Aldehyde dehydrogenase 3A1 is robustly upregulated in gastric cancer stem-like cells and associated with tumorigenesis

Strategies for the Isolation and Identification of Gastric Cancer Stem Cells

Gastric cancer stem cells (GCSCs) originate from both gastric adult stem cells and bone marrow cells and are conspicuously present within the histological milieu of gastric cancer tissue. GCSCs play pivotal and multifaceted roles in the initiation, progression, and recurrence of gastric cancer. Hence, the characterization of GCSCs not only facilitates precise target identification for prospective therapeutic interventions in gastric cancer but also has significant implications for targeted therapy and the prognosis of gastric cancer. The prevailing techniques for GCSC purification involve their isolation using surface-specific cell markers, such as those identified by flow cytometry and immunomagnetic bead sorting techniques. In addition, in vitro culture and side-population cell sorting are integral methods in this context. This review discusses the surface biomarkers, isolation techniques, and identification methods of GCSCs, as well as their role in the treatment of gastric cancer.

Volatilomic profiles of gastric juice in gastric cancer patients

Volatilomics is a powerful tool capable of providing novel biomarkers for the diagnosis of gastric cancer. The main objective of this study was to characterize the volatilomic signatures of gastric juice in order to identify potential alterations induced by gastric cancer. Gas chromatography with mass spectrometric detection, coupled with headspace solid phase microextraction as the pre-concentration technique, was used to identify volatile organic compounds (VOCs) released by gastric juice samples collected from 78 gastric cancer patients and two cohorts of controls (80 and 96 subjects) from four different locations (Latvia, Ukraine, Brazil, and Colombia). 1440 distinct compounds were identified in samples obtained from patients and 1422 in samples provided by controls. However, only 6% of the VOCs exhibited an incidence higher than 20%. Amongst the volatiles emitted, 18 showed differences in their headspace concentrations above gastric juice of cancer patients and controls. Ten of these (1-propanol, 2,3-butanedione, 2-pentanone, benzeneacetaldehyde, 3-methylbutanal, butylated hydroxytoluene, 2-pentyl-furan, 2-ethylhexanal, 2-methylpropanal and phenol) appeared at significantly higher levels in the headspace of the gastric juice samples obtained from patients; whereas, eight species showed lower abundance in patients than found in controls. Given that the difference in the volatilomic signatures can be explained by cancer-related changes in the activity of certain enzymes or pathways, the former set can be considered potential biomarkers for gastric cancer, which may assist in developing non-invasive breath tests for the diagnosis of this disease. Further studies are required to elucidate further the mechanisms that underlie the changes in the volatilomic profile as a result of gastric cancer.

Chronic restraint stress promotes oral squamous cell carcinoma development by inhibiting ALDH3A1 via stress response hormone

BACKGROUND

Chronic restraint stress (CRS) has iteratively been reported to be possibly implicated in the development of numerous cancer types. However, its role in oral squamous cell carcinoma (OSCC) has not been well elucidated. Here we intended to evaluate the role and mechanism.

METHODS

The effects of CRS were investigated in xenograft models of OSCC by using transcriptome sequencing, LC-MS, ELISA and RT-PCR. Moreover, the role of CRS and ALDH3A1 on OSCC cells was researched by using Trans-well, flow cytometry, western blotting, immunofluorescence, ATP activity and OCR assay. Furthermore, immunohistochemical staining was employed to observe the cell proliferation and invasion of OSCC in xenotransplantation models.

RESULTS

CRS promoted the progression of OSCC in xenograft models, stimulated the secretion of norepinephrine and the expression of ADRB2, but decreased the expression of ALDH3A1. Moreover, CRS changed energy metabolism and increased mitochondrial metabolism markers. However, ALDH3A1 overexpression suppressed proliferation, EMT and mitochondrial metabolism of OSCC cells.

CONCLUSION

Inhibition of ALDH3A1 expression plays a pivotal role in CRS promoting tumorigenic potential of OSCC cells, and the regulatory of ALDH3A1 on mitochondrial metabolism may be involved in this process.

Investigating the Functional Roles of Aldehyde Dehydrogenase 3A1 in Human Corneal Epithelial Cells

Aldehyde dehydrogenase 3A1 (ALDH3A1) oxidizes medium-chain aldehydes to their corresponding carboxylic acids. It is expressed at high rates in the human cornea, where it has been characterized as a multi-functional protein displaying various cytoprotective modes of action. Previous studies identified its association with the DNA damage response (DDR) pathway. Here, we utilized a stable transfected HCE-2 (human corneal epithelium) cell line expressing ALDH3A1, to investigate the molecular mechanisms underlying the cytoprotective role(s) of ALDH3A1. Our data revealed morphological differences among the ALDH3A1-expressing and the mock-transfected HCE-2 cells accompanied by differential expression of E-cadherin. Similarly, the ALDH3A1/HCE-2 cells demonstrated higher mobility, reduced proliferation, upregulation of ZEB1, and downregulation of CDK3, and p57. The expression of ALDH3A1 also affected cell cycle progression by inducing the sequestration of HCE-2 cells at the G2/M phase. Following 16 h cell treatments with either H₂O₂ or etoposide, a significantly lower percentage of ALDH3A1/HCE-2 cells were apoptotic compared to the respective treated mock/HCE-2 cells. Interestingly, the protective effect of ALDH3A1 expression under these oxidative and genotoxic conditions was accompanied by a reduced formation of γ-H2AX foci and higher levels of total and phospho (Ser15) p53. Finally, ALDH3A1 was found to be localized both in the cytoplasm and the nucleus of transfected HCE-2 cells. Its cellular compartmentalization was not affected by oxidant treatment, while the mechanism by which ALDH3A1 translocates to the nucleus remains unknown. In conclusion, ALDH3A1 protects cells from both apoptosis and DNA damage by interacting with key homeostatic mechanisms associated with cellular morphology, cell cycle, and DDR.

