Cancer stem cells and their niche in the progression of squamous cell carcinoma

The biomarkers for maintenance Cancer stem cell features can be applicable in precision medicine of head and neck squamous cell carcinoma

Cancer stem cells (CSCs) play a crucial role in tumor relapse, proliferation, invasion, and drug resistance in head and neck squamous cell carcinoma (HNSCC). This narrative review aims to synthesize data from articles published between 2019 and 2023 on biomarkers for detecting CSCs in HNSCC and changes in molecular pathways, genetics, epigenetics, and non-coding RNAs (ncRNAs) in CSCs relevant to precision medicine approaches in HNSCC management. The search encompassed 41 in vitro studies and 22 clinical studies. CSCs exhibit diverse molecular profiles and unique biomarker expression patterns, offering significant potential for HNSCC diagnosis, treatment, and prognosis, thereby enhancing patient survival. Their remarkable self-renewal ability and adaptability are closely linked to tumorigenicity development and maintenance. Assessing biomarkers before and after therapy can aid in identifying various cell types associated with cancer progression and relapse. Screening for CSCs, senescent tumor cells, and cells correlated with the senescence process post-treatment has proven highly beneficial. However, the clinical application of precision medicine in HNSCC management is hindered by the lack of specific and definitive CSC biomarkers. Furthermore, our limited understanding of CSC plasticity, governed by genomic, transcriptomic, and epigenomic alterations during tumorigenesis, as well as the bidirectional interaction of CSCs with the tumor microenvironment, underscores the need for further research. Well-designed studies involving large patient cohorts are, therefore, essential to establish a standardized protocol and address these unresolved queries.

Metabolic vulnerability of cancer stem cells and their niche

Cancer stem cells (CSC) are the leading cause of the failure of anti-tumor treatments. These aggressive cancer cells are preserved and sustained by adjacent cells forming a specialized microenvironment, termed niche, among which tumor-associated macrophages (TAMs) are critical players. The cycle of tricarboxylic acids, fatty acid oxidation path, and electron transport chain have been proven to play central roles in the development and maintenance of CSCs and TAMs. By improving their oxidative metabolism, cancer cells are able to extract more energy from nutrients, which allows them to survive in nutritionally defective environments. Because mitochondria are crucial bioenergetic hubs and sites of these metabolic pathways, major hopes are posed for drugs targeting mitochondria. A wide range of medications targeting mitochondria, electron transport chain complexes, or oxidative enzymes are currently investigated in phase 1 and phase 2 clinical trials against hard-to-treat tumors. This review article aims to highlight recent literature on the metabolic adaptations of CSCs and their supporting macrophages. A focus is provided on the resistance and dormancy behaviors that give CSCs a selection advantage and quiescence capacity in particularly hostile microenvironments and the role of TAMs in supporting these attitudes. The article also describes medicaments that have demonstrated a robust ability to disrupt core oxidative metabolism in preclinical cancer studies and are currently being tested in clinical trials.

Cancer stem cells and their niche in cancer progression and therapy

High recurrence and metastasis rates and poor prognoses are the major challenges of current cancer therapy. Mounting evidence suggests that cancer stem cells (CSCs) play an important role in cancer development, chemoradiotherapy resistance, recurrence, and metastasis. Therefore, targeted CSC therapy has become a new strategy for solving the problems of cancer metastasis and recurrence. Since the properties of CSCs are regulated by the specific tumour microenvironment, the so-called CSC niche, which targets crosstalk between CSCs and their niches, is vital in our pursuit of new therapeutic opportunities to prevent cancer from recurring. In this review, we aim to highlight the factors within the CSC niche that have important roles in regulating CSC properties, including the extracellular matrix (ECM), stromal cells (e.g., associated macrophages (TAMs), cancer-associated fibroblasts (CAFs), and mesenchymal stem cells (MSCs)), and physiological changes (e.g., inflammation, hypoxia, and angiogenesis). We also discuss recent progress regarding therapies targeting CSCs and their niche to elucidate developments of more effective therapeutic strategies to eliminate cancer.

