Coordinated expression of REG4 and aldehyde dehydrogenase 1 regulating tumourigenic capacity of diffuse-type gastric carcinoma-initiating cells is inhibited by TGF-β

Dual-responsive near-infrared turn-on fluorescent probe for cancer stem cell-specific visualization

Aldehyde dehydrogenase 1A1 (ALDH1A1) stands out as one of the most reliable intracellular biomarkers for stem cells because it is expressed in both cancer stem cells (CSCs) and normal somatic stem cells (NSCs). Although several turn-on fluorescent probes for ALDH1A1 have been developed to visualize CSCs in cancer cells, the discrimination of CSCs from NSCs is difficult. We here report an AND-type dual-responsive fluorescent probe, CHO_βgal, the near-infrared fluorescence of which can be turned on after responding to both ALDH1A1 and β-galactosidase. The AND-type dual responsiveness enables CSCs to be clearly visualized, whereas NSCs are non-emissive in microscopy. CSC-positive metastasis model lungs were successfully discriminated from normal lungs in ex vivo staining experiments using CHO_βgal, whereas the single-input ALDH1A1-responsive probe failed to achieve this discrimination owing to pronounced false-positive fluorescence output from lung NSCs. In tissue slice staining experiments, even in the presence of adjacent normal tissues, the peripheral region-specific localization of CSCs was clear. The versatility of CHO_βgal holds promise not only as a fundamental in vitro research tool for visualizing CSCs but also as a valuable asset in practical tissue staining diagnosis, significantly contributing to the assessment of cancer malignancy.

Tumor cell stemness in gastrointestinal cancer: regulation and targeted therapy

The cancer stem cells are a rare group of self-renewable cancer cells capable of the initiation, progression, metastasis and recurrence of tumors, and also a key contributor to the therapeutic resistance. Thus, understanding the molecular mechanism of tumor stemness regulation, especially in the gastrointestinal (GI) cancers, is of great importance for targeting CSC and designing novel therapeutic strategies. This review aims to elucidate current advancements in the understanding of CSC regulation, including CSC biomarkers, signaling pathways, and non-coding RNAs. We will also provide a comprehensive view on how the tumor microenvironment (TME) display an overall tumor-promoting effect, including the recruitment and impact of cancer-associated fibroblasts (CAFs), the establishment of an immunosuppressive milieu, and the induction of angiogenesis and hypoxia. Lastly, this review consolidates mainstream novel therapeutic interventions targeting CSC stemness regulation.

An individualized stemness-related signature to predict prognosis and immunotherapy responses for gastric cancer using single-cell and bulk tissue transcriptomes

BACKGROUND

Currently, many stemness-related signatures have been developed for gastric cancer (GC) to predict prognosis and immunotherapy outcomes. However, due to batch effects, these signatures cannot accurately analyze patients one by one, rendering them impractical in real clinical scenarios. Therefore, we aimed to develop an individualized and clinically applicable signature based on GC stemness.

METHODS

Malignant epithelial cells from single-cell RNA-Seq data of GC were used to identify stemness-related signature genes based on the CytoTRACE score. Using two bulk tissue datasets as training data, the enrichment scores of the signature genes were applied to classify samples into two subtypes. Then, using the identified subtypes as criteria, we developed an individualized stemness-related signature based on the within-sample relative expression orderings of genes.

RESULTS

We identified 175 stemness-related signature genes, which exhibited significantly higher AUCell scores in poorly differentiated GCs compared to differentiated GCs. In training datasets, GC samples were classified into two subtypes with significantly different survival times and genomic characteristics. Utilizing the two subtypes, an individualized signature was constructed containing 47 gene pairs. In four independent testing datasets, GC samples classified as high risk exhibited significantly shorter survival times, higher infiltration of M2 macrophages, and lower immune responses compared to low-risk samples. Moreover, the potential therapeutic targets and corresponding drugs were identified for the high-risk group, such as CD248 targeted by ontuxizumab.

CONCLUSIONS

We developed an individualized stemness-related signature, which can accurately predict the prognosis and efficacy of immunotherapy for each GC sample.

ALDEFLUOR activity, ALDH isoforms, and their clinical significance in cancers

High aldehyde dehydrogenase (ALDH) activity is a metabolic feature of adult stem cells and various cancer stem cells (CSCs). The ALDEFLUOR system is currently the most commonly used method for evaluating ALDH enzyme activity in viable cells. This system is applied extensively in the isolation of normal stem cells and CSCs from heterogeneous cell populations. For many years, ALDH1A1 has been considered the most important subtype among the 19 ALDH family members in determining ALDEFLUOR activity. However, in recent years, studies of many types of normal and tumour tissues have demonstrated that other ALDH subtypes can also significantly influence ALDEFLUOR activity. In this article, we briefly review the relationships between various members of the ALDH family and ALDEFLUOR activity. The clinical significance of these ALDH isoforms in different cancers and possible directions for future studies are also summarised.

The origin of gastric cancer stem cells and their effects on gastric cancer: Novel therapeutic targets for gastric cancer

Gastric cancer (GC) is one of the most prevalent malignancies and the most common causes of cancer-related mortality worldwide. Furthermore, the prognosis of advanced GC remains poor even after surgery combined with chemoradiotherapy. As a small group of cells with unlimited differentiation and self-renewal ability in GC, accumulating evidence shows that GC stem cells (GCSCs) are closely associated with the refractory characteristics of GC, such as drug resistance, recurrence, and metastasis. With the extensive development of research on GCSCs, GCSCs seem to be promising therapeutic targets for GC. However, the relationship between GCSCs and GC is profound and intricate, and its mechanism of action is still under exploration. In this review, we elaborate on the source and key concepts of GCSCs, systematically summarize the role of GCSCs in GC and their underlying mechanisms. Finally, we review the latest information available on the treatment of GC by targeting GCSCs. Thus, this article may provide a theoretical basis for the future development of the novel targets based on GCSCs for the treatment of GC.

REG4 promotes the proliferation and anti-apoptosis of cancer

Regenerating islet-derived 4 (REG4) gene was discovered by high-throughput sequencing of ulcerative colitis cDNA libraries. REG4 is involved in infection and inflammation by enhancing macrophage polarization to M2, via activation of epidermal growth factor receptor (EGFR)/Akt/cAMP-responsive element binding and the killing inflammatory Escherichia coli, and closely linked to tumorigenesis. Its expression was transcriptionally activated by caudal type homeobox 2, GATA binding protein 6, GLI family zinc finger 1, SRY-box transcription factor 9, CD44 intracytoplasmic domain, activating transcription factor 2, and specificity protein 1, and translationally activated by miR-24. REG4 can interact with transmembrane CD44, G protein-coupled receptor 37, mannan and heparin on cancer cells. Its overexpression was observed in gastric, colorectal, pancreatic, gallbladder, ovarian and urothelial cancers, and is closely linked to their aggressive behaviors and a poor prognosis. Additionally, REG4 expression and recombinant REG4 aggravated such cellular phenotypes as tumorigenesis, proliferation, anti-apoptosis, chemoradioresistance, migration, invasion, peritoneal dissemination, tumor growth, and cancer stemness via EGFR/Akt/activator protein-1 and Akt/glycogen synthase kinase three β/β-catenin/transcription factor 4 pathways. Sorted REG4-positive deep crypt secretory cells promote organoid formation of single Lgr5 (+) colon stem cells by Notch inhibition and Wnt activation. Histologically, REG4 protein is specifically expressed in neuroendocrine tumors and signet ring cell carcinomas of the gastrointestinal tract, pancreas, ovary, and lung. It might support the histogenesis of gastric intestinal–metaplasia–globoid dysplasia–signet ring cell carcinoma. In this review, we summarized the structure, biological functions, and effects of REG4 on inflammation and cancer. We conclude that REG4 may be employed as a biomarker of tumorigenesis, subsequent progression and poor prognosis of cancer, and may be a useful target for gene therapy.

