Comparison of the cytotoxicity of the nitroaromatic drug flutamide to its cyano analogue in the hepatocyte cell line TAMH: evidence for complex I inhibition and mitochondrial dysfunction using toxicogenomic screening

Replacement of nitro function by free boronic acid in non-steroidal anti-androgens

A new series of potential flutamide-like antiandrogens has been designed and synthesized to treat prostate cancer. This new series results from our research, which has been aimed at discovering new compounds that can be used for androgen deprivation treatment. The antiandrogens were designed and synthesized by varying the acyl part, linker, and substitution of the benzene ring in the 4-nitro-3-trifluoromethylanilide scaffold of non-steroidal androgens. In addition, the characteristic feature of the nitro group was replaced by a boronic acid functionality. Compound 9a was found to be more effective against LAPC-4 than the standard antiandrogens flutamide, hydroxyflutamide, and bicalutamide. Moreover, it exhibited lower toxicity against the non-cancerous cell line HK-2. The initial in silico study did not show evidence of covalent bonding to the androgen receptor, which was confirmed by an NMR binding experiment with arginine methyl ester. The structure-activity relationships discovered in this study could provide directions for further research on non-steroidal antiandrogens.

Fexinidazole optimization: enhancing anti-leishmanial profile, metabolic stability and hERG safety

The lack of adequate anti-leishmanial therapies has led to the continued suffering of millions of people from developing nations. Moreover, optimism for a therapeutic intervention by fexinidazole was dashed due to the inability to maintain cures and control unwanted side effects. To solve these shortcomings, the structural elements of fexinidazole responsible for anti-leishmanial activity and toxicities were explored. Accordingly, a systematic analog design approach was taken for the synthesis of 24 novel analogs. We established the structural features important for activity and identified modifications that improved the hERG receptor safety and liver microsomal metabolic stability. Compared to fexinidazole, the S-configured imidazolooxazole analog 51 exhibited 25-fold greater potency against miltefosine resistant L. donovani amastigotes, greater metabolic stability and little hERG receptor inhibition. Replacement of the toxicophore nitro group for a cyano group resulted in a complete loss of anti-leishmanial activity. The SAR findings should be useful in the further development of this important class of anti-leishmanial agents.

Investigation of TGF-α-overexpressing mouse hepatocytes (TAMH) cultured as spheroids for use in hepatotoxicity screening of drug candidates

The immortalized mouse liver cell line TAMH has been described as a valuable tool for studying hepatotoxic mechanisms, but until now, it has only been reported to grow as a monolayer in culture. However, culturing hepatocytes as three-dimensional (3D) spheroids has been shown to result in improved liver-specific functions (e.g., metabolic capacity) by better mimicking the in vivo environment. This approach may lead to more reliable detection of drug-induced liver injury (DILI) in the early phase of drug discovery, preventing post-marketing drug withdrawals. Here, we investigated the cultivation of TAMH as 3D spheroids, characterizing them with optical and transmission electron microscopy as well as analyzing their gene expression at mRNA level (especially drug-metabolizing enzymes) compared to TAMH monolayer. In addition, comparisons were made with spheroids grown from the human hepatoblastoma cell line HepG2, another current spheroid model. The results indicate that TAMH spheroids express hepatic structures and show elevated levels of some of the key phase I and II drug-metabolizing enzymes, in contrast to TAMH monolayer. The in vitro hepatotoxic potencies of the drugs acetaminophen and flupirtine maleate were found to be very similar between TAMH spheroidal and the monolayer cultures. Both the advantages and disadvantages of TAMH spheroids as an in vitro hepatotoxicity model compared to monolayer model are discussed.

Mechanism of non-steroidal anti-androgen-induced liver injury: Reactive metabolites of flutamide and bicalutamide activate inflammasomes

Flutamide is a non-steroidal anti-androgen agent, which is mainly used for the treatment of prostate cancer. Flutamide is known to cause severe adverse events, which includes idiosyncratic liver injury. However, details of the mechanism of these adverse reactions have not been elucidated. We investigated whether flutamide induces the release of damage-associated molecular patterns (DAMPs) that activate inflammasomes. We also tested bicalutamide, enzalutamide, apalutamide, and darolutamide for their ability to activate inflammasomes in differentiated THP-1 cells. The supernatant from the incubation of flutamide and bicalutamide with human hepatocarcinoma functional liver cell-4 (FLC-4) cells increased caspase-1 activity and production of IL-1ß by differentiated THP-1 cells. In the supernatant of FLC-4 cells with flutamide and bicalutamide, the heat shock protein (HSP) 40 or 60 was significantly increased. Addition of a carboxylesterase or a CYP inhibitor to the FLC-4 cells prevented release of HSPs from the FLC-4 cells. These results suggested that the reactive metabolites of flutamide and bicalutamide can cause the release of DAMPs from hepatocytes and activate inflammasomes. Inflammasome activation may be an important step in the activation of the immune system by flutamide or bicalutamide, which in some patients, can cause immune-related adverse events.

Electrochemical Nitration with Nitrite

Aromatic nitration has tremendous importance in organic chemistry as nitroaromatic compounds serve as versatile building blocks. This study represents the electrochemical aromatic nitration with NBu4 NO2 , which serves a dual role as supporting electrolyte and as a safe, readily available, and easy-to-handle nitro source. Stoichiometric amounts of 1,1,1-3,3,3-hexafluoroisopropan-2-ol (HFIP) in MeCN significantly increase the yield by solvent control. The reaction mechanism is based on electrochemical oxidation of nitrite to NO2 , which initiates the nitration reaction in a divided electrolysis cell with inexpensive graphite electrodes. Overall, the reaction is demonstrated for 20 examples with yields of up to 88 %. Scalability is demonstrated by a 13-fold scale-up.

