Publications by authors named "Alexander J Stevens"

17 Publications

  • Page 1 of 1

Integration of paraquat pharmacokinetic data across species using PBPK modelling.

Toxicol Appl Pharmacol 2021 04 22;417:115462. Epub 2021 Feb 22.

Syngenta Crop Protection LLC, Research Triangle Park, NC 27709, USA. Electronic address:

Paraquat dichloride (PQ) is a non-selective herbicide which has been the subject of numerous toxicology studies over more than 50 years. This paper describes the development of a physiologically-based pharmacokinetic (PBPK) model of PQ kinetics for the rat, mouse and dog, firstly to aid the interpretation of studies in which no kinetic measurements were made, and secondly to enable the future extension of the model to humans. Existing pharmacokinetic data were used to develop a model for the rat and mouse. Simulations with this preliminary model were then used to identify key data gaps and to design a new blood binding study to reduce uncertainty in critical aspects of the model. The new data provided evidence to support the model structure, and its predictive performance was then assessed against dog and rat datasets not used in model development. The PQ-specific model parameters are the same for all three species, with only the physiological parameters varying between species. This consistency across species provides a strong basis for extrapolation to other species, as demonstrated here for the dog. The model enables a wide range of PQ data to be linked together to provide a broad understanding of PQ pharmacokinetics in rodents and the dog, showing that the key aspects of PQ kinetics in these species are understood and adequately encapsulated within the model.
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http://dx.doi.org/10.1016/j.taap.2021.115462DOI Listing
April 2021

Paraquat pharmacokinetics in primates and extrapolation to humans.

Toxicol Appl Pharmacol 2021 04 22;417:115463. Epub 2021 Feb 22.

Syngenta Crop Protection LLC, Research Triangle Park, NC 27709, USA. Electronic address:

By extending our Paraquat (PQ) work to include primates we have implemented a modelling and simulation strategy that has enabled PQ pharmacokinetic data to be integrated into a single physiologically based pharmacokinetic (PBPK) model that enables more confident extrapolation to humans. Because available data suggested there might be differences in PQ kinetics between primates and non-primates, a radiolabelled study was conducted to characterize pharmacokinetics and excretion in Cynomolgus monkeys. Following single intravenous doses of 0.01 or 0.1 mg paraquat dichloride/kg bw, plasma PQ concentration-time profiles were dose-proportional. Excretion up to 48 h (predominantly urinary) was 82.9%, with ca. 10% remaining unexcreted. In vitro blood binding was similar across Cynomolgus monkeys, humans and rat. Our PBPK model for the rat, mouse and dog, employing a single set of PQ-specific parameters, was scaled to Cynomolgus monkeys and well represented the measured plasma concentration-time profiles over 14 days. Addition of a cartilage compartment to the model better captured the percent remaining in the monkeys at 48 h, whilst having negligible effect on model predictions for the other species. The PBPK model performed well for all four species, demonstrating there is little difference in PQ kinetics between non-primates and primates enabling a more confident extrapolation to humans. Scaling of the PBPK model to humans, with addition of a human-specific dermal submodel based on in vitro human dermal absorption data, provides a valuable tool that could be employed in defining internal dosimetry to complement human health risk assessments.
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http://dx.doi.org/10.1016/j.taap.2021.115463DOI Listing
April 2021

Comparative metabolism of xenobiotic chemicals by cytochrome P450s in the nematode Caenorhabditis elegans.

Sci Rep 2018 09 6;8(1):13333. Epub 2018 Sep 6.

Syngenta, Jealott's Hill International Research Centre, Bracknell, Berkshire, RG42 6EY, UK.

We investigated the metabolic capabilities of C. elegans using compounds whose metabolism has been well characterised in mammalian systems. We find that similar metabolites are produced in C. elegans as in mammals but that C. elegans is deficient in CYP1-like metabolism, as has been seen in other studies. We show that CYP-34A9, CYP-34A10 and CYP-36A1 are the principal enzymes responsible for the metabolism of tolbutamide in C. elegans. These are related to the mammalian enzymes that metabolise this compound but are not the closest homologs suggesting that sequence comparison alone will not predict functional conservation among cytochrome P450s. In mammals, metabolite production from amytryptiline and dextromethorphan is dependent on specific cytochrome P450s. However, in C. elegans we did not find evidence of similar specificity: the same metabolites were produced but in small amounts by numerous cytochrome P450s. We conclude that, while some aspects of cytochrome P450 mediated metabolism in C. elegans are similar to mammals, there are differences in the production of some metabolites and in the underlying genetics of metabolism.
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http://dx.doi.org/10.1038/s41598-018-31215-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6127299PMC
September 2018

Discovery and structure-activity relationships of a series of pyroglutamic acid amide antagonists of the P2X7 receptor.

