The potential role of embryonic cells in the IN VITRO bioactivation of teratogens was investigated, with limb bud mesenchyme cells, (LB), and mid brain cells,(CNS), derived from 13 day old rat embryos. The cells were cultured for 5 days and during this period differentiated into foci of chondrocytes (LB) or neurones (CNS). The development of the cells in culture mirrored the IN VIVO development and therefore can be used as a teratogen screen. The presence of constitutive forms of cytochrome P450 isoenzyme forms b, c and d (Levin et. al. 1978 nomenclature) were detected in both cell types after the 5 day culture period by immunocytochemistry. Isoenzyme cytochrome P450 b was found to be non-inducible, whereas isoenzymes c and d were found to be inducible by both transplacental administration of 3-methylcholanthrene (3MC) and B-naphthoflavone (BNF) and by IN VITRO coincubation with 3MC and BNF. There was a difference in the developmental profile of the appearance of isoenzyme forms b and c over the 5 day culture period. Having established the presence of embryonic cytochrome P450's in the culture system the role of metabolism in the bioactivation of diphenylhydantoin (DPH) was investigated. Five approaches were used: 1. Modulation of cytochrome P450 activity IN VITRO by coincubation with a variety of inhibitors caused an increase in DPH toxicity to the extent of 13-82% in LB and 3-52% in CNS cells. 2. Modulation of cytochrome P450 activity IN VITRO by coincubation with inducers, only LB cells coincubated with 3MC caused a 21% increase in DPH toxicity. 3. Modulation of cytochrome P450 activity IN VITRO by transplacentally administered inducers; only LB cells derived from 3MC or BNF pretreated dams increased DPH toxicity, by 20 and 30% respectively. In addition, only LB cells from BNF pretreated dams had the ability to activate the pro-teratogen cyclophosphamide (CPA), (CPA is only toxic to LB cells in the presence of an external metabolising source). 4. Modulation of the formation of the potentially reactive arene oxide intermediate of DPH showed that although the degree of covalent binding could be modulated this did not correlate with the modulation in toxicity and it was therefore concluded that the arene oxide intermediate did not play an important role in DPH teratogenesis. 5. Identification by HPLC analysis of DPH metabolites formed by the cells IN VITRO. Cells (especially LB) were capable of hydroxylation and hydantoin ring cleavage.

Yes / The duocarmycins belong to a class of agent which has great potential for use in cancer therapy. Their exquisite potency means they are too toxic for systemic use, and targeted approaches are required to unlock their clinical potential. In this study, we have explored seco-OH-chloromethylindoline (CI) duocarmycin-based bioprecursors for their potential for cytochrome P450 (CYP)-mediated cancer cell kill. We report on synthetic and biological explorations of racemic seco-CI-MI, where MI is a 5-methoxy indole motif, and dehydroxylated analogues. We show up to a 10-fold bioactivation of de-OH CI-MI and a fluoro bioprecursor analogue in CYP1A1-transfected cells. Using CYP bactosomes, we also demonstrate that CYP1A2 but not CYP1B1 or CYP3A4 has propensity for potentiating these compounds, indicating preference for CYP1A bioactivation.

Yes / The duocarmycins belong to a class of agent which has great potential for use in cancer therapy. Their exquisite potency means they are too toxic for systemic use, and targeted approaches are required to unlock their clinical potential. In this study, we have explored seco-OH-chloromethylindoline (CI) duocarmycin-based bioprecursors for their potential for cytochrome P450 (CYP)-mediated cancer cell kill. We report on synthetic and biological explorations of racemic seco-CI-MI, where MI is a 5-methoxy indole motif, and dehydroxylated analogues. We show up to a 10-fold bioactivation of de-OH CI-MI and a fluoro bioprecursor analogue in CYP1A1-transfected cells. Using CYP bactosomes, we also demonstrate that CYP1A2 but not CYP1B1 or CYP3A4 has propensity for potentiating these compounds, indicating preference for CYP1A bioactivation. / The authors would like to thank Yorkshire Cancer Research (Program grant B381PA) for supporting our work focused on exploring CYPs as targets for prodrug development. The human recombinant CYP1A1 was a gift from Prof Emily E. Scott, University of Michigan; the enzyme was produced via NIH funded grant (R37 GM076343).

