Isolation and Characterization of Cancer Stem Cells of the Non-Small-Cell Lung Cancer (A549) Cell Line

Comparison of methods for cancer stem cell detection in prognosis of early stages NSCLC

BACKGROUND

Despite advances in diagnosis and treatment in lung cancer, therapies still fail to improve patient management due to resistance mechanisms and relapses. As Cancer stem cells (CSCs) directly contribute to tumor growth and therapeutic resistance, their clinical detection represents a major challenge. However specific and additional CSC markers lack. Thus, our aim was to achieve selective detection of CSCs with specific glycan patterns and assess the CSCs burden to predict the risk of relapse in NSCLC tumors.

METHODS

The lung CSCs detection and sorting with a lectin MIX were assessed and compared to CD133 in vitro. Then, its putative role as CSC biomarker was evaluated in vivo and its clinical significance on 221 NSCLC patients.

RESULTS

We showed a significant CSCs enrichment in the MIX+ sorted fraction compared to CD133+ cells and confirmed its high tumorigenic capacity. The MIX prognostic value on the overall survival from early stages patients was validated suggesting its potential for detecting CSCs directly linked to tumor aggressiveness.

CONCLUSION

The MIX could be more relevant for detecting and sorting CSCs than CD133. Moreover, its prognosis value could enable clinicians to better classify early-stage patients at high risk of relapse in order to tailor therapeutic decisions.

Maximizing the relevance and reproducibility of A549 cell culture using FBS-free media

Scientists are using in vitro methods to answer important research questions and implementing strategies to maximize the reliability and human relevance of these methods. One strategy is to replace the use of fetal bovine serum (FBS)-an undefined and variable mixture of biomolecules-in cell culture media with chemically defined or xeno-free medium. In this study, A549 cells, a human lung alveolar-like cell line commonly used in respiratory research, were transitioned from a culture medium containing FBS to media without FBS. A successful transition was determined based on analysis of cell morphology and functionality. Following transition to commercially available CnT-Prime Airway (CELLnTEC) or X-VIVO™ 10 (Lonza) medium, the cells were characterized by microscopic evaluation and calculation of doubling time. Their genotype, morphology, and functionality were assessed by monitoring the expression of gene markers for lung cell types, surfactant production, cytokine release, the presence of multilamellar bodies, and cell viability following sodium dodecyl sulphate exposure. Our results showed that A549 cells successfully transitioned to FBS-free media under submerged and air-liquid-interface conditions. Cells grown in X-VIVO™ 10 medium mimicked cellular characteristics of FBS-supplemented media while those grown in CnT-Prime Airway medium demonstrated characteristics possibly more reflective of normal human alveolar epithelial cells.

The Effect of Chronic Exposure of Graphene Nanoplates on the Viability and Motility of A549 Cells

Graphene and its derivatives are popular nanomaterials used worldwide in many technical fields and biomedical applications. Due to such massive use, their anticipated accumulation in the environment is inevitable, with a largely unknown chronic influence on living organisms. Although repeatedly tested in chronic in vivo studies, long-term cell culture experiments that explain the biological response to these nanomaterials are still scarce. In this study, we sought to evaluate the biological responses of established model A549 tumor cells exposed to a non-toxic dose of pristine graphene for eight weeks. Our results demonstrate that the viability of the A549 cells exposed to the tested graphene did not change as well as the rate of their growth and proliferation despite nanoplatelet accumulation inside the cells. In addition, while the enzymatic activity of mitochondrial dehydrogenases moderately increased in exposed cells, their overall mitochondrial damage along with energy production changes was also not detected. Conversely, chronic accumulation of graphene nanoplates in exposed cells was detected, as evidenced by electron microscopy associated with impaired cellular motility.

Exosomal Proteins and Lipids as Potential Biomarkers for Lung Cancer Diagnosis, Prognosis, and Treatment

Simple Summary

Exosomes (or extracellular vesicles) are known to mediate intercellular communication and to transmit molecular signals between cells. Molecules carried by exosomes have their own molecular roles in affecting surrounding and distant environment, as well as recipient cells. Molecular components of exosomes can be used as cancer biomarkers for diagnosis and prognosis, being promising therapeutic targets for the interruption of cellular signals. Therefore, the understanding of the molecular compositions and their functional indications of exosomes has the potential to help doctors to diagnose and monitor diseases and to allow researchers to design and develop potential targeted therapies. This review aims to provide a comprehensive protein and lipid characterization of lung cancer exosomes and to explore their molecular functions and mechanisms regulating physiological and pathological processes. This organization offers informative insight for lung cancer diagnosis and treatment.