Development of an Antibiotic Resistance Breaker to Resensitize Drug-Resistant Staphylococcus aureus: In Silico and In Vitro Approach

Efflux pumps are one of the predominant microbial resistant mechanisms leading to the development of multidrug resistance. In Staphylococcus aureus, overexpression of NorA protein enables the efflux of antibiotics belonging to the class of fluoroquinolones and, thus, makes S. aureus resistant. Hence, NorA efflux pumps are being extensively exploited as the potential drug target to evade bacterial resistance and resensitize bacteria to the existing antibiotics. Although several molecules are reported to inhibit NorA efflux pump effectively, boronic acid derivatives were shown to have promising NorA efflux pump inhibition. In this regard, the current study exploits 6-(3-phenylpropoxy)pyridine-3-boronic acid to further improve the activity and reduce cytotoxicity using the bioisostere approach, a classical medicinal chemistry concept. Using the SWISS-Bioisostere online tool, from the parent compound, 42 compounds were obtained upon the replacement of the boronic acid. The 42 compounds were docked with modeled NorA protein, and key molecular interactions of the prominent compounds were assessed. The top hit compounds were further analyzed for their drug-like properties using ADMET studies. The identified potent lead, 5-nitro-2-(3-phenylpropoxy)pyridine (5-NPPP), was synthesized, and in vitro efficacy studies have been proven to show enhanced efflux inhibition, thus acting as a potent antibiotic breaker to resensitize S. aureus without elucidating any cytotoxic effect to the host Hep-G2 cell lines.

Role of respiratory uncoupling in drug-induced mitochondrial permeability transition

Mitochondrial injury contributes to severe drug-induced liver injury. Particularly, mitochondrial permeability transition (MPT) is thought to be relevant to cytolytic hepatitis. However, the mechanism of drug-induced MPT is unclear and prediction of MPT is not adequately evaluated in the preclinical stage. In a previous study, we found that troglitazone, a drug withdrawn due to liver injury, induced MPT via mild depolarization probably resulting from uncoupling. Herein, we investigated whether other drugs that induce MPT share similar properties as troglitazone, using isolated mitochondria from rat liver. Of the 22 test drugs examined, six drugs, including troglitazone, induced MPT and showed an uncoupling effect. Additionally, receiver operating characteristic analysis was conducted to predict the MPT potential from the respiratory control ratio, an indicator of uncoupling intensity. Results showed that 2.5 was the best threshold that exhibited high sensitivity (1.00) and high specificity (0.81), indicating that uncoupling was correlated with MPT potential. Activation of calcium-independent phospholipase A2 appeared to be involved in uncoupling-induced MPT. Furthermore, a strong relationship between MPT intensity and the uncoupling effect among similar compounds was confirmed. These results may help in predicting MPT potential using cultured cells and modifying the chemical structures of the drugs to reduce MPT risk.

Increased uterine androgen receptor protein abundance results in implantation and mitochondrial defects in pregnant rats with hyperandrogenism and insulin resistance

Abstract

In this study, we show that during normal rat pregnancy, there is a gestational stage-dependent decrease in androgen receptor (AR) abundance in the gravid uterus and that this is correlated with the differential expression of endometrial receptivity and decidualization genes during early and mid-gestation. In contrast, exposure to 5α-dihydrotestosterone (DHT) and insulin (INS) or DHT alone significantly increased AR protein levels in the uterus in association with the aberrant expression of endometrial receptivity and decidualization genes, as well as disrupted implantation. Next, we assessed the functional relevance of the androgen-AR axis in the uterus for reproductive outcomes by treating normal pregnant rats and pregnant rats exposed to DHT and INS with the anti-androgen flutamide. We found that AR blockage using flutamide largely attenuated the DHT and INS-induced maternal endocrine, metabolic, and fertility impairments in pregnant rats in association with suppressed induction of uterine AR protein abundance and androgen-regulated response protein and normalized expression of several endometrial receptivity and decidualization genes. Further, blockade of AR normalized the expression of the mitochondrial biogenesis marker Nrf1 and the mitochondrial functional proteins Complexes I and II, VDAC, and PHB1. However, flutamide treatment did not rescue the compromised mitochondrial structure resulting from co-exposure to DHT and INS. These results demonstrate that functional AR protein is an important factor for gravid uterine function. Impairments in the uterine androgen-AR axis are accompanied by decreased endometrial receptivity, decidualization, and mitochondrial dysfunction, which might contribute to abnormal implantation in pregnant PCOS patients with compromised pregnancy outcomes and subfertility.

Key messages

The proper regulation of uterine androgen receptor (AR) contributes to a normal pregnancy process, whereas the aberrant regulation of uterine AR might be linked to polycystic ovary syndrome (PCOS)-induced pregnancy-related complications.

In the current study, we found that during normal rat pregnancy there is a stage-dependent decrease in AR abundance in the gravid uterus and that this is correlated with the differential expression of the endometrial receptivity and decidualization genes Spp1, Prl, Igfbp1, and Hbegf.

Pregnant rats exposed to 5α-dihydrotestosterone (DHT) and insulin (INS) or to DHT alone show elevated uterine AR protein abundance and implantation failure related to the aberrant expression of genes involved in endometrial receptivity and decidualization in early to mid-gestation.

Treatment with the anti-androgen flutamide, starting from pre-implantation, effectively prevents DHT + INS-induced defects in endometrial receptivity and decidualization gene expression, restores uterine mitochondrial homeostasis, and increases the pregnancy rate and the numbers of viable fetuses.

This study adds to our understanding of the mechanisms underlying poor pregnancy outcomes in PCOS patients and the possible therapeutic use of anti-androgens, including flutamide, after spontaneous conception.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00109-021-02104-z.

Environmental persistence, hazard, and mitigation challenges of nitroaromatic compounds

Nitroaromatic compounds (NACs) are extensively used in different industries and are synthesized in large quantity due to their heavy demand worldwide. The broad use of NACs poses a serious pollution threat. The treatment processes used for the removal of NACs are not effective and sustainable, leading to their release into the environment. The nitro group attached to benzene ring makes the compounds recalcitrant due to which they persist in the environment. Being hazardous to human as well as other living organisms, NACs are listed in the USEPA's priority pollutant group. This review provides updated information on the sources of NACs, prevalence in different environmental matrices, and recent developments in methods of their detection, with emphasis on current trends as well as future prospects. The harmful effects of NACs due to exposure through different routes are also highlighted. Further, the technologies reported for the treatment of NACs, including physico-chemical and biological methods, and the challenges faced for their effective implementation are discussed. Thus, the review discusses relevant issues in detail making suitable recommendations, which can be helpful in guiding further research in this subject.

