Aldehyde dehydrogenase inhibitors: a comprehensive review of the pharmacology, mechanism of action, substrate specificity, and clinical application

Advances in the Detection of Dithiocarbamate Fungicides: Opportunities for Biosensors

Dithiocarbamate fungicides (DTFs) are widely used to control various fungal diseases in crops and ornamental plants. Maximum residual limits in the order of ppb-ppm are currently imposed by legislation to prevent toxicity problems associated with excessive use of DTFs. The specific analytical determination of DTFs is complicated by their low solubility in water and organic solvents. This review summarizes the current analytical procedures used for the analysis of DTF, including chromatography, spectroscopy, and sensor-based methods and discusses the challenges related to selectivity, sensitivity, and sample preparation. Biosensors based on enzymatic inhibition demonstrated potential as analytical tools for DTFs and warrant further research, considering novel enzymes from extremophilic sources. Meanwhile, Raman spectroscopy and various sensors appear very promising, provided the selectivity issues are solved.

The discovery of novel small molecule allosteric activators of aldehyde dehydrogenase 2

Aldehyde dehydrogenase 2 (ALDH2) plays important role in ethanol metabolism, and also serves as an important shield from the damage occurring under oxidative stress. A special inactive variant was found carried by 35-45% of East Asians. The variant carriers have recently been found at the higher risk for the diseases related to the damage occurring under oxidative stress, such as cardiovascular and cerebrovascular diseases. As a result, ALDH2 activators may potentially serve as a new class of therapeutics. Herein, N-benzylanilines were found as novel allosteric activators of ALDH2 by computational virtual screening using ligand-based and structure-based screening parallel screening strategy. Then a structural optimization was performed and has led to the discovery of the compound C6. It has good activity in vitro and in vivo, which could reduce infarct size by ∼70% in ischemic stroke rat models. This study provided good lead compounds for the further development of ALDH2 activators.

Betel quid dependence mechanism and potential cessation therapy

BACKGROUND

Global reports estimate the number of betel quid (BQ) chewers up to 600 million. The proportion of betel quid dependence (BQD) is 20%-90% among current users. BQD mechanisms are not fully understood, and no pharmacological solution exists for its cessation therapy.

METHODS

We present a systematic review on BQD mechanisms and examine potential cessation therapeutic drugs. We conducted a systematic literature search in PubMed and Web of Science databases and identified the latest 10 years' relevant articles for reviews.

RESULTS

Functional magnetic resonance imaging results demonstrate that neurological mechanisms link the brain reward, cognitive, and impulsive systems in BQ or BQD users. The use of the areca nut increases both brain serotonin and noradrenaline levels, whereas arecoline, a potentially addictive areca nut component, has monoamine oxidase-A (MAO-A) inhibitor-like properties. MAO-A inhibitors prevent neurotransmitter breakdown and increase dopamine and serotonin concentrations in the brain. A reduction of daily BQ use was observed among patients with depression after antidepressant therapy, including MAO-A inhibitor and selective serotonin reuptake inhibitor (SSRI). Arecoline is a nicotinic acetylcholine receptor agonist expressed in Xenopus oocytes. However, relatively negligible amounts of nicotine are detected in the areca nut.

CONCLUSION

In conclusion, the current evidence provides a better understanding of the neurological and pharmacological mechanisms behind BQD. Arecoline, an MAO-A inhibitor, may account for BQD. Future translational studies are needed to verify the efficacy of potential BQD cessation drugs. MAO-A inhibitor and SSRI would thus be potentially promising targets for clinical trials.

Development of 2,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one inhibitors of aldehyde dehydrogenase 1A (ALDH1A) as potential adjuncts to ovarian cancer chemotherapy

There is strong evidence that inhibition of one or more Aldehyde Dehydrogenase 1A (ALDH1A) isoforms may be beneficial in chemotherapy-resistant ovarian cancer and other tumor types. While many previous efforts have focused on development of ALDH1A1 selective inhibitors, the most deadly ovarian cancer subtype, high-grade serous (HGSOC), exhibits elevated expression of ALDH1A3. Herein, we report continued development of pan-ALDH1A inhibitors to assess whether broad spectrum ALDH1A inhibition is an effective adjunct to chemotherapy in this critical tumor subtype. Optimization of the CM39 scaffold, aided by metabolite ID and several new ALDH1A1 crystal structures, led to improved biochemical potencies, improved cellular ALDH inhibition in HGSOC cell lines, and substantial improvements in microsomal stability culminating in orally bioavailable compounds. We demonstrate that two compounds 68 and 69 are able to synergize with chemotherapy in a resistant cell line and patient-derived HGSOC tumor spheroids, indicating their suitability for future in vivo proof of concept experiments.

Recognition of a disulfiram ethanol reaction in the emergency department is not always straightforward

OBJECTIVES

Disulfiram is an adjunct in the treatment of alcohol use disorders, but case reports indicate that disulfiram ethanol reactions are not always recognized in the emergency department. Our first aim is to remind of this risk with two case reports of life-threatening reactions not immediately considered by the emergency physician. The second aim is to estimate the probability that a disulfiram reaction goes unrecognized with the use of a retrospective study of patients admitted to the emergency department.

METHODS

Clinical files of patients admitted between October 1, 2010 and September 30, 2014 to the emergency department were retrospectively screened for the key words "ethanol use" and "disulfiram". Their diagnoses were then scored by a panel regarding the probability of an interaction.

RESULTS

Seventy-nine patients were included, and a disulfiram-ethanol reaction was scored as either 'highly likely', 'likely' or 'possible' in 54.4% and as 'doubtful' or 'certainly not present' in 45.6% of the patients. The interrater agreement was 0.71 (95% CI: 0.64-0.79). The diagnosis was not considered or only after a delay in 44.2% of the patients with a 'possible' to 'highly likely' disulfiram interaction. One patient with a disulfiram overdose died and was considered as a 'possible' interaction.

DISCUSSION AND CONCLUSIONS

A disulfiram ethanol interaction can be life threatening and failure to consider the diagnosis in the emergency department seems frequent. Prospective studies with documentation of the intake of disulfiram and evaluation of the value of acetaldehyde as a biomarker are needed to determine the precise incidence. Improving knowledge of disulfiram interactions and adequate history taking of disulfiram intake may improve the care for patients.

Bone marrow stromal cells induce an ALDH+ stem cell-like phenotype and enhance therapy resistance in AML through a TGF-β-p38-ALDH2 pathway

The bone marrow microenvironment (BME) in acute myeloid leukemia (AML) consists of various cell types that support the growth of AML cells and protect them from chemotherapy. Mesenchymal stromal cells (MSCs) in the BME have been shown to contribute immensely to leukemogenesis and chemotherapy resistance in AML cells. However, the mechanism of stroma-induced chemotherapy resistance is not known. Here, we hypothesized that stromal cells promote a stem-like phenotype in AML cells, thereby inducing tumorigenecity and therapy resistance. To test our hypothesis, we co-cultured AML cell lines and patient samples with BM-derived MSCs and determined aldehyde dehydrogenase (ALDH) activity and performed gene expression profiling by RNA sequencing. We found that the percentage of ALDH+ cells increased dramatically when AML cells were co-cultured with MSCs. However, among the 19 ALDH isoforms, ALDH2 and ALDH1L2 were the only two that were significantly upregulated in AML cells co-cultured with stromal cells compared to cells cultured alone. Mechanistic studies revealed that the transforming growth factor-β1 (TGF-β1)-regulated gene signature is activated in AML cells co-cultured with MSCs. Knockdown of TGF-β1 in BM-MSCs inhibited stroma-induced ALDH activity and ALDH2 expression in AML cells, whereas treatment with recombinant TGF-β1 induced the ALDH+ phenotype in AML cells. We also found that TGF-β1-induced ALDH2 expression in AML cells is mediated by the non-canonical pathway through the activation of p38. Interestingly, inhibition of ALDH2 with diadzin and CVT-10216 significantly inhibited MSC-induced ALDH activity in AML cells and sensitized them to chemotherapy, even in the presence of MSCs. Collectively, BM stroma induces ALDH2 activity in AML cells through the non-canonical TGF-β pathway. Inhibition of ALDH2 sensitizes AML cells to chemotherapy.