Abstract

Exosomes participate in cell–cell communication by transferring molecular components between cells. Previous studies have shown that exosomal molecules derived from cancer cells and liquid biopsies can serve as biomarkers for cancer diagnosis and prognosis. The exploration of the molecules transferred by lung cancer-derived exosomes can advance the understanding of exosome-mediated signaling pathways and mechanisms. However, the molecular characterization and functional indications of exosomal proteins and lipids have not been comprehensively organized. This review thoroughly collected data concerning exosomal proteins and lipids from various lung cancer samples, including cancer cell lines and cancer patients. As potential diagnostic and prognostic biomarkers, exosomal proteins and lipids are available for clinical use in lung cancer. Potential therapeutic targets are mentioned for the future development of lung cancer therapy. Molecular functions implying their possible roles in exosome-mediated signaling are also discussed. Finally, we emphasized the importance and value of lung cancer stem cell-derived exosomes in lung cancer therapy. In summary, this review presents a comprehensive description of the protein and lipid composition and function of lung cancer-derived exosomes for lung cancer diagnosis, prognosis, and treatment.

Tanshinone IIA Shows Higher Antiproliferative Activities than Sinapic Acid in 4 Cancer Cell Lines and Simultaneously Induces Apoptosis and Necroptosis in Human Lung Cancer A549 Cells

Tanshinone IIA (Tan IIA) and sinapic acid (SA) are 2 components separately isolated from 2 Asian medicinal plants, Hydnophytum formicarum Jack and Salvia miltiorrhiza Bunge. The antitumor activities of them were worth exploring, therefore, we examined their antitumor activities in A549, HCT116, HeLa, and Colo320 cancer cell lines by means of WST-1 assay. The results show that Tan IIA exerted far higher (IC50 from 1.0 ± 0.0 to 166.3 ± 24.0 µg/mL) antiproliferative activities than SA (IC50 from 2236.3 ± 484.1 to >10 000.0 µg/mL). Of the 4 cell lines, A549 cells were the most sensitive to Tan IIA; thus, we used Western blotting to explore the cytotoxic mechanisms of Tan IIA in A549 cells and found that they rely on simultaneous induction of apoptosis and necroptosis in the cells. Apoptosis was hallmarked by the induction of cleaved caspase-3 by Tan IIA and necroptosis by the necroptotic marker proteins cyclophilin A and high mobility group box 1 (HMGB1), as well as increased lactate dehydrogenase (LDH) activities. The necroptotic effect was confirmed by the necroptosis inhibitor necrostatin-1 (Nec-1), which eliminated these effects and restored cell survival rates. The levels of cyclophilin A decreased in response to the pan-caspase inhibitor z-VAD-fmk, and those of cleaved caspase-3 decreased in response to Nec-1. Conclusively, Tan IIA has the potential to prevent lung cancer and the mechanism seems to be apoptosis and necroptosis, of which the relationship is mutually interdependent. This is the first report of Tan IIA eliciting necroptosis in A549 cells. Tan IIA may be used for necroptosis-based cancer therapy, especially to overcome apoptosis resistance.

Effective Drug Concentration and Selectivity Depends on Fraction of Primitive Cells

Poor efficiency of chemotherapeutics in the eradication of Cancer Stem Cells (CSCs) has been driving the search for more active and specific compounds. In this work, we show how cell density-dependent stage culture profiles can be used in drug development workflows to achieve more robust drug activity (IC₅₀ and EC₅₀) results. Using flow cytometry and light microscopy, we characterized the cytological stage profiles of the HL-60-, A-549-, and HEK-293-derived sublines with a focus on their primitive cell content. We then used a range of cytotoxic substances—C-123, bortezomib, idarubicin, C-1305, doxorubicin, DMSO, and ethanol—to highlight typical density-related issues accompanying drug activity determination. We also showed that drug EC₅₀ and selectivity indices normalized to primitive cell content are more accurate activity measurements. We tested our approach by calculating the corrected selectivity index of a novel chemotherapeutic candidate, C-123. Overall, our study highlights the usefulness of accounting for primitive cell fractions in the assessment of drug efficiency.

