All-trans retinoic acid targets gastric cancer stem cells and inhibits patient-derived gastric carcinoma tumor growth

Verteporfin targeting YAP1/TAZ-TEAD transcriptional activity inhibits the tumorigenic properties of gastric cancer stem cells

Gastric carcinomas (GC) are heterogeneous tumors, composed of a subpopulation of cluster of differentiation-44 (CD44)+ tumorigenic and chemoresistant cancer stem cells (CSC). YAP1 and TAZ oncoproteins (Y/T) interact with TEA domain family member 1 (TEAD) transcription factors to promote cell survival and proliferation in multiple tissues. Their activity and role in GC remain unclear. This work aimed to analyze Y/T-TEAD activity and molecular signature in gastric CSC, and to assess the effect of verteporfin, a Food and Drug Administration-approved drug preventing Y/T-TEAD interaction, on gastric CSC tumorigenic properties. Y/T-TEAD molecular signature was investigated using bioinformatical (KmPlot database), transcriptomic and immunostaining analyses in patient-derived GC and cell lines. Verteporfin effects on Y/T-TEAD transcriptional activity, CSC proliferation and tumorigenic properties were evaluated using in vitro tumorsphere assays and mouse models of patient-derived GC xenografts. High expressions of YAP1, TAZ, TEAD1, TEAD4 and their target genes were associated with low overall survival in nonmetastatic human GC patients (n = 444). This Y/T-TEAD molecular signature was enriched in CD44+ patient-derived GC cells and in cells resistant to conventional chemotherapy. Verteporfin treatment inhibited Y/T-TEAD transcriptional activity, cell proliferation and CD44 expression, and decreased the pool of tumorsphere-forming CD44⁺ /aldehyde dehydrogenase (ALDH)^high gastric CSC. Finally, verteporfin treatment inhibited GC tumor growth in vivo; the residual tumor cells exhibited reduced expressions of CD44 and ALDH1, and more importantly, they were unable to initiate new tumorspheres in vitro. All these data demonstrate that Y/T-TEAD activity controls gastric CSC tumorigenic properties. The repositioning of verteporfin targeting YAP1/TAZ-TEAD activity could be a promising CSC-based strategy for the treatment of GC.

How does Helicobacter pylori cause gastric cancer through connexins: An opinion review

Helicobacter pylori (H. pylori) is a Gram-negative bacterium with a number of virulence factors, such as cytotoxin-associated gene A, vacuolating cytotoxin A, its pathogenicity island, and lipopolysaccharide, which cause gastrointestinal diseases. Connexins function in gap junctional homeostasis, and their downregulation is closely related to gastric carcinogenesis. Investigations into H. pylori infection and the fine-tuning of connexins in cells or tissues have been reported in previous studies. Therefore, in this review, the potential mechanisms of H. pylori-induced gastric cancer through connexins are summarized in detail.

Cancer stem cells in esophageal squamous cell cancer

Cancer stem cells (CSCs) are hypothesized to govern the origin, progression, drug resistance, recurrence and metastasis of human cancer. CSCs have been identified in nearly all types of human cancer, including esophageal squamous cell cancer (ESCC). Four major methods are typically used to isolate or enrich CSCs, including: i) fluorescence-activated cell sorting or magnetic-activated cell sorting using cell-specific surface markers; ii) stem cell markers, including aldehyde dehydrogenase 1 family member A1; iii) side population cell phenotype markers; and iv) microsphere culture methods. ESCC stem cells have been identified using a number of these methods. An increasing number of stem cell signatures and pathways have been identified, which have assisted in the clarification of molecular mechanisms that regulate the stemness of ESCC stem cells. Certain viruses, such as human papillomavirus and hepatitis B virus, are also considered to be important in the formation of CSCs, and there is a crosstalk between stemness and viruses-associated genes/pathways, which may suggest a potential therapeutic strategy for the eradication of CSCs. In the present review, findings are summarized along these lines of inquiry.

Chlorogenic acid effectively treats cancers through induction of cancer cell differentiation

Rationale: Inducing cancer differentiation is a promising approach to treat cancer. Here, we identified chlorogenic acid (CA), a potential differentiation inducer, for cancer therapy, and elucidated the molecular mechanisms underlying its differentiation-inducing effects on cancer cells.

Methods: Cancer cell differentiation was investigated by measuring malignant behavior, including growth rate, invasion/migration, morphological change, maturation, and ATP production. Gene expression was analyzed by microarray analysis, qRT-PCR, and protein measurement, and molecular biology techniques were employed for mechanistic studies. LC/MS analysis was the method of choice for chemical detection. Finally, the anticancer effect of CA was evaluated both in vitro and in vivo.

Results: Cancer cells treated with CA showed reduced proliferation rate, migration/invasion ability, and mitochondrial ATP production. Treating cancer cells with CA resulted in elevated SUMO1 expression through acting on its 3'UTR and stabilizing the mRNA. The increased SUMO1 caused c-Myc sumoylation, miR-17 family downregulation, and p21 upregulation leading to G₀/G₁ arrest and maturation phenotype. CA altered the expression of differentiation-related genes in cancer cells but not in normal cells. It inhibited hepatoma and lung cancer growth in tumor-bearing mice and prevented new tumor development in naïve mice. In glioma cells, CA increased expression of specific differentiation biomarkers Tuj1 and GFAP inducing differentiation and reducing sphere formation. The therapeutic efficacy of CA in glioma cells was comparable to that of temozolomide. CA was detectable both in the blood and brain when administered intraperitoneally in animals. Most importantly, CA was safe even at very high doses.

