Aldehyde dehydrogenase 1a1 is dispensable for stem cell function in the mouse hematopoietic and nervous systems

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.

Human Aldehyde Dehydrogenases: A Superfamily of Similar Yet Different Proteins Highly Related to Cancer

The superfamily of human aldehyde dehydrogenases (hALDHs) consists of 19 isoenzymes which are critical for several physiological and biosynthetic processes and play a major role in the organism's detoxification via the NAD(P) dependent oxidation of numerous endogenous and exogenous aldehyde substrates to their corresponding carboxylic acids. Over the last decades, ALDHs have been the subject of several studies as it was revealed that their differential expression patterns in various cancer types are associated either with carcinogenesis or promotion of cell survival. Here, we attempt to provide a thorough review of hALDHs' diverse functions and 3D structures with particular emphasis on their role in cancer pathology and resistance to chemotherapy. We are especially interested in findings regarding the association of structural features and their changes with effects on enzymes' functionalities. Moreover, we provide an updated outline of the hALDHs inhibitors utilized in experimental or clinical settings for cancer therapy. Overall, this review aims to provide a better understanding of the impact of ALDHs in cancer pathology and therapy from a structural perspective.

Stem cell decoupling underlies impaired lymphoid development during aging

Mammalian aging is associated with multiple defects of hematopoiesis, most prominently with the impaired development of T and B lymphocytes. This defect is thought to originate in hematopoietic stem cells (HSCs) of the bone marrow, specifically due to the age-dependent accumulation of HSCs with preferential megakaryocytic and/or myeloid potential ("myeloid bias"). Here, we tested this notion using inducible genetic labeling and tracing of HSCs in unmanipulated animals. We found that the endogenous HSC population in old mice shows reduced differentiation into all lineages including lymphoid, myeloid, and megakaryocytic. Single-cell RNA sequencing and immunophenotyping (CITE-Seq) showed that HSC progeny in old animals comprised balanced lineage spectrum including lymphoid progenitors. Lineage tracing using the aging-induced HSC marker Aldh1a1 confirmed the low contribution of old HSCs across all lineages. Competitive transplantations of total bone marrow cells with genetically marked HSCs revealed that the contribution of old HSCs was reduced, but compensated by other donor cells in myeloid cells but not in lymphocytes. Thus, the HSC population in old animals becomes globally decoupled from hematopoiesis, which cannot be compensated in lymphoid lineages. We propose that this partially compensated decoupling, rather than myeloid bias, is the primary cause of the selective impairment of lymphopoiesis in older mice.

The Molecular Context of Oxidant Stress Response in Cancer Establishes ALDH1A1 as a Critical Target: What This Means for Acute Myeloid Leukemia

The protein family of aldehyde dehydrogenases (ALDH) encompasses nineteen members. The ALDH1 subfamily consists of enzymes with similar activity, having the capacity to neutralize lipid peroxidation products and to generate retinoic acid; however, only ALDH1A1 emerges as a significant risk factor in acute myeloid leukemia. Not only is the gene ALDH1A1 on average significantly overexpressed in the poor prognosis group at the RNA level, but its protein product, ALDH1A1 protects acute myeloid leukemia cells from lipid peroxidation byproducts. This capacity to protect cells can be ascribed to the stability of the enzyme under conditions of oxidant stress. The capacity to protect cells is evident both in vitro, as well as in mouse xenografts of those cells, shielding cells effectively from a number of potent antineoplastic agents. However, the role of ALDH1A1 in acute myeloid leukemia has been unclear in the past due to evidence that normal cells often have higher aldehyde dehydrogenase activity than leukemic cells. This being true, ALDH1A1 RNA expression is significantly associated with poor prognosis. It is hence imperative that ALDH1A1 is methodically targeted, particularly for the acute myeloid leukemia patients of the poor prognosis risk group that overexpress ALDH1A1 RNA.

A Sequential Targeting Strategy Interrupts AKT-Driven Subclone-Mediated Progression in Glioblastoma

PURPOSE

Therapy resistance and fatal disease progression in glioblastoma are thought to result from the dynamics of intra-tumor heterogeneity. This study aimed at identifying and molecularly targeting tumor cells that can survive, adapt, and subclonally expand under primary therapy.

EXPERIMENTAL DESIGN

To identify candidate markers and to experimentally access dynamics of subclonal progression in glioblastoma, we established a discovery cohort of paired vital cell samples obtained before and after primary therapy. We further used two independent validation cohorts of paired clinical tissues to test our findings. Follow-up preclinical treatment strategies were evaluated in patient-derived xenografts.

RESULTS

We describe, in clinical samples, an archetype of rare ALDH1A1+ tumor cells that enrich and acquire AKT-mediated drug resistance in response to standard-of-care temozolomide (TMZ). Importantly, we observe that drug resistance of ALDH1A1+ cells is not intrinsic, but rather an adaptive mechanism emerging exclusively after TMZ treatment. In patient cells and xenograft models of disease, we recapitulate the enrichment of ALDH1A1+ cells under the influence of TMZ. We demonstrate that their subclonal progression is AKT-driven and can be interfered with by well-timed sequential rather than simultaneous antitumor combination strategy.

CONCLUSIONS

Drug-resistant ALDH1A1+/pAKT+ subclones accumulate in patient tissues upon adaptation to TMZ therapy. These subclones may therefore represent a dynamic target in glioblastoma. Our study proposes the combination of TMZ and AKT inhibitors in a sequential treatment schedule as a rationale for future clinical investigation.

A Novel ALDH1A1 Inhibitor Blocks Platinum-Induced Senescence and Stemness in Ovarian Cancer

Ovarian cancer is a deadly disease attributed to late-stage detection as well as recurrence and the development of chemoresistance. Ovarian cancer stem cells (OCSCs) are hypothesized to be largely responsible for the emergence of chemoresistant tumors. Although chemotherapy may initially succeed at decreasing the size and number of tumors, it leaves behind residual malignant OCSCs. In this study, we demonstrate that aldehyde dehydrogenase 1A1 (ALDH1A1) is essential for the survival of OCSCs. We identified a first-in-class ALDH1A1 inhibitor, compound 974, and used 974 as a tool to decipher the mechanism of stemness regulation by ALDH1A1. The treatment of OCSCs with 974 significantly inhibited ALDH activity, the expression of stemness genes, and spheroid and colony formation. An in vivo limiting dilution assay demonstrated that 974 significantly inhibited CSC frequency. A transcriptomic sequencing of cells treated with 974 revealed a significant downregulation of genes related to stemness and chemoresistance as well as senescence and the senescence-associated secretory phenotype (SASP). We confirmed that 974 inhibited the senescence and stemness induced by platinum-based chemotherapy in functional assays. Overall, these data establish that ALDH1A1 is essential for OCSC survival and that ALDH1A1 inhibition suppresses chemotherapy-induced senescence and stemness. Targeting ALDH1A1 using small-molecule inhibitors in combination with chemotherapy therefore presents a promising strategy to prevent ovarian cancer recurrence and has the potential for clinical translation.

