene glycol (PEG)-based hydrogelation. To reveal the biological mechanisms behind the activity of the optimized hydrogels towards CSCs, proteins binding onto the hydrogel were analyzed by liquid chromatography with tandem mass spectrometry (LC-MS/MS), and the potential therapeutic targets were validated by looking at gene expression and patients' outcome in the TCGA database.

RESULTS

PA531, a heteropolymer composed of 2-methoxyethyl methacrylate (MEMA) and 2-(diethylamino)ethyl methacrylate (DEAEMA) (5.5:4.5) that specifically supports the growth and maintenance of CSCs was identified by polymer microarray screening using the human PAAD cell line KLM1. The polymer PA531 was converted into five hydrogels (PA531-HG1 to HG5) and developed to give an optimized scaffold with the highest CSC niche-mimicking activities. From this polymer that recapitulated CSC binding and control, the proteins fetuin-B and angiotensinogen were identified as candidate target molecules with clinical significance due to the correlation between gene expression levels and prognosis in PAAD patients and the proteins associated with the niche-mimicking polymer.

CONCLUSION

This study screened for biofunctional polymers suitable for recapitulation of the pancreatic CSC niche and one hydrogel with high niche-mimicking abilities was successfully fabricated. Two soluble factors with clinical significance were identified as potential candidates for biomarkers and therapeutic targets in pancreatic cancers. Such a biomaterial-based approach could be a new platform in drug discovery and therapy development against CSCs, via targeting of their niche.

Influence of Bruton's Tyrosine Kinase (BTK) on Epithelial-Mesenchymal Transition (EMT) Processes and Cancer Stem Cell (CSC) Enrichment in Head and Neck Squamous Cell Carcinoma (HNSCC)

Constitutively active kinases play a crucial role in carcinogenesis, and their inhibition is a common target for molecular tumor therapy. We recently discovered the expression of two oncogenic isoforms of Bruton's Tyrosine Kinase (BTK) in head and neck squamous cell carcinoma (HNSCC), Btk-p80 and BTK-p65. However, the precise role of BTK in HNSCC remains unclear. Analyses of a tissue microarray containing benign and malignant as well as inflammatory tissue samples of the head and neck region revealed the preferential expression of BTK-p80 in malignant tissue, whereas BTK-p65 expression was confirmed in over 80% of analyzed metastatic head and neck tumor cases. Therefore, processes associated with metastasis, like cancer stem cell (CSC) enrichment and the epithelial-mesenchymal transition (EMT), which in turn depend on an appropriate cytokine milieu, were analyzed. Treatment of HNSCC-derived cell lines cultured under 3D conditions with the BTK inhibitor AVL-292 caused reduced sphere formation, which was accompanied by reduced numbers of ALDH1A1+ CSCs as well as biological changes associated with the EMT. Moreover, we observed reduced NF-κB expression as well as altered NF-κB dependent pro-tumorigenic and EMT-associated cytokine release of IL-6, IFNγ, and TNFα when BTK activity was dampened. Therefore, an autocrine regulation of the oncogenic BTK-dependent process in HNSCC can be suggested, with BTK inhibition expected to be an effective treatment option for HNSCC.

Cancer stem cell in prostate cancer progression, metastasis and therapy resistance

Prostate cancer (PCa) is the most diagnosed malignancy in the men worldwide. Cancer stem cells (CSCs) are the sub-population of cells present in the tumor which possess unique properties of self-renewal and multilineage differentiation thus thought to be major cause of therapy resistance, disease relapse, and mortality in several malignancies including PCa. CSCs have also been shown positive for the common stem cells markers such as ALDH EZH2, OCT4, SOX2, c-MYC, Nanog etc. Therefore, isolation and characterization of CSCs specific markers which may discriminate CSCs and normal stem cells are critical to selectively eliminate CSCs. Rapid advances in the field offers a theoretical explanation for many of the enduring uncertainties encompassing the etiology and an optimism for the identification of new stem-cell targets, development of reliable and efficient therapies in the future. The emerging reports have also provided unprecedented insights into CSCs plasticity, quiescence, renewal, and therapeutic response. In this review, we discuss the identification of PCa stem cells, their unique properties, stemness-driving pathways, new diagnostics, and therapeutic interventions.

The Significance of Cancer Stem Cells and Epithelial-Mesenchymal Transition in Metastasis and Anti-Cancer Therapy

Cancer stem cells (CSCs) have been identified and characterized in both hematopoietic and solid tumors. Their existence was first predicted by Virchow and Cohnheim in the 1870s. Later, many studies showed that CSCs can be identified and isolated by their expression of specific cell markers. The significance of CSCs with respect to tumor biology and anti-cancer treatment lies in their ability to maintain quiescence with very slow proliferation, indefinite self-renewal, differentiation, and trans-differentiation such as epithelial-mesenchymal transition (EMT) and its reverse process mesenchymal-epithelial transition (MET). The ability for detachment, migration, extra- and intravasation, invasion and thereby of completing all necessary steps of the metastatic cascade highlights their significance for metastasis. CSCs comprise the cancer cell populations responsible for tumor growth, resistance to therapies and cancer metastasis. In this review, the history of the CSC theory, their identification and characterization and their biology are described. The contribution of the CSC ability to undergo EMT for cancer metastasis is discussed. Recently, novel strategies for drug development have focused on the elimination of the CSCs specifically. The unique functional and molecular properties of CSCs are discussed as possible therapeutic vulnerabilities for the development of novel anti-metastasis treatments. Prospectively, this may provide precise personalized anti-cancer treatments with improved therapeutic efficiency with fewer side effects and leading to better prognosis.