The Effects of Lentivirus-Mediated Gene Silencing of RARβ on the Stemness Capability of Non-Small Cell Lung Cancer

Retinoic acid receptor beta is a nuclear receptor protein that binds to retinoic acid (RA) to mediate cellular signalling in embryogenic morphogenesis, cell growth, and differentiation. However, the function of RARβ in cancer stem cells (CSCs) has yet to be determined. This study aimed to understand the role of RARβ in regulating cell growth and differentiation of lung cancer stem cells. Based on the clonogenic assay, spheroid assay, mRNA levels of stem cell transcription factors, and cell cycle being arrested at the G0/G1 phase, the suppression of RARβ resulted in significant inhibition of A549 parental cell growth. This finding was contradictory to the results seen in CSCs, where RARβ inhibition enhanced the cell growth of putative and non-putative CSCs. These results suggest that RARβ suppression may act as an essential regulator in A549 parental cells, but not in the CSCs population. The findings in this study demonstrated that the loss of RARβ promotes tumorigenicity in CSCs. Microarray analysis revealed that various cancer pathways were significantly activated following the suppression of RARβ. The changes seen might compensate for the loss of RARβ function, CSCs population's aggressiveness, which led to the CSCs population's aggressiveness. Thus, understanding the role of RARβ in regulating the stemness of CSCs may lead to targeted therapy for lung CSCs.

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.

Cancer Stem Cell-Inducing Media Activates Senescence Reprogramming in Fibroblasts

Cellular senescence is a tumor-suppressive mechanism blocking cell proliferation in response to stress. However, recent evidence suggests that senescent tumor cells can re-enter the cell cycle to become cancer stem cells, leading to relapse after cancer chemotherapy treatment. Understanding how the senescence reprogramming process is a precursor to cancer stem cell formation is of great medical importance. To study the interplay between senescence, stemness, and cancer, we applied a stem cell medium (SCM) to human embryonic fibroblasts (MRC5 and WI-38) and cancer cell lines (A549 and 293T). MRC5 and WI-38 cells treated with SCM showed symptoms of oxidative stress and became senescent. Transcriptome analysis over a time course of SCM-induced senescence, revealed a developmental process overlapping with the upregulation of genes for growth arrest and the senescence-associated secretory phenotype (SASP). We demonstrate that histone demethylases jumonji domain-containing protein D3 (Jmjd3) and ubiquitously transcribed tetratricopeptide repeat, X chromosome (Utx), which operate by remodeling chromatin structure, are implicated in the senescence reprogramming process to block stem cell formation in fibroblasts. In contrast, A549 and 293T cells cultured in SCM were converted to cancer stem cells that displayed the phenotype of senescence uncoupled from growth arrest. The direct overexpression of DNA methyltransferases (Dnmt1 and Dnmt3A), ten-eleven translocation methylcytosine dioxygenases (Tet1 and Tet3), Jmjd3, and Utx proteins could activate senescence-associated beta-galactosidase (SA-β-gal) activity in 293T cells, suggesting that epigenetic alteration and chromatin remodeling factors trigger the senescence response. Overall, our study suggests that chromatin machinery controlling senescence reprogramming is significant in cancer stem cell formation.

Effect of SIRT1 activators and inhibitors on CD44+/CD133+‑enriched non‑small cell lung cancer cells

Lung cancer is one of the most commonly diagnosed cancers and it is associated with high rates of morbidity and mortality. Metastasis and relapse of the tumor depend on the survival and proliferation of lung cancer stem cells (LCSCs). The ability to identify CSCs may prevent recurrence and lead to more effective treatments. Sirtuins are a group of deacetylases that include seven variants (SIRT1‑7), with sirtuin 1 (SIRT1) being the most intensively investigated. Evidence suggests that SIRT1 is both a tumor‑suppressor gene and an oncogene. SIRT1 can deacetylate the tumor‑suppressor protein p53 to decrease its activity. SIRT1 activators increase the deacetylation of p53, whereas SIRT1 inhibitors can stimulate p53 by inhibiting deacetylation. In the present study, CD44+ and CD133+‑enriched A549 (non‑small cell lung cancer) cells collected using the CD44 and CD133 CSC surface markers by fluorescence‑activated cell sorting method were treated with SIRT1 inhibitors (tenovin‑6 and sirtinol) and SIRT1 activators (resveratrol and SRT1720), and their effects on apoptosis, as well as the mRNA and protein expression of SIRT1 and p53 were investigated. Of these agents, it was found that resveratrol increased p53 expression by 4.1‑fold, decreased SIRT1 expression by 0.2‑fold, and it was the most potent inducer of apoptosis.