Predicting the cytotoxicity of chemicals using ensemble learning methods and molecular fingerprints

The prediction of compound cytotoxicity is an important part of the drug discovery process. However, it usually appears as poor predictive performance because the datasets are high-throughput and have a class-imbalance problem. In this study, several strategies of performing a structure-activity relationship study for a cytotoxic endpoint in the AID364 dataset were explored to solve the class-imbalance problem. Random forest adaboost was used as the base learners for 10 types of molecular fingerprints and an ensemble method and six data-balancing methods were applied to balance the classes. As a result, the ensemble model using MACCS fingerprint was found to be the best, giving area under the curve of 85.2% ± 0.35%, sensitivity of 81.8% ± 0.65%, and specificity of 76.0% ± 0.12% in fivefold cross-validation and area under the curve of 78.8%, sensitivity of 55.5% and specificity of 78.5% in external validation. Good performance also appeared on other datasets with different sizes/degrees of imbalance. To explore the structural commonality of cytotoxic compounds, several substructures were identified as an important reference for substructure alerts. The convincing results indicate that the proposed models are helpful in predicting the cytotoxicity of chemicals.

Nitro-Group-Containing Drugs

The nitro group is considered to be a versatile and unique functional group in medicinal chemistry. Despite a long history of use in therapeutics, the nitro group has toxicity issues and is often categorized as a structural alert or a toxicophore, and evidence related to drugs containing nitro groups is rather contradictory. In general, drugs containing nitro groups have been extensively associated with mutagenicity and genotoxicity. In this context, efforts toward the structure-mutagenicity or structure-genotoxicity relationships have been undertaken. The current Perspective covers various aspects of agents that contain nitro groups, their bioreductive activation mechanisms, their toxicities, and approaches to combat their toxicity issues. In addition, recent advances in the field of anticancer, antitubercular and antiparasitic agents containing nitro groups, along with a patent survey on hypoxia-activated prodrugs containing nitro groups, are also covered.

Androgens in women: Hormone-modulating therapies for skin disease

Androgen-mediated cutaneous disorders (AMCDs) in women, including acne, hirsutism, and female pattern hair loss, can be treated with hormone-modulating therapies. In the second article in this Continuing Medical Education series, we discuss the hormone-modulating therapies available to dermatologists for the treatment of AMCDs, including combined oral contraceptives, spironolactone, finasteride, dutasteride, and flutamide. Available hormone-modulating treatments used for each AMCDs are reviewed, along with mechanisms of androgen modulation, safety profile, contraindications, monitoring parameters, and evidence of efficacy. Medications discussed include those that are approved by the US Food and Drug Administration for certain AMCDs and some that are used off-label. Despite the ubiquity of hormone-modulating therapies used for AMCDs, this review highlights the need for more rigorous studies to evaluate these therapies for acne, hirsutism, and female pattern hair loss.

Design and synthesis of potent dual inhibitors of JAK2 and HDAC based on fusing the pharmacophores of XL019 and vorinostat

Specifically blocking more than one oncogenic pathway simultaneously in a cancer cell with a combination of different drugs is the mainstay of the majority of cancer treatments. Being able to do this via two targeted pathways without inducing side effects through a general mechanism, such as chemotherapy, could bring benefit to patients. In this work we describe a new dual inhibitor of the JAK-STAT and HDAC pathways through designing and developing two types of molecule based on the JAK2 selective inhibitor XL019 and the pan-HDAC inhibitor, vorinostat. Both series of compounds had examples with low nanomolar JAK2 and HDAC1/6 inhibition. In some cases good HDAC1 selectivity was achieved while retaining HDAC6 activity. The observed potency is explained through molecular docking studies of all three enzymes. One example, 69c had 16-25 fold selectivity against the three other JAK-family proteins JAK1, JAK3 and TYK2. A number of compounds had sub-micromolar potencies against a panel of 4 solid tumor cell lines and 4 hematological cell lines with the most potent compound, 45h, having a cellular IC₅₀ of 70 nM against the multiple myeloma cell line KMS-12-BM. Evidence of both JAK and HDAC pathway inhibition is presented in Hela cells showing that both pathways are modulated. Evidence of apoptosis with two compounds in 4 sold tumor cell lines is also presented.

Flutamide Induces Hepatic Cell Death and Mitochondrial Dysfunction via Inhibition of Nrf2-Mediated Heme Oxygenase-1

Flutamide is a widely used nonsteroidal antiandrogen for prostate cancer therapy, but its clinical application is restricted by the concurrent liver injury. Increasing evidence suggests that flutamide-induced liver injury is associated with oxidative stress, though the precise mechanism is poorly understood. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a master transcription factor regulating endogenous antioxidants including heme oxygenase-1 (HO-1). This study was designed to delineate the role of Nrf2/HO-1 in flutamide-induced hepatic cell injury. Our results showed that flutamide concentration dependently induced cytotoxicity, hydrogen peroxide accumulation, and mitochondrial dysfunction as indicated by mitochondrial membrane potential loss and ATP depletion. The protein expression of Nrf2 and HO-1 was induced by flutamide at 12.5 μM but was downregulated by higher concentrations of flutamide. Silencing either Nrf2 or HO-1 was found to aggravate flutamide-induced hydrogen peroxide accumulation and mitochondrial dysfunction as well as inhibition of the Nrf2 pathway. Moreover, preinduction of HO-1 by Copp significantly attenuated flutamide-induced oxidative stress and mitochondrial dysfunction, while inhibition of HO-1 by Snpp aggravated these deleterious effects. These findings suggest that flutamide-induced hepatic cell death and mitochondrial dysfunction is assoicated with inhibition of Nrf2-mediated HO-1. Pharmacologic intervention of Nrf2/HO-1 may provide a promising therapeutic approach in flutamide-induced liver injury.