Aldehyde Dehydrogenase 1 in Gastric Cancer

Gastric cancer (GC) is a disease that threatens human health. It is thus crucial to clarify the mechanisms involved in GC development and discover diagnostic biomarkers and therapeutics. As a cancer stem cell marker, aldehyde dehydrogenase 1 (ALDH1) is involved in the development, progression, and treatment of GC. This review evaluated the prognostic value of ALDH1 and explored its mechanism of action in GC. Importantly, ALDH1 is an informative biomarker in clinical practice as it has specific relationships with indicators, such as metastasis and overall survival. Additionally, ALDH1 interacts with genes and exhibits properties that mimic stem cell characteristics amongst other mechanisms employed in the occurrence and progression of GC. Our results, therefore, provide evidence of possible clinical utility of ALDH1 as a GC therapeutic target.

Reg4 Interacts with CD44 to Regulate Proliferation and Stemness of Colorectal and Pancreatic Cancer Cells

Regenerating Gene 4 (Reg4) is highly upregulated in gastrointestinal (GI) malignancies including colorectal and pancreatic cancers. Numerous studies demonstrated an association between higher Reg4 expression and tumor aggressiveness, intrinsic resistance to apoptotic death, and poor outcomes from GI malignancies. However, the precise receptor and underlying signaling mechanism have remained unknown. Although we previously reported a Reg4-mediated induction of EGFR activity in colorectal cancer cells, a direct interaction between Reg4 and EGFR was not observed. This study is focused on identifying the cell surface binding partner of Reg4 and dissecting its role in colorectal cancer and pancreatic cancer growth and stem cell survival. In vitro models of human colorectal cancer and pancreatic cancer were used to evaluate the results. Results of this study find: (i) Reg4 interacts with CD44, a transmembrane protein expressed by a population of colorectal cancer and pancreatic cancer cells; (ii) Reg4 activates regulated intramembrane proteolysis of CD44 resulting in γ-secretase-mediated cleavage and release of the CD44 intracytoplasmic domain (CD44ICD) that functions as a transcriptional activator of D-type cyclins involved in the regulation of cancer cell proliferation and Klf4 and Sox2 expression involved in regulating pluripotency of cancer stem cells; and (iii) Reg4 significantly increases colorectal cancer and pancreatic cancer cell proliferation and their clonogenic potential in stem cell assays.

IMPLICATIONS

These results suggest that pro-proliferative and pro-stemness effects of Reg4 are mediated through γ-secretase-mediated CD44/CD44ICD signaling, hence strategies to disrupt Reg4-CD44-γ-secretase-CD44ICD signaling axis may increase cancer cell susceptibility to chemo- and radiotherapeutics.

Molecular mechanism of therapeutic approaches for human gastric cancer stem cells

Gastric cancer (GC) is a primary cause of cancer-related mortality worldwide, and even after therapeutic gastrectomy, survival rates remain poor. The presence of gastric cancer stem cells (GCSCs) is thought to be the major reason for resistance to anticancer treatment (chemotherapy or radiotherapy), and for the development of tumor recurrence, epithelial–mesenchymal transition, and metastases. Additionally, GCSCs have the capacity for self-renewal, differentiation, and tumor initiation. They also synthesize antiapoptotic factors, demonstrate higher performance of drug efflux pumps, and display cell plasticity abilities. Moreover, the tumor microenvironment (TME; tumor niche) that surrounds GCSCs contains secreted growth factors and supports angiogenesis and is thus responsible for the maintenance of the growing tumor. However, the genesis of GCSCs is unclear and exploration of the source of GCSCs is essential. In this review, we provide up-to-date information about GCSC-surface/intracellular markers and GCSC-mediated pathways and their role in tumor development. This information will support improved diagnosis, novel therapeutic approaches, and better prognosis using GCSC-targeting agents as a potentially effective treatment choice following surgical resection or in combination with chemotherapy and radiotherapy. To date, most anti-GCSC blockers when used alone have been reported as unsatisfactory anticancer agents. However, when used in combination with adjuvant therapy, treatment can improve. By providing insights into the molecular mechanisms of GCSCs associated with tumors in GC, the aim is to optimize anti-GCSCs molecular approaches for GC therapy in combination with chemotherapy, radiotherapy, or other adjuvant treatment.

Cancer Stem Cells and the Tumor Microenvironment in Gastric Cancer

Gastric cancer (GC) remains one of the leading causes of cancer-related death worldwide. Cancer stem cells (CSCs) might be responsible for tumor initiation, relapse, metastasis and treatment resistance of GC. The tumor microenvironment (TME) comprises tumor cells, immune cells, stromal cells and other extracellular components, which plays a pivotal role in tumor progression and therapy resistance. The properties of CSCs are regulated by cells and extracellular matrix components of the TME in some unique manners. This review will summarize current literature regarding the effects of CSCs and TME on the progression and therapy resistance of GC, while emphasizing the potential for developing successful anti-tumor therapy based on targeting the TME and CSCs.

Reg4 regulates pancreatic regeneration following pancreatitis via modulating the Notch signaling

Pancreatic regeneration after acute pancreatitis is critical in the normal restoration of pancreatic exocrine function, the inhibition of which can cause severe complications including pancreatic exocrine insufficiency. However, the regulators of pancreatic regeneration and the underlying mechanisms remain uncovered. Here, using the inducible Tet-on system, we found that regenerating family member 4 (Reg4) knockdown significantly impaired pancreatic regeneration after pancreatitis. Both acinar-to-ductal metaplasia and the resolution of pancreatitis during regeneration were affected by Reg4 knockdown. Further investigations confirmed that Reg4 exerted its function through regulating Notch activation both in vitro and in vivo. Our study revealed Reg4 as a new regulator and potential therapeutic target for pancreatic regeneration.