Identification of Key Volatile Organic Compounds Released by Gastric Tissues as Potential Non-Invasive Biomarkers for Gastric Cancer

BACKGROUND

Volatilomics is a powerful tool capable of providing novel biomarkers for medical diagnosis and therapy monitoring. The objective of this study is to identify potential volatile biomarkers of gastric cancer.

METHODS

The volatilomic signatures of gastric tissues obtained from two distinct populations were investigated using gas chromatography with mass spectrometric detection.

RESULTS

Amongst the volatiles emitted, nineteen showed differences in their headspace concentrations above the normal and cancer tissues in at least one population of patients. Headspace levels of seven compounds (hexanal, nonanal, cyclohexanone, 2-nonanone, pyrrole, pyridine, and phenol) were significantly higher above the cancer tissue, whereas eleven volatiles (ethyl acetate, acetoin, 2,3-butanedione, 3-methyl-1-butanol, 2-pentanone, γ-butyrolactone, DL-limonene, benzaldehyde, 2-methyl-1-propanol, benzonitrile, and 3-methyl-butanal) were higher above the non-cancerous tissue. One compound, isoprene, exhibited contradictory alterations in both cohorts. Five compounds, pyridine, ethyl acetate, acetoin, 2,3-butanedione, and 3-methyl-1-butanol, showed consistent cancer-related changes in both populations.

CONCLUSIONS

Pyridine is found to be the most promising biomarker candidate for detecting gastric cancer. The difference in the volatilomic signatures can be explained by cancer-related changes in the activity of certain enzymes, or pathways. The results of this study confirm that the chemical fingerprint formed by volatiles in gastric tissue is altered by gastric cancer.

Aldehyde dehydrogenase in solid tumors and other diseases: Potential biomarkers and therapeutic targets

The family of aldehyde dehydrogenases (ALDHs) contains 19 isozymes and is involved in the oxidation of endogenous and exogenous aldehydes to carboxylic acids, which contributes to cellular and tissue homeostasis. ALDHs play essential parts in detoxification, biosynthesis, and antioxidants, which are of important value for cell proliferation, differentiation, and survival in normal body tissues. However, ALDHs are frequently dysregulated and associated with various diseases like Alzheimer's disease, Parkinson's disease, and especially solid tumors. Notably, the involvement of the ALDHs in tumor progression is responsible for the maintenance of the stem-cell-like phenotype, triggering rapid and aggressive clinical progressions. ALDHs have captured increasing attention as biomarkers for disease diagnosis and prognosis. Nevertheless, these require further longitudinal clinical studies in large populations for broad application. This review summarizes our current knowledge regarding ALDHs as potential biomarkers in tumors and several non-tumor diseases, as well as recent advances in our understanding of the functions and underlying molecular mechanisms of ALDHs in disease development. Finally, we discuss the therapeutic potential of ALDHs in diseases, especially in tumor therapy with an emphasis on their clinical implications.

The Concept of Cancer Stem Cells: Elaborating on ALDH1B1 as an Emerging Marker of Cancer Progression

Cancer is a multifactorial, complex disease exhibiting extraordinary phenotypic plasticity and diversity. One of the greatest challenges in cancer treatment is intratumoral heterogeneity, which obstructs the efficient eradication of the tumor. Tumor heterogeneity is often associated with the presence of cancer stem cells (CSCs), a cancer cell sub-population possessing a panel of stem-like properties, such as a self-renewal ability and multipotency potential. CSCs are associated with enhanced chemoresistance due to the enhanced efflux of chemotherapeutic agents and the existence of powerful antioxidant and DNA damage repair mechanisms. The distinctive characteristics of CSCs make them ideal targets for clinical therapeutic approaches, and the identification of efficient and specific CSCs biomarkers is of utmost importance. Aldehyde dehydrogenases (ALDHs) comprise a wide superfamily of metabolic enzymes that, over the last years, have gained increasing attention due to their association with stem-related features in a wide panel of hematopoietic malignancies and solid cancers. Aldehyde dehydrogenase 1B1 (ALDH1B1) is an isoform that has been characterized as a marker of colon cancer progression, while various studies suggest its importance in additional malignancies. Here, we review the basic concepts related to CSCs and discuss the potential role of ALDH1B1 in cancer development and its contribution to the CSC phenotype.

