Antibiotic class with potent in vivo activity targeting lipopolysaccharide synthesis in Gram-negative bacteria

Here, we describe the identification of an antibiotic class acting via LpxH, a clinically unexploited target in lipopolysaccharide synthesis. The lipopolysaccharide synthesis pathway is essential in most Gram-negative bacteria and there is no analogous pathway in humans. Based on a series of phenotypic screens, we identified a hit targeting this pathway that had activity on efflux-defective strains of Escherichia coli. We recognized common structural elements between this hit and a previously published inhibitor, also with activity against efflux-deficient bacteria. With the help of X-ray structures, this information was used to design inhibitors with activity on efflux-proficient, wild-type strains. Optimization of properties such as solubility, metabolic stability and serum protein binding resulted in compounds having potent in vivo efficacy against bloodstream infections caused by the critical Gram-negative pathogens E. coli and Klebsiella pneumoniae. Other favorable properties of the series include a lack of pre-existing resistance in clinical isolates, and no loss of activity against strains expressing extended-spectrum-β-lactamase, metallo-β-lactamase, or carbapenemase-resistance genes. Further development of this class of antibiotics could make an important contribution to the ongoing struggle against antibiotic resistance.

Transfer of cetirizine/levocetirizine into human breast milk and estimation of drug exposure to infants through breastfeeding: A human lactation study from the ConcePTION project

Data on drug transfer into human breast milk are sparse. This study aimed to quantify concentrations of cetirizine and levocetirizine in breast milk and to estimate drug exposure to infants. Breastfeeding women at least 8 weeks postpartum and using cetirizine or its pure (R)-enantiomer levocetirizine were eligible to participate. Breast milk samples were collected at six predefined times during a dose interval (0, 2, 4, 8, 12 and 24 h after drug intake) at steady state. Infant drug exposure was estimated by calculating the absolute infant dose (AID) and the weight-adjusted relative infant dose (RID). In total, 32 women were eligible for final inclusion, 31 women using cetirizine and one woman using levocetirizine. Means of the individual maximum and average cetirizine milk concentrations were 41.0 and 16.8 μg/L, respectively. Maximum concentrations occurred on average 2.4 h after intake, and the mean half-life in milk was 7.0 h. Estimated AID and RID for cetirizine in a day were 2.5 μg/kg and 1.9%, respectively. The corresponding values for levocetirizine were 1.1 μg/kg and 1.9%. No severe adverse events were reported. Our findings demonstrate that the transfer of cetirizine and levocetirizine into breast milk is low and compatible with breastfeeding.

Simple and rapid quantification of cetirizine, venlafaxine, and O-desmethylvenlafaxine in human breast milk, and metformin in human milk and plasma with UHPLC-MS/MS

The majority of women have health problems that require medication after giving birth. Complications such as allergies, postpartum depression, and diabetes are often treated with drugs such as cetirizine, venlafaxine, and metformin, respectively. These treatments are considered safe during lactation, but information of the transfer of drugs to breast milk and possible effects on the infant is scarce. Therefore, this needs to be systematically investigated in larger populations. To enable the determination of drug transfer, we here describe the validation of two rapid, sensitive, and high-throughput analysis methods for 1) simultaneous quantification of cetirizine, venlafaxine, and O-desmethylvenlafaxine in human breast milk, and 2) metformin in human breast milk and plasma. In both methods, a simple protein precipitation protocol with acetonitrile and benchtop-centrifugation was used prior to compound analysis with liquid-chromatography tandem mass spectrometry. The methods had linear ranges between 0.39 - 194.5 ng/mL for cetirizine, 0.28 - 138.7 ng/mL for venlafaxine, 0.26 - 131.7 ng/mL for O-desmethylvenlafaxine, in milk, and 0.65 - 193.7 ng/mL for metformin in both milk and plasma. Intra-run and inter-run precision and accuracy were ≤ 9% for cetirizine, venlafaxine, and O-desmethylvenlafaxine in milk, and ≤ 7% for metformin in milk and plasma. Cetirizine was measured to median milk concentrations of 13 ng/mL (range: 0.65 - 65 ng/mL) in 228 donor samples from breast-feeding women.

Imitation of β-lactam binding enables broad-spectrum metallo-β-lactamase inhibitors

Carbapenems are vital antibiotics, but their efficacy is increasingly compromised by metallo-β-lactamases (MBLs). Here we report the discovery and optimization of potent broad-spectrum MBL inhibitors. A high-throughput screen for NDM-1 inhibitors identified indole-2-carboxylates (InCs) as potential β-lactamase stable β-lactam mimics. Subsequent structure-activity relationship studies revealed InCs as a new class of potent MBL inhibitor, active against all MBL classes of major clinical relevance. Crystallographic studies revealed a binding mode of the InCs to MBLs that, in some regards, mimics that predicted for intact carbapenems, including with respect to maintenance of the Zn(II)-bound hydroxyl, and in other regards mimics binding observed in MBL-carbapenem product complexes. InCs restore carbapenem activity against multiple drug-resistant Gram-negative bacteria and have a low frequency of resistance. InCs also have a good in vivo safety profile, and when combined with meropenem show a strong in vivo efficacy in peritonitis and thigh mouse infection models.