Feline SCCs of the Head and Neck Display Partial Epithelial-Mesenchymal Transition and Harbor Stem Cell-like Cancer Cells

Squamous cell carcinoma of the head and neck (HNSCC) is a malignant cancer disease in humans and animals. There is ample evidence that the high plasticity of cancer cells, i.e., their ability to switch from an epithelial to a mesenchymal, endothelial, and stem cell-like phenotype, chiefly contributes to progression, metastasis, and multidrug resistance of human HNSCCs. In feline HNSCC, the field of cancer cell plasticity is still unexplored. In this study, fourteen feline HNSCCs with a known feline papillomavirus (FPV) infection status were subjected to histopathological grading and subsequent screening for expression of epithelial, mesenchymal, and stem cell markers by immunohistochemistry (IHC) and immunofluorescence staining (IF). Irrespective of the FPV infection status, all tumors except one corresponded to high-grade, invasive lesions and concurrently expressed epithelial (keratins, E-cadherin, β-catenin) and mesenchymal (vimentin, N-cadherin, CD146) proteins. This finding is indicative for partial epithelial-mesenchymal transition (pEMT) events in the lesions, as similarly described for human HNSCCs. IF double staining revealed the presence of CD44/CD271 double-positive cells notably within the tumors' invasive fronts that likely correspond to cancer stem cells. Taken together, the obtained findings suggest that feline HNSCCs closely resemble their human counterparts with respect to tumor cell plasticity.

Exploring the dynamic interplay between cancer stem cells and the tumor microenvironment: implications for novel therapeutic strategies

Cancer stem cells (CSCs) have emerged as key contributors to tumor initiation, growth, and metastasis. In addition, CSCs play a significant role in inducing immune evasion, thereby compromising the effectiveness of cancer treatments. The reciprocal communication between CSCs and the tumor microenvironment (TME) is observed, with the TME providing a supportive niche for CSC survival and self-renewal, while CSCs, in turn, influence the polarization and persistence of the TME, promoting an immunosuppressive state. Consequently, these interactions hinder the efficacy of current cancer therapies, necessitating the exploration of novel therapeutic approaches to modulate the TME and target CSCs. In this review, we highlight the intricate strategies employed by CSCs to evade immune surveillance and develop resistance to therapies. Furthermore, we examine the dynamic interplay between CSCs and the TME, shedding light on how this interaction impacts cancer progression. Moreover, we provide an overview of advanced therapeutic strategies that specifically target CSCs and the TME, which hold promise for future clinical and translational studies in cancer treatment.

OCT4's role and mechanism underlying oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC), a common malignancy of the head and neck, ranks sixth worldwide in terms of cancers with the most negative impact, owing to tumor relapse rates, cervical lymphnode metastasis, and the lack of an efficacious systemic therapy. Its prognosis is poor, and its mortality rate is high. Octamer-binding transcription factor 4 (OCT4) is a member of the Pit-Oct-Unc (POU) family and is a key reprogramming factor that produces a marked effect in preserving the pluripotency and self-renewal state of embryonic stem cells (ESCs). According to recent studies, OCT4 participates in retaining the survival of OSCC cancer stem cells (CSCs), which has far-reaching implications for the occurrence, recurrence, metastasis, and prognosis of oral carcinogenesis. Therefore, we summarize the structure, subtypes, and function of OCT4 as well as its role in the occurrence, progression, and prognosis of OSCC.

Expression of the Embryonic Cancer Stem Cells' Biomarkers SOX2 and OCT3/4 in Oral Leukoplakias and Squamous Cell Carcinomas: A Preliminary Study

INTRODUCTION

Cancer stem cells (CSCs) are incriminated for initiating the process of carcinogenesis either de novo or through the transformation of oral potentially malignant disorders (OPMDs) to oral squamous cell carcinoma (OSCC). The aim of this study was to detect the expression of embryonic-type CSC markers OCT3/4 and SOX2 in OSCCs and oral leukoplakias (OLs), the most common of OPMDs.