Clinicopathological Significance and Prognostic Implications of REG4 Immunohistochemical Expression in Colorectal Cancer

Background and objectives: The present study aimed to evaluate the clinicopathological significance and prognostic implications of REG4 immunohistochemical expression in colorectal cancer (CRC). Materials and Methods: We performed immunohistochemical analysis for REG4 cytoplasmic expression in 266 human CRC tissues. Correlations between REG4 expression, clinicopathological characteristics, and survival were investigated in CRC. Results: REG4 was expressed in 84 of 266 CRC tissues (31.6%). REG4 expression was significantly more frequent in the right colon than that in the left colon and rectum (p = 0.002). However, we observed no significant correlation between REG4 expression and other clinicopathological parameters. REG4 expression was significantly higher in CRCs with low stroma than in those with high stroma (p = 0.006). In addition, REG4 was more frequently expressed in CRCs with the mucinous component than in those without it (p < 0.001). There was no significant correlation between REG4 expression and overall recurrence-free survival (p = 0.132 and p = 0.480, respectively). Patients with REG4 expression showed worse overall and recurrence-free survival in the high-stroma subgroup (p = 0.001 and p = 0.017, respectively), but no such correlation was seen in the low stroma subgroup (p = 0.232 and p = 0.575, respectively). Conclusions: REG4 expression was significantly correlated with tumor location, amount of stroma, and mucinous component in CRCs. In patients with high stroma, REG4 expression was significantly correlated with poor overall and recurrence-free survival.

LncRNA FEZF1-AS1 Modulates Cancer Stem Cell Properties of Human Gastric Cancer Through miR-363-3p/HMGA2

Gastric cancer (GC) is a leading cause of cancer-related death with poor prognosis. Growing evidence has shown that long noncoding ribonucleic acid (lncRNA) FEZ family zinc finger 1 antisense RNA 1(FEZF1-AS1), an "oncogene," regulates tumor progression and supports cancer stem cell. However, the tumorigenic mechanism of FEZF1-AS1 on gastric cancer stem cell (GCSC) is yet to be investigated. Here, we discovered that FEZF1-AS1 was upregulated in GC tissues and cell lines. Knockdown of FEZF1-AS1 inhibited sphere formation and decreased expression of stem factors and markers. Moreover, FEZF1-AS1 silence also suppressed cell proliferation, viability, invasion, and migration of GCSCs. MiR-363-3p is used as a target of FEZF1-AS1, because its expression was suppressed by FEZF1-AS1 in GCSCs. FEZF1-AS1 could sponge miR-363-3p and increased the expression of high-mobility group AT-hook 2 (HMGA2). The expression of FEZF1-AS1 and miR-363-3p, as well as that of miR-363-3p and HMGA2, was negatively correlated in GC tissues. Finally, FEZF1-AS1 contributed to promotion of GCSCs progression partially through inhibition of miR-363-3p. Subcutaneous xenotransplanted tumor model revealed that silence of FEZF1-AS1 suppressed in vivo tumorigenic ability of GSCS via downregulation of HMGA2. In general, our findings clarified the critical regulatory role of FEZF1-AS1/miR-363-3p/HMGA2 axis in GCSC progression, providing a potential therapeutic target for GC.

CD133+/CD166+ human gastric adenocarcinoma cells present the properties of neoplastic stem cells and emerge more malignant features

AIMS

The recurrence and metastasis of gastric cancer has always been an important factor affecting the prognosis of gastric cancer. Cancer stem cells can promote the recurrence and growth of gastric cancer. The identification and isolation of gastric cancer stem cells contribute to the origin, progress and treatment strategy of gastric cancer. The aim of this study was to identify and isolate gastric cancer stem cells, and provide targets for the treatment of gastric cancer.

METHODS

Magnetic-activated cell sorting was used to isolate CD133+/CD166+ cell populations from human gastric adenocarcinoma cell lines (BGC-823 and SGC-7901). Sphere formation, cell proliferation, resistance to chemotherapy, colony formation, migration invasion and tumorigenicity in vivo of these cell populations were evaluated. Moreover, RT-qPCR and Western blot were used to investigate the expression level of the stem cell markers Nanog, Sox2, Oct-4, and c-Myc.

RESULTS

CD133+/CD166+ cell subpopulations presented more malignant features than CD133-/CD166-, CD133-/CD166+, CD133+/CD166- cell populations and parental cells. Moreover, the mRNA and protein expression level of Oct-4 and c-Myc were higher in CD133+/CD166+ cells than in parental cells or other cell populations.

CONCLUSION

The CD133+/CD166+ populations of human gastric cancer cell lines BGC-823 and SGC-7901 have cancer stem cell characteristics.

The Role of Cancer Stem Cells in Drug Resistance in Gastroesophageal Junction Adenocarcinoma

Gastroesophageal junction adenocarcinomas (GEJA) have dramatically increased in incidence in the western world since the mid-20^th century. Their prognosis is poor, and conventional anti-cancer therapies do not significantly improve survival outcomes. These tumours are comprised of a heterogenous population of both cancer stem cells (CSC) and non-CSCs, with the former playing a crucial role in tumorigenesis, metastasis and importantly drug resistance. Due to the ability of CSCs to self-replicate indefinitely, their resistance to anti-cancer therapies poses a significant barrier to effective treatment of GEJA. Ongoing drug development programmes aim to target and eradicate CSCs, however their characterisation and thus identification is difficult. CSC regulation is complex, involving an array of signalling pathways, which are in turn influenced by a number of entities including epithelial mesenchymal transition (EMT), microRNAs (miRNAs), the tumour microenvironment and epigenetic modifications. Identification of CSCs commonly relies on the expression of specific cell surface markers, yet these markers vary between different malignancies and indeed are often co-expressed in non-neoplastic tissues. Development of targeted drug therapies against CSCs thus requires an understanding of disease-specific CSC markers and regulatory mechanisms. This review details the current knowledge regarding CSCs in GEJA, with particular emphasis on their role in drug resistance.

The Clinical Significance and Mechanisms of REG4 in Human Cancers

Regenerating islet-derived type 4 (REG4), a member of the calcium-dependent lectin gene superfamily, is abnormally expressed in various cancers, such as colorectal, gastric, gallbladder, pancreatic, ovarian, prostate, and lung cancer. REG4 is associated with a relatively unfavorable prognosis and clinicopathologic features in cancers, including advanced tumor and nodal stage, histological differentiation, and liver and peritoneal metastasis. Moreover, REG4-positive cancer cells show more frequent resistance to chemoradiotherapy, especially 5-FU-based chemotherapy. REG4 participates in many aspects of carcinogenesis, including cell proliferation, apoptosis, cell cycle, invasion, metastasis, and drug resistance. The underlying mechanisms are complex and involve a series of signaling mediators and multiple pathways. Thus, REG4 may be a potential diagnostic and prognostic biomarker as well as a candidate therapeutic target in cancer patients. In this review, we systematically summarize the advances about the clinical significance, biological functions, and mechanisms underlying REG4 in cancer to provide new directions for future cancer research.

