Graham J. Atwell

University of Auckland, Окленд, Auckland, New Zealand

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Publications (126)569.01 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Duocarmycins are highly cytotoxic natural products that have potential for development into anticancer agents. Herein we describe proposed but previously unidentified NH analogues of the DNA-alkylating subunit and characterise these by solvolysis studies, NMR and computational modelling. These compounds are shown to be the exclusive intermediates in the solvolysis of their seco precursors and to possess very similar structural features to the widely studied O-based analogues, apart from an unusually high basicity. The measured pKa of 10.5 implies that the NH compounds are fully protonated under physiological conditions. Remarkably, their extremely high reactivity (calculated hydrolysis rate 108 times higher for protonated NH compared to the neutral O analogue) is still compatible with potent cytotoxicity, provided the active species is formed in the presence of cells. These surprising findings are of relevance to the design of duocarmycin-based tumour-selective therapies.
    No preview · Article · Sep 2014 · ChemBioChem
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    ABSTRACT: Inhibitors of the aldo-keto reductase enzyme AKR1C3 are of interest as potential drugs for leukemia and hormone-related cancers. A series of non-carboxylate morpholino(phenylpiperazin-1-yl)methanones were prepared by palladium-catalysed coupling of substituted phenyl or pyridyl bromides with the known morpholino(piperazin-1-yl)methanone, and shown to be potent (IC50∼100nM) and very isoform-selective inhibitors of AKR1C3. Lipophilic electron-withdrawing substituents on the phenyl ring were positive for activity, as was an H-bond acceptor on the other terminal ring, and the ketone moiety (as a urea) was essential. These structure-activity relationships are consistent with an X-ray structure of a representative compound bound in the AKR1C3 active site, which showed H-bonding between the carbonyl oxygen of the drug and Tyr55 and His117 in the 'oxyanion hole' of the enzyme, with the piperazine bridging unit providing the correct twist to allow the terminal benzene ring to occupy the lipophilic pocket and align with Phe311.
    No preview · Article · Jan 2014 · Bioorganic & medicinal chemistry
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    ABSTRACT: A high-throughput screen identified 3-(3,4-dihydroisoquinolin-2(1H)-ylsulfonyl)benzoic acid as a novel, highly potent (low nM), and isoform-selective (1500-fold) inhibitor of aldo-keto reductase AKR1C3: a target of interest in both breast and prostate cancer. Crystal structure studies showed that the carboxylate group occupies the oxyanion hole in the enzyme, while the sulfonamide provides the correct twist to allow the dihydroisoquinoline to bind in an adjacent hydrophobic pocket. SAR studies around this lead showed that the positioning of the carboxylate was critical, although it could be substituted by acid isosteres and amides. Small substituents on the dihydroisoquinoline gave improvements in potency. A set of "reverse sulfonamides" showed a 12-fold preference for the R stereoisomer. The compounds showed good cellular potency, as measured by inhibition of AKR1C3 metabolism of a known dinitrobenzamide substrate, with a broad rank order between enzymic and cellular activity, but amide analogues were more effective than predicted by the cellular assay.
    Full-text · Article · Aug 2012 · Journal of Medicinal Chemistry
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    ABSTRACT: Drug lipophilicity is a vital physicochemical parameter that influences drug absorption, distribution, metabolism, excretion and toxicology. A comparative study of a homologous series based on a pharmaceutically active drug represents a powerful approach to the study of the effects of drug lipophilicity. We have developed a rapid and sensitive LC-MS/MS method suitable for such a homologous series and applied it to a series of DNA binding benzonaphthyridine-based antitumour drugs of differing lipophilicity. The method used a gradient elution with a run time of 7 min for simultaneous quantitation of five analogues in a pooled sample. Method validation was carried out in plasma (human and mouse) and mouse tissues (brain, heart, kidney, liver and lung). It had a limit of quantitation of 0.001 μmol/L and was linear (0.001-0.3 μmol/L) in all matrices with acceptable intra- and inter-assay precision and accuracy. This method allowed the pharmacokinetic parameters of these compounds in mice to be related to their lipophilicity as determined by their partition coefficient (LogD). Both the plasma CL (r=0.95; P=2×10⁻⁷) and V(ss) (r=0.95; P=2×10⁻⁷) exhibited a significant positive correlation with LogD values after intravenous bolus administration to mice. Consequently the plasma mean residence time for each of these five analogues decreased with increasing lipophilicity. There was also a significant positive correlation (r=0.91; P=2×10⁻⁷) between LogD values and the brain to plasma AUC ratio indicating the importance of lipophilicity in the distribution of these compounds into the brain tissue.
