The hitchhikers guide to cancer stem cell theory: Markers, pathways and therapy

An overview of current research on cancer stem cells: a bibliometric analysis

BACKGROUND

Cancer stem cells (CSCs) represent a potential mechanism contributing to tumorigenesis, metastasis, recurrence, and drug resistance. The objective of this study is to investigate the status quo and advancements in CSC research utilizing bibliometric analysis.

METHODS

Publications related to CSCs from 2010 to 2022 were collected from the Web of Science Core Collection database. Various analytical tools including CiteSpace, VOSviewer, Scimago Graphica, and GraphPad Prism were used to visualize aspects such as co-authorship, co-occurrence, and co-citation within CSC research to provide an objective depiction of the contemporary status and developmental trajectory of the CSC field.

RESULTS

A total of 22,116 publications were included from 1942 journals written by 95,992 authors. Notably, China emerged as the country with the highest number of publications, whereas the United States exerted the most significant influence within the field. MD Anderson Cancer Center emerged as the institution making the most comprehensive contributions. Wicha M.S. emerged as the most prolific and influential researcher. Among journals, Cancers emerged as a focal point for CSC research, consistently publishing a wealth of high-quality papers. Furthermore, it was observed that most journals tended to approach CSC research from molecular, biological, and immunological perspectives. The research into CSCs encompassed a broad array of topics, including isolation and enrichment techniques, biomarkers, biological characteristics, cancer therapy strategies, and underlying biological regulatory mechanisms. Notably, exploration of the tumor microenvironment and extracellular vesicles emerged as burgeoning research frontiers for CSCs.

CONCLUSION

The research on CSCs has garnered growing interest. A trend toward multidisciplinary homogeneity is emerging within the realm of CSCs. Further investigation could potentially center on the patients of extracellular vesicles and the tumor microenvironment in relation to CSCs.

Cancer Metastasis and Treatment Resistance: Mechanistic Insights and Therapeutic Targeting of Cancer Stem Cells and the Tumor Microenvironment

Cancer metastasis and treatment resistance are the main causes of treatment failure and cancer-related deaths. Their underlying mechanisms remain to be fully elucidated and have been attributed to the presence of cancer stem cells (CSCs)-a small population of highly tumorigenic cancer cells with pluripotency and self-renewal properties, at the apex of a cellular hierarchy. CSCs drive metastasis and treatment resistance and are sustained by a dynamic tumor microenvironment (TME). Numerous pathways mediate communication between CSCs and/or the surrounding TME. These include a paracrine renin-angiotensin system and its convergent signaling pathways, the immune system, and other signaling pathways including the Notch, Wnt/β-catenin, and Sonic Hedgehog pathways. Appreciation of the mechanisms underlying metastasis and treatment resistance, and the pathways that regulate CSCs and the TME, is essential for developing a durable treatment for cancer. Pre-clinical and clinical studies exploring single-point modulation of the pathways regulating CSCs and the surrounding TME, have yielded partial and sometimes negative results. This may be explained by the presence of uninhibited alternative signaling pathways. An effective treatment of cancer may require a multi-target strategy with multi-step inhibition of signaling pathways that regulate CSCs and the TME, in lieu of the long-standing pursuit of a 'silver-bullet' single-target approach.

The Improved Anticancer Activities of Piperine Nanoliposome Conjugated CD133 Monoclonal Antibody Against NTERA-2 Cancer Stem Cells

Black pepper ( Piper nigrum L.) is widely grown in the Chu-se district of Gia Lai province in Vietnam. The pepper, used as a spice, also serves as a traditional medicine in many countries. Black pepper contains many different substances; the most active of these is piperine, which exerts anti-oxidant, anti-inflammatory, and anti-cancer effects. However, piperine is a poorly absorbed alkaloid, and high concentrations may be toxic. Therefore, its medicinal uses remain limited. Here, we extracted piperine from black peppers collected at Chu Se, created piperine and anti-CD133 monoclonal antibodies (mAb^CD133) containing nanoliposomal complexes (PMCs), and evaluated their inhibitory effects on cancer stem cells (CSCs) in vitro. The physical properties of PMCs showed an approximated diamater of 170 nm, a PDI of 0.23, zeta potential of −9.38 mV, and an encapsulated efficiency of 73.33 ± 9.09%. The PMCs significantly inhibited NTERA-2 cell growth (IC50 = 435.3 ± 4.3 µM), but were not toxic to healthy cells (IC50 >500 µM). The PMCs remarkably affected the CSC surface marker expressed level of which the CD44+/CD133+ population was only 2.12% compared with 21.72% for blank nanoliposomes. The NTERA-2 antiproliferative activities of PMCs might be associated with their G2 cell cycle phase arresting and caspase-3 inducible activities (up to 1.51 times) ( P < 0.05). The nanoliposomal complex also significantly inhibited the proliferation of NTERA-2 cells in three dimensional tumorspheroids with an IC50 = 245.82 ± 11.44 µM and reduced the size by up to 41.50 ± 4.31% ( P < 0.05). Thus, the PMCs proved their enhanced potential biomedical and pharmacological applications in targeted cancer therapies.