Genotoxic aldehydes in the hematopoietic system

Reactive aldehydes are potent genotoxins that threaten the integrity of hematopoietic stem cells and blood production. To protect against aldehydes, mammals have evolved a family of enzymes to detoxify aldehydes, and the Fanconi anemia DNA repair pathway to process aldehyde-induced DNA damage. Loss of either protection mechanisms in humans results in defective hematopoiesis and predisposition to leukemia. This review will focus on the impact of genotoxic aldehydes on hematopoiesis, the sources of endogenous aldehydes, and potential novel protective pathways.

Retinoid signaling regulates angiogenesis and blood-retinal barrier integrity in neonatal mouse retina

OBJECTIVE

The neonatal mouse retina is a well-characterized experimental model for investigating factors impacting retinal angiogenesis and inner blood-retinal barrier (BRB) integrity. Retinoic acid (RA) is an essential signaling molecule. RA is needed for vasculogenic development in embryos and endothelial barrier integrity in zebrafish retina and adult mouse brain, however the function of this signaling molecule in developing mammalian retinal vasculature remains unknown. This study aims to investigate the role of RA signaling in angiogenesis and inner BRB integrity in mouse neonatal retina.

METHODS

RA distribution in the developing neurovascular retina was assessed in mice carrying an RA-responsive transgene. RA function in retinal angiogenesis was determined by treating C57BL/6 neonatal pups with a pharmacological inhibitor of RA signaling BMS493 or control vehicle. BRB integrity assessed by monitoring leakage of injected tracer into extravascular retinal tissue.

RESULTS

RA signaling activity is present in peripheral astrocytes in domains corresponding to RA activity of the underlying neural retina. RA inhibition impaired retinal angiogenesis and reduced endothelial cell proliferation. RA inhibition also compromised BRB integrity. Vascular leakage was not associated with altered expression of CLDN5, PLVAP, LEF1 or VEcad.

CONCLUSIONS

RA signaling is needed for angiogenesis and integrity of the BRB in the neonatal mouse retina.

Lower RNA expression of ALDH1A1 distinguishes the favorable risk group in acute myeloid leukemia

The expression and activity of enzymes that belong to the aldehyde dehydrogenases is a characteristic of both normal and malignant stem cells. ALDH1A1 is an enzyme critical in cancer stem cells. In acute myeloid leukemia (AML), ALDH1A1 protects leukemia-initiating cells from a number of antineoplastic agents, which include inhibitors of protein tyrosine kinases. Furthermore, ALDH1A1 proves vital for the establishment of human AML xenografts in mice. We review here important studies characterizing the role of ALDH1A1 in AML and its potential as a therapeutic target. We also analyze datasets from leading studies, and show that decreased ALDH1A1 RNA expression consistently characterizes the AML patient risk group with a favorable prognosis, while there is a consistent association of high ALDH1A1 RNA expression with high risk and poor overall survival. Our review and analysis reinforces the notion to employ both novel as well as existing inhibitors of the ALDH1A1 protein against AML.

Genomic expansion of Aldh1a1 protects beavers against high metabolic aldehydes from lipid oxidation

The North American beaver is an exceptionally long-lived and cancer-resistant rodent species. Here, we report the evolutionary changes in its gene coding sequences, copy numbers, and expression. We identify changes that likely increase its ability to detoxify aldehydes, enhance tumor suppression and DNA repair, and alter lipid metabolism, potentially contributing to its longevity and cancer resistance. Hpgd, a tumor suppressor gene, is uniquely duplicated in beavers among rodents, and several genes associated with tumor suppression and longevity are under positive selection in beavers. Lipid metabolism genes show positive selection signals, changes in copy numbers, or altered gene expression in beavers. Aldh1a1, encoding an enzyme for aldehydes detoxification, is particularly notable due to its massive expansion in beavers, which enhances their cellular resistance to ethanol and capacity to metabolize diverse aldehyde substrates from lipid oxidation and their woody diet. We hypothesize that the amplification of Aldh1a1 may contribute to the longevity of beavers.

Zhang et al. examine the genome of North American beavers and find evolutionary changes that could contribute to beavers’ longevity. In particular, Aldh1a1, encoding an enzyme for aldehyde detoxification, is massively expanded in the beaver genome, protecting them against exposure to aldehydes from lipid oxidation and their woody diet.

Expression of NR5A2, NUP153, HNF4A, USP15 and FNDC3B is consistent with their use as novel biomarkers for bovine mammary stem/progenitor cells

Mammary stem cells (MaSC) are essential for growth and maintenance of mammary epithelium. Previous studies have utilized morphological characteristics or retention of bromodeoxyuridine (BrdU) label to identify MaSC and progenitor cells, these approaches may not be feasible or may not identify all resident stem cells. Alternatively, these special cells may be identified by assessing protein and mRNA expression of appropriate markers. The focus of this study was to assess the staining patterns and in situ quantification of novel candidate markers for bovine MaSC/progenitor cells. The candidate markers for MaSC/progenitor cells for immunohistochemical analysis were: NR5A2, NUP153, HNF4A, USP15 and FNDC3B and for in situ transcripts quantification were HNF4A and NUP153. We also evaluated protein expression pattern of presumptive MaSC markers known from the literature namely, ALDH1, MSI1 and Notch3. We found that NR5A2, NUP153, HNF4A and USP15-labeled cells represented 2.5-6% of epithelial cells prepubertally and were distributed in a fashion consistent with the location and abundance of MaSC/progenitor cells. A transient increase (10-37%) in expression of these markers was observed at peak lactation. FNDC3B was localized mainly in the nucleus prepubertally and in the cytoplasm of myoepithelial cells and nuclei of a limited number of alveolar cells during lactation. Abundant expression (~ 48%) and luminal localization of ALDH1 precludes its use as a bovine MaSC marker but may include transamplifying progenitor cells. MSI1 staining was consistent with MaSC localization. Onset of lumen formation in mammary ducts of prepubertal gland was associated with Notch 3 expression in the apical surface of luminal cells. RNAscope analysis of HNF4A and NUP153 transcripts in calf mammary gland showed very low copy numbers in a few epithelial cells, supporting the idea that these markers are expressed by fewer cells of epithelial origin. This study suggests that NR5A2, NUP153, HNF4A, USP15 and FNDC3B are likely markers for bovine MaSC/progenitor cells. Quantification of RNA transcripts of HNF4A and NUP153 in bovine MEC as potential MaSC markers are novel. Further studies to correlate protein expression of these markers with their transcripts level using single cell analysis in larger samples in lactating cow at different physiological stages are warranted.