The Biological Roles and Molecular Mechanisms of Long Non-Coding RNA MEG3 in the Hallmarks of Cancer

Long non-coding RNAs (lncRNAs) are critical regulators in various biological processes involved in the hallmarks of cancer. Maternally expressed gene 3 (MEG3) is lncRNA that regulates target genes through transcription, translation, post-translational modification, and epigenetic regulation. MEG3 has been known as a tumor suppressor, and its downregulation could be found in various cancers. Furthermore, clinical studies revealed that impaired MEG3 expression is associated with poor prognosis and drug resistance. MEG3 exerts its tumor suppressive effect by suppressing various cancer hallmarks and preventing cells from acquiring cancer-specific characteristics; as it could suppress tumor cells proliferation, invasion, metastasis, and angiogenesis; it also could promote tumor cell death and regulate tumor cell metabolic reprogramming. Hence, MEG3 is a potential prognostic marker, and overexpressing MEG3 might become a potential antitumor therapeutic strategy. Herein, we summarize recent knowledge regarding the role of MEG3 in regulating tumor hallmarks as well as the underlying molecular mechanisms. Furthermore, we also discuss the clinical importance of MEG3, as well as their potential in tumor prognosis and antitumor therapeutic strategies.

Role of the Hypoxic-Secretome in Seed and Soil Metastatic Preparation

During tumor growth, the delivery of oxygen to cells is impaired due to aberrant or absent vasculature. This causes an adaptative response that activates the expression of genes that control several essential processes, such as glycolysis, neovascularization, immune suppression, and the cancer stemness phenotype, leading to increased metastasis and resistance to therapy. Hypoxic tumor cells also respond to an altered hypoxic microenvironment by secreting vesicles, factors, cytokines and nucleic acids that modify not only the immediate microenvironment but also organs at distant sites, allowing or facilitating the attachment and growth of tumor cells and contributing to metastasis. Hypoxia induces the release of molecules of different biochemical natures, either secreted or inside extracellular vesicles, and both tumor cells and stromal cells are involved in this process. The mechanisms by which these signals that can modify the premetastatic niche are sent from the primary tumor site include changes in the extracellular matrix, recruitment and activation of different stromal cells and immune or nonimmune cells, metabolic reprogramming, and molecular signaling network rewiring. In this review, we will discuss how hypoxia might alter the premetastatic niche through different signaling molecules.

Bufalin Inhibits Tumorigenesis, Stemness, and Epithelial-Mesenchymal Transition in Colorectal Cancer through a C-Kit/Slug Signaling Axis

Colorectal cancer (CRC) is a major source of morbidity and mortality, characterized by intratumoral heterogeneity and the presence of cancer stem cells (CSCs). Bufalin has potent activity against many tumors, but studies of its effect on CRC stemness are limited. We explored bufalin's function and mechanism using CRC patient-derived organoids (PDOs) and cell lines. In CRC cells, bufalin prevented nuclear translocation of β-catenin and down-regulated CSC markers (CD44, CD133, LGR5), pluripotency factors, and epithelial-mesenchymal transition (EMT) markers (N-Cadherin, Slug, ZEB1). Functionally, bufalin inhibited CRC spheroid formation, aldehyde dehydrogenase activity, migration, and invasion. Network analysis identified a C-Kit/Slug signaling axis accounting for bufalin's anti-stemness activity. Bufalin treatment significantly downregulated C-Kit, as predicted. Furthermore, overexpression of C-Kit induced Slug expression, spheroid formation, and bufalin resistance. Similarly, overexpression of Slug resulted in increased expression of C-Kit and identical functional effects, demonstrating a pro-stemness feedback loop. For further study, we established PDOs from diagnostic colonoscopy. Bufalin differentially inhibited PDO growth and proliferation, induced apoptosis, restored E-cadherin, and downregulated CSC markers CD133 and C-Myc, dependent on C-Kit/Slug. These findings suggest that the C-Kit/Slug axis plays a pivotal role in regulating CRC stemness, and reveal that targeting this axis can inhibit CRC growth and progression.

Salinomycin-Loaded High-Density Lipoprotein Exerts Promising Anti-Ovarian Cancer Effects by Inhibiting Epithelial-Mesenchymal Transition

Background

Effective treatments for ovarian cancer remain elusive, and survival rates have long been considered grim. Ovarian cancer stem cells (OCSCs) and epithelial–mesenchymal transition (EMT) are associated with cancer progression and metastasis, as well as drug resistance and eventual treatment failure. Salinomycin (Sal) has an extensive effect on a variety of cancer stem cells (CSCs); however, its poor water solubility and toxicity to healthy tissues at high doses limit further research into its potential as an anti-cancer drug. We proposed a therapeutic strategy by constructing a tumor-targeting carrier that mimics high-density lipoprotein (HDL) to synthesize salinomycin-loaded high-density lipoprotein (S-HDL). This strategy helps reduce the side effects of salinomycin, thereby improving its clinical benefits.

Methods

OCSCs were isolated from ovarian cancer cells (OCCs) and the uptake of HDL nanoparticles was observed using laser confocal microscopes. After the cell viability analysis revealed the inhibitory effect of S-HDL on OCCs and OCSCs, the main biological processes influenced by S-HDL were predicted with a transcriptome sequencing analysis and verified in vitro and in vivo.

Results

Cellular uptake analysis showed that the HDL delivery system was able to significantly enhance the uptake of Sal by OCCs, tentatively validating the targeting role of recombinant HDL, so that S-HDL could reduce the toxicity of Sal and increase its anti-ovarian cancer effects. Conversely, S-HDL could exert anti-ovarian cancer effects by inhibiting the proliferation of OCCs and OCSCs, promoting apoptosis, blocking EMT, and suppressing stemness and angiogenesis-related protein expression in vitro and in vivo.

Conclusion

S-HDL had stronger anti-ovarian cancer effects than unencapsulated Sal. Thus, it may be a potential agent for ovarian cancer treatment in the future.

Cancer Stem Cells in Tumor Microenvironment of Adenocarcinoma of the Stomach, Colon, and Rectum

Gastrointestinal adenocarcinomas are one of the world's deadliest cancers. Cancer stem cells and the tissue microenvironment are highly regulated by cell and molecular mechanisms. Cancer stem cells are essential for maintenance and progression and are associated with resistance to conventional treatments. This article reviews the current knowledge of the role of the microenvironment during the primary establishment of gastrointestinal adenocarcinomas in the stomach, colon, and rectum and its relationship with cancer stem cells. We also describe novel developments in cancer therapeutics, such as targeted therapy, and discuss the advantages and disadvantages of different treatments for improving gastrointestinal cancer prognosis.

