CD44 and CD24 cannot act as cancer stem cell markers in human lung adenocarcinoma cell line A549

Satureja bachtiarica Induces Cancer Cell Death in Breast and Glioblastoma Cancer in 2D/3D Models and Suppresses Breast Cancer Stem Cells

Overcoming drug resistance and specifically targeting cancer stem cells (CSCs) are critical challenges in improving cancer therapy. Nowadays, the use of novel and native medicinal plants can provide new sources for further investigations for this purpose. The aim of this study was to assess the potential of S. bachtiarica, an endemic plant with diverse medicinal applications, in suppressing and targeting cancer and cancer stem cells in glioblastoma and breast cancer. The effect of S. bachtiarica on viability, migration, invasion, and clonogenic potential of MDAMB-231 and U87-MG cells was assessed in both two- and three-dimensional cell culture models. Additionally, we evaluated its effects on the self-renewal capacity of mammospheres. The experimental outcomes indicated that S. bachtiarica decreased the viability and growth rate of cells and spheroids by inducing apoptosis and inhibited colony formation, migration, and invasion of cells and spheroids. Additionally, colony and sphere-forming ability, as well as the expression of genes associated with EMT and stemness were reduced in mammospheres treated with S. bachtiarica. In conclusion, this study provided valuable insights into the anti-cancer effects of S. bachtiarica, particularly in relation to breast CSCs. Therefore, S. bachtiarica may be a potential adjuvant for the treatment of cancer.

Cellular Effects of Selected Unsymmetrical Bisacridines on the Multicellular Tumor Spheroids of HCT116 Colon and A549 Lung Cancer Cells in Comparison to Monolayer Cultures

Multicellular tumor spheroids are a good tool for testing new anticancer drugs, including those that may target cancer stem cells (CSCs), which are responsible for cancer progression, metastasis, and recurrence. Therefore, we applied this model in our studies of highly active antitumor unsymmetrical bisacridines (UAs). We investigated the cellular response induced by UAs in 2D and 3D cultures of HCT116 colon and A549 lung cancer cells, with an additional focus on their impact on the CSC-like population. We showed that UAs affected the viability of the studied cells, as well as their spherogenic potential in the 2D and 3D cultures. Furthermore, we proved that the most promising UAs (C-2045 and C-2053) induced apoptosis in the HCT116 and A549 spheres to a similar, or even higher, extent than what was found in monolayer conditions. Next, we identified the population of the CSC-like cells in the 2D and 3D cultures of the studied cell lines by determining the levels of CD166, CD133, CD44, and EpCAM markers. We showed that the selected UAs affected the CSC-like population in both of the cell lines, and that A549 was affected more profoundly in 3D than in 2D cultures. Thus, the UAs exhibited high antitumor properties in both the 2D and 3D conditions, which makes them promising candidates for future therapeutic applications.

Silibinin exhibits anti-tumor effects in a breast cancer stem cell model by targeting stemness and induction of differentiation and apoptosis

Introduction: Malignant breast cancer (BC) frequently contains a rare population of cells called cancer stem cells which underlie tumor relapse and metastasis, and targeting these cells may improve treatment options and outcomes for patients with BC. The aim of the present study was to determine the effect of silibinin on the self-renewal capacity, tumorgenicity, and metastatic potential of mammospheres. Methods: The effect of silibinin on viability and proliferation of MCF-7, MDA-MB-231 mammospheres, and MDA-MB-468 cell aggregation was determined after 72-120 hours of treatment. Colony and sphere formation ability, and the expression of stemness, differentiation, and epithelial-mesenchymal-transition (EMT)-associated genes were assessed by reverse transcription-quantitative polymerase chain reaction (qRT-PCR) in mammospheres treated with an IC₅₀ dose of silibinin. Additionally, the antitumor capacity of silibinin was assessed in vivo, in mice. Results: The results of the present study showed that silibinin decreased the viability of all mammospheres derived from MCF-7, MDA-MB-231, and MDA-MB-468 cell aggregation in a dose-dependent manner. Colony and sphere-forming ability, as well as the expression of genes associated with EMT were reduced in mammospheres treated with silibinin. Additionally, the expression of genes associated with stemness and metastasis was also decreased and the expression of genes associated with differentiation were increased. Intra-tumoral injection of 2 mg/kg silibinin decreased tumor volumes in mice by 2.8 fold. Conclusion: The present study demonstrated that silibinin may have exerted its anti-tumor effects in BC by targeting the BC stem cells, reducing the tumorgenicity and metastasis. Therefore, silibinin may be a potential adjuvant for treatment of BC.

Potential to Eradicate Cancer Stemness by Targeting Cell Surface GRP78

Cancer stemness is proposed to be the main cause of metastasis and tumor relapse after conventional therapy due to the main properties of cancer stem cells. These include unlimited self-renewal, the low percentage in a cell population, asymmetric/symmetric cell division, and the hypothetical different nature for absorbing external substances. As the mechanism of how cancer stemness is maintained remains unknown, further investigation into the basic features of cancer stemness is required. Many articles demonstrated that glucose-regulated protein 78 (GRP78) plays a key role in cancer stemness, suggesting that this molecule is feasible for targeting cancer stem cells. This review summarizes the history of finding cancer stem cells, as well as the functions of GRP78 in cancer stemness, for discussing the possibility of targeting GRP78 to eradicate cancer stemness.

