Identification of Novel Isatin Derivative Bearing a Nitrofuran Moiety as Potent Multi-Isoform Aldehyde Dehydrogenase Inhibitor.

Aldehyde dehydrogenases (ALDHs) are a family of enzymes that aid in detoxification and are overexpressed in several different malignancies. There is a correlation between increased expression of ALDH and a poor prognosis, stemness, and resistance to several drugs. Several ALDH inhibitors have been generated due to the crucial role that ALDH plays in cancer stem cells. All of these inhibitors, however, are either ineffective, very toxic, or have yet to be subjected to rigorous testing on their effectiveness. Although various drug-like compounds targeting ALDH have been reported in the literature, none have made it to routine use in the oncology clinic. As a result, new potent, non-toxic, bioavailable, and therapeutically effective ALDH inhibitors are still needed. In this study, we designed and synthesized potent multi-ALDH isoform inhibitors based on the isatin and indazole pharmacophore. Molecular docking studies and enzymatic tests revealed that among all of the synthesized analogs, compound 3 is the most potent inhibitor of ALDH1A1, ALDH3A1, and ALDH1A3, exhibiting 51.32%, 51.87%, and 36.65% inhibition, respectively. The ALDEFLUOR assay further revealed that compound 3 acts as an ALDH broad spectrum inhibitor at 500 nM. Compound 3 was also the most cytotoxic to cancer cells, with an IC50 in the range of 2.1 to 3.8 µM for ovarian, colon, and pancreatic cancer cells, compared to normal and embryonic kidney cells (IC50 7.1 to 8.7 µM). Mechanistically, compound 3 increased ROS activity due to potent multi-ALDH isoform inhibition, which increased apoptosis. Taken together, this study identified a potent multi-isoform ALDH inhibitor that could be further developed as a cancer therapeutic.

Aldh inhibitor restores auditory function in a mouse model of human deafness.

Genetic hearing loss is a common health problem with no effective therapy currently available. DFNA15, caused by mutations of the transcription factor POU4F3, is one of the most common forms of autosomal dominant non-syndromic deafness. In this study, we established a novel mouse model of the human DFNA15 deafness, with a Pou4f3 gene mutation (Pou4f3Δ) identical to that found in a familial case of DFNA15. The Pou4f3(Δ/+) mice suffered progressive deafness in a similar manner to the DFNA15 patients. Hair cells in the Pou4f3(Δ/+) cochlea displayed significant stereociliary and mitochondrial pathologies, with apparent loss of outer hair cells. Progression of hearing and outer hair cell loss of the Pou4f3(Δ/+) mice was significantly modified by other genetic and environmental factors. Using Pou4f3(-/+) heterozygous knockout mice, we also showed that DFNA15 is likely caused by haploinsufficiency of the Pou4f3 gene. Importantly, inhibition of retinoic acid signaling by the aldehyde dehydrogenase (Aldh) and retinoic acid receptor inhibitors promoted Pou4f3 expression in the cochlear tissue and suppressed the progression of hearing loss in the mutant mice. These data demonstrate Pou4f3 haploinsufficiency as the main underlying cause of human DFNA15 deafness and highlight the therapeutic potential of Aldh inhibitors for treatment of progressive hearing loss.

Nuclear Factor Erythroid 2-Related Factor 2 Depletion Sensitizes Pancreatic Cancer Cells to Gemcitabine via Aldehyde Dehydrogenase 3a1 Repression.