Conclusion: CA might be a safe and effective differentiation-inducer for cancer therapy. “Educating” cancer cells to differentiate, rather than killing them, could be a novel therapeutic strategy for cancer.

Therapeutic targeting of gastrointestinal cancer stem cells

Gastrointestinal cancers remain a tremendous burden on society. Despite advances in therapy options, including chemotherapy and radiation, cancer mortality from recurrences and metastases occur frequently. Cancer stem cells (CSCs) drive disease recurrence and metastasis, as these cells are uniquely equipped to self-renew and evade therapy. Therefore, cancer eradication requires treatment strategies that target CSCs in addition to differentiated cancer cells. This review highlights current literature on therapies targeting CSCs in gastrointestinal cancer.

Pin1 inhibition potently suppresses gastric cancer growth and blocks PI3K/AKT and Wnt/β-catenin oncogenic pathways

Gastric cancer is the second leading cause of cancer-related mortality and the fourth most common cancer globally. High intratumor heterogeneity of advanced gastric cancer poses great challenges to targeted therapy due to simultaneous activation of many redundant cancer-driving pathways. A central common signaling mechanism in cancer is proline-directed phosphorylation, which is further regulated by the unique proline isomerase Pin1. Pin1 inhibition exerts anticancer activity by blocking multiple cancer-driving pathways in some cancers, but its role in gastric cancer is not fully understood. Here we detected Pin1 protein expression in 1065 gastric cancer patients and paired normal tissues using immunohistochemistry and Western blot, and then examined the effects of Pin1 overexpression, and genetic and chemical Pin1 inhibition using Pin1 short hairpin RNA or small molecule inhibitor all-trans retinoic acid (ATRA) on tumorigenesis of human gastric cancer in vitro and in vivo, followed by biochemical analyses to elucidate Pin1 regulated oncogenic pathways. We found that Pin1 was significantly overexpressed in primary and metastasized tumors, with Pin1 overexpression being correlated with advanced stage and poor prognosis. Furthermore, whereas Pin1 overexpression promoted the transformed phenotype in immortalized and nontransformed human gastric cells, either genetic or chemical Pin1 inhibition in multiple human gastric cancer cells potently suppressed cell growth, G1/S transition and colony formation in vitro, as well as tumor growth in xenograft tumor models in vivo, which were further supported by downregulation of multiple key oncoproteins in PI3K/AKT and Wnt/β-catenin signaling pathways. These results not only provide the first evidence for a critical role of Pin1 in the tumorigenesis of gastric cancer but also suggest that targeting Pin1 using ATRA or other inhibitors offers an effective new therapeutic approach for treating advanced gastric cancer.

Orthotopic Patient-Derived Xenografts of Gastric Cancer to Decipher Drugs Effects on Cancer Stem Cells and Metastatic Dissemination

Gastric cancer is the third leading cause of cancer mortality worldwide. Cancer stem cells (CSC) are at the origin of tumor initiation, chemoresistance, and the formation of metastases. However, there is a lack of mouse models enabling the study of the metastatic process in gastric adenocarcinoma (GC). The aims of this study were to develop original mouse models of patient-derived primary GC orthotopic xenografts (PDOX) allowing the development of distant metastases as preclinical models to study the anti-metastatic efficiency of drugs such as the phosphatidylinositol 3-kinase (PI3K) inhibitor Buparlisib (BKM120). Luciferase-encoding cells generated from primary GC were injected into the stomach wall of immunocompromised mice; gastric tumor and metastases development were followed by bioluminescence imaging. The anti-CSC properties of BKM120 were evaluated on the GC cells’ phenotype (CD44 expression) and tumorigenic properties in vitro and in vivo on BKM120-treated mice. After eight weeks, PDOX mice formed tumors in the stomach as well as distant metastases, that were enriched in CSC, in the liver, the lung, and the peritoneal cavity. BKM120 treatment significantly inhibited the CSC properties in vitro and reduced the number of distant metastases in mice. These new preclinical models offer the opportunity to study the anti-metastatic efficiency of new CSC-based therapeutic strategies.

ALDH as a Stem Cell Marker in Solid Tumors

Aldehyde dehydrogenase (ALDH) is an enzyme that participates in important cellular mechanisms as aldehyde detoxification and retinoic acid synthesis; moreover, ALDH activity is involved in drug resistance, a characteristic of cancer stem cells (CSCs). Even though ALDH is found in stem cells, CSCs and progenitor cells, this enzyme has been successfully used to identify and isolate cell populations with CSC properties from several tumor origins. ALDH is allegedly involved in cell differentiation through its product, retinoic acid. However, direct or indirect ALDH inhibition, using specific inhibitors or retinoic acid, has shown a reduction in ALDH activity, along with the loss of stem cell traits, reduction of cell proliferation, invasion, and drug sensitization. For these reasons, ALDH and retinoic acid are promising therapeutic targets. This review summarizes the current evidence for ALDH as a CSCs marker in solid tumors, as well as current knowledge about the functional roles of ALDH in CSCs. We discuss the controversy of ALDH activity to maintain CSC stemness, or conversely, to promote cell differentiation. Finally, we review the advances in using ALDH inhibitors as anti-cancer drugs.