Bioorg Med Chem Lett 2010 Sep 14;20(17):5080-4. Epub 2010 Jul 14.

Neurosciences Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park, Harlow, Essex, UK.

A computational lead-hopping exercise identified compound 4 as a structurally distinct P2X(7) receptor antagonist. Structure-activity relationships (SAR) of a series of pyroglutamic acid amide analogues of 4 were investigated and compound 31 was identified as a potent P2X(7) antagonist with excellent in vivo activity in animal models of pain, and a profile suitable for progression to clinical studies.
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http://dx.doi.org/10.1016/j.bmcl.2010.07.033DOI Listing
September 2010

Structure-activity relationships and in vivo activity of (1H-pyrazol-4-yl)acetamide antagonists of the P2X(7) receptor.

Bioorg Med Chem Lett 2010 Aug 8;20(15):4653-6. Epub 2010 Jun 8.

Neurosciences Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park, Harlow, Essex CM19 5AW, UK.

Structure-activity relationships (SAR) of analogues of lead compound 1 were investigated and compound 16 was selected for further study in animal models of pain. Compound 16 was shown to be a potent antihyperalgesic agent in both the rat acute complete Freund's adjuvant (CFA) model of inflammatory pain [Iadarola, M. J.; Douglass, J.; Civelli, O.; Naranjo, J. R. rain Res.1988, 455, 205] and the knee joint model of chronic inflammatory pain [Wilson, A. W.; Medhurst, S. J.; Dixon, C. I.; Bontoft, N. C.; Winyard, L. A.; Brackenborough, K. T.; De Alba, J.; Clarke, C. J.; Gunthorpe, M. J.; Hicks, G. A.; Bountra, C.; McQueen, D. S.; Chessell, I. P. Eur. J. Pain2006, 10, 537].
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http://dx.doi.org/10.1016/j.bmcl.2010.05.107DOI Listing
August 2010

Synthesis and structure-activity relationships of a series of (1H-pyrazol-4-yl)acetamide antagonists of the P2X7 receptor.

Bioorg Med Chem Lett 2010 May 30;20(10):3161-4. Epub 2010 Mar 30.

Neurosciences Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park, Harlow, Essex, CM19 5AW, United Kingdom.

High-throughput screening identified compound 1 as a potent P2X(7) receptor antagonist suitable for lead optimisation. Structure-activity relationships (SAR) of a series of (1H-pyrazol-4-yl)acetamides were investigated and compound 32 was identified as a potent P2X(7) antagonist with enhanced potency and favourable physicochemical and pharmacokinetic properties.
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http://dx.doi.org/10.1016/j.bmcl.2010.03.096DOI Listing
May 2010

The discovery and optimisation of benzazepine sulfonamide and sulfones as potent agonists of the motilin receptor.

Bioorg Med Chem Lett 2009 Nov 12;19(22):6452-8. Epub 2009 Sep 12.

Immuno-Inflammation Centre of Excellence for Drug Discovery, GlaxoSmithKline, Medicines Research Centre, Gunnels Wood Road, Stevenage, Herts SG12NY, UK.

Optimisation of a series of benzazepine sulfonamide hit compounds identified from high throughput screening led to the discovery of a new series of tractable, potent motilin receptor agonists.
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http://dx.doi.org/10.1016/j.bmcl.2009.09.027DOI Listing
November 2009

Identification of [4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)-2-pyrimidinyl] amines and ethers as potent and selective cyclooxygenase-2 inhibitors.

Bioorg Med Chem Lett 2009 Aug 26;19(15):4504-8. Epub 2009 Feb 26.

Pain and Neuroexcitability Discovery Performance Unit, Neurosciences Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK.