A Tribute to Professor Per Artursson - Scientist, Explorer, Mentor, Innovator, and Giant in Pharmaceutical Research

This issue of the Journal of Pharmaceutical Sciences is dedicated to Professor Per Artursson and the groundbreaking contributions he has made and continues to make in the Pharmaceutical Sciences. Per is one of the most cited researchers in his field, with more than 30,000 citations and an h-index of 95 as of September 2020. Importantly, these citations are distributed over the numerous fields he has explored, clearly showing the high impact the research has had on the discipline. We provide a short portrait of Per, with emphasis on his personality, driving forces and the inspirational sources that shaped his career as a world-leading scientist in the field. He is a curious scientist who deftly moves between disciplines and has continued to innovate, expand boundaries, and profoundly impact the pharmaceutical sciences throughout his career. He has developed new tools and provided insights that have significantly contributed to today's molecular and mechanistic approaches to research in the fields of intestinal absorption, cellular disposition, and exposure-efficacy relationships of pharmaceutical drugs. We want to celebrate these important contributions in this special issue of the Journal of Pharmaceutical Sciences in Per's honor.

Improved predictions of time-dependent drug-drug interactions by determination of cytosolic drug concentrations

The clinical impact of drug-drug interactions based on time-dependent inhibition of cytochrome P450 (CYP) 3A4 has often been overpredicted, likely due to use of improper inhibitor concentration estimates at the enzyme. Here, we investigated if use of cytosolic unbound inhibitor concentrations could improve predictions of time-dependent drug-drug interactions. First, we assessed the inhibitory effects of ten time-dependent CYP3A inhibitors on midazolam 1′-hydroxylation in human liver microsomes. Then, using a novel method, we determined the cytosolic bioavailability of the inhibitors in human hepatocytes, and used the obtained values to calculate their concentrations at the active site of the enzyme, i.e. the cytosolic unbound concentrations. Finally, we combined the data in mechanistic static predictions, by considering different combinations of inhibitor concentrations in intestine and liver, including hepatic concentrations corrected for cytosolic bioavailability. The results were then compared to clinical data. Compared to no correction, correction for cytosolic bioavailability resulted in higher accuracy and precision, generally in line with those obtained by more demanding modelling. The best predictions were obtained when the inhibition of hepatic CYP3A was based on unbound maximal inhibitor concentrations corrected for cytosolic bioavailability. Our findings suggest that cytosolic unbound inhibitor concentrations improves predictions of time-dependent drug-drug interactions for CYP3A.

Small-molecule inhibitor of OGG1 suppresses proinflammatory gene expression and inflammation

The onset of inflammation is associated with reactive oxygen species and oxidative damage to macromolecules like 7,8-dihydro-8-oxoguanine (8-oxoG) in DNA. Because 8-oxoguanine DNA glycosylase 1 (OGG1) binds 8-oxoG and because Ogg1-deficient mice are resistant to acute and systemic inflammation, we hypothesized that OGG1 inhibition may represent a strategy for the prevention and treatment of inflammation. We developed TH5487, a selective active-site inhibitor of OGG1, which hampers OGG1 binding to and repair of 8-oxoG and which is well tolerated by mice. TH5487 prevents tumor necrosis factor-α-induced OGG1-DNA interactions at guanine-rich promoters of proinflammatory genes. This, in turn, decreases DNA occupancy of nuclear factor κB and proinflammatory gene expression, resulting in decreased immune cell recruitment to mouse lungs. Thus, we present a proof of concept that targeting oxidative DNA repair can alleviate inflammatory conditions in vivo.

Identification of Triazolothiadiazoles as Potent Inhibitors of the dCTP Pyrophosphatase 1

The dCTP pyrophosphatase 1 (dCTPase) is involved in the regulation of the cellular dNTP pool and has been linked to cancer progression. Here we report on the discovery of a series of 3,6-disubstituted triazolothiadiazoles as potent dCTPase inhibitors. Compounds 16 and 18 display good correlation between enzymatic inhibition and target engagement, together with efficacy in a cellular synergy model, deeming them as a promising starting point for hit-to-lead development.

Structure–metabolism-relationships in the microsomal clearance of piperazin-1-ylpyridazines

In this study, we provide insight into the metabolic profile of a series of piperazin-1-ylpyridazines suffering from rapid in vitro intrinsic clearance in a metabolic stability assay using liver microsomes.

Optimizing DMPK Properties: Experiences from a Big Pharma DMPK Department

BACKGROUND

The disposition of a drug is dependent on interactions between the body and the drug, its molecular properties and the physical and biological barriers presented in the body. In order for a drug to have a desired pharmacological effect it has to have the right properties to be able to reach the target site in sufficient concentration. This review details how drug metabolism and pharmacokinetics (DMPK) and physicochemical deliveries played an important role in data interpretation and compound optimization at AstraZeneca R&D in Södertälje, Sweden.

METHODS

A selection of assays central in the evaluation of the DMPK properties of new chemical entities is presented, with guidance and consideration on assay outcome interpretation. Early in projects, solubility, LogD, permeability and metabolic stability were measured to support effective optimization of DMPK properties. Changes made to facilitate high throughput, efficient bioanalysis and the handling of large amounts of samples are described. Already early in drug discovery, we used an integrated approach for the prediction of the fate of drugs in human (early dose to man) based on data obtained from in vitro experiments. The early dose to man was refined with project progression, which triggered more intricate assays and experiments. At later stages, preclinical in vivo pharmacokinetic (PK) data was integrated with pharmacodynamics (PD) to allow predictions of required dose, dose intervals and exposure profile to achieve the desired effect in man.