As the central regulator of the oxidative stress response, nuclear factor erythroid 2-related factor 2 (Nrf2) is attracting great interest as a therapeutic target for various cancers, and the possible clinical applications of novel Nrf2 inhibitors have been explored in Nrf2-activated cancers. In the present study, we specifically investigated halofuginone, which is derived from a natural plant alkaloid. We found that halofuginone administration decreased the number of pancreatic intraepithelial neoplasias in pancreas-specific Kras and p53 mutant (KPC) mice. In Nrf2-activated pancreatic cancer cell lines established from KPC mice, halofuginone rapidly depleted Nrf2 in Nrf2-activated cancer cells. Both in vitro and in vivo, it sensitized Nrf2-activated pancreatic cancer cells to gemcitabine, which is the first-line chemotherapy in clinical practice. In our mechanistic study, we found that halofuginone downregulated aldehyde dehydrogenase 3a1 (ALDH3A1) in mouse pancreatic cancer cells. The Nrf2 inducer diethyl maleate upregulated ALDH3A1, and knockdown of Aldh3a1 sensitized Nrf2-activated cancer cells to gemcitabine, strongly suggesting that ALDH3A1 is regulated by Nrf2 and that it contributes to gemcitabine resistance. The current study demonstrated the therapeutic benefits of halofuginone in Nrf2-activated pancreatic cancers. SIGNIFICANCE STATEMENT: We identified nuclear factor erythroid 2-related factor 2 (Nrf2) and its downstream target aldehyde dehydrogenase 3a1 (ALDH3A1) as novel therapeutic targets in pancreatic cancer. They negatively affect the efficacy of a conventional chemotherapeutic agent, gemcitabine. We confirmed that Nrf2 plays a pivotal role in the induction of ALDH3A1.

The interaction of disulfiram and H2S metabolism in inhibition of aldehyde dehydrogenase activity and liver cancer cell growth.

Disulfiram (DSF), a sulfur-containing compound, has been used to treat chronic alcoholism and cancer for decades by inactivating aldehyde dehydrogenase (ALDH). Hydrogen sulfide (H2S) is a new gasotransmitter and regulates various cellular functions by S-sulfhydrating cysteine in the target proteins. H2S exhibits similar properties to DSF in the sensitization of cancer cells. The interaction of DSF and H2S on ALDH activity and liver cancer cell survival are not clear. Here it was demonstrated that DSF facilitated H2S release from thiol-containing compounds, and DSF and H2S were both capable of regulating ALDH through inhibition of gene expression and enzymatic activity. The supplement of H2S sensitized human liver cancer cells (HepG2) to DSF-inhibited cell viability. The expression of cystathionine gamma-lyase (a major H2S-generating enzyme) was lower but ALDH was higher in mouse liver cancer stem cells (Dt81Hepa1-6) in comparison with their parental cells (Hepa1-6), and H2S was able to inhibit liver cancer stem cell adhesion. In conclusion, these data point to the potential of combining DSF and H2S for inhibition of cancer cell growth and tumor development by targeting ALDH.

Mulberry leaves extract ameliorates alcohol-induced liver damages through reduction of acetaldehyde toxicity and inhibition of apoptosis caused by oxidative stress signals.

Mulberry leaves (Morus alba L.), which are traditional Chinese herbs, exert several biological functions, such as antioxidant, anti-inflammation, antidiabetic, and antitumor. Alcohol intake increases inflammation and oxidative stress, and this increase causes liver injury and leads to liver steatosis, cirrhosis, and hepatocellular carcinoma, which are major health problems worldwide. Previous report indicated that mulberry leaf extract (MLE) exited hepatoprotection effects against chronic alcohol-induced liver damages. In this present study, we investigated the effects of MLE on acute alcohol and liver injury induced by its metabolized compound called acetaldehyde (ACE) by using in vivo and in vitro models. Administration of MLE reversed acute alcohol-induced liver damages, increased acetaldehyde (ACE) level, and decreased aldehyde dehydrogenase activity in a dose-dependent manner. Acute alcohol exposure-induced leukocyte infiltration and pro-inflammation factors, including cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6), were blocked by MLE in proportion to MLE concentration. MLE prevented alcohol-induced liver apoptosis via enhanced caveolin-1 expression and attenuated EGFR/STAT3/iNOS pathway using immunohistochemical analysis. ACE induced proteins, such as iNOS, COX-2, TNF-α, and IL-6, and inhibited superoxide dismutase expression, whereas co-treated with MLE reversed these proteins expression. MLE also recovered alcohol-induced apoptosis in cultured Hep G2 cells. Overall, our findings indicated that MLE ameliorated acute alcohol-induced liver damages by reducing ACE toxicity and inhibiting apoptosis caused by oxidative stress signals. Our results implied that MLE might be a potential agent for treating alcohol liver disease.

Glyceryl Trinitrate: History, Mystery, and Alcohol Intolerance.