Disclosing the antitumour potential of the marine bromoditerpene sphaerococcenol A on distinct cancer cellular models

Nature has revealed to be a key source of innovative anticancer drugs. This study evaluated the antitumour potential of the marine bromoditerpene sphaerococcenol A on different cancer cellular models. Dose-response analyses (0.1-100 µM; 24 h) were accomplished in eight different tumour cell lines (A549, CACO-2, HCT-15, MCF-7, NCI-H226, PC-3, SH-SY5Y, SK-MEL-28). Deeper studies were conducted on MFC-7 cells, namely, determination of hydrogen peroxide (H₂O₂) levels and evaluation of apoptosis biomarkers (phosphatidylserine membrane translocation, mitochondrial dysfunction, Caspase-9 activity, and DNA changes). The ability of the compound to induce genotoxicity was verified in L929 fibroblasts. Sphaerococcenol A capacity to impact colorectal-cancer stem cells (CSCs) tumourspheres (HT29, HCT116, SW620) was evaluated by determining tumourspheres viability, number, and area, as well as the proteasome inhibitory activity. Sphaerococcenol A hepatoxicity was studied in AML12 hepatocytes. The compound exhibited cytotoxicity in all malignant cell lines (IC₅₀ ranging from 4.5 to 16.6 µM). MCF-7 cells viability loss was accompanied by H₂O₂ generation, mitochondrial dysfunction, Caspase-9 activation and DNA nuclear morphology changes. Furthermore, the compound displayed the lowest IC₅₀ on HT29-derived tumourspheres (0.70 µM), followed by HCT116 (1.77 µM) and SW620 (2.74 µM), impacting the HT29 tumoursphere formation by reducing their number and area. Finally, the compound displayed low cytotoxicity on AML12 hepatocytes without genotoxicity. Overall, sphaerococcenol A exhibits broad cytotoxic effects on different tumour cells, increasing H₂O₂ production and apoptosis. It also affects colorectal CSCs-enriched tumoursphere development. These data highlight the relevance to include sphaerococcenol A in further pharmacological studies aiming cancer treatments.

Non-coding RNAs and glioblastoma: Insight into their roles in metastasis

Glioma, also known as glioblastoma multiforme (GBM), is the most prevalent and most lethal primary brain tumor in adults. Gliomas are highly invasive tumors with the highest death rate among all primary brain malignancies. Metastasis occurs as the tumor cells spread from the site of origin to another site in the brain. Metastasis is a multifactorial process, which depends on alterations in metabolism, genetic mutations, and the cancer microenvironment. During recent years, the scientific study of non-coding RNAs (ncRNAs) has led to new insight into the molecular mechanisms involved in glioma. Many studies have reported that ncRNAs play major roles in many biological procedures connected with the development and progression of glioma. Long ncRNAs (lncRNAs), microRNAs (miRNAs), and circular RNAs (circRNAs) are all types of ncRNAs, which are commonly dysregulated in GBM. Dysregulation of ncRNAs can facilitate the invasion and metastasis of glioma. The present review highlights some ncRNAs that have been associated with metastasis in GBM. miRNAs, circRNAs, and lncRNAs are discussed in detail with respect to their relevant signaling pathways involved in metastasis.

Subsets of cancer cells expressing CX3CR1 are endowed with metastasis-initiating properties and resistance to chemotherapy

Metastasis-initiating cells (MICs) display stem cell-like features, cause metastatic recurrences and defy chemotherapy, which leads to patients' demise. Here we show that prostate and breast cancer patients harbor contingents of tumor cells with high expression of CX3CR1, OCT4a (POU5F1), and NANOG. Impairing CX3CR1 expression or signaling hampered the formation of tumor spheroids by cell lines from which we isolated small subsets co-expressing CX3CR1 and stemness-related markers, similarly to patients' tumors. These rare CX3CR1High cells show transcriptomic profiles enriched in pathways that regulate pluripotency and endowed with metastasis-initiating behavior in murine models. Cancer cells lacking these features (CX3CR1Low) were capable of re-acquiring CX3CR1-associated features over time, implying that MICs can continuously emerge from non-stem cancer cells. CX3CR1 expression also conferred resistance to docetaxel, and prolonged treatment with docetaxel selected CX3CR1High phenotypes with de-enriched transcriptomic profiles for apoptotic pathways. These findings nominate CX3CR1 as a novel marker of stem-like tumor cells and provide conceptual ground for future development of approaches targeting CX3CR1 signaling and (re)expression as therapeutic means to prevent or contain metastasis initiation.

Circular RNAs in stem cells: from basic research to clinical implications

Circular RNAs (circRNAs) are a special class of endogenous RNAs with a wide variety of pathophysiological functions via diverse mechanisms, including transcription, microRNA (miRNA) sponge, protein sponge/decoy, and translation. Stem cells are pluripotent cells with unique properties of self-renewal and differentiation. Dysregulated circRNAs identified in various stem cell types can affect stem cell self-renewal and differentiation potential by manipulating stemness. However, the emerging roles of circRNAs in stem cells remain largely unknown. This review summarizes the major functions and mechanisms of action of circRNAs in stem cell biology and disease progression. We also highlight circRNA-mediated common pathways in diverse stem cell types and discuss their diagnostic significance with respect to stem cell-based therapy.