RESULTS AND CONCLUSIONS

A well-defined work flow of DMPK activities from early lead identification up to the selection of a candidate drug was developed. This resulted in a cost effective and efficient optimization of chemical series, and facilitated informed decision making throughout project progress.

Validation and development of MTH1 inhibitors for treatment of cancer

BACKGROUND

Previously, we showed cancer cells rely on the MTH1 protein to prevent incorporation of otherwise deadly oxidised nucleotides into DNA and we developed MTH1 inhibitors which selectively kill cancer cells. Recently, several new and potent inhibitors of MTH1 were demonstrated to be non-toxic to cancer cells, challenging the utility of MTH1 inhibition as a target for cancer treatment.

MATERIAL AND METHODS

Human cancer cell lines were exposed in vitro to MTH1 inhibitors or depleted of MTH1 by siRNA or shRNA. 8-oxodG was measured by immunostaining and modified comet assay. Thermal Proteome profiling, proteomics, cellular thermal shift assays, kinase and CEREP panel were used for target engagement, mode of action and selectivity investigations of MTH1 inhibitors. Effect of MTH1 inhibition on tumour growth was explored in BRAF V600E-mutated malignant melanoma patient derived xenograft and human colon cancer SW480 and HCT116 xenograft models.

RESULTS

Here, we demonstrate that recently described MTH1 inhibitors, which fail to kill cancer cells, also fail to introduce the toxic oxidized nucleotides into DNA. We also describe a new MTH1 inhibitor TH1579, (Karonudib), an analogue of TH588, which is a potent, selective MTH1 inhibitor with good oral availability and demonstrates excellent pharmacokinetic and anti-cancer properties in vivo.

CONCLUSION

We demonstrate that in order to kill cancer cells MTH1 inhibitors must also introduce oxidized nucleotides into DNA. Furthermore, we describe TH1579 as a best-in-class MTH1 inhibitor, which we expect to be useful in order to further validate the MTH1 inhibitor concept.

Discovery of the First Potent and Selective Inhibitors of Human dCTP Pyrophosphatase 1

The dCTPase pyrophosphatase 1 (dCTPase) regulates the intracellular nucleotide pool through hydrolytic degradation of canonical and noncanonical nucleotide triphosphates (dNTPs). dCTPase is highly expressed in multiple carcinomas and is associated with cancer cell stemness. Here we report on the development of the first potent and selective dCTPase inhibitors that enhance the cytotoxic effect of cytidine analogues in leukemia cells. Boronate 30 displays a promising in vitro ADME profile, including plasma and mouse microsomal half-lives, aqueous solubility, cell permeability and CYP inhibition, deeming it a suitable compound for in vivo studies.

MTH1 inhibition eradicates cancer by preventing sanitation of the dNTP pool

Cancers have dysfunctional redox regulation resulting in reactive oxygen species production, damaging both DNA and free dNTPs. The MTH1 protein sanitizes oxidized dNTP pools to prevent incorporation of damaged bases during DNA replication. Although MTH1 is non-essential in normal cells, we show that cancer cells require MTH1 activity to avoid incorporation of oxidized dNTPs, resulting in DNA damage and cell death. We validate MTH1 as an anticancer target in vivo and describe small molecules TH287 and TH588 as first-in-class nudix hydrolase family inhibitors that potently and selectively engage and inhibit the MTH1 protein in cells. Protein co-crystal structures demonstrate that the inhibitors bind in the active site of MTH1. The inhibitors cause incorporation of oxidized dNTPs in cancer cells, leading to DNA damage, cytotoxicity and therapeutic responses in patient-derived mouse xenografts. This study exemplifies the non-oncogene addiction concept for anticancer treatment and validates MTH1 as being cancer phenotypic lethal.

Assessment of interaction potential of AZD2066 using in vitro metabolism tools, physiologically based pharmacokinetic modelling and in vivo cocktail data

PURPOSE

Static and dynamic (PBPK) prediction models were applied to estimate the drug-drug interaction (DDI) risk of AZD2066. The predictions were compared to the results of an in vivo cocktail study. Various in vivo measures for tolbutamide as a probe agent for cytochrome P450 2C9 (CYP2C9) were also compared.

METHODS

In vitro inhibition data for AZD2066 were obtained using human liver microsomes and CYP-specific probe substrates. DDI prediction was performed using PBPK modelling with the SimCYP simulator™ or static model. The cocktail study was an open label, baseline, controlled interaction study with 15 healthy volunteers receiving multiple doses of AD2066 for 12 days. A cocktail of single doses of 100 mg caffeine (CYP1A2 probe), 500 mg tolbutamide (CYP2C9 probe), 20 mg omeprazole (CYP2C19 probe) and 7.5 mg midazolam (CYP3A probe) was simultaneously applied at baseline and during the administration of AZD2066. Bupropion as a CYP2B6 probe (150 mg) and 100 mg metoprolol (CYP2D6 probe) were administered on separate days. The pharmacokinetic parameters for the probe drugs and their metabolites in plasma and urinary recovery were determined.