Identification of a peptide ligand for human ALDH3A1 through peptide phage display: Prediction and characterization of protein interaction sites and inhibition of ALDH3A1 enzymatic activity

Aldehyde dehydrogenase 3A1 (ALDH3A1) by oxidizing medium chain aldehydes to their corresponding carboxylic acids, is involved in the detoxification of toxic byproducts and is considered to play an important role in antioxidant cellular defense. ALDH3A1 has been implicated in various other functions such as cell proliferation, cell cycle regulation, and DNA damage response. Recently, it has been identified as a putative biomarker of prostate, gastric, and lung cancer stem cell phenotype. Although ALDH3A1 has multifaceted functions in both normal and cancer homeostasis, its modes of action are currently unknown. To this end, we utilized a random 12-mer peptide phage display library to identify efficiently human ALDH3A1-interacting peptides. One prevailing peptide (P1) was systematically demonstrated to interact with the protein of interest, which was further validated in vitro by peptide ELISA. Bioinformatic analysis indicated two putative P1 binding sites on the protein surface implying biomedical potential and potent inhibitory activity of the P1 peptide on hALDH3A1 activity was demonstrated by enzymatic studies. Furthermore, in search of potential hALDH3A1 interacting players, a BLASTp search demonstrated that no protein in the database includes the full-length amino acid sequence of P1, but identified a list of proteins containing parts of the P1 sequence, which may prove potential hALDH3A1 interacting partners. Among them, Protein Kinase C Binding Protein 1 and General Transcription Factor II-I are candidates of high interest due to their cellular localization and function. To conclude, this study identifies a novel peptide with potential biomedical applications and further suggests a list of protein candidates be explored as possible hALDH3A1-interacting partners in future studies.

Prognostic and immunological role of acetaldehyde dehydrogenase 1B1 in human tumors: A pan-cancer analysis

Acetaldehyde dehydrogenases (ALDH) 1B1 is associated with a poor prognosis in pancreatic cancer, colorectal cancer, and osteosarcoma. Overexpression of ALDH also impairs tumor immunity. However, it is unclear how ALDH1B1 is associated with patient prognosis and immune infiltration in different cancer types. This is an original research based on bioinformatics analysis. In this study, we investigated the expression and prognostic value of ALDH1B1 in pan-cancer specimens using several databases, including GEPIA2 and Kaplan-Meier Plotter. The GEPIA2 and TIMER2 databases were used to explore correlations between ALDH1B1 expression and immune infiltration in cancers, especially head and neck squamous cell carcinoma (HNSC) and stomach adenocarcinoma (STAD). Finally, the expression of ALDH1B1 was validated by qPCR and immunohistochemistry. The expression of ALDH1B1 differed in most cancers compared to normal tissue controls. ALDH1B1 has an important impact on the prognosis different cancer types, and the high expression of ALDH1B1 is inversely associated with survival in patients with HNSC. A significant positive correlation was identified between ALDH1B1 expression in HNSC and immune infiltration. The poor prognosis associated with high expression of ALDH1B1 may be related to the promotion of M2 polarization of tumor-associated macrophages. Furthermore, markers of immune cell infiltration, such as exhausted T cells and regulatory T cells showed different patterns of ALDH1B1-associated immune infiltration. ALDH1B1 can serve as a prognostic biomarker in pan-cancer types and is correlated with immune infiltration.

Targeting Gastric Cancer Stem Cells to Enhance Treatment Response

Gastric cancer (GC) was the fourth deadliest cancer in the world in 2020, and about 770,000 people died from GC that year. The death of patients with GC is mainly caused by the metastasis, recurrence, and chemotherapy resistance of GC cells. The cancer stem cell theory defines cancer stem cells (CSCs) as a key factor in the metastasis, recurrence, and chemotherapy resistance of cancer. It considers targeting gastric cancer stem cells (GCSCs) to be an effective method for the treatment of GC. For GCSCs, genes or noncoding RNAs are important regulatory factors. Many experimental studies have found that some drugs can target the stemness of gastric cancer by regulating these genes or noncoding RNAs, which may bring new directions for the clinical treatment of gastric cancer. Therefore, this review mainly discusses related genes or noncoding RNAs in GCSCs and drugs that target its stemness, thereby providing some information for the treatment of GC.

Volatilomic Signatures of AGS and SNU-1 Gastric Cancer Cell Lines

In vitro studies can help reveal the biochemical pathways underlying the origin of volatile indicators of numerous diseases. The key objective of this study is to identify the potential biomarkers of gastric cancer. For this purpose, the volatilomic signatures of two human gastric cancer cell lines, AGS (human gastric adenocarcinoma) and SNU-1 (human gastric carcinoma), and one normal gastric mucosa cell line (GES-1) were investigated. More specifically, gas chromatography mass spectrometry has been applied to pinpoint changes in cell metabolism triggered by cancer. In total, ten volatiles were found to be metabolized, and thirty-five were produced by cells under study. The volatiles consumed were mainly six aldehydes and two heterocyclics, whereas the volatiles released embraced twelve ketones, eight alcohols, six hydrocarbons, three esters, three ethers, and three aromatic compounds. The SNU-1 cell line was found to have significantly altered metabolism in comparison to normal GES-1 cells. This was manifested by the decreased production of alcohols and ketones and the upregulated emission of esters. The AGS cells exhibited the increased production of methyl ketones containing an odd number of carbons, namely 2-tridecanone, 2-pentadecanone, and 2-heptadecanone. This study provides evidence that the cancer state modifies the volatilome of human cells.