Expression profile of intestinal stem cell and cancer stem cell markers in gastric cancers with submucosal invasion

Cancer stem cells (CSCs) are believed to be responsible for tumor growth, invasion, and metastasis. Submucosal invasion, which greatly enhances metastasis risk, is a critical step in gastric cancer (GC) progression. To identify stem cell-related markers associated with submucosal invasion and lymph node (LN) metastasis in GCs, we investigated the expression of candidate CSC markers (CD133, CD44, and ALDH1A) and intestinal stem cell (ISC) markers (EPHB2, OLFM4, and LGR5) in early GCs that manifested submucosal invasion. We discovered that EPHB2 and LGR5 expression was frequently confined to the basal area of the lamina propria (basal pattern) in mucosal cancer, and the proportion of stem cell marker-positive cells substantially increased during submucosal invasion. CD44 expression showed a focal pattern, ALDH1A was predominantly expressed diffusely, and there was no expansion of CD44 or ALDH1A expression in the submucosal cancer cells. Unexpectedly, no CSC markers showed any associations with LN metastasis, and only loss of EPHB2 expression was associated with increased LN metastasis. Treatment of RSPO2, a niche factor, along with Wnt 3a, to GC cells led to increased EPHB2 and LGR5 mRNA levels. RNA in situ hybridization confirmed specific RSPO2 expression in the smooth muscle cells of the muscularis mucosa, suggesting that RSPO2 is responsible for the increased expression of ISC markers in GC cells at the basal areas. In summary, no stem cell markers were associated with increased LN metastasis in early GCs. Conversely, isolated EPHB2 expression was associated with lower LN metastasis. EPHB2 and LGR5 showed a basal distribution pattern along with enhanced expression in submucosal invading cells in early GCs, which was induced by a niche factor, RSPO2, from the muscularis mucosa.

CRISPR screens identify cholesterol biosynthesis as a therapeutic target on stemness and drug resistance of colon cancer

Cancer stem cells (CSCs) are responsible for tumor progression, recurrence, and drug resistance. To identify genetic vulnerabilities of colon cancer, we performed targeted CRISPR dropout screens comprising 657 Drugbank targets and 317 epigenetic regulators on two patient-derived colon CSC-enriched spheroids. Next-generation sequencing of pooled genomic DNAs isolated from surviving cells yielded therapeutic candidates. We unraveled 44 essential genes for colon CSC-enriched spheroids propagation, including key cholesterol biosynthetic genes (HMGCR, FDPS, and GGPS1). Cholesterol biosynthesis was induced in colon cancer tissues, especially CSC-enriched spheroids. The genetic and pharmacological inhibition of HMGCR/FDPS impaired self-renewal capacity and tumorigenic potential of the spheroid models in vitro and in vivo. Mechanistically, HMGCR or FDPS depletion impaired cancer stemness characteristics by activating TGF-β signaling, which in turn downregulated expression of inhibitors of differentiation (ID) proteins, key regulators of cancer stemness. Cholesterol and geranylgeranyl diphosphate (GGPP) rescued the growth inhibitory and signaling effect of HMGCR/FDPS blockade, implying a direct role of these metabolites in modulating stemness. Finally, cholesterol biosynthesis inhibitors and 5-FU demonstrated antitumor synergy in colon CSC-enriched spheroids, tumor organoids, and xenografts. Taken together, our study unravels novel genetic vulnerabilities of colon CSC-enriched spheroids and suggests cholesterol biosynthesis as a potential target in conjunction with traditional chemotherapy for colon cancer treatment.

Identification of cancer stem cell-related biomarkers in intestinal-type and diffuse-type gastric cancer by stemness index and weighted correlation network analysis

Background

Cancer stem cells (CSCs) play an important role in drug resistance, recurrence, and metastasis of tumors. Considering the heterogeneity of tumors, this study aimed to explore the key genes regulating stem cells in intestinal-type and diffuse-type gastric cancer.

Methods

RNA-seq data and related clinical information were downloaded from The Cancer Genome Atlas (TCGA). WGCNA was used to clustered differentially expressed genes with similar expression profiles to form modules. Furtherly, based on the mRNA expression-based stemness index (mRNAsi), significant modules and key genes were identified. Next, the expression of key genes was further verified by the Oncomine database.

Results

MRNAsi scores of GC were significantly higher than that of normal tissue. Additionally, mRNAsi scores of intestinal-type GC (IGC) were significantly higher than that of diffuse-type GC (DGC). WGCNA showed that the blue module of IGC and the brown module of DGC were both the most significantly associated with mRNAsi. We screened out 16 and 43 key genes for IGC and DGC and found that these genes were closely related, respectively. Functional analysis showed the relationship between the key genes confirmed in the Oncomine database and the fate of cells.

Conclusions

In this study, 16 and 43 genes related to the characteristics of CSCs were identified in IGC and DGC, respectively. These genes were both associated with cell cycle, which could serve as therapeutic targets for the inhibition of stem cells from both types of GC.

Cancer Stem Cells and Its Role in Angiogenesis and Vasculogenic Mimicry in Gastrointestinal Cancers

Cancer stem cells (CSCs) are able to promote initiation, survival and maintenance of tumor growth and have been involved in gastrointestinal cancers (GICs) such as esophageal, gastric and colorectal. It is well known that blood supply facilitates cancer progression, recurrence, and metastasis. In this regard, tumor-induced angiogenesis begins with expression of pro-angiogenic molecules such as vascular endothelial growth factor (VEGF), which in turn lead to neovascularization and thus to tumor growth. Another pattern of blood supply is called vasculogenic mimicry (VM). It is a reminiscent of the embryonic vascular network and is carried out by CSCs that have the capability of transdifferentiate and form vascular-tube structures in absence of endothelial cells. In this review, we discuss the role of CSCs in angiogenesis and VM, since these mechanisms represent a source of tumor nutrition, oxygenation, metabolic interchange and facilitate metastasis. Identification of CSCs mechanisms involved in angiogenesis and VM could help to address therapeutics for GICs.

Tumour Cell Secretome in Chemoresistance and Tumour Recurrence

Chemoresistance is a major factor driving tumour relapse and the high rates of cancer-related deaths. Understanding how cancer cells overcome chemotherapy-induced cell death is critical in promoting patient survival. One emerging mechanism of chemoresistance is the tumour cell secretome (TCS), an array of protumorigenic factors released by tumour cells. Chemotherapy exposure can also alter the composition of the TCS, known as therapy-induced TCS, and can promote tumour relapse and the formation of an immunosuppressive tumour microenvironment (TME). Here, we outline how the TCS can protect cancer cells from chemotherapy-induced cell death. We also highlight recent evidence describing how therapy-induced TCS can impact cancer stem cell (CSC) expansion and tumour-associated immune cells to enable tumour regrowth and antitumour immunity.

Regulation of REG4 Expression and Prediction of 5-Fluorouracil Sensitivity by CDX2 in Ovarian Mucinous Carcinoma

BACKGROUND/AIM

The biological importance of the caudal-related homeobox transcription factor CDX2 in acquiring resistance to anticancer drugs has been studied in ovarian mucinous carcinoma. CDX2 promotes the expression of multidrug resistance 1 (MDR1) and confers resistance to paclitaxel. The regenerating islet-derived family member 4 (REG4) gene is a potential target gene of CDX2. In this study, we investigated the relationship between the expression of CDX2 and Reg IV and the regulation of Reg IV expression and examined novel chemotherapeutic regimens.

MATERIALS AND METHODS

The regulation of Reg IV expression by CDX2 and sensitivity of 5-fluorouracil (5-FU) were evaluated using ovarian mucinous cancer cell lines.