No / Duocarmycin natural products are promising anti-cancer cytotoxins but too potent for systemic use. Re-engineering of the duocarmycin scaffold has enabled the discovery of prodrugs designed for bioactivation by tissue-specific cytochrome P450 enzymes. Lead prodrugs bioactivated by both P450 isoforms CYP1A1 and CYP2W1 have shown promising results in xenograft studies, however to fully understand the potential of these agents it is desirable to compare dual-targeting compounds with isoform-selective analogs. Such redesign requires insight into the molecular interactions with these P450 enzymes. Herein binding and metabolism of the individual stereoisomers of the indole-based duocarmycin prodrug ICT2700 and a nontoxic benzofuran analog ICT2726 were evaluated with CYP1A1 and CYP2W1, revealing differences exploitable for drug design. While enantiomers of both compounds bound to and were metabolized by CYP1A1, the stereochemistry of the chloromethyl fragment was critical for CYP2W1 interactions. CYP2W1 differentially binds the S enantiomer of ICT2726 and its metabolite profile could potentially be used as a biomarker to identify CYP2W1 functional activity. In contrast to benzofuran-based ICT2726, CYP2W1 differentially binds the R isomer of the indole-based ICT2700 over the S stereoisomer. Thus the ICT2700 R configuration warrants further investigation as a scaffold to favor CYP2W1-selective bioactivation. Furthermore, structures of both duocarmycin S enantiomers with CYP1A1 reveal orientations correlating with nontoxic metabolites and further drug design optimization could lead to a decrease of CYP1A1 bioactivation. Overall, distinctive structural features present in the two P450 active sites can be useful for improving P450-and thus tissue-selective-bioactivation. Significance Statement Prodrug versions of the natural product duocarmycin can be metabolized by human tissue-specific cytochrome P450 enzymes 1A1 and 2W1 to form an ultrapotent cytotoxin and/or high affinity 2W1 substrates to potentially probe functional activity in situ The current work defines the binding and metabolism by both P450 enzymes to support the design of duocarmycins selectively activated by only one human P450 enzyme. / National Institutes of Health and Yorkshire Cancer Research Program Grant (B381PA)

The neuronal nitric oxide synthase (nNOS) inhibitor 7-nitroindazole (7-NI) protects against the neurotoxicity of MPTP in a mouse model of neurodegeneration. Since 7-NI also inhibits the monoamine oxidase-B (MAO-B) catalyzed bioactivation of MPTP, the role of nNOS inhibition as a mediator of 7-NI's neuroprotective properties have been challenged. In order to examine in greater detail the neuroprotective effects of indazolyl derivatives, the synthesis of water soluble indazolyltetrahydropyridinyl derivatives as potential "prodrugs" that may undergo MAO bioactivation in the brain was undertaken. During the course of the studies on the synthesis of indazolylpyridinium derivatives, precursors to these "prodrugs", an interesting reaction involving the rearrangement of 4-(2H-indazolyl)-1-methylpyridinium iodide to the corresponding 1H-isomer was encountered. A detailed investigation of this rearrangement reaction is reported in this thesis. The syntheses and interaction of nitroindazolyltetrahydropyridinyl "prodrugs" with MAO-B have been investigated previously. Molecular docking studies that attempt to explain the MAO-B substrate and inhibitor properties of members of this series of compounds are described. Finally, the MAO-A substrate properties of nitroindazolyltetrahydropyridinyl derivatives are reported. / Ph. D.