MATERIALS AND METHODS

The study type is experimental, and the study design is characterized as semiquantitative research, which belongs to the branch of experimental research. The experiment was conducted in the Department of Oral Medicine/Pathology, School of Dentistry, Aristotle University of Thessaloniki, Greece. This study focuses on the semiquantitative immunohistochemical (IHC) pattern of expression of CSCs protein-biomarkers SOX2 and OCT3/4, in paraffin embedded samples of 21 OSCCs of different grades of differentiation and 30 cases of OLs with different grades of dysplasia, compared to five cases of normal oral mucosa in both terms of cells' stain positivity and intensity. Statistical analysis was performed through SPSS 2017 Pearson Chi-square and the significance level was set at 0.05 (p=0.05). The expression of the respective genes of SOX2 and OCT3/4 was studied through quantitative polymerase chain reaction (qPCR), in paraffin-embedded samples of 12 cases of OLs with mild/non dysplasia and 19 cases moderately/poorly differentiated OSCCs(n=19) and five normal mucosa using the Independent Paired T-test.

RESULTS

The genes SOX2 and Oct3/4 were expressed in all examined cases although no statistically significant correlations among normal, OL and OSCC, were established. A nuclear/membrane staining of OCT3/4 was noticed only in three out of 21 OSCCs but in none of OLs or normal cases (without statistical significance). A characteristic nuclear staining of SOX2 was noticed in the majority of the samples, mostly in the basal and parabasal layers of the epithelium. SOX2 was significantly detected in the OSCCs group (strong positivity in 17/21) than in the OL group (30 cases, mostly mildly stained) (p-value=0.007), and the normal oral epithelium (mild stained, p=0.065). Furthermore, SOX2 was overexpressed in well differentiated OSCCs group (5/OSCCs, strongly stained) rather than in mildly dysplastic and non-dysplastic OLs samples (14/OLs, mildly stained) (p-value =0.035).

CONCLUSION

The characteristic expression of SOX2 but not of OCT3/4 in OLs' and OSCCs' lesions suggests the presence of neoplastic cells with certain CSC characteristics whose implication in the early stages of oral tumorigenesis could be further evaluated. The clinical use of SOX2, as prognostic factor, requires further experimental evaluation in larger number of samples.

Advantages of the Combinatorial Molecular Targeted Therapy of Head and Neck Cancer-A Step before Anakoinosis-Based Personalized Treatment

The molecular initiators of Head and Heck Squamous Cell Carcinoma (HNSCC) are complex. Human Papillomavirus (HPV) infection is linked to an increasing number of HNSCC cases, but HPV-positive tumors generally have a good prognosis. External factors that promote the development of HPV-negative HNSCC include tobacco use, excessive alcohol consumption, and proinflammatory poor oral hygiene. On a molecular level, several events, including the well-known overexpression of epidermal growth factor receptors (EGFR) and related downstream signaling pathways, contribute to the development of HNSCC. Conventional chemotherapy is insufficient for many patients. Thus, molecular-based therapy for HNSCC offers patients a better chance at a cure. The first molecular target for therapy of HNSCC was EGFR, inhibited by monoclonal antibody cetuximab, but its use in monotherapy is insufficient and induces resistance. This article describes attempts at combinatorial molecular targeted therapy of HNSCC based on several molecular targets and exemplary drugs/drug candidates. The new concept of anakoinosis-based therapy, which means treatment that targets the intercellular and intracellular communication of cancer cells, is thought to be the way to improve the clinical outcome for HNSCC patients. The identification of a link between molecular targeted therapy and anakoinosis raises the potential for further progress in HPV-negative HNSCC therapy.

WDR3 promotes stem cell-like properties in prostate cancer by inhibiting USF2-mediated transcription of RASSF1A

BACKGROUND

WD repeat domain 3 (WDR3) is involved in tumor growth and proliferation, but its role in the pathological mechanism of prostate cancer (PCa) is still unclear.

METHODS

WDR3 gene expression levels were obtained by analyzing databases and our clinical specimens. The expression levels of genes and proteins were determined by a real-time polymerase chain reaction, western blotting and immunohistochemistry, respectively. Cell-counting kit-8 assays were used to measure the proliferation of PCa cells. Cell transfection was used to investigate the role of WDR3 and USF2 in PCa. Fluorescence reporter and chromatin immunoprecipitation assays were used to detect USF2 binding to the promoter region of RASSF1A. Mouse experiments were used to confirm the mechanism in vivo.