Glyceryl trinitrate (GTN) is one of the earliest known treatments for angina with a fascinating history that bridges three centuries. However, despite its central role in the nitric oxide (NO) story as a NO-donating compound, establishing the precise mechanism of how GTN exerts its medicinal benefit has proven to be far more difficult. This review brings together the explosive and vasodilatory nature of this three-carbon molecule while providing an update on the likely in vivo pathways through which GTN, and the rest of the organic nitrate family, release NO, nitrite, or a combination of both, while also trying to explain nitrate tolerance. Over the last 20 years the alcohol detoxification enzyme, aldehyde dehydrogenase (ALDH), has undoubtedly emerged as the front runner to explaining GTN's bioactivation. This is best illustrated by reduced GTN efficacy in subjects carrying the single point mutation (Glu504Lys) in ALDH, which is also responsible for alcohol intolerance, as characterized by flushing. While these findings are significant for anyone following the GTN story, they appear particularly relevant for healthcare professionals, and especially so, if administering GTN to patients as an emergency treatment. In short, although the GTN puzzle has not been fully solved, clinical study data continue to cement the importance of ALDH, as uncovered in 2002, as a key GTN activator.

Combinatorial Therapeutic Effect of Inhibitors of Aldehyde Dehydrogenase and Mitochondrial Complex I, and the Chemotherapeutic Drug, Temozolomide against Glioblastoma Tumorspheres.

Resident cancer cells with stem cell-like features induce drug tolerance, facilitating survival of glioblastoma (GBM). We previously showed that strategies targeting tumor bioenergetics present a novel emerging avenue for treatment of GBM. The objective of this study was to enhance the therapeutic effects of dual inhibition of tumor bioenergetics by combination of gossypol, an aldehyde dehydrogenase inhibitor, and phenformin, a biguanide compound that depletes oxidative phosphorylation, with the chemotherapeutic drug, temozolomide (TMZ), to block proliferation, stemness, and invasiveness of GBM tumorspheres (TSs). Combination therapy with gossypol, phenformin, and TMZ induced a significant reduction in ATP levels, cell viability, stemness, and invasiveness compared to TMZ monotherapy and dual therapy with gossypol and phenformin. Analysis of differentially expressed genes revealed up-regulation of genes involved in programmed cell death, autophagy, and protein metabolism and down-regulation of those associated with cell metabolism, cycle, and adhesion. Combination of TMZ with dual inhibitors of tumor bioenergetics may, therefore, present an effective strategy against GBM by enhancing therapeutic effects through multiple mechanisms of action.

STA-55, an Easily Accessible, Broad-Spectrum, Activity-Based Aldehyde Dehydrogenase Probe.

Aldehyde dehydrogenases (ALDHs) convert aldehydes into carboxylic acids and are often upregulated in cancer. They have been linked to therapy resistance and are therefore potential therapeutic targets. However, only a few selective and potent inhibitors are currently available for this group of enzymes. Competitive activity-based protein profiling (ABPP) would aid the development and validation of new selective inhibitors. Herein, a broad-spectrum activity-based probe that reports on several ALDHs is presented. This probe was used in a competitive ABPP protocol against three ALDH inhibitors in lung cancer cells to determine their selectivity profiles and establish their target engagement.

Host-parasite co-metabolic activation of antitrypanosomal aminomethyl-benzoxaboroles.

Recent development of benzoxaborole-based chemistry gave rise to a collection of compounds with great potential in targeting diverse infectious diseases, including human African Trypanosomiasis (HAT), a devastating neglected tropical disease. However, further medicinal development is largely restricted by a lack of insight into mechanism of action (MoA) in pathogenic kinetoplastids. We adopted a multidisciplinary approach, combining a high-throughput forward genetic screen with functional group focused chemical biological, structural biology and biochemical analyses, to tackle the complex MoAs of benzoxaboroles in Trypanosoma brucei. We describe an oxidative enzymatic pathway composed of host semicarbazide-sensitive amine oxidase and a trypanosomal aldehyde dehydrogenase TbALDH3. Two sequential reactions through this pathway serve as the key underlying mechanism for activating a series of 4-aminomethylphenoxy-benzoxaboroles as potent trypanocides; the methylamine parental compounds as pro-drugs are transformed first into intermediate aldehyde metabolites, and further into the carboxylate metabolites as effective forms. Moreover, comparative biochemical and crystallographic analyses elucidated the catalytic specificity of TbALDH3 towards the benzaldehyde benzoxaborole metabolites as xenogeneic substrates. Overall, this work proposes a novel drug activation mechanism dependent on both host and parasite metabolism of primary amine containing molecules, which contributes a new perspective to our understanding of the benzoxaborole MoA, and could be further exploited to improve the therapeutic index of antimicrobial compounds.