β-Nicotyrine is a minor tobacco alkaloid found in both tobacco plants and tobacco smoke. Preliminary studies have shown that β-nicotyrine is pneumotoxic and that the toxicity is mediated via its metabolites formed in reactions catalyzed by cytochrome P-450. The in vitro metabolic fate of β-nicotyrine has been examined in rat liver microsomal preparations and rabbit lung and liver microsomal preparations utilizing HPLC UV-diode array analysis. Four metabolites have been identified from the incubation mixtures of β-nicotyrine with rabbit lung and liver microsomal preparations. The primary in vitro metabolites are two unstable pyrrolinone species, 1-methyl-5-(3-pyridyl)-4-pyrrolin-2-one and 1-methyl-5-(3-pyridyl)-3-pyrrolin-2-one, which exist in equilibrium. The pyrrolinones undergo autoxidation to form a secondary metabolite, 5-hydroxy-1-methyl-S-(3-pyridyl)-3-pyrrolin-2-one, and hydrolysis to form 5'-hydroxycotinine. The autoxidation is likely to involve a free radical process. Evidence to support this proposal has been obtained by studies on 2-acetoxy-1-methyl-5-(3-pyridyl)pyrrole, a latent form of the pyrrolinones. Free radicals generated following hydrolysis of the acetoxypyrrole derivative have been trapped and detected by ESR analysis by spin trapping techniques. In contrast, only the starting substrate β-nicotyrine was found in the incubation mixture of β-nicotyrine with rat liver microsomes. The in vivo metabolic fate of β-nicotyrine has been examined in rabbits and mice by HPLC UV-diode array and GC-EIMS analysis of urine extracts. Three metabolites have been identified. Besides S'-hydroxycotinine and 5-hydroxy-1-methyl-5-(3-pyridyl)-3-pyrrolin-2-one, observed in the in vitro studies, 3'-hydroxycotinine is also found and determined to be the principal urinary metabolite of β-nicotyrine in both species. The stereochemistry of this 3'-hydroxycotinine is <i>cis</i>. This is in contrast to the <i>trans</i> stereochemistry of the urinary metabolite of (S)-cotinine and (S)-nicotine. The mechanism of formation of <i>cis</i>-3'-hydroxycotinine from β-nicotyrine is proposed to involve a free radical process leading to the formation of the precursor 3-hydroxy-1-methyl-5-(3- pyridyl)-4-pyrrolin-2-one. This intermediate then undergoes a carbon-carbon double bond reduction to yield the final product. This proposal is supported by in vivo studies on 5-hydroxy-1-methyl-5-(3-pyridyl)-3-pyrrolin-2-one which undergoes reduction to 5'-hydroxycotinine. Furthermore, 2-acetoxy-1-methyl-5- (3-pyridyl)pyrrole goes to <i>cis</i>-3'-hydroxycotinine as the major urinary metabolite. The results of these studies point to a potentially novel metabolic bioactivation pathway of (S)-nicotine that could be relevant to some of the toxic effects observed in chronic tobacco users. / Ph. D.

Metabolism of xenobiotic drug molecules can result in the formation of metabolites which are more chemically reactive than the parent drug from which they are derived. These reactive species have the potential to covalently modify biological macromolecules if they are not detoxified. The formation of drug-protein adducts carries a potential risk of clinical toxicities and idiosyncratic adverse drug reactions which can, in severe cases, result in hospitalisation and even death. Current methods for the evaluation of the risk for a drug to cause adverse drug reactions due to drug-protein binding rely on risk factors such as quantitative covalent binding value, structure, dose etc. The objective of this project was to develop methods for the detection of reactive metabolites directly bound to proteins, which could be used in future evaluations of the mechanisms of binding of candidates in drug development. Three compounds known to produce reactive metabolites, acetaminophen, SB-648969 and amodiaquine, were used as tool substrates. In vitro incubations with human liver microsomes and individual cytochrome P450 enzymes (as Supersomes ) were used to produce reactive metabolite species and binding with the incubation proteins evaluated. Analysis of the intact proteins, peptides generated via trypsin digestion of the incubation protein, and amino acids generated via digestion with pronase were evaluated using a combination of LC/MS and LC-MS/MS. Reactive metabolite trapping experiments with glutathione were used to provide information about the likely structure of the bound species and the specificity of binding, and were useful in the development of sensitive targeted precursor ion scanning and multiple reaction monitoring methods. [14C] radiolabelled acetaminophen and SB-649868 were used to assess the quantitative levels of binding (&lt;5% modification of protein in both cases). Radiodetection using accelerator mass spectrometry (AMS) was used to evaluate the stoichiometry of binding and aid the identification of adducted peptides through retention time comparison. Chemical and electrochemical methods were utilised to produce stable solutions of N-acetyl-p-benzoquinone imine (NAPQI) and amodiaquine quinone imine (AQQI), reactive metabolites of acetaminophen and amodiaquine, respectively, which were bound to selected proteins and used as chromatographic and mass spectrometric standards. These methods were used to successfully identify an acetaminophen-modified peptide (T56) of cytochrome P450 CYP2E1. No modified proteins were observed for the SB-649868 incubations, however, examination of the AMS chromatograms for the incubations with acetaminophen and SB-649868 revealed a difference in the stoichiometry of binding, with one modified peptide observed with acetaminophen, and several for the incubations with SB-649868. The detection and identification of drug-protein adducts remains extremely challenging due to the low levels of any adducts observed, which can be exacerbated by binding on multiple sites of a protein; however this project has demonstrated that sensitive and selective LC/MS methods can be successfully developed to identify drug-protein adducts.