RESULTS

In vitro AZD2066 inhibited CYP1A2, CYP2B6, CYP2C9, CYP2C19 and CYP2D6. The static model predicted in vivo interaction with predicted AUC ratio values of >1.1 for all CYP (except CYP3A4). The PBPK simulations predicted no risk for clinical relevant interactions. The cocktail study showed no interaction for the CYP2B6 and CYP2C19 enzymes, a possible weak inhibition of CYP1A2, CYP2C9 and CYP3A4 activities and a slight inhibition (29 %) of CYP2D6 activity. The tolbutamide phenotyping metrics indicated that there were significant correlations between CLform and AUCTOL, CL, Aemet and LnTOL24h. The MRAe in urine showed no correlation to CLform.

CONCLUSIONS

DDI prediction using the static approach based on total concentration indicated that AZD20066 has a potential risk for inhibition. However, no DDI risk could be predicted when a more in vivo-like dynamic prediction method with the PBPK with SimCYP™ software based on early human PK data was used and more parameters (i.e. free fraction in plasma, no DDI risk) were taken into account. The clinical cocktail study showed no or low risks for clinical relevant DDI interactions. Our findings are in line with the hypothesis that the dynamic prediction method predicts DDI in vivo in humans better than the static model based on total plasma concentrations.

Metabolism of 2-substituted quinolines with antileishmanial activity studied in vitro with liver microsomes, hepatocytes and recombinantly expressed enzymes analyzed by LC/MS

Liver microsome and hepatocyte-mediated biotransformation of three oral antileishmanial 2-substituted quinolines were investigated. One quinoline contains an n-propyl group (1) and the other a propenyl chain functionalized at the gamma position either by a nitrile (2) or an alcohol (3). The different isoforms of rat cytochrome P450 responsible for biotransformation of 1 were also investigated. Compounds 2 and 3 mainly reacted with glutathione, preventing further metabolism. Compound 3 however, the reaction being reversible, could be released from glutathione and take alternative reaction pathways. Microsomal incubations of 1 mainly led to hydroxylation of the side chain, involving many cytochromes, predominantly CYP2B1, CYP2A6 and CYP1A1 (at more than 80%). In contrary, minor metabolites hydroxylated on the quinoline ring involved a few cytochromes. The hydroxylated products of 1 were conjugated with glucuronic acid in rat hepatocyte incubations.

Characterization of the cytochrome P450 enzymes and enzyme kinetic parameters for metabolism of BVT.2938 using different in vitro systems

An important step in the drug development process is identification of enzymes responsible for metabolism of drug candidates and determination of enzyme kinetic parameters. These data are used to increase understanding of the pharmacokinetics and possible metabolic-based drug interactions of drug candidates. The aim of the present study was to characterize the cytochrome P450 enzymes and enzyme kinetic parameters for metabolism of BVT.2938 [1-(3-{2-[(2-ethoxy-3-pyridinyl)oxy]ethoxy}-2-pyrazinyl)-2(R)-methylpiperazine], a potent and selective 5HT2c-receptor agonist. The enzyme kinetic parameters were determined for formation of three main metabolites of BVT.2938 using human liver microsomes and expressed cytochrome P450 (CYP) isoforms. The major metabolite was formed by hydroxylation of the pyridine ring (CL(int)=27 microl/mgmin), and was catalysed by both CYP2D6*1 and CYP1A1, with K(m) values corresponding to 1.4 and 2.7 microM, respectively. The results from enzyme kinetic studies were confirmed by incubation of BVT.2938 in the presence of the chemical inhibitor of CYP2D6*1, quinidine. Quinidine inhibited the formation of the major metabolite by approximately 90%. Additionally, studies with recombinant expressed CYP isoforms from rat indicated that formation of the major metabolite of BVT.2938 was catalysed by CYP2D2. This result was further confirmed by experiments with liver slices from different rat strains, where the formation of the metabolite correlated with phenotype of CYP2D2 isoform (Sprague-Dawley male, extensive; Dark Agouti male, intermediate; Dark Agouti female, poor metabolizer). The present study showed that the major metabolite of BVT.2938 is formed by hydroxylation of the pyridine ring and catalysed by CYP2D6*1. CYP1A1 is also involved in this reaction and its role in extra-hepatic metabolism of BVT.2938 might be significant.

DNA adduct formation of 14 heterocyclic aromatic amines in mouse tissue after oral administration and characterization of the DNA adduct formed by 2-amino-9H-pyrido[2,3-b]indole (AalphaC), analysed by 32P_HPLC

