Aldehyde dehydrogenases in acute myeloid leukemia

Investigating the biology of microRNA links to ALDH1A1 reveals candidates for preclinical testing in acute myeloid leukemia

Aldehyde dehydrogenase 1 family member A1 (ALDH1A1) is a member of the aldehyde dehydrogenase gene subfamily that encode enzymes with the ability to oxidize retinaldehyde. It was recently shown that high ALDH1A1 RNA abundance correlates with a poor prognosis in acute myeloid leukemia (AML). AML is a hematopoietic malignancy associated with high morbidity and mortality rates. Although there are a number of agents that inhibit ALDH activity, it would be crucial to develop methodologies for adjustable genetic interference, which would permit interventions on several oncogenic pathways in parallel. Intervention in multiple oncogenic pathways is theoretically possible with microRNAs (miRNAs or miRs), a class of small non‑coding RNAs that have emerged as key regulators of gene expression in AML. A number of miRNAs have shown the ability to interfere with ALDH1A1 gene expression directly in solid tumor cells, and these miRNAs can be evaluated in AML model systems. There are indications that a few of these miRNAs actually do have an association with AML disease course, rendering them a promising target for genetic intervention in AML cells.

OGG1 as an Epigenetic Reader Affects NFκB: What This Means for Cancer

8-oxoguanine glycosylase 1 (OGG1), which was initially identified as the enzyme that catalyzes the first step in the DNA base excision repair pathway, is now also recognized as a modulator of gene expression. What is important for cancer is that OGG1 acts as a modulator of NFκB-driven gene expression. Specifically, oxidant stress in the cell transiently halts enzymatic activity of substrate-bound OGG1. The stalled OGG1 facilitates DNA binding of transactivators, such as NFκB to their cognate sites, enabling the expression of cytokines and chemokines, with ensuing recruitment of inflammatory cells. Recently, we highlighted chief aspects of OGG1 involvement in regulation of gene expression, which hold significance in lung cancer development. However, OGG1 has also been implicated in the molecular underpinning of acute myeloid leukemia. This review analyzes and discusses how these cells adapt through redox-modulated intricate connections, via interaction of OGG1 with NFκB, which provides malignant cells with alternative molecular pathways to transform their microenvironment, enabling adjustment, promoting cell proliferation, metastasis, and evading killing by therapeutic agents.

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.

Aldehyde Dehydrogenase Genes as Prospective Actionable Targets in Acute Myeloid Leukemia

It has been previously shown that the aldehyde dehydrogenase (ALDH) family member ALDH1A1 has a significant association with acute myeloid leukemia (AML) patient risk group classification and that AML cells lacking ALDH1A1 expression can be readily killed via chemotherapy. In the past, however, a redundancy between the activities of subgroup members of the ALDH family has hampered the search for conclusive evidence to address the role of specific ALDH genes. Here, we describe the bioinformatics evaluation of all nineteen member genes of the ALDH family as prospective actionable targets for the development of methods aimed to improve AML treatment. We implicate ALDH1A1 in the development of recurrent AML, and we show that from the nineteen members of the ALDH family, ALDH1A1 and ALDH2 have the strongest association with AML patient risk group classification. Furthermore, we discover that the sum of the expression values for RNA from the genes, ALDH1A1 and ALDH2, has a stronger association with AML patient risk group classification and survival than either one gene alone does. In conclusion, we identify ALDH1A1 and ALDH2 as prospective actionable targets for the treatment of AML in high-risk patients. Substances that inhibit both enzymatic activities constitute potentially effective pharmaceutics.

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.