Stem Cell Factor SOX9 Interacts with a Cell Death Regulator RIPK1 and Results in Escape of Cancer Stem Cell Death

High-grade ovarian cancer (HGOC) is the most lethal gynecological cancer, with high metastasis and recurrence. Cancer stem cells (CSCs) are responsible for its apoptosis resistance, cancer metastasis, and recurrence. Thus, targeting CSCs would be a promising strategy for overcoming chemotherapy resistance and improving patient prognosis in HGOC. Among upregulated oncogenic proteins in HGOC, we found that transcription factor SOX9 showed a strong correlation with stemness-regulating ALDH1A1 and was localized predominantly in the cytoplasm of HGOC with lymph node metastasis. In order to address the role of unusual cytoplasmic SOX9 and to explore its underlying mechanism in HGOC malignancy, a Y2H assay was used to identify a necroptotic cell death-associated cytoplasmic protein, receptor-interacting serine/threonine protein kinase 1 (RIPK1), as a novel SOX9-interacting partner and further mapped their respective interacting domains. The C-terminal region containing the transactivation domain of SOX9 interacted with the death domain of R1PK1. Consistent with its stemness-promoting function, SOX9 knockdown in vitro resulted in changes in cell morphology, cell cycle, stem cell marker expression, cell invasion, and sphere formation. Furthermore, in vivo knockdown completely inhibited tumor growth in mouse xenograft model. We propose that cytoplasmic SOX9-mediated cell death suppression would contribute to cancer stem cell survival in HGOC.

Induction of Apoptosis in Human Pancreatic Cancer Stem Cells by the Endoplasmic Reticulum-Targeted Alkylphospholipid Analog Edelfosine and Potentiation by Autophagy Inhibition

Pancreatic cancer is one of the most lethal malignancies with a poor and gloomy prognosis and the highest mortality-to-incidence ratio. Pancreatic cancer remains an incurable malignancy, and current therapies are ineffective. We isolated cancer stem cells (CSCs) from the human PANC-1 pancreatic cancer cell line as CD44⁺CD24⁺EpCAM⁺ cells. These CSCs form pancreatic cancer spheres or spheroids and develop tumors in SCID mice after subcutaneous injection of as few as 100 cells per mouse. Here, we found that the alkylphospholipid analog edelfosine inhibited CSC pancreatic cancer spheroid formation and induced cell death, as assessed by an increase in the percentage of cells in the sub-G₀/G₁ region by means of flow cytometry, indicative of DNA breakdown and apoptosis. This correlated with an increase in caspase-3 activity and PARP breakdown, as a major substrate of caspase-3, following PANC-1 CSC treatment with edelfosine. The antitumor ether lipid edelfosine colocalized with the endoplasmic reticulum in both PANC-1 cells as well as PANC-1 CSCs by using a fluorescent edelfosine analog, and induced an endoplasmic reticulum stress response in both PANC-1 cells and PANC-1 CSCs, with a potent CHOP/GADD153 upregulation. Edelfosine elicited a strong autophagy response in both PANC-1 cells and PANC-1 CSCs, and preincubation of CSCs with autophagy inhibitors, chloroquine or bafilomycin A1, enhanced edelfosine-induced apoptosis. Primary cultures from pancreatic cancer patients were sensitive to edelfosine, as well as their respective isolated CSCs. Nontumorigenic pancreatic human cell line HPNE and normal human fibroblasts were largely spared. These data suggest that pancreatic CSCs isolated from established cell lines and pancreatic cancer patients are sensitive to edelfosine through its accumulation in the endoplasmic reticulum and induction of endoplasmic reticulum stress.

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.

Therapeutic combination silencing VEGF and SOX10 increases the antiangiogenic effect in the mouse melanoma model B16-F10 - in vitro and in vivo studies

INTRODUCTION

Gene therapy is an innovative form of treatment of genetic diseases, in which psiRNA molecules silencing specific genes are applied.

AIM

The study evaluated the anti-tumour effect of psiRNA silencing preparations of the vascular endothelial growth factor (VEGF) and Sry-related HMG-Box gene 10 (SOX10) on melanoma (B16-F10) by inhibiting angiogenesis.

MATERIAL AND METHODS

The preparations based on plasmid vectors psiRNA silencing the gene SOX10 and VEGF that form complexes with cationic lipid (psiRNA/carrier) have been developed. psiRNA preparations were tested on the mouse melanoma cell line B16-F10, both in vitro and in vivo. The silencing activity of transfected melanoma cells with the obtained psiRNA preparations was examined using the qPCR and Western blot methods. The anti-tumour activity of psiRNA preparations on melanoma tumour cells was then evaluated in a mouse in vivo model.

RESULTS

In vitro studies have shown that the B16-F10 cells efficiently transfect non-viral preparations - psiRNA: Lyovec (74-89%). Worth mentioning is the fact that silencing SOX10 in B16-F10 melanoma cells increases the expression of the COL18A1 gene (compared to the preparation inhibiting only VEGF), which codes the endostatin to stop angiogenesis. In vivo results show that the level of haemoglobin in tumours of mice treated with psiRNA formulations was over 6 times lower than controls and tumour mass was 60-80% lower.

CONCLUSIONS

The novel study proves that simultaneous inhibition of SOX10 and VEGF enhances the antiangiogenic action and thus contributes to a significant halt of disease development. In addition, these data expand knowledge about SOX10 regulation and functions.

Stem Cells and Cancer Stem Cells: The Jekyll and Hyde Scenario and Their Implications in Stem Cell Therapy

"Jekyll and Hyde" refers to persons with an unpredictably dual personality, who are battling between good and evil within themselves In this regard, even cells consist of good and evil counterparts. Normal stem cells (NSCs) and cancer stem cells (CSCs) are two types of cells that share some similar characteristics but have distinct functions that play a major role in physiological and pathophysiological development. In reality, NSCs such as the adult and embryonic stem cells, are the good cells and the ultimate treatment used in cell therapy. CSCs are the corrupted cells that are a subpopulation of cancer cells within the cancer microenvironment that grow into a massive tumour or malignancy that needs to be treated. Hence, understanding the connection between NSCs and CSCs is important not just in cancer development but also in their therapeutic implication, which is the focus of this review.