Anti-Tumor Effects of Biomimetic Sulfated Glycosaminoglycans on Lung Adenocarcinoma Cells in 2D and 3D In Vitro Models

Lung cancer development relies on cell proliferation and migration, which in turn requires interaction with extracellular matrix (ECM) components such as glycosaminoglycans (GAGs). The mechanisms through which GAGs regulate cancer cell functions are not fully understood but they are, in part, mediated by controlled interactions with cytokines and growth factors (GFs). In order to mechanistically understand the effect of the degree of sulfation (DS) of GAGs on lung adenocarcinoma (LUAD) cells, we synthesized sulfated alginate (AlgSulf) as sulfated GAG mimics with DS = 0.0, 0.8, 2.0, and 2.7. Human (H1792) and mouse (MDA-F471) LUAD cell lines were treated with AlgSulf of various DSs at two concentrations 10 and 100 µg/mL and their anti-tumor properties were assessed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), trypan blue exclusion, and wound healing assays for 2D models and sphere formation assay for the 3D model. The proliferation and number of live MDA-F471 cells at the concentration of 100 µg/mL decreased significantly with the increase in the DS of biomimetic GAGs. In addition, the increase in the DS of biomimetic GAGs decreased cell migration (p < 0.001 for DS = 2.0 and 2.7 compared to control) and decreased the diameter and number of spheres formed (p < 0.001). The increased DS of biomimetic GAGs attenuated the expression of cancer stem cell (CSC)/progenitor markers in the 3D cultures. In conclusion, GAG-mimetic AlgSulf with increased DS exhibit enhanced anti-proliferative and migratory properties while also reducing growth of KRAS-mutant LUAD spheres in vitro. We suggest that these anti-tumor effects by GAG-mimetic AlgSulf are possibly due to differential binding to GFs and consequential decreased cell stemness. AlgSulf may be suitable for applications in cancer therapy after further in vivo validation.

Dual disruption of aldehyde dehydrogenases 1 and 3 promotes functional changes in the glutathione redox system and enhances chemosensitivity in nonsmall cell lung cancer

Aldehyde dehydrogenases (ALDHs) are multifunctional enzymes that oxidize diverse endogenous and exogenous aldehydes. We conducted a meta-analysis based on The Cancer Genome Atlas and Gene Expression Omnibus data and detected genetic alterations in ALDH1A1, ALDH1A3, or ALDH3A1, 86% of which were gene amplification or mRNA upregulation, in 31% of nonsmall cell lung cancers (NSCLCs). The expression of these isoenzymes impacted chemoresistance and shortened survival times in patients. We hypothesized that these enzymes provide an oxidative advantage for the persistence of NSCLC. To test this hypothesis, we used genetic and pharmacological approaches with DIMATE, an irreversible inhibitor of ALDH1/3. DIMATE showed cytotoxicity in 73% of NSCLC cell lines tested and demonstrated antitumor activity in orthotopic xenografts via hydroxynonenal-protein adduct accumulation, GSTO1-mediated depletion of glutathione and increased H₂O₂. Consistent with this result, ALDH1/3 disruption synergized with ROS-inducing agents or glutathione synthesis inhibitors to trigger cell death. In lung cancer xenografts with high to moderate cisplatin resistance, combination treatment with DIMATE promoted strong synergistic responses with tumor regression. These results indicate that NSCLCs with increased expression of ALDH1A1, ALDH1A3, or ALDH3A1 may be targeted by strategies involving inhibitors of these isoenzymes as monotherapy or in combination with chemotherapy to overcome patient-specific drug resistance.

Aldehyde Dehydrogenase, Liver Disease and Cancer

Acetaldehyde dehydrogenase 2 (ALDH2) is the key enzyme responsible for metabolism of the alcohol metabolite acetaldehyde in the liver. In addition to conversion of the acetaldehyde molecule, ALDH is also involved in other cellular functions. Recently, many studies have investigated the involvement of ALDH expression in viral hepatitis, alcoholic liver disease (ALD), non-alcoholic fatty liver disease (NAFLD), liver fibrosis, and liver cancer. Notably, ALDH2 expression has been linked with liver cancer risk, as well as pathogenesis and prognosis, and has emerged as a promising therapeutic target. Of note, approximately 8% of the world's population, and approximately 30-40% of the population in East Asia carry an inactive ALDH2 gene. This review summarizes new progress in understanding tissue-specific acetaldehyde metabolism by ALDH2 as well as the association of ALDH2 gene polymorphisms with liver disease and cancer. New research directions emerging in the field are also briefly discussed.

Serial Xenotransplantation in NSG Mice Promotes a Hybrid Epithelial/Mesenchymal Gene Expression Signature and Stemness in Rhabdomyosarcoma Cells

Serial xenotransplantation of sorted cancer cells in immunodeficient mice remains the most complex test of cancer stem cell (CSC) phenotype. However, we have demonstrated in various sarcomas that putative CSC surface markers fail to identify CSCs, thereby impeding the isolation of CSCs for subsequent analyses. Here, we utilized serial xenotransplantation of unsorted rhabdomyosarcoma cells in NOD/SCID gamma (NSG) mice as a proof-of-principle platform to investigate the molecular signature of CSCs. Indeed, serial xenotransplantation steadily enriched for rhabdomyosarcoma stem-like cells characterized by enhanced aldehyde dehydrogenase activity and increased colony and sphere formation capacity in vitro. Although the expression of core pluripotency factors (SOX2, OCT4, NANOG) and common CSC markers (CD133, ABCG2, nestin) was maintained over the passages in mice, gene expression profiling revealed gradual changes in several stemness regulators and genes linked with undifferentiated myogenic precursors, e.g., SOX4, PAX3, MIR145, and CDH15. Moreover, we identified the induction of a hybrid epithelial/mesenchymal gene expression signature that was associated with the increase in CSC number. In total, 60 genes related to epithelial or mesenchymal traits were significantly altered upon serial xenotransplantation. In silico survival analysis based on the identified potential stemness-associated genes demonstrated that serial xenotransplantation of unsorted rhabdomyosarcoma cells in NSG mice might be a useful tool for the unbiased enrichment of CSCs and the identification of novel CSC-specific targets. Using this approach, we provide evidence for a recently proposed link between the hybrid epithelial/mesenchymal phenotype and cancer stemness.

Correlating tumor-infiltrating lymphocytes and lung cancer stem cells: a cross-sectional study

Background

Lung cancer stem cells (LCSCs) are endowed with high aldehyde dehydrogenase (ALDH) expression and play roles in tumor proliferation, metastasis, and drug resistance. Their elusive nature may allow them to escape the immune response by tumor-infiltrating lymphocytes (TILs), which can positively affect the outcome in non-small cell lung cancer (NSCLC) patients. Despite independent investigations on both LCSCs and TILs, the relationship between the two has been very marginally considered. We analyzed whether these two cell types may be related as a prerequisite for novel diagnostic and therapeutic approaches.

Methods

In this cross-sectional study, NSCLC human surgical specimens from 12 patients were tested by ALDEFLUOR assay to identify ALDH^high cells. Fluorescence-activated cell sorting (FACS) analyses for CD3+, CD4+, and CD8+ TILs were performed in combination with immunohistochemistry evaluation.

Results

Statistically positive correlations were found between ALDH+ and CD8+, and between ALDH+ and CD3+ cells populations; no correlation was found between ALDH+ and CD4+ cells. The expression of CD3+ and CD8+ by cells accounted for 40.1% and 58.7%, respectively, of the variability of ALDH+ cell expression by an R-squared index, which highlights the strong correlation between TILs and LCSCs. Immunohistochemistry revealed 6-25% positive cells.

Conclusions

We report a correlation between cytotoxic TILs and LCSCs, which may contribute to the future development of targeted therapies focusing on the different roles of lymphocytes against lung cancer.