Acute Myeloid Leukemia Stem Cells: Origin, Characteristics, and Clinical Implications

The stem cells of acute myeloid leukemia (AML) are the malignancy initiating cells whose survival ultimately drives growth of these lethal diseases. Here we review leukemia stem cell (LSC) biology, particularly as it relates to the very heterogeneous nature of AML and to its high disease relapse rate. Leukemia ontogeny is presented, and the defining functional and phenotypic features of LSCs are explored. Surface and metabolic phenotypes of these cells are described, particularly those that allow distinction from features of normal hematopoietic stem cells (HSCs). Opportunities for use of this information for improving therapy for this challenging group of diseases is highlighted, and we explore the clinical needs which may be addressed by emerging LSC data. Finally, we discuss current gaps in the scientific understanding of LSCs.

p65/RelA NF-κB fragments generated by RIPK3 activity regulate tumorigenicity, cell metabolism, and stemness characteristics

Receptor‐interacting protein kinase 3 (RIPK3) can induce necroptosis, apoptosis, or cell proliferation and is silenced in several hematological malignancies. We previously reported that RIPK3 activity independent of its kinase domain induces caspase‐mediated p65/RelA cleavage, resulting in N‐terminal 1‐361 and C‐terminal 362‐549 fragments. We show here that a noncleavable p65/RelA D361E mutant expressed in DA1‐3b leukemia cells decreases mouse survival times and that coexpression of p65/RelA fragments increases the tumorigenicity of B16F1 melanoma cells. This aggressiveness in vivo did not correlate with NF‐κB activity measured in vitro. The fragments and p65/RelA D361E mutant induced different expression profiles in DA1‐3b and B16F1 cells. Stemness markers were affected: p65/RelA D361E increased ALDH activity in DA1‐3b cells, and fragment expression increased melanoma sphere formation in B16/F1 cells. p65/RelA fragments and the D361E noncleavable mutant decreased oxidative or glycolytic cell metabolism, with differences observed between models. Thus, p65/RelA cleavage initiated by kinase‐independent RIPK3 activity in cancer cells is not neutral and induces pleiotropic effects in vitro and in vivo that may vary across tumor types.

Ferroptosis: Cancer Stem Cells Rely on Iron until "to Die for" It

Cancer stem cells (CSCs) are a distinct subpopulation of tumor cells with stem cell-like features. Able to initiate and sustain tumor growth and mostly resistant to anti-cancer therapies, they are thought responsible for tumor recurrence and metastasis. Recent accumulated evidence supports that iron metabolism with the recent discovery of ferroptosis constitutes a promising new lead in the field of anti-CSC therapeutic strategies. Indeed, iron uptake, efflux, storage and regulation pathways are all over-engaged in the tumor microenvironment suggesting that the reprogramming of iron metabolism is a crucial occurrence in tumor cell survival. In particular, recent studies have highlighted the importance of iron metabolism in the maintenance of CSCs. Furthermore, the high concentration of iron found in CSCs, as compared to non-CSCs, underlines their iron addiction. In line with this, if iron is an essential macronutrient that is nevertheless highly reactive, it represents their Achilles’ heel by inducing ferroptosis cell death and therefore providing opportunities to target CSCs. In this review, we first summarize our current understanding of iron metabolism and its regulation in CSCs. Then, we provide an overview of the current knowledge of ferroptosis and discuss the role of autophagy in the (regulation of) ferroptotic pathways. Finally, we discuss the potential therapeutic strategies that could be used for inducing ferroptosis in CSCs to treat cancer.

Rational Design of a Red Fluorescent Sensor for ALDH1A1 Displaying Enhanced Cellular Uptake and Reactivity

High aldehyde dehydrogenase 1A1 (ALDH1A1) activity has emerged as a reliable marker for the identification of both normal and cancer stem cells. To facilitate the detection, molecular imaging, and sorting of stem cells, a green fluorescent probe based on the xanthene dye scaffold was recently developed. However, green dyes are less amenable to multicolor imaging because most commercial reagents are also green. Overcoming this limitation will enable the simultaneous tracking of multiple stem cell markers. Herein, we report the development of a red congener, red-AlDeSense. Through chemical tuning we were able to achieve excellent isoform selectivity and chemostability, a good turn on response, and enhanced cellular uptake and reactivity. Importantly, red-AlDeSense represents one of only a few turn-on sensors in the red region that use the d-PeT quenching mechanism. By employing red-AlDeSense and a green anti-CD44 antibody, we were able to demonstrate staining of these two stem cell markers is independent of one another in A549 lung adenocarcinoma cells.