ALDH3A1 driving tumor metastasis is mediated by p53/BAG1 in lung adenocarcinoma

Lung adenocarcinoma (LUAD) is a lethal malignancy with metastasis, a major tumor feature that predominantly correlated with progression, but the molecules that mediated tumor metastasis remain elusive. To declare the critical regulatory genes, RNA sequencing data in LUAD patients was acquired from The Cancer Genome Atlas (TCGA) and found that ALDH3A1 was distinctly highly expressed in LUAD patients with metastasis (M1) compared with those without metastasis (M0), linked to the property of cancer stem cell and epithelial-mesenchymal transition (EMT). Besides, high ALDH3A1 expression predicted a poor prognosis. Knockdown of ALDH3A1 showed decreased proliferation, migration, and invasion in A549 cell line. Furthermore, BAG1 was regulated by ALDH3A1 through p53, enhanced cell proliferation, and predicted clinical prognosis. Our findings collectively uncovered a novel mechanism that orchestrates tumor cells' metastasis, and decreasing ALDH3A1 represented a potential therapeutic target for reprogramming metastasis.

Genes involved in the epithelial-mesenchymal transition in oral cancer: A systematic review

OBJECTIVE

Epithelial-mesenchymal transition (EMT) is considered the initial step in the invasion-metastasis cascade. The aim of this systematic review was to study the signature of genes involved in the EMT process in oral cancer (OC) confirmed by protein expression and its possible relationship with oral squamous cell carcinoma (OSCC) prognostic variables.

MATERIALS AND METHODS

A search of the scientific literature was carried out with no start date restriction until 17 September 2020 in the electronic databases Pubmed/MEDLINE, Web of Science, Cochrane Library and Scopus, following specific eligibility criteria. The methodological quality of the included studies was assessed using the Newcastle-Ottawa tool.

RESULTS

A total of 8 retrospective cohort studies were included, all of them performed in China and with low risk of bias. Overexpression of the genes HNRNPC, ITGA5, HMGA2 and SRSF3, and low expression of ALDH3A1 and ARID2 promote EMT in OC. The more advanced clinical stages of the TNM classification were significantly associated with overexpression of HNRNPC, ITGA5, HMGA2 and SRSF3, and low expression of ARID2.

CONCLUSIONS

HNRNPC, ITGA5, HMGA2, SRSF3, ALDH3A1 and ARID2 genes were associated with EMT process. Over- or under-expression of these genes is associated with worse stages of OSCC and/or worse prognosis of the tumor. Further studies on this topic are needed in different countries to be able to confirm these results, since the detection of these genes can help to know which tumors have a worse prognosis.

Proteomic characteristics and identification of PM2.5-induced differentially expressed proteins in hepatocytes and c-Myc silenced hepatocytes

Proteomics and bioinformatics were applied to explore PM_2.5-induced differentially expressed proteins (DEPs) in hepatocytes (L02 cells) and c-Myc-silenced hepatocytes. L02 cells and c-Myc-silenced hepatocytes were treated with PM_2.5 for 24 h. Fifty-two DEPs were screened in L02 hepatocytes, of which 28 were upregulated and 24 were downregulated. Forty-one DEPs were screened in the c-Myc-silenced hepatocytes, of which 31 were upregulated and 10 were downregulated. GO analysis showed that DEPs in L02 cells were mainly concentrated in the cytosol and were involved in biological processes such as the response to metal ions. DEPs in c-Myc-silenced cells were mainly enriched in the extracellular space and were involved in lipoprotein metabolism. KEGG analysis showed that DEPs in L02 cells were mainly involved in arachidonic acid metabolism and mineral absorption. DEPs in c-Myc-silenced cells were mainly enriched in pathways involving nerve absorption, complement and coagulation cascades, and other pathways. Twenty key proteins, including Metallothionein-2A (MT2A), Metallothionein-1X (MT1X), zinc transporter ZIP10 (SLC39A10) and Serine protease 23 (PRSS23) were screened in two groups through analysis of protein-protein interactions. Based on the identification of the selected DEPs, PRSS23 and SLC39A10 might be the potential biomarker of PM_2.5-induced carcinogenesis, which provide the scientific basis for further research into the carcinogenic mechanisms of PM_2.5.