Downregulation of microRNA-196a inhibits stem cell self-renewal ability and stemness in non-small-cell lung cancer through upregulating GPX3 expression

Studies have reported a high expression profile of microRNA-196a (miR-196a) in many cancers, which potently plays important roles in carcinogenesis. However, the involvement of miR-196a in affecting non-small cell lung cancer (NSCLC) carcinogenesis still remains uncertain. NSCLC-related differentially expressed genes were retrieved for this study according to the microarray-based analysis, which demonstrated that miR-196a may be involved in NSCLC progression via regulation of the Jun N-terminal kinase (JNK) pathway by targeting glutathione peroxidase 3 (GPX3). Hence, this study aimed to explore the relationship among miR-196a, GPX3, and the JNK pathway and to investigate its functional regulations in NSCLC. Initially, highly-expressed miR-196a and lowly-expressed GPX3 were determined in NSCLC tissues and cells. Next, the NSCLC cells were manipulated with a series of mimic, inhibitor or shRNA to investigate the impact of miR-196a and GPX3 on CSC viability, proliferation, self-renewal ability and stemness. The in vivo effect of miR-196a was measured in nude mice xenografted with NSCLC cells. The results demonstrated that downregulation of miR-196a and restoration of GPX3 inhibited CSC viability, proliferation, self-renewal ability, stemness and tumorigenicity. Meanwhile, the underlying relationship among miR-196a, GPX3 and JNK pathway was explored by treatment with the JNK pathway inhibitor (SP600125), or sh-GPX3. Downregulated miR-196a and upregulated GPX3 could elevate the GPX3 protein expression and reduce the extent of JNK and c-Jun phosphorylation. Taken together, miR-196a promotes the development of NSCLC via activation of the JNK pathway through down-regulation of GPX3 and serve as a potential therapeutic target in NSCLC.

Therapeutic effects of lenvatinib in combination with rAd-p53 for the treatment of non-small cell lung cancer

The aim of the present study was to analyze the effects of the combined treatment of lenvatinib and adenoviral delivered p53 gene (rAd-p53) on non-small cell lung cancer (NSCLC) cells and a total of 120 patients with NSCLC. The therapeutic effects of gene therapy of rAd-p53 and target therapy of Lenvatinib were investigated in NSCLC patients. The anti-tumor effects of combined treatment of llenvatinib and rAd-p53 was administered orally once-daily in NSCLC patients. Patients with NSCLC were divided into three groups and received lenvatinib (n=40), rAd-p53 (n=40) or combined treatment of lenvatinib and rAd-p53 (n=40) for a total of 30 days. Results showed that p53 was down-regulated and VEGFR, FGFR and PDGFR-β were up-regulated in NSCLC tissues compared to adjacent normal tissues. Combined treatment of Lenvatinib and rAd-p53 markedly inhibited NSCLC cell growth, migration and invasion, and promoted apoptosis compared to either lenvatinib or rAd-p53 alone. The most common treatment-related adverse events included hypertension, diarrhea, nausea, proteinuria and body weight loss. Outcomes indicated that combined treatment of lenvatinib and rAd-p53 markedly inhibited tumor growth compared to lenvatinib and rAd-p53 alone for NSCLC patients. Combined treatment of lenvatinib and rAd-p53 did not exhibit drug accumulation after 30-day treatment. In conclusion, these outcomes indicate that combined treatment of lenvatinib and rAd-p53 may be an efficient therapeutic schedule for the treatment of NSCLC patients.

Neuralized1a regulates asymmetric division in mouse Lewis lung carcinoma cells

Asymmetric division (ASD), the unique characteristic of normal stem cells, is regarded as a stemness marker when applied to the study of cancer stem cells (CSCs). However, the role of ASD in the self-renewal of CSCs and its regulation remain largely unknown. Here, we first established a mouse Lewis lung carcinoma CSC cell line that could undergo asymmetric division (LLC-ASD cells) derived from the parental mouse Lewis lung carcinoma cancer cells (LLC-Parental cells). In vitro assessment of stemness by RT-qPCR and western blot analysis of stem cell markers, clonogenic assay (p < 0.001), single cell spheroid formation assay (p < 0.05) and 96-well-plate single-cell cloning assay (p < 0.01) indicated that the LLC-ASD cells exhibited stronger stemness features in comparison to the LLC-Parental cells. In vivo, tumorigenicity of LLC-ASD cells, transplanted subcutaneously to the nude mice, was increased compared to that of LLC-parental cells (p < 0.05). Further, Neuralized1a, a regulator of ASD in normal stem cells, was highly expressed in the LLC-ASD cells. Silencing Neuralized1a expression in LLC-ASD cells by siRNA weakened the stemness features measured by the in vitro assays listed above (p < 0.05). The tumorigenic ability was also decreased in the nude mice upon Neuralized1a silencing (p < 0.05). Collectively, the present study suggests that Neuralized1a regulates the stemness of LLC-ASD cells which could be the new marker and therapeutic target of CSCs.