Single-cell RNA-seq reveals the genesis and heterogeneity of tumor microenvironment in pancreatic undifferentiated carcinoma with osteoclast-like giant-cells

BACKGROUND

Undifferentiated carcinoma with osteoclast-like giant cells (OGCs) of pancreas (UCOGCP) is a rare subtype of pancreatic ductal adenocarcinoma (PDAC), which had poorly described histopathological and clinical features.

METHODS

In this study, single-cell RNA sequencing (scRNA-seq) was used to profile the distinct tumor microenvironment of UCOGCP using samples obtained from one UCOGCP patient and three PDAC patients. Bioinformatic analysis was carried out and immunohistochemical (IHC) staining was used to support the findings of bioinformatic analysis. After quality control of the raw data, a total of 18,376 cells were obtained from these four samples for subsequent analysis. These cells were divided into ten main cell types following the Seurat analysis pipeline. Among them, the UCOGCP sample displayed distinct distribution patterns from the rest samples in the epithelial cell, myeloid cell, fibroblast, and endothelial cell clusters. Further analysis supported that the OGCs were generated from stem-cell-like mesenchymal epithelial cells (SMECs).

RESULTS

Functional analysis showed that the OGCs cluster was enriched in antigen presentation, immune response, and stem cell differentiation. Gene markers such as LOX, SPERINE1, CD44, and TGFBI were highly expressed in this SMECs cluster which signified poor prognosis. Interestingly, in myeloid cell, fibroblasts, and endothelial cell clusters, UCOGCP contained higher percentage of these cells and unique subclusters, compared with the rest of PDAC samples.

CONCLUSIONS

Analysis of cell communication depicted that CD74 plays important roles in the formation of the microenvironment of UCOGCP. Our findings illustrated the genesis and function of OGCs, and the tumor microenvironment (TME) of UCOGCP, providing insights for prognosis and treatment strategy for this rare type of pancreatic cancer.

Anti-cancer peptide-based therapeutic strategies in solid tumors

Background

Nowadays, conventional medical treatments such as surgery, radiotherapy, and chemotherapy cannot cure all types of cancer. A promising approach to treat solid tumors is the use of tumor-targeting peptides to deliver drugs or active agents selectively.

Result

Introducing beneficial therapeutic approaches, such as therapeutic peptides and their varied methods of action against tumor cells, can aid researchers in the discovery of novel peptides for cancer treatment. The biomedical applications of therapeutic peptides are highly interesting. These peptides, owing to their high selectivity, specificity, small dimensions, high biocompatibility, and easy modification, provide good opportunities for targeted drug delivery. In recent years, peptides have shown considerable promise as therapeutics or targeting ligands in cancer research and nanotechnology.

Conclusion

 This study reviews a variety of therapeutic peptides and targeting ligands in cancer therapy. Initially, three types of tumor-homing and cell-penetrating peptides (CPPs) are described, and then their applications in breast, glioma, colorectal, and melanoma cancer research are discussed.

A pilot study on biological characteristics of human CD24(+) stem cells from the apical papilla

Background/purpose

CD24 is a specific cell surface marker for undifferentiated dental stem cells from apical papilla (SCAPs) seen only during root development, before the tooth emerges through gum. But the comprehensive role of CD24 in the SCAPs is unclear. This study aims to clarify the exact roles of CD24 in SCAPs.

Materials and methods

SCAPs were divided into CD24 (+)-SCAPs (high percentage CD24) and CD24 (-)-SCAPs (low percentage CD24) via flow cytometry. The proliferation, migration and osteogenic/adipogenic differentiation of the two groups were detected, RT-PCR was performed to detect the expression of osteogenic/adipogenic related genes and thegene expression were analyzed.

Results

The proliferative and migratory ability of CD24 (-)-SCAPs were significantly stronger than that of CD24 (+)-SCAPs. Although, the mineralization process and the osteogenic genes expression were not significantly difference in the two groups. Both CD24 (+)-SCAPs and CD24 (-)-SCAPs differentiated into adipocytes. The adipogenic differentiation in CD24 (+)-SCAPs was better than that in CD24 (-)-SCAPs, after 3 weeks of adipogenic induction. However, the expression of adipogenic related gene, PPAR γ2 mRNA in CD24 (+)-SCAPs was lower than that in CD24 (-)-SCAPs after 1 week of adipogenic induction. But the trend changed for the opposite after 3 weeks.

Conclusion

The study proposes that CD24 has a regulatory effect on the adipogenic differentiation of SCAPs, and this may be attained by targeting the PPAR γ2 mRNA. Concurrently, it was found that CD24 plays an inhibitory role in the proliferation and migration of SCAPs, which may minimize the manifestation of diseases caused by an abnormal cell growth.