RESULTS

By analyzing the database and our clinical specimens, we found that WDR3 expression was significantly increased in PCa tissues. Overexpression of WDR3 enhanced PCa cell proliferation, decreased cell apoptosis rate, increased spherical cell number and increased indicators of stem cell-like properties. However, these effects were reversed by WDR3 knockdown. WDR3 was negatively correlated with USF2, which was degraded by promoting ubiquitination of USF2, and USF2 interacted with promoter region-binding elements of RASSF1A to depress PCa stemness and growth. In vivo studies showed that WDR3 knockdown reduced tumor size and weight, reduced cell proliferation and enhanced cell apoptosis.

CONCLUSIONS

WDR3 ubiquitinated USF2 and inhibited its stability, whereas USF2 interacted with promoter region-binding elements of RASSF1A. USF2 transcriptionally activated RASSF1A, which inhibited the carcinogenic effect of WDR3 overexpression.

Cancers of unknown primary: Survival by histologic type, demographic features, and treatment in the U.S. Military Health System

BACKGROUND

Cancers of unknown primary (CUP), a group of heterogenous metastatic cancers lacking a known primary site, have poor prognosis. This study compared survival of CUP by histologic type, patient characteristics, and treatment in the U.S. Military Health System (MHS), which provides universal care to its members.

METHODS

Patients histologically diagnosed with CUP were identified from the U.S. Department of Defense (DoD)'s Automated Central Tumor Registry. Median survival with 95 % confidence intervals was calculated for demographic and treatment variables by histologic type. A multivariable accelerated failure time model estimated time ratios and 95 % confidence intervals.

RESULTS

The study included 3358 CUP patients. The most prevalent CUP in this study was well- and moderately-differentiated adenocarcinomas. Median survival varied by histologic type with squamous cell carcinoma having the longest at 25.1 months and poorly-differentiated carcinomas having the shortest at 3.0 months. For each histologic type, survival was generally similar by sex and active-duty status although women with well- and moderately-differentiated adenocarcinoma had longer survival than their male counterparts. Younger patients tended to have longer survival than those aged 65 years or older. Generally, there were no racial differences in survival except poorer survival for Black patients than White patients in the group of other histologic types. Patients with chemotherapy and radiation treatment generally had improved survival whereas patients with squamous cell carcinoma who received chemotherapy had shorter survival than those without.

CONCLUSION

Survival generally did not differ between racial groups, which may be related to equal healthcare access despite racial background. Further studies are warranted to better understand how survival in the MHS compares with that in the general U.S.

POPULATION

Detection of Equine Papillomaviruses and Gamma-Herpesviruses in Equine Squamous Cell Carcinoma

Squamous cell carcinoma (SCC) seriously compromises the health and welfare of affected horses. Although robust evidence points to equine papillomavirus type 2 (EcPV2) causing genital lesions, the etiopathogenesis of equine SCC is still poorly understood. We screened a series of SCCs from the head-and-neck (HN), (peri-)ocular and genital region, and site-matched controls for the presence of EcPV2-5 and herpesvirus DNA using type-specific EcPV PCR, and consensus nested herpesvirus PCR followed by sequencing. EcPV2 DNA was detected in 45.5% of HN lesions, 8.3% of (peri-)ocular SCCs, and 100% of genital tumors, whilst control samples from tumor-free horses except one tested EcPV-negative. Two HNSCCs harbored EcPV5, and an ocular lesion EcPV4 DNA. Herpesvirus DNA was detected in 63.6%, 66.6%, 47.2%, and 14.2% of horses with HN, ocular, penile, and vulvar SCCs, respectively, and mainly identified as equine herpesvirus 2 (EHV2), 5 (EHV5) or asinine herpesvirus 5 (AsHV5) DNA. In the tumor-free control group, 9.6% of oral secretions, 46.6% of ocular swabs, 47% of penile samples, and 14.2% of vaginal swabs scored positive for these herpesvirus types. This work further highlights the role of EcPV2 as an oncovirus and is the first to provide information on the prevalence of (gamma-)herpesviruses in equine SCCs.

Complex interaction and heterogeneity among cancer stem cells in head and neck squamous cell carcinoma revealed by single-cell sequencing

BACKGROUND

Cancer stem cells (CSCs) have been characterized to be responsible for multidrug resistance, metastasis, recurrence, and immunosuppressive in head and neck squamous cell carcinoma (HNSCC). However, the diversity of CSCs remains to be investigated. In this study, we aimed to determine the heterogeneity of CSCs and its effect on the formation of tumor microenvironment (TME).