Design, synthesis and the structure-activity relationship of agonists targeting on the ALDH2 catalytic tunnel

ALDH2, a key enzyme in the alcohol metabolism process, detoxifies several kinds of toxic small molecular aldehydes, which induce severe organ damages. The development of novel Alda-1 type ALDH2 activators was mostly relied on HTS but not rational design so far. To clarify the structure-activity relationship (SAR) of the skeleton of Alda-1 analogs by synthesis of the least number of analogs, we prepared 31 Alda-1 analogs and 3 isoflavone derivatives and evaluated for their ALDH2-activating activity. Among these, the ALDH2-activating activity of mono-halogen-substituted (Cl and Br) N-piperonylbenzamides 3b and 3 k, and non-aromatic amides 8a-8c, were 1.5-2.1 folds higher than that of Alda-1 at 20 μM. The relationship between binding affinity in computer aided molecular docking model and the ALDH2-activating activity assays were clarified as follows: for Alda-1 analogs, with the formation of halogen bonds, the enzyme-activating activity was found to follow a specific regression curve within the range between -5 kcal/mol and -4 kcal/mol. For isoflavone derivatives, the basic moiety on the B ring enhance the activating activity. These results provide a new direction of utilizing computer-aided modeling to design novel ALDH2 agonists in the future.

Discovery and development of selective aldehyde dehydrogenase 1A1 (ALDH1A1) inhibitors

ALDH1A1, one important member of 19 ALDHs, can metabolize reactive aldehydes to their corresponding carboxylic acid derivatives and play important physiological and toxicological roles in many areas, including CNS, metabolic disorders, and cancers. Overexpression of ALDH1A1 correlates with poor prognosis and tumor aggressiveness, is associated with drug resistance in traditional chemotherapy for cancer treatment and contributes to obesity, diabetes, and inflammation. So, inhibition of ALDH1A1 may offer new therapeutic options for patients with cancer, obesity, diabetes, and inflammation. Up to now, many ALDH1A1 inhibitors with different scaffolds have been identified and developed as useful chemical tools for better understanding of the functions of ALDH1A1 in physiologic and pathophysiologic conditions. In this review, the advances in the discovery and development of selective ALDH1A1 inhibitors are summarized, and opportunities and challenges associated with this field are also discussed.

GABA metabolism is crucial for long-term survival of anoxia in annual killifish embryos

In most vertebrates, a lack of oxygen quickly leads to irreparable damages to vital organs, such as the brain and heart. However, there are some vertebrates that have evolved mechanisms to survive periods of no oxygen (anoxia). The annual killifish (Austrofundulus limnaeus) survives in ephemeral ponds in the coastal deserts of Venezuela and their embryos have the remarkable ability to tolerate anoxia for months. When exposed to anoxia, embryos of A. limnaeus respond by producing significant amounts of γ-aminobutyric acid (GABA). This study aims to understand the role of GABA in supporting the metabolic response to anoxia. To explore this, we investigated four developmentally distinct stages of A. limnaeus embryos that vary in their anoxia tolerance. We measured GABA and lactate concentrations across development in response to anoxia and aerobic recovery. We then inhibited enzymes responsible for the production and degradation of GABA and observed GABA and lactate concentrations, as well as embryo mortality. Here, we show for the first time that GABA metabolism affects anoxia tolerance in A. limnaeus embryos. Inhibition of enzymes responsible for GABA production (glutamate decarboxylase) and degradation (GABA-transaminase and succinic acid semialdehyde dehydrogenase) led to increased mortality, supporting a role for GABA as an intermediate product and not a metabolic end-product. We propose multiple roles for GABA during anoxia and aerobic recovery in A. limnaeus embryos, serving as a neurotransmitter, an energy source, and an anti-oxidant.

Mechanism of cystathionine-β-synthase inhibition by disulfiram: The role of bis(N,N-diethyldithiocarbamate)-copper(II)

BACKGROUND

Hydrogen sulfide (H₂S) is an endogenous mammalian gasotransmitter. Cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) are the principal enzymes responsible for its biogenesis. A recent yeast screen suggested that disulfiram (a well-known inhibitor of aldehyde dehydrogenase and a clinically used drug in the treatment of alcoholism) may inhibit CBS in a cell-based environment. However, prior studies have not observed any direct inhibition of CBS by disulfiram. We investigated the potential role of bioconversion of disulfiram to bis(N,N-diethyldithiocarbamate)-copper(II) complex (CuDDC) in the inhibitory effect of disulfiram on H₂S production and assessed its effect in two human cell types with high CBS expression: HCT116 colon cancer cells and Down syndrome (DS) fibroblasts.

METHODS

H₂S production from recombinant human CBS, CSE and 3-MST was measured using the fluorescent H₂S probe AzMC. Mouse liver homogenate (a rich source of CBS) was also employed to measure H₂S biosynthesis. The interaction of copper with accessible protein cysteine residues was evaluated using the DTNB method. Cell proliferation and viability were measured using the BrdU and MTT methods. Cellular bioenergetics was evaluated by Extracellular Flux Analysis.

RESULTS

While disulfiram did not exert any significant direct inhibitory effect on any of the H₂S-producing enzymes, its metabolite, CuDDC was a potent inhibitor of CBS and CSE. The mode of its action is likely related to the complexed copper molecule. In cell-based systems, the effects of disulfiram were variable. In colon cancer cells, no significant effect of disulfiram was observed on H₂S production or proliferation or viability. In contrast, in DS fibroblasts, disulfiram inhibited H₂S production and improved proliferation and viability. Copper, on its own, failed to have any effects on either cell type, likely due to its low cell penetration. CuDDC inhibited H₂S production in both cell types studied and exerted the functional effects that would be expected from a CBS inhibitor: inhibition of cell proliferation of cancer cells and a bell-shaped effect (stimulation of proliferation at low concentration and inhibition of these responses at higher concentration) in DS cells. Control experiments using a chemical H₂S donor showed that, in addition to inhibiting CBS and CSE, part of the biological effects of CuDDC relates to a direct reaction with H₂S, which occurs through its complexed copper.

CONCLUSIONS

Disulfiram, via its metabolite CuDDC acts as an inhibitor of CBS and a scavenger of H₂S, which, in turn, potently suppresses H₂S levels in various cell types. Inhibition of H₂S biosynthesis may explain some of the previously reported actions of disulfiram and CuDDC in vitro and in vivo. Disulfiram or CuDDC may be considered as potential agents for the experimental therapy of various pathophysiological conditions associated with H₂S overproduction.

Impact of missense mutations in the ALDH7A1 gene on enzyme structure and catalytic function

Certain mutations in the ALDH7A1 gene cause pyridoxine-dependent epilepsy (PDE), an autosomal recessive metabolic disease characterized by seizures, and in some cases, intellectual disability. The mutational spectrum of PDE is vast and includes over 70 missense mutations. This review summarizes the current state of biochemical and biophysical research on the impact of PDE missense mutations on the structure and catalytic activity of ALDH7A1. Paradoxically, some mutations that target active site residues have a relatively modest impact on structure and function, while those remote from the active site can have profound effects. For example, missense mutations targeting remote residues in oligomer interfaces tend to strongly impact catalytic function by inhibiting formation of the active tetramer. These results shows that it remains very difficult to predict the impact of missense mutations, even when the structure of the wild-type enzyme is known. Additional biophysical analyses of many more disease-causing mutations are needed to develop the rules for predicting the impact of genetic mutations on enzyme structure and catalytic function.