Cigarette smoke upregulates Notch-1 signaling pathway and promotes lung adenocarcinoma progression

Notch-1 pathway plays an important role in lung carcinoma, stem cell regulation, cellular communication, growth and differentiation. Cigarette smoke is involved in the regulation of Notch signaling. However, current data regarding the impact of cigarette smoke on the Notch pathway in lung cancer progression are limited. The present study aimed to explore whether cigarette smoke exposure altered Notch-1 pathway in ex-vivo (surgical samples of lung parenchyma from non-smoker and smoker patients with lung adenocarcinoma) and in vitro (adenocarcinoma A549 cell line) approaches. The expression of Notch-1, Jagged-1 and CD133 in surgical samples was evaluated by immunohistochemistry. A549 were exposed to cigarette smoke extracts (2.5% and 5% CSE for 6, 24 and 48 h) and the expression of Notch-1, Jagged-1 and Hes-1 was evaluated by Real-Time PCR and Western Blot (nuclear fractions). Expression and localization of Notch-1, Hes-1, CD133 and ABCG2 were assessed by immunofluorescence. The expression of survivin and Ki-67 was assessed by flow cytometry following CSE exposure and inhibition of Notch-1 signaling. Smokers lung parenchyma exhibited higher expression of Notch-1. CSE exposure increased Notch-1 and Hes-1 gene and nuclear protein expression in A549. Immunofluorescence confirmed higher expression of nuclear Hes-1 in CSE-stimulated A549 cells. CSE increased both survivin and Ki-67 expression and this effect was reverted by inhibition of the Notch-1 pathway. In conclusion, these data show that cigarette smoke may promote adenocarcinoma progression by activating the Notch-1 pathway thus supporting its role as hallmark of lung cancer progression and as a new target for lung cancer treatment.

CD24, A Review of its Role in Tumor Diagnosis, Progression and Therapy

CD24, is a mucin-like GPI-anchored molecules. By immunohistochemistry, it is widely detected in many solid tumors, such as breast cancers, genital system cancers, digestive system cancers, neural system cancers and so on. The functional roles of CD24 are either fulfilled by combination with ligands or participate in signal transduction, which mediate the initiation and progression of neoplasms. However, the character of CD24 remains to be intriguing because there are still opposite voices about the impact of CD24 on tumors. In preclinical studies, CD24 target therapies, including monoclonal antibodies, target silencing by RNA interference and immunotherapy, have shown us brighten futures on the anti-tumor application. Nevertheless, evidences based on clinical studies are urgently needed. Here, with expectancy to spark new ideas, we summarize the relevant studies about CD24 from a tumor perspective.

Discovering and Characterizing of Survivin Dominant Negative Mutants With Stronger Pro-apoptotic Activity on Cancer Cells and CSCs

Survivin as a member of the inhibitor of apoptosis proteins (IAPs) family is undetectable in normal cells, but highly expressed in cancer cells and cancer stem cells (CSCs) which makes it an attractive target in cancer therapy. Survivin dominant negative mutants have been reported as competitive inhibitors of endogenous survivin protein in cancer cells. However, there is a lack of systematic comparative studies on which mutants have stronger effect on promoting apoptosis in cancer cells, which will hinder the development of novel anti-cancer drugs. Here, based on the previous study of survivin and its analysis of the relationship between structure and function, we designed and constructed a series of different amino acid mutants from survivin (TmSm34, TmSm48, TmSm84, TmSm34/48, TmSm34/84, and TmSm34/48/84) fused cell-permeable peptide TATm at the N-terminus, and a dominant negative mutant TmSm34/84 with stronger pro-apoptotic activity was selected and evaluated systematically in vitro. The double-site mutant of survivin (TmSm34/84) showed more robust pro-apoptotic activity against A549 cells than others, and could reverse the resistance of A549 CSCs to adriamycin (ADM) (reversal index up to 7.01) by decreasing the expression levels of survivin, P-gp, and Bcl-2 while increasing cleaved caspase-3 in CSCs. This study indicated the selected survivin dominant negative mutant TmSm34/84 is promising to be an excellent candidate for recombinant anti-cancer protein by promoting apoptosis of cancer cells and their stem cells and sensitizing chemotherapeutic drugs.

DCLK1, a promising colorectal cancer stem cell marker, regulates tumor progression and invasion through miR-137 and miR-15a dependent manner

Cancer stem cells (CSCs) are thought to be a major player in tumor initiation, progression, and metastasis. Targeting CSCs for elimination presents a promising therapeutic strategy; however, this approach will require a stronger understanding of CSC biology and identification of CSC-specific markers. The present study was conducted to examine the correlation between DCLK1 and miR-137 and miR-15a levels in colorectal cancer. A total of 222 samples, including 181 colorectal cancer specimens, 24 adenomatosis, and 17 non-adenomatosis colonic polyps, were stained for DCLK1 expression using immunohistochemistry. Also, expression of miR-137 and miR-15a was assessed in colorectal cancer with high and low DCLK1 expression levels. Most colorectal cancer specimens (76%) showed strong expression of DCLK1, whereas only 21% of adenomatous and none of non-adenomatous colonic polyps showed strong DCLK1 expression. A significant difference in DCLK1 expression was found between colorectal cancer, adenomatous, and non-adenomatous colonic polyps (P < 0.001). Higher expression of DCLK1 was more frequently detected in colorectal cases with larger tumor size (P = 0.03), poor differentiation (P = 0.03), and lymph node involvement (P = 0.04). Comparison of miR-137 and miR-15a in colorectal cancer cases revealed a significant inverse correlation with DCLK1 expression (P = 0.03 and P = 0.04, respectively). DCLK1 may act as a candidate marker for colorectal cancer stem cells. The critical role of DCLK1 in colorectal cancer suggests that it may represent an early diagnostic marker and therapeutic target; however, further investigation is warranted.