Phenotypic Heterogeneity in Tumor Progression, and Its Possible Role in the Onset of Cancer

Heterogeneity among isogenic cells/individuals has been known for at least 150 years. Even Mendel, working on pea plants, realized that not all tall plants were identical. However, Mendel was more interested in the discontinuous variation between genetically distinct individuals. The concept of environment dictating distinct phenotypes among isogenic individuals has since been shown to impact the evolution of populations in numerous examples at different scales of life. In this review, we discuss how phenotypic heterogeneity and its evolutionary implications exist at all levels of life, from viruses to mammals. In particular, we discuss how a particular disease condition (cancer) is impacted by heterogeneity among isogenic cells, and propose a potential role that phenotypic heterogeneity might play toward the onset of the disease.

Ferroptosis: An emerging approach for targeting cancer stem cells and drug resistance

Resistance to chemotherapeutic agents remains a major challenge in the fierce battle against cancer. Cancer stem cells (CSCs) are a small population of cells in tumors that possesses the ability to self-renew, initiate tumors, and cause resistance to conventional anticancer agents. Targeting this population of cells was proven as a promising approach to eliminate cancer recurrence and improve the clinical outcome. CSCs are less susceptible to death by classical anticancer agents inducing apoptosis. CSCs can be eradicated by ferroptosis, which is a non-apoptotic-regulated mechanism of cell death. The induction of ferroptosis is an attractive strategy to eliminate tumors due to its ability to selectively target aggressive CSCs. The current review critically explored the crosstalk and regulatory pathways controlling ferroptosis, which can selectively induce CSCs death. In addition, successful chemotherapeutic agents that achieve better therapeutic outcomes through the induction of ferroptosis in CSCs were discussed to highlight their promising clinical impact.

Doxorubicin and α-Mangostin oppositely affect luminal breast cancer cell stemness evaluated by a new retinaldehyde-dependent ALDH assay in MCF-7 tumor spheroids

According to cancer stem cell theory, only a limited number of self-renewing and cloning cells are responsible for tumor relapse after a period of remittance. The aim of the present study was to investigate the effects of Doxorubicin and α-Mangostin, two antiproliferative drugs, on both tumor bulk and stem cells in multicellular tumor spheroids originated from the luminal MCF-7 breast cancer cell line. A new and original fluorimetric assay was used to selectively measure the activity of the retinaldehyde-dependent isoenzymes of aldehyde dehydrogenase (RALDH), which are markers of a subpopulation of breast cancer stem cells. The administration of 5 μg/ml (12.2 μM) α-Mangostin for 48 h provoked: i) a marked disaggregation of the spheroids, leading to a doubling of their volume (p < 0.01), ii) a 40 % decrease in cell viability (p < 0.01), evaluated by the acid phosphatase assay, and iii) a reduction by more than 90 % of RALDH activity. By contrast, Doxorubicin given for 48 h in the range of 0.1-40 μM did not significantly reduce cell viability and caused only a modest modification of the spheroid morphology. Moreover, 40 μM Doxorubicin increased RALDH activity 2.5-fold compared to the untreated sample. When the two drugs were administered together using 5 μg/ml α-Mangostin, the IC₅₀ of Doxorubicin referred to cell viability decreased six-fold and the RALDH activity was further reduced. In conclusion, the combined administration of Doxorubicin and α-Mangostin provoked a significant cytotoxicity and a remarkable inhibition of RALDH activity in MCF-7 tumor spheroids, suggesting that these drugs could be effective in reducing cell stemness in luminal breast cancer.