Modulating tumor infiltrating myeloid cells to enhance bispecific antibody-driven T cell infiltration and anti-tumor response

BACKGROUND

Tumor microenvironment (TME) is a dynamic cellular milieu to promote tumor angiogenesis, growth, proliferation, and metastasis, while derailing the host anti-tumor response. TME impedes bispecific antibody (BsAb) or chimeric antigen receptor (CAR)-driven T cells infiltration, survival, and cytotoxic efficacy. Modulating tumor infiltrating myeloid cells (TIMs) could potentially improve the efficacy of BsAb.

METHODS

We evaluated the effects of TIM modulation on BsAb-driven T cell infiltration into tumors, their persistence, and in vivo anti-tumor response. Anti-GD2 BsAb and anti-HER2 BsAb built on IgG-[L]-scFv platform were tested against human cancer xenografts in BALB-Rag2-/-IL-2R-γc-KO (BRG) mice. Depleting antibodies specific for polymorphonuclear myeloid-derived suppressor cell (PMN-MDSC), monocytic MDSC (M-MDSC), and tumor associated macrophage (TAM) were used to study the role of each TIM component. Dexamethasone, an established anti-inflammatory agent, was tested for its effect on TIMs.

RESULTS

BsAb-driven T cells recruited myeloid cells into human tumor xenografts. Each TIM targeting therapy depleted cells of interest in blood and in tumors. Depletion of PMN-MDSCs, M-MDSCs, and particularly TAMs was associated with enhanced T cell infiltration into tumors, significantly improving tumor control and survival in multiple cancer xenograft models. Dexamethasone premedication depleted monocytes in circulation and TAMs in tumors, enhanced BsAb-driven T cell infiltration, and anti-tumor response with survival benefit.

CONCLUSION

Reducing TIMs markedly enhanced anti-tumor effects of BsAb-based T cell immunotherapy by improving intratumoral T cell infiltration and persistence. TAM depletion was more effective than PMN- or M-MDSCs depletion at boosting the anti-tumor response of T cell engaging BsAb.

Nanotherapeutic approach to tackle chemotherapeutic resistance of cancer stem cells

Estimates indicate that cancer will become the leading cause of mortality worldwide in the future. Tumorigenesis is a complex process that involves self-sufficiency in signs of growth, insensitivity to anti-growth signals, prevention of apoptosis, unlimited replication, sustained angiogenesis, tissue invasion, and metastasis. Cancer stem cells (CSCs) have an important role in tumor development and resistance. Here we will approach phenotypic plasticity capacity, highly efficient DNA repair systems, anti-apoptotic machinery, sustained stemness features, interaction with the tumor microenvironment, and Notch, Wnt, and Hedgehog signaling pathways. The researches about CSCs as a target in cancer treatment has been growing. Many different options have pointed beneficial results, such as pathways and CSC-surface markers targeting. Besides its limitations, nanotherapeutics have emerged as a potential strategy in this context since they aim to improve pharmacokinetics, biodistribution, and reduce the side effects observed in traditional treatments. Nanoparticles have been studied in this field, mostly for drug delivery and a multitherapy approach. Another widely researched approaches in this area are related to heat therapy, such as photothermal therapy, photodynamic therapy and magnetic hyperthermia, besides molecular targeting. This review will contemplate the most relevant studies that have shown the effects of nanotherapeutics. In conclusion, although the studies analyzed are mostly preclinical, we believe that there is strong evidence that nanoparticles can increase the chances of a better prognosis to cancer in the future. It is also essential to transpose these findings to the clinic to confirm and better understand the role of nanotherapeutics in this context.

Autophagy inhibition reinforces stemness together with exit from dormancy of polydisperse glioblastoma stem cells

Therapeutic resistance and infiltrative capacities justify the aggressiveness of glioblastoma. This is due to cellular heterogeneity, especially the presence of stemness-related cells, i.e. Cancer Stem Cells (CSC). Previous studies focused on autophagy and its role in CSCs maintenance; these studies gave conflicting results as they reported either sustaining or disruptive effects. In the present work, we silenced two autophagy related genes -either Beclin1 or ATG5- by shRNA and we explored the ensuing consequences on CSCs markers’ expression and functionalities. Our results showed that the down regulation of autophagy led to enhancement in expression of CSCs markers, while proliferation and clonogenicity were boosted. Temozolomide (TMZ) treatment failed to induce apoptotic death in shBeclin1-transfected cells, contrary to control. We optimized the cellular subset analysis with the use of Sedimentation Field Flow Fractionation, a biological event monitoring- and cell sorting-dedicated technique. Fractograms of both shBeclin1 and shATG5 cells exhibited a shift of elution peak as compared with control cells, showing cellular dispersion and intrinsic sub-fraction modifications. The classical stemness fraction (i.e. F3) highlighted data obtained with the overall cellular population, exhibiting enhancement of stemness markers and escape from dormancy. Our results contributed to illustrate CSCs polydispersity and to show how these cells develop capacity to bypass autophagy inhibition, thanks to their acute adaptability and plasticity.

Proteases Regulate Cancer Stem Cell Properties and Remodel Their Microenvironment

Proteolytic activity is perturbed in tumors and their microenvironment, and proteases also affect cancer stem cells (CSCs). CSCs are the therapy-resistant subpopulation of cancer cells with tumor-initiating capacity that reside in specialized tumor microenvironment niches. In this review, we briefly summarize the significance of proteases in regulating CSC activities with a focus on brain tumor glioblastoma. A plethora of proteases and their inhibitors participate in CSC invasiveness and affect intercellular interactions, enhancing CSC immune, irradiation, and chemotherapy resilience. Apart from their role in degrading the extracellular matrix enabling CSC migration in and out of their niches, we review the ability of proteases to modulate CSC properties, which prevents their elimination. When designing protease-oriented therapies, the multifaceted roles of proteases should be thoroughly investigated.