Lung tumorspheres reveal cancer stem cell-like properties and a score with prognostic impact in resected non-small-cell lung cancer

The high resistance against current therapies found in non-small-cell lung cancer (NSCLC) has been associated to cancer stem-like cells (CSCs), a population for which the identification of targets and biomarkers is still under development. In this study, primary cultures from early-stage NSCLC patients were established, using sphere-forming assays for CSC enrichment and adherent conditions for the control counterparts. Patient-derived tumorspheres showed self-renewal and unlimited exponential growth potentials, resistance against chemotherapeutic agents, invasion and differentiation capacities in vitro, and superior tumorigenic potential in vivo. Using quantitative PCR, gene expression profiles were analyzed and NANOG, NOTCH3, CD44, CDKN1A, SNAI1, and ITGA6 were selected to distinguish tumorspheres from adherent cells. Immunoblot and immunofluorescence analyses confirmed that proteins encoded by these genes were consistently increased in tumorspheres from adenocarcinoma patients and showed differential localization and expression patterns. The prognostic role of genes significantly overexpressed in tumorspheres was evaluated in a NSCLC cohort (N = 661) from The Cancer Genome Atlas. Based on a Cox regression analysis, CDKN1A, SNAI1, and ITGA6 were found to be associated with prognosis and used to calculate a gene expression score, named CSC score. Kaplan–Meier survival analysis showed that patients with high CSC score have shorter overall survival (OS) in the entire cohort [37.7 vs. 60.4 months (mo), p = 0.001] and the adenocarcinoma subcohort [36.6 vs. 53.5 mo, p = 0.003], but not in the squamous cell carcinoma one. Multivariate analysis indicated that this gene expression score is an independent biomarker of prognosis for OS in both the entire cohort [hazard ratio (HR): 1.498; 95% confidence interval (CI), 1.167–1.922; p = 0.001] and the adenocarcinoma subcohort [HR: 1.869; 95% CI, 1.275–2.738; p = 0.001]. This score was also analyzed in an independent cohort of 114 adenocarcinoma patients, confirming its prognostic value [42.90 vs. not reached (NR) mo, p = 0.020]. In conclusion, our findings provide relevant prognostic information for lung adenocarcinoma patients and the basis for developing novel therapies. Further studies are required to identify suitable markers and targets for lung squamous cell carcinoma patients.

Basic fibroblast growth factor signalling regulates cancer stem cells in lung cancer A549 cells

OBJECTIVES

The basic fibroblast growth factor (bFGF)/fibroblast growth factor receptor (FGFR) signal transductional pathway plays an important role not only in tumour, but also in tumour stem cells. Thus, this study was designed to investigate the effects of bFGF signalling on cancer stem cells of lung cancer.

METHODS

We blocked bFGF/FGFR signalling in cisplatin (DDP) selected A549 by knocking down bFGF via RNA interference, and subsequently, the stem cell marker of OCT-4 was determined, and cell proliferation, clone formation, invasiveness, apoptosis and drug resistance abilities of DDP selected A549 cells were investigated.

KEY FINDINGS

The expressions of bFGF and OCT-4 in DDP selected A549 were higher than that of A549 cells. The findings suggested blocking of bFGF/FGFR signalling resulted in downregulation of bFGF, reduction in cell proliferation, clone formation, invasion and drug resistance abilities, and increase in cell apoptosis. Furthermore, our results also revealed OCT-4 was reduced after bFGF signalling blocking.

CONCLUSIONS

In conclusion, our study suggested that bFGF/FGFR signalling plays an important role in maintaining lung cancer stem cell characteristics and regulating expression of cancer stem cell marker of OCT-4.

Actinomycin D inhibits the expression of the cystine/glutamate transporter xCT via attenuation of CD133 synthesis in CD133+ HCC

Liver cancer is one of the most frequently occurring types of cancer with high mortality rate. Hepatocellular carcinoma (HCC) frequently metastasizes to lung, portal vein, and portal lymph nodes and most HCCs show strong resistance to conventional anticancer drugs. Cancer stem cells (CSCs) are considered to be responsible for resistance to therapies. Hence, recent advancements in the use of liver cancer stem cells (LCSCs) are rapidly gaining recognition as an efficient and organized means for developing antitumor agents. We aimed to use a non-target-based high-throughput screening (HTS) approach to specifically target α-fetoprotein (AFP)⁺/cluster of differentiation (CD)133⁺ HCC present in mixed populations of HCC cells and hepatocytes. Herein, we identified actinomycin D (ActD) as a potential antitumor agent that significantly inhibits activity of LCSCs without affecting the co-cultured hepatocytes. To determine the mechanism of ActD-induced tumor-specificity in LCSC, we applied various cell-based assay models in vitro. In fact, ActD significantly increased reactive oxygen species (ROS) accumulation and DNA damage in Huh7 HCC cells, but not in Fa2N-4 cells, immortalized hepatocytes. Treatment of spheroid-forming LCSCs with ActD effectively decreased spheroid formation and the CD133⁺ HCC cell population. Importantly, these ActD-mediated effects are a result of inhibition of cystine/glutamate transporter xCT expression, via attenuation of CD133 synthesis. These results indicate that ActD suppresses stemness and malignant properties in HCC cells through destabilization of xCT, by inhibition of CD133 expression in LCSCs. The effects of ActD on LCSCs provide novel therapeutic strategies for targeting cancer stem-like cells in liver cancer.