Do cancer stem cells exist? A pilot study combining a systematic review with the hierarchy-of-hypotheses approach

The phenomenon of cancer cell heterogeneity has been explained by different hypotheses, each entailing different therapy strategies. The most recent is the cancer stem cell model, which says that tumourigenicity and self-renewal are restricted to rare stem cell-like cancer cells. Since its conception, conflicting evidence has been published. In this study, we tested the applicability of a new approach developed in the field of ecology, the hierarchy-of-hypotheses approach, for the Cancer Stem Cell hypothesis. This approach allows to structure a broad concept into more specific sub-hypotheses, which in turn can be connected to available empirical studies. To generate a dataset with empirical studies, we conducted a systematic literature review in the Web of Science limited to the first 1000 publications returned by the search. From this pool, 51 publications were identified that tested whether a cell sub-population had cancer stem cell properties. By classifying the studies according to: (1) assessed indicators, (2) experimental assays and (3) model cancer cells used, we built a hierarchical structure of sub-hypotheses. The empirical tests from the selected studies were subsequently assigned to this hierarchy of hypotheses, and the percentage of supporting, undecided and questioning evidence was calculated for each sub-hypothesis, as well as additional experimental characteristics. Our approach successfully allowed us to determine that within our dataset, the empirical support for the CSC hypothesis was only 49.0%. The support of different sub-hypotheses was highly variable. Most noticeable, the conception that putative cancer stem cells are a rare subset of cells could not be confirmed by most studies (13.5% support). The empirical support varied also between types of cancer, animal models and cell isolation method used. For the first time, this study showed the applicability of the hierarchy-of-hypotheses approach for synthesizing and evaluating empirical evidence for a broad hypothesis in the field of bio-medical research.

Tetrahydrocurcumin, Curcumin, and 5-Fluorouracil Effects on Human Esophageal Carcinoma Cells

Background:

Esophageal cancer responds poorly to traditional therapies, and novel treatments are needed. The phytochemical curcumin is a potential treatment for Esophageal Squamous Cell Carcinoma (ESCC). A curcumin metabolite, tetrahydrocurcumin (THCUR), has anti-cancer effects and greater bioavailability than curcumin.

Objective:

Evaluate THCUR as an anti-cancer agent relative to curcumin and a standard cancer drug, 5-fluorouracil (5-FU), along with treatment interactions.

Materials and Methods:

Assay cell proliferation and viability following individual and combined delivery of the compounds to three ESSC cell lines (TE-1, TE-8, and KY-5) that have different percentages of Cancer Stem Cells (CSCs).

Results:

Curcumin was significantly more effective than 5-FU in all three cell lines. It also had the greatest effect on KY-5 cells, which have the highest CSC properties, consistent with the ability of curcumin to target CSCs. Effects on ESCC cell proliferation were not detected from 40µM THCUR, a dosage above the IC50 of curcumin and 5-FU. However, THCUR at this dosage in combination with 5-FU significantly suppressed TE-1 cell proliferation, but 5-FU alone did not. As TE-1 has low CSC properties relative to the two other cell lines, it was expected to have the least resistance to chemotherapeutic treatments. Surprisingly, TE-1 was the most resistant to inhibition by 5-FU.

Conclusion:

These results and the greater stability and water solubility of THCUR than curcumin support further testing of THCUR in combination with standard treatments, particularly for chemoresistant ESCC. In contrast to concerns that curcuminoids taken by patients through diet or diet supplements might interfere with chemotherapy, suppression of 5-FU efficacy by curcumin was not observed.

Cancer Stem Cells in Head and Neck Carcinomas: Identification and Possible Therapeutic Implications

The recurrence and/or lack of response of certain tumors to radio- and chemotherapy has been attributed to a small subpopulation of cells termed cancer stem cells (CSCs). CSCs have been identified in many tumors (including solid and hematological tumors). CSCs are characterized by their capacity for self-renewal, their ability to introduce heterogeneity within a tumor mass and its metastases, genomic instability, and their insensitivity to both radiation and chemotherapy. The latter highlights the clinical importance of studying this subpopulation since their resistance to traditional treatments may lead to metastatic disease and/or tumor relapse. Head and neck squamous cell carcinomas (HNSCCs) are the sixth most common malignancy worldwide with the highest incidence occurring in East Asia and eastern and southern Africa. Several cellular subpopulations believed to have CSC properties have been isolated from HNSCCs, but at present, identification and characterization of CSCs remains an experimental challenge with no established or standardized protocols in place to confirm their identity. In this review we discuss current approaches to the study of CSCs with a focus on HNSCCs, particularly in the context of what this might mean from a therapeutic perspective.