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 ß-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.

Human Endogenous Formaldehyde as an Anticancer Metabolite: Its Oxidation Downregulation May Be a Means of Improving Therapy.

Malignant cells are characterized by an increased content of endogenous formaldehyde formed as a by-product of biosynthetic processes. Accumulation of formaldehyde in cancer cells is combined with activation of the processes of cellular formaldehyde clearance. These mechanisms include increased ALDH and suppressed ADH5/FDH activity, which oncologists consider poor and favorable prognostic markers, respectively. Here, the sources and regulation of formaldehyde metabolism in cancer cells are reviewed. The authors also analyze the participation of oncoproteins such as fibulins, FGFR1, HER2/neu, FBI-1, and MUC1-C in the control of genes related to formaldehyde metabolism, suggesting the existence of two mutually exclusive processes in cancer cells: 1) production and 2) oxidation and elimination of formaldehyde from the cell. The authors hypothesize that the study of the anticancer properties of disulfiram and alpha lipoic acid - which affect the balance of formaldehyde in the body - may serve as the basis of future anticancer therapy.

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.

The Repurposed Drug Disulfiram Inhibits Urease and Aldehyde Dehydrogenase and Prevents In Vitro Growth of the Oomycete Pythium insidiosum.

Pythium insidiosum is an oomycete microorganism that causes a life-threatening infectious disease, called pythiosis, in humans and animals. The disease has been increasingly reported worldwide. Conventional antifungal drugs are ineffective against P. insidiosum Treatment of pythiosis requires the extensive removal of infected tissue (i.e., eye and leg), but inadequate surgery and recurrent infection often occur. A more effective treatment is needed for pythiosis patients. Drug repurposing is a promising strategy for the identification of a U.S. Food and Drug Administration-approved drug for the control of P. insidiosum Disulfiram has been approved to treat alcoholism, but it exhibits antimicrobial activity against various pathogens. In this study, we explored whether disulfiram possesses an anti-P. insidiosum activity. A total of 27 P. insidiosum strains, isolated from various hosts and geographic areas, were susceptible to disulfiram in a dose-dependent manner. The MIC range of disulfiram against P. insidiosum (8 to 32 mg/liter) was in line with that of other pathogens. Proteogenomic analysis indicated that several potential targets of disulfiram (i.e., aldehyde dehydrogenase and urease) were present in P. insidiosum By homology modeling and molecular docking, disulfiram can bind the putative aldehyde dehydrogenase and urease of P. insidiosum at low energies (i.e., -6.1 and -4.0 Kcal/mol, respectively). Disulfiram diminished the biochemical activities of these enzymes. In conclusion, disulfiram can inhibit the growth of many pathogenic microorganisms, including P. insidiosum The drug can bind and inactivate multiple proteins of P. insidiosum, which may contribute to its broad antimicrobial property. Drug repurposing of disulfiram could be a new treatment option for pythiosis.

In Vivo Anti-Tumor Effects of Citral on 4T1 Breast Cancer Cells via Induction of Apoptosis and Downregulation of Aldehyde Dehydrogenase Activity.

Breast cancer is the most commonly diagnosed cancer and the leading cause of cancer death among females globally. The tumorigenic activities of cancer cells such as aldehyde dehydrogenase (ALDH) activity and differentiation have contributed to relapse and eventual mortality in breast cancer. Thus, current drug discovery research is focused on targeting breast cancer cells with ALDH activity and their capacity to form secondary tumors. Citral (3,7-dimethyl-2,6-octadienal), from lemon grass (Cymbopogon citrates), has been previously reported to have a cytotoxic effect on breast cancer cells. Hence, this study was conducted to evaluate the in vivo effect of citral in targeting ALDH activity of breast cancer cells. BALB/c mice were challenged with 4T1 breast cancer cells followed by daily oral feeding of 50 mg/kg citral or distilled water for two weeks. The population of ALDH+ tumor cells and their capacity to form secondary tumors in both untreated and citral treated 4T1 challenged mice were assessed by Aldefluor assay and tumor growth upon cell reimplantation in normal mice, respectively. Citral treatment reduced the size and number of cells with ALDH+ activity of the tumors in 4T1-challenged BALB/c mice. Moreover, citral-treated mice were also observed with smaller tumor size and delayed tumorigenicity after reimplantation of the primary tumor cells into normal mice. These findings support the antitumor effect of citral in targeting ALDH+ cells and tumor recurrence in breast cancer cells.