Lung cancer stem cells and their aggressive progeny, controlled by EGFR/MIG6 inverse expression, dictate a novel NSCLC treatment approach

The lung cancer stem cell (LuCSC) model comprises an attractive framework to explore acquired drug resistance in non-small cell lung cancer (NSCLC) treatment. Here, we used NSCLC cell line model to translate cellular heterogeneity into tractable populations to understand the origin of lung cancers and drug resistance. The epithelial LuCSCs, presumably arising from alveolar bipotent stem/progenitor cells, were lineage naïve, noninvasive, and prone to creating aggressive progeny expressing AT2/AT1 markers. LuCSC-holoclones were able to initiate rimmed niches, where their specialization created pseudo-alveoli structures. Mechanistically, LuCSC transitioning from self-renewal (β-catenin and Nanog signaling) to malignant lineage differentiation is regulated by EGFR activation and the inverse inhibition of tumor suppressor MIG6. We further identified the functional roles of endogenous EGFR signaling in mediating progeny invasiveness and their ligands in LuCSC differentiation. Importantly, drug screening demonstrated that EGFR driving progeny were strongly responsive to TKIs; however, the LuCSCs were exclusively resistant but sensitive to AMPK agonist Metformin, antibiotic Salinomycin and to a lesser degree Carboplatin. Our data reveals previously an unknown mechanism of NSCLC resistance to EGFR-TKIs, which is associated with LuCSCs bearing a silenced EGFR and inversely expressed MIG6 suppressor gene. Taken altogether, successful NSCLC treatment requires development of a novel combination of drugs, efficiently targeting both LuCSCs and heterogeneous progeny.

Histone Modification Marks Strongly Regulate CDH1 Promoter in Prostospheres as A Model of Prostate Cancer Stem Like Cells

Objective

Cadherin-1 (CDH1) plays an important role in the metastasis, while expression of this protein is under control of epigenetic changes on its gene promoter. Therefore we evaluated both DNA methylation (DNAmet) and histone modification marks of CDH1 in prostate cancer stem like cells (PCSLCs).

Materials and Methods

In this experimental study, we isolated PCSLCs using cell surface marker and prostaspheroid formation, respectively. The cells isolated from both methods were characterized and then the levels of H3K4me2, H3K27me3, H3K9me2/3 and H3K9ac as well as DNAmet were assessed in CDH1 promoter of the isolated cells.

Results

The CD44⁺ CD49^hi cells were not validated as PCSLCs. However, prostaspheres overexpressed stemness related genes and had higher ability of invasion potential, associated with reduction in CDH1 expression. Epigenetic status analysis showed that CDH1 promoter was hypo-methylated. Histone modifications of H3K9ac and H3K4me3 were significantly reduced, in parallel with an increased level of H3K27me3.

Conclusion

Our results suggest that slight decrease of DNAmet of the CpG island in CDH1 promoter does not significantly contribute to the change of CDH1 expression. Therefore, histone modifications are responsible in repressing CDH1 in PCSLCs.

Nicotine inhibits CD24 expression in Lewis lung carcinoma cells by upregulation of RAS expression

Cluster of ddifferentiation 24 (CD24) is a widely used cancer stem cell (CSC) marker in numerous cancer types. However, a number of studies have shown that CD24 is a prognostic marker, but not a CSC marker for lung adenocarcinoma. In the present study, firstly, bioinformatic analyses were used to identify the CD24 mRNA levels in the subtypes of lung cancer. Secondly, CD24high and CD24low cells were isolated from the side population of Lewis lung carcinoma (LLC) cells using flow cytometry. Furthermore, the stemness of CD24high and CD24low cells were determined in vivo and in vitro. Lastly, the mechanism(s) of nicotine-inhibited CD24 expression in LLC cells were assessed. The main findings of this study are that: i) CD24 could be used as a prognostic marker for human lung adenocarcinoma; ii) the in vitro and in vivo experiments did not determine a significant influence of CD24 on the tumorgenicity of LLC cells; and iii) nicotine inhibited CD24 expression in LLC cells by upregulation of RAS. However, the detailed mechanism(s) of these results require further analysis.