The novel Isatin analog KS99 targets stemness markers in acute myeloid leukemia

Leukemic stem cells are multipotent, self-renewing, highly proliferative cells that can withstand drug treatments. Although currently available treatments potentially destroy blast cells, they fail to eradicate leukemic progenitor cells completely. Aldehyde dehydrogenase and STAT3 are frequently up-regulated in pre-leukemic stem cells as well as in acute myeloid leukemia (AML) expressing the CD34⁺CD38⁻ phenotype. The Isatin analog, KS99 has shown anticancer activity against multiple myeloma which may, in part, be mediated by inhibition of Bruton’s tyrosine kinase activation. Here we demonstrate that KS99 selectively targets leukemic stem cells with high aldehyde dehydrogenase activity and inhibits phosphorylation of STAT3. KS99 targeted cells co-expressing CD34, CD38, CD123, TIM-3, or CD96 immunophenotypes in AML, alone or in combination with the standard therapeutic agent cytarabine. AML with myelodysplastic-related changes was more sensitive than de novo AML with or without NPM1 mutation. KS99 treatment reduced the clonogenicity of primary human AML cells as compared to normal cord blood mononuclear cells. Downregulation of phosphorylated Bruton’s tyrosine kinase, STAT3, and aldehyde dehydrogenase was observed, suggesting interaction with KS99 as predicted through docking. KS99 with or without cytarabine showed in vivo preclinical efficacy in human and mouse AML animal models and prolonged survival. KS99 was well tolerated with overall negligible adverse effects. In conclusion, KS99 inhibits aldehyde dehydrogenase and STAT3 activities and causes cell death of leukemic stem cells, but not normal hematopoietic stem and progenitor cells.

Update of ALDH as a Potential Biomarker and Therapeutic Target for AML

Studies employing mouse transplantation have illustrated the role of aldehyde dehydrogenase (ALDH) defining hematopoietic stem cells (HSCs) and leukemia stem cells (LSCs). Besides being a molecular marker, ALDH mediates drug resistance in AML, which induces poor prognosis of the patients. In AML patients, either CD34⁺ALDH^br population or CD34⁺CD38^-ALDH^int population was found to denote LSCs and minimal residual disease (MRD). A bunch of reagents targeting ALDH directly or indirectly have been evaluated. ATRA, disulfiram, and dimethyl ampal thiolester (DIMATE) are all shown to be potential candidates to open new perspective for AML treatment. However, inconsistent results have been shown for markers of LSCs, which makes it even more difficult to differentiate LSCs and HSCs. In this review, we elevated the role of ALDH to be a potential marker to define and distinguish HSCs and LSCs and its importance in prognosis and target therapy in AML patients. In addition to immunophenotypical markers, ALDH is also functionally active in defining and distinguishing HSCs and LSCs and offers intracellular protections against cytotoxic drugs. Targeting ALDH may be a potential strategy to improve AML treatment. Additional studies concerning specific targeting ALDH and mechanisms of its roles in LSCs are warranted.

The stem cell/cancer stem cell marker ALDH1A3 regulates the expression of the survival factor tissue transglutaminase, in mesenchymal glioma stem cells

Tissue transglutaminase (tTG), a dual-function enzyme with GTP-binding and acyltransferase activities, has been implicated in the survival and chemotherapy resistance of aggressive cancer cells and cancer stem cells, including glioma stem cells (GSCs). Using a model system comprising two distinct subtypes of GSCs referred to as proneural (PN) and mesenchymal (MES), we find that the phenotypically aggressive and radiation therapy-resistant MES GSCs exclusively express tTG relative to PN GSCs. As such, the self-renewal, proliferation, and survival of these cells was sensitive to treatment with tTG inhibitors, with a benefit being observed when combined with the standard of care for high grade gliomas (i.e. radiation or temozolomide). Efforts to understand the molecular drivers of tTG expression in MES GSCs revealed an unexpected link between tTG and a common marker for stem cells and cancer stem cells, Aldehyde dehydrogenase 1A3 (ALDH1A3). ALDH1A3, as well as other members of the ALDH1 subfamily, can function in cells as a retinaldehyde dehydrogenase to generate retinoic acid (RA) from retinal. We show that the enzymatic activity of ALDH1A3 and its product, RA, are necessary for the observed expression of tTG in MES GSCs. Additionally, the ectopic expression of ALDH1A3 in PN GSCs is sufficient to induce the expression of tTG in these cells, further demonstrating a causal link between ALDH1A3 and tTG. Together, these findings ascribe a novel function for ALDH1A3 in an aggressive GSC phenotype via the up-regulation of tTG, and suggest the potential for a similar role by ALDH1 family members across cancer types.