<p>A screening method was developed for identification of catalytically active enzymes in combinatorial cDNA libraries of mutated glutathione transferase (GST) derivatives expressed in <i>E. coli</i>. The method is based on spraying monochlorobimane (MCB) directly over bacterial colonies growing on agar. The substrate MCB become fluorescent under UV light, when the bacterial colony contains active GSTs catalyzing the conjugation with endogenous glutathione. Eleven out of twelve GSTs investigated where active with MCB. This method can be used to screen libraries generated from most cytosolic GSTs in the search for proteins with altered functions and structures. Azathioprine (Aza), a thiopurine that has been used clinically for 40 years was investigated with 14 GSTs. Three enzymes showed prominent catalytic activities with Aza and all of them are highly expressed in the liver. We estimated the contribution of the three enzymes GSTs A1-1, A2-2 and M1-1 bioactivation of Aza in the liver and concluded that it was about 2 orders of magnitude more effective than the uncatalyzed reaction. GST bioactivation of Aza could clarify aspects of idiosyncratic reactions observed in some individuals. Two other thiopurine prodrugs, cis-acetylvinylthiopurine (cAVTP) and trans-acetylvinylthioguanine (tAVTG), were investigated with the same 14 GSTs. The results displayed diverse catalytic activities. A mechanism of consecutive reactions was proposed. The studies contribute to knowledge under what conditions the drug should optimally be administered. A study of the same prodrugs with several mutants from the Mu class characterized by a point mutation of a hypervarible residue. We conclude that the effects of the mutations were qualitatively parallel for cAVTP and tAVTG, but they vary significantly in magnitude; steric hindrance may interfere with transition-state stabilization. From the evolutionary perspective the data show that a point mutation can alternatively enhance or attenuate the activity with a particular substrate and illustrate the functional plasticity of GSTs.</p>

<P align=justify>Aromatische Amine und Amide (aAA) sind aufgrund ihrer starken Verbreitung in der menschlichen Umwelt und ihres kanzerogenen Potenzials von großer toxikologischer Bedeutung. Die Kanzerogenität der aAA wird durch die Mutagenität hochreaktiver Stoffwechselprodukte vermittelt, die in zwei sequenziellen katalytischen Reaktionen entstehen. Die erste ist meistens eine <I>N</I>-Hydroxylierung, die oft durch Cytochrom P450 1A2 (CYP1A2) katalysiert wird. Daran schließt sich eine <I>O</I>-Konjugation durch Sulfotransferasen (SULT) oder <I>N</I>-Acetyltransferasen (NAT) an. Die Bioaktivierung ist ein kritischer Parameter für die Übertragbarkeit von Ergebnissen aus Tiermodellen auf den Menschen. </P><P align=justify>Rekombinante <I>in vitro</I> Systeme, die fremdstoffmetabolisierende Enzyme verschiedener Spezies exprimieren, ermöglichen die vergleichende Untersuchung der Bioaktivierung im Menschen und in Versuchstieren. Ziel des Projektes war die Aufklärung der Bioaktivierung der aAA durch humane Enzyme. Im Vordergrund stand die Untersuchung der Rolle humaner SULT in diesem Prozess. Es wurden rekombinante <I>in vitro</I> Systeme, konstruiert, die CYP1A2 und SULT des Menschen koexprimieren. SULT-cDNAs wurden in den Säugerzell Expressionsvektor pMPSV kloniert und in Standardindikatorzellen für Mutagenitätsuntersuchungen (V79 Zellen aus dem Chinesischen Hamster) transfiziert. Das Expressionsniveau von CYP1A2 und SULT wurde mittels Immunblotanalyse und radiometrischen Aktivitätsmessungen charakterisiert. In den rekombinanten Zellen wurden vier aAA als Modellsubstanzen (2-Acetylaminofluoren, 2-Aminoanthracen, 3&prime;-Methyl-4-dimethylaminoazobenzol, 2,4-Diaminotoluol) auf ihre Mutagenität am <I>hprt</I>-Locus hin untersucht.