    No preview · Article · Jan 2012 · Journal of pharmaceutical and biomedical analysis
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    ABSTRACT: A series of 3-substituted (5-nitro-2,3-dihydro-1H-benzo[e]indol-1-yl)methyl sulfonate (nitroCBI) prodrugs containing sulfonate leaving groups undergo hypoxia-selective metabolism to form potent DNA minor groove alkylating agents. They were evaluated (along with chloride leaving group analogs for comparison) for their cytotoxicity against cultures of SKOV3 and HT29 human tumor cell lines under both aerobic and hypoxic conditions. Sulfonates with neutral side chains (e.g., 5,6,7-trimethoxyindole; TMI) show consistently higher hypoxic cytotoxicity ratios (HCRs) (34-246) than the corresponding chloro analogs (2.8-3.1) in SKOV3 cells, but these trends do not hold for compounds with cationic or polar neutral side chains.
    Full-text · Article · Aug 2011 · Bioorganic & medicinal chemistry
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    ABSTRACT: Hitting the hypoxic target: Combining a nitro prodrug with a water-soluble phosphate converts duocarmycin analogues from highly toxic DNA-alkylating agents to highly selective antitumor compounds. These prodrugs (see scheme) have outstanding activity against hypoxic tumor cells in vivo, cells which are usually considered the most resistant to conventional therapy.
    Full-text · Article · Mar 2011 · Angewandte Chemie International Edition
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    ABSTRACT: PR-104, a bioreductive prodrug in clinical trial, is a phosphate ester which is rapidly metabolized to the corresponding alcohol PR-104A. This dinitrobenzamide mustard is activated by reduction to hydroxylamine (PR-104H) and amine (PR-104M) metabolites selectively in hypoxic cells, and also independently of hypoxia by aldo-keto reductase (AKR) 1C3 in some tumors. Here, we evaluate reductive metabolism of PR-104A in mice and its significance for host toxicity. The pharmacokinetics of PR-104, PR-104A and its reduced metabolites were investigated in plasma and tissues of mice (with and without SiHa or H460 tumor xenografts) and effects of potential oxidoreductase inhibitors were evaluated. Pharmacokinetic studies identified extensive non-tumor reduction of PR-104A to the 5-amine PR-104H (identity of which was confirmed by chemical synthesis), especially in liver. However, high concentrations of PR-104H in tumors that suggested intra-tumor activation is also significant. The tissue distribution of PR-104M/H was broadly consistent with the target organ toxicities of PR-104 (bone marrow, intestines and liver). Surprisingly, hepatic nitroreduction was not enhanced when the liver was made more hypoxic by hepatic artery ligation or breathing of 10% oxygen. A screen of non-steroidal anti-inflammatory drugs identified naproxen as an effective AKR1C3 inhibitor in human tumor cell cultures and xenografts, suggesting its potential use to ameliorate PR-104 toxicity in patients. However, neither naproxen nor the pan-CYP inhibitor 1-aminobenzotriazole inhibited normal tissue reduction of PR-104A in mice. PR-104 is extensively reduced in mouse tissues, apparently via oxygen-independent two-electron reduction, with a tissue distribution that broadly reflects toxicity.