Heterocyclic aromatic amines (HAAs) are produced during cooking of proteinaceous food such as meat and fish. Humans eating a normal diet are regularly exposed to these food-borne substances. HAAs have proved to be carcinogenic in animals and to induce early lesions in the development of cancer. DNA adduct levels in mouse liver have been measured by 32P-HPLC after oral administration each of 14 different HAAs. The highest DNA adduct levels were detected for 3-amino-1-methyl-5H-pyrido[4,3-b]-indole (Trp-P-2), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and 2-amino-9H-pyrido[2,3-b]indole (AalphaC), respectively. To assess a relative risk in a human population, a relative risk index was calculated by combining the DNA adduct levels in mouse liver with human daily intake of heterocyclic amines in a US and in a Swedish population. Such calculations suggest that AalphaC presents the highest risk for humans, e.g. nine-fold higher compared with the most abundant amines in food, 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP). Therefore, the distribution of DNA adducts in different tissues of mouse was investigated after oral administration of AalphaC. The highest AalphaC-DNA adduct levels were found in liver (137 adducts/10(8) normal nucleotides) followed by heart, kidney, lung, large intestine, small intestine, stomach and spleen, in descending order. To characterize the chemical structure of the major DNA adduct, chemical synthesis was performed. The major DNA adduct from the in vivo experiments was characterized by five different methods. On the basis of these results, the adduct was characterized as N2-(deoxyguanin-8-yl)-2-amino-9H-pyrido [2,3-b]indole. Considering the abundance of AalphaC not only in grilled meat, but also in other products like grilled chicken, vegetables and cigarette smoke and in light of the results of the present study, it is suggested that the human cancer risk for AalphaC might be underestimated.

Development of an Assay Using 4-Trifluoromethylumbelliferyl as a Marker Substrate for Assessment of Drug–Drug Interactions to Multiple Isoforms of UDP-Glucuronosyltransferases

Glucuronidation is catalyzed by UDP-glucuronosyltransferases (UGTs) and is one of the most important pathways for elimination of xenobiotics. The aim of the present study was to develop an in vitro assay for assessment of drug-drug interactions related to UGTs applicable to early drug discovery. 4-Trifluoromethylumbelliferyl was tested as a marker substrate for six human recombinant expressed UGT isoforms: 1A1, 1A3, 1A4, 1A6, 1A9, and 2B7. It was shown that 4-trifluoromethylumbelliferyl was glucuronidated by all UGTs tested, except UGT1A4. By using a short HPLC gradient (7 min) and fluorescence detection, the enzyme kinetic parameters for these reactions were obtained. All reactions were found to follow classical Michaelis-Menten kinetics, with K(m) values between 29 microM (UGT1A9) and 80 microM (UGT1A3). The method was validated by using several known competitive inhibitors of UGTs. The most potent inhibition was observed for the reaction between 17alpha-ethynylestradiol and UGT1A1 (K(i) = 10.5 microM), and the weakest interaction was detected for acetaminophen and UGT1A9 (IC(50) > 1 mM). Taken together, we report the development of an assay using 4-trifluoromethylumbelliferyl as a marker substrate for five different human UGT isoforms suitable for the assessment of drug-drug interactions related to UGTs during early drug discovery.

Relationship between content and activity of cytochrome P450 and induction of heterocyclic amine DNA adducts in human liver samples in vivo and in vitro

This study was designed to estimate a correlation between metabolic activation phenotypes and formation of DNA adducts by heterocyclic amines (HCA) in 15 liver samples from healthy donors. The correlation between the amount of endogenous DNA adducts and the content of cytochrome P450 in human liver samples in vivo was statistically significant at r(2) = 0.71 and P < 0.005. Furthermore, the isolated human liver microsomes were treated in vitro with two HCAs, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 2-amino-9H-pyrido[2,3-b]indole (A alpha C), which have been recognized to induce two DNA adducts: 3',5'-diphosphate-N-(2'-deoxyguanosin-8-yl)-PhIP (3',5'-pdGp-C8-PhIP) and 3',5'-diphosphate-N-(2'-deoxyguanosin-8-yl)-A alpha C (3',5'-pdGp-C8-A alpha C). The correlations between the amount of DNA adducts induced by both compounds in vitro and the content of cytochrome P450 in human microsomes are statistically significant at r(2) = 0.69 and r(2) = 0.62 (P < 0.001), respectively. Furthermore, the level of DNA adducts after treatment with PhIP and A alpha C correlated with the activities of three isozymes of cytochrome P450: CYP1A1, CYP1A2, and CYP3A4. Therefore, three chemical inhibitors were used in the experiments: ellipticine against CYP1A1, furafylline against CYP1A2, and troleandomycin against CYP3A4. The highest inhibition levels in the formation of 3',5'-pdGp-C8-PhIP and 3',5'-pdGp-C8-A alpha C adducts were estimated to occur in the presence of furafylline at 56% and 69%, respectively. Ellipticine was involved in the inhibition of 40% of 3',5'-pdG-C8-PhIP adducts and in only 18% of the inhibition of 3',5'-pdGp-C8-A alpha C adducts. Troleandomycin did not significantly inhibit the formation of 3',5'-pdGp-C8-PhIP adducts under these conditions, but it inhibited the formation of 31% of the 3',5'-pdGpC8-A alpha C adducts. We conclude that the formation of DNA adducts can be used as a relevant marker of interindividual variability in the metabolic activation of HCAs in humans.