Inhibition of NF-κB Signaling Reduces the Stemness Characteristics of Lung Cancer Stem Cells

Cancer stem cells (CSCs) are a subpopulation of cancer cells that play a pivotal role in tumor development, invasion, metastasis, and recurrence. We and others have reported significant involvement of the NF-κB pathway in regulating CSCs of non-small cell lung cancer (NSCLC). In this study, we evaluated the effects of NF-κB inhibition on self-renewal, stemness, migration, and expression of genes involved in the epithelial to mesenchymal transition (EMT) and apoptosis resistance in lung CSCs. Different concentrations of the NF-κB inhibitor BMS-345541 (0.4, 4.0, and 10.0 µM), an inhibitor the NF-κB upstream kinase IKKβ, were used to treat both lung CSCs (CD166⁺CD44⁺, CD166⁺EpCAM⁺) and non-CSC NSCLC cells (CD166⁻CD44⁻, CD166⁻EpCAM⁻) in A549 and H2170 cell lines. We assessed the impact of BMS-345541 on the ability to form tumorspheres (self-renewal assay), expression of stemness genes (SOX2, OCT4, NANOG, SCA-1, and KLF4), migration, and expression of EMT and apoptosis-related genes. Inhibition of NF-κB by BMS-345541 effectively reduced the stemness, self-renewal, and migration capacity of lung CSCs. Moreover, expression of genes involved in the EMT (SNAI1 and TWIST) and apoptosis resistance (BCL-2, BAX, and BIRC5) was significantly reduced following the treatments, suggesting that NF-κB inhibition is sufficient to prevent the EMT and induce apoptosis in lung CSCs. Our findings suggest that NF-κB inhibition could reduce the capability of CSCs to maintain their population within the tumor mass, potentially decelerating cancer progression, relapse, and chemotherapy resistance.

Comparison of tumor biology of two distinct cell sub-populations in lung cancer stem cells

Characterization of the stem-like properties of cancer stem cells (CSCs) remain indirect and qualitative, especially the ability of CSCs to undergo asymmetric cell division for self renewal and differentiation, a unique property of cells of stem origin. It is partly due to the lack of stable cellular models of CSCs. In this study, we developed a new approach for CSC isolation and purification to derive a CSC-enriched cell line (LLC-SE). By conducting five consecutive rounds of single cell cloning using the LLC-SE cell line, we obtained two distinct sub-population of cells within the Lewis lung cancer CSCs that employed largely symmetric division for self-renewal (LLC-SD) or underwent asymmetric division for differentiation (LLC-ASD). LLC-SD and LLC-ASD cell lines could be stably passaged in culture and be distinguished by cell morphology, stem cell marker, spheroid formation and subcutaneous tumor initiation efficiency, as well as orthotopic lung tumor growth, progression and survival. The ability LLC-ASD cells to undergo asymmetric division was visualized and quantified by the asymmetric segregation of labeled BrdU and NUMB to one of the two daughter cells in anaphase cell division. The more stem-like LLC-SD cells exhibited higher capacity for tumorigenesis and progression and shorter survival. As few as 10 LLC-SD could initiate subcutaneous tumor growth when transplanted to the athymic mice. Collectively, these observations suggest that the SD-type of cells appear to be on the top of the hierarchical order of the CSCs. Furthermore, they have lead to generated cellular models of CSC self-renewal for future mechanistic investigations.

Targeting Lung Cancer Stem Cells: Research and Clinical Impacts

Lung cancer is the most common cancer worldwide, accounting for 1.8 million new cases and 1.6 million deaths in 2012. Non-small cell lung cancer (NSCLC), which is one of two types of lung cancer, accounts for 85–90% of all lung cancers. Despite advances in therapy, lung cancer still remains a leading cause of death. Cancer relapse and dissemination after treatment indicates the existence of a niche of cancer cells that are not fully eradicated by current therapies. These chemoresistant populations of cancer cells are called cancer stem cells (CSCs) because they possess the self-renewal and differentiation capabilities similar to those of normal stem cells. Targeting the niche of CSCs in combination with chemotherapy might provide a promising strategy to eradicate these cells. Thus, understanding the characteristics of CSCs has become a focus of studies of NSCLC therapies.