The ionophore antibiotic gramicidin A inhibits pancreatic cancer stem cells associated with CD47 down-regulation

Background

Pancreatic cancer stem cells (CSCs), a special population of cells, renew themselves infinitely and resist to various treatment. Gramicidin A (GrA), an ionophore antibiotic derived from microorganism, can form channels across the cell membrane and disrupt cellular ionic homeostasis, leading to cell dysfunction and death. As reported, the ionophore antibiotic salinomycin (Sal) has been proved to kill CSCs effectively. Whether GrA owns the potential as a therapeutic drug for CSCs still remains unknown. This study investigated the effect of GrA on pancreatic CSCs and the mechanism.

Methods

Tumorsphere formation assay was performed to assess pancreatic CSCs self-renewal potential. In vitro hemolysis assay was determined to test the borderline concentration of GrA. CCK-8 assay was used to detect pancreatic cancer cell proliferation capability. Flow cytometry was performed to detect cell apoptosis and mitochondrial membrane potential. Scanning and transmission electron microscopy was used to observe ultrastructural morphological changes on cell membrane surface and mitochondria, respectively. Western blot analysis was used to determine relative protein expression levels. Immunofluorescence staining was performed to observe CD47 re-distribution.

Results

GrA at 0.05 μM caused tumorspheres disintegration and decrease in number of pancreatic cancer BxPC-3 and MIA PaCa-2 cells. GrA and Sal both inhibited cancer cell proliferation. The IC50 values of GrA and Sal for BxPC-3 cells were 0.025 μM and 0.363 μM; while for MIA PaCa-2 cells were 0.032 μM and 0.163 μM, respectively. Compared on equal concentrations, the efficacy of GrA was stronger than that of Sal. GrA at 0.1 μM or lower did not cause hemolysis. GrA induced ultrastructural changes, such as the decrease of microvilli-like protrusions on cell surface membrane and the swelling of mitochondria. GrA down-regulated the expression levels of CD133, CD44, and CD47; in addition, CD47 re-distribution was observed on cell surface. Moreover, GrA showed synergism with gemcitabine in suppressing cancer cell proliferation.

Conclusions

The study found that GrA was highly active against pancreatic CSCs. It indicates that GrA exerts inhibitory effects against pancreatic CSCs associated with CD47 down-regulation, implying that GrA might play a positive role in modulating the interaction between macrophages and tumor cells.

The Carcinogenome Project: In Vitro Gene Expression Profiling of Chemical Perturbations to Predict Long-Term Carcinogenicity

BACKGROUND

Most chemicals in commerce have not been evaluated for their carcinogenic potential. The de facto gold-standard approach to carcinogen testing adopts the 2-y rodent bioassay, a time-consuming and costly procedure. High-throughput in vitro assays are a promising alternative for addressing the limitations in carcinogen screening.

OBJECTIVES

We developed a screening process for predicting chemical carcinogenicity and genotoxicity and characterizing modes of actions (MoAs) using in vitro gene expression assays.

METHODS

We generated a large toxicogenomics resource comprising [Formula: see text] expression profiles corresponding to 330 chemicals profiled in HepG2 (human hepatocellular carcinoma cell line) at multiple doses and replicates. Predictive models of carcinogenicity and genotoxicity were built using a random forest classifier. Differential pathway enrichment analysis was performed to identify pathways associated with carcinogen exposure. Signatures of carcinogenicity and genotoxicity were compared with external sources, including Drugmatrix and the Connectivity Map.

RESULTS

Among profiles with sufficient bioactivity, our classifiers achieved 72.2% Area Under the ROC Curve (AUC) for predicting carcinogenicity and 82.3% AUC for predicting genotoxicity. Chemical bioactivity, as measured by the strength and reproducibility of the transcriptional response, was not significantly associated with long-term carcinogenicity in doses up to [Formula: see text]. However, sufficient bioactivity was necessary for a chemical to be used for prediction of carcinogenicity. Pathway enrichment analysis revealed pathways consistent with known pathways that drive cancer, including DNA damage and repair. The data is available at https://clue.io/CRCGN_ABC , and a portal for query and visualization of the results is accessible at https://carcinogenome.org .