Identification of BVT.2938 metabolites by LC/MS and LC/MS/MS after in vitro incubations with liver microsomes and hepatocytes

The metabolism of the 5HT2c agonist BVT.2938, 1-(3-[2-[(2-ethoxy-3-pyridinyl)oxy]ethoxy]-2-pyrazinyl)-2(R)-methylpiperazine, was studied in vitro by incubation with rat, monkey and human liver microsomes as well as cryopreserved hepatocytes, followed by liquid chromatography/mass spectrometry (LC/MS) and LC/MS/MS analysis on a quadrupole-time of flight mass spectrometer for structural elucidation. Deuterium exchange on column was used to differentiate between hydroxylation and N-oxidation. Liver microsomes were incubated in two different buffer systems with optimum conditions for cytochrome P450 activity or UDP-glucuronosyltransferase activity. The major phase I metabolites of BVT.2938 originated from O-deethylation of the pyridine ring, O-dealkylation of the ethylene bridge, pyrazine ring hydroxylation, hydroxylation of pyridine ring and piperazine ring N-hydroxylation. When a hydrogen carbonate buffer system was supplemented with UDPGA, the piperazine carbamoyl-glucuronide from the parent compound was identified together with several glucuronides of the phase I metabolites. The metabolite pattern in hepatocytes was similar to microsomes except that the sulphate at the N-position of the piperazine ring of BVT.2938 was identified, while the carbamoyl-glucuronide was missing. Excellent correlation was obtained between radioactivity detection and the chemiluminescent nitrogen detector when the nitrogen content of the analytes was taken into account.

Oxidation of protein tyrosine phosphatases as a pharmaceutical mechanism of action: a study using 4-hydroxy-3,3-dimethyl-2H-benzo[g]indole-2,5(3H)-dione

Growth factor and insulin signal transduction comprise series of protein kinases and protein phosphatases whose combined activities serve to propagate the growth factor signal in a regulated fashion. It was shown previously that such signaling cascades generate hydrogen peroxide inside cells. Recent work has implied that one function of this might be to enhance the feed-forward signal through the reversible oxidation and inhibition of protein tyrosine phosphatases (PTPs). We identified compound 4-hydroxy-3,3-dimethyl-2H-benzo[g]indole-2,5(3H)-dione (BVT.948) as an agent that is able to inhibit PTP activity in vitro noncompetitively, a mechanism involving oxidation of the catalytic cysteine residue. We investigated the pharmaceutical utility of this compound by examining its effects in a series of in vitro cellular and in vivo assays. Results showed that BVT.948 was able to enhance insulin signaling in cells, although it did not increase tyrosine phosphorylation globally. Furthermore, the compound was active in vivo, enhancing insulin tolerance tests in ob/ob mice, therefore apparently enhancing insulin sensitivity. BVT.948 was able to inhibit several other PTPs tested and also was efficient at inhibiting several cytochrome P450 (P450) isoforms in vitro. The data suggest that inhibitors of PTPs that display noncompetitive kinetics must be viewed with caution because they may oxidize the enzyme irreversibly. Furthermore, although such compounds display interesting biological effects in vitro and in vivo, their general pharmaceutical utility may be limited due to undesired effects on P450 enzymes.

Susceptibility factors and DNA adducts in peripheral blood mononuclear cells of aluminium smelter workers exposed to polycyclic aromatic hydrocarbons

Formation of DNA adducts as a result of exposure to polycyclic aromatic hydrocarbons (PAH) was studied in 98 potroom workers from an aluminium smelting plant and in 55 blue-collar workers without occupational PAH exposure. DNA from peripheral blood mononuclear cells (PBMC) was used for quantitation of individual PAH-DNA adducts by 32P-postlabelling/high performance liquid chromatography (HPLC) analysis. Four individual DNA adducts (denoted A, B, C and D) were quantified in 141 of a total of 153 subjects. Genetic polymorphisms for cytochrome P-4501A1 ( CYP1A1), microsomal epoxide hydrolase, N-acetyltransferase 2, glutathione transferases M1, P1 and T1 ( GSTM1, GSTP1 and GSTT1, respectively) and NAD(P)H: quinone oxidoreductase 1 (NQO1) were analysed. For 52 subjects, analysis of mRNA inducibility of CYP1A1 was performed. No statistically significant differences in the levels of total or individual DNA adducts A, C and D were found between potroom workers and control subjects. All potroom workers and the subgroup of potroom workers who reported to never/sometimes use personal respiratory protection ( n=72) were found to have a significantly higher likelihood of having high levels of adduct B than control subjects [odds ratio (OR) =3.4 with 95% confidence interval (CI) of 1.3-9.2, and OR=4.2 with 95% CI 1.6-11.5, respectively]. In the subgroup, levels of adducts A and B were found to be significantly higher among workers with employment time of less than 6 months ( n=5). Also, the levels of the individual DNA adducts were to some extent modified by genetic polymorphisms in CYP1A1, GSTM1, GSTP1 and NQO1 and by CYP1A1 inducibility. In conclusion, levels of adduct B, identified by 32P-postlabelling/HPLC methodology as an indicator of PAH exposure in aluminium production, were modified by the use of respiratory protection, length of employment and genetic polymorphisms.