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

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

ALDH1A inhibition sensitizes colon cancer cells to chemotherapy.

BACKGROUND: Recent evidence in cancer research, developed the notion that malignant tumors consist of different subpopulations of cells, one of them, known as cancer stem cells, being attributed many important properties such as enhanced tumorigenicity, proliferation potential and profound multidrug resistance to chemotherapy. Several key stem cells markers were identified in colon cancer. In our study we focused on the aldehyde dehydrogenase type 1 (ALDH1) expression in colon cancer-derived cell lines HT-29/eGFP, HCT-116/eGFP and LS-180/eGFP, and its role in the chemoresistance and tumorigenic potential. METHODS: The effect of pharmacological inhibition of ALDH activity by diethylaminobenzaldehyde (DEAB) and also effect of molecular inhibition by specific siRNA was evaluated in vitro in cultures of human colorectal cell lines. The expression level of different isoenzymes of aldehyde dehydrogenase was determined using qPCR. Changes in cell biology were evaluated by expression analysis, western blot and apoptosis assay. The efficiency of cytotoxic treatment in the presence of different chemotherapeutic drugs was analyzed by fluorimetric assay. Tumorigenicity of cells with specific ALDH1A1 siRNA was tested in xenograft model in vivo. RESULTS: Treatment by DEAB partially sensitized the tested cell lines to chemotherapeutics. Subsequently the molecular inhibition of specific isoforms of ALDH by ALDH1A1 or ALDH1A3 siRNA led to sensitizing of cell lines HT-29/eGFP, HCT-116/eGFP to capecitabine and 5-FU. On the model of athymic mice we observed the effect of molecular inhibition of ALDH1A1 in HT-29/eGFP cells by siRNA. We observed inhibition of proliferation of subcutaneous xenografts in comparison to control cells. CONCLUSION: This research, verifies the significance of the ALDH1A isoforms in multidrug resistance of human colorectal cancer cells and its potential as a cancer stem cell marker. This provides the basis for the development of new approaches regarding the treatment of patients with colorectal adenocarcinoma and potentially the treatment of other tumor malignancies.

Design, synthesis, and ex vivo evaluation of a selective inhibitor for retinaldehyde dehydrogenase enzymes.

The retinaldehyde dehydrogenase (RALDH) enzymes, RALDH1, RALDH2, and RALDH3, catalyze the irreversible oxidation of retinaldehyde to all-trans-retinoic acid (ATRA). Despite the importance of the RALDH enzymes in embryonic development, postnatal growth and differentiation, and in several disease states, there are no commercially available inhibitors that specifically target these isozymes. We report here the development and characterization of a small molecule inhibitor dichloro-all-trans-retinone (DAR) (Summers et al., 2017) that is an irreversible inhibitor of RALDH1, 2, and 3 that effectively inhibits RALDH1, 2, and 3 in the nanomolar range but has no inhibitory activity against mitochondrial ALDH2. These results provide support for the development of DAR as a specific ATRA synthesis inhibitor for a variety of experimental and clinical applications.

Cancer stem cell mediated acquired chemoresistance in head and neck cancer can be abrogated by aldehyde dehydrogenase 1 A1 inhibition.