Abalone Collagen Extracts Potentiate Stem Cell Properties of Human Epidermal Keratinocytes

Stem cell activities in human tissues are critical for tissue integrity and function. Maintaining keratinocyte stem cells (KSCs) stemness helps sustain healthy skin by supporting keratinocyte renewal, involving the formation of epidermal barriers. In this study, abalone collagen (AC) extracts with molecular weights of 3 kDa (AC 1) and 300 kDa (AC 2) were compared to the epidermal growth factor (EGF) for their effects on cell proliferation, cell migration (wound healing), spheroid formation, and the expression level of stem cell markers on human keratinocytes (HaCaT cells). Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell proliferation was quantified by ATP and DNA content analysis and Sulforhodamine B (SRB) assays. Cell migration assay was determined using the scratch wound healing test. Spheroid formation was evaluated and the expression level of stem cell markers was investigated by western blot analysis. The results showed that AC 1 at the concentration of 100 µg/mL could stimulate HaCaT cell proliferation, migration, spheroid formation, and the expression level of stem cell markers (keratin 19, β-catenin, ALDH1A1) compared to the control. In conclusion, a smaller molecular weight of abalone collagen extract exhibits a better effect on keratinocytes proliferation, migration, and stemness, which could be a potential active ingredient in cosmeceutical products.

Engineered Animal Models Designed for Investigating Ethanol Metabolism, Toxicity and Cancer

Excessive consumption of alcohol is a leading cause of lifestyle-induced morbidity and mortality worldwide. Although long-term alcohol abuse has been shown to be detrimental to the liver, brain and many other organs, our understanding of the exact molecular mechanisms by which this occurs is still limited. In tissues, ethanol is metabolized to acetaldehyde (mainly by alcohol dehydrogenase and cytochrome p450 2E1) and subsequently to acetic acid by aldehyde dehydrogenases. Intracellular generation of free radicals and depletion of the antioxidant glutathione (GSH) are believed to be key steps involved in the cellular pathogenic events caused by ethanol. With continued excessive alcohol consumption, further tissue damage can result from the production of cellular protein and DNA adducts caused by accumulating ethanol-derived aldehydes. Much of our understanding about the pathophysiological consequences of ethanol metabolism comes from genetically-engineered mouse models of ethanol-induced tissue injury. In this review, we provide an update on the current understanding of important mouse models in which ethanol-metabolizing and GSH-synthesizing enzymes have been manipulated to investigate alcohol-induced disease.

A Pan-ALDH1A Inhibitor Induces Necroptosis in Ovarian Cancer Stem-like Cells

Ovarian cancer is typified by the development of chemotherapy resistance. Chemotherapy resistance is associated with high aldehyde dehydrogenase (ALDH) enzymatic activity, increased cancer "stemness," and expression of the stem cell marker CD133. As such, ALDH activity has been proposed as a therapeutic target. Although it remains controversial which of the 19 ALDH family members drive chemotherapy resistance, ALDH1A family members have been primarily linked with chemotherapy resistant and stemness. We identified two ALDH1A family selective inhibitors (ALDH1Ai). ALDH1Ai preferentially kills CD133+ ovarian cancer stem-like cells (CSCs). ALDH1Ai induce necroptotic CSC death, mediated, in part, by the induction of mitochondrial uncoupling proteins and reduction in oxidative phosphorylation. ALDH1Ai is highly synergistic with chemotherapy, reducing tumor initiation capacity and increasing tumor eradication in vivo. These studies link ALDH1A with necroptosis and confirm the family as a critical therapeutic target to overcome chemotherapy resistance and improve patient outcomes.

High expression of aldehyde dehydrogenase 1 and tissue necrosis factor alpha may relate to chronic infection of buffalo mammary gland

Aldehyde dehydrogenase 1 (ALDH1) and hepatocyte nuclear factor 4A (HNF4A) are the putative mammary stem cell markers. Tissue necrosis factor alpha (TNFA) is involved in inflammation-associated carcinogenesis and cell proliferation. In this study, the gene expression profile of ALDH1, HNF4A and TNFA of buffalo mammary tissue using real-time quantitative PCR (RT-qPCR). Analysis of RT-qPCR data revealed that the relative expression (log2 fold change) of ALDH1 and TNFA during mastitis (vs. lactation) was increased (P < .05) by 2.98 and 4.71, respectively. The relative expression (log2 fold change; -7.39) of stem cell marker, HNF4A was decreased (P < .05) during mastitis. Histological analysis of mammary tissue during mastitis showed thickening of stroma and occasionally hyperplasia, predominantly in prepubertal and non-lactating animals. Although, the level of expression of these genes may vary, depending upon the physiological stage of the animals, however expression of ALDH1 and TNFA was high during mastitis. A systematic study on large samples of buffalo mammary tissue with appropriate comparisons needs to be evaluated with these markers for prognosis of buffalo mammary health.

Analysis of hematopoietic stem cells using a composite approach

Stem cells or Cancer stem cells (CSCs) have now been identified in different type of tissues by using surface markers. Functional assays such as ALDEFLUOR and side population which are marker independent have been additional approaches. However, whether all these approaches identify the same population of cells remain uncertain. To address this issue we have used hematopoietic stem cells as a model. Peripheral blood stem cells enumerated by CD34 are used routinely in bone marrow transplantation which supports the recovery of bone marrow after ablative chemotherapy or radiation. Hematopoietic stem cells (HSCs) were obtained from normal donor bone marrow (n = 5) and G-CSF stimulated peripheral blood stem cells (PBSCs) (n = 5) from patients undergoing leukapheresis prior to bone marrow transplantation. The stem cells were identified by combining CD34 expression with functional assays (ALDEFLUOR and side population). The cell cycle profile was further determined by simultaneous labeling of these cells with Hoechst and Pyronin Y. The simultaneous analysis showed that both CD34+ and CD34- cells co-exist with ALDH1A1+ cells but side population did not segregate with CD34+ cells. Though stem cell populations identified by functional assays were different, the cell cycle analysis showed that both ALDH1A1+ and CD34+ cells were in the G1 phase of cell cycle rather than in the quiescent (G0) phase.

Targeting LIN28B reprograms tumor glucose metabolism and acidic microenvironment to suppress cancer stemness and metastasis

The altered metabolism and acidic microenvironment plays an important role in promoting tumor malignant characteristics. A small population of cancer stem cells (CSCs) were considered as a therapy target to reserve tumor relapse, resistance, and metastasis. However, the molecular mechanism that regulates CSCs metabolism remains poorly understood. In this study, we demonstrate a fundamental role of stemness gene LIN28B in maintaining CSCs glycolysis metabolism. Using LIN28B-expressing cancer cell lines, we found that the rate of extracellular acidification, glucose uptake, and lactate secretion are all suppressed by LIN28B knockdown in vitro and in vivo. Importantly, metabolic analyses reveal that CSCs have enhanced aerobic glycolysis metabolic characteristics and the glycolytic product lactate further promotes cancer associated stemness properties. LIN28B silencing suppresses MYC expression that further increases miR-34a-5p level. Furthermore, the glycolysis metabolism of human breast cancer cell line MDA-MB-231 is suppressed by either MYC siRNA or miR-34a-5p mimic. Clinically, high MYC and low miR-34a-5p level are correlated with high LIN28B expression and poor prognosis in human breast cancer patients. Notably, blocking LIN28B/MYC/miR-34a-5p signaling pathway by LIN28B-specific inhibitor causes dramatic inhibition of tumor growth and metastasis in immunodeficient orthotopic mouse models of human breast cancer cell MDA-MB-231. Taken together, our findings offer a preclinical investigation of targeting LIN28B to suppress CSCs glycolysis metabolism and tumor progression that may improve the therapeutic benefit for cancer patients.