The Volatilomic Footprints of Human HGC-27 and CLS-145 Gastric Cancer Cell Lines

The presence of certain volatile biomarkers in the breath of patients with gastric cancer has been reported by several studies; however, the origin of these compounds remains controversial. In vitro studies, involving gastric cancer cells may address this problem and aid in revealing the biochemical pathways underlying the production and metabolism of gastric cancer volatile indicators. Gas chromatography with mass spectrometric detection, coupled with headspace needle trap extraction as the pre-concentration technique, has been applied to map the volatilomic footprints of human HGC-27 and CLS-145 gastric cancer cell lines and normal Human Stomach Epithelial Cells (HSEC). In total, 27 volatile compounds are found to be associated with metabolism occurring in HGC-27, CLS-145, and HSEC. Amongst these, the headspace concentrations of 12 volatiles were found to be reduced compared to those above just the cultivating medium, namely there was an observed uptake of eight aldehydes (2-methylpropanal, 2-methyl-2-propenal, 2-methylbutanal, 3-methylbutanal, hexanal, heptanal, nonanal, and benzaldehyde), three heterocyclic compounds (2-methyl-furan, 2-ethyl-furan, and 2-pentyl-furan), and one sulfur-containing compound (dimethyl disulphide). For the other 15 volatiles, the headspace concentrations above the healthy and cancerous cells were found to be higher than those found above the cultivating medium, namely the cells were found to release three esters (ethyl acetate, ethyl propanoate, and ethyl 2-methylbutyrate), seven ketones (2-pentanone, 2-heptanone, 2-nonanone, 2-undecanone, 2-tridecanone, 2-pentadecanone, and 2-heptadecanone), three alcohols (2-methyl-1-butanol, 3-methyl-1-butanol, and 2-ethyl-1-hexanol), one aromatic compound (toluene), and one sulfur containing compound [2-methyl-5-(methylthio) furan]. In comparison to HSEC, HGC-27 cancer cell lines were found to have significantly altered metabolism, manifested by an increased production of methyl ketones containing an odd number of carbons. Amongst these species, three volatiles were found exclusively to be produced by this cell line, namely 2-undecanone, 2-tridecanone, and 2-heptadecanone. Another interesting feature of the HGC-27 footprint is the lowered level of alcohols and esters. The CLS-145 cells exhibited less pronounced changes in their volatilomic pattern compared to HSEC. Their footprint was characterized by the upregulated production of esters and 2-ethyl-hexanol and downregulated production of other alcohols. We have therefore demonstrated that it is possible to differentiate between cancerous and healthy gastric cells using biochemical volatile signatures.

Aldehyde Dehydrogenase 1B1 Is Associated with Altered Cell Morphology, Proliferation, Migration and Chemosensitivity in Human Colorectal Adenocarcinoma Cells

Aldehyde dehydrogenases (ALDHs) are NAD(P)⁺-dependent enzymes that catalyze the oxidation of endogenous and exogenous aldehydes to their corresponding carboxylic acids. ALDHs participate in a variety of cellular mechanisms, such as metabolism, cell proliferation and apoptosis, as well as differentiation and stemness. Over the last few years, ALDHs have emerged as cancer stem cell markers in a wide spectrum of solid tumors and hematological malignancies. In this study, the pathophysiological role of ALDH1B1 in human colorectal adenocarcinoma was investigated. Human colon cancer HT29 cells were stably transfected either with human green fluorescent protein (GFP)-tagged ALDH1B1 or with an empty lentiviral expression vector. The overexpression of ALDH1B1 was correlated with altered cell morphology, decreased proliferation rate and reduced clonogenic efficiency. Additionally, ALDH1B1 triggered a G2/M arrest at 24 h post-cell synchronization, probably through p53 and p21 upregulation. Furthermore, ALDH1B1-overexpressing HT29 cells exhibited enhanced resistance against doxorubicin, fluorouracil (5-FU) and etoposide. Finally, ALDH1B1 induced increased migratory potential and displayed epithelial–mesenchymal transition (EMT) through the upregulation of ZEB1 and vimentin and the consequent downregulation of E-cadherin. Taken together, ALDH1B1 confers alterations in the cell morphology, cell cycle progression and gene expression, accompanied by significant changes in the chemosensitivity and migratory potential of HT29 cells, underlying its potential significance in cancer progression.

Cancer Stem Cells-Origins and Biomarkers: Perspectives for Targeted Personalized Therapies