DISCUSSION

We demonstrated an in vitro screening approach using gene expression profiling to predict carcinogenicity and infer MoAs of chemical perturbations. https://doi.org/10.1289/EHP3986.

Neural Transcription Factors in Disease Progression

Progression to the malignant state is fundamentally dependent on transcriptional regulation in cancer cells. Optimum abundance of cell cycle proteins, angiogenesis factors, immune evasion markers, etc. is needed for proliferation, metastasis or resistance to treatment. Therefore, dysregulation of transcription factors can compromise the normal prostate transcriptional network and contribute to malignant disease progression.The androgen receptor (AR) is considered to be a key transcription factor in prostate cancer (PCa) development and progression. Consequently, androgen pathway inhibitors (APIs) are currently the mainstay in PCa treatment, especially in castration-resistant prostate cancer (CRPC). However, emerging evidence suggests that with increased administration of potent APIs, prostate cancer can progress to a highly aggressive disease that morphologically resembles small cell carcinoma, which is referred to as neuroendocrine prostate cancer (NEPC), treatment-induced or treatment-emergent small cell prostate cancer. This chapter will review how neuronal transcription factors play a part in inducing a plastic stage in prostate cancer cells that eventually progresses to a more aggressive state such as NEPC.

Of Cytometry, Stem Cells and Fountain of Youth

Outlined are advances of cytometry applications to identify and sort stem cells, of laser scanning cytometry and ImageStream imaging instrumentation to further analyze morphometry of these cells, and of mass cytometry to classify a multitude of cellular markers in large cell populations. Reviewed are different types of stem cells, including potential candidates for cancer stem cells, with respect to their "stemness", and other characteristics. Appraised is further progress in identification and isolation of the "very small embryonic-like stem cells" (VSELs) and their autogenous transplantation for tissue repair and geroprotection. Also assessed is a function of hyaluronic acid, the major stem cells niche component, as a guardian and controller of stem cells. Briefly appraised are recent advances and challenges in the application of stem cells in regenerative medicine and oncology and their future role in different disciplines of medicine, including geriatrics.

Yap1 promotes the survival and self-renewal of breast tumor initiating cells via inhibiting Smad3 signaling

Tumor initiating cells (TICs) serve as the root of tumor growth. After identifying TICs in spontaneous breast tumors of the MMTV-Wnt1 mouse model, we confirmed the specific expression and activation of Yes-associated protein 1 (Yap1) within TICs. To investigate the role of Yap1 in the self-renewal of breast TICs and the underlying mechanism, we sorted CD49f^highEpCAM^low cells as breast TICs. Active Yap1 with ectopic expression in breast TICs promoted their colony formation in vitro (p< 0.01) and self-renewal in vivo (p< 0.01), and led to a 4-fold increase in TIC frequency (p< 0.05). A conditional knock-out mouse was reconstructed to generate Yap1 knock-out breast tumors. The loss of Yap1 led to a dramatic growth disadvantage of breast TICs in vitro (p< 0.01) and in vivo (p< 0.01), and it also led to an over 200-fold decrease in TIC frequency (p< 0.01). The expression of active Yap1 was negatively correlated with that of phosphorylated Smad3 (p-Smad3). Transforming growth factor β (TGF-β) served as a strong enhancer of Smad3 and an inhibitor of clonogenesis of TICs. The presence of SIS3, a specific inhibitor of Smad3, could rescue the TGF-β -induced growth inhibition and reverse the Smad3 inhibition by Yap1. Analysis of a database containing 2,072 human breast cancer samples showed that higher expressions of Yap1 correlated with a poorer outcome of a 15-year survival rate and median overall survival (mOS)in patients, especially in those with basal breast tumors without estrogen receptor 1 (ER) expression. The findings indicate that active Yap1 promotes the self-renewal of breast TICs by inhibiting Smad3 signaling.