Aldehyde Dehydrogenases: Not Just Markers, but Functional Regulators of Stem Cells

Aldehyde dehydrogenase (ALDH) is a superfamily of enzymes that detoxify a variety of endogenous and exogenous aldehydes and are required for the biosynthesis of retinoic acid (RA) and other molecular regulators of cellular function. Over the past decade, high ALDH activity has been increasingly used as a selectable marker for normal cell populations enriched in stem and progenitor cells, as well as for cell populations from cancer tissues enriched in tumor-initiating stem-like cells. Mounting evidence suggests that ALDH not only may be used as a marker for stem cells but also may well regulate cellular functions related to self-renewal, expansion, differentiation, and resistance to drugs and radiation. ALDH exerts its functional actions partly through RA biosynthesis, as all-trans RA reverses the functional effects of pharmacological inhibition or genetic suppression of ALDH activity in many cell types in vitro. There is substantial evidence to suggest that the role of ALDH as a stem cell marker comes down to the specific isoform(s) expressed in a particular tissue. Much emphasis has been placed on the ALDH1A1 and ALDH1A3 members of the ALDH1 family of cytosolic enzymes required for RA biosynthesis. ALDH1A1 and ALDH1A3 regulate cellular function in both normal stem cells and tumor-initiating stem-like cells, promoting tumor growth and resistance to drugs and radiation. An improved understanding of the molecular mechanisms by which ALDH regulates cellular function will likely open new avenues in many fields, especially in tissue regeneration and oncology.

Protagonist or antagonist? The complex roles of retinoids in the regulation of hematopoietic stem cells and their specification from pluripotent stem cells

Hematopoietic stem cells (HSCs) are multipotent cells responsible for the maintenance of the hematopoietic system throughout life. Dysregulation of the balance in HSC self-renewal, death, and differentiation can have serious consequences such as myelodysplastic syndromes or leukemia. All-trans retinoic acid (ATRA), the biologically active metabolite of vitamin A/RA, has been shown to have pleiotropic effects on hematopoietic cells, enhancing HSC self-renewal while also increasing differentiation of more mature progenitors. Furthermore, ATRA has been shown to have key roles in regulating the specification and formation of hematopoietic cells from pluripotent stem cells including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). Here, we summarize the known roles of vitamin A and RA receptors in the regulation of hematopoiesis from HSCs, ES, and iPSCs.

DDB2 represses ovarian cancer cell dedifferentiation by suppressing ALDH1A1

Cancer stem cells (CSCs), representing the root of many solid tumors including ovarian cancer, have been implicated in disease recurrence, metastasis, and therapeutic resistance. Our previous study has demonstrated that the CSC subpopulation in ovarian cancer can be limited by DNA damage-binding protein 2 (DDB2). Here, we demonstrated that the ovarian CSC subpopulation can be maintained via cancer cell dedifferentiation, and DDB2 is able to suppress this non-CSC-to-CSC conversion by repression of ALDH1A1 transcription. Mechanistically, DDB2 binds to the ALDH1A1 gene promoter, facilitating the enrichment of histone H3K27me3, and competing with the transcription factor C/EBPβ for binding to this region, eventually inhibiting the promoter activity of the ALDH1A1 gene. The de-repression of ALDH1A1 expression contributes to DDB2 silencing-augmented non-CSC-to-CSC conversion and expansion of the CSC subpopulation. We further showed that treatment with a selective ALDH1A1 inhibitor blocked DDB2 silencing-induced expansion of CSCs, and halted orthotopic xenograft tumor growth. Together, our data demonstrate that DDB2, functioning as a transcription repressor, can abrogate ovarian CSC properties by downregulating ALDH1A1 expression.

Disulfiram/copper targets stem cell-like ALDH+ population of multiple myeloma by inhibition of ALDH1A1 and Hedgehog pathway

Multiple myeloma stem cells (MMSCs) have been considered as the major cause resulting in relapse. Eradicating MMSCs may be an effective strategy to improve the outcome of multiple myeloma (MM). Increased activity of aldehyde dehydrogenase (ALDH) has been found in MMSCs, but whether inhibiting ALDH activity can eliminate MMSCs remains unknown. Disulfiram (DS) has been reported as an inhibitor of ALDH, and increasing studies showed it has anti-cancer effects in a copper (Cu)-dependent manner. In this study, we isolated ALDH⁺ cells of MM by Aldefluor assay and demonstrated they possessed tumorigenesis capacities in vitro and in vivo. Next, we investigated the effects of DS with or without Cu on suppressing the stemness of MM both in vitro and in vivo. We found that DS/Cu eliminated the stem cell-like ALDH⁺ cells. Furthermore, we demonstrated that DS/Cu inhibited the expression of stem cell transcription factors NANOG and OCT4, and abolished the clonogenicity of MM. We also showed that DS/Cu reduced the tumor growth and inhibited stemness of MM in xenograft model. We further found the specific target of DS/Cu is ALDH1A1 and DS/Cu inhibited the Hedgehog (Hh) pathway transcription factors Gli1 and Gli2 regulated by ALDH1A1 at least in part. Our data suggest that DS/Cu can inhibit the ALDH⁺ stem cell-like cells through ALDH1A1 and Hh pathway, which may be a promising therapeutic agent in eradicating stem cell-like cells of MM.

Improved de novo genomic assembly for the domestic donkey

Donkeys and horses share a common ancestor dating back to about 4 million years ago. Although a high-quality genome assembly at the chromosomal level is available for the horse, current assemblies available for the donkey are limited to moderately sized scaffolds. The absence of a better-quality assembly for the donkey has hampered studies involving the characterization of patterns of genetic variation at the genome-wide scale. These range from the application of genomic tools to selective breeding and conservation to the more fundamental characterization of the genomic loci underlying speciation and domestication. We present a new high-quality donkey genome assembly obtained using the Chicago HiRise assembly technology, providing scaffolds of subchromosomal size. We make use of this new assembly to obtain more accurate measures of heterozygosity for equine species other than the horse, both genome-wide and locally, and to detect runs of homozygosity potentially pertaining to positive selection in domestic donkeys. Finally, this new assembly allowed us to identify fine-scale chromosomal rearrangements between the horse and the donkey that likely played an active role in their divergence and, ultimately, speciation.

Aldehyde dehydrogenase 1A1 in stem cells and cancer

The human genome contains 19 putatively functional aldehyde dehydrogenase (ALDH) genes, which encode enzymes critical for detoxification of endogenous and exogenous aldehyde substrates through NAD(P)+-dependent oxidation. ALDH1 has three main isotypes, ALDH1A1, ALDH1A2, and ALDH1A3, and is a marker of normal tissue stem cells (SC) and cancer stem cells (CSC), where it is involved in self-renewal, differentiation and self-protection. Experiments with murine and human cells indicate that ALDH1 activity, predominantly attributed to isotype ALDH1A1, is tissue- and cancer-specific. High ALDH1 activity and ALDH1A1 overexpression are associated with poor cancer prognosis, though high ALDH1 and ALDH1A1 levels do not always correlate with highly malignant phenotypes and poor clinical outcome. In cancer therapy, ALDH1A1 provides a useful therapeutic CSC target in tissue types that normally do not express high levels of ALDH1A1, including breast, lung, esophagus, colon and stomach. Here we review the functions and mechanisms of ALDH1A1, the key ALDH isozyme linked to SC populations and an important contributor to CSC function in cancers, and we outline its potential in future anticancer strategies.