METHODS

We depicted the landscape of HNSCC transcriptome profile by single-cell RNA-sequencing analysis of 20 HNSCC tissues from public databases, to reveal the Cell components, trajectory changes, signaling network, malignancy status and functional enrichment of CSCs within tumors.

RESULTS

Immune checkpoint molecules CD276, LILRB2, CD47 were significantly upregulated in CSCs, enabling host antitumor response to be weakened or damaged. Notably, naive CSCs were divided to 2 different types of cells with different functions, exhibiting functional diversity. In addition, CSCs underwent self-renewal and tumor metastasis activity through WNT and ncWNT signaling. Among them, Regulon regulators (IRF1_394g, IRF7_160g, NFKB1_12g, NFKB2_33g and STAT1_356g) were activated in subgroups 2 and 3, suggesting their pivotal roles in the inflammatory response process in tumors. Among all CSCs, naive CSCs appear to be the most malignant resulting in a worse prognosis.

CONCLUSIONS

Our study reveals the major signal transduction and biological function of CSCs during HNSCC progression, highlighting the heterogeneity of CSCs and their underlying mechanisms in the formation of an immunosuppressive TME. Therefore, our study about heterogeneity of CSCs in HNSCC can bring new insights for the treatment of HNSCC.

Epithelial-to-Mesenchymal Transition in Metastasis: Focus on Laryngeal Carcinoma

In epithelial neoplasms, such as laryngeal carcinoma, the survival indexes deteriorate abruptly when the tumor becomes metastatic. A molecular phenomenon that normally appears during embryogenesis, epithelial-to-mesenchymal transition (EMT), is reactivated at the initial stage of metastasis when tumor cells invade the adjacent stroma. The hallmarks of this phenomenon are the abolishment of the epithelial and acquisition of mesenchymal traits by tumor cells which enhance their migratory capacity. EMT signaling is mediated by complex molecular pathways that regulate the expression of crucial molecules contributing to the tumor’s metastatic potential. Effectors of EMT include loss of adhesion, cytoskeleton remodeling, evasion of apoptosis and immune surveillance, upregulation of metalloproteinases, neovascularization, acquisition of stem-cell properties, and the activation of tumor stroma. However, the current approach to EMT involves a holistic model that incorporates the acquisition of potentials beyond mesenchymal transition. As EMT is inevitably associated with a reverse mesenchymal-to-epithelial transition (MET), a model of partial EMT is currently accepted, signifying the cell plasticity associated with invasion and metastasis. In this review, we identify the cumulative evidence which suggests that various aspects of EMT theory apply to laryngeal carcinoma, a tumor of significant morbidity and mortality, introducing novel molecular targets with prognostic and therapeutic potential.

Diversity of the Origin of Cancer Stem Cells in Oral Squamous Cell Carcinoma and Its Clinical Implications

Simple Summary

Oral squamous cell carcinoma (OSCC) histopathologically accounts for ≥90% of oral cancer. In this review article, we focus on the diversity of the origin of OSCC and also discuss cancer stem cells (CSCs). CSCs are a subset of cancer cells that occupy a very small portion of the cancer mass and have characteristics of stem cells. When gene abnormalities accumulate in somatic stem cells, those cells transform into CSCs. CSCs as the origin of cancer then autonomously grow and develop into cancer. The histopathological phenotype of cancer cells is determined by the original characteristics of the somatic stem cells and/or surrounding environment. OSCC may be divided into the following three categories with different malignancy based on the origin of CSCs: cancer from oral epithelial stem cell-derived CSCs, cancer from stem cells in salivary gland-derived CSCs, and cancer from bone marrow-derived stem cell-derived CSCs.

Abstract

Oral squamous cell carcinoma (OSCC) histopathologically accounts for ≥90% of oral cancer. Many clinicopathological risk factors for OSCC have also been proposed, and postoperative therapy is recommended in guidelines based on cancer stage and other risk factors. However, even if the standard treatment is provided according to the guidelines, a few cases rapidly recur or show cervical and distant metastasis. In this review article, we focus on the diversity of the origin of OSCC. We also discuss cancer stem cells (CSCs) as a key player to explain the malignancy of OSCC. CSCs are a subset of cancer cells that occupy a very small portion of the cancer mass and have characteristics of stem cells. When gene abnormalities accumulate in somatic stem cells, those cells transform into CSCs. CSCs as the origin of cancer then autonomously grow and develop into cancer. The histopathological phenotype of cancer cells is determined by the original characteristics of the somatic stem cells and/or surrounding environment. OSCC may be divided into the following three categories with different malignancy based on the origin of CSCs: cancer from oral epithelial stem cell-derived CSCs, cancer from stem cells in salivary gland-derived CSCs, and cancer from bone marrow-derived stem cell-derived CSCs.