In vivo monitoring of CD44+ cancer stem-like cells by γ-irradiation in breast cancer

There is increasing evidence that cancer contains cancer stem cells (CSCs) that are capable of regenerating a tumor following chemotherapy or radiotherapy. CD44 and CD133 are used to identify CSCs. This study investigated non-invasive in vivo monitoring of CD44-positive cancer stem-like cells in breast cancer by γ-irradiation using molecular image by fusing the firefly luciferase (fLuc) gene with the CD44 promoter. We generated a breast cancer cell line stably expressing fLuc gene by use of recombinant lentiviral vector controlled by CD44 promoter (MCF7-CL). Irradiated MCF7-CL spheres showed upregulated expression of CD44 and CD133, by immunofluorescence and flow cytometry. Also, gene expression levels of CSCs markers in irradiated spheres were clearly increased. CD44⁺ CSCs increased fLuc expression and tumor growth in vivo and in vitro. When MCF7-CL was treated with siCD44 and irradiated, CD44 expression was inhibited and cell survival ratio was decreased. MCF7-CL subsets were injected into the mice and irradiated by using a cobalt-60 source. Then, in vivo monitoring was performed to observe the bioluminescence imaging (BLI). When breast cancer was irradiated, relative BLI signal was increased, but tumor volume was decreased compared to non-irradiated tumor. These results indicate that increased CD44 expression, caused by general feature of CSCs by irradiation and sphere formation, can be monitored by using bioluminescence imaging. This system could be useful to evaluate CD44-expressed CSCs in breast cancer by BLI in vivo as well as in vitro for radiotherapy.

[Cancer stem cell markers and their prognostic value]

Based on an analysis of a large number of sources of literature, the paper gives general information on the markers for cancer stem cells (CSCs), which allow the detection of this rare cell subpopulation, on the possibilities of estimating their immunohistochemical or immunofluorescent expression in tumors, and on the prognostic and predictive values of these molecules. For their detection, investigators generally use definite molecules, the so-called markers of CSCs, among which there are CD44, CD133, CD24, aldehyde dehydrogenase, and others. The expression of these molecules in the tumor tissue obtained from patients affects survival rates and permits the prediction of a response to therapy. A better insight into the immunophenotype of CSCs, the role of CSC markers in retaining the special properties of this call population, and the clinical significance of the expression of CSC markers will be able to elaborate new approaches to therapy for malignancies.

Cancer stem-like cell behavior in anaplastic thyroid cancer: A challenging dilemma

AIMS

Anaplastic thyroid carcinoma (ATC) is an undifferentiated tumor of the thyroid which is characterized with poor prognosis, leading to its aggressive behavior and resistance to conventional therapies. Cancer stem cells (CSCs) are tumor cells that have self-renewal and clonal tumor initiation. Like other cancers, many studies have shown that ATC also has tumor cells with properties like stem cells. To evaluate the concept of cancer stem-like cell theory of ATC, we conducted this study to emphasize both on the concept of cancer stemness origin of these cells and target them for further therapeutic purposes. In the current study, we showed that two ATC cell lines, SW1736 and C643, have subpopulations (SP) that are similar to CSCs.

MATERIALS AND METHODS

Using MACS technique, cells positive for CD133 were isolated and subsequently validated with flow cytometry. For further analysis, expression of some stemness markers was evaluated.

KEY FINDINGS

ABCG2, CD133, and Sox2 were significantly up-regulated, while Nestin was down-regulated in CD133(pos) subpopulation compared to CD133(neg) cells. In contrast to previous reports that over-expression of Nestin was considered as a marker for thyroid CSCs, we noticed that expression of Nestin was declined in stem cell-like tumor cells, derived from ATC cell lines.

SIGNIFICANCE

This study reconfirmed the concept of cancer stem-like cell identity of SW1736 and C643 cells. Indeed, the characterization of CSCs should not be merely based on surface markers. Cell origin and genetic background should be additionally considered on CSCs subpopulation of ATCs for therapeutics.

Aldehyde dehydrogenase as a marker and functional mediator of metastasis in solid tumors

There is accumulating evidence indicating that aldehyde dehydrogenase (ALDH) activity selects for cancer cells with increased aggressiveness, capacity for sustained proliferation, and plasticity in primary tumors. However, emerging data also suggests an important mechanistic role for the ALDH family of isoenzymes in the metastatic activity of tumor cells. Recent studies indicate that ALDH correlates with either increased or decreased metastatic capacity in a cellular context-dependent manner. Importantly, it appears that different ALDH isoforms support increased metastatic capacity in different tumor types. This review assesses the potential of ALDH as biological marker and mechanistic mediator of metastasis in solid tumors. In many malignancies, most notably in breast cancer, ALDH activity and expression appears to be a promising marker and potential therapeutic target for treating metastasis in the clinical setting.