Potential Therapies Targeting Metabolic Pathways in Cancer Stem Cells

Cancer stem cells (CSCs) are heterogeneous cells with stem cell-like properties that are responsible for therapeutic resistance, recurrence, and metastasis, and are the major cause for cancer treatment failure. Since CSCs have distinct metabolic characteristics that plays an important role in cancer development and progression, targeting metabolic pathways of CSCs appears to be a promising therapeutic approach for cancer treatment. Here we classify and discuss the unique metabolisms that CSCs rely on for energy production and survival, including mitochondrial respiration, glycolysis, glutaminolysis, and fatty acid metabolism. Because of metabolic plasticity, CSCs can switch between these metabolisms to acquire energy for tumor progression in different microenvironments compare to the rest of tumor bulk. Thus, we highlight the specific conditions and factors that promote or suppress CSCs properties to portray distinct metabolic phenotypes that attribute to CSCs in common cancers. Identification and characterization of the features in these metabolisms can offer new anticancer opportunities and improve the prognosis of cancer. However, the therapeutic window of metabolic inhibitors used alone or in combination may be rather narrow due to cytotoxicity to normal cells. In this review, we present current findings of potential targets in these four metabolic pathways for the development of more effective and alternative strategies to eradicate CSCs and treat cancer more effectively in the future.

Potential Therapies Targeting Metabolic Pathways in Cancer Stem Cells

Cancer stem cells (CSCs) are heterogeneous cells with stem cell-like properties that are responsible for therapeutic resistance, recurrence, and metastasis, and are the major cause for cancer treatment failure. Since CSCs have distinct metabolic characteristics that plays an important role in cancer development and progression, targeting metabolic pathways of CSCs appears to be a promising therapeutic approach for cancer treatment. Here we classify and discuss the unique metabolisms that CSCs rely on for energy production and survival, including mitochondrial respiration, glycolysis, glutaminolysis, and fatty acid metabolism. Because of metabolic plasticity, CSCs can switch between these metabolisms to acquire energy for tumor progression in different microenvironments compare to the rest of tumor bulk. Thus, we highlight the specific conditions and factors that promote or suppress CSCs properties to portray distinct metabolic phenotypes that attribute to CSCs in common cancers. Identification and characterization of the features in these metabolisms can offer new anticancer opportunities and improve the prognosis of cancer. However, the therapeutic window of metabolic inhibitors used alone or in combination may be rather narrow due to cytotoxicity to normal cells. In this review, we present current findings of potential targets in these four metabolic pathways for the development of more effective and alternative strategies to eradicate CSCs and treat cancer more effectively in the future.

Tadalafil Reverses the Effect of Three-Dimensional Cell Culture System on Stem Cell Features in A549 and SK-MES-1

Background: Non-small cell lung cancer is the most common type of lung cancer and is a frequent cause of death. In our research, A549 and SK-MES-1 were used to assess the effect of three-dimensional (3D) culture compared to that of two-dimensional (2D) monolayers in cell proliferation, migration, and invasion, response to chemotherapy, as well as the expression of epithelial to mesenchymal transition (EMT) and cancer stem cell (CSC)-related markers. As tadalafil is a phosphodiesterase type 5 (PDE5) inhibitor with the potential to target CSC maintenance in multiple cancer cell lines, we assessed its function in 3D culture and detected the downstream pathway genes. Methods: We compared the viability and proliferation capacity of A549 and SK-MES-1 cells in 2D and 3D culture by cell counting kit (CCK)-8, foci formation, and Live/Dead double stain (Operetta CLS High content screening). Migration, invasion, and other functions were also assessed. To elucidate the underlying mechanisms, the expression of EMT and CSC markers was analyzed by quantitative real-time PCR (qPCR) and Western blot. Results: A549 and SK-MES-1 cells formed spheroids heterogeneous in shape and size. In our 3D spheroid systems, cells went through EMT, and were also capacitated with higher stemness and chemoresistance. Combination use of tadalafil and cisplatin showed higher chemotherapy efficiency in the 3D model, compared to that of the 2D cell culture. Conclusion: Our research aims at the notable differences between these two cellular systems in terms of cell functions, EMT, and stemness-associated gene expression and chemo-response. We showed that a commonly used drug, tadalafil, showed more pronounced inhibitory effects when cells were cultured in the 3D model. Since the 3D culture system could imitate the in vivo behavior of cancer cells within the tumor, we advocate that this system is superior to traditional 2D culture and should be used in the investigation of new therapeutic compounds.

Microbes in lung cancer initiation, treatment, and outcome: Boon or bane?

Lung cancer is the top reason for cancer-related deaths worldwide. The 5-year overall survival rate of lung cancer is approximately 20 % due to the delayed diagnosis and low response rate to regular treatments. Microbiota, both host-microbiota and alien pathogenic microbiota, have been investigated to be involved in a complicated and contradictory relationship with lung cancer initiation, treatments, and prognosis. Disorders of certain host-microbiota and pathogen infection are associated with the risk of lung cancers based on epidemiological evidence, and antibiotics (ATBs) could dramatically impair anti-cancer treatment efficacy, including chemotherapy and immunotherapy. Moreover, probiotics and microbe-mediated drugs are potential approaches to enhance regular anti-tumor treatments. Therefore, the knowledge of the complex dual effect of microbes on lung cancer is beneficial to take their essence and remove their dross. This review offers insight into the current trends and advancements in microbiota or microbial components related to lung cancer.

Identification of a lncRNA prognostic signature-related to stem cell index and its significance in colorectal cancer

Background: The relationship between long noncoding RNAs (lncRNAs) and the mRNA stemness index (mRNAsi) in colorectal cancer (CRC) is still unclear. Materials & methods: The mRNAsi, mRNAsi-related lncRNAs and their clinical significance were analyzed by bioinformatic approaches in The Cancer Genome Atlas (TCGA)-COREAD dataset. Results: mRNAsi was negatively related to pathological features but positively related to overall survival and recurrence-free survival in CRC. A five mRNAsi-related lncRNAs prognostic signature was further developed and showed independent prognostic factors related to overall survival in CRC patients, due to the five mRNAsi-related lncRNAs involved in several pathways of the cancer stem cells and malignant cancer cell phenotypes. Conclusion: The present study highlights the potential roles of mRNAsi-related lncRNAs as alternative prognostic markers.

