Inhibition of cytosolic class 3 aldehyde dehydrogenase by antisense oligonucleotides in rat hepatoma cells

Transcriptomics and molecular docking reveal the potential mechanism of lycorine against pancreatic cancer

BACKGROUND

Pancreatic cancer is an extremely malignant digestive tumor, however, owing to its high drug resistance of pancreatic cancer, the search for more effective anti-pancreatic cancer drugs is urgently needed. Lycorine, an alkaloid of natural plant origin, exerts antitumor effects on a variety of tumors.

PURPOSE

This study aimed to investigate the therapeutic effect of lycorine on pancreatic cancer and elucidate its potential molecular mechanism.

METHODS

Two pancreatic cancer cell lines, PANC-1 and BxPC-3, were used to investigate the therapeutic effects of lycorine on pancreatic cancer in vitro using the CCK8 assay, colony formation assay, 5-Ethynyl-2'- deoxyuridine (EdU) incorporation assay, flow cytometry, and western blotting. Transcriptome sequencing and gene set enrichment analysis (GSEA) were used to analyze the differentially expressed genes and pathways after lycorine treatment. Molecular docking, quantitative real-time PCR (qRT-PCR), oil red O staining, small interfering RNA (siRNA) transfection, and other experiments were performed to further validate the differentially expressed genes and pathways. In vivo experiments were conducted to investigate lycorine's inhibitory effects and toxicity on pancreatic cancer using a tumor-bearing mouse model.

RESULTS

Lycorine inhibited the proliferation of pancreatic cancer cells, caused G2/M phase cycle arrest and induced apoptosis. Transcriptome sequencing and GSEA showed that lycorine inhibition of pancreatic cancer was associated with fatty acid metabolism, and aldehyde dehydrogenase 3A1 (ALDH3A1) was a significantly enriched target in the fatty acid metabolism process. ALDH3A1 expression was significantly upregulated in pancreatic cancer and was closely associated with prognosis. Molecular docking showed that lycorine binds strongly to ALDH3A1. Further studies revealed that lycorine inhibited the fatty acid oxidation (FAO) process in pancreatic cancer cells and induced cell growth inhibition and apoptosis through ALDH3A1. Lycorine also showed significant suppressive effects in tumor-bearing mice. Importantly, it did not result in significant toxicity to liver and kidney of mice, demonstrating its therapeutic potential as a safe antitumor agent.

CONCLUSION

Lycorine inhibited pancreatic cancer cell proliferation, blocked the cell cycle, and induced apoptosis by targeting ALDH3A1. FAO inhibition was identified for the first time as a possible mechanism for the anticancer effects of lycorine. These findings enrich the theory of targeted therapy for pancreatic cancer, expand our understanding of the pharmacological targets of lycorine, and provide a reference for exploring its natural components.

Association of environmental exposure to chromium with differential DNA methylation: An epigenome-wide study

Introduction: Previous studies have reported that chromium (Cr)-induced epigenetic alterations and DNA methylation play a vital role in the pathogenesis of diseases induced by chromium exposure. Epigenomic analyses have been limited and mainly focused on occupational chromium exposure; their findings are not generalizable to populations with environmental Cr exposure. Methods: We identified the differential methylation of genes and regions to elucidate the mechanisms of toxicity related to environmental chromium exposure. DNA methylation was measured in blood samples collected from individuals in Cr-contaminated (n = 10) and unexposed areas (n = 10) by using the Illumina Infinium HumanMethylation850K array. To evaluate the relationship between chromium levels in urine and CpG methylation at 850 thousand sites, we investigated differentially methylated positions (DMPs) and differentially methylated regions (DMRs) by using linear models and DMRcate method, respectively. The model was adjusted for biologically relevant variables and estimated cell-type compositions. Results: At the epigenome-wide level, we identified five CpGs [cg20690919 (p _{FDR =}0.006), cg00704664 (p _{FDR =}0.024), cg10809143 (p _{FDR =}0.043), cg27057652 (p _{FDR =}0.047), cg05390480 (p _{FDR =}0.024)] and one DMR (chr17: 19,648,718-19,648,972), annotated to ALDH3A1 genes (p < 0.05) as being significantly associated with log₂ transformed urinary chromium levels. Discussion: Environmental chromium exposure is associated with DNA methylation, and the significant DMPs and DMR being annotated to cause DNA damage and genomic instability were found in this work. Research involving larger samples is required to further explore the epigenetic effect of environmental chromium exposure on health outcomes through DNA methylation.