The expression, induction and pharmacological activity of CYP1A2 are post-transcriptionally regulated by microRNA hsa-miR-132-5p

Cytochrome P450 1A2 (CYP1A2) is one of the most abundant and important drug metabolizing enzymes in human liver. However, little is known about the post-transcriptional regulation of CYP1A2, especially the mechanisms involving microRNAs (miRNAs). This study applied a systematic approach to investigate the post-transcriptional regulation of CYP1A2 by miRNAs. Candidate miRNAs targeting the 3'-untranslated region (3'-UTR) of CYP1A2 were screened in silico, resulting in the selection of sixty-two potential miRNAs for further analysis. The levels of two miRNAs, hsa-miR-132-5p and hsa-miR-221-5p, were inversely correlated with the expression of CYP1A2 mRNA transcripts in normal human liver tissue samples represented in The Cancer Genome Atlas (TCGA) dataset. The interactions between these miRNAs and cognate CYP1A2 mRNA sequences were evaluated using luciferase reporter gene studies and electrophoretic mobility shift assays, by which a direct interaction was confirmed involving hsa-miR-132-5p and a cognate binding site present in the CYP1A2 3'-UTR. Experiments by which hsa-miR-132-5p or random miRNA controls were introduced into HepG2, Huh-7 and HepaRG hepatic cell lines showed that only hsa-miR-132-5p suppressed the endogenous and lansoprazole-induced expression of CYP1A2, at biological activity, protein production, and mRNA transcript levels. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and lactate dehydrogenase (LDH) assays showed that hsa-miR-132-5p attenuates CYP1A2-mediated, lansoprazole-enhanced, flutamide-induced hepatic cell toxicity. Results from multilayer experiments demonstrate that hsa-miR-132-5p suppresses the expression of CYP1A2 and that this suppression is able to decrease the extent of an adverse drug-drug interaction involving lansoprazole and flutamide.

In silico prediction of the mutagenicity of nitroaromatic compounds using a novel two-QSAR approach

Certain drugs are nitroaromatic compounds, which are potentially toxic. As such, it is of practical importance to assess and predict their mutagenic potency in the process of drug discovery. A classical quantitative structure-activity relationship (QSAR) model was developed using the linear partial least square (PLS) scheme to understand the underline mutagenic mechanism and a non-classical QSAR model was derived using the machine learning-based hierarchical support vector regression (HSVR) to predict the mutagenicity of nitroaromatic compounds based on a series of mutagenicity data (TA98-S9). It was observed that HSVR performed better than PLS as manifested by the predictions of the samples in the training set, test set, and outlier set as well as various statistical validations. A mock test designated to mimic real challenges also confirmed the better performance of HSVR. Furthermore, HSVR exhibited superiority in predictivity, generalization capabilities, consistent performance, and robustness when compared with various published predictive models. PLS, conversely, revealed some mechanistically interpretable relationships between descriptors and mutagenicity. Thus, this two-QSAR approach using the predictive HSVR and interpretable PLS models in a synergistic fashion can be adopted to facilitate drug discovery and development by designing safer drug candidates with nitroaromatic moiety.

TAMH: A Useful In Vitro Model for Assessing Hepatotoxic Mechanisms

In vitro models for hepatotoxicity can be useful tools to predict in vivo responses. In this review, we discuss the use of the transforming growth factor-α transgenic mouse hepatocyte (TAMH) cell line, which is an attractive model to study drug-induced liver injury due to its ability to retain a stable phenotype and express drug-metabolizing enzymes. Hepatotoxicity involves damage to the liver and is often associated with chemical exposure. Since the liver is a major site for drug metabolism, drug-induced liver injury is a serious health concern for certain agents. At the molecular level, various mechanisms may protect or harm the liver during drug-induced hepatocellular injury including signaling pathways and endogenous factors (e.g., Bcl-2, GSH, Nrf2, or MAPK). The interplay between these and other pathways in the hepatocyte can change upon drug or drug metabolite exposure leading to intracellular stress and eventually cell death and liver injury. This review focuses on mechanistic studies investigating drug-induced toxicity in the TAMH line and how alterations to hepatotoxic mechanisms in this model relate to the in vivo situation. The agents discussed herein include acetaminophen (APAP), tetrafluoroethylcysteine (TFEC), flutamide, PD0325901, lapatinib, and flupirtine.

Identification of the Additional Mitochondrial Liabilities of 2-Hydroxyflutamide When Compared With its Parent Compound, Flutamide in HepG2 Cells

The androgen receptor antagonist, flutamide, is strongly associated with idiosyncratic drug-induced liver injury (DILI). Following administration, flutamide undergoes extensive first-pass metabolism to its primary metabolite, 2-hydroxyflutamide. Flutamide is a known mitochondrial toxicant; however there has been limited investigation into the potential mitochondrial toxicity of 2-hydroxyflutamide and its contribution to flutamide-induced liver injury. In this study we have used the acute glucose or galactose-conditioning of HepG2 cells to compare the mitochondrial toxicity of flutamide, 2-hydroxyflutamide and the structurally-related, non-hepatotoxic androgen receptor antagonist, bicalutamide. Compound-induced changes in mitochondrial oxygen consumption rate were assessed using Seahorse technology. Permeabilization of cells and delivery of specific substrates and inhibitors of the various respiratory complexes provided more detailed information on the origin of mitochondrial perturbations. These analyses were supported by assessment of downstream impacts including changes in cellular NAD(+)/NADH ratio. Bicalutamide was not found to be a mitochondrial toxicant, yet flutamide and 2-hydroxyflutamide significantly reduced basal and maximal respiration. Both flutamide and 2-hydroxyflutamide significantly reduced respiratory complex I-linked respiration, though 2-hydroxyflutamide also significantly decreased complex II and V-linked respiration; liabilities not demonstrated by the parent compound. This study has identified for the first time, the additional mitochondrial liabilities of the major metabolite, 2-hydroxyflutamide compared with its parent drug, flutamide. Given the rapid production of this metabolite upon administration of flutamide, but not bicalutamide, we propose that the additional mitochondrial toxicity of 2-hydroxyflutamide may fundamentally contribute to the idiosyncratic DILI seen in flutamide-treated, but not bicalutamide-treated patients.