Utilization of lung cancer cell lines for the study of lung cancer stem cells

Lung cancer is one of the most lethal types of cancer, and its poor prognosis is primarily due to drug resistance and cancer recurrence. As it is associated with a low five-year survival rate, lung cancer stem cells (LCSCs) have been the subject of numerous recent studies. For these studies of LCSCs, lung cancer cell lines are more commonly used than lung cancer tissues obtained from patients, as they are easier to acquire. The methods utilized for the identification of LCSCs from lung cancer cell lines include fluorescence activated cell sorting (FACS), magnetic activated cell sorting (MACS), sphere-forming assay and bacterial surface display library screening. As LCSCs have certain proteins expressed on the surface (CD133, CD44 and CD24) or in the cytoplasm (ALDH and ABCG2), which may act as specific markers, the most frequently used technique to identify and obtain LCSCs is FACS. The current lack of recognized biomarkers in LCSCs makes the identification of LCSCs problematic. Furthermore, the various proportions of LCSCs in specific cell lines, as revealed by numerous previous studies, may cause the LCSC model to be questioned with regard to whether the utilization of certain lung cancer cell lines is dependable for LCSC studies. The current review focuses on lung cancer cell lines that are used for the study of LCSCs and the methods available to identify LCSCs with various markers. The present study also aimed to determine the proportion of LCSCs present in specific cell lines reported by various studies, and to discuss the suitability of specific lung cancer cell lines for the study of LCSCs.

Hypericin affects cancer side populations via competitive inhibition of BCRP

OBJECTIVE

Cancer stem-like cells (CSLCs) are considered a root of tumorigenicity and resistance. However, their identification remains challenging. The use of the side population (SP) assay as a credible marker of CSLCs remains controversial. The SP assay relies on the elevated activity of ABC transporters that, in turn, can be modulated by hypericin (HYP), a photosensitizer and bioactive compound of St. John's Wort (Hypericum perforatum), a popular over-the-counter antidepressant. Here we aimed to comprehensively characterize the SP phenotype of cancer cells and to determine the impact of HYP on these cells.

METHODS

Flow cytometry and sorting-based assays were employed, including CD24-, CD44-, CD133-, and ALDH-positivity, clonogenicity, 3D-forming ability, ABC transporter expression and activity, and intracellular accumulation of HYP/Hoechst 33342. The tumorigenic ability of SP, nonSP, and HYP-treated cells was verified by xenotransplantation into immunodeficient mice.

RESULTS

The SP phenotype was associated with elevated expression of several investigated transporters and more intensive growth in non-adherent conditions but not with higher clonogenicity, tumorigenicity or ALDH-positivity. Despite stimulated BCRP level and MRP1 activity, HYP reversibly decreased the SP proportion, presumably via competitive inhibition of BCRP. HYP-selected SP cells acquired additional traits of resistance and extensively eliminated HYP.

CONCLUSIONS

Our results suggest that SP is not an unequivocal CSLC-marker. However, SP could play an important role in modulating HYP-treatment and serve as a negative predictive tool for HYP-based therapies. Moreover, the use of supplements containing HYP by cancer patients should be carefully considered, due to its proposed effect on drug efflux and complex impact on tumor cells, which have not yet been sufficiently characterized.

NRP1-positive lung cancer cells possess tumor-initiating properties

Tumor-initiating cells possess the capacity for self-renewal and to create heterogeneous cell lineages within a tumor. Therefore, the identification and isolation of cancer stem cells is an essential step in the analysis of their biology. The aim of the present study was to determine whether the cell surface protein neuropilin 1 (NRP1) can be used as a biomarker of stem-like cells in lung cancer tumors. For this purpose, NRP1-negative (NRP1-) and NRP1-positive (NRP1+) cell subpopulations from two lung cancer cell lines were sorted by flow cytometry. The NRP1+ cell subpopulation showed an increased expression of pluripotency markers OCT-4, Bmi-1 and NANOG, as well as higher cell migration, clonogenic and self-renewal capacities. NRP1 gene knockdown resulted not only in a decreased expression of stemness markers but also in a decrease in the clonogenic, cell migration and self-renewal potential. In addition, the NRP1+ cell subpopulation exhibited dysregulated expression of epithelial-to-mesenchymal transition-associated genes, including the ΔNp63 isoform protein, a previously reported characteristic of cancer stem cells. Notably, a genome-wide expression analysis of NRP1-knockdown cells revealed a potential new NRP1 pathway involving OLFML3 and genes associated with mitochondrial function. In conclusion, we demonstrated that NRP1+ lung cancer cells have tumor-initiating properties. NRP1 could be a useful biomarker for tumor-initiating cells in lung cancer tumors.

Lung cancer-associated brain metastasis: Molecular mechanisms and therapeutic options

BACKGROUND

Lung cancer is the most common cause of cancer-related mortality in humans. There are several reasons for this high rate of mortality, including metastasis to several organs, especially the brain. In fact, lung cancer is responsible for approximately 50% of all brain metastases, which are very difficult to manage. Understanding the cellular and molecular mechanisms underlying lung cancer-associated brain metastasis brings up novel therapeutic promises with the hope to ameliorate the severity of the disease. Here, we provide an overview of the molecular mechanisms underlying the pathogenesis of lung cancer dissemination and metastasis to the brain, as well as promising horizons for impeding lung cancer brain metastasis, including the role of cancer stem cells, the blood-brain barrier, interactions of lung cancer cells with the brain microenvironment and lung cancer-driven systemic processes, as well as the role of growth factor/receptor tyrosine kinases, cell adhesion molecules and non-coding RNAs. In addition, we provide an overview of current and novel therapeutic approaches, including radiotherapy, surgery and stereotactic radiosurgery, chemotherapy, as also targeted cancer stem cell and epithelial-mesenchymal transition (EMT)-based therapies, micro-RNA-based therapies and other small molecule or antibody-based therapies. We will also discuss the daunting potential of some combined therapies.