RESULTS

The correlation of CDX2 with Reg IV expression was demonstrated in ovarian mucinous carcinoma. Reg IV expression was enhanced by transfection of CDX2 and was suppressed by inhibition of CDX2 expression. OMC-3 cells with ectopically overexpressed CDX2 showed enhanced apoptosis and sensitivity to 5-FU.

CONCLUSION

CDX2 promotes resistance to paclitaxel and sensitivity to 5-FU. Novel 5-FU-based chemotherapy based on CDX2 may be used in ovarian mucinous carcinoma.

Single-chain Antibody Against Reg4 Suppresses Gastric Cancer Cell Growth and Enhances 5-FU-induced Cell Death in vitro

BACKGROUND

Regenerating islet-derived gene family member 4 (Reg4), a well-investigated growth factor in the regenerative pancreas, has recently been reported to be highly associated with a majority of gastrointestinal cancers. Pathological hyper-expression or artificial over-expression of Reg4 causes acceleration of tumor growth, migration, and resistance to chemotherapeutic 5-Fluorouracil (5-FU). Until now, no method has been successfully established for eliminating the effects of Reg4 protein.

METHODS

This study reports the production of an engineered immunoglobin, a single-chain variable fragment (scFv-Reg4), to specifically bind Reg4 and block the bioactivity. The complementary-determining regions (CDRs) against Reg4 were assigned using MOE and ZDOCK servers. The binding affinity (KD) was determined by bio-layer interferometry (BLI). MKN45 and AGS cell proliferation was determined by Thiazolyl blue tetrazolium bromide (MTT) method and the cell apoptosis was detected by flow cytometry assay.

RESULTS

The KD of scFv-Reg4 to Reg4 was determined to be 1.91×10-8. In MKN45 and AGS cell lines, scFv- Reg4 depressed Reg4-stimulated cell proliferation and the inhibitory rates were 27.7±1.5% and 17.3±2.6%, respectively. Furthermore, scFv significantly enhanced 5-FU-induced cell death, from 23.0±1.0% to 28.4±1.2% in MKN45 and 28.2±0.7% to 36.6±0.6% in AGS cells. Treatment with scFv alone could lyse cancer cells to a certain extent, but no significance has been observed.

CONCLUSION

The single-chain antibody (scFv-Reg4) significantly inhibited gastric cancer cell proliferation and synergistically enhanced the lethal effect of 5-FU. Thus, traditional chemo-/radio- therapeutics supplemented with scFv-Reg4 may provide advances in the strategy for gastrointestinal cancer treatment.

Gastric Cancer Stem Cells: Current Insights into the Immune Microenvironment and Therapeutic Targets

Gastric cancer (GC) is a leading cause of cancer-related death worldwide. Cancer stem cells (CSCs) are known to be involved in chemotherapy resistance and the development of metastases. Although CSCs harbor self-renewal and tumorigenic abilities, the immune microenvironment surrounding CSCs provides various factors and supports the maintenance of CSC properties. The current review summarizes the accumulating findings regarding the relationship between the immune microenvironment and gastric CSCs (GCSCs), which will support the possibility of developing novel therapeutic strategies for targeting GCSCs.

The role of hedgehog signaling in gastric cancer: molecular mechanisms, clinical potential, and perspective

Patients with advanced gastric cancer usually have a poor prognosis and limited therapeutic options. Overcoming this challenge requires novel targets and effective drugs. The Hedgehog (Hh) signaling pathway plays a crucial role in the development of the gastrointestinal tract and maintenance of the physiologic function of the stomach. Aberrantly activated Hh signaling is implicated in carcinogenesis as well as maintenance of cancer stem cells. Somatic mutations in the components of Hh signaling (PTCH1 and SMO) have been shown to be a major cause of basal cell carcinoma, and dozens of Hh inhibitors have been developed. To date, two inhibitors (GDC-0449 and LDE225) have been approved by the U.S. Food and Drug Administration to treat basal cell carcinoma and medulloblastoma. Here, we review the role of the Hh signaling in the carcinogenesis and progression of gastric cancer and summarize recent findings on Hh inhibitors in gastric cancer. Hedgehog signaling is often aberrantly activated and plays an important role during inflammation and carcinogenesis of gastric epithelial cells. Further study of the precise mechanisms of Hh signaling in this disease is needed for the validation of therapeutic targets and evaluation of the clinical utility of Hh inhibitors for gastric cancer.

Four Decades After the Discovery of Regenerating Islet-Derived (Reg) Proteins: Current Understanding and Challenges

Regenerating islet-derived (Reg) proteins have emerged as multifunctional agents with pro-proliferative, anti-apoptotic, differentiation-inducing and bactericidal properties. Over the last 40 years since first discovered, Reg proteins have been implicated in a gamut of maladies including diabetes, various types of cancer of the digestive tract, and Alzheimer disease. Surprisingly though, a consensus is still absent on the regulation of their expression, and molecular underpinning of their function. Here, we provide a critical appraisal of recent findings in the field of Reg protein biology. Specifically, the structural characteristics are reviewed particularly in connection with established or purported functions of different members of the Reg family. Moreover, Reg expression patterns in different tissues both under normal and pathophysiological conditions are summarized. Putative receptors and cascades reported to relay Reg signaling inciting cellular responses are presented aiming at a better appreciation of the biological activities of the distinct Reg moieties. Challenges are also discussed that have hampered thus far the rapid progress in this field such as the use of non-standard nomenclature for Reg molecules among various research groups, the existence of multiple Reg members with significant degree of homology and possibly compensatory modes of action, and the need for common assays with robust readouts of Reg activity. Coordinated research is warranted going forward, given that several research groups have independently linked Reg proteins to diseased states and raised the possibility that these biomolecules can serve as therapeutic targets and biomarkers.

Expression of cancer stem cell markers is prognostic in metastatic gastroesophageal adenocarcinoma

Gastroesophageal adenocarcinoma is a common and highly lethal malignancy. Cancer stem cells (CSCs) have a key role in the development and progression of metastatic disease. While expression of CSC markers CD44, CD133 and aldehyde dehydrogenase 1 (ALDH1) in locoregional gastroesophageal cancer is known to be associated with poorer clinical outcomes, the significance of CSC marker expression in distal metastatic disease is unknown. We investigated the clinicopathological and prognostic associations of the CSC markers, CD44, CD133, and ALDH1, on metastatic deposits from gastroesophageal adenocarcinomas, and evaluated the association of CSC expression with urokinase-type plasminogen activator receptor (uPAR) expression. Of the 36 patients included in the study, 16 (44%) were positive for CD44, 13 (36%) were positive for CD133, and 26 (72%) were positive for ALDH1. CD44 expression was significantly associated with poorer overall survival (OS) in univariate [hazard ratio (HR) 2.9, 95% confidence interval (CI) 1.3-6.9, p=0.008] and multivariate analyses (HR 2.5, 95%CI 1.1-6.2, p=0.04). ALDH1 expression was significantly associated with poorer OS in univariate (HR 2.4, 95% CI 1.01-5.7, p=0.04) analysis but was not significant in multivariate analysis. Both CD44 and ALDH1 expression were significantly associated with uPAR expression. We found no association between CD133 expression and OS. CD44 expression on metastatic disease from gastroesophageal adenocarcinomas is an independent prognostic marker associated with poorer OS. These results expand current evidence to support the role of CSCs as biomarkers in metastatic gastroesophageal cancer.