    Full-text · Article · Mar 2011 · Cancer Chemotherapy and Pharmacology
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    ABSTRACT: Purpose PR-104, a bioreductive prodrug in clinical trial, is a phosphate ester which is rapidly metabolized to the corresponding alcohol PR-104A. This dinitrobenzamide mustard is activated by reduction to hydroxylamine (PR-104H) and amine (PR-104M) metabolites selectively in hypoxic cells, and also independently of hypoxia by aldo-keto reductase (AKR) 1C3 in some tumors. Here, we evaluate reductive metabolism of PR-104A in mice and its significance for host toxicity. Methods The pharmacokinetics of PR-104, PR-104A and its reduced metabolites were investigated in plasma and tissues of mice (with and without SiHa or H460 tumor xenografts) and effects of potential oxidoreductase inhibitors were evaluated. Results Pharmacokinetic studies identified extensive non-tumor reduction of PR-104A to the 5-amine PR-104H (identity of which was confirmed by chemical synthesis), especially in liver. However, high concentrations of PR-104H in tumors that suggested intra-tumor activation is also significant. The tissue distribution of PR-104M/H was broadly consistent with the target organ toxicities of PR-104 (bone marrow, intestines and liver). Surprisingly, hepatic nitroreduction was not enhanced when the liver was made more hypoxic by hepatic artery ligation or breathing of 10% oxygen. A screen of non-steroidal anti-inflammatory drugs identified naproxen as an effective AKR1C3 inhibitor in human tumor cell cultures and xenografts, suggesting its potential use to ameliorate PR-104 toxicity in patients. However, neither naproxen nor the pan-CYP inhibitor 1-aminobenzotriazole inhibited normal tissue reduction of PR-104A in mice. Conclusions PR-104 is extensively reduced in mouse tissues, apparently via oxygen-independent two-electron reduction, with a tissue distribution that broadly reflects toxicity.
    Full-text · Article · Mar 2011 · Cancer Chemotherapy and Pharmacology
  • G. J. ATWELL · W. R. WILSON · W. A. DENNY
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Oct 2010 · ChemInform
  • M. BOYD · P. D. W. BOYD · G. J. ATWELL · W. R. WILSON · W. A. DENNY
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Aug 2010 · ChemInform
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    ABSTRACT: Nitro seco-1,2,9,9a-tetrahydrocyclopropa[c]benz[e]indol-4-ones (nitroCBIs) are a new class of prodrugs for antitumor therapy that undergo hypoxia-selective metabolism to form potent DNA minor groove alkylating agents. Although hindered by poor aqueous solubility, several examples have shown activity against hypoxic tumor cells in vivo. Here we investigate structural properties that influence hypoxic selectivity in vitro, and show that for high hypoxic selectivity nitroCBIs should combine an electron-withdrawing group of H-bond donor capacity on the A-ring, with a basic substituent on the minor groove-binding side chain. Substitution on the A-ring is compatible with the introduction of functionality that can improve water solubility.
    No preview · Article · Jul 2010 · Bioorganic & medicinal chemistry
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Jun 2010 · ChemInform
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    ABSTRACT: 2-Nitroaryl amides of general structure I are proposed as bioreducible prodrugs, capable of releasing cytotoxic aminoaniline mustards V on bioactivation by spontaneous cyclization of the resulting 2-aminoarylamides II via a tetrahedral intermediate, III. This concept allows separate optimization of the substituent effects influencing nitro-group reduction and mustard reactivity. A series of model 2-aminoaryl amides has been synthesized, and their rates of cyclization have been studied; these varied by a factor of more than 50,000-fold (kobs from 0.00040 to 21 min-1) at pH 2.4. For three compounds studied in detail, the rates were linearly dependent of pH, indicating that no change in the mechanism of the rate-determining step occurs over the pH range studied. The nucleophilicity of the amino group had a modest influence on the kinetics of cyclization, with electron-withdrawing groups slowing the rate. The geometry of the compound was also important, with structure-activity relationships indicating that the rate of cyclization is greatly enhanced by the preorganization of the molecule. In contrast, 4-substitution on the leaving aniline by a variety of groups had little effect on the cyclization reaction. These results are consistent with the rate-determining step being formation of the tetrahedral intermediate. These model studies suggest that the phenyldimethylacetamide system could be developed as a prodrug system for the bioreductively-triggered release of amines. Further substantial rate enhancements appear possible by alterations in the geometry of the system, whereas substitution of electron-withdrawing groups (required to raise the nitro-group reduction potential into the appropriate range) has only relatively modest retardation effects on rates of cyclization. More rigid systems may also be useful; a nitronaphthaleneacetamide analogue cyclized spontaneously during nitro-group reduction, suggesting a very short half-life for the reduced intermediate (amine or hydroxylamine).