The use of biomarkers in diagnosis, therapy and prognosis has gained increasing interest over the last decades. In particular, the analysis of biomarkers in cancer patients within the pre- and post-therapeutic period is required to identify several types of cells, which carry a risk for a disease progression and subsequent post-therapeutic relapse. Cancer stem cells (CSCs) are a subpopulation of tumor cells that can drive tumor initiation and can cause relapses. At the time point of tumor initiation, CSCs originate from either differentiated cells or adult tissue resident stem cells. Due to their importance, several biomarkers that characterize CSCs have been identified and correlated to diagnosis, therapy and prognosis. However, CSCs have been shown to display a high plasticity, which changes their phenotypic and functional appearance. Such changes are induced by chemo- and radiotherapeutics as well as senescent tumor cells, which cause alterations in the tumor microenvironment. Induction of senescence causes tumor shrinkage by modulating an anti-tumorigenic environment in which tumor cells undergo growth arrest and immune cells are attracted. Besides these positive effects after therapy, senescence can also have negative effects displayed post-therapeutically. These unfavorable effects can directly promote cancer stemness by increasing CSC plasticity phenotypes, by activating stemness pathways in non-CSCs, as well as by promoting senescence escape and subsequent activation of stemness pathways. At the end, all these effects can lead to tumor relapse and metastasis. This review provides an overview of the most frequently used CSC markers and their implementation as biomarkers by focussing on deadliest solid (lung, stomach, liver, breast and colorectal cancers) and hematological (acute myeloid leukemia, chronic myeloid leukemia) cancers. Furthermore, it gives examples on how the CSC markers might be influenced by therapeutics, such as chemo- and radiotherapy, and the tumor microenvironment. It points out, that it is crucial to identify and monitor residual CSCs, senescent tumor cells, and the pro-tumorigenic senescence-associated secretory phenotype in a therapy follow-up using specific biomarkers. As a future perspective, a targeted immune-mediated strategy using chimeric antigen receptor based approaches for the removal of remaining chemotherapy-resistant cells as well as CSCs in a personalized therapeutic approach are discussed.

ALDH3A1 acts as a prognostic biomarker and inhibits the epithelial mesenchymal transition of oral squamous cell carcinoma through IL-6/STAT3 signaling pathway

Objectives: Aldehyde dehydrogenase 3A1 (ALDH3A1) is a member of the ALDH superfamily and its relationship with oral squamous cell carcinoma (OSCC) still unknown. In our subject, we aimed to reveal the expression pattern and clinical value of ALDH3A1 in OSCC and its biological function in OSCC cell lines.

Materials and methods: The expression level of ALDH3A1 in paired OSCC tissues and adjacent noncancerous tissues were detected by quantitative real-time PCR, Western blot and immunohistochemistry. The relationship between ALDH3A1 expression and clinical characteristics was analyzed. Besides, cell-counting kit 8, colony formation, wound healing, transwell invasion, apoptosis and cell cycle assays were employed to assess the role of ALDH3A1 in OSCC cells. To explore the influence of ALDH3A1 on OSCC epithelial-to-mesenchymal transition (EMT), the expression of EMT markers (E-cadherin, vimentin, snail, MMP3) on OSCC cells were detected, and possible mechanisms were analyzed.

Results: In OSCC tissues, ALDH3A1 was significantly decreased compared to the adjacent normal tissues. Lower ALDH3A1 expression in OSCC tissues was associated with a higher incidence of lymph node metastasis (LNM). Moreover, the overall survival of OSCC with low ALDH3A1 expression was significantly worse compared to that of OSCC with high ALDH3A1 expression. Restored expression of ALDH3A1 suppressed cell proliferation, migration and invasion in OSCC cells. Further experiments showed that ALDH3A1 might inhibit EMT in OSCC via a regulation of the IL-6/STAT3 signal pathway.

Conclusion: These data indicate that ALDH3A1 may serve as a biomarker and may be developed into a novel treatment for OSCC.

ALDH3A1 Overexpression in Melanoma and Lung Tumors Drives Cancer Stem Cell Expansion, Impairing Immune Surveillance through Enhanced PD-L1 Output

Melanoma and non-small-cell lung carcinoma (NSCLC) cell lines are characterized by an intrinsic population of cancer stem-like cells (CSC), and high expression of detoxifying isozymes, the aldehyde dehydrogenases (ALDHs), regulating the redox state. In this study, using melanoma and NSCLC cells, we demonstrate that ALDH3A1 isozyme overexpression and activity is closely associated with a highly aggressive mesenchymal and immunosuppressive profile. The contribution of ALDH3A1 to the stemness and immunogenic status of melanoma and NSCLC cells was evaluated by their ability to grow in 3D forming tumorspheres, and by the expression of markers for stemness, epithelial to mesenchymal transition (EMT), and inflammation. Furthermore, in specimens from melanoma and NSCLC patients, we investigated the expression of ALDH3A1, PD-L1, and cyclooxygenase-2 (COX-2) by immunohistochemistry. We show that cells engineered to overexpress the ALDH3A1 enzyme enriched the CSCs population in melanoma and NSCLC cultures, changing their transcriptome. In fact, we found increased expression of EMT markers, such as vimentin, fibronectin, and Zeb1, and of pro-inflammatory and immunosuppressive mediators, such as NFkB, prostaglandin E2, and interleukin-6 and -13. ALDH3A1 overexpression enhanced PD-L1 output in tumor cells and resulted in reduced proliferation of peripheral blood mononuclear cells when co-cultured with tumor cells. Furthermore, in tumor specimens from melanoma and NSCLC patients, ALDH3A1 expression was invariably correlated with PD-L1 and the pro-inflammatory marker COX-2. These findings link ALDH3A1 expression to tumor stemness, EMT and PD-L1 expression, and suggest that aldehyde detoxification is a redox metabolic pathway that tunes the immunological output of tumors.