The Role of MicroRNAs in the Regulation of Gastric Cancer Stem Cells: A Meta-Analysis of the Current Status

Gastric cancer (GC) remains one of the major causes of cancer-related mortality worldwide. As for other types of cancers, several limitations to the success of current therapeutic GC treatments may be due to cancer drug resistance that leads to tumor recurrence and metastasis. Increasing evidence suggests that cancer stem cells (CSCs) are among the major causative factors of cancer treatment failure. The research of molecular CSC mechanisms and the regulation of their properties have been intensively studied. To date, molecular gastric cancer stem cell (GCSC) characterization remains largely incomplete. Among the GCSC-targeting approaches to overcome tumor progression, recent studies have focused their attention on microRNA (miRNA). The miRNAs are short non-coding RNAs which play an important role in the regulation of numerous cellular processes through the modulation of their target gene expression. In this review, we summarize and discuss recent findings on the role of miRNAs in GCSC regulation. In addition, we perform a meta-analysis aimed to identify novel miRNAs involved in GCSC homeostasis.

Distinct biological characterization of the CD44 and CD90 phenotypes of cancer stem cells in gastric cancer cell lines

Recent study implicates that gastric cancer stem cells (CSCs) are capable of generating multiple types of cells to promote tumor growth and heterogeneity important for the development of gastric cancer. However, knowledge is limited regarding the expression and characteristics of marker-positive gastric CSCs. Therefore, gastric CSCs from a series of human gastric cancer cell lines (SNU-5, SNU-16, BGC-823, PAMC-82, MKN-45, and NCI-N87) using four putative CSC surface markers (CD44, CD90, CD133, and epithelial-cell adhesion molecule) were investigated the underlying mechanisms regulating such subpopulations. Only SNU-5 and SNU-16 exhibited independent co-expression of CD44⁺ and CD90⁺, which exhibited spheroid-colony formation in vitro and tumor formation in immunodeficient mice. Functional studies revealed that CD44⁺ cells were more invasive compared with CD90⁺ cells, whereas CD90⁺ cells exhibited higher levels of proliferation than CD44⁺ cells. Furthermore, serial xenotransplantation in mice of CD44⁺/CD90⁺ cells derived from SNU-5 and SNU-16 revealed rapid growth of CD90⁺ cells in subcutaneous lesions and a high metastatic capacity of CD44⁺ cells in the lung. Mechanistic analyses revealed that CD44⁺ cells underwent epithelial-to-mesenchymal transition (EMT) following acquisition of mesenchymal features, whereas CD90⁺ cells enhanced the activation of retinoblastoma phosphorylation at Ser780 and oncogenic cell cycle regulators. The expression of CD44 and CD90 in gastric cancer tissues was associated with distant metastasis and the differentiation state of tumors. These results demonstrated that CD44 and CD90 are specific biomarkers capable of identifying and isolating metastatic and tumorigenic CSCs through their ability to regulate EMT and the cell cycle in gastric cancer cell lines.

A subset of diffuse-type gastric cancer is susceptible to mTOR inhibitors and checkpoint inhibitors

Background

Mechanistic target of rapamycin (mTOR) pathway is essential for the growth of gastric cancer (GC), but mTOR inhibitor everolimus was not effective for the treatment of GCs. The Cancer Genome Atlas (TCGA) researchers reported that most diffuse-type GCs were genomically stable (GS). Pathological analysis suggested that some diffuse-type GCs developed from intestinal-type GCs.

Methods

We established patient-derived xenograft (PDX) lines from diffuse-type GCs, and searched for drugs that suppressed their growth. Diffuse-type GCs were classified into subtypes by their gene expression profiles.

Results

mTOR inhibitor temsirolimus strongly suppressed the growth of PDX-derived diffuse-type GC-initiating cells, which was regulated via Wnt-mTOR axis. These cells were microsatellite unstable (MSI) or chromosomally unstable (CIN), inconsistent with TCGA report. Diffuse-type GCs in TCGA cohort could be classified into two clusters, and GS subtype was major in cluster I while CIN and MSI subtypes were predominant in cluster II where PDX-derived diffuse-type GC cells were included. We estimated that about 9 and 55% of the diffuse-type GCs in cluster II were responders to mTOR inhibitors and checkpoint inhibitors, respectively, by identifying PIK3CA mutations and MSI condition in TCGA cohort. These ratios were far greater than those of diffuse-type GCs in cluster I or intestinal-type GCs. Further analysis suggested that diffuse-type GCs in cluster II developed from intestinal-type GCs while those in cluster I from normal gastric epithelial cells.

Conclusion

mTOR inhibitors and checkpoint inhibitors might be useful for the treatment of a subset of diffuse-type GCs which may develop from intestinal-type GCs.

Electronic supplementary material

The online version of this article (10.1186/s13046-019-1121-3) contains supplementary material, which is available to authorized users.

Chronic TGF-β exposure drives stabilized EMT, tumor stemness, and cancer drug resistance with vulnerability to bitopic mTOR inhibition

Tumors comprise cancer stem cells (CSCs) and their heterogeneous progeny within a stromal microenvironment. In response to transforming growth factor-β (TGF-β), epithelial and carcinoma cells undergo a partial or complete epithelial-mesenchymal transition (EMT), which contributes to cancer progression. This process is seen as reversible because cells revert to an epithelial phenotype upon TGF-β removal. However, we found that prolonged TGF-β exposure, mimicking the state of in vivo carcinomas, promotes stable EMT in mammary epithelial and carcinoma cells, in contrast to the reversible EMT induced by a shorter exposure. The stabilized EMT was accompanied by stably enhanced stem cell generation and anticancer drug resistance. Furthermore, prolonged TGF-β exposure enhanced mammalian target of rapamycin (mTOR) signaling. A bitopic mTOR inhibitor repressed CSC generation, anchorage independence, cell survival, and chemoresistance and efficiently inhibited tumorigenesis in mice. These results reveal a role for mTOR in the stabilization of stemness and drug resistance of breast cancer cells and position mTOR inhibition as a treatment strategy to target CSCs.