    No preview · Article · Jun 2010 · Journal of Medicinal Chemistry
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Jun 2010 · ChemInform
  • B. M. SYKES · G. J. ATWELL · W. A. DENNY · C. J. O'CONNOR
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    ABSTRACT: The reductive cyclization of several 2-nitroarylamides was studied by radiolytic reduction, examining the effects of substituents on the nitrophenyl ring and on the leaving aniline and variations in the nature of the link between the nitrophenyl ring and the leaving aniline, The stoichiometry of the reduction and the identification of N-hydroxylactam and aniline products suggest that the major initial products of such a reduction of the nitroamides are the corresponding hydroxylamines. Under anaerobic conditions, cyclization via the hydroxylamines was considerably faster (up to 160-fold) than via the corresponding amines under comparable conditions, but was similarly influenced by changes in geometry, Unlike cyclization via the amines, rates of cyclization via the hydroxylamines were sensitive to substitution on the leaving aniline, being accelerated by electron-withdrawing groups. The rate-determining step in the cyclization of the hydroxylamines is proposed to be breakdown of the tetrahedral intermediate.
    No preview · Article · Mar 2010 · ChemInform
  • [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    No preview · Article · Mar 2010 · ChemInform
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    Yongchuan Gu · Graham J Atwell · William R Wilson
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    ABSTRACT: PR-104 is the phosphate ester of a 3,5-dinitrobenzamide nitrogen mustard (PR-104A) that is reduced to active hydroxylamine and amine metabolites by reductases in tumors. In this study, we evaluate the excretion of [(3)H]PR-104 in mice and determine its metabolite profile in mice, rats, dogs, and humans after a single intravenous dose. Total radioactivity was rapidly and quantitatively excreted in mice, with cumulative excretion of 46% in urine and 50% in feces. The major urinary metabolites in mice were products from oxidative N-dealkylation and/or glutathione conjugation of the nitrogen mustard moiety, including subsequent mercapturic acid pathway metabolites. A similar metabolite profile was seen in mouse bile, mouse plasma, and rat urine and plasma. Dogs and humans also showed extensive thiol conjugation but little evidence of N-dealkylation. Humans, like rodents, showed appreciable reduced metabolites in plasma, but concentrations of the cytotoxic amine metabolite (PR-104M) were higher in mice than humans. The most conspicuous difference in metabolite profile was the much more extensive O-beta-glucuronidation of PR-104A in dogs and humans than in rodents. The structure of the O-beta-glucuronide (PR-104G) was confirmed by independent synthesis. Its urinary excretion was responsible for 13 +/- 2% of total dose in humans but only 0.8 +/- 0.1% in mice. Based on these metabolite profiles, biotransformation of PR-104 in rodents is markedly different from that in humans, suggesting that rodents may not be appropriate for modeling human biotransformation and toxicology of PR-104.
    Full-text · Article · Dec 2009 · Drug metabolism and disposition: the biological fate of chemicals
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    ABSTRACT: Nitrochloromethylbenzindolines (nitroCBIs) are a new class of hypoxia-activated prodrugs for antitumor therapy. The recently reported prototypes undergo hypoxia-selective metabolism to form potent DNA minor groove alkylating agents and are selectively toxic to some but not all hypoxic tumor cell lines. Here we report a series of 31 analogues that bear an extra electron-withdrawing substituent that serves to raise the one-electron reduction potential of the nitroCBI. We identify a subset of compounds, those with a basic side chain and sulfonamide or carboxamide substituent, that have consistently high hypoxic selectivity. The best of these, with a 7-sulfonamide substituent, displays hypoxic cytotoxicity ratios of 275 and 330 in Skov3 and HT29 human tumor cell lines, respectively. This compound (28) is efficiently and selectively metabolized to the corresponding aminoCBI, is selectively cytotoxic under hypoxia in all 11 cell lines examined, and demonstrates activity against hypoxic tumor cells in a human tumor xenograft in vivo.