ALDHs in normal and malignant hematopoietic cells: Potential new avenues for treatment of AML and other blood cancers

Multiple studies have demonstrated that ALDH1A1 is elevated in hematopoietic stem cells (HSCs). As a means to better characterize such cells, we previously developed the fluorescent ALDH1A1 substrate Aldefluor to facilitate HSC identification and isolation. This has proven useful for counting and isolating HSCs from human bone marrow, peripheral blood and cord blood as well as stem cells in other tissues and organisms. Given the high level expression of ALDH1A1, we explored its biology and that of other ALDHs in HSCs and found that ALDH1A1 and ALDH3A1 were important in metabolizing reactive aldehydes (RAlds) and reactive oxygen species (ROS). In murine models, loss of these two isoforms resulted in a variety of effects on HSC biology, increased DNA damage and predisposition to leukemia formation when combined with a genetic driver of HSC proliferation and self-renewal. Loss of ALDH activity may also predispose to marrow failure and AML in Fanconi's anemia (FA). ALDHs also have importance in mediating drug resistance in AML, may be useful in the identification of leukemia stem cells (LSCs) and ALDH activity levels may have prognostic significance. Together these findings suggest that further studying ALDH biology in AML and other blood cancers may provide important insights into malignant transformation and may point the way to the development of novel diagnostics and therapies.

Targeted therapy for a subset of acute myeloid leukemias that lack expression of aldehyde dehydrogenase 1A1

Aldehyde dehydrogenase 1A1 (ALDH1A1) activity is high in hematopoietic stem cells and functions in part to protect stem cells from reactive aldehydes and other toxic compounds. In contrast, we found that approximately 25% of all acute myeloid leukemias expressed low or undetectable levels of ALDH1A1 and that this ALDH1A1⁻ subset of leukemias correlates with good prognosis cytogenetics. ALDH1A1⁻ cell lines as well as primary leukemia cells were found to be sensitive to treatment with compounds that directly and indirectly generate toxic ALDH substrates including 4-hydroxynonenal and the clinically relevant compounds arsenic trioxide and 4-hydroperoxycyclophosphamide. In contrast, normal hematopoietic stem cells were relatively resistant to these compounds. Using a murine xenotransplant model to emulate a clinical treatment strategy, established ALDH1A1⁻ leukemias were also sensitive to in vivo treatment with cyclophosphamide combined with arsenic trioxide. These results demonstrate that targeting ALDH1A1⁻ leukemic cells with toxic ALDH1A1 substrates such as arsenic and cyclophosphamide may be a novel targeted therapeutic strategy for this subset of acute myeloid leukemias.

Aldehyde dehydrogenase 2 in aplastic anemia, Fanconi anemia and hematopoietic stem cells

Maintenance of the hematopoietic stem cell (HSC) compartment depends on the ability to metabolize exogenously and endogenously generated toxins, and to repair cellular damage caused by such toxins. Reactive aldehydes have been demonstrated to cause specific genotoxic injury, namely DNA interstrand cross-links. Aldehyde dehydrogenase 2 (ALDH2) is a member of a 19 isoenzyme ALDH family with different substrate specificities, subcellular localization, and patterns of expression. ALDH2 is localized in mitochondria and is essential for the metabolism of acetaldehyde, thereby placing it directly downstream of ethanol metabolism. Deficiency in ALDH2 expression and function are caused by a single nucleotide substitution and resulting amino acid change, called ALDH2*2. This genetic polymorphism affects 35-45% of East Asians (about ~560 million people), and causes the well-known Asian flushing syndrome, which results in disulfiram-like reactions after ethanol consumption. Recently, the ALDH2*2 genotype has been found to be associated with marrow failure, with both an increased risk of sporadic aplastic anemia and more rapid progression of Fanconi anemia. This review discusses the unexpected interrelationship between aldehydes, ALDH2 and hematopoietic stem cell biology, and in particular its relationship to Fanconi anemia.

Nuclear aldehyde dehydrogenase 1A1 (ALDH1A1) expression is a favorable prognostic indicator in colorectal carcinoma

AIM

To assess the expression pattern of aldehyde dehydrogenase 1A1 (ALDH1A1) in the normal-adenoma-primary carcinoma-liver metastasis sequence, and investigate its association with clinicopathological features and outcomes.

METHODS

Immunohistochemistry for ALDH1A1 was performed on two cohorts. One used tissue microarrays (TMAs) of 395 primary colorectal carcinomas, and the other used whole-tissue sections from 217 adenomas, 265 primary carcinomas, and 72 liver metastatic carcinomas. Both the epithelial and stromal expression of ALDH1A1 were evaluated. Both cytoplasmic and nuclear expression were assessed in epithelial cells.

RESULTS

In the TMA and whole-tissue cohorts, univariate analysis indicated that the cytoplasmic expression of ALDH1A1 cannot be considered as a prognosis marker of CRCs. In the whole-tissue cohort, nuclear expression was found in a small subgroup of CRC patients. Here, both univariate and multivariate analysis showed that nuclear expression was significantly associated with longer disease-specific survival. In addition, we found that nuclear expression in low-grade adenoma was predominant over high-grade adenoma, primary CRC and the correpsonding liver metastasis.

CONCLUSIONS

Whole-tissue is better than TMA for the detection of ALDH1A1 nuclear staining in CRC patients, and nuclear expression is associated with a better outcome. Cytoplasmic expression is not a suitable prognostic marker of CRC.

The prognostic roles of ALDH1 isoenzymes in gastric cancer

Increased aldehyde dehydrogenase 1 (ALDH1) activity has been determined to be present in the stem cells of several kinds of cancers including gastric cancer (GC). Nevertheless, which ones of ALDH1's isoenzymes are leading to ALDH1 activity remains elusive. In this study, we examined the prognostic value and hazard ratio (HR) of individual ALDH1 isoenzymes in patients with GC using "The Kaplan-Meier plotter" database. mRNA high expression level of ALDH1A1 was not found to be significantly correlated with the overall survival (OS) of all patients with GC followed for 20 years, HR =0.86 (95% confidence interval [CI]: 0.7-1.05), P=0.13. mRNA high expression level of ALDH1A2 was also not significantly correlated with OS for all patients with GC, HR =1.13 (95% CI: 0.91-1.41), P=0.25. mRNA high expression level of ALDH1A3 was found to be significantly correlated with worsened OS in either intestinal-type patients, HR =2.24 (95% CI: 1.44-3.49), P=0.00026, or diffuse-type patients, HR =1.91 (95% CI: 1.02-3.59), P=0.04. Interestingly, mRNA high expression level of ALDH1B1 was found to be significantly correlated with better OS for all patients with GC, HR =0.66 (95% CI: 0.53-0.81), P=7.8e-05, and mRNA high expression level of ALDH1L1 was found to be significantly correlated with worsened OS for all patients with GC, HR =1.23 (95% CI: 1-1.51), P=0.048. Furthermore, our results also indicate that ALDH1A3 and ALDH1L1 are potential major contributors to the ALDH1 activity in GC, since mRNA high expression levels of ALDH1A3 and ALDH1L1 were found to be significantly correlated with worsened OS for all patients with GC. Based on our study, ALDH1A3 and ALDH1L1 are potential prognostic markers and therapeutic targets for patients with GC.