Overcoming Chloroquine Resistance in Malaria: Design, Synthesis, and Structure-Activity Relationships of Novel Hybrid Compounds

Resistance to antimalarial therapies, including artemisinin, has emerged as a significant challenge. Reversal of acquired resistance can be achieved using agents that resensitize resistant parasites to a previously efficacious therapy. Building on our initial work describing novel chemoreversal agents (CRAs) that resensitize resistant parasites to chloroquine (CQ), we herein report new hybrid single agents as an innovative strategy in the battle against resistant malaria. Synthetically linking a CRA scaffold to chloroquine produces hybrid compounds with restored potency toward a range of resistant malaria parasites. A preferred compound, compound 35, showed broad activity and good potency against seven strains resistant to chloroquine and artemisinin. Assessment of aqueous solubility, membrane permeability, and in vitro toxicity in a hepatocyte line and a cardiomyocyte line indicates that compound 35 has a good therapeutic window and favorable drug-like properties. This study provides initial support for CQ-CRA hybrid compounds as a potential treatment for resistant malaria.

Comparative hepatoprotective effects of tocotrienol analogs against drug-induced liver injury

Oxidative stress plays a major part in the pathogenesis of drug-induced liver injury. Yet, overcoming it with other xenobiotics impose additional risks. In this study, we consider the use of natural-occurring and purified Vitamin E analogs as hepatoprotective agents. Vitamin E is well-known for its intrinsic antioxidant property even though the differential effect of specific analogs of tocopherol (TP) and tocotrienol (T3) is still not ascertained. This study investigates the protective effect of T3 analogs (α-, δ-, γ−) in comparison with α-TP followed by assessing the underlying mechanisms of the cytoprotective T3 analog(s) in two xenobiotics-induced liver injury models using (1) acetaminophen (APAP)- and (2) hydrogen peroxide (H₂O₂). Both α-TP and α-T3 exerted cytoprotective effects while only lower concentration of γ-T3 was effective in inhibiting both toxicants induced injury. α-TP/α-T3 protected hepatocytes from APAP and H₂O₂-induced liver injury through arresting free radicals and inhibiting oxidative stress (inhibition of reactive oxygen species, lipid peroxidation and mitochondrial permeability transition). There was also demonstrable inhibition of the apoptotic pathway (inhibition of caspse-3 activity and overexpression of Bcl-_XL), accompanied with an induction of liver regeneration (PCNA and NF-kB). The cellular uptake of α-T3 was higher than α-TP at the same treatment dosage after 24 h. Overall, α-T3 seems to be a more potent hepatoprotective analog among the tocotrienols and α-TP at the same in vitro treatment dosage. In summary, these results suggest that α-TP/α-T3 elicit hepatoprotective effects against toxicants-induced damage mainly through activation of antioxidant responses at an early stage to prevent the exacerbation of injury.

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Purified T3 analogs were compared for their hepatoprotective effects against two toxicants-induced liver injuries.

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α-TP/α-T3 and lower concentration of γ-T3 exerted significant cytoprotective effects.

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α-TP/α-T3 inhibits oxidative stress and apoptosis while induces liver regeneration.

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α-T3 is the most potent hepatoprotective analog among T3 and α-TP at same dose.

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α-TP/α-T3 prevented toxicants-induced injury mainly through antioxidant responses.

Oxidation potentials of N-modified derivatives of the analgesic flupirtine linked to potassium KV 7 channel opening activity but not hepatocyte toxicity

Openers of neuronal voltage-gated potassium channels (KV ) are of interest as therapeutic agents for treating pain (flupirtine) and epilepsy (retigabine). In an effort to better understand the mechanisms of action and toxicity of flupirtine, we synthesized nine novel analogues with varying redox behavior. Flupirtine can be oxidatively metabolized into azaquinone diimines; thus, the oxidation potentials of flupirtine and its analogues were measured by cyclic voltammetry. KV 7.2/3 (KCNQ2/3) opening activity was determined by an established assay with HEK293 cells overexpressing these channels. A link was found between the oxidation potentials of the compounds and their EC50 values for potassium channel opening activity. On the other hand, no correlation was observed between oxidation potentials and cytotoxicity in cultures of transgenic mouse hepatocytes (TAMH). These results support the idea that oxidative metabolites of flupirtine contribute to the mechanism of action, similar to what was recently proposed for acetaminophen (paracetamol), but not to hepatotoxicity.

Integration of pharmacokinetic and NRF2 system biology models to describe reactive oxygen species production and subsequent glutathione depletion in liver microfluidic biochips after flutamide exposure

We present a systems biology analysis of rat primary hepatocytes response after exposure to 10 μM and 100 μM flutamide in liver microfluidic biochips. We coupled an in vitro pharmacokinetic (PK) model of flutamide to a system biology model of its reactive oxygen species (ROS) production and scavenging by the Nrf2 regulated glutathione production. The PK model was calibrated using data on flutamide kinetics, hydroxyflutamide and glutathione conjugates formation in microfluidic conditions. The parameters of Nrf2-related gene activities and the subsequent glutathione depletion were calibrated using microarray data from our microfluidic experiments and literature information. Following a 10 μM flutamide exposure, the model predicted a recovery time to baseline levels of glutathione (GSH) and ROS in agreement with our experimental observations. At 100 μM, the model predicted that metabolism saturation led to an important accumulation of flutamide in cells, a high ROS production and complete GSH depletion. The high levels of ROS predicted were consistent with the necrotic switch observed by transcriptomics, and the high cell mortality we had experimentally observed. The model predicted a transition between recoverable GSH depletion and deep GSH depletion at about 12.5 μM of flutamide (single perfusion exposure). Our work shows that in vitro biochip experiments can provide supporting information for complex in silico modeling including data from extra cellular and intra cellular levels. We believe that this approach can be an efficient strategy for a global integrated methodology in predictive toxicology.