EZH2 regulates a SETDB1/ΔNp63α axis via RUNX3 to drive a cancer stem cell phenotype in squamous cell carcinoma

Enhancer of zeste homolog 2 (EZH2) and SET domain bifurcated 1 (SETDB1, also known as ESET) are oncogenic methyltransferases implicated in a number of human cancers. These enzymes typically function as epigenetic repressors of target genes by methylating histone H3 K27 and H3-K9 residues, respectively. Here, we show that EZH2 and SETDB1 are essential to proliferation in 3 SCC cell lines, HSC-5, FaDu, and Cal33. Additionally, we find both of these proteins highly expressed in an aggressive stem-like SCC sub-population. Depletion of either EZH2 or SETDB1 disrupts these stem-like cells and their associated phenotypes of spheroid formation, invasion, and tumor growth. We show that SETDB1 regulates this SCC stem cell phenotype through cooperation with ΔNp63α, an oncogenic isoform of the p53-related transcription factor p63. Furthermore, EZH2 is upstream of both SETDB1 and ΔNp63α, activating these targets via repression of the tumor suppressor RUNX3. We show that targeting this pathway with inhibitors of EZH2 results in activation of RUNX3 and repression of both SETDB1 and ΔNp63α, antagonizing the SCC cancer stem cell phenotype. This work highlights a novel pathway that drives an aggressive cancer stem cell phenotype and demonstrates a means of pharmacological intervention.

Characteristics of the cancer stem cell niche and therapeutic strategies

Distinct regions harboring cancer stem cells (CSCs) have been identified within the microenvironment of various tumors, and as in the case of their healthy counterparts, these anatomical regions are termed “niche.” Thus far, a large volume of studies have shown that CSC niches take part in the maintenance, regulation of renewal, differentiation and plasticity of CSCs. In this review, we summarize and discuss the latest findings regarding CSC niche morphology, physical terrain, main signaling pathways and interactions within them. The cellular and molecular components of CSCs also involve genetic and epigenetic modulations that mediate and support their maintenance, ultimately leading to cancer progression. It suggests that the crosstalk between CSCs and their niche plays an important role regarding therapy resistance and recurrence. In addition, we updated diverse therapeutic strategies in different cancers in basic research and clinical trials in this review. Understanding the complex heterogeneity of CSC niches is a necessary pre-requisite for designing superior therapeutic strategies to target CSC-specific factors and/or components of the CSC niche.

Tumor Cell Plasticity in Equine Papillomavirus-Positive Versus-Negative Squamous Cell Carcinoma of the Head and Neck

Squamous cell carcinoma of the head and neck (HNSCC) is a common malignant tumor in humans and animals. In humans, papillomavirus (PV)-induced HNSCCs have a better prognosis than papillomavirus-unrelated HNSCCs. The ability of tumor cells to switch from epithelial to mesenchymal, endothelial, or therapy-resistant stem-cell-like phenotypes promotes disease progression and metastasis. In equine HNSCC, PV-association and tumor cell phenotype switching are poorly understood. We screened 49 equine HNSCCs for equine PV (EcPV) type 2, 3 and 5 infection. Subsequently, PV-positive versus -negative lesions were analyzed for expression of selected epithelial (keratins, β-catenin), mesenchymal (vimentin), endothelial (COX-2), and stem-cell markers (CD271, CD44) by immunohistochemistry (IHC) and immunofluorescence (IF; keratins/vimentin, CD44/CD271 double-staining) to address tumor cell plasticity in relation to PV infection. Only EcPV2 PCR scored positive for 11/49 equine HNSCCs. IHC and IF from 11 EcPV2-positive and 11 EcPV2-negative tumors revealed epithelial-to-mesenchymal transition events, with vimentin-positive cells ranging between <10 and >50%. CD44- and CD271-staining disclosed the intralesional presence of infiltrative tumor cell fronts and double-positive tumor cell subsets independently of the PV infection status. Our findings are indicative of (partial) epithelial–mesenchymal transition events giving rise to hybrid epithelial/mesenchymal and stem-cell-like tumor cell phenotypes in equine HNSCCs and suggest CD44 and CD271 as potential malignancy markers that merit to be further explored in the horse.