Targeting Oxidative Phosphorylation Reverses Drug Resistance in Cancer Cells by Blocking Autophagy Recycling

The greatest challenge in cancer therapy is posed by drug-resistant recurrence following treatment. Anticancer chemotherapy is largely focused on targeting the rapid proliferation and biosynthesis of cancer cells. This strategy has the potential to trigger autophagy, enabling cancer cell survival through the recycling of molecules and energy essential for biosynthesis, leading to drug resistance. Autophagy recycling contributes amino acids and ATP to restore mTOR complex 1 (mTORC1) activity, which leads to cell survival. However, autophagy with mTORC1 activation can be stalled by reducing the ATP level. We have previously shown that cytosolic NADH production supported by aldehyde dehydrogenase (ALDH) is critical for supplying ATP through oxidative phosphorylation (OxPhos) in cancer cell mitochondria. Inhibitors of the mitochondrial complex I of the OxPhos electron transfer chain and ALDH significantly reduce the ATP level selectively in cancer cells, terminating autophagy triggered by anticancer drug treatment. With the aim of overcoming drug resistance, we investigated combining the inhibition of mitochondrial complex I, using phenformin, and ALDH, using gossypol, with anticancer drug treatment. Here, we show that OxPhos targeting combined with anticancer drugs acts synergistically to enhance the anticancer effect in mouse xenograft models of various cancers, which suggests a potential therapeutic approach for drug-resistant cancer.

The Role of ALDH in the Metastatic Potential of Osteosarcoma Cells and Potential ALDH Targets

Aldehyde dehydrogenases are a family of enzymes that oxidize aldehydes to carboxylic acids. These enzymes are important in cellular homeostasis during oxidative stress by the elimination of toxic aldehyde by-products from various cellular processes. In osteosarcoma, aldehyde dehydrogenase 1A1has been described as a cancer stem cell marker. Its activity has been found to correlate with metastatic potential and the metastatic phenotype. As such, a more complete understanding of aldehyde dehydrogenase in osteosarcoma will give us a deeper knowledge of its impact on osteosarcoma metastatic potential. Our hope is that this knowledge can be translated into novel antimetastatic therapeutic strategies and thus improve osteosarcoma prognoses.

Disulfiram Treatment Normalizes Body Weight in Obese Mice

Obesity is a top public health concern, and a molecule that safely treats obesity is urgently needed. Disulfiram (known commercially as Antabuse), an FDA-approved treatment for chronic alcohol addiction, exhibits anti-inflammatory properties and helps protect against certain types of cancer. Here, we show that in mice disulfiram treatment prevented body weight gain and abrogated the adverse impact of an obesogenic diet on insulin responsiveness while mitigating liver steatosis and pancreatic islet hypertrophy. Additionally, disulfiram treatment reversed established diet-induced obesity and metabolic dysfunctions in middle-aged mice. Reductions in feeding efficiency and increases in energy expenditure were associated with body weight regulation in response to long-term disulfiram treatment. Loss of fat tissue and an increase in liver fenestrations were also observed in rats on disulfiram. Given the potent anti-obesogenic effects in rodents, repurposing disulfiram in the clinic could represent a new strategy to treat obesity and its metabolic comorbidities.

Inhibition, crystal structures, and in-solution oligomeric structure of aldehyde dehydrogenase 9A1

Aldehyde dehydrogenase 9A1 (ALDH9A1) is a human enzyme that catalyzes the NAD⁺-dependent oxidation of the carnitine precursor 4-trimethylaminobutyraldehyde to 4-N-trimethylaminobutyrate. Here we show that the broad-spectrum ALDH inhibitor diethylaminobenzaldehyde (DEAB) reversibly inhibits ALDH9A1 in a time-dependent manner. Possible mechanisms of inhibition include covalent reversible inactivation involving the thiohemiacetal intermediate and slow, tight-binding inhibition. Two crystal structures of ALDH9A1 are reported, including the first of the enzyme complexed with NAD⁺. One of the structures reveals the active conformation of the enzyme, in which the Rossmann dinucleotide-binding domain is fully ordered and the inter-domain linker adopts the canonical β-hairpin observed in other ALDH structures. The oligomeric structure of ALDH9A1 was investigated using analytical ultracentrifugation, small-angle X-ray scattering, and negative stain electron microscopy. These data show that ALDH9A1 forms the classic ALDH superfamily dimer-of-dimers tetramer in solution. Our results suggest that the presence of an aldehyde substrate and NAD⁺ promotes isomerization of the enzyme into the active conformation.

Interaction of Ethanol and Oral ANS-6637, a Selective ALDH2 Inhibitor in Males: A Randomized, Double-Blind, Placebo-Controlled, Single-Ascending Dose Cohort Study

BACKGROUND

ANS-6637, an orally bioavailable selective and reversible aldehyde dehydrogenase-2 (ALDH2) inhibitor, is under development for drug and alcohol use disorders. During the elimination of alcohol, ALDH2 metabolizes acetaldehyde to acetate; inhibiting this enzyme can lead to aversive reactions due to the accumulation of acetaldehyde. Thus, understanding the safety and tolerability of ANS-6637 in combination with alcohol is essential.

TRIAL DESIGN AND METHODS

Forty eight healthy males participated in a randomized, double-blind, placebo-controlled, single-ascending dose cohort study of oral ANS-6637. Eligible participants were randomized to ANS-6637 (n = 36) or placebo (n = 12) in a 3:1 fashion in each of 6 dose cohorts (8 per cohort; ANS-6637 dose levels were 25, 50, 100, 200, 400, and 600 mg). Two hours after receiving study drug, participants drank up to 5 standard drinks, 1 every 30 minutes. Safety assessments, pharmacodynamic measures, and pharmacokinetic blood samples were obtained.

RESULTS

Flushing was the most common adverse event (AE) associated with ANS-6637 (24 of 36 participants) compared with placebo (3 of 12). Statistically significant, but modest, increases in heart rate (HR) occurred (+10.5 bpm after 2 drinks; +16.9 to + 20.5 bpm after 3^rd through 5^th drink). No participant met HR or systolic blood pressure criteria for stopping ethanol administration. There were no clinically significant QTc interval prolongations. Individuals receiving ANS-6637 reported lower ratings of liking, alcohol effects, and feeling drunk.

CONCLUSIONS

A single oral dose of ANS-6637 with up to 5 standards drinks over 2.5 hours was generally well tolerated in healthy males. The most common pharmacological response was flushing and an increase in HR, which are known effects of acetaldehyde accumulation and consistent with inhibition of ALDH2 with oral ANS-6637 in combination with alcohol. The results of this alcohol interaction study support further testing of ANS-6637 in individuals who consume alcohol heavily.