Cancer stem cell impact on clinical oncology

Cancer is a widespread worldwide chronic disease. In most cases, the high mortality rate from cancer correlates with a lack of clear symptoms, which results in late diagnosis for patients, and consequently, advanced tumor disease with poor probabilities for cure, since many patients will show chemo- and radio-resistance. Several mechanisms have been studied to explain chemo- and radio-resistance to anti-tumor therapies, including cell signaling pathways, anti-apoptotic mechanisms, stemness, metabolism, and cellular phenotypes. Interestingly, the presence of cancer stem cells (CSCs), which are a subset of cells within the tumors, has been related to therapy resistance. In this review, we focus on evaluating the presence of CSCs in different tumors such as breast cancer, gastric cancer, lung cancer, and hematological neoplasias, highlighting studies where CSCs were identified in patient samples. It is evident that there has been a great drive to identify the cell surface phenotypes of CSCs so that they can be used as a tool for anti-tumor therapy treatment design. We also review the potential effect of nanoparticles, drugs, natural compounds, aldehyde dehydrogenase inhibitors, cell signaling inhibitors, and antibodies to treat CSCs from specific tumors. Taken together, we present an overview of the role of CSCs in tumorigenesis and how research is advancing to target these highly tumorigenic cells to improve oncology patient outcomes.

Targeting Cancer Stem Cells to Overcome Chemoresistance

Cancers are heterogeneous at the cell level, and the mechanisms leading to cancer heterogeneity could be clonal evolution or cancer stem cells. Cancer stem cells are resistant to most anti-cancer treatments and could be preferential targets to reverse this resistance, either targeting stemness pathways or cancer stem cell surface markers. Gold nanoparticles have emerged as innovative tools, particularly for photo-thermal therapy since they can be excited by laser to induce hyperthermia. Gold nanoparticles can be functionalized with antibodies to specifically target cancer stem cells. Preclinical studies using photo-thermal therapy have demonstrated the feasibility of targeting chemo-resistant cancer cells to reverse clinical chemoresistance. Here, we review the data linking cancer stem cells and chemoresistance and discuss the way to target them to reverse resistance. We particularly focus on the use of functionalized gold nanoparticles in the treatment of chemo-resistant metastatic cancers.

Gastric Cancer Stem Cells: Mechanisms and Therapeutic Approaches

Gastric cancer (GC) is the third leading cause of cancer-related deaths worldwide. GC stem-like cells (GCSCs), with unlimited self-renewal, differentiation, and tumor-regenerating capacities, contribute significantly to the refractory features of GC and have gained increasing attention for their role in GC drug resistance, relapse, and metastasis. Therapies targeting GCSCs seem to be one of the most promising methods to improve the outcomes of GC patients. Extensive investigations have attempted to outline the regulatory mechanisms in GCSCs and to develop GCSCs-targeting therapies with which to diminish GC drug resistance, metastasis and relapse. To the best of our knowledge, there is a lack of reviews summarizing these studies. In this review, we systematically recapitulated findings regarding the regulatory mechanisms of GCSCs, as well as therapies that target GCSCs, hoping to support the development of prognostic biomarkers and GCSCs-targeting anticancer therapies in GC.

Retinol palmitate and ascorbic acid: Role in oncological prevention and therapy

Cancer development has been directly related to oxidative stress. During chemotherapy, some cancer patients use dietary antioxidants to avoid nutritional deficiencies due to cancer treatment. Among the antioxidants consumed, there are vitamins, including retinyl palmitate (PR) and ascorbic acid (AA), which have the capacity to reduce free radicals formation, protect cellular structures and maintain the cellular homeostasis. This systematic review evaluated the antioxidant and antitumor mechanisms of retinol palmitate (a derivative of vitamin A) and/or ascorbic acid (vitamin C) in cancer-related studies. Ninety-seven (97) indexed articles in the databases PubMed and Science Direct, published between 2013 and 2017, including 23 clinical studies (5 for every single compound while 13 in interaction) and 74 non-clinical studies (37 for retinol palmitate, 36 for ascorbic acid and 1 in interaction) were considered. Antioxidant and antitumor effects, with controversies over dosage and route of administration, were observed for the test compounds in their isolated form or associated in clinical studies. Prevention of cancer risks against oxidative damage was seen in lower doses of retinol palmitate and/or vitamin C. However, at high doses, they can generate reactive oxygen species, cytotoxicity and apoptosis in test systems. Non-clinical studies using cell lines have allowed understanding the mechanisms related to antioxidants and antitumor effects of the isolated compounds, however, studies on vitamin interactions, acting as antioxidants and/or antitumor are still rare and controversial. More studies, mainly related to modulation of antineoplastic drugs are needed for understanding the risks and benefits of their use during treatment in order to achieve effectiveness in cancer therapy and patient's quality of life.