Mesenchymal stem cell-derived exosomes promote hepatic regeneration in drug-induced liver injury models

Introduction

Mesenchymal stem cell-conditioned medium (MSC-CM) has been shown to have protective effects against various cellular-injury models. This mechanism of protection, however, has yet to be elucidated. Recently, exosomes were identified as the active component in MSC-CM. The aim of this study is to investigate the effect of MSC-derived exosomes in an established carbon tetrachloride (CCl₄)-induced liver injury mouse model. This potential effect is then validated by using in vitro xenobiotic-induced liver-injury assays: (1) acetaminophen (APAP)- and (2) hydrogen peroxide (H₂O₂)-induced liver injury.

Methods

The exosomes were introduced concurrent with CCl₄ into a mouse model through different routes of administration. Biochemical analysis was performed based on the blood and liver tissues. Subsequently the exosomes were treated in APAP and H₂O₂-toxicants with in vitro models. Cell viability was measured, and biomarkers indicative of regenerative and oxidative biochemical responses were determined to probe the mechanism of any hepatoprotective activity observed.

Results

In contrast to mice treated with phosphate-buffered saline, CCl₄ injury in mice was attenuated by concurrent-treatment exosomes, and characterized by an increase in hepatocyte proliferation, as demonstrated with proliferating cell nuclear antigen (PCNA) elevation. Significantly higher cell viability was demonstrated in the exosomes-treated group compared with the non-exosome-treated group in both injury models. The higher survival rate was associated with upregulation of the priming-phase genes during liver regeneration, which subsequently led to higher expression of proliferation proteins (PCNA and cyclin D1) in the exosomes-treated group. Exosomes also inhibited the APAP- and H₂O₂-induced hepatocytes apoptosis through upregulation of Bcl-_xL protein expression. However, exosomes do not mitigate hepatocyte injury via modulation of oxidative stress.

Conclusions

In summary, these results suggest that MSC-derived exosomes can elicit hepatoprotective effects against toxicants-induced injury, mainly through activation of proliferative and regenerative responses.

Nitroaromatic compounds: Environmental toxicity, carcinogenicity, mutagenicity, therapy and mechanism

Vehicle pollution is an increasing problem in the industrial world. Aromatic nitro compounds comprise a significant portion of the threat. In this review, the class includes nitro derivatives of benzene, biphenyls, naphthalenes, benzanthrone and polycyclic aromatic hydrocarbons, plus nitroheteroaromatic compounds. The numerous toxic manifestations are discussed. An appreciable number of drugs incorporate the nitroaromatic structure. The mechanistic aspects of both toxicity and therapy are addressed in the context of a unifying mechanism involving electron transfer, reactive oxygen species, oxidative stress and antioxidants.

Metabolomics-on-a-chip of hepatotoxicity induced by anticancer drug flutamide and Its active metabolite hydroxyflutamide using HepG2/C3a microfluidic biochips

We used the recently introduced "metabolomics-on-a-chip" approach to test secondary drug toxicity in bioartificial organs. Bioartificial organs cultivated in microfluidic culture conditions provide a beneficial environment, in which the cellular cytoprotective mechanisms are enhanced, compared with Petri dish culture conditions. We investigated the metabolic response of HepG2/C3a cells exposed to flutamide, an anticancer prodrug, and hydroxyflutamide (HF), its active metabolite, in a microfluidic biochip. The cellular response was analyzed by (1)H nuclear magnetic resonance spectroscopy to identify cell-specific molecule-response markers. The metabolic response to flutamide results in a disruption of glucose homeostasis and in mitochondrial dysfunctions. This flutamide-specific metabolic response was illustrated by a reduction of the extracellular glucose and fructose consumptions and a general reduction of the tricarboxylic acid cycle activity leading to the reduction of the consumption of several amino acids. We also found a higher production of 3-hydroxybutyrate and lactate, and the reduction of the albumin production compared with controls. The toxic metabolic signature associated with the active metabolite HF was illustrated by a high-energy demand and an increase in several amino acid metabolism. Finally, for both molecules, the hepatotoxicity was correlated to the glutathione (GSH) metabolism illustrated by the levels of the 2-hydroxybutyrate and pyroglutamate productions and the increase of the glutamate and glycine productions. Thus, the entire set of results contributed to extract specific mechanistic toxic signatures and their relation to hepatotoxicity, which appeared consistent with literature reports. As new finding of HepG2/C3a cells hepatotoxicity, we propose a metabolic network with a related list of metabolite variations to describe the GSH depletion when followed by a cell death for the HepG2/C3a cells cultivated in our polydimethylsiloxane microfluidic biochips. Our findings illustrate the potential of metabolomics-on-a-chip as an in vitro alternative method for predictive toxicology.

A molecular and phenotypic integrative approach to identify a no-effect dose level for antiandrogen-induced testicular toxicity

The safety assessment of chemicals for humans relies on identifying no-observed adverse effect levels (NOAELs) in animal toxicity studies using standard methods. With the advent of high information content technologies, especially microarrays, it is pertinent to determine the impact of molecular data on the NOAELs. Consequently, we conducted an integrative study to identify a no-transcriptomic effect dose using microarray analyses coupled with quantitative reverse transcriptase PCR (RT-qPCR) and determined how this correlated with the NOAEL. We assessed the testicular effects of the antiandrogen, flutamide (FM), in a rat 28-day toxicity study using doses of 0.2-30 mg/kg/day. Plasma testosterone levels and testicular histopathology indicated a NOAEL of 1 mg/kg/day. A no-effect dose of 0.2 mg/kg/day was established based on molecular data relevant to the phenotypic changes. We observed differential gene expression starting from 1 mg/kg/day and a deregulation of more than 1500 genes at 30 mg/kg/day. Dose-related changes were identified for the major pathways (e.g., fatty acid metabolism) associated with the testicular lesion (Leydig cell hyperplasia) that were confirmed by RT-qPCR. These data, along with protein accumulation profiles and FM metabolite concentrations in testis, supported the no-effect dose of 0.2 mg/kg/day. Furthermore, the microarray data indicated a dose-dependent change in the fatty acid catabolism pathway, a biological process described for the first time to be affected by FM in testicular tissue. In conclusion, the present data indicate the existence of a transcriptomic threshold, which must be exceeded to progress from a normal state to an adaptative state and subsequently to adverse toxicity.