LncRNA DUXAP10 Upregulation and the Hedgehog Pathway Activation Are Critically Involved in Chronic Cadmium Exposure-Induced Cancer Stem Cell-Like Property

Cadmium (Cd) is a well-known lung carcinogen. However, the mechanism of Cd carcinogenesis remains to be clearly defined. Cd has been shown to act as a weak mutagen, suggesting that it may exert tumorigenic effect through nongenotoxic ways, such as epigenetic mechanisms. Long noncoding RNAs (lncRNAs) refer to RNA molecules that are longer than 200 nucleotides in length but lack protein-coding capacities. Regulation of gene expressions by lncRNAs is considered as one of important epigenetic mechanisms. The goal of this study is to investigate the mechanism of Cd carcinogenesis focusing on the role of lncRNA dysregulations. Cd-induced malignant transformation of human bronchial epithelia BEAS-2B cells was accomplished by a 9-month low-dose Cd (CdCl2, 2.5 µM) exposure. The Cd-exposed cells formed significantly more colonies in soft agar, displayed cancer stem cell (CSC)-like property, and formed tumors in nude mice. Mechanistically, chronic low-dose Cd exposure did not cause significant genotoxic effects but dysregulated lncRNA expressions. Further Q-PCR analysis confirmed the significant upregulation of the oncogenic lncRNA DUXAP10 in Cd-transformed cells. DUXAP10 knockdown in Cd-transformed cells significantly reduced their CSC-like property. Further mechanistic studies showed that the Hedgehog pathway is activated in Cd-transformed cells and inhibition of this pathway reduces Cd-induced CSC-like property. DUXAP10 knockdown caused the Hedgehog pathway inactivation in Cd-transformed cells. Furthermore, Pax6 expression was upregulated in Cd-transformed cells and Pax6 knockdown significantly reduced their DUXAP10 levels and CSC-like property. In summary, these findings suggest that the lncRNA DUXAP10 upregulation may play an important role in Cd carcinogenesis.

Long non-coding RNA TTN-AS1/microRNA-199a-3p/runt-related transcription factor 1 gene axis regulates the progression of oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) has a high degree of malignancy, which affects the quality of life and prognosis of patients with OSCC. Our study aimed to reveal the function of long non-coding RNA TTN-AS1/microRNA-199a-3p (miR-199a-3p)/runt-related transcription factor 1 (RUNX1) axis in OSCC progression, thereby providing a novel OSCC effective strategy. Real-time quantitative polymerase chain reaction and western blotting were performed to detect the expression of TTN-AS1, miR-199a-3p, and RUNX1 in OSCC. Several cell functional experiments, including Cell Counting Kit-8, flow cytometry, and cell adhesion assays, were used to assess cell proliferation, apoptosis, adhesion, and migration. A luciferase assay was performed to confirm the interaction between TTN-AS1, miR-199a-3p, and RUNX1. Our results revealed that TTN-AS1 and RUNX1 were upregulated in OSCC tissues and cells, whereas miR-199a-3p expression was downregulated. Knockdown of TTN-AS1 or RUNX1 suppressed cell proliferation, adhesion, and migration but induced apoptosis. Additionally, miR-199a-3p inhibitor partly relieved the effects of silencing TTN-AS1 and RUNX1 in OSCC cells due to their targeting relationship. In conclusion, TTN-AS1 and RUNX1 could promote OSCC progression and miR-199a-3p partly relieved the effects of TTN-AS1 and RUNX1.