Preclinical pharmacology of a lipophenol in a mouse model of light-induced retinopathy

Environmental light has deleterious effects on the outer retina in human retinopathies, such as ABCA4-related Stargardt’s disease and dry age-related macular degeneration. These effects involve carbonyl and oxidative stress, which contribute to retinal cell death and vision loss. Here, we used an albino Abca4^−/− mouse model, the outer retina of which shows susceptibility to acute photodamage, to test the protective efficacy of a new polyunsaturated fatty acid lipophenol derivative. Anatomical and functional analyses demonstrated that a single intravenous injection of isopropyl-phloroglucinol-DHA, termed IP-DHA, dose-dependently decreased light-induced photoreceptor degeneration and preserved visual sensitivity. This protective effect persisted for 3 months. IP-DHA did not affect the kinetics of the visual cycle in vivo or the activity of the RPE65 isomerase in vitro. Moreover, IP-DHA administered by oral gavage showed significant protection of photoreceptors against acute light damage. In conclusion, short-term tests in Abca4-deficient mice, following single-dose administration and light exposure, identify IP-DHA as a therapeutic agent for the prevention of retinal degeneration.

Treating retinal damage in both aging and young patients might now be easier, thanks to treatment with a lipophenol, an omega-3 fatty acid linked to an antioxidant. The retina is the part of the eye that senses light, aided by light-sensitive pigments. However, these light-sensitive pigments can be converted by light to toxic byproducts, and in some individuals, these toxic byproducts can accumulate, damaging the retina and leading to vision loss. Philippe Brabet at the Montpellier Institute of Neuroscience in France and co-workers found that lipophenol treatment protected retinal cells from damage in a mouse model of retinal disease, and that a single dose has been effective in preserving vision. These results may help in finding new treatments for retinal diseases such as Stargardt disease and age-related macular degeneration.

Dual-mTOR Inhibitor Rapalink-1 Reduces Prostate Cancer Patient-Derived Xenograft Growth and Alters Tumor Heterogeneity

Bone metastasis is the leading cause of prostate cancer (PCa) mortality, frequently marking the progression to castration-resistant PCa. Dysregulation of the androgen receptor pathway is a common feature of castration-resistant PCa, frequently appearing in association with mTOR pathway deregulations. Advanced PCa is also characterized by increased tumor heterogeneity and cancer stem cell (CSC) frequency. CSC-targeted therapy is currently being explored in advanced PCa, with the aim of reducing cancer clonal divergence and preventing disease progression. In this study, we compared the molecular pathways enriched in a set of bone metastasis from breast and prostate cancer from snap-frozen tissue. To further model PCa drug resistance mechanisms, we used two patient-derived xenografts (PDX) models of bone-metastatic PCa, BM18, and LAPC9. We developed in vitro organoids assay and ex vivo tumor slice drug assays to investigate the effects of mTOR- and CSC-targeting compounds. We found that both PDXs could be effectively targeted by treatment with the bivalent mTORC1/2 inhibitor Rapalink-1. Exposure of LAPC9 to Rapalink-1 but not to the CSC-targeting drug disulfiram blocked mTORC1/2 signaling, diminished expression of metabolic enzymes involved in glutamine and lipid metabolism and reduced the fraction of CD44+ and ALDEFluorhigh cells, in vitro. Mice treated with Rapalink-1 showed a significantly delayed tumor growth compared to control and cells recovered from the tumors of treated animals showed a marked decrease of CD44 expression. Taken together these results highlight the increased dependence of advanced PCa on the mTOR pathway, supporting the development of a targeted approach for advanced, bone metastatic PCa.

4-hydroxy-2-nonenal decreases coronary endothelial cell migration: Potentiation by aldehyde dehydrogenase 2 inhibition

4-hydroxynonenal (4HNE) is a reactive aldehyde, which is involved in oxidative stress associated pathogenesis. The cellular toxicity of 4HNE is mitigated by aldehyde dehydrogenase (ALDH) 2. Thus, we hypothesize that ALDH2 inhibition exacerbates 4HNE-induced decrease in coronary endothelial cell (EC) migration in vitro. To test our hypothesis, we pharmacologically inhibited ALDH2 in cultured mouse coronary ECs (MCECs) by disulfiram (DSF) (2.5 μM) before challenging the cells with different doses of 4HNE (25, 50 and 75 μM) for 4, 12, 16 and 24 h. We evaluated MCEC migration by scratch wound migration assay. 4HNE attenuated MCEC migration significantly relative to control (P < .05), which was exacerbated with DSF pretreatment (P < .05). DSF pretreatment exacerbated 4HNE-induced decrease in ALDH2 activity in MCECs. Next, we showed that 75 μM 4HNE significantly decreased the intracellular mRNA levels of vascular endothelial growth factor (VEGF), VEGF receptor 2 (VEGFR2), focal adhesion kinase (FAK) and other promigratory genes compared to control, which were further decreased by DSF pretreatment. 75 μM 4HNE also decreased the protein levels of VEGFR2, FAK, phospho-FAK, Src and paxillin in MCECs. Thus, we conclude that ALDH2 inhibition potentiates 4HNE-induced decrease in MCECs migration in vitro.

An Updated Review of Disulfiram: Molecular Targets and Strategies for Cancer Treatment

Repurposing already approved drugs as new anticancer agents is a promising strategy considering the advantages such as low costs, low risks and less time-consumption. Disulfiram (DSF), as the first drug for antialcoholism, was approved by the U.S. Food and Drug Administration (FDA) over 60 years ago. Increasing evidence indicates that DSF has great potential for the treatment of various human cancers. Several mechanisms and targets of DSF related to cancer therapy have been proposed, including the inhibition of ubiquitin-proteasome system (UPS), cancer cell stemness and cancer metastasis, and alteration of the intracellular reactive oxygen species (ROS). This article provides a brief review about the history of the use of DSF in humans and its molecular mechanisms and targets of anticancer therapy, describes DSF delivery strategies for cancer treatment, summarizes completed and ongoing cancer clinical trials involving DSF, and offers strategies to better use DSF in cancer therapies.

Ferroptosis is involved in alcohol-induced cell death in vivo and in vitro

A critical pathogenic factor in the development of lethal liver failure is cell death induced by the accumulation of lipid reactive oxygen species. In this study, we discovered and illuminated a new mechanism that led to alcoholic liver disease via ferroptosis, an iron-dependent regulated cell death. Study in vitro showed that both necroptosis inhibitor and ferroptosis inhibitors performed significantly protective effect on alcohol-induced cell death, while apoptosis inhibitor and autophagy inhibitor had no such effect. Our data also indicated that alcohol caused the accumulation of lipid peroxides and the mRNA expression of prostaglandin-endoperoxide synthase 2, reduced the protein expression of the specific light-chain subunit of the cystine/glutamate antiporter and glutathione peroxidase 4. Importantly, ferrostatin-1 significantly ameliorated liver injury that was induced by overdosed alcohol both in vitro and in vivo. These findings highlight that targeting ferroptosis serves as a hepatoprotective strategy for alcoholic liver disease treatment.

Diversity of small molecule HIV-1 latency reversing agents identified in low- and high-throughput small molecule screens

The latency phenomenon produced by human immunodeficiency virus (HIV-1) prevents viral clearance by current therapies, and consequently development of a cure for HIV-1 disease represents a formidable challenge. Research over the past decade has resulted in identification of small molecules that are capable of exposing HIV-1 latent reservoirs, by reactivation of viral transcription, which is intended to render these infected cells sensitive to elimination by immune defense recognition or apoptosis. Molecules with this capability, known as latency-reversing agents (LRAs) could lead to realization of proposed HIV-1 cure strategies collectively termed "shock and kill," which are intended to eliminate the latently infected population by forced reactivation of virus replication in combination with additional interventions that enhance killing by the immune system or virus-mediated apoptosis. Here, we review efforts to discover novel LRAs via low- and high-throughput small molecule screens, and summarize characteristics and biochemical properties of chemical structures with this activity. We expect this analysis will provide insight toward further research into optimized designs for new classes of more potent LRAs.