IL-6 promotes prostate tumorigenesis and progression through autocrine cross-activation of IGF-IR

As an established mediator of inflammation, IL-6 is implicated to facilitate prostate cancer progression to androgen independence through transactivation of the androgen receptor. However, whether IL-6 plays a causative role in de novo prostate tumorigenesis was never investigated. We now provide the first evidence that IL-6 can induce tumorigenic conversion and further progression to an invasive phenotype of non-tumorigenic benign prostate epithelial cells. Moreover, we find that paracrine IL-6 stimulates autocrine IL-6 loop and autocrine activation of IGF-IR to confer the tumorigenic property and that activation of STAT3 is critical in these processes. Inhibition of STAT3 activation or IGF-IR signaling suppresses IL-6-mediated malignant conversion and the associated invasive phenotype. Inhibition of STAT3 activation suppresses IL-6-induced upregulation of IGF-IR and its ligands IGF-I and IGF-II. These findings indicate IL-6 signaling cooperates with IGF-IR signaling in the prostate microenvironment to promote prostate tumorigenesis and progression to aggressiveness. Our findings suggest that STAT3 and IGF-IR may represent potential effective targets for prevention or treatment of prostate cancer.

Attenuated progression of diet-induced steatohepatitis in glutathione-deficient mice

In nonalcoholic fatty liver disease (NAFLD), depletion of hepatic antioxidants may contribute to the progression of steatosis to nonalcoholic steatohepatitis (NASH) by increasing oxidative stress that produces lipid peroxidation, inflammation, and fibrosis. We investigated whether depletion of glutathione (GSH) increases NASH-associated hepatic pathology in mice fed a diet deficient in methionine and choline (MCD diet). Wild-type (wt) mice and genetically GSH-deficient mice lacking the modifier subunit of glutamate cysteine ligase (Gclm null mice), the rate-limiting enzyme for de novo synthesis of GSH, were fed the MCD diet, a methionine/choline-sufficient diet, or standard chow for 21 days. We assessed NASH-associated hepatic pathology, including steatosis, fibrosis, inflammation, and hepatocyte ballooning, and used the NAFLD Scoring System to evaluate the extent of changes. We measured triglyceride levels, determined the level of lipid peroxidation products, and measured by qPCR the expression of mRNAs for several proteins associated with lipid metabolism, oxidative stress, and fibrosis. MCD-fed GSH-deficient Gclm null mice were to a large extent protected from MCD diet-induced excessive fat accumulation, hepatocyte injury, inflammation, and fibrosis. Compared with wt animals, MCD-fed Gclm null mice had much lower levels of F₂-isoprostanes, lower expression of acyl-CoA oxidase, carnitine palmitoyltransferase 1a, uncoupling protein-2, stearoyl-coenzyme A desaturase-1, transforming growth factor-β, and plasminogen activator inhibitor-1 mRNAs, and higher activity of catalase, indicative of low oxidative stress, inhibition of triglyceride synthesis, and lower expression of profibrotic proteins. Global gene analysis of hepatic RNA showed that compared with wt mice, the livers of Gclm null mice have a high capacity to metabolize endogenous and exogenous compounds, have lower levels of lipogenic proteins, and increased antioxidant activity. Thus, metabolic adaptations resulting from severe GSH deficiency seem to protect against the development of steatohepatitis.

Mitochondrial gene profiling: translational perspectives

The last decade has witnessed the development of multiple microarray platforms designed to study, in a comprehensive fashion, the expression and sequence of both mitochondrial and nuclear genes that encode mitochondrial proteins. Mitochondrial dysfunction has been implicated in a number of severe medical conditions including cancer, metabolic diseases (i.e., cardiovascular, diabetes and obesity) and neurodegenerative disorders and it is responsible for the adverse effects of numerous drugs. Profiling of the genetic and genomic status of mitochondria with focused microarrays offers the promise of rapidly and robustly identifying novel biomarkers for early disease diagnoses and prognoses, predicting of drug safety, liability, and selecting and stratifying of patients in clinical trials.

Differential regulation of mitogen-activated protein kinase pathways by acetaminophen and its nonhepatotoxic regioisomer 3'-hydroxyacetanilide in TAMH cells

Acetaminophen (APAP), a widely used analgesic and antipyretic that is considered to be relatively safe at recommended doses, is the leading cause of drug-induced liver failure in the United States. 3'-Hydroxyacetanilide (AMAP), a regioisomer of APAP, is useful as a comparative tool for studying APAP-induced toxicity because it is nontoxic relative to APAP. Transforming growth factor-alpha transgenic mouse hepatocytes were treated with both isomers to investigate mitogen-activated protein kinase (MAPK) cascades in order to differentiate their toxicological outcomes. Posttranslational modifications of MAPK signaling were assessed using immunoblotting and Bioplex technology, whereas gene expression changes were measured using Affymetrix Mouse Gene 1.0 ST arrays. APAP treatment led to higher levels of glutathione depletion at 6 and 24 h compared with AMAP in mitochondria. Glutathione depletion was preceded by increased levels of c-Jun N-terminal kinase (JNK) phosphorylation at 2 and 6 h after APAP treatment compared with AMAP, whereas AMAP treatment led to increased extracellular signal-regulated protein kinase (ERK) phosphorylation at 2 and 6 h compared with APAP. Furthermore, APAP treatment significantly upregulated jun oncogene (c-Jun) gene expression, which was confirmed by Western blotting for both the phosphorylated and the nonphosphorylated forms of c-Jun protein. Transfection with JNK siRNA attenuated APAP toxicity after 24 h, suggesting that higher levels of APAP-induced activation of JNK were related to higher rates of cell death. In summary, genomic regulation of MAPK-related transcription factors coupled with posttranslational activation of their upstream kinases is critical in differentiating the toxicities of APAP and AMAP.