Macrophages and cancer stem cells: a malevolent alliance

Myeloid cells infiltrating tumors are gaining ever growing attention in the last years because their pro-tumor and immunosuppressive functions are relevant for disease progression and therapeutic responses. The functional ambiguity of tumor-associated macrophages (TAMs), mostly promoting tumor evolution, is a challenging hurdle. This is even more evident in the case of cancer stem cells (CSCs); as active participants in the specialized environment of the cancer stem cell niche, TAMs initiate a reciprocal conversation with CSCs. TAMs contribute to protect CSCs from the hostile environment (exogenous insults, toxic compounds, attacks from the immune cells), and produce several biologically active mediators that modulate crucial developmental pathways that sustain cancer cell stemness. In this review, we have focused our attention on the interaction between TAMs and CSCs; we describe how TAMs impact on CSC biology and, in turn, how CSCs exploit the tissue trophic activity of macrophages to survive and progress. Since CSCs are responsible for therapy resistance and tumor recurrence, they are important therapeutic targets. In view of the recent success in oncology obtained by stimulating the immune system, we discuss some macrophage-targeted therapeutic strategies that may also affect the CSCs and interrupt their malevolent alliance.

Cancer Stem Cells in Oropharyngeal Cancer

Oropharyngeal cancer (OPC), which is a common type of head and neck squamous cell carcinoma (HNSCC), is associated with tobacco and alcohol use, and human papillomavirus (HPV) infection. Underlying mechanisms and as a result prognosis of the HPV-positive and HPV-negative OPC patients are different. Like stem cells, the ability of self-renewal and differentiate, cancer stem cells (CSCs) have roles in tumor invasion, metastasis, drug resistance, and recurrence after therapy. Research revealed their roles to some extent in all of these processes but there are still many unresolved points to connect to CSC-targeted therapy. In this review, we will focus on what we currently know about CSCs of OPC and limitations of our current knowledge. We will present perspectives that will broaden our understanding and recent literature which may connect to therapy.

Chronic intermittent hypoxia promoted lung cancer stem cell-like properties via enhancing Bach1 expression

Background

An adverse role for obstructive sleep apnea (OSA) in cancer aggressiveness and mortality has recently emerged from clinical and animal studies, and the reasons have not been fully determined. Cancer stem cells (CSCs) are regarded as the main cause of carcinoma metastasis. So far, the relationship between OSA and lung CSCs has not been explored.

Method

In the present study, we established an orthotopic mouse model of primary lung cancer and utilized chronic intermittent hypoxia (CIH) exposure to mimic OSA status.

Results

We observed that CIH endows lung cancer with greater metastatic potential, evidenced by increased tumor growth, tumor seeding, and upregulated CSC-related gene expression in the lungs. Notably, the transcription factor BTB and CNC homology 1 (Bach1), a key factor in responding to conditions of oxidative stress, is increased in lung cancer after CIH exposure in vitro and in vivo. Meanwhile, exposing lung cancer cells to CIH promoted cell proliferation, clonal diversity, induced stem-like cell marker expression, and gave rise to CSCs at a relatively higher frequency. Furthermore, the increase of mitochondrial ROS (mtROS) and CSC-marker expression induced by CIH exposure was abolished in Bach1 shRNA-treated lung cancer cells.

Conclusions

Our results indicated that CIH promoted lung CSC-like properties by activating mtROS, which was partially mediated by Bach1.

Cancer stem cells and their niche in the progression of squamous cell carcinoma

Most cancers harbor a small population of highly tumorigenic cells known as cancer stem cells (CSCs). Because of their stem cell-like properties and resistance to conventional therapies, CSCs are considered to be a rational target for curable cancer treatment. However, despite recent advances in CSC research, CSC-targeted therapies are not as successful as was initially hoped. The proliferative, invasive, and drug-resistant properties of CSCs are regulated by the tumor microenvironment associated with them, the so-called CSC niche. Thus, targeting tumor-promoting cellular crosstalk between CSCs and their niches is an attractive avenue for developing durable therapies. Using mouse models of squamous cell carcinoma (SCC), we have demonstrated that tumor cells responding to transforming growth factor β (TGF-β) function as drug-resistant CSCs. The gene expression signature of TGF-β-responding tumor cells has accelerated the identification of novel pathways that drive invasive tumor progression. Moreover, by focusing on the cytokine milieu and macrophages in the proximity of TGF-β-responding tumor cells, we recently uncovered the molecular basis of a CSC-niche interaction that emerges during early tumor development. This review article summarizes the specialized tumor microenvironment associated with CSCs and discusses mechanisms by which malignant properties of CSCs are maintained and promoted.