Molecular pathology underlying the robustness of cancer stem cells

Intratumoral heterogeneity is tightly associated with the failure of anticancer treatment modalities including conventional chemotherapy, radiation therapy, and molecularly targeted therapy. Such heterogeneity is generated in an evolutionary manner not only as a result of genetic alterations but also by the presence of cancer stem cells (CSCs). CSCs are proposed to exist at the top of a tumor cell hierarchy and are undifferentiated tumor cells that manifest enhanced tumorigenic and metastatic potential, self-renewal capacity, and therapeutic resistance. Properties that contribute to the robustness of CSCs include the abilities to withstand redox stress, to rapidly repair damaged DNA, to adapt to a hyperinflammatory or hyponutritious tumor microenvironment, and to expel anticancer drugs by the action of ATP-binding cassette transporters as well as plasticity with regard to the transition between dormant CSC and transit-amplifying progenitor cell phenotypes. In addition, CSCs manifest the phenomenon of metabolic reprogramming, which is essential for maintenance of their self-renewal potential and their ability to adapt to changes in the tumor microenvironment. Elucidation of the molecular underpinnings of these biological features of CSCs is key to the development of novel anticancer therapies. In this review, we highlight the pathological relevance of CSCs in terms of their hallmarks and identification, the properties of their niche—both in primary tumors and at potential sites of metastasis—and their resistance to oxidative stress dependent on system xc (−).

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Intratumoral heterogeneity driven by CSCs is responsible for therapeutic resistance.

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CTCs survive in the distant organs and achieve colonization, causing metastasis.

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E/M hybrid cancer cells due to partial EMT exhibit the highest metastatic potential.

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The CSC niche regulates stemness in metastatic disease as well as in primary tumor.

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Activation of system xc(-) by CD44 variant in CSCs is a promising therapeutic target.

Nanopore Sequencing Reveals Global Transcriptome Signatures of Mitochondrial and Ribosomal Gene Expressions in Various Human Cancer Stem-like Cell Populations

Simple Summary

Cancer is the leading cause of death in the industrialized world. In particular, so-called cancer stem cells (CSCs) play a crucial role in disease progression, as they are known to contribute to tumor growth and metastasis. Thus, CSCs are heavily investigated in a broad range of cancers. Nevertheless, global transcriptomic profiling of CSC populations derived from different tumor types is rare. We established three CSC populations from tumors in the uterus, brain, lung, and prostate and assessed their global transcriptomes using nanopore full-length cDNA sequencing, a new technique to assess insights into global gene profile. We observed common expression in all CSCs for distinct genes encoding proteins for organelles, such as ribosomes, mitochondria, and proteasomes. Additionally, we detected high expressions of inflammation- and immunity-related genes. Conclusively, we observed high similarities between all CSCs independent of their tumor of origin, which may build the basis for identifying novel therapeutic strategies targeting CSCs.

Abstract

Cancer stem cells (CSCs) are crucial mediators of tumor growth, metastasis, therapy resistance, and recurrence in a broad variety of human cancers. Although their biology is increasingly investigated within the distinct types of cancer, direct comparisons of CSCs from different tumor types allowing comprehensive mechanistic insights are rarely assessed. In the present study, we isolated CSCs from endometrioid carcinomas, glioblastoma multiforme as well as adenocarcinomas of lung and prostate and assessed their global transcriptomes using full-length cDNA nanopore sequencing. Despite the expression of common CSC markers, principal component analysis showed a distinct separation of the CSC populations into three clusters independent of the specific type of tumor. However, GO-term and KEGG pathway enrichment analysis revealed upregulated genes related to ribosomal biosynthesis, the mitochondrion, oxidative phosphorylation, and glycolytic pathways, as well as the proteasome, suggesting a great extent of metabolic flexibility in CSCs. Interestingly, the GO term “NF-kB binding” was likewise found to be elevated in all investigated CSC populations. In summary, we here provide evidence for high global transcriptional similarities between CSCs from various tumors, which particularly share upregulated gene expression associated with mitochondrial and ribosomal activity. Our findings may build the basis for identifying novel therapeutic strategies targeting CSCs.

The Role of Cancer Stem Cells in Colorectal Cancer: From the Basics to Novel Clinical Trials

The treatment options available for colorectal cancer (CRC) have increased over the years and have significantly improved the overall survival of CRC patients. However, the response rate for CRC patients with metastatic disease remains low and decreases with subsequent lines of therapy. The clinical management of patients with metastatic CRC (mCRC) presents a unique challenge in balancing the benefits and harms while considering disease progression, treatment-related toxicities, drug resistance and the patient's overall quality of life. Despite the initial success of therapy, the development of drug resistance can lead to therapy failure and relapse in cancer patients, which can be attributed to the cancer stem cells (CSCs). Thus, colorectal CSCs (CCSCs) contribute to therapy resistance but also to tumor initiation and metastasis development, making them attractive potential targets for the treatment of CRC. This review presents the available CCSC isolation methods, the clinical relevance of these CCSCs, the mechanisms of drug resistance associated with CCSCs and the ongoing clinical trials targeting these CCSCs. Novel therapeutic strategies are needed to effectively eradicate both tumor growth and metastasis, while taking into account the tumor microenvironment (TME) which plays a key role in tumor cell plasticity.