Efficiency of All-Trans Retinoic Acid on Gastric Cancer: A Narrative Literature Review

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide with a five-year survival rate of around 25%, and 4% when diagnosed at a metastatic stage. Cancer stem cells (CSC) have recently been characterized as being responsible for resistance to radio/chemotherapies and metastasis formation, opening up perspectives for new targeted therapies. Those CSCs express biomarkers such as cluster of differentiation 44 (CD44) and display high aldehyde dehydrogenase activity that converts vitamin A-derived retinal into retinoic acids. All-trans retinoic acid (ATRA), which has pro-differentiating properties, has revolutionized the prognosis of acute promyelotic leukemia by increasing its remission rate from 15% to 85%. Recent studies have started to show that ATRA also has an anti-tumoral role on solid cancers such as GC. The purpose of this review is therefore to summarize the work that evaluated the effects of ATRA in GC and to evaluate whether its anti-cancerous action involves gastric CSCs targeting. It has been demonstrated that ATRA can block the cell cycle, enhance apoptosis, and decrease gastric CSCs properties in GC cell lines, tumorspheres, and patient-derived xenograft mice models. Therefore, retinoids and new synthetic retinoids seem to be a promising step forward in targeted therapy of gastric CSC in combination with existing chemotherapies. Future studies should probably focus on these points.

Factors Within the Endoneurial Microenvironment Act to Suppress Tumorigenesis of MPNST

Background: Deciphering avenues to adequately control malignancies in the peripheral nerve will reduce the need for current, largely-ineffective, standards of care which includes the use of invasive, nerve-damaging, resection surgery. By avoiding the need for en bloc resection surgery, the likelihood of retained function or efficient nerve regeneration following the control of tumor growth is greater, which has several implications for long-term health and well-being of cancer survivors. Nerve tumors can arise as malignant peripheral nerve sheath tumors (MPNST) that result in a highly-aggressive form of soft tissue sarcoma. Although the precise cause of MPNST remains unknown, studies suggest that dysregulation of Schwann cells, mediated by the microenvironment, plays a key role in tumor progression. This study aimed to further characterize the role of local microenvironment on tumor progression, with an emphasis on identifying factors within tumor suppressive environments that have potential for therapeutic application.

Methods: We created GFP-tagged adult induced tumorigenic Schwann cell lines (iSCs) and transplanted them into various in vivo microenvironments. We used immunohistochemistry to document the response of iSCs and performed proteomics analysis to identify local factors that might modulate divergent iSC behaviors.

Results: Following transplant into the skin, spinal cord or epineurial compartment of the nerve, iSCs formed tumors closely resembling MPNST. In contrast, transplantation into the endoneurial compartment of the nerve significantly suppressed iSC proliferation. Proteomics analysis revealed a battery of factors enriched within the endoneurial compartment, of which one growth factor of interest, ciliary neurotrophic factor (CNTF) was capable of preventing iSCs proliferation in vitro.

Conclusions: This dataset describes a novel approach for identifying biologically relevant therapeutic targets, such as CNTF, and highlights the complex relationship that tumor cells have with their local microenvironment. This study has significant implications for the development of future therapeutic strategies to fight MPNSTs, and, consequently, improve peripheral nerve regeneration and nerve function.

Dynamism, Sensitivity, and Consequences of Mesenchymal and Stem-Like Phenotype of Cancer Cells

There are remarkable similarities in the description of cancer stem cells (CSCs) and cancer cells with mesenchymal phenotype. Both cell types are highly tumorigenic, resistant against common anticancer treatment, and thought to cause metastatic growth. Moreover, cancer cells are able to switch between CSC and non-CSC phenotypes and vice versa, to ensure the necessary balance within the tumor. Likewise, cancer cells can switch between epithelial and mesenchymal phenotypes via well-described transition (EMT/MET) that is thought to be crucial for tumor propagation. In this review, we discuss whether, and to which extend, the CSCs and mesenchymal cancer cells are overlapping phenomena in terms of mechanisms, origin, and implication for cancer treatment. As well, we describe the dynamism of both phenotypes and involvement of the tumor microenvironment in CSC reversion and in EMT.

Acetylcholine induces stem cell properties of gastric cancer cells of diffuse type

Gastric cancer is the third leading cause of cancer-related death worldwide, but the mechanisms of gastric carcinogenesis are not completely understood. Recently, the role of cholinergic neuronal pathways in promoting this process has been demonstrated. Our aim was to extend these studies and to evaluate, using an in vitro model of tumorspheres, the effect of acetylcholine on human gastric cancer cells, and the role of acetylcholine receptors and of the nitric oxide pathway, in this effect. The gastric cancer cell line MKN-45 of the diffuse type of gastric cancer was cultured in the presence of acetylcholine, or different agonists or inhibitors of muscarinic and nicotinic acetylcholine receptors, or nitric oxide donor or inhibitor of the nitric oxide pathway, and the number and size of tumorspheres were assessed. The expression of cancer stem cell markers (CD44 and aldehyde dehydrogenase) was also evaluated by immunofluorescence and quantitative reverse transcription polymerase chain reaction. We showed that acetylcholine increased both the number and size of tumorspheres and that this effect was reproduced with both muscarinic and nicotinic acetylcholine receptors agonists and was inhibited by both receptor antagonists. The nitric oxide donor stimulated the tumorsphere formation, while the nitric oxide synthesis inhibitor inhibited the stimulatory effect of acetylcholine. Moreover, acetylcholine increased the expression of stem cell markers on gastric cancer cells. These results indicate that acetylcholine induces the stem cell properties of gastric cancer cells and both muscarinic and nicotinic receptors and a nitrergic pathway might be involved in this effect.