A novel series of [4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)-2-pyrimidine-based cyclooxygenase-2 (COX-2) inhibitors, which have a different arrangement of substituents compared to the more common 1,2-diarylheterocycle based molecules, have been discovered. For example, 2-(butyloxy)-4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)pyrimidine (47), a member of the 2-pyrimidinyl ether series, has been shown to be a potent and selective inhibitor with a favourable pharmacokinetic profile, high brain penetration and good efficacy in rat models of hypersensitivity.
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http://dx.doi.org/10.1016/j.bmcl.2009.02.085DOI Listing
August 2009

Discovery of N-(3-fluorophenyl)-1-[(4-([(3S)-3-methyl-1-piperazinyl]methyl)phenyl)acetyl]-4-piperidinamine (GSK962040), the first small molecule motilin receptor agonist clinical candidate.

J Med Chem 2009 Feb;52(4):1180-9

Immuno-Inflammation Centre of Excellence for Drug Discovery, GlaxoSmithKline, Medicines Research Centre, Gunnels Wood Road, Stevenage, Herts, SG1 2NY, UK.

N-(3-fluorophenyl)-1-[(4-([(3S)-3-methyl-1-piperazinyl]methyl)phenyl)acetyl]-4-piperidinamine 12 (GSK962040) is a novel small molecule motilin receptor agonist. It possesses excellent activity at the recombinant human motilin receptor and also at the native rabbit motilin receptor where its agonist activity results in potentiation of the amplitude of neuronal-mediated contractions of isolated gastric antrum tissue. Compound 12 also possesses highly promising pharmacokinetic profiles in both rat and dog, and these results, in combination with further profiling in human native tissue and an in vivo model of gastrointestinal transit in the rabbit, have led to its selection as a candidate for further development.
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http://dx.doi.org/10.1021/jm801332qDOI Listing
February 2009

The discovery of biaryl carboxamides as novel small molecule agonists of the motilin receptor.

Bioorg Med Chem Lett 2008 Dec 19;18(24):6429-36. Epub 2008 Oct 19.

Immuno-Inflammation Centre of Excellence for Drug Discovery, GlaxoSmithKline, Medicines Research Centre, Gunnels Wood Road, Stevenage, Herts SG1 2NY, UK.

Optimisation of urea (5), identified from high throughput screening and subsequent array chemistry, has resulted in the identification of pyridine carboxamide (33) which is a potent motilin receptor agonist possessing favourable physicochemical and ADME profiles. Compound (33) has demonstrated prokinetic-like activity both in vitro and in vivo in the rabbit and therefore represents a promising novel small molecule motilin receptor agonist for further evaluation as a gastroprokinetic agent.
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http://dx.doi.org/10.1016/j.bmcl.2008.10.072DOI Listing
December 2008

Design and synthesis of 6-phenylnicotinamide derivatives as antagonists of TRPV1.

Bioorg Med Chem Lett 2008 Oct 31;18(20):5609-13. Epub 2008 Aug 31.

Neurology CEDD, GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK.

6-Phenylnicotinamide (2) was previously identified as a potent TRPV1 antagonist with activity in an in vivo model of inflammatory pain. Optimization of this lead through modification of both the biaryl and heteroaryl components has resulted in the discovery of 6-(4-fluorophenyl)-2-methyl-N-(2-methylbenzothiazol-5-yl)nicotinamide (32; SB-782443) which possesses an excellent overall profile and has been progressed into pre-clinical development.
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http://dx.doi.org/10.1016/j.bmcl.2008.08.105DOI Listing
October 2008

N-Tetrahydroquinolinyl, N-quinolinyl and N-isoquinolinyl biaryl carboxamides as antagonists of TRPV1.

Bioorg Med Chem Lett 2006 Sep 27;16(17):4533-6. Epub 2006 Jun 27.

Neurology and GI Center of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park, Harlow, Essex, UK.

Starting from the high throughput screening hit (3), novel N-tetrahydroquinolinyl, N-quinolinyl and N-isoquinolinyl carboxamides have been identified as potent antagonists of the ion channel TRPV1. The N-quinolinylnicotinamide (46) showed excellent potency at human, guinea pig and rat TRPV1, a favourable in vitro DMPK profile and activity in an in vivo model of inflammatory pain.
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http://dx.doi.org/10.1016/j.bmcl.2006.06.026DOI Listing
September 2006

Discovery of SB-705498: a potent, selective and orally bioavailable TRPV1 antagonist suitable for clinical development.