A Therapeutic Strategy for Chemotherapy-Resistant Gastric Cancer via Destabilization of Both β-Catenin and RAS

Treatment of advanced gastric cancer patients with current standard chemotherapeutic agents frequently results in resistance, leading to poor overall survival. However, there has been no success in developing strategies to overcome it. We showed the expression levels of both β-catenin and RAS were significantly increased and correlated in tissues of 756 gastric cancer (GC) patients and tissues of primary- and acquired-resistance patient-derived xenograft tumors treated with 5-fluorouracil and oxaliplatin modulated with leucovorin (FOLFOX). On the basis of our previous studies, where small molecules to suppress colorectal cancer (CRC) via degrading both β-catenin and RAS were developed, we tested the effectiveness of KYA1797K, a representative compound functioning by binding axin, in the growth of GC cells. The efficacy test of the drugs using gastric tumor organoids of Apc^1638N mice showed that the CD44 and ALDH1A3 cancer stem cell markers were induced by FOLFOX, but not by KYA1797K. KYA1797K also efficiently suppressed tumors generated by re-engrafting the FOLFOX-resistant patient-derived xenograft (PDX) tumors, which also showed resistance to paclitaxel. Overall, the small-molecule approach degrading both β-catenin and RAS has potential as a therapeutic strategy for treating GC patients resistant to current standard chemotherapies.

"Energetic" Cancer Stem Cells (e-CSCs): A New Hyper-Metabolic and Proliferative Tumor Cell Phenotype, Driven by Mitochondrial Energy

Here, we provide the necessary evidence that mitochondrial metabolism drives the anchorage-independent proliferation of CSCs. Two human breast cancer cell lines, MCF7 [ER(+)] and MDA-MB-468 (triple-negative), were used as model systems. To directly address the issue of metabolic heterogeneity in cancer, we purified a new distinct sub-population of CSCs, based solely on their energetic profile. We propose the term “energetic” cancer stem cells (e-CSCs), to better describe this novel cellular phenotype. In a single step, we first isolated an auto-fluorescent cell sub-population, based on their high flavin-content, using flow-cytometry. Then, these cells were further subjected to a detailed phenotypic characterization. More specifically, e-CSCs were more glycolytic, with higher mitochondrial mass and showed significantly elevated oxidative metabolism. e-CSCs also demonstrated an increased capacity to undergo cell cycle progression, as well as enhanced anchorage-independent growth and ALDH-positivity. Most importantly, these e-CSCs could be effectively targeted by treatments with either (i) OXPHOS inhibitors (DPI) or (ii) a CDK4/6 inhibitor (Ribociclib). Finally, we were able to distinguish two distinct phenotypic sub-types of e-CSCs, depending on whether they were grown as 2D-monolayers or as 3D-spheroids. Remarkably, under 3D anchorage-independent growth conditions, e-CSCs were strictly dependent on oxidative mitochondrial metabolism. Unbiased proteomics analysis demonstrated the up-regulation of gene products specifically related to the anti-oxidant response, mitochondrial energy production, and mitochondrial biogenesis. Therefore, mitochondrial inhibitors should be further developed as promising anti-cancer agents, to directly target and eliminate the “fittest” e-CSCs. Our results have important implications for using e-CSCs, especially those derived from 3D-spheroids, (i) in tumor tissue bio-banking and (ii) as a new cellular platform for drug development.

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.

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.

Chemoproteomics-Enabled Covalent Ligand Screening Reveals ALDH3A1 as a Lung Cancer Therapy Target

Chemical genetics is a powerful approach for identifying therapeutically active small molecules, but identifying the mechanisms of action underlying hit compounds remains challenging. Chemoproteomic platforms have arisen to tackle this challenge and enable rapid mechanistic deconvolution of small-molecule screening hits. Here, we have screened a cysteine-reactive covalent ligand library to identify hit compounds that impair cell survival and proliferation in nonsmall cell lung carcinoma cells, but not in primary human bronchial epithelial cells. Through this screen, we identified a covalent ligand hit, DKM 3-42, which impaired both in situ and in vivo lung cancer pathogenicity. We used activity-based protein profiling to discover that the primary target of DKM 3-42 was the catalytic cysteine in aldehyde dehydrogenase 3A1 (ALDH3A1). We performed further chemoproteomics-enabled covalent ligand screening directly against ALDH3A1, and identified a more potent and selective lead covalent ligand, EN40, which inhibits ALDH3A1 activity and impairs lung cancer pathogenicity. We show here that ALDH3A1 represents a potentially novel therapeutic target for lung cancers that express ALDH3A1 and put forth two selective ALDH3A1 inhibitors. Overall, we show the utility of combining chemical genetics screening of covalent ligand libraries with chemoproteomic approaches to rapidly identify anticancer leads and targets.

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.