Serum miR-658 induces metastasis of gastric cancer by activating PAX3-MET pathway: A population-based study

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Combination treatment of all-trans retinoic acid (ATRA) and γ-secretase inhibitor (DAPT) cause growth inhibition and apoptosis induction in the human gastric cancer cell line

Current medication for gastric cancer patients has a low success rate with resistance and side effects. According to recent studies, γ-secretase inhibitors is used as therapeutic drugs in cancer. Moreover, all-trans retinoic acid (ATRA) is a natural compound proposed for the treatment/chemo-prevention of cancers. The aim of this study was to explore the effects of ATRA in combination with N-[N-(3,5-difluorophenacetyl-l-alanyl)]-S-phenylglycine t-butyl ester (DAPT) as γ-secretase inhibitor on viability and apoptosis of the AGS and MKN-45 derived from human gastric cancer. AGS and MKN-45 gastric cancer cell lines were treated with different concentrations of ATRA or DAPT alone or ATRA plus DAPT. The viability, death detection and apoptosis of cells was examined by MTT assay and Ethidium bromide/acridine orange staining. The distribution of cells in different phases of cell cycle was also evaluated through flow cytometry analyses. In addition, caspase 3/7 activity and the expression of caspase-3 and bcl-2 were examined. DAPT and ATRA alone decreased gastric cancer cells viability in a concentration dependent manner. The combination of DAPT and ATRA exhibited significant synergistic inhibitory effects. The greater percentage of cells were accumulated in G0/G1 phase of cell cycle in combination treatment. The combination of DAPT and ATRA effectively increased the proportion of apoptotic cells and the level of caspase 3/7 activities compared to single treatment. Moreover, augmented caspase-3 up-regulation and bcl-2 down-regulation were found following combined application of DAPT and ATRA. The combination of DAPT and ATRA led to more reduction in viability and apoptosis in respect to DAPT or ATRA alone in the investigated cell lines.

Modulation of oncogenic miRNA biogenesis using functionalized polyamines

MicroRNAs are key factors in the regulation of gene expression and their deregulation has been directly linked to various pathologies such as cancer. The use of small molecules to tackle the overexpression of oncogenic miRNAs has proved its efficacy and holds the promise for therapeutic applications. Here we describe the screening of a 640-compound library and the identification of polyamine derivatives interfering with in vitro Dicer-mediated processing of the oncogenic miR-372 precursor (pre-miR-372). The most active inhibitor is a spermine-amidine conjugate that binds to the pre-miR-372 with a K_D of 0.15 µM, and inhibits its in vitro processing with a IC₅₀ of 1.06 µM. The inhibition of miR-372 biogenesis was confirmed in gastric cancer cells overexpressing miR-372 and a specific inhibition of proliferation through de-repression of the tumor suppressor LATS2 protein, a miR-372 target, was observed. This compound modifies the expression of a small set of miRNAs and its selective biological activity has been confirmed in patient-derived ex vivo cultures of gastric carcinoma. Polyamine derivatives are promising starting materials for future studies about the inhibition of oncogenic miRNAs and, to the best of our knowledge, this is the first report about the application of functionalized polyamines as miRNAs interfering agents.

Increased Musashi-2 and Decreased NUMB Protein Levels Observed in Human Colorectal Cancer are reverted to Normal Levels by ATRA-Induced Cell Differentiation

Background:

Musashi stem cell (SC) proteins (MSI-1 & MSI-2) are known to become over expressed during colorectal tumorigenesis in humans and mice. MSI-1 overexpression induces tumorigenesis through Notch activation via inactivation of NUMB. Previous studies also show that MSI-2 overexpression in mice induces intestinal tumorigenesis but the mechanism is independent of NUMB. However, whether the MSI-2/NUMB pathway contributes to colorectal cancer (CRC) development in humans is still undetermined.

Methods:

We evaluated expression of MSI-2 and NUMB proteins in matched normal and CRC patient samples, as well as in human CRC cell lines. We also determined whether induction of cellular differentiation by all-trans retinoic acid (ATRA) influences MSI-2 and NUMB expression.

Results:

Analysis of matched patient tissue samples and CRC cell lines showed that MSI-2 protein expression is significantly increased and NUMB expression is decreased in CRCs compared to the normal colonic tissue. Immunostaining of normal and adenomatous colonic epithelium revealed that MSI-1+ andMSI-2+ SCs reside in the SC niche and they become overpopulated during colon tumorigenesis. Moreover, promoting cellular differentiation by ATRA reduces MSI-2 protein levels, while increasing NUMB protein levels in human CRC cell lines.

Conclusions:

MSI-2/NUMB protein expression is altered during colon tumorigenesis, and indicates that MSI-2/NUMB signaling in human colonic stem cells is closely linked to normal colonic epithelial homeostasis.

Implications:

The ability to normalize MSI-2/NUMB signaling by inducing differentiation of cancer SCs suggests a novel therapeutic approach for CRC treatment.