CONCLUSIONS

The identification of molecular mechanisms underlying lung cancer metastasis has opened up new avenues towards their eradication and provides interesting opportunities for future research aimed at the development of novel targeted therapies.

Cancer stem cell research in Iran: potentials and challenges

Treatment modalities can reduce cancer-related mortality; however, a majority of patients develop drug resistance, metastasis and relapse. It has been proposed that tumorigenic characteristics of tumors are related to a proportion of cancer cells, termed cancer stem cells (CSCs). Following the first evidence regarding the existence of CSC population in acute myeloid leukemia in 1997, publications in CSCs field showed an explosive trend in all cancer types around the world. First research paper in the field of CSCs in Iran was published in 2004 on prostate cancer. Subsequently, an annual number of publications in the field of CSCs displayed a rapidly growing trend. Therefore, in the current review, we have presented a comprehensive evaluation of the CSCs research in Iran.

Sustainability of CD24 expression, cell proliferation and migration, cisplatin-resistance, and caspase-3 expression during mesenchymal-epithelial transition induced by the removal of TGF-β1 in A549 lung cancer cells

Epithelial-mesenchymal transition (EMT) is a notable mechanism underlying cancer cell metastasis. Transforming growth factor β1 (TGF-β1) has been used to induce EMT; however, there is a lack of information regarding the role of TGF-β1 in mesenchymal-epithelial transition (MET). In the present study, EMT was induced in A549 lung cancer cells using TGF-β1 (TGF-β1-treated group) and MET was induced sequentially from the TGF-β1-treated group by removing the TGF-β1 (MET/return group). Untreated A549 lung cancer cells were used as a control. Characteristic features, including cancer stem cell markers [cluster of differentiation (CD)24, CD44 and CD133], cell proliferation and migration and diverse intracellular mechanisms, were observed in all groups. Using western blot analysis, the TGF-β1-treated group demonstrated increased vimentin and reduced E-cadherin expression, whereas the MET/return group demonstrated the opposite trend. Among cancer stem cell markers, the population of CD24^low cells was reduced in the TGF-β1-treated group. Furthermore, the G2/M phase cell cycle population, cisplatin-sensitivity, and cell proliferation and migration ability were increased in the TGF-β1-treated group. These features were unaltered in the MET/return group when compared to the TGF-β1-treated group. Immunoblotting revealed an increase in the levels of SMAD3, phosphorylated SMAD3, phosphorylated extracellular signal-regulated kinase and caspase-3, and a decrease in active caspase-3 levels in the TGF-β1-treated group. Increased caspase-3 and reduced active caspase-3 levels were observed in the MET/return group, similar to those in the TGF-β1-treated group; however, levels of other signalling proteins were unchanged compared with the control group. EMT induced by TGF-β1 was not preserved; however, stemness-associated properties (CD24 expression, caspase-3 expression, cell proliferation and cisplatin-resistance) were sustained following removal of TGF-β1.

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.

Lung cancer and β-glucans: review of potential therapeutic applications

The potential of natural substances with immunotherapeutic properties has long been studied. β-glucans, a cell wall component of certain bacteria and fungi, potentiate the immune system against microbes and toxic substances. Moreover, β-glucans are known to exhibit direct anticancer effects and can suppress cancer proliferation through immunomodulatory pathways. Mortality of lung cancer has been alarmingly increasingly worldwide; therefore, treatment of lung cancer is an urgent necessity. Numerous researchers are now dedicated to using β-glucans as a therapy for lung cancer. In the present attempt, we have reviewed the studies addressing therapeutic effects of β-glucans in primary and metastatic lung cancer published in the time period of 1991-2016.

Evidence for embryonic stem-like signature and epithelial-mesenchymal transition features in the spheroid cells derived from lung adenocarcinoma

Identification of the cellular and molecular aspects of lung cancer stem cells (LCSCs) that are suggested to be the main culprit of tumor initiation, maintenance, drug resistance, and relapse is a prerequisite for targeted therapy of lung cancer. In the current study, LCSCs subpopulation of A549 cells was enriched, and after characterization of the spheroid cells, complementary DNA (cDNA) microarray analysis was applied to identify differentially expressed genes (DEGs) between the spheroid and parental cells. Microarray results were validated using quantitative real-time reverse transcription-PCR (qRT-PCR), flow cytometry, and western blotting. Our results showed that spheroid cells had higher clonogenic potential, up-regulation of stemness gene Sox2, loss of CD44 expression, and gain of CD24 expression compared to parental cells. Among a total of 160 genes that were differentially expressed between the spheroid cells and the parental cells, 104 genes were up-regulated and 56 genes were down-regulated. Analysis of cDNA microarray revealed an embryonic stem cell-like signature and over-expression of epithelial-mesenchymal transition (EMT)-associated genes in the spheroid cells. cDNA microarray results were validated at the gene expression level using qRT-PCR, and further validation was performed at the protein level by flow cytometry and western blotting. The embryonic stem cell-like signature in the spheroid cells supports two important notions: maintenance of CSCs phenotype by dedifferentiating mechanisms activated through oncogenic pathways and the origination of CSCs from embryonic stem cells (ESCs). PI3/AKT3, as the most common up-regulated pathway, and other pathways related to aggressive tumor behavior and EMT process can confer to the spheroid cells' high potential for metastasis and distant seeding.