Mass Spectrometry-Based Tools to Characterize DNA-Protein Cross-Linking by Bis-Electrophiles

DNA-protein cross-links (DPCs) are unusually bulky DNA adducts that form in cells as a result of exposure to endogenous and exogenous agents including reactive oxygen species, ultraviolet light, ionizing radiation, environmental agents (e.g. transition metals, formaldehyde, 1,2-dibromoethane, 1,3-butadiene) and common chemotherapeutic agents. Covalent DPCs are cytotoxic and mutagenic due to their ability to interfere with faithful DNA replication and to prevent accurate gene expression. Key to our understanding of the biological significance of DPC formation is identifying the proteins most susceptible to forming these unusually bulky and complex lesions and quantifying the extent of DNA-protein cross-linking in cells and tissues. Recent advances in bottom-up mass spectrometry-based proteomics have allowed for an unbiased assessment of the whole protein DPC adductome after in vitro and in vivo exposures to cross-linking agents. This MiniReview summarizes current and emerging methods for DPC isolation and analysis by mass spectrometry-based proteomics. We also highlight several examples of successful applications of these novel methodologies to studies of DPC lesions induced by bis-electrophiles such as formaldehyde, 1,2,3,4-diepoxybutane, nitrogen mustards and cisplatin.

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.

Measurement of Endogenous versus Exogenous Formaldehyde-Induced DNA-Protein Crosslinks in Animal Tissues by Stable Isotope Labeling and Ultrasensitive Mass Spectrometry

DNA-protein crosslinks (DPC) arise from a wide range of endogenous and exogenous chemicals, such as chemotherapeutic drugs and formaldehyde. Importantly, recent identification of aldehydes as endogenous genotoxins in Fanconi anemia has provided new insight into disease causation. Because of their bulky nature, DPCs pose severe threats to genome stability, but previous methods to measure formaldehyde-induced DPCs were incapable of discriminating between endogenous and exogenous sources of chemical. In this study, we developed methods that provide accurate and distinct measurements of both exogenous and endogenous DPCs in a structurally specific manner. We exposed experimental animals to stable isotope-labeled formaldehyde ([(13)CD2]-formaldehyde) by inhalation and performed ultrasensitive mass spectrometry to measure endogenous (unlabeled) and exogenous ((13)CD2-labeled) DPCs. We found that exogenous DPCs readily accumulated in nasal respiratory tissues but were absent in tissues distant to the site of contact. This observation, together with the finding that endogenous formaldehyde-induced DPCs were present in all tissues examined, suggests that endogenous DPCs may be responsible for increased risks of bone marrow toxicity and leukemia. Furthermore, the slow rate of DPC repair provided evidence for the persistence of DPCs. In conclusion, our method for measuring endogenous and exogenous DPCs presents a new perspective for the potential health risks inflicted by endogenous formaldehyde and may inform improved disease prevention and treatment strategies. Cancer Res; 76(9); 2652-61. ©2016 AACR.

Haploidentical Donors: Can Faster Transplantation Be Life-Saving for Patients with Advanced Disease?

Haploidentical stem cell transplantation is a therapeutic option for patients without an HLA-matched donor. It is increasingly being used worldwide due to the application of posttransplantation cyclophosphamide and is associated with lower incidence of graft-versus-host disease and treatment-related mortality. Haploidentical donors are generally available for most patients and stem cells can be rapidly obtained. Delays in transplantation while waiting for unrelated donor cells can be potentially problematic for patients with advanced disease at risk for progression; thus, the use of haploidentical donors, especially in this setting, can be life-saving. Here we reviewed the literature on haploidentical stem cell transplantation performed with posttransplantation cyclophosphamide.