Profiling of the transcriptional response to all-trans retinoic acid in breast cancer cells reveals RARE-independent mechanisms of gene expression

Retinoids, derivatives of vitamin A, are key physiological molecules with regulatory effects on cell differentiation, proliferation and apoptosis. As a result, they are of interest for cancer therapy. Specifically, models of breast cancer have varied responses to manipulations of retinoid signaling. This study characterizes the transcriptional response of MDA-MB-231 and MDA-MB-468 breast cancer cells to retinaldehyde dehydrogenase 1A3 (ALDH1A3) and all-trans retinoic acid (atRA). We demonstrate limited overlap between ALDH1A3-induced gene expression and atRA-induced gene expression in both cell lines, suggesting that the function of ALDH1A3 in breast cancer progression extends beyond its role as a retinaldehyde dehydrogenase. Our data reveals divergent transcriptional responses to atRA, which are largely independent of genomic retinoic acid response elements (RAREs) and consistent with the opposing responses of MDA-MB-231 and MDA-MB-468 to in vivo atRA treatment. We identify transcription factors associated with each gene set. Manipulation of the IRF1 transcription factor demonstrates that it is the level of atRA-inducible and epigenetically regulated transcription factors that determine expression of target genes (e.g. CTSS, cathepsin S). This study provides a paradigm for complex responses of breast cancer models to atRA treatment, and illustrates the need to characterize RARE-independent responses to atRA in a variety of models.

Anti-inflammatory drug resistance selects putative cancer stem cells in a cellular model for genetically predisposed colon cancer

Mutations in the adenomatous polyposis coli (Apc) tumor suppressor gene represent the primary genetic defect in colon carcinogenesis. Apc^+/- mouse models exhibit pre-invasive small intestinal adenomas. Cell culture models exhibiting Apc defects in the colon and quantifiable cancer risk provide a novel clinically relevant approach. The tumor-derived Apc^-/- colonic epithelial cell line 1638N COL-Pr₁ represented the experimental model. The anti-inflammatory drugs sulindac (SUL) and celecoxib (CLX) represented the test compounds. Compared with non-tumorigenic Apc^+/+ C57COL cells, the Apc^+/- 1638N COL cells and Apc^-/- 1638N COL-Pr₁ cells exhibited progressive loss of homeostatic growth control. Compared with Apc^+/- cells, Apc^-/- cells displayed increased expression of biomarkers specific for hyper-proliferation. Treatment of Apc^-/- cells with SUL and CLX resulted in inhibition of anchorage-independent colony formation in vitro, which is indicative of reduced cancer risk in vivo. Mechanistically, SUL and CLX suppressed the expression of the Apc target genes β-catenin, cyclin D1, c-Myc and cyclooxygenase-2. Long-term treatment with high concentrations of SUL and CLX led to the selection of hyper-proliferative drug-resistant phenotypes. The Apc^-/- SUL-resistant phenotype displayed spheroid formation and enhanced the expression of the stem cell-specific molecular markers CD44, CD133 and c-Myc. These data demonstrated the growth-inhibitory efficacy of SUL and CLX and indicated that drug resistance leads to the selection of a putative cancer stem cell phenotype. The study outcome validates a stem cell-targeted mechanistic approach to identify testable alternative leads for chemotherapy-resistant colon cancer.

Gastric cancer: Basic aspects

Gastric cancer is one of the most incident and deadliest malignancies in the world. Gastric cancer is a heterogeneous disease and the end point of a long and multistep process, which results from the stepwise accumulation of numerous (epi)genetic alterations, leading to dysregulation of oncogenic and tumor suppressor pathways. Gastric cancer stem cells have emerged as fundamental players in cancer development and as contributors to gastric cancer heterogeneity. For this special issue, we will report last year's update on the gastric cancer molecular classification, and in particular address the gastric cancer groups who could benefit from immune checkpoint therapy. We will also review the latest advances on gastric cancer stem cells, their properties as gastric cancer markers and therapeutic targets, and associated signaling pathways. The understanding of the molecular basis underlying gastric cancer heterogeneity and of the role played by gastric cancer stem cells in cancer development and heterogeneity is of major significance, not only for identifying novel targets for cancer prevention and treatment, but also for clinical management and patient stratification for targeted therapies.

Transcriptional suppression of microRNA-27a contributes to laryngeal cancer differentiation via GSK-3β-involved Wnt/β-catenin pathway

miR-27a regulates cell differentiation in a variety of diseases. However, whether and how miR-27a participates in laryngeal cancer cell differentiation remains unknown. Therefore, we explored role and molecular mechanism of miR-27a in laryngeal cancer differentiation in the study. We found that miR-27a expression was inversely correlated with laryngeal cancer differentiation degree based on the clinical pathological diagnosis of each patient. miR-27 asignificantly rescued differentiation and inhibited β-catenin, LEF1, OCT4 and SOX2 in Wnt/β-catenin pathway in all-trans-retinoic acid (ATRA)-induced laryngeal cancer cells. Bindings of RARα to miR-27a and miR-27a to GSK-3β were confirmed by ChIP and Luciferase reporter assays, respectively. In conclusion, miR-27a is a negative regulator in laryngeal cancer differentiation. RARα-mediated miR-27a transcriptional inactivation releases the inhibition of miR-27a on GSK-3β leading to laryngeal cancer differentiation through GSK-3β-involved Wnt/β-catenin pathway, suggesting that miR-27a is a usefully therapeutic target at least in ATRA-induced laryngeal cancer differentiation.