ALDH3A1 is overexpressed in a subset of hepatocellular carcinoma characterised by activation of the Wnt/ß-catenin pathway

Aldehyde dehydrogenase isoforms, ALDH1A1 and ALDH3A1, are associated with poor clinical outcome and resistance to chemotherapy in a wide variety of human malignancies. So far, their expression and prognostic significance in hepatocellular carcinoma (HCC) remains unknown. The aim of our study was to investigate their expression in HCC, and to correlate this to clinical, pathological and molecular features. ALDH1A1 and ALDH3A1 expression was first evaluated by microarray analysis in a series of 60 HCCs and five tumour-free liver tissue samples. Our findings related to ALDH3A1 were further validated by immunohistochemistry in a series of 81 HCCs and 23 hepatocellular adenomas (HCA). Microarray analysis showed no difference in ALDH1A1 expression between HCCs and tumour-free liver tissue. In contrast, ALDH3A1 was strongly upregulated in a subset of HCCs characterised by activation of the Wnt/ß-catenin pathway and CTNNB1 mutations. Using immunohistochemistry, we confirmed that high ALDH3A1 expression is associated with nuclear staining for ß-catenin and strong homogeneous staining for glutamine synthetase, two classical Wnt/ß-catenin pathway activation markers. Consistent with this finding, in tumour-free liver tissue, ALDH3A1 expression was observed in centrilobular hepatocytes, in which the Wnt/ß-catenin pathway is known to be physiologically activated. We also observed higher ALDH3A1 expression in CTNNB1-mutated HCA when compared with other subtypes. No correlation between ALDH3A1 expression and patient survival or tumour recurrence was observed.In conclusion, ALDH3A1 is a marker of activation of the Wnt/ß-catenin pathway in HCC, HCA and tumour-free liver tissue. Further studies may help to elucidate the potential role of ALDH3A1 in HCC development and resistance to chemotherapy.

Aldehyde dehydrogenases and cell proliferation

Aldehyde dehydrogenases (ALDHs) oxidize aldehydes to the corresponding carboxylic acids using either NAD or NADP as a coenzyme. Aldehydes are highly reactive aliphatic or aromatic molecules that play an important role in numerous physiological, pathological, and pharmacological processes. ALDHs have been discovered in practically all organisms and there are multiple isoforms, with multiple subcellular localizations. More than 160 ALDH cDNAs or genes have been isolated and sequenced to date from various sources, including bacteria, yeast, fungi, plants, and animals. The eukaryote ALDH genes can be subdivided into several families; the human genome contains 19 known ALDH genes, as well as many pseudogenes. Noteworthy is the fact that elevated activity of various ALDHs, namely ALDH1A2, ALDH1A3, ALDH1A7, ALDH2*2, ALDH3A1, ALDH4A1, ALDH5A1, ALDH6, and ALDH9A1, has been observed in normal and cancer stem cells. Consequently, ALDHs not only may be considered markers of these cells, but also may well play a functional role in terms of self-protection, differentiation, and/or expansion of stem cell populations. The ALDH3 family includes enzymes able to oxidize medium-chain aliphatic and aromatic aldehydes, such as peroxidic and fatty aldehydes. Moreover, these enzymes also have noncatalytic functions, including antioxidant functions and some structural roles. The gene of the cytosolic form, ALDH3A1, is localized on chromosome 17 in human beings and on the 11th and 10th chromosome in the mouse and rat, respectively. ALDH3A1 belongs to the phase II group of drug-metabolizing enzymes and is highly expressed in the stomach, lung, keratinocytes, and cornea, but poorly, if at all, in normal liver. Cytosolic ALDH3 is induced by polycyclic aromatic hydrocarbons or chlorinated compounds, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin, in rat liver cells and increases during carcinogenesis. It has been observed that this increased activity is directly correlated with the degree of deviation in hepatoma and lung cancer cell lines, as is the case in chemically induced hepatoma in rats. High ALDH3A1 expression and activity have been correlated with cell proliferation, resistance against aldehydes derived from lipid peroxidation, and resistance against drug toxicity, such as oxazaphosphorines. Indeed, cells with a high ALDH3A1 content are more resistant to the cytostatic and cytotoxic effects of lipidic aldehydes than are those with a low content. A reduction in cell proliferation can be observed when the enzyme is directly inhibited by the administration of synthetic specific inhibitors, antisense oligonucleotides, or siRNA or indirectly inhibited by the induction of peroxisome proliferator-activated receptor γ (PPARγ) with polyunsaturated fatty acids or PPARγ transfection. Conversely, cell proliferation is stimulated by the activation of ALDH3A1, whether by inhibiting PPARγ with a specific antagonist, antisense oligonucleotides, siRNA, or a medical device (i.e., composite polypropylene prosthesis for hernia repair) used to induce cell proliferation. To date, the mechanisms underlying the effects of ALDHs on cell proliferation are not yet fully clear. A likely hypothesis is that the regulatory effect is mediated by the catabolism of some endogenous substrates deriving from normal cell metabolism, such as 4-hydroxynonenal, which have the capacity to either stimulate or inhibit the expression of genes involved in regulating proliferation.