Synergistic Roles of Curcumin in Sensitising the Cisplatin Effect on a Cancer Stem Cell-Like Population Derived from Non-Small Cell Lung Cancer Cell Lines

Cancer stem cells (CSCs) represent a small subpopulation within a tumour. These cells possess stem cell-like properties but also initiate resistance to cytotoxic agents, which contributes to cancer relapse. Natural compounds such as curcumin that contain high amounts of polyphenols can have a chemosensitivity effect that sensitises CSCs to cytotoxic agents such as cisplatin. This study was designed to investigate the efficacy of curcumin as a chemo-sensitiser in CSCs subpopulation of non-small cell lung cancer (NSCLC) using the lung cancer adenocarcinoma human alveolar basal epithelial cells A549 and H2170. The ability of curcumin to sensitise lung CSCs to cisplatin was determined by evaluating stemness characteristics, including proliferation activity, colony formation, and spheroid formation of cells treated with curcumin alone, cisplatin alone, or the combination of both at 24, 48, and 72 h. The mRNA level of genes involved in stemness was analysed using quantitative real-time polymerase chain reaction. Liquid chromatography-mass spectrometry was used to evaluate the effect of curcumin on the CSC niche. A combined treatment of A549 subpopulations with curcumin reduced cellular proliferation activity at all time points. Curcumin significantly (p < 0.001) suppressed colonies formation by 50% and shrank the spheroids in CSC subpopulations, indicating inhibition of their self-renewal capability. This effect also was manifested by the down-regulation of SOX2, NANOG, and KLF4. Curcumin also regulated the niche of CSCs by inhibiting chemoresistance proteins, aldehyde dehydrogenase, metastasis, angiogenesis, and proliferation of cancer-related proteins. These results show the potential of using curcumin as a therapeutic approach for targeting CSC subpopulations in non-small cell lung cancer.

Drug resistance and Cancer stem cells

Therapy resistance is a major problem when treating cancer patients as cancer cells develop mechanisms that counteract the effect of therapeutic compounds, leading to fit and more aggressive clones that contribute to poor prognosis. Therapy resistance can be both intrinsic and/or acquired. These are multifactorial events, and some are related to factors including adaptations in cancer stem cells (CSCs), epithelial-mesenchymal transition (EMT), deregulation of key signaling pathways, drug efflux through ABC transporters, acquired mutations, evading apoptosis, and activation of DNA damage response among others. Among these factors, CSCs represent the major source of therapy resistance. CSCs are a subset of tumor cells that are capable of self-renewal and multilineage progenitor expansion that are known to be intrinsically resistant to anticancer treatments. Multiple clones of CSCs pre-exist, and some can adopt and expand easily to changes in the tumor microenvironment (TME) and/or in response to radio- and chemotherapy. A combination of both intrinsic and extrinsic factors contributes to CSC-mediated therapy resistance. In this review, we will focus on CSCs and therapy resistance as well as suggest strategies to eliminate CSCs and, therefore, overcome resistance. Video abstract.

Cancer stem cells and macrophages: molecular connections and future perspectives against cancer

Cancer stem cells (CSCs) have been considered the key drivers of cancer initiation and progression due to their unlimited self-renewal capacity and their ability to induce tumor formation. Macrophages, particularly tumor-associated macrophages (TAMs), establish a tumor microenvironment to protect and induce CSCs development and dissemination. Many studies in the past decade have been performed to understand the molecular mediators of CSCs and TAMs, and several studies have elucidated the complex crosstalk that occurs between these two cell types. The aim of this review is to define the complex crosstalk between these two cell types and to highlight potential future anti-cancer strategies.

The Great Escape: The Power of Cancer Stem Cells to Evade Programmed Cell Death

Cancer is one of the primary causes of death worldwide. Tumour malignancy is related to tumor heterogeneity, which has been suggested to be due to a small subpopulation of tumor cells named cancer stem cells (CSCs). CSCs exert a key role in metastasis development, tumor recurrence, and also epithelial-mesenchymal transition, apoptotic resistance, self-renewal, tumorigenesis, differentiation, and drug resistance. Several current therapies fail to eradicate tumors due to the ability of CSCs to escape different programmed cell deaths. Thus, developing CSC-selective and programmed death-inducing therapeutic approaches appears to be of primary importance. In this review, we discuss the main programmed cell death occurring in cancer and the promising CSC-targeting agents developed in recent years. Even if the reported studies are encouraging, further investigations are necessary to establish a combination of agents able to eradicate CSCs or inhibit their growth and proliferation.

Therapeutic Approaches for Metastases from Colorectal Cancer and Pancreatic Ductal Carcinoma

Metastasis is the process of dissemination of a tumor, whereby cells from the primary site dislodge and find their way to other tissues where secondary tumors establish. Metastasis is the primary cause of death related to cancer. This process warrants changes in original tumoral cells and their microenvironment to establish a metastatic niche. Traditionally, cancer therapy has focused on metastasis prevention by systematic treatments or direct surgical re-sectioning. However, metastasis can still occur. More recently, new therapies direct their attention to targeting cancer stem cells. As they propose, these cells could be the orchestrators of the metastatic niche. In this review, we describe conventional and novel developments in cancer therapeutics for liver and lung metastasis. We further discuss the resistance mechanisms of targeted therapy, the advantages, and disadvantages of diverse treatment approaches, and future novel strategies to enhance cancer prognosis.

Cancer Stemness: p53 at the Wheel

The tumor suppressor p53 maintains an equilibrium between self-renewal and differentiation to sustain a limited repertoire of stem cells for proper development and maintenance of tissue homeostasis. Inactivation of p53 disrupts this balance and promotes pluripotency and somatic cell reprogramming. A few reports in recent years have indicated that prevalent TP53 oncogenic gain-of-function (GOF) mutations further boosts the stemness properties of cancer cells. In this review, we discuss the role of wild type p53 in regulating pluripotency of normal stem cells and various mechanisms that control the balance between self-renewal and differentiation in embryonic and adult stem cells. We also highlight how inactivating and GOF mutations in p53 stimulate stemness in cancer cells. Further, we have explored the various mechanisms of mutant p53-driven cancer stemness, particularly emphasizing on the non-coding RNA mediated epigenetic regulation. We have also analyzed the association of cancer stemness with other crucial gain-of-function properties of mutant p53 such as epithelial to mesenchymal transition phenotypes and chemoresistance to understand how activation of one affects the other. Given the critical role of cancer stem-like cells in tumor maintenance, cancer progression, and therapy resistance of mutant p53 tumors, targeting them might improve therapeutic efficacy in human cancers with TP53 mutations.