Chemoresistance leading to disease relapse is one of the major challenges to improve outcome in head and neck cancers. Cancer Stem Cells (CSCs) are increasingly being implicated in chemotherapy resistance, this study investigates the correlation between CSC behavior and acquired drug resistance in in vitro cell line models. Cell lines resistant to Cisplatin (Cal-27 CisR, Hep-2 CisR) and 5FU (Cal-27 5FUR) with high Resistance Indices (RI) were generated (RI ≥ 3) by short-term treatment of head and neck squamous cell carcinoma (HNSCC) cell lines with chemotherapeutic drugs (Cisplatin, Docetaxel, 5FU), using a dose-incremental strategy. The cell lines (Cal-27 DoxR, Hep-2 DoxR, Hep-2 5FUR) that showed low RI, nevertheless had a high cross resistance to Cisplatin/5FU (P < 0.05). Cal-27 CisR and DoxR showed 12-14% enrichment of CD44+ cells, while CisR/5FUR showed 4-6% increase in ALDH1A1+ cells as compared to parental cells (P < 0.05). Increased expression of stem cell markers (CD44, CD133, NOTCH1, ALDH1A1, OCT4, SOX2) in these cell lines, correlated with enhanced spheroid/colony formation, migratory potential, and increased in vivo tumor burden (P < 0.05). Inhibition of ALDH1A1 in Cal-27 CisR led to down regulation of the CSC markers, reduction in migratory, self-renewal and tumorigenic potential (P < 0.05) accompanied by an induction of sensitivity to Cisplatin (P < 0.05). Further, ex vivo treatment of explants (n = 4) from HNSCC patients with the inhibitor (NCT-501) in combination with Cisplatin showed a significant decrease in proliferating cells as compared to individual treatment (P = 0.001). This study hence suggests an ALDH1A1-driven, CSC-mediated mechanism in acquired drug resistance of HNSCC, which may have therapeutic implications. © 2016 Wiley Periodicals, Inc.

ALDH Enzyme Expression Is Independent of the Spermatogenic Cycle, and Their Inhibition Causes Misregulation of Murine Spermatogenic Processes.

Perturbations in the vitamin A metabolism pathway could be a significant cause of male infertility, as well as a target toward the development of a male contraceptive, necessitating the need for a better understanding of how testicular retinoic acid (RA) concentrations are regulated. Quantitative analyses have recently demonstrated that RA is present in a pulsatile manner along testis tubules. However, it is unclear if the aldehyde dehydrogenase (ALDH) enzymes, which are responsible for RA synthesis, contribute to the regulation of these RA concentration gradients. Previous studies have alluded to fluctuations in ALDH enzymes across the spermatogenic cycle, but these inferences have been based primarily on qualitative transcript localization experiments. Here, we show via various quantitative methods that the three well-known ALDH enzymes (ALDH1A1, ALDH1A2, and ALDH1A3), and an ALDH enzyme previously unreported in the murine testis (ALDH8A1), are not expressed in a stage-specific manner in the adult testis, but do fluctuate throughout juvenile development in perfect agreement with the first appearance of each advancing germ cell type. We also show, via treatments with a known ALDH inhibitor, that lowered testicular RA levels result in an increase in blood-testis barrier permeability, meiotic recombination, and meiotic defects. Taken together, these data further our understanding of the complex regulatory actions of RA on various spermatogenic events and, in contrast with previous studies, also suggest that the ALDH enzymes are not responsible for regulating the recently measured RA pulse.

The Alcohol Intolerance Produced by Isoniazid Is Not Due to a Disulfiram-Like Reaction Despite Aldehyde Dehydrogenase Inhibition.

BACKGROUND/AIMS: Isoniazid (ISO) has been reported to inhibit the hepatic aldehyde dehydrogenase (ALDH) and to cause a disulfiram (DIS)-like reaction, albeit there are no reports demonstrating increased blood acetaldehyde levels after co-administration of ISO with alcohol. The aim of our study was to clarify whether the alcohol intolerance produced by ISO is indeed due to a typical DIS-like reaction. METHODS: DIS and ISO were administered to Wistar rats and the hepatic ethanol (ETH) metabolizing enzyme activities along with the levels of brain monoamines were determined. Blood acetaldehyde levels were also evaluated after co-administration of ETH with DIS or ISO. RESULTS: Despite inhibition of the hepatic ALDH, ISO did not result in elevated blood acetaldehyde levels after ETH administration, probably due to the induction of cytochrome P450 2E1 which theoretically leads to an increased elimination rate of acetaldehyde preventing its accumulation. Moreover, ISO produced some minor, but statistically significant, alterations in central monoaminergic neurotransmission. CONCLUSION: Our results demonstrate for the first time that despite ALDH inhibition ISO does not provoke a typical DIS-like reaction since it does not increase blood acetaldehyde levels after co-administration with ETH. The possibility that the ETH intolerance observed in ISO treatment is a central synergistic effect cannot be excluded.