The "two-faced" effects of reactive oxygen species and the lipid peroxidation product 4-hydroxynonenal in the hallmarks of cancer

Reacytive Oxygen Species (ROS) have long been considered to be involved in the initiation, progression and metastasis of cancer. However, accumulating evidence points to the benefical role of ROS. Moreover, ROS production, leading to apoptosis, is the mechanism by which many chemotherapeutic agents can act. Beside direct actions, ROS elicit lipid peroxidation, leading to the production of 4-hydroxynoneal (HNE). Interestingly, HNE also seems to have a dual behaviour with respect to cancer. In this review we present recent literature data which outline the "two-faced" character of oxidative stress and lipid peroxidation in carcinogenesis and in the hallmarks of cancer.

Arachidonic acid suppresses growth of human lung tumor A549 cells through down-regulation of ALDH3A1 expression

Expression of aldehyde dehydrogenase 3A1 (ALDH3A1) in certain normal and tumor cells is associated with protection against the growth inhibitory effect of reactive aldehydes generated during membrane lipid peroxidation. We found that human lung tumor (A549) cells, which express high levels of ALDH3A1 protein, were significantly less susceptible to the antiproliferative effects of 4-hydroxynonenal compared to human hepatoma HepG2 or SK-HEP-1 cells that lack ALDH3A1 expression. However, A549 cells became susceptible to lipid peroxidation products when they were treated with arachidonic acid. The growth suppression of A549 cells induced by arachidonic acid was associated with increased levels of lipid peroxidation and with reduced ALDH3A1 enzymatic activity, protein, and mRNA levels. Furthermore, arachidonic acid treatment of the A549 cells resulted in an increased expression of peroxisome proliferator-activated receptor gamma (PPARgamma), whereas NF-kappaB binding activity was inhibited. Blocking PPARgamma using a selective antagonist, GW9662, prevented the arachidonic acid-mediated reduction of ALDH3A1 expression as well as the growth inhibition of A549 cells, suggesting the central role of PPARgamma in these phenomena. The increase in PPARgamma and the reduction in ALDH3A1 were also prevented by exposing cells to vitamin E concomitant with arachidonic acid treatment. In conclusion, our data show that the arachidonic acid-induced suppression of A549 cell growth is associated with increased lipid peroxidation and decreased ALDH3A1 expression, which may be due to activation of PPARgamma.

Insights into oxazaphosphorine resistance and possible approaches to its circumvention