    No preview · Article · Nov 2009 · Journal of Medicinal Chemistry
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    ABSTRACT: PR-104 is a dinitrobenzamide mustard currently in clinical trial as a hypoxia-activated prodrug. Its major metabolite, PR-104A, is metabolized to the corresponding hydroxylamine (PR-104H) and amine (PR-104M), resulting in activation of the nitrogen mustard moiety. We characterize DNA damage responsible for cytotoxicity of PR-104A by comparing sensitivity of repair-defective hamster Chinese hamster ovary cell lines with their repair-competent counterparts. PR-104H showed a repair profile similar to the reference DNA cross-linking agents chlorambucil and mitomycin C, with marked hypersensitivity of XPF(-/-), ERCC1(-/-), and Rad51D(-/-) cells but not of XPD(-/-) or DNA-PK(CS)(-/-) cells. This pattern confirmed the expected dependence on the ERCC1-XPF endonuclease, implicated in unhooking DNA interstrand cross-links at blocked replication forks, and homologous recombination repair (HRR) in restarting collapsed forks. However, even under anoxia, the hypersensitivity of XPF(-/-), ERCC1(-/-), and Rad51D(-/-) cells to PR-104A itself was lower than for chlorambucil. To test whether this reflects inefficient PR-104A reduction, a soluble form of human NADPH:cytochrome P450 oxidoreductase was stably expressed in Rad51D(-/-) cells and their HRR-restored counterpart. This expression increased hypoxic metabolism of PR-104A to PR-104H and PR-104M as well as hypoxia-selective cytotoxicity of PR-104A and its dependence on HRR. We conclude that PR-104A cytotoxicity is primarily due to DNA interstrand cross-linking by its reduced metabolites, although under conditions of inefficient PR-104A reduction (low reductase expression or aerobic cells), a second mechanism contributes to cell killing. This study shows that hypoxia, reductase activity, and DNA interstrand cross-link repair proficiency are key variables that interact to determine PR-104A sensitivity.
    Full-text · Article · Jul 2009 · Molecular Cancer Therapeutics
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    ABSTRACT: The dinitrobenzamide mustards are a class of bioreductive nitro-aromatic anticancer prodrugs, of which a phosphorylated analog (PR-104) is currently in clinical development. They are bioactivated by tumor reductases to form DNA cross-linking cytotoxins. However, their biotransformation in normal tissues has not been examined. Here we report the aerobic in vitro metabolism of three N-(2 hydroxyethyl)-3,5-dinitrobenzamide 2-mustards and the corresponding nonmustard analog in human, mouse, rat, and dog hepatic S9 preparations. These compounds have a range of mustard structures (-N(CH(2)CH(2)X)(2) where X = H, Cl, Br, or OSO(2)Me). Four metabolic routes were identified: reduction of either nitro group, N-dealkylation of the mustard, plus O-acetylation, and O-glucuronidation of the hydroxyethyl side chain. Reduction of the nitro group ortho to the mustard resulted in intramolecular alkylation and is considered to be an inactivation pathway, whereas reduction of the nitro group para to the mustard generated potential DNA cross-linking cytotoxins. N-Dealkylation inactivated the mustard moiety but may result in the formation of toxic acetaldehyde derivatives. Increasing the size of the nitrogen mustard leaving group abrogated the ortho-nitroreduction and N-dealkylation routes and thereby improved overall metabolic stability but had little effect on aerobic para-nitroreduction. All four compounds underwent O-glucuronidation of the hydroxyethyl side chain and further studies to elucidate the relative importance of this pathway in vivo are in progress.
    Full-text · Article · Mar 2008 · Drug metabolism and disposition: the biological fate of chemicals

Publication Stats

4k Citations
569.01 Total Impact Points

Institutions

  • 1981-2014
    • University of Auckland
      • • Auckland Cancer Society Research Centre
      • • Department of Medicine
      • • School of Medical Sciences
      • • Faculty of Medical and Health Sciences
      Окленд, Auckland, New Zealand
  • 1993
    • McMaster University
      Hamilton, Ontario, Canada
  • 1990
    • University of Wisconsin–Madison
      • Department of Pharmacology
      Madison, Wisconsin, United States
  • 1977-1979
    • Cancer Society of New Zealand
      Wellington, Wellington, New Zealand
  • 1974-1977
    • Auckland Museum
      Окленд, Auckland, New Zealand