Ciprofloxacin Improves the Stemness of Human Dermal Papilla Cells

Improvement in the expansion method of adult stem cells may augment their use in regenerative therapy. Using human dermal papilla cell line as well as primary dermal papilla cells as model systems, the present study demonstrated that ciprofloxacin treatment could prevent the loss of stemness during culture. Clonogenicity and stem cell markers of dermal papilla cells were shown to gradually decrease in the culture in a time-dependent manner. Treatment of the cells with nontoxic concentrations of ciprofloxacin could maintain both stem cell morphology and clonogenicity, as well as all stem cells markers. We found that ciprofloxacin exerted its effect through ATP-dependent tyrosine kinase/glycogen synthase kinase3β dependent mechanism which in turn upregulated β-catenin. Besides, ciprofloxacin was shown to induce epithelial-mesenchymal transition in DPCs as the transcription factors ZEB1 and Snail were significantly increased. Furthermore, the self-renewal proteins of Wnt/β-catenin pathway, namely, Nanog and Oct-4 were significantly upregulated in the ciprofloxacin-treated cells. The effects of ciprofloxacin in preserving stem cell features were confirmed in the primary dermal papilla cells directly obtained from human hair follicles. Together, these results revealed a novel application of ciprofloxacin for stem cell maintenance and provided the underlying mechanisms that are responsible for the stemness in dermal papilla cells.

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

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

Characterization of two distinct structural classes of selective aldehyde dehydrogenase 1A1 inhibitors

Aldehyde dehydrogenases (ALDH) catalyze the irreversible oxidation of aldehydes to their corresponding carboxylic acid. Alterations in ALDH1A1 activity are associated with such diverse diseases as cancer, Parkinson's disease, obesity, and cataracts. Inhibitors of ALDH1A1 could aid in illuminating the role of this enzyme in disease processes. However, there are no commercially available selective inhibitors for ALDH1A1. Here we characterize two distinct chemical classes of inhibitors that are selective for human ALDH1A1 compared to eight other ALDH isoenzymes. The prototypical members of each structural class, CM026 and CM037, exhibit submicromolar inhibition constants but have different mechanisms of inhibition. The crystal structures of these compounds bound to ALDH1A1 demonstrate that they bind within the aldehyde binding pocket of ALDH1A1 and exploit the presence of a unique glycine residue to achieve their selectivity. These two novel and selective ALDH1A1 inhibitors may serve as chemical tools to better understand the contributions of ALDH1A1 to normal biology and to disease states.

Comparative and evolutionary studies of vertebrate ALDH1A-like genes and proteins

Vertebrate ALDH1A-like genes encode cytosolic enzymes capable of metabolizing all-trans-retinaldehyde to retinoic acid which is a molecular 'signal' guiding vertebrate development and adipogenesis. Bioinformatic analyses of vertebrate and invertebrate genomes were undertaken using known ALDH1A1, ALDH1A2 and ALDH1A3 amino acid sequences. Comparative analyses of the corresponding human genes provided evidence for distinct modes of gene regulation and expression with putative transcription factor binding sites (TFBS), CpG islands and micro-RNA binding sites identified for the human genes. ALDH1A-like sequences were identified for all mammalian, bird, lizard and frog genomes examined, whereas fish genomes displayed a more restricted distribution pattern for ALDH1A1 and ALDH1A3 genes. The ALDH1A1 gene was absent in many bony fish genomes examined, with the ALDH1A3 gene also absent in the medaka and tilapia genomes. Multiple ALDH1A1-like genes were identified in mouse, rat and marsupial genomes. Vertebrate ALDH1A1, ALDH1A2 and ALDH1A3 subunit sequences were highly conserved throughout vertebrate evolution. Comparative amino acid substitution rates showed that mammalian ALDH1A2 sequences were more highly conserved than for the ALDH1A1 and ALDH1A3 sequences. Phylogenetic studies supported an hypothesis for ALDH1A2 as a likely primordial gene originating in invertebrate genomes and undergoing sequential gene duplication to generate two additional genes, ALDH1A1 and ALDH1A3, in most vertebrate genomes.

Cancer stem-like cells and thyroid cancer

Thyroid cancer is one of the most rapidly increasing malignancies. The reasons for this increase is not completely known, but increases in the diagnosis of papillary thyroid microcarcinomas and follicular variant of papillary thyroid carcinomas along with the enhanced detection of well-differentiated thyroid carcinomas are probably all contributing factors. Although most cases of well-differentiated thyroid carcinomas are associated with an excellent prognosis, a small percentage of patients with well-differentiated thyroid carcinomas as well as most patients with poorly differentiated and anaplastic thyroid carcinomas have recurrent and/or metastatic disease that is often fatal. The cancer stem-like cell (CSC) model suggests that a small number of cells within a cancer, known as CSCs, are responsible for resistance to chemotherapy and radiation therapy, as well as for recurrent and metastatic disease. This review discusses current studies about thyroid CSCs, the processes of epithelial-to-mesenchymal transition (EMT), and mesenchymal-to-epithelial transition that provide plasticity to CSC growth, in addition to the role of microRNAs in CSC development and regulation. Understanding the biology of CSCs, EMT and the metastatic cascade should lead to the design of more rational targeted therapies for highly aggressive and fatal thyroid cancers.

Donor CD4+ Foxp3+ regulatory T cells are necessary for posttransplantation cyclophosphamide-mediated protection against GVHD in mice

Posttransplantation cyclophosphamide (PTCy) is an effective prophylaxis against graft-versus-host disease (GVHD). However, it is unknown whether PTCy works singularly by eliminating alloreactive T cells via DNA alkylation or also by restoring the conventional (Tcon)/regulatory (Treg) T-cell balance. We studied the role of Tregs in PTCy-mediated GVHD prophylaxis in murine models of allogeneic blood or marrow transplantation (alloBMT). In 2 distinct MHC-matched alloBMT models, infusing Treg-depleted allografts abrogated the GVHD-prophylactic activity of PTCy. Using allografts in which Foxp3(+) Tregs could be selectively depleted in vivo, either pre- or post-PTCy ablation of donor thymus-derived Tregs (tTregs) abolished PTCy protection against GVHD. PTCy treatment was associated with relative preservation of donor Tregs. Experiments using combinations of Foxp3(-) Tcons and Foxp3(+) Tregs sorted from different Foxp3 reporter mice indicated that donor Treg persistence after PTCy treatment was predominantly caused by survival of functional tTregs that retained Treg-specific demethylation and also induction of peripherally derived Tregs. Finally, adoptive transfer of tTregs retrieved from PTCy-treated chimeras rescued PTCy-treated, Treg-depleted recipients from lethal GVHD. Our findings indicate that PTCy-mediated protection against GVHD is not singularly dependent on depletion of donor alloreactive T cells but also requires rapidly recovering donor Tregs to initiate and maintain alloimmune regulation.