Cellular immunotherapy as maintenance therapy prolongs the survival of the patients with small cell lung cancer

BACKGROUND

Small cell lung cancer (SCLC) relapses rapidly after the initial response to chemotherapy and shows drug-resistance. This study was to investigate the efficacy and safety of cellular immunotherapy (CIT) with autologous natural killer (NK), γδT, and cytokine-induced killer (CIK) cells as maintenance therapy for SCLC patients.

METHODS

A pilot prospective cohort study was conducted with SCLC patients who had responded to initial chemotherapy. Patients elected to receive either CIT as maintenance therapy (study group), or to be followed-up without further treatment (control group). Progression-free survival (PFS), overall survival (OS), and adverse effects were investigated.

RESULTS

We recruited 58 patients (29 in each group). The patient characteristics of the 2 groups were well balanced. PFS was not significantly different between the groups, but OS was significantly longer in the study group than the control (20 vs. 11.5 months, P = 0.005; hazard ratio [HR], 0.434, 95 % confidence interval [CI], 0.236-0.797, P = 0.007). Among patients with limited-stage disease, there was no difference in PFS between the groups, but OS was longer in the study group compared to the control (26.5 vs. 11.8 months, P = 0.033; HR, 0.405, 95 % CI, 0.169-0.972, P = 0.043). Among patients with extensive-stage disease, both PFS and OS were longer in the study group than the control (5 vs. 2.7 months, P = 0.037; HR, 0.403, 95 % CI, 0.162-1.003, P = 0.051, and 14.5 vs. 9 months, P = 0.038; HR, 0.403, 95 % CI, 0.165-0.987, P = 0.047, respectively). No significant adverse reactions occurred in patients undergoing CIT.

CONCLUSIONS

CIT maintenance therapy in SCLC prolonged survival with only minimal side effects. Integrating CIT into current treatment may be a novel strategy for SCLC therapy, although further multi-center randomized studies are needed.

Regulation of miRNAs affects radiobiological response of lung cancer stem cells

Radiotherapy (RT) is a key therapeutic strategy for lung cancer, the most common cause of cancer-related deaths worldwide, but radioresistance often occurs and leads to failure of RT. It is therefore important to clarify the mechanism underlying radioresistance in lung cancer. Cancer stem cells (CSCs) are considered the fundamental reason for radioresistance. MicroRNAs (miRNAs) have been regarded as important regulatory molecules of CSCs, carcinogenesis, and treatment response of cancers. It is crucial to clarify how regulation of miRNAs affects repair of DNA damage, redistribution, repopulation, reoxygenation, and radiosensitivity (5R) of lung cancer stem cells (LCSCs). A thorough understanding of the regulation of miRNAs affecting 5R of LCSCs has potential impact on identifying novel targets and thus may improve the efficacy of lung cancer radiotherapy.

Hitting the Bull's-Eye in Metastatic Cancers-NSAIDs Elevate ROS in Mitochondria, Inducing Malignant Cell Death

Tumor metastases that impede the function of vital organs are a major cause of cancer related mortality. Mitochondrial oxidative stress induced by hypoxia, low nutrient levels, or other stresses, such as genotoxic events, act as key drivers of the malignant changes in primary tumors to enhance their progression to metastasis. Emerging evidence now indicates that mitochondrial modifications and mutations resulting from oxidative stress, and leading to OxPhos stimulation and/or enhanced reactive oxygen species (ROS) production, are essential for promoting and sustaining the highly metastatic phenotype. Moreover, the modified mitochondria in emerging or existing metastatic cancer cells, by their irreversible differences, provide opportunities for selectively targeting their mitochondrial functions with a one-two punch. The first blow would block their anti-oxidative defense, followed by the knockout blow—promoting production of excess ROS, capitulating the terminal stage—activation of the mitochondrial permeability transition pore (mPTP), specifically killing metastatic cancer cells or their precursors. This review links a wide area of research relevant to cellular mechanisms that affect mitochondria activity as a major source of ROS production driving the pro-oxidative state in metastatic cancer cells. Each of the important aspects affecting mitochondrial function are discussed including: hypoxia, HIFs and PGC1 induced metabolic changes, increased ROS production to induce a more pro-oxidative state with reduced antioxidant defenses. It then focuses on how the mitochondria, as a major source of ROS in metastatic cancer cells driving the pro-oxidative state of malignancy enables targeting drugs affecting many of these altered processes and why the NSAIDs are an excellent example of mitochondria-targeted agents that provide a one-two knockout activating the mPTP and their efficacy as selective anticancer metastasis drugs.