Identification of ALDH1A3 as a Viable Therapeutic Target in Breast Cancer Metastasis-Initiating Cells

The development of efficacious therapies targeting metastatic spread of breast cancer to the brain represents an unmet clinical need. Accordingly, an improved understanding of the molecular underpinnings of central nervous system spread and progression of breast cancer brain metastases (BCBM) is required. In this study, the clinical burden of disease in BCBM was investigated, as well as the role of aldehyde dehydrogenase 1A3 (ALDH1A3) in the metastatic cascade leading to BCBM development. Initial analysis of clinical survival trends for breast cancer and BCBM determined improvement of breast cancer survival rates; however, this has failed to positively affect the prognostic milestones of triple-negative breast cancer (TNBC) brain metastases (BM). ALDH1A3 and a representative epithelial-mesenchymal transition (EMT) gene signature (mesenchymal markers, CD44 or Vimentin) were compared in tumors derived from BM, lung metastases (LM), or bone metastases (BoM) of patients as well as mice after injection of TNBC cells. Selective elevation of the EMT signature and ALDH1A3 were observed in BM, unlike LM and BoM, especially in the tumor edge. Furthermore, ALDH1A3 was determined to play a role in BCBM establishment via regulation of circulating tumor cell adhesion and migration phases in the BCBM cascade. Validation through genetic and pharmacologic inhibition of ALDH1A3 via lentiviral shRNA knockdown and a novel small-molecule inhibitor demonstrated selective inhibition of BCBM formation with prolonged survival of tumor-bearing mice. Given the survival benefits via targeting ALDH1A3, it may prove an effective therapeutic strategy for BCBM prevention and/or treatment.

Cystathionine-β-Synthase: Molecular Regulation and Pharmacological Inhibition

Cystathionine-β-synthase (CBS), the first (and rate-limiting) enzyme in the transsulfuration pathway, is an important mammalian enzyme in health and disease. Its biochemical functions under physiological conditions include the metabolism of homocysteine (a cytotoxic molecule and cardiovascular risk factor) and the generation of hydrogen sulfide (H2S), a gaseous biological mediator with multiple regulatory roles in the vascular, nervous, and immune system. CBS is up-regulated in several diseases, including Down syndrome and many forms of cancer; in these conditions, the preclinical data indicate that inhibition or inactivation of CBS exerts beneficial effects. This article overviews the current information on the expression, tissue distribution, physiological roles, and biochemistry of CBS, followed by a comprehensive overview of direct and indirect approaches to inhibit the enzyme. Among the small-molecule CBS inhibitors, the review highlights the specificity and selectivity problems related to many of the commonly used "CBS inhibitors" (e.g., aminooxyacetic acid) and provides a comprehensive review of their pharmacological actions under physiological conditions and in various disease models.

N,N-diethylaminobenzaldehyde targets aldehyde dehydrogenase to eradicate human pancreatic cancer cells

Pancreatic cancer is a common cause of worldwide cancer-related mortality with a poor 5-year survival rate. Aldehyde dehydrogenase (ALDH) activity is a possible marker for malignant stem cells in solid organ systems, including the pancreas, and N,N-diethylaminobenzaldehyde (DEAB) is able to inhibit ALDH activity. In the present study, the role of DEAB in the treatment of pancreatic cancer cells and the potential underlying mechanisms were investigated. The ALDH activities of pancreatic cancer cell lines treated with or without DEAB were analyzed by an ALDEFLUOR™ assay. The Cell Counting Kit-8 and colony formation assays, and cell cycle analysis were used to evaluate the viability, colony-forming ability and cell quiescence of cell lines under DEAB treatment, respectively. DEAB and/or gemcitabine-induced cell apoptosis was assessed by flow cytometry. DEAB reduced ALDH activity and inhibited the proliferation, colony-forming ability and cell quiescence of pancreatic cancer cell lines. Compared with respective controls, DEAB alone and the combination of gemcitabine and DEAB significantly decreased cell viability and increased cell apoptosis. Moreover, reverse transcription-PCR and western blotting were used to measure the expressions of B cell lymphoma 2 (Bcl2) associated X protein (Bax) and Bcl2 mRNA and protein. The anti-cancer effect of DEAB was associated with upregulation of Bax expression. Therefore, targeting ALDH with DEAB may be a potential therapeutic choice for pancreatic cancer, demonstrating a synergic effect with gemcitabine.

Molecular Dynamics Analysis of a Rationally Designed Aldehyde Dehydrogenase Gives Insights into Improved Activity for the Non-Native Cofactor NAD

The aldehyde dehydrogenase from Thermoplasma acidophilum was previously implemented as a key enzyme in a synthetic cell-free reaction cascade for the production of alcohols. In order to engineer the enzyme's cofactor specificity from NADP⁺ to NAD⁺, we identified selectivity-determining residues with the CSR-SALAD tool and investigated further positions based on the crystal structure. Stepwise combination of the initially discovered six point mutations allowed us to monitor the cross effects of each mutation, resulting in a final variant with reduced K_M for the non-native cofactor NAD⁺ (from 18 to 0.6 mM) and an increased activity for the desired substrate d-glyceraldehyde (from 0.4 to 1.5 U/mg). Saturation mutagenesis of the residues at the entrance of the substrate pocket could eliminate substrate inhibition. Molecular dynamics simulations showed a significant gain of flexibility at the cofactor binding site for the final variant. The concomitant increase in stability against isobutanol and only a minor reduction in its temperature stability render the final variant a promising candidate for future optimization of our synthetic cell-free enzymatic cascade.

Aldehyde dehydrogenase 3A1 confers oxidative stress resistance accompanied by altered DNA damage response in human corneal epithelial cells

Aldehyde dehydrogenase 3A1 is constitutively expressed in a taxon-specific manner in the cornea, where, due to its high abundance, it has been characterized as a corneal crystallin. ALDH3A1 has been proposed to be a multifaceted protein that protects cellular homeostasis through several modes of action. The present study examines the mechanisms by which ALDH3A1 exerts its cytoprotective role under conditions of oxidative stress. To this end, we have utilized an isogenic HCE-2 (human corneal epithelium) cell line pair differing in the expression of ALDH3A1. Single cell gel electrophoresis assay and H2DCFDA analysis revealed that the expression of ALDH3A1 protected HCE-2 cells from H₂O₂-, tert-butyl peroxide- and etoposide-induced oxidative and genotoxic effects. Furthermore, comparative qPCR analysis revealed that a panel of cell cycle (Cyclins B1, B2, D, E), apoptosis (p53, BAX, BCL-2, BCL-XL) and DNA damage response (DNA-PK, NBS1) genes were up-regulated in the ALDH3A1 expressing HCE-2 cells. Moreover, the expression profile of a variety of DNA damage signaling (DDS)-related genes, was investigated (under normal and oxidative stress conditions) by utilizing the RT² profiler™ PCR array in both isogenic HCE-2 cell lines. Our results demonstrated that several genes associated with ATM/ATR signaling, cell cycle regulation, apoptosis and DNA damage repair were differentially expressed under all conditions tested. In conclusion, this study suggests that ALDH3A1 significantly contributes to the antioxidant defense of corneal homeostasis by maintaining DNA integrity possibly through altering the expression of specific DDS-related genes. Further studies will shed light on the precise role(s) of this multifunctional protein.