Novel Gastric Cancer Stem Cell-Related Marker LINGO2 Is Associated with Cancer Cell Phenotype and Patient Outcome

The expression of leucine-rich repeat and immunoglobulin-like domain-containing nogo receptor-interacting protein 2 (LINGO2) has been reported in Parkinson’s disease; however, its role in other diseases is unknown. Gastric cancer is the second leading cause of cancer death. Cancer stem cells (CSC) are a subpopulation of cancer cells that contribute to the initiation and invasion of cancer. We identified LINGO2 as a CSC-associated protein in gastric cancers both in vitro and in patient-derived tissues. We studied the effect of LINGO2 on cell motility, stemness, tumorigenicity, and angiogenic capacity using cells sorted based on LINGO2 expression and LINGO2-silenced cells. Tissue microarray analysis showed that LINGO2 expression was significantly elevated in advanced gastric cancers. The overall survival of patients expressing high LINGO2 was significantly shorter than that of patients with low LINGO2. Cells expressing high LINGO2 showed elevated cell motility, angiogenic capacity, and tumorigenicity, while LINGO2 silencing reversed these properties. Silencing LINGO2 reduced kinase B (AKT)/extracellular signal-regulated kinase (ERK)/ERK kinase (MEK) phosphorylation and decreased epithelial-mesenchymal transition (EMT)-associated markers—N-Cadherin and Vimentin and stemness-associated markers— POU class 5 homeobox 1 (OCT4) and Indian hedgehog (IHH), and markedly decreased the CD44⁺ population. These indicate the involvement of LINGO2 in gastric cancer initiation and progression by altering cell motility, stemness, and tumorigenicity, suggesting LINGO2 as a putative target for gastric cancer treatment.

Sulforaphane inhibits gastric cancer stem cells via suppressing sonic hedgehog pathway

Sulforaphane (SFN) is the major component extracted from broccoli/broccoli sprouts. It has been shown to possess anti-cancer activity. Gastric cancer is common cancer worldwide. The objective of this work was to evaluate the inhibitory effect of SFN on gastric cancer by Sonic hedgehog (Hh) Pathway. The results found that tumorsphere formation and the expression levels of gastric cancer stem cells (CSCs) markers were significantly decreased after SFN treatment. SFN also exerted inhibitory effects by suppressing proliferation and inducing apoptosis in gastric CSCs. Intriguingly, SFN inhibited the activation of Sonic Hh, a key pathway in maintaining the stemness of gastric CSCs. Upregulation of Sonic Hh pathway diminished the inhibitory effects of SFN on gastric CSCs. Collectively, these data revealed that SFN could be a potent natural compound targeting gastric CSCs via suppression of Sonic Hh pathway, which might be an promising agent for gastric cancer intervention.

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.

Towards precision medicine: linking genetic and cellular heterogeneity in gastric cancer

Molecular and cellular heterogeneity are phenomena that are revolutionizing oncology research and becoming critical to the idea of personalized medicine. Recent comprehensive molecular profiling has identified molecular subtypes of gastric cancer (GC) and linked them to clinical information. Moreover, GC stem cells (gCSCs) have been identified and found to be responsible for GC initiation and progression, Helicobacter pylori oncogenic action and therapy resistance. Addressing molecular heterogeneity is critical for achieving an optimal therapeutic approach against GC as well as targeting gCSCs. In this review, we outline the implications of molecular and cellular heterogeneity in the treatment of GC and we summarize the clinical impact of the most important regulators of gCSCs.

Tumor heterogeneity of gastric cancer: From the perspective of tumor-initiating cell

Gastric cancer (GC) remains one of the most common and malignant types of cancer due to its rapid progression, distant metastasis, and resistance to conventional chemotherapy, although efforts have been made to understand the underlying mechanism of this resistance and to improve clinical outcome. It is well recognized that tumor heterogeneity, a fundamental feature of malignancy, plays an essential role in the cancer development and chemoresistance. The model of tumor-initiating cell (TIC) has been proposed to explain the genetic, histological, and phenotypical heterogeneity of GC. TIC accounts for a minor subpopulation of tumor cells with key characteristics including high tumorigenicity, maintenance of self-renewal potential, giving rise to both tumorigenic and non-tumorigenic cancer cells, and resistance to chemotherapy. Regarding tumor-initiating cell of GC (GATIC), substantial studies have been performed to (1) identify the putative specific cell markers for purification and functional validation of GATICs; (2) trace the origin of GATICs; and (3) decode the regulatory mechanism of GATICs. Furthermore, recent studies demonstrate the plasticity of GATIC and the interaction between GATIC and its surrounding factors (TIC niche or tumor microenvironment). All these investigations pave the way for the development of GATIC-targeted therapy, which is in the phase of preclinical studies and clinical trials. Here, we interpret the heterogeneity of GC from the perspectives of TIC by reviewing the above-mentioned fundamental and clinical studies of GATICs. Problems encountered during the GATIC investigations and the potential solutions are also discussed.

Decreased TGFBR3/betaglycan expression enhances the metastatic abilities of renal cell carcinoma cells through TGF-β-dependent and -independent mechanisms

TGF-β regulates both the tumor-forming and migratory abilities of various types of cancer cells. However, it is unclear how the loss of TGF-β signaling components affects these abilities in clear-cell renal cell carcinoma (ccRCC). In this study, we investigated the role of TGFBR3 (TGF-β type III receptor, also known as betaglycan) in ccRCC. Database analysis revealed decreased expression of TGFBR3 in ccRCC tissues, which correlated with poor prognosis in patients. Orthotopic inoculation experiments using immunocompromised mice indicated that low TGFBR3 expression in ccRCC cells enhanced primary tumor formation and lung metastasis. In the presence of TGFBR3, TGF-β2 decreased the aldehyde dehydrogenase (ALDH)-positive ccRCC cell population, in which renal cancer-initiating cells are enriched. Loss of TGFBR3 also enhanced cell migration in cell culture and induced expression of several mesenchymal markers in a TGF-β-independent manner. Increased lamellipodium formation by FAK-PI3K signaling was observed with TGFBR3 downregulation, and this contributed to TGF-β-independent cell migration in ccRCC cells. Taken together, our findings reveal that loss of TGFBR3 endows ccRCC cells with multiple metastatic abilities through TGF-β-dependent and independent pathways.

ALDH enzyme activity is regulated by Nodal and histamine in the A549 cell line

The present study aimed to examine whether the enzyme activity of aldehyde dehydrogenase (ALDH) was regulated by Nodal and histamine in the human alveolar adenocarcinoma A549 cell line. The regulated enzyme activity of ALDH was analyzed by flow cytometry in the A549 cell line. ALDH1 and Nodal expression was investigated by immunohistochemistry in28 cases of lung mixed adenocarcinoma. The enzyme activity of ALDH was upregulated by histamine and agonists of histamine H1 receptor (H1R) and histamine H2 receptor (H2R). ALDH activity was also downregulated by recombinant human Nodal and antagonists of H1R and H2R in the A549 cell line. In addition, expression of Nodal and ALDH1 were inversely correlated in lung mixed adenocarcinoma. ALDH enzyme activity was regulated by Nodal and histamine in lung adenocarcinoma.

New Opportunities and Challenges to Defeat Cancer Stem Cells

Cancer stem cells (CSCs) are a subpopulation of cancer cells that are capable of self-renewal, proliferation, differentiation, plastic adaptation, and immune regulation, thereby mediating tumorigenesis, metastasis, and therapy resistance. CSCs are associated with cancer progression and clinical outcome in cancer patients. Successful targeting of CSCs will therefore be necessary to eradicate and cure cancer. Functional regulators of stem cell (stemness) signaling pathways in human cancers have brought new opportunities to target CSCs and reframe cancer-targeting strategies in clinical settings. However, challenges remain due to a lack of complete understanding of CSC plasticity/heterogeneity and the limited efficacy of individual stemness inhibitors in cancer treatment. In this article we review CSC signaling pathways and the current state of CSC-targeting therapeutics in combinatory treatments in clinical trials.