Formation of DNA adducts from oil-derived products analyzed by 32P-HPLC

The aim of this study was to investigate the genotoxic potential of DNA adducts and to compare DNA adduct levels and patterns in petroleum vacuum distillates, coal tar distillate, bitumen fume condensates, and related substances that have a wide range of boiling temperatures. An in vitro assay was used for DNA adduct analysis with human and rat S-9 liver extract metabolic activation followed by 32P-postlabeling and 32P-high-performance liquid chromatography (32p-HPLC). For petroleum distillates originating from one crude oil there was a correlation between in vitro DNA adduct formation and mutagenic index, which showed an increase with a distillation temperature of 250 degrees C and a peak around a distillation point of approximately 400 degrees C. At higher temperatures, the genotoxicity (DNA adducts and mutagenicity) rapidly declined to very low levels. Different petroleum products showed a more than 100-fold range in DNA adduct formation, with severely hydrotreated base oil and bitumen fume condensates being lowest. Coal tar distillates showed ten times higher levels of DNA adduct formation than the most potent petroleum distillate. A clustered DNA adduct pattern was seen over a wide distillation range after metabolic activation with liver extracts of rat or human origin. These clusters were eluted in a region where alkylated aromatic hydrocarbons could be expected. The DNA adduct patterns were similar for base oil and bitumen fume condensates, whereas coal tar distillates had a wider retention time range of the DNA adducts formed. Reference substances were tested in the same in vitro assay. Two- and three-ringed nonalkylated aromatics were rather low in genotoxicity, but some of the three- to four-ringed alkylated aromatics were very potent inducers of DNA adducts. Compounds with an amino functional group showed a 270-fold higher level of DNA adduct formation than the same structures with a nitro functional group. The most potent DNA adduct inducers of the 16 substances tested were, in increasing order, 9,10-dimethylanthracene, 7,12-dimethylbenz[a]anthracene and 9-vinylanthracene. Metabolic activation with human and rat liver extracts gave rise to the same DNA adduct clusters. When bioactivation with material from different human individuals was used, there was a significant correlation between the CYP 1A1 activity and the capacity to form DNA adducts. This pattern was also confirmed using the CYP 1A1 inhibitor ellipticine. The 32P-HPLC method was shown to be sensitive and reproducible, and it had the capacity to separate DNA adduct-forming substances when applied to a great variety of petroleum products.

Effects of human intestinal flora on mutagenicity of and DNA adduct formation from food and environmental mutagens

Although the intestinal flora is believed to have a critical role in carcinogenesis, little is known about the role of the human intestinal flora on the effects of mutagens in vivo. The aim of the present study was to address a possible role of the human intestinal flora in carcinogenesis, by exploiting human-flora-associated (HFA) mice. The capacity of human faeces to activate or inactivate 2-amino-3-methyl-3H:-imidazo[4,5-f]quinoline (IQ) and 2-nitrofluorene was determined using the Ames assay. Human faecal suspensions that were active in this regard were then selected and orally inoculated into germfree NMRI mice to generate HFA mice. HFA, germfree, conventionalized and conventional mice were administered IQ, 2-amino-9H:-pyrido[2,3-b]indole (2-amino-alpha-carboline; AAC) and 2-nitrofluorene. The activity of human intestinal flora against mutagens could be transferred into the mice. In comparing germfree mice and mice harbouring an intestinal flora, the presence of a flora was essential for the activities of faeces against mutagens. After administration of IQ and 2-nitrofluorene, DNA adducts were observed in the mice with a flora, while adducts were extremely low or absent in germfree animals. DNA adducts after AAC treatment were higher in germfree mice in some tissues including colon than in mice with bacteria. Differences in DNA adduct formation were also observed between HFA mice and mice with mouse flora in many tissues. These results clearly indicate that the intestinal flora have an active role in DNA adduct formation and that the role is different for the different chemicals to which the animals are exposed. The results also demonstrate that the human intestinal flora have different effects from the mouse flora on DNA adduct formation as well as in vitro metabolic activities against mutagens. Studies using HFA mice could thus provide much-needed information on the role of the human intestinal flora on carcinogenesis in vivo.

Analysis of aromatic DNA adducts in laryngeal biopsies

Epidemiological studies have confirmed the correlation between tobacco smoking, environmental pollution and the incidence of cancers of the respiratory tract. The occurrence of laryngeal cancer in Poland is relatively high compared to other European countries. Since 1969 the mortality related to larynx cancer appears to be increasing. Tobacco smoke contains an abundance of such carcinogenic compounds as polycyclic aromatic hydrocarbons (PAH), aromatic amines and N-nitrosoamines, which can react with DNA and form adducts. We analyzed aromatic DNA adducts in laryngeal tissues from patients with primary laryngeal, which was confirmed histopathologically to be squamous cell carcinoma. The group consisted of 33 patients (5 women and 28 men). Total laryngectomy was performed in patients. A detergentphenol method was used for DNA isolation. Aromatic DNA adducts were analyzed by a 32P-postlabelling technique with butanol extraction and high performance liquid chromatography. The presence of aromatic DNA adducts was demonstrated in all tissues. Large interindividual differences of DNA adduct levels were seen in each tissue studied. There was a higher mean level of DNA adducts in interarytenoid area non-tumors (51.96/10(8) +/- 91.71 NN) than in non-tumor tissue elsewhere (46.91/10(8) +/- 46.36 NN) and tumor tissue (43.52/10(8) +/- 45.88 NN). Adduct levels were correlated with age, sex, cigarette smoking and TNM stage.