</P><P align=justify>Die aAA waren in Zellen, die keine rekombinanten Enzyme oder lediglich CYP1A2 exprimierten, nicht mutagen. In Zellen, die CYP1A2 und SULT der Subfamilie 1A koexprimierten, erzeugten sie bereits in geringen Konzentrationen klare mutagene Effekte (0,3 &#181;M für 2-Acetylaminofluoren <br /> und 3&prime;-Methyl-4-dimethylaminoazobenzol; 0,1 &#181;M für 2-Aminoanthracen; 10 &#181;M für 2,4-Diaminotoluol). Die stärkste Aktivierung von 2-Acetylaminofluoren und 3&prime;-Methyl-4-dimethylaminoazobenzol erfolgte in der Zelllinie, die CYP1A2 und SULT1A2 koexprimierte; die stärkste Aktivierung von 2,4-Diaminotoluol und 2-Aminoanthracen erfolgte in der Zelllinie, die CYP1A2 und SULT1A1 koexprimierte. </P><P align=justify>Sowohl SULT1A1 als auch SULT1A2 sind im Menschen genetisch polymorph. Ein unterschiedlich starkes Aktivierungspotenzial der Alloenzyme könnte eine individuell unterschiedliche Suszeptibilität für die durch aAA ausgelöste Kanzerogenese bedingen. In HPRT-Mutationsuntersuchungen mit rekombinanten Zellen zeigten die allelischen Varianten der SULT1A2 starke Unterschiede in ihrem Aktivierungpotenzial. Nur in der Zelllinie, die das Alloenzym SULT1A2*1 mit CYP1A2 koexprimierte, wurde 2-Acetylaminofluoren zum Mutagen aktiviert. Zur Aktivierung von 3&prime;-Methyl-4-dimethylaminoazobenzol waren jedoch sowohl das Alloenzym SULT1A2*1 als auch das Alloenzym SULT1A2*2 in der Lage. Die Alloenzyme der SULT1A1 zeigten ein ähnlich gutes Aktivierungspotenzial für aAA. </P><P align=justify>In früheren Studien wurde gezeigt, dass die SULT1C1 der Ratte eine wichtige Rolle bei der Aktivierung der aAA in dieser Spezies spielt. Dahingegen war die humane SULT1C1 nicht in der Lage die untersuchten aAA zu aktivieren. Die Kenntnis solcher Spezieunterschiede könnte wichtig sein um unterschiedliche Organotropismen aAA in Menschen und Tiermodellen zu erklären, da SULT mit starker Gewebespezifität exprimiert werden und das Expressionsmuster für die einzelnen SULT-Formen in Menschen und Ratten sich stark unterscheidet.</P><br> / <P align=justify>Aromatic amines and amides (aAA) represent a group of chemicals with great toxicological importance due to their wide distribution in the environment and their carcinogenic potency. The carcinogenicity of aAA is mediated by the mutagenic action of highly reactive metabolites. They are frequently formed by <I>N</I>-hydroxylation of the exocyclic amino group, usually catalysed by cytochrome P450 1A2 (CYP1A2) and subsequent <I>O</I>-conjugation by phase-II enzymes e.g. sulfotransferases (SULT) or <I>N</I>-acetyltransferases. </P> <P align=justify>The bioactivation constitutes a critical parameter for the transfer of results from animal models on man. Recombinant <I>in vitro</I> systems expressing xenobiotic metabolizing enzymes of different species allow the comparative study of the bioactivation in humans and animal models. <BR>The aim of this project was to elucidate the bioactivation of aAA by human xenobiotic enzymes. The investigation focused on the role of SULT in this process. SULT-cDNAs were cloned into the mammalian expression vector pMPSV and transfected in V79 Chinese Hamster cells, which represent standard indicator cells for mutagenicity tests. Selected SULT-cDNAs were also co-expressed with human CYP1A2. These cells were able to catalyse internally both enzymatic reactions that are necessary for the bioactivation of aAA. The expression level of CYP1A2 and SULT in the co-expressing cell clones was characterised by immunoblot analysis and radiometric SULT-activity measurement. The mutagenicity of four aAA model compounds, 2-aminoanthracene, 2-acetylaminofluorene, 3'-methyl-4-dimethylaminoazobenzene and 2,4-diaminotoluene, at the <I>hprt</I> locus of the recombinant cell lines was investigated.