NAD- and NADPH-Contributing Enzymes as Therapeutic Targets in Cancer: An Overview

Actively proliferating cancer cells require sufficient amount of NADH and NADPH for biogenesis and to protect cells from the detrimental effect of reactive oxygen species. As both normal and cancer cells share the same NAD biosynthetic and metabolic pathways, selectively lowering levels of NAD(H) and NADPH would be a promising strategy for cancer treatment. Targeting nicotinamide phosphoribosyltransferase (NAMPT), a rate limiting enzyme of the NAD salvage pathway, affects the NAD and NADPH pool. Similarly, lowering NADPH by mutant isocitrate dehydrogenase 1/2 (IDH1/2) which produces D-2-hydroxyglutarate (D-2HG), an oncometabolite that downregulates nicotinate phosphoribosyltransferase (NAPRT) via hypermethylation on the promoter region, results in epigenetic regulation. NADPH is used to generate D-2HG, and is also needed to protect dihydrofolate reductase, the target for methotrexate, from degradation. NAD and NADPH pools in various cancer types are regulated by several metabolic enzymes, including methylenetetrahydrofolate dehydrogenase, serine hydroxymethyltransferase, and aldehyde dehydrogenase. Thus, targeting NAD and NADPH synthesis under special circumstances is a novel approach to treat some cancers. This article provides the rationale for targeting the key enzymes that maintain the NAD/NADPH pool, and reviews preclinical studies of targeting these enzymes in cancers.

3,6-Anhydro-L-Galactose Dehydrogenase VvAHGD is a Member of a New Aldehyde Dehydrogenase Family and Catalyzes by a Novel Mechanism with Conformational Switch of Two Catalytic Residues Cysteine 282 and Glutamate 248

3,6-anhydro-α-L-galactose (L-AHG) is one of the main monosaccharide constituents of red macroalgae. In the recently discovered bacterial L-AHG catabolic pathway, L-AHG is first oxidized by a NAD(P)⁺-dependent dehydrogenase (AHGD), which is a key step of this pathway. However, the catalytic mechanism(s) of AHGDs is still unclear. Here, we identified and characterized an AHGD from marine bacterium Vibrio variabilis JCM 19239 (VvAHGD). The NADP⁺-dependent VvAHGD could efficiently oxidize L-AHG. Phylogenetic analysis suggested that VvAHGD and its homologs represent a new aldehyde dehydrogenase (ALDH) family with different substrate preferences from reported ALDH families, named the L-AHGDH family. To explain the catalytic mechanism of VvAHGD, we solved the structures of VvAHGD in the apo form and complex with NADP⁺ and modeled its structure with L-AHG. Based on structural, mutational, and biochemical analyses, the cofactor channel and the substrate channel of VvAHGD are identified, and the key residues involved in the binding of NADP⁺ and L-AHG and the catalysis are revealed. VvAHGD performs catalysis by controlling the consecutive connection and interruption of the cofactor channel and the substrate channel via the conformational changes of its two catalytic residues Cys282 and Glu248. Comparative analyses of structures and enzyme kinetics revealed that differences in the substrate channels (in shape, size, electrostatic surface, and residue composition) lead to the different substrate preferences of VvAHGD from other ALDHs. This study on VvAHGD sheds light on the diversified catalytic mechanisms and evolution of NAD(P)⁺-dependent ALDHs.

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.

Development of a Novel Multi-Isoform ALDH Inhibitor Effective as an Antimelanoma Agent

The aldehyde dehydrogenases (ALDH) are a major family of detoxifying enzymes that contribute to cancer progression and therapy resistance. ALDH overexpression is associated with a poor prognosis in many cancer types. The use of multi-ALDH isoform or isoform-specific ALDH inhibitors as anticancer agents is currently hindered by the lack of viable candidates. Most multi-ALDH isoform inhibitors lack bioavailability and are nonspecific or toxic, whereas most isoform-specific inhibitors are not effective as monotherapy due to the overlapping functions of ALDH family members. The present study details the development of a novel, potent, multi-isoform ALDH inhibitor, called KS100. The rationale for drug development was that inhibition of multiple ALDH isoforms might be more efficacious for cancer compared with isoform-specific inhibition. Enzymatic IC50s of KS100 were 207, 1,410, and 240 nmol/L toward ALDH1A1, 2, and 3A1, respectively. Toxicity of KS100 was mitigated by development of a nanoliposomal formulation, called NanoKS100. NanoKS100 had a loading efficiency of approximately 69% and was stable long-term. NanoKS100 was 5-fold more selective for killing melanoma cells compared with normal human fibroblasts. NanoKS100 administered intravenously at a submaximal dose (3-fold lower) was effective at inhibiting xenografted melanoma tumor growth by approximately 65% without organ-related toxicity. Mechanistically, inhibition by KS100 significantly reduced total cellular ALDH activity to increase reactive oxygen species generation, lipid peroxidation, and accumulation of toxic aldehydes leading to apoptosis and autophagy. Collectively, these data suggest the successful preclinical development of a nontoxic, bioavailable, nanoliposomal formulation containing a novel multi-ALDH isoform inhibitor effective in the treatment of cancer.

Immune - Goblet cell interaction in the conjunctiva

The conjunctiva is a goblet cell rich mucosal tissue. Goblet cells are supported by tear growth factors and IL-13 produced by resident immune cells. Goblet cell secretions are essential for maintaining tear stability and ocular surface homeostasis. In addition to producing tear stabilizing mucins, they also produce cytokines and retinoic acid that condition monocyte-derived phagocytic cells in the conjunctiva. Aqueous tear deficiency from lacrimal gland disease and systemic inflammatory conditions results in goblet cell loss that amplifies dry eye severity. Reduced goblet cell density is correlated with more severe conjunctival disease, increased IFN-γ expression and antigen presenting cell maturation. Sterile Alpha Motif (SAM) pointed domain epithelial specific transcription factor (Spdef) gene deficient mice that lack goblet cells have increased infiltration of monocytes and dendritic cells with greater IL-12 expression in the conjunctiva. Similar findings were observed in the conjunctiva of aged mice. Reduced retinoic acid receptor (RXRα) signaling also increases conjunctival monocyte infiltration, IFN-γ expression and goblet cell loss. Evidence suggests that dry eye therapies that suppress IFN-γ expression preserve conjunctival goblet cell number and function and should be considered in aqueous deficiency.

Structural and kinetic features of aldehyde dehydrogenase 1A (ALDH1A) subfamily members, cancer stem cell markers active in retinoic acid biosynthesis

Aldehyde dehydrogenases catalyze the NAD(P)⁺-dependent oxidation of aldehydes to their corresponding carboxylic acids. The three-dimensional structures of the human ALDH1A enzymes were recently obtained, while a complete kinetic characterization of them, under the same experimental conditions, is lacking. We show that the three enzymes, ALDH1A1, ALDH1A2 and ALDH1A3, have similar topologies, although with decreasing volumes in their substrate-binding pockets. The activity with aliphatic and retinoid aldehydes was characterized side-by-side, using an improved HPLC-based method for retinaldehyde. Hexanal was the most efficient substrate. ALDH1A1 displayed lower K_m values with hexanal, trans-2-hexenal and citral, compared to ALDH1A2 and ALDH1A3. ALDH1A2 was the best enzyme for the lipid peroxidation product, 4-hydroxy-2-nonenal, in terms of k_cat/K_m. The catalytic efficiency towards all-trans and 9-cis-retinaldehyde was in general lower than for alkanals and alkenals. ALDH1A2 and ALDH1A3 showed higher catalytic efficiency for all-trans-retinaldehyde. The lower specificity of ALDH1A3 for 9-cis-retinaldehyde against the all-trans- isomer might be related to the smaller volume of its substrate-binding pocket. Magnesium inhibited ALDH1A1 and ALDH1A2, while it activated ALDH1A3, which is consistent with cofactor dissociation being the rate-limiting step for ALDH1A1 and ALDH1A2, and deacylation for ALDH1A3, with hexanal as a substrate. We mutated both ALDH1A1 (L114P) and ALDH1A2 (N475G, A476V, L477V, N478S) to mimic their counterpart substrate-binding pockets. ALDH1A1 specificity for citral was traced to residue 114 and to residues 458 to 461. Regarding retinaldehyde, the mutants did not show significant differences with their respective wild-type forms, suggesting that the mutated residues are not critical for retinoid specificity.