Metabolic regulation of stem cell function

Stem cell function is regulated by intrinsic mechanisms, such as transcriptional and epigenetic regulators, as well as extrinsic mechanisms, such as short-range signals from the niche and long-range humoral signals. Interactions between these regulatory mechanisms and cellular metabolism are just beginning to be identified. In multiple systems, differentiation is accompanied by changes in glycolysis, oxidative phosphorylation and the levels of reactive oxygen species. Indeed, metabolic pathways regulate proliferation and differentiation by regulating energy production and the generation of substrates for biosynthetic pathways. Some metabolic pathways appear to function differently in stem cells as compared with restricted progenitors and differentiated cells. They also appear to influence stem cell function by regulating signal transduction, epigenetic marks and oxidative stress. Studies to date illustrate the importance of metabolism in the regulation of stem cell function and suggest complex cross-regulation likely exists between metabolism and other stem cell regulatory mechanisms.

Essential role of aldehyde dehydrogenase 1A3 for the maintenance of non-small cell lung cancer stem cells is associated with the STAT3 pathway

PURPOSE

Lung cancer stem cells (CSC) with elevated aldehyde dehydrogenase (ALDH) activity are self-renewing, clonogenic, and tumorigenic. The purpose of our study is to elucidate the mechanisms by which lung CSCs are regulated.

EXPERIMENTAL DESIGN

A genome-wide gene expression analysis was performed to identify genes differentially expressed in the ALDH(+) versus ALDH -: cells. RT-PCR, Western blot analysis, and Aldefluor assay were used to validate identified genes. To explore the function in CSCs, we manipulated their expression followed by colony and tumor formation assays.

RESULTS

We identified a subset of genes that were differentially expressed in common in ALDH(+) cells, among which ALDH1A3 was the most upregulated gene in ALDH(+) versus ALDH -: cells. shRNA-mediated knockdown of ALDH1A3 in non-small cell lung cancer (NSCLC) resulted in a dramatic reduction in ALDH activity, clonogenicity, and tumorigenicity, indicating that ALDH1A3 is required for tumorigenic properties. In contrast, overexpression of ALDH1A3 by itself it was not sufficient to increase tumorigenicity. The ALDH(+) cells also expressed more activated STAT3 than ALDH -: cells. Inhibition of STAT3 or its activator EZH2 genetically or pharmacologically diminished the level of ALDH(+) cells and clonogenicity. Unexpectedly, ALDH1A3 was highly expressed in female, never smokers, well-differentiated tumors, or adenocarcinoma. ALDH1A3 low expression was associated with poor overall survival.

CONCLUSIONS

Our data show that ALDH1A3 is the predominant ALDH isozyme responsible for ALDH activity and tumorigenicity in most NSCLCs, and that inhibiting either ALDH1A3 or the STAT3 pathway are potential therapeutic strategies to eliminate the ALDH(+) subpopulation in NSCLCs.

Germline genetic variants in ABCB1, ABCC1 and ALDH1A1, and risk of hematological and gastrointestinal toxicities in a SWOG Phase III trial S0221 for breast cancer

Hematological and gastrointestinal toxicities are common among patients treated with cyclophosphamide and doxorubicin for breast cancer. To examine whether single-nucleotide polymorphisms (SNPs) in key pharmacokinetic genes were associated with risk of hematological or gastrointestinal toxicity, we analyzed 78 SNPs in ABCB1, ABCC1 and ALDH1A1 in 882 breast cancer patients enrolled in the SWOG trial S0221 and treated with cyclophosphamide and doxorubicin. A two-SNP haplotype in ALDH1A1 was associated with an increased risk of grade 3 and 4 hematological toxicity (odds ratio=1.44, 95% confidence interval=1.16-1.78), which remained significant after correction for multiple comparisons. In addition, four SNPs in ABCC1 were associated with gastrointestinal toxicity. Our findings provide evidence that SNPs in pharmacokinetic genes may have an impact on the development of chemotherapy-related toxicities. This is a necessary first step toward building a clinical tool that will help assess risk of adverse outcomes before undergoing chemotherapy.

Aldehyde dehydrogenases in acute myeloid leukemia

Acute myeloid leukemia (AML) affects approximately 15,000 persons per year in the United States and is the sixth leading cause of cancer-related deaths. The treatment of AML has advanced little in the past thirty years, in part because of the biologic heterogeneity of the disease and the difficulty in targeting AML cells while sparing normal hematopoietic cells. Advances in preventing and treating AML are likely to occur once the cellular and molecular differences between leukemia and normal hematopoietic cells are better understood. Aldehyde dehydrogenase (ALDH) activity is highly expressed in hematopoietic stem cells (HSCs), while, in contrast, a subset of AMLs are lacking this activity. This difference may be relevant to the development of AML and may also provide a better avenue for treating this disease. In this review, we summarize what is known about the ALDHs in normal HSCs and AML and propose strategies for capitalizing on these differences in the treatment of acute leukemia, and possibly other cancers as well.

The cancer stem cell marker aldehyde dehydrogenase is required to maintain a drug-tolerant tumor cell subpopulation

Selective kinase inhibitors have emerged as an important class of cancer therapeutics, and several such drugs are now routinely used to treat advanced-stage disease. However, their clinical benefit is typically short-lived because of the relatively rapid acquisition of drug resistance following treatment response. Accumulating preclinical and clinical data point to a role for a heterogeneous response to treatment within a subpopulation of tumor cells that are intrinsically drug-resistant, such as cancer stem cells. We have previously described an epigenetically determined reversibly drug-tolerant subpopulation of cancer cells that share some properties with cancer stem cells. Here, we define a requirement for the previously established cancer stem cell marker ALDH (aldehyde dehydrogenase) in the maintenance of this drug-tolerant subpopulation. We find that ALDH protects the drug-tolerant subpopulation from the potentially toxic effects of elevated levels of reactive oxygen species (ROS) in these cells, and pharmacologic disruption of ALDH activity leads to accumulation of ROS to toxic levels, consequent DNA damage, and apoptosis specifically within the drug-tolerant subpopulation. Combining ALDH inhibition with other kinase-directed treatments delayed treatment relapse in vitro and in vivo, revealing a novel combination treatment strategy for cancers that might otherwise rapidly relapse following single-agent therapy.

A red-shifted fluorescent substrate for aldehyde dehydrogenase

Selection of cells positive for aldehyde dehydrogenase (ALDH) activity from a green fluorescent background is difficult with existing reagents. Here we report a red-shifted fluorescent substrate for ALDH, AldeRed 588-A, for labeling viable ALDH^pos cells. We demonstrate that AldeRed 588-A successfully isolates ALDH^hi human hematopoietic stem cells from heterogeneous cord blood mononuclear cells. AldeRed 588-A can be used for multi-color applications to fractionate ALDH^pos cells in the presence of green fluorophores including the ALDEFLUOR™ reagent and cells expressing eGFP. AldeRed 588-A stains ALDH^pos murine pancreatic centroacinar and terminal duct cells, as visualized by fluorescent microscopy. AldeRed588-A provides a useful tool to select stem cells or study ALDH within a green fluorescent background.