The oxazaphosphorines cyclophosphamide, ifosfamide and trofosfamide remain a clinically useful class of anticancer drugs with substantial antitumour activity against a variety of solid tumors and hematological malignancies. A major limitation to their use is tumour resistance, which is due to multiple mechanisms that include increased DNA repair, increased cellular thiol levels, glutathione S-transferase and aldehyde dehydrogenase activities, and altered cell-death response to DNA damage. These mechanisms have been recently re-examined with the aid of sensitive analytical techniques, high-throughput proteomic and genomic approaches, and powerful pharmacogenetic tools. Oxazaphosphorine resistance, together with dose-limiting toxicity (mainly neutropenia and neurotoxicity), significantly hinders chemotherapy in patients, and hence, there is compelling need to find ways to overcome it. Four major approaches are currently being explored in preclinical models, some also in patients: combination with agents that modulate cellular response and disposition of oxazaphosphorines; antisense oligonucleotides directed against specific target genes; introduction of an activating gene (CYP3A4) into tumor tissue; and modification of dosing regimens. Of these approaches, antisense oligonucleotides and gene therapy are perhaps more speculative, requiring detailed safety and efficacy studies in preclinical models and in patients. A fifth approach is the design of novel oxazaphosphorines that have favourable pharmacokinetic and pharmacodynamic properties and are less vulnerable to resistance. Oxazaphosphorines not requiring hepatic CYP-mediated activation (for example, NSC 613060 and mafosfamide) or having additional targets (for example, glufosfamide that also targets glucose transport) have been synthesized and are being evaluated for safety and efficacy. Characterization of the molecular targets associated with oxazaphosphorine resistance may lead to a deeper understanding of the factors critical to the optimal use of these agents in chemotherapy and may allow the development of strategies to overcome resistance.

Aldehyde dehydrogenase 3 expression is decreased by clofibrate via PPAR gamma induction in JM2 rat hepatoma cell line

In normal liver aldehyde dehydrogenase 3 (ALDH3) is poorly expressed. In hepatoma cells, its expression increases in direct correlation with the degree of deviation and increased ALDH3 activity is one cause of resistance to the toxicity of drugs and lipid peroxidation aldehydes. Hepatoma cells with high ALDH3 content are more resistant to the cytotoxic effect of aldehydes than those with low ALDH3, and inhibition of the enzyme with aldehydes, specific inhibitors or antisense oligonucleotides (AS-ODN), decreases cell growth. It remains open how ALDH3 influences cell growth or cell phenotype. Recently, we have shown that enrichment of a highly deviated rat hepatoma cell line, JM2, with arachidonic acid, a natural ligand of peroxisome proliferator activated receptors (PPARs), inhibits growth, partially restores ALDH2 and ALDH3 to their normal levels and induces PPAR expression. In the present study we address the effect of clofibrate, a hypolipidemic drug and synthetic PPAR ligand on ALDH gene expression. We show that treatment of JM2 cells with clofibrate inhibits cell growth, induces PPARgamma and decreases ALDH3 expression. To determine the relationship between PPARgamma and ALDH3 expression, we exposed JM2 cells to AS-ODN against PPARgamma. AS-ODN reduced PPARgamma content and prevented the inhibitory effect of clofibrate on cell proliferation and ALDH3 expression. Since these results indicate that ALDH3 expression is under PPAR control, we examined the 5' flanking sequence of the ALDH3 gene, but were unable to find any sequence similar to any known peroxisome proliferator response element. We thus believe that the effect of PPARgamma on ALDH3 occurs via other transcription factors, whose identity remain to be determined. The results indicate that PPARgamma plays a key role in regulation of growth and differentiation of hepatoma cells, and that ALDH3 collaborates in modulating cell proliferation and in determining some aspects of the hepatoma phenotype, i.e. resistance to drugs and to lipid peroxidation products.

Antisense oligonucleotides against aldehyde dehydrogenase 3 inhibit hepatoma cell proliferation by affecting MAP kinases

The increased activity of enzymes that eliminate anti-tumour drugs or their metabolites is one of the important limiting factors in therapeutic protocols. Among these enzymes, aldehyde dehydrogenase 3 (ALDH3) is considered a mechanism by which tumour cells evade the cytotoxic effects exerted by cyclophosphamide and drugs acting by free radical generation. It is also important in metabolising cytostatic aldehydes derived from lipid peroxidation. Therefore, ALDH3 may play a role in regulating cell proliferation in tumour cells with high activity of this enzyme. We previously reported that antisense oligonucleotides (AS-ODN) against ALDH3 strongly inhibit hepatoma cell growth, suggesting that this effect could be due to the accumulation of cytostatic aldehydes in the cells. In this research we demonstrate that AS-ODN against ALDH3 increase the quantity of malondialdehyde in the cells, and inhibit cell proliferation by affecting the MAPK pathway: a reduction of pRaf-1 and pERK1,2 was observed. These results confirm the importance of aldehydes derived from lipid peroxidation and of ALDH3 in regulating hepatoma proliferation. Moreover, the results indicate the use of AS-ODN against ALDH3 as a possible strategy to reduce growth in tumours overexpressing this enzyme.