Detection of ALDH1 activity in rabbit hepatic VX2 tumors and isolation of ALDH1 positive cancer stem cells

Background

Aldehyde dehydrogenase 1 (ALDH1) activity has been implicated in the therapeutic drug resistance of many malignancies and has been widely used as a marker to identify stem-like cells, including in primary liver cancer. Cancer stem cells (CSCs) are thought to play a crucial role in cancer progression and metastasis. In order to clarify the validity of the rabbit VX2 liver cancer model, we questioned if it expresses ALDH1 as a potential marker of CSCs. Hepatocellular carcinoma is a common malignancy worldwide and has poor prognosis. Most of the animal models used to study hepatocellular carcinoma are rodent models which lack clinical relevance. The rabbit VX2 model is a large animal model useful for preclinical and for developing drugs targeting cancer stem cells.

Materials and methods

We used flow cytometry to identify rabbit VX2 liver tumor cells that express ALDH1A1 activity at a high level and confirmed the results with RT-PCR, immunohistochemical and western blot analyses. Further, mRNA and protein expression analysis of tumor samples also express the markers for stemness like klf4, oct3/4, CD44 and nanog as well as the differentiation marker α-fetoprotein.

Results

We used Aldefluor flow cytometry-based assay to identify cells with high ALDH1 activity in the rabbit VX2 liver cancer model. We used the brightest 4.39 % of the total cancer cell population in our study. We performed semi-quantitative as well as real time PCR to characterize the stemness derived from VX2 tumors and tissues from normal rabbit liver. We demonstrated that VX2 tumors have higher expression of cancer stem cell markers such as AlDH1A1 and CD44 in comparison to normal rabbit liver cells. Additionally, real time PCR analysis of the same samples using syber-green demonstrated the significant change (p > 0.05) in the expression of genes. We validated the gene expression of the stemness markers by performing western blot and immunofluorescence. We showed that cancer stem cell markers (AlDH1A1, CD44) and the differentiation marker α-fetoprotein were upregulated in VX2 tumor cells. The same extent of upregulation was observed in stemness markers (klf4, oct3/4 and nanog) in VX2 tumors in comparison to normal rabbit liver.

Conclusion

The overall results of this study indicate that ALDH1 is a valid CSC marker for VX2 cancer. This finding suggests that the rabbit VX2 liver cancer model is useful in studying drug resistance in hepatocellular carcinoma and may be useful for basic and preclinical studies of other types of human cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0785-0) contains supplementary material, which is available to authorized users.

Clinicopathological significance of ALDH1A1 in lung, colorectal, and breast cancers: a meta-analysis

AIM

Aldehyde dehydrogenase 1 family member A1 (ALDH1A1) is a putative cancer stem cell marker. This meta-analysis evaluated ALDH1A1 expression's clinicopathological associations with lung cancer (LC), colorectal cancer (CRC) and breast cancer (BC).

MATERIALS & METHODS

Publications were retrieved from various databases and assessed for relevance and quality. Relationships between ALDH1A1 expression and clinicopathological characteristics were evaluated using Review Manager 5.2 software.

RESULTS

Thirty-eight studies were included (6057 patients). ALDH1A1 expression was significantly associated with the presence of LC; lymph node metastasis, clinical stage and differentiation in LC and BC; and molecular subtype in BC (p < 0.05). There were no significant association with BC tumor size and CRC.

CONCLUSION

ALDH1A1 may be a stem cell marker in LC and BC.

Relevance of leukemic stem cells in acute myeloid leukemia: heterogeneity and influence on disease monitoring, prognosis and treatment design

Acute myeloid leukemia is a bone marrow disease characterized by a block in differentiation of the myeloid lineage with a concomitant uncontrolled high proliferation rate. Development of acute myeloid leukemia from stem cells with specific founder mutations, leads to an oligoclonal disease that progresses into a very heterogeneous leukemia at diagnosis. Measurement of leukemic stem cell load and characterization of these cells are essential for prediction of relapse and target identification, respectively. Prediction of relapse by monitoring the disease during minimal residual disease detection is challenged by clonal shifts during therapy. To overcome this, characterization of the potential relapse-initiating cells is required using both flow cytometry and molecular analysis since leukemic stem cells can be targeted both on extracellular features and on stem-cell specific signal transduction pathways.