Metformin targets gastric cancer stem cells

Gastric cancer is the third leading cause of cancer-related deaths worldwide and has still a poor prognosis. Therefore, new therapeutic strategies are needed: among them, targeting cancer stem cells (CSCs) could offer new opportunities. The aim of our study was to evaluate the anti-tumoural effect of metformin on gastric cancer in vitro and in vivo and especially, to determine whether this molecule could target the gastric CSCs. Metformin effects were evaluated on the proliferation and tumourigenic properties of the gastric CSCs from patient-derived primary tumour xenografts (PDXs) and cancer cell lines (MKN45, AGS and MKN74) in vitro in conventional 2 dimensional (2D) and in 3 dimensional (3D) culture systems, in which only CSCs are able to form tumourspheres and in mouse xenograft models in vivo. Metformin induced a cell cycle arrest, which decreased cell proliferation in the 2D cultures. In a 3D culture system, metformin decreased the number of tumourspheres, revealing its capacity to target the CSCs. This effect was confirmed by the study of the expression of CSC markers (CD44 and Sox2) and differentiation markers (Kruppel-like factor 4 and MUC5AC), which were decreased or increased in response to metformin, respectively. Finally, in vivo treatment of PDXs with metformin led to a tumour growth delay and decreased the self-renewal ability of the CSCs. These results suggest that the use of metformin could represent an efficient strategy to inhibit tumour growth by targeting gastric CSCs.

Prognostic significance of glutathione peroxidase 2 in gastric carcinoma

Increasing evidence suggests that the glutathione peroxidase 2 may actually play important roles in tumorigenesis and progression in various human cancers such as colorectal carcinomas and lung adenocarcinomas. However, the role of glutathione peroxidase 2 in gastric carcinoma remains to be determined. In this study, the expression and prognostic significance of glutathione peroxidase 2 in gastric carcinoma were investigated and the well-known prognostic factor Ki-67 labeling index was also assessed as positive control. Glutathione peroxidase 2 expression levels in the tumor tissue specimens, the matched adjacent normal tissue specimens, and the lymph node metastases of 176 patients with gastric carcinoma were evaluated by quantitative polymerase chain reaction, western blotting, and immunohistochemical staining. The associations between glutathione peroxidase 2 expression levels, as determined by immunohistochemical staining, and multiple clinicopathological characteristics were determined by Pearson's chi-square test and Spearman's correlation analysis. The relationships between glutathione peroxidase 2 expression and other clinicopathological variables and patient prognoses were analyzed further by the Kaplan-Meier method, the log-rank test, and Cox multivariate regression. The quantitative polymerase chain reaction, western blotting, and immunohistochemical staining results showed that glutathione peroxidase 2 expression levels were upregulated in both the primary tumor foci and the lymph node metastases of patients with gastric carcinoma (all p values < 0.05). Furthermore, Pearson's chi-square tests, as well as Spearman's correlation analysis, revealed that glutathione peroxidase 2 expression levels were strongly correlated with the Ki-67 labeling index, differentiation, histological patterns, Lauren classifications, lymph node metastasis, vascular invasion, tumor-node-metastasis stages, Helicobacter pylori infection, and overall survival (all p values < 0.05). Kaplan-Meier analysis, as well as the log-rank test and multivariate Cox regression analysis, showed that multiple clinicopathological risk factors and glutathione peroxidase 2 expression were novel independent prognostic factors for gastric carcinoma (all p values < 0.05). Glutathione peroxidase 2 expression is a novel independent prognostic biomarker for gastric carcinoma that may be used to devise personalized therapeutic regimens and precision treatments for this disease.

ω-3 free fatty acids and all-trans retinoic acid synergistically induce growth inhibition of three subtypes of breast cancer cell lines

All-trans retinoic acid (ATRA), one of vitamin A derivatives, shows greater growth inhibition of breast cancer cell for ER-positive than ER-negative cells, while triple negative breast cancer cell such as MDA-MB-231 cell is poorly responsive to ATRA treatment. In this study, we found that combination of ω-3 free fatty acids (ω-3 FFAs) and ATRA exhibited synergistic inhibition of cell growth in three subtypes (ER⁺ MCF7, HER2⁺ SK-BR-3, Triple negative HCC1806 and MDA-MB-231 cells) of human breast cancer cell lines. The combined treatment of ω-3 FFAs and ATRA resulted in cell cycle arrest. ω-3 FFAs combined with ATRA synergistically provoked cell apoptosis via the caspase signals but not p53. These findings suggest that combined chemotherapy of ω-3 FFAs with ATRA is beneficial for improvement of ATRA sensitivity in breast cancer cells.

Screening the active compounds of Phellodendri Amurensis cortex for treating prostate cancer by high-throughput chinmedomics

Screening the active compounds of herbal medicines is of importance to modern drug discovery. In this work, an integrative strategy was established to discover the effective compounds and their therapeutic targets using Phellodendri Amurensis cortex (PAC) aimed at inhibiting prostate cancer as a case study. We found that PAC could be inhibited the growth of xenograft tumours of prostate cancer. Global constituents and serum metabolites were analysed by UPLC-MS based on the established chinmedomics analysis method, a total of 54 peaks in the spectrum of PAC were characterised in vitro and 38 peaks were characterised in vivo. Among the 38 compounds characterised in vivo, 29 prototype components were absorbed in serum and nine metabolites were identified in vivo. Thirty-four metabolic biomarkers were related to prostate cancer, and PAC could observably reverse these metabolic biomarkers to their normal level and regulate the disturbed metabolic profile to a healthy state. A chinmedomics approach showed that ten absorbed constituents, as effective compounds, were associated with the therapeutic effect of PAC. In combination with bioactivity assays, the action targets were also predicted and discovered. As an illustrative case study, the strategy was successfully applied to high-throughput screening of active compounds from herbal medicine.