Enrichment and characterization of cancer stem cells from a human non-small cell lung cancer cell line

Tumor cells from the same origin comprise different cell populations. Among them, cancer stem cells (CSCs) have higher tumorigenicity. It is necessary to enrich CSCs to determine an effective way to suppress and eliminate them. In the present study, using the non-adhesive culture system, tumor spheres were successfully generated from human A549 non-small cell lung cancer (NSCLC) cell line within 2 weeks. Compared to A549 adherent cells, sphere cells had a higher self-renewal ability and increased resistance to cytotoxic drugs. Sphere cells were more invasive and expressed stem cell markers including octamer‑binding transcription factor 4 (Oct4) and sex-determining region Y-box 2 (Sox2) at high levels. CD133, a disputed marker of lung CSCs, was also upregulated. Tumor sphere cells showed higher tumorigenic ability in vivo, indicating that more CSCs were enriched in the sphere cells. More blood vessels were formed in the tumor generated by sphere cells suggesting the interaction between CSCs and blood vessel. A reliable model of enriching CSCs from the human A549 NSCLC cell line was established that was simple and cost-effective compared to other methods.

Hypoxia-induced cell stemness leads to drug resistance and poor prognosis in lung adenocarcinoma

BACKGROUND

Since cancer stem cells exhibit embryonic-like self-renewal characteristics and malignant behavior, including drug resistance and metastasis, they may be the origin of tumorigenesis and cancer recurrence. Cancer cell stemness is also highly relevant to cancer in hypoxic environments.

METHODS

In our study, we used cobalt dichloride (CoCl2) to create a hypoxic environment for lung adenocarcinoma A549 cells and the cisplatine-resistant cell line A549/DDP. The cancer stem-like CD166 positive population and the cells' stemness were detected by flowcytometry and quantitative real-time PCR after separation using magnetic antibodies. Drug resistance to cisplatine, docetaxel and pemetrexed was also measured. Finally, a tissue array was used to analyze the relationship between hypoxia-induced stemness and overall survival after radical surgery.

RESULTS

Data showed that chemical-induced hypoxia changed cell stemness by enhancing stem cell transcription factors and markers of chemotherapeutic drug resistance. The CD166-positive cancer stem cell-like population showed greater drug resistance than the CD166-negative cells. Tissue array studies also suggested a poorer prognosis for patients whose tissue expressed higher CD166 levels.

CONCLUSION

Our findings indicate that chemical hypoxia may augment cancer cell stemness and drug resistance in CD166-positive stem cells. Therefore, targeting the stem-like cell population, especially CD166-positive cells, may represent a novel therapeutic strategy to treat lung cancer.

Is CD133 expression a prognostic biomarker of non-small-cell lung cancer? A systematic review and meta-analysis

Background

The clinical and prognostic significance of CD133 in non-small-cell lung cancer (NSCLC) remains controversial. To clarify a precise determinant of the clinical significance of CD133, we conducted a systematic review and meta-analysis to evaluate the association of CD133 with prognosis and clinicopathological features of NSCLC patients.

Methods

The electronic and manual searches were performed through the database of Pubmed, Medline, Web of Science, Scopus, and Chinese CNKI (from January 1, 1982 to January 1, 2014) for titles and abstracts by using the following keywords: “CD133”, “ac133” or “Prominin-1”, and “lung cancer” to identify the studies eligible for our analysis. Meta-analysis was performed by using Review Manager 5.0 and the outcomes included the overall survival and various clinicopathological features.

Results

A total of 23 studies were finally included, and our results showed that CD133 level was significantly correlated with the overall survival (OR = 2.25, 95% CI: 1.24–4.07, P = 0.008) of NSCLC patients but not with the disease free survival (OR = 1.33, 95% CI = 0.77–2.30, P = 0.31). With respect to clinicopathological features, CD133 level was positively correlated with lymph node metastasis (OR = 1.99, 95%CI = 1.06–3.74, P = 0.03), but not correlated with the histological classification (OR = 1.00, 95%CI = 0.81–1.23, P = 0.99(ac), OR = 0.87, 95%CI = 0.61–1.24, P = 0.45(sc)), or differentiation (OR = 0.94, 95%CI 0.53–1.68, Z = 0.20, P = 0.84 random-effect) of NSCLC patients.

Conclusion

High level of CD133 expression trends to correlate with a worse prognosis and a higher rate of lymph node metastasis in NSCLC patients, revealing CD133 as a potential pathological prognostic marker for NSCLC patients.