Epithelial–mesenchymal transition and gastric cancer stem cell

Gastric cancer remains a big health problem in China. Gastric cancer cells contain a small subpopulation of cells that exhibit capabilities of differentiation and tumorigenicity. A putative explanation for ineffective therapy is the presence of cancer stem-like cells. Side population cells, which have cancer stem-like cells’ property, are characterized by the high efflux ability of Hoechst 33342 dye. Side population cells have been isolated from gastric cancer cell lines in previous studies. The epithelial–mesenchymal transition is very important in the invasion and metastasis of epithelial-derived cancers. More and more studies showed that gastric cancer stem-like cells possess high invasive ability and epithelial–mesenchymal transition property. A brief overview of the recent advancements in gastric cancer stem-like cells and epithelial–mesenchymal transition will be helpful for providing novel insight into gastric cancer treatment.

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.

Epithelial, mesenchymal and hybrid epithelial/mesenchymal phenotypes and their clinical relevance in cancer metastasis

Cancer metastasis occurs through local invasion of circulating tumour cells (CTCs), intravasation, transportation to distant sites, and their extravasation followed by colonisation at secondary sites. Epithelial-mesenchymal transition (EMT) is a normal developmental phenomenon, but its aberrant activation confers tumour cells with enhanced cell motility, metastatic properties, resistant to therapies and cancer stem cell (CSC) phenotype in epithelium-derived carcinoma. Experimental studies from various research papers have been reviewed to determine the factors, which interlink cancer stemness and cellular plasticity with EMT. Although existence of CSCs has been linked with EMT, nevertheless, there are controversies with the involvement of type of tumour cells, including cells with E (epithelial) and M (mesenchymal) phenotype alone or hybrid E/M phenotype in different types of cancers. Studies on CTCs with hybrid E/M phenotypes during different stages of cancer metastasis reveal strong association with tumour -initiation potential, cellular plasticity and types of cancer cells. Cells with the hybrid E/M state are strictly controlled by phenotypic stability factors coupled to core EMT decision-making circuits, miR200/ZEB and miR-34/Snail. Understanding the regulatory functions of EMT program in cancer metastasis can help us to characterise the biomarkers of prognostic and therapeutic potential. These biomarkers when targeted may act as metastatic suppressors, inhibit cellular plasticity and stemness ability of tumour cells and can block metastatic growth.

Secreted heat shock protein 90 promotes prostate cancer stem cell heterogeneity

Heat-shock protein 90 (Hsp90), a highly conserved molecular chaperone, is frequently upregulated in tumors, and remains an attractive anti-cancer target. Hsp90 is also found extracellularly, particularly in tumor models. Although extracellular Hsp90 (eHsp90) action is not well defined, eHsp90 targeting attenuates tumor invasion and metastasis, supporting its unique role in tumor progression. We herein investigated the potential role of eHsp90 as a modulator of cancer stem-like cells (CSCs) in prostate cancer (PCa). We report a novel function for eHsp90 as a facilitator of PCa stemness, determined by its ability to upregulate stem-like markers, promote self-renewal, and enhance prostasphere growth. Moreover, eHsp90 increased the side population typically correlated with the drug-resistant phenotype. Intriguingly, tumor cells with elevated surface eHsp90 exhibited a marked increase in stem-like markers coincident with increased expression of the epithelial to mesenchymal (EMT) effector Snail, indicating that surface eHsp90 may enrich for a unique CSC population. Our analysis of distinct effectors modulating the eHsp90-dependent CSC phenotyperevealed that eHsp90 is a likely facilitator of stem cell heterogeneity. Taken together, our findings provide unique functional insights into eHsp90 as a modulator of PCa plasticity, and provide a framework towards understanding its role as a driver of tumor progression.

Variable aldehyde dehydrogenase activity and effects on chemosensitivity of primitive human leukemic cells

Aldehyde dehydrogenase (ALDH) activity is an established feature of primitive normal human hematopoietic cells, in which it has been associated with a high expression of the 1A1 isoform of ALDH. High ALDH 1A1 activity has been reported to also characterize cells that propagate malignant populations arising in other tissues, but the regulation and basis of ALDH activity in primary human leukemic cells has not been well studied. We obtained samples from patients with newly diagnosed acute myeloid leukemia (AML; n = 21) and chronic myeloid leukemia (CML; n = 8) and analyzed different phenotypically and functionally defined subsets for their ALDH activity using the ALDEFLUOR^® kit and expression of the ALDH1A1 gene. We detected cells with high ALDH activity (ALDH^pos) in all samples from AML and CML patients. These were consistently enriched in the CD34⁺ population of these samples, but typically not in the CD34⁺CD38^- subset. Leukemic cells with direct clonogenic activity in vitro or those able to repopulate the bone marrow of sublethally irradiated non-obese diabetic (NOD)/severe combined immunodeficiency (SCID) mice were both ALDH^pos and ALDH^neg. Interestingly, ALDH1A1 transcripts were highest in the ALDH^neg leukemic cells and, in studies with leukemic cell lines, exposure to an inhibitor of ALDH activity variably affected sensitivity to daunorubicin. Cells with high ALDH activity are commonly found within the CD34⁺ population of primary human leukemic cells but, unlike in normal hematopoietic tissues, do not selectively or consistently comprise those with proliferative potential or other distinct functional properties.