The acetylation patterns of histones H3 and H4 along Vicia faba chromosomes are different

The acetylation pattern of H3 was studied on field bean chromosomes by means of indirect immunofluorescence using polyclonal antibodies recognizing H3 isoforms acetylated at lysine positions 9/18, 14 and 23. H3 was found to be hypoacetylated at lysine residues 9/18 and 14 within the heterochromatic regions composed of tandem repetitive Fok-I elements. Hyperacetylation of these residues was observed at the nucleolar organizing region (NOR) and in heterochromatic regions composed of repeats other than Fok-I elements. In contrast, H4 was underacetylated (H4.Ac5, 8, 12) or uniformly acetylated (H4.Ac16) at all heterochromatic regions, and acetylated above the average at all four lysines only within the NOR. Acetylation of lysine-23 of H3 was uniform, except for the NOR that showed no fluorescence. Inhibition of deacetylase during and after replication of heterochromatin by trichostatin A had no influence on the acetylation status of H3 but mediated an increase in acetylation of lysines 5, 12 and 16 of H4 above the average in the field bean heterochromatin. Thus, the chromosomal acetylation patterns of H4 and H3 of this species revealed common and divergent features. Whereas the acetylation level of H4 correlates well with the potential transcriptional activity and inversely with the time of replication of defined chromatin domains of Vicia faba, this is not generally true for H3.

Histone H4 acetylation in plant heterochromatin is altered during the cell cycle

Using polyclonal antibodies directed against acetylated isoforms of histone H4 (H4 acetylated at lysine positions 5, 8, 12, 16 and H4 tetraacetylated), indirect immunofluorescence revealed hyperacetylation for all H4 variants at the nucleolus organizer region (NOR) of metaphase chromosomes of the field bean Vicia faba. The transcriptionally inactive and late-replicating heterochromatin regions proved to be hypoacetylated at lysine positions 5, 8 and 12. The remaining chromatin showed average fluorescence. These patterns were altered when deacetylase was blocked by exposure of root tip meristems to trichostatin A for more than 2 h prior to fixation. Under these conditions, all lysine positions, except lysine 8, appeared to be hyperacetylated at the NOR and in addition at the prominent heterochromatin domains. This observation represents a hitherto unique switch of histone acetylation pattern during the cell cycle. This is apparently caused by deposition of acetylated H4. Ac5, 12 and 16 or by acetylation directly after replication, which later on becomes reduced (H4.Ac16) or even reversed (H4.Ac5 and 12) by deacetylase before cells enter mitosis.

Formation and repair of O6-methylguanine in recombination hot spots of plant chromosomes

Mutagen-induced chromatid aberrations are not randomly distributed along the metaphase chromosomes. In the field bean (Vicia faba), defined late-replicating and transcriptionally inactive heterochromatic regions are preferentially involved. After exposure to the alkylating agent N-methyl-N-nitrosourea (MNU) (10(-3) M, 1 hour), 70% of all aberrations are clustered within 6 segments containing tandemly repeated FokI elements of 59 bp, which comprise approximately 10% of the genome. Using immuno-slot-blot analyses, we have studied the frequency of O6-methylguanine (O6-MeG), a mutagenic lesion important for aberration induction, in total genomic DNA as well as in FokI sequences of the field bean after exposure to MNU. In either case, similar numbers of adducts per nucleotide were found immediately after treatment as well as after 18 hours of recovery, when most adducts were removed and significant amounts of chromatid aberrations were detectable. Peculiarities of long FokI element arrays (e.g., formation of specific tertiary structures), resulting in error-prone recombination repair, rather than preferential formation or delayed repair of O6-MeG are apparently responsible for aberration clustering in these hot spot regions.

Removal of O6-methylguanine from plant DNA in vivo is accelerated under conditions of clastogenic adaptation

Previously it was shown that the clastogenic efficiency of high doses of alkylating agents in plant root meristems can be reduced significantly by conditioning pretreatment with either a low dose of the same agents, a sublethal heat shock, or heavy metal salts. The molecular mechanisms responsible for these protective effects are still unclear. Here we report on the quantification of O6-methylguanine [O6-MeG] by immuno-slot-blot analysis in DNA of root tip meristems of field bean (Vicia faba) seedlings under conditions of clastogenic adaptation. When root tips were pretreated with a low, conditioning dose of N-methyl-N-nitrosourea (MNU, 10(-4) M, 1 hour) 2 hours before exposure to a high dose of the same clastogen (10(-3) M, 1 hour), the frequency of chromatid aberrations was reduced by more than 50% at a recovery time of 1 B hours, as compared to treatment with the high dose alone. The same was observed when conditioning pretreatment was by a sublethal heat shock [10 minutes, 40 degrees C] or a heavy metal salt (Cd(NO)3, 10(-7) M, 1 hour). The frequency of O6-MeG immediately after exposure to a conditioning and a subsequent challenge treatment was reduced by 43% as compared to treatment with only the high dose. At a recovery time of 18 hours the corresponding frequency of adducts was reduced by 68.3% (related to the initial level) after treatment with the high dose alone, and by 81.3% under adaptive conditions. Sublethal heat shock or heavy metal salt used as conditioning pretreatments also resulted in a decrease of adducts immediately after treatment with the challenge dose. From these data and from prevention of the effects by pretreatment with cycloheximide or O6-benzylguanine we conclude that under conditions of clastogenic adaptation O6-MeG is more efficiently removed from the DNA, presumably by induction of an alkyl acceptor protein such as O6-methylguanine-DNA methyltransferase [MGMT]. This could explain the observed protective effects (clastogenic adaptation.