Identifying and targeting cancer stem cells in the treatment of gastric cancer

Current treatment regimens for gastric cancer are not adequate. Cancer stem cells (CSCs) may be a key driving factor for growth and metastasis of this tumor type. In contrast to the conventional clonal evolution hypothesis, CSCs can initiate tumor formation, self‐renew, and differentiate into tumor‐propagating cells. Because gastric cancer can originate from CSCs, it is necessary to review current targets of signaling pathways for CSCs in gastric cancer that are being studied in clinical trials. These pathways are known to regulate the self‐renewal and differentiation process in gastric CSCs. A better understanding of the clinical results of trials that target gastric CSCs will lead to better outcomes for patients with gastric cancer. Cancer 2017;123:1303–1312. © 2017 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

Cancer stem cells may be a key driving factor in the growth and metastasis of gastric cancer. Because gastric cancer can originate from cancer stem cells, it is necessary to review current targets of signaling pathways for cancer stem cells in gastric cancer that are being studied in clinical trials.

Predictive Value of Stemness Factor Sox2 in Gastric Cancer Is Associated with Tumor Location and Stage

Cancer stem cells (CSCs) are thought to be the "root" of cancer. Although stemness-related factors ALDH1A1 and Sox2 have been used as markers to identify gastric CSCs, the expression pattern and significance of these factors in gastric cancer have not been sufficiently demonstrated. In this study, the expressions of ALDH1A1 and Sox2 were detected by immunohistochemistry in 122 gastric cancer specimens. And the correlation between Sox2 or ALDH1A1 expression and clinicopathological parameters and overall survival data were analyzed. The positive rate of ALDH1A1 expression was 60%, but there was no significant difference between survival rates of ALDH1A1-positive and ALDH1A1-negative patients. Sox2 was expressed in 42% of specimens and was associated with poor prognosis of patients (P = 0.015). Stratified analysis showed that Sox2 expression correlated with shorter lifespan only in patients with cardiac gastric cancers (P = 0.002) or stage I or II gastric cancers (P = 0.002); but not in patients with non-cardiac cancers (P = 0.556) or stage III or IV gastric cancers (P = 0.121). Analysis on a database cohort validated the correlation between Sox2 expression and poor prognosis in stage II cancer. Also, expression of Sox2 was associated with lymphnode metastasis in patients with cardiac gastric cancer (P = 0.037). A multivariate analysis revealed that Sox2 was an independent prognostic factor in cardiac gastric cancer. Our results indicate that predictive value of Sox2 in gastric cancer is associated with cardiac cancer location and with early cancer stages (I and II).

Use of retinoic acid/aldehyde dehydrogenase pathway as potential targeted therapy against cancer stem cells

A large number of studies have investigated possible drug resistance mechanisms of cancer cells and suggested strategies to overcome it. In this review, we outline the role and function of aldehyde dehydrogenase (ALDH) activity in multiple cellular functions and in cancer stem cells (CSCs) and focus on the role of retinoic acid (RA), one of the products of ALDH isozymes. We discuss our observation that ATRA and other RAs can suppress ALDH activity and decrease different ALDH isozyme proteins and result in detrimental effects on cell proliferation, invasion and chemotherapy sensitivity. We review the known uses of different RAs in the treatment of cancers. We review the use of RAs in combination with chemo-/radiotherapy and the major signaling pathways affected in different tumor types. We provide follow-up on studies that may have used our prior observation with the aim of targeting the CSCs. We conclude with summary of the findings and potential impact of published studies on future use of RAs in the targeting of CSCs and drug resistance.

The effect of several intertrial intervals on the 1 Hz interference effect

Gynecologic cancers cause over 600,000 deaths annually in women worldwide. The development of chemoresistance after initial rounds of chemotherapy contributes to tumor relapse and death due to gynecologic malignancies. In this regard, cancer stem cells (CSCs), a subpopulation of stem cells with the ability to undergo self-renewal and clonal evolution, play a key role in tumor progression and drug resistance. Aldehyde dehydrogenases (ALDH) are a group of enzymes shown to be robust CSC markers in gynecologic and other malignancies. These enzymes also play functional roles in CSCs, including detoxification of aldehydes, scavenging of reactive oxygen species (ROS), and retinoic acid (RA) signaling, making ALDH an attractive therapeutic target in various clinical scenarios. In this review, we discuss the critical roles of the ALDH in driving stemness in different gynecologic malignancies. We review inhibitors of ALDH, both general and isoform-specific, which have been used to target CSCs in gynecologic cancers. Many of these inhibitors have been shown to be effective in preclinical models of gynecologic malignancies, supporting further development in the clinic. Furthermore, ALDH inhibitors, including 673A and CM037, synergize with chemotherapy to reduce tumor growth. Thus, ALDH-targeted therapies hold promise for improving patient outcomes in gynecologic malignancies.