</P><br /> <P align=justify>These aAA were not or only marginally mutagenic in wild type cells or in recombinant cells expressing CYP1A2 alone. If CYP1A2 was co-expressed with SULT forms of the 1A subfamily clear mutagenic effects occured in low concentrations of the aAA (0,3 &#181;M for 2-acetylaminofluorene and 3&prime;-methyl-4-dimethylaminoazobenzene; 0,1 &#181;M for 2-aminoanthracene; 10 &#181;M for 2,4-diaminotoluene). The strongest activation of 2-acetylaminofluorene and 3'-methyl-4-dimethylaminoazobenzene was mediated by SULTA2 and of 2-aminoanthracene and 2,4-diaminotoluene by SULT1A1. </P><br /> <P align=justify>SULT1A1 and SULT1A2 are expressed polymorphically in humans. Differences in the activation potency of distinct alloenzymes for aAA may cause divergent individual susceptibilities for cancer induced by aAA. Briefly, the allelic variants of SULT1A2 showed substantial differences regarding their activation potencies for the investigated aAA. Only alloenzyme SULT1A2*1 was able to activate 2-acetylaminofluorene to a mutagen whereas 3&prime;-methyl-4-di-methylaminoazobenzene was activated by alloenzymes SULT1A2*1 and SULT1A2*2. The investigated alloenzymes of SULT1A1 showed equal activation potencies for aAA. </P><br /> <P align=justify>In previous studies it had been shown that the SULT1C1 plays an important role in the activation of aAA in rats. However, the human SULT1C1 was not able to activate the investigated aAA in the study presented here. Such species differences might be important for the elucidation of divergent organotropisms of aAA in humans and animal models, since SULT are expressed with strong tissue specificities and the pattern of expression in humans and rats is severely different.</P><br>

In order to investigate the structural features responsible for the cytotoxicity of the naturally occurring lignan nordihydroguaiaretic acid, the synthesis of four structural analogues of NDGA is proposed for the purpose of studying their oxidative metabolism. One analogue in particular (1), a mono-catechol analogue, is successfully synthesized employing a double Stobbe condensation approach. Following synthesis of this compound a series of oxidation experiments is performed consisting of: incubation in rat liver microsomes with and without the trapping agent glutathione (GSH), oxidation with mushroom tyrosinase, oxidation with silver oxide, and oxidation with horseradish peroxidase. Results are analyzed via HPLC and UPLC-MS. It is found that 1 does not autoxidize at pH 7.4 as NDGA does. Two products are produced during incubation of 1 in rat liver microsomes with UPLC-ESI(-)-MS results giving m/z of 879.2 and 574.18. This is consistent with 1 plus 2 GSH and 1 plus 1 GSH respectively; confirming 1 will oxidize to an electrophilic moiety. Oxidation with mushroom tyrosinase is found to produce high levels of product two with m/z 574.2. Oxidation with horseradish peroxidase is found to produce high levels of the m/z 879.2 product. Silver Oxide produced multiple products rather than the expected one major product, but most are found to be inconsistent with the products seen during rat liver microsomal incubation, and are not pursued.