A novel pathogenic classification of cancers

According to contemporary epidemiological and experimental evidence, we propose a novel classification of cancers based on pathogenesis instead of classifications based on histological appearance of cancer. This new scheme first defines cancers as either 1. inborn errors of development or 2. sporadic ones, and then sub-defines the former into 1A. inborn inherited errors of development, being those due to mutations contributed by one or both parents' gametes to the developing conceptus, and 1B. inborn induced errors of development when the malformations and/or cancers are due to environmental carcinogenic exposure during pregnancy. It is anticipated that the origin of an increasing number of so-called sporadic cancers will turn out to be linked to the inborn induced errors of development group.

Cancer stem cells: a systems biology view of their role in prognosis and therapy

Evidence has accumulated that characterizes highly tumorigenic cancer cells residing in heterogeneous populations. The accepted term for such a subpopulation is cancer stem cells (CSCs). While many questions still remain about their precise role in the origin, progression, and drug resistance of tumors, it is clear they exist. In this review, a current understanding of the nature of CSC, their potential usefulness in prognosis, and the need to target them will be discussed. In particular, separate studies now suggest that the CSC is plastic in its phenotype, toggling between tumorigenic and nontumorigenic states depending on both intrinsic and extrinsic conditions. Because of this, a static view of gene and protein levels defined by correlations may not be sufficient to either predict disease progression or aid in the discovery and development of drugs to molecular targets leading to cures. Quantitative dynamic modeling, a bottom up systems biology approach whereby signal transduction pathways are described by differential equations, may offer a novel means to overcome the challenges of oncology today. In conclusion, the complexity of CSCs can be captured in mathematical models that may be useful for selecting molecular targets, defining drug action, and predicting sensitivity or resistance pathways for improved patient outcomes.

Intratumoral heterogeneity: Clonal cooperation in epithelial-to-mesenchymal transition and metastasis

Although phenotypic intratumoral heterogeneity was first described many decades ago, the advent of next-generation sequencing has provided conclusive evidence that in addition to phenotypic diversity, significant genotypic diversity exists within tumors. Tumor heterogeneity likely arises both from clonal expansions, as well as from differentiation hierarchies existent in the tumor, such as that established by cancer stem cells (CSCs) and non-CSCs. These differentiation hierarchies may arise due to genetic mutations, epigenetic alterations, or microenvironmental influences. An additional differentiation hierarchy within epithelial tumors may arise when only a few tumor cells trans-differentiate into mesenchymal-like cells, a process known as epithelial-to-mesenchymal transition (EMT). Again, this process can be influenced by both genetic and non-genetic factors. In this review we discuss the evidence for clonal interaction and cooperation for tumor maintenance and progression, particularly with respect to EMT, and further address the far-reaching effects that tumor heterogeneity may have on cancer therapy.

The cancer stem cell hypothesis: a guide to potential molecular targets

Common cancer theories hold that tumor is an uncontrolled somatic cell proliferation caused by the progressive addition of random mutations in critical genes that control cell growth. Nevertheless, various contradictions related to the mutation theory have been reported previously. These events may be elucidated by the persistence of residual tumor cells, called Cancer Stem Cells (CSCs) responsible for tumorigenesis, tumor maintenance, tumor spread, and tumor relapse. Herein, we summarize the current understanding of CSCs, with a focus on the possibility to identify specific markers of CSCs, and discuss the clinical application of targeting CSCs for cancer treatment.

Advantages and clinical applications of natural killer cells in cancer immunotherapy

The past decade has witnessed a burgeoning of research and further insight into the biology and clinical applications of natural killer (NK) cells. Once thought to be simple innate cells important only as cytotoxic effector cells, our understanding of NK cells has grown to include memory-like responses, the guidance of adaptive responses, tissue repair, and a delicate paradigm for how NK cells become activated now termed "licensing" or "arming." Although these cells were initially discovered and named for their spontaneous ability to kill tumor cells, manipulating NK cells in therapeutic settings has proved difficult and complex in part due to our emerging understanding of their biology. Therapies involving NK cells may either activate endogenous NK cells or involve transfers of exogenous cells by hematopoietic stem cell transplantation or adoptive cell therapy. Here, we review the basic biology of NK cells, highlighting characteristics which make NK cells particularly useful in cancer therapies. We also explore current treatment strategies that have been used for cancer as well as discuss potential future directions for the field.