Neurochemical Evidence of Preclinical and Clinical Reports on Target-Based Therapy in Alcohol Used Disorder

Alcohol use disorder (AUD) is a chronic relapsing disorder, which enforces a person to compulsively seek alcohol, restricting control over alcohol intake leads to emergence of an undesired emotional state during abstinence. There are recent advances for better understanding of neurocircuitry involved in the pathophysiology of AUD. Alcohol interaction with neuronal membrane proteins results in changes in neuronal circuits. It is also linked with the potential medication and their clinical validation concerning their pharmacological targets for alcoholic abstinence. This review covers research work from the past few decades on the therapeutic advances on treatment of alcohol dependence; further detailing the fundamental neurochemical mechanisms after alcohol administration. It also covers interaction of alcohol with GABAergic, glutaminergic, dopaminergic, serotonergic and opioid systems. This review further elaborated the neurobiology of noradrenergic, cholinergic and cannabinoid systems and their interaction with AUD. Elaborative information of potential drug targets under current exploration for AUD treatment with their mechanisms are reported here along with clinical outcomes and the associated side effects.

Fetal Alcohol Spectrum Disorder: Embryogenesis Under Reduced Retinoic Acid Signaling Conditions

Fetal Alcohol Spectrum Disorder (FASD) is a complex set of developmental malformations, neurobehavioral anomalies and mental disabilities induced by exposing human embryos to alcohol during fetal development. Several experimental models and a series of developmental and biochemical approaches have established a strong link between FASD and reduced retinoic acid (RA) signaling. RA signaling is involved in the regulation of numerous developmental decisions from patterning of the anterior-posterior axis, starting at gastrulation, to the differentiation of specific cell types within developing organs, to adult tissue homeostasis. Being such an important regulatory signal during embryonic development, mutations or environmental perturbations that affect the level, timing or location of the RA signal can induce multiple and severe developmental malformations. The evidence connecting human syndromes to reduced RA signaling is presented here and the resulting phenotypes are compared to FASD. Available data suggest that competition between ethanol clearance and RA biosynthesis is a major etiological component in FASD.

Aldehyde Dehydrogenase Inhibition Ameliorates Cardiac Dysfunction and Exacerbates Hypotension Caused by Alcohol in Female Rats

BACKGROUND

Aldehyde dehydrogenase 2 (ALDH2) protects against alcohol-evoked cardiac dysfunction in male rodents, but its role in the estrogen (E2 )-dependent hypersensitivity of female rats to alcohol-evoked myocardial oxidative stress and dysfunction is not known.

METHODS

We addressed this question by studying the effect of cyanamide (ALDH2 inhibitor) on cardiac function, blood pressure, alcohol-metabolizing enzyme (alcohol dehydrogenase, cytochrome P450 2E1, catalase, and ALDH2) activities, and cardiac redox status (reactive oxygen species, ROS; malondialdehyde, MDA) in the absence or presence of ethanol (EtOH) in female sham-operated (SO) and ovariectomized (OVX) rats.

RESULTS

Cyanamide attenuated the EtOH-evoked myocardial dysfunction (reduced dP/dtmax and LVDP) in SO rats. EtOH, cyanamide, or their combination did not alter dP/dtmax or LVDP in OVX rats. Cyanamide induced cardiac oxidative stress and abrogated the subsequent alcohol-evoked increases in ROS and MDA levels in SO rats. Neither EtOH nor cyanamide influenced ROS or MDA levels in OVX rats. Importantly, cyanamide exaggerated EtOH-evoked hypotension in SO and uncovered this hypotensive response in OVX rats, which implicates ALDH2 in the vasodilating effect of EtOH.

CONCLUSIONS

Contrary to our hypothesis, cyanamide attenuated the E2 -dependent cardiac dysfunction caused by alcohol, likely by preconditioning the heart to oxidative stress, while exacerbating the vasodilating effect of alcohol. The latter might predispose to syncope when cyanamide and alcohol are combined in females.

Monocytes as Endothelial Progenitor Cells (EPCs), Another Brick in the Wall to Disentangle Tumor Angiogenesis

Bone marrow contains endothelial progenitor cells (EPCs) that, upon pro-angiogenic stimuli, migrate and differentiate into endothelial cells (ECs) and contribute to re-endothelialization and neo-vascularization. There are currently no reliable markers to characterize EPCs, leading to their inaccurate identification. In the past, we showed that, in a panel of tumors, some cells on the vessel wall co-expressed CD14 (monocytic marker) and CD31 (EC marker), indicating a putative differentiation route of monocytes into ECs. Herein, we disclosed monocytes as potential EPCs, using in vitro and in vivo models, and also addressed the cancer context. Monocytes acquired the capacity to express ECs markers and were able to be incorporated into blood vessels, contributing to cancer progression, by being incorporated in tumor neo-vasculature. Reactive oxygen species (ROS) push monocytes to EC differentiation, and this phenotype is reverted by cysteine (a scavenger and precursor of glutathione), which indicates that angiogenesis is controlled by the interplay between the oxidative stress and the scavenging capacity of the tumor microenvironment.

Development of a Retinal-Based Probe for the Profiling of Retinaldehyde Dehydrogenases in Cancer Cells

Retinaldehyde dehydrogenases belong to a superfamily of enzymes that regulate cell differentiation and are responsible for detoxification of anticancer drugs. Chemical tools and methods are of great utility to visualize and quantify aldehyde dehydrogenase (ALDH) activity in health and disease. Here, we present the discovery of a first-in-class chemical probe based on retinal, the endogenous substrate of retinal ALDHs. We unveil the utility of this probe in quantitating ALDH isozyme activity in a panel of cancer cells via both fluorescence and chemical proteomic approaches. We demonstrate that our probe is superior to the widely used ALDEFLUOR assay to explain the ability of breast cancer (stem) cells to produce all-trans retinoic acid. Furthermore, our probe revealed the cellular selectivity profile of an advanced ALDH1A1 inhibitor, thereby prompting us to investigate the nature of its cytotoxicity. Our results showcase the application of substrate-based probes in interrogating pathologically relevant enzyme activities. They also highlight the general power of chemical proteomics in driving the discovery of new biological insights and its utility to guide drug discovery efforts.

Mitochondrially-targeted treatment strategies

Disruption of mitochondrial function is a common feature of inherited mitochondrial diseases (mitochondriopathies) and many other infectious and non-infectious diseases including viral, bacterial and protozoan infections, inflammatory and chronic pain, neurodegeneration, diabetes, obesity and cardiovascular diseases. Mitochondria therefore become an attractive target for developing new therapies. In this review we describe critical mechanisms involved in the maintenance of mitochondrial functionality and discuss strategies used to identify and validate mitochondrial targets in different diseases. We also highlight the most recent preclinical and clinical findings using molecules targeting mitochondrial bioenergetics, morphology, number, content and detoxification systems in common pathologies.