Genetical toxicogenomics in Drosophila identifies master-modulatory loci that are regulated by developmental exposure to lead

The genetics of gene expression in recombinant inbred lines (RILs) can be mapped as expression quantitative trait loci (eQTLs). So-called "genetical genomics" studies have identified locally acting eQTLs (cis-eQTLs) for genes that show differences in steady-state RNA levels. These studies have also identified distantly acting master-modulatory trans-eQTLs that regulate tens or hundreds of transcripts (hotspots or transbands). We expand on these studies by performing genetical genomics experiments in two environments in order to identify trans-eQTL that might be regulated by developmental exposure to the neurotoxin lead. Flies from each of 75 RIL were raised from eggs to adults on either control food (made with 250 microM sodium acetate), or lead-treated food (made with 250 microM lead acetate, PbAc). RNA expression analyses of whole adult male flies (5-10 days old) were performed with Affymetrix DrosII whole genome arrays (18,952 probesets). Among the 1389 genes with cis-eQTL, there were 405 genes unique to control flies and 544 genes unique to lead-treated ones (440 genes had the same cis-eQTLs in both samples). There are 2396 genes with trans-eQTL which mapped to 12 major transbands with greater than 95 genes. Permutation analyses of the strain labels but not the expression data suggests that the total number of eQTL and the number of transbands are more important criteria for validation than the size of the transband. Two transbands, one located on the 2nd chromosome and one on the 3rd chromosome, co-regulate 33 lead-induced genes, many of which are involved in neurodevelopmental processes. For these 33 genes, rather than allelic variation at one locus exerting differential effects in two environments, we found that variation at two different loci are required for optimal effects on lead-induced expression.

Comparison of in vitro bioactivation of flutamide and its cyano analogue: evidence for reductive activation by human NADPH:cytochrome P450 reductase

Flutamide (FLU), a nonsteroidal antiandrogen drug widely used in the treatment of prostate cancer, has been associated with idiosyncratic hepatotoxicity in patients. It is proposed that bioactivation of FLU and subsequent binding of reactive metabolite(s) to cellular proteins play a causative role. A toxicogenomic study comparing FLU and its nitro to cyano analogue (CYA) showed that the nitroaromatic group of FLU enhanced cytotoxicity to hepatocytes, indicating that reduction of the nitroaromatic group may represent a potential route of FLU-induced hepatotoxicity [Coe et al. (2007) Chem. Res. Toxicol. 20, 1277-1290]. In the current study, we compared in vitro bioactivation of FLU and CYA in human liver microsomes and cryopreserved human hepatocytes. A nitroreduction metabolite FLU-6 was formed in liver microsomal incubations of FLU under atmospheric oxygen levels and, to a greater extent, under anaerobic conditions. Seven glutathione (GSH) adducts of FLU, FLU-G1-7, were tentatively identified in human liver microsomal incubations using liquid chromatography-tandem mass spectrometry (LC/ MS/MS), while CYA formed only four corresponding GSH adducts, CYA-G1-4, under the same conditions. Of particular interest was the formation of FLU-G5-7 from FLU, where the nitroaromatic group of FLU was reduced to an amino group. A tentative pathway is that upon nitroreduction, the para-diamines undergo cytochrome P450 (P450)-catalyzed two-electron oxidations to form corresponding para-diimine intermediates that react with GSH to form GSH adducts FLU-G5-7, respectively. The identities of FLU-G5-7 were further confirmed by LC/MS/MS analyses of microsomal incubations of a synthesized standard FLU-6. In an attempt to identify enzymes involved in the nitroreduction of FLU, NADPH:cytochrome P450 reductase (CPR) was shown to reduce FLU to FLU-6 under both aerobic and anaerobic conditions. Furthermore, the formation of FLU-G5-7 was completely blocked by the addition of a reversible CPR inhibitor, alpha-lipoic acid, to the incubations of FLU under aerobic conditions. In summary, these results clearly demonstrate that nitroreduction of FLU by CPR contributes to bioactivation and potentially to hepatotoxicity of FLU.

Toxicogenomic biomarkers for liver toxicity

Toxicogenomics (TGx) is a widely used technique in the preclinical stage of drug development to investigate the molecular mechanisms of toxicity. A number of candidate TGx biomarkers have now been identified and are utilized for both assessing and predicting toxicities. Further accumulation of novel TGx biomarkers will lead to more efficient, appropriate and cost effective drug risk assessment, reinforcing the paradigm of the conventional toxicology system with a more profound understanding of the molecular mechanisms of drug-induced toxicity. In this paper, we overview some practical strategies as well as obstacles for identifying and utilizing TGx biomarkers based on microarray analysis. Since clinical hepatotoxicity is one of the major causes of drug development attrition, the liver has been the best documented target organ for TGx studies to date, and we therefore focused on information from liver TGx studies. In this review, we summarize the current resources in the literature in regard to TGx studies of the liver, from which toxicologists could extract potential TGx biomarker gene sets for better hepatotoxicity risk assessment.

Sequential and concerted gene expression changes in a chronic in vitro model of parkinsonism

Many mechanisms of neurodegeneration have been implicated in Parkinson's disease, but which ones are most important and potential interactions among them are unclear. To provide a broader perspective on the parkinsonian neurodegenerative process, we have performed a global analysis of gene expression changes caused by chronic, low-level exposure of neuroblastoma cells to the mitochondrial complex I inhibitor and parkinsonian neurotoxin rotenone. Undifferentiated SK-N-MC human neuroblastoma cells were grown in the presence of rotenone (5 nM), and RNA was extracted at three different time points (baseline, 1 week, and 4 weeks) for labeling and hybridization to Affymetrix Human U133 Plus 2.0 GeneChips. Our results show that rotenone induces concerted alterations in gene expression that change over time. Particularly, alterations in transcripts related to DNA damage, energy metabolism, and protein metabolism are prominent during chronic complex I inhibition. These data suggest that early augmentation of capacity for energy production in response to mitochondrial inhibition might be deleterious to cellular function and survival. These experiments provide the first transcriptional analysis of a rotenone model of Parkinson's disease and insight into which mechanisms of neurodegeneration may be targeted for therapeutic intervention.