Preclinical Evaluation of MEDI0641, a Pyrrolobenzodiazepine-Conjugated Antibody-Drug Conjugate Targeting 5T4

Antibody-drug conjugates (ADC) are used to selectively deliver cytotoxic agents to tumors and have the potential for increased clinical benefit to cancer patients. 5T4 is an oncofetal antigen overexpressed on the cell surface in many carcinomas on both bulk tumor cells as well as cancer stem cells (CSC), has very limited normal tissue expression, and can internalize when bound by an antibody. An anti-5T4 antibody was identified and optimized for efficient binding and internalization in a target-specific manner, and engineered cysteines were incorporated into the molecule for site-specific conjugation. ADCs targeting 5T4 were constructed by site-specifically conjugating the antibody with payloads that possess different mechanisms of action, either a DNA cross-linking pyrrolobenzodiazepine (PBD) dimer or a microtubule-destabilizing tubulysin, so that each ADC had a drug:antibody ratio of 2. The resulting ADCs demonstrated significant target-dependent activity in vitro and in vivo; however, the ADC conjugated with a PBD payload (5T4-PBD) elicited more durable antitumor responses in vivo than the tubulysin conjugate in xenograft models. Likewise, the 5T4-PBD more potently inhibited the growth of 5T4-positive CSCs in vivo, which likely contributed to its superior antitumor activity. Given that the 5T4-PBD possessed both potent antitumor activity as well as anti-CSC activity, and thus could potentially target bulk tumor cells and CSCs in target-positive indications, it was further evaluated in non-GLP rat toxicology studies that demonstrated excellent in vivo stability with an acceptable safety profile. Taken together, these preclinical data support further development of 5T4-PBD, also known as MEDI0641, against 5T4⁺ cancer indications. Mol Cancer Ther; 16(8); 1576-87. ©2017 AACR.

A unified model of the hierarchical and stochastic theories of gastric cancer

Gastric cancer (GC) is a life-threatening disease worldwide. Despite remarkable advances in treatments for GC, it is still fatal to many patients due to cancer progression, recurrence and metastasis. Regarding the development of novel therapeutic techniques, many studies have focused on the biological mechanisms that initiate tumours and cause treatment resistance. Tumours have traditionally been considered to result from somatic mutations, either via clonal evolution or through a stochastic model. However, emerging evidence has characterised tumours using a hierarchical organisational structure, with cancer stem cells (CSCs) at the apex. Both stochastic and hierarchical models are reasonable systems that have been hypothesised to describe tumour heterogeneity. Although each model alone inadequately explains tumour diversity, the two models can be integrated to provide a more comprehensive explanation. In this review, we discuss existing evidence supporting a unified model of gastric CSCs, including the regulatory mechanisms of this unified model in addition to the current status of stemness-related targeted therapy in GC patients.

Isolation of cancer progenitor cells from cancer stem cells in gastric cancer

The success of cancer treatment may depend on the complete elimination of cancer stem cells (CSCs). However, data regarding the current characterization of CSCs in different types of tumor are inconsistent, possibly due to the mixture of CSCs with cancer progenitor cells (CPCs). Therefore, it is important to exclude CPCs for the characterization of CSCs. The present study aimed to characterize gastric cancer stem cells (GCSC) by separating GCPC from gastric progenitor cells (GCSC) with flow cytometry. In total, 615 murine gastric cancer (GC) cells were divided into aldehyde dehydrogenase (ALDH)^high, ALDH^low and ALDH^neg groups by flow cytometry according to their ALDH activity. With decreased ALDH activity, the expression levels of stemness-associated markers, CD133⁺, octamer-binding transcription factory-4 and sex determining region Y-box 2 decreased. The ALDH^high and ALDH^low cells proliferated and formed tumor spheres in ultra-low adhesion medium without serum, however, the latter formed larger tumor spheres. In mice transplanted with 5,000 cells, the rate of tumor formation in the ALDH^low group was significantly higher, compared with that in the ALDH^high group. Of note, an increased number of mice developed tumors in the ALDH^high group 16 weeks following the injection of 500 cells, whereas tumors appeared at 8 weeks in the ALDH^low group. The mice in the ALDH^neg group exhibited less tumor formation under these conditions. These results demonstrated that ALDH^high cells had characteristics of GCSCs with a high level of self-renewal ability, but were in a relative resting stage. The ALDH^low cells had characteristics of GCPCs with limited self-renewal ability, but were in a rapid proliferation stage. These findings suggested that the separation of GCPCs from GCSCs is important for elucidating the biology of GCSCs and identifying strategies to eliminate GCSCs in GC.

Isolation, identification, and characterization of cancer stem cells: A review

Cancer stem cells (CSCs) or tumor-initiating cells (TICs) as a small subset of neoplastic cells are able to produce a tumor (tumorigenesis), maintain the population of tumorigenic cells (self-renewal), and generate the heterogeneous cells constructing the entire tumor (pluripotency). The research on stationary and circulating CSCs due to resistance to conventional therapies and inability in complete eradication of cancer is critical for developing novel therapeutic strategies for a more effective reduction in the risk of tumor metastasis and cancer recurrence. This review compiles information about different methods of detection and dissociation, side population, cellular markers, and establishment culture of CSCs, as well as characteristics of CSCs such as tumorigenicity, and signaling pathways associated with self-renewal and the capability of the same histological tumor regeneration in various cancers.

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).

Mesothelial Cells Create a Novel Tissue Niche That Facilitates Gastric Cancer Invasion

Peritoneal mesothelial cells (PMC) cover organ surfaces in the abdominal cavity. In this study, lineage tracing revealed that the PMCs guide cancer cell invasion in the gastric wall and in peritoneal metastatic lesions. Serosal PMCs covering the stomach surface entered the gastric wall to create a novel niche that favored gastric cancer cell invasion. PMC infiltration was induced by incorporation of cancer cell-derived, Wnt3a-containing extracellular vesicles. Infiltrated PMCs in turn promoted subserosal invasion of cancer cells. Mutual attraction between cancer cells and PMCs accelerated tumor invasion in the gastric wall, and PMC-led cancer cell invasion in disseminated tumors within the abdominal wall and diaphragm. Addition of the carboxyl terminus of Dickkopf-1 attenuated directional invasion of PMCs toward cancer cells both in vitro and in the gastric wall in vivo PMCs were sensitive to the aldehyde dehydrogenase (ALDH) inhibitor disulfiram (DSF), as ALDH activity is elevated in PMCs. Wnt3a upregulated ALDH, and addition of DSF inhibited the invasive properties of PMCs, whereas DSF pretreatment suppressed gastric infiltration of PMCs and subserosal invasion by cancer cells. Our results suggest that stabilization of PMCs may become an effective therapy for the prevention of local invasion and metastasis of gastric cancer. Cancer Res; 77(3); 684-95. ©2016 AACR.