Design, synthesis characterization and biological evaluation of novel multi-isoform ALDH inhibitors as potential anticancer agents

The aldehyde dehydrogenases (ALDHs) are a family of detoxifying enzymes that are overexpressed in various cancers. Increased expression of ALDH is associated with poor prognosis, stemness, and drug resistance. Because of the critical role of ALDH in cancer stem cells, several ALDH inhibitors have been developed. Nonetheless, all these inhibitors either lack efficacy or are too toxic or have not been tested extensively. Thus, the continued development of ALDH inhibitors is warranted. In this study, we designed and synthesized potent multi-ALDH isoform inhibitors based on the isatin backbone. The early molecular docking studies and enzymatic tests revealed that 3(a-l) and 4(a-l) are the potent ALDH1A1, ALDHA2, and ALDH3A1 inhibitors. ALDH inhibitory IC₅₀s of 3(a-l) and 4(a-l) were 230 nM to >10,000 nM for ALDH1A1, 939 nM to >10,000 nM for ALDH2 and 193 nM to >10,000 nM for ALDH3A1. The most potent compounds 3(h-l) had IC₅₀s for killing melanoma cells ranged from 2.1 to 5.7 μM, while for colon cancer cells, it ranged from 2.5 to 5.8 μM and for multiple myeloma cells ranging from 0.3 to 4.7 μM. Toxicity studies of 3(h-l) revealed that 3h to be the least toxic multi-ALDH isoform inhibitor. Mechanistically, 3(h-l) caused increased ROS activity, lipid peroxidation, and toxic aldehyde accumulation, secondary to potent multi-ALDH isoform inhibition leading to increased apoptosis and G2/M cell cycle arrest. Together, the study details the design, synthesis, and evaluation of potent, multi-isoform ALDH inhibitors to treat cancers.

The molecular aspects of absorption and metabolism of carotenoids and retinoids in vertebrates

Vitamin A is an essential nutrient necessary for numerous basic physiological functions, including reproduction and development, immune cell differentiation and communication, as well as the perception of light. To evade the dire consequences of vitamin A deficiency, vertebrates have evolved specialized metabolic pathways that enable the absorption, transport, and storage of vitamin A acquired from dietary sources as preformed retinoids or provitamin A carotenoids. This evolutionary advantage requires a complex interplay between numerous specialized retinoid-transport proteins, receptors, and enzymes. Recent advances in molecular and structural biology resulted in a rapid expansion of our understanding of these processes at the molecular level. This progress opened new avenues for the therapeutic manipulation of retinoid homeostasis. In this review, we summarize current research related to the biochemistry of carotenoid and retinoid-processing proteins with special emphasis on the structural aspects of their physiological actions. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

Structure and mechanism of piperideine-6-carboxylate dehydrogenase from Streptomyces clavuligerus

The core of β-lactam antibiotics originates from amino acids of primary metabolism in certain microorganisms. β-Lactam-producing bacteria, including Streptomyces clavuligerus, synthesize the precursor of the amino acid α-aminoadipic acid by the catabolism of lysine in two steps. The second reaction, the oxidation of piperideine-6-carboxylate (or its open-chain form α-aminoadipate semialdehyde) to α-aminoadipic acid, is catalysed by the NAD⁺-dependent enzyme piperideine-6-carboxylate dehydrogenase (P6CDH). This structural study, focused on ligand binding and catalysis, presents structures of P6CDH from S. clavuligerus in its apo form and in complexes with the cofactor NAD⁺, the product α-aminoadipic acid and a substrate analogue, picolinic acid. P6CDH adopts the common aldehyde dehydrogenase fold, consisting of NAD-binding, catalytic and oligomerization domains. The product binds in the oxyanion hole, close to the catalytic residue Cys299. Clear density is observed for the entire cofactor, including the nicotinamide riboside, in the binary complex. NAD⁺ binds in an extended conformation with its nicotinamide ring overlapping with the binding site of the carboxylate group of the product, implying that the conformation of the cofactor may change during catalysis. The binding site of the substrate analogue overlaps with that of the product, suggesting that the cyclic form of the substrate, piperideine-6-carboxylate, may be accepted as a substrate by the enzyme. The catalytic mechanism and the roles of individual residues are discussed in light of these results.

Citral Inhibition of Human Salivary Aldehyde Dehydrogenase

Human salivary aldehyde dehydrogenase (hsALDH) protects us from the toxic effect of aldehydes. It has both diagnostic and therapeutic importance. Citral possesses many biological and pharmacological properties. The aim of this work was to investigate the inhibitory effect and the mechanism of inhibition of citral on hsALDH. Citral inhibits the dehydrogenase activity of hsALDH. It decreased the substrate affinity and to a lesser extent, the catalytic efficiency of hsALDH. Citral showed linear mixed-type inhibition with a higher tendency of competitive behavior with little, but significant, non-competitive inhibition. The nucleophilicity of active site Cys residue is not a significant contributing factor in the inhibition process. Citral shows uncompetitive inhibition towards the co-enzyme (NAD⁺). α-helix and β-sheet content of the enzyme were changed in presence of citral. Biophysical studies showed that citral quenches the intrinsic fluorescence of hsALDH in a static manner by forming complex with the enzyme. Molecular docking study showed that both the isomers of citral bind to the catalytic site of hsALDH interacting with few evolutionary preserved amino acid residues through multiple non-covalent interactions. Ligand efficiency metrics values indicate that citral is an efficient ligand for the enzyme in terms of its physicochemical and pharmacokinetic properties.

Gastric cancer depends on aldehyde dehydrogenase 3A1 for fatty acid oxidation

The major source of ATP in cancer cells remains unclear. Here, we examined energy metabolism in gastric cancer cells and found increased fatty acid oxidation and increased expression of ALDH3A1. Metabolic analysis showed that lipid peroxidation by reactive oxygen species led to spontaneous production of 4-hydroxynonenal, which was converted to fatty acids with NADH production by ALDH3A1, resulting in further fatty acid oxidation. Inhibition of ALDH3A1 by knock down using siRNA of ALDH3A1 resulted in significantly reduced ATP production by cancer cells, leading to apoptosis. Oxidative phosphorylation by mitochondria in gastric cancer cells was driven by NADH supplied via fatty acid oxidation. Therefore, blockade of ALDH3A1 together with mitochondrial complex I using gossypol and phenformin led to significant therapeutic effects in a preclinical gastric cancer model.

The biological activity of bispecific trastuzumab/pertuzumab plant biosimilars may be drastically boosted by disulfiram increasing formaldehyde accumulation in cancer cells

Studies of breast cancer therapy have examined the improvement of bispecific trastuzumab/pertuzumab antibodies interacting simultaneously with two different epitopes of the human epidermal growth factor receptor 2 (HER2). Here, we describe the creation and production of plant-made bispecific antibodies based on trastuzumab and pertuzumab plant biosimilars (bi-TPB-PPB). Using surface plasmon resonance analysis of bi-TPB-PPB antibodies binding with the HER2 extracellular domain, we showed that the obtained Kd values were within the limits accepted for modified trastuzumab and pertuzumab. Despite the ability of bi-TPB-PPB antibodies to bind to Fcγ receptor IIIa and HER2 oncoprotein on the cell surface, a proliferation inhibition assay did not reveal any effect until α1,3-fucose and β1,2-xylose in the Asn297-linked glycan were removed. Another approach to activating bi-TPB-PPB may be associated with the use of disulfiram (DSF) a known aldehyde dehydrogenase 2 (ALDH2) inhibitor. We found that disulfiram is capable of killing breast cancer cells with simultaneous formaldehyde accumulation. Furthermore, we investigated the capacity of DSF to act as an adjuvant for bi-TPB-PPB antibodies. Although the content of ALDH2 mRNA was decreased after BT-474 cell treatment with antibodies, we only observed cell proliferation inhibiting activity of bi-TPB-PPB in the presence of disulfiram. We concluded that disulfiram can serve as a booster and adjuvant for anticancer immunotherapy.