Bioorg Med Chem Lett 2006 Jun 31;16(12):3287-91. Epub 2006 Mar 31.

Neurology and GI CEDD, New Frontiers Science Park, GlaxoSmithKline, Third Avenue, Harlow, Essex CM19 5AW, UK.

Small molecule antagonists of the vanilloid receptor TRPV1 (also known as VR1) are disclosed. Pyrrolidinyl ureas such as 8 and 15 (SB-705498) emerged as lead compounds following optimisation of the previously described urea SB-452533. Pharmacological studies using electrophysiological and FLIPR-Ca2+-based assays showed that compounds such as 8 and 15 were potent antagonists versus the multiple chemical and physical modes of TRPV1 activation (namely capsaicin, acid and noxious heat). Furthermore, 15 possessed suitable developability properties to enable progression of this compound into in vivo studies and subsequently clinical development.
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http://dx.doi.org/10.1016/j.bmcl.2006.03.030DOI Listing
June 2006

Improving the in vitro prediction of in vivo central nervous system penetration: integrating permeability, P-glycoprotein efflux, and free fractions in blood and brain.

J Pharmacol Exp Ther 2006 Mar 5;316(3):1282-90. Epub 2005 Dec 5.

Drug Metabolism and Pharmacokinetics Department, Neurology, and Gastrointestinal Centre of Excellence for Drug Discovery, GlaxoSmithKline R&D, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK.

This work examines the inter-relationship between the unbound drug fractions in blood and brain homogenate, passive membrane permeability, P-glycoprotein (Pgp) efflux ratio, and log octanol/water partition coefficients (cLogP) in determining the extent of central nervous system (CNS) penetration observed in vivo. The present results demonstrate that compounds often considered to be Pgp substrates in rodents (efflux ratio greater than 5 in multidrug resistant Madin-Darby canine kidney cells) with poor passive permeability may still exhibit reasonable CNS penetration in vivo; i.e., where the unbound fractions and nonspecific tissue binding act as a compensating force. In these instances, the efflux ratio and in vitro blood-brain partition ratio may be used to predict the in vivo blood-brain ratio. This relationship may be extended to account for the differences in CNS penetration observed in vivo between mdr1a/b wild type and knockout mice. In some instances, cross-species differences that might initially seem to be related to differing transporter expression can be rationalized from knowledge of unbound fractions alone. The results presented in this article suggest that the information exists to provide a coherent picture of the nature of CNS penetration in the drug discovery setting, allowing the focus to be shifted away from understanding CNS penetration toward the more important aspect of understanding CNS efficacy.
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http://dx.doi.org/10.1124/jpet.105.092916DOI Listing
March 2006

Discovery of small molecule antagonists of TRPV1.

Bioorg Med Chem Lett 2004 Jul;14(14):3631-4

Neurology and GI CEDD, New Frontiers Science Park, GlaxoSmithKline, Third Avenue, Harlow, Essex CM19 5AW, UK.

Small molecule antagonists of the vanilloid receptor 1 (TRPV1, also known as VR1) are disclosed. Ureas such as 5 (SB-452533) were used to explore the structure activity relationship with several potent analogues identified. Pharmacological studies using electrophysiological and FLIPR Ca(2+) based assays showed compound 5 was an antagonist versus capsaicin, noxious heat and acid mediated activation of TRPV1. Study of a quaternary salt of 5 supports a mode of action in which compounds from this series cause inhibition via an extracellularly accessible binding site on the TRPV1 receptor.
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http://dx.doi.org/10.1016/j.bmcl.2004.05.028DOI Listing
July 2004

SB-656104-A, a novel selective 5-HT7 receptor antagonist, modulates REM sleep in rats.

Br J Pharmacol 2003 Jun;139(4):705-14

Psychiatry Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park (North), Harlow, Essex.

1 (6-((R)-2-[2-[4-(4-Chloro-phenoxy)-piperidin-1-yl]-ethyl]-pyrrolidine-1-sulphonyl)-1H-indole hydrochloride) (SB-656104-A), a novel 5-hydroxytryptamine (5-HT(7)) receptor antagonist, potently inhibited [(3)H]-SB-269970 binding to the human cloned 5-HT(7(a)) (pK(i) 8.7+/-0.1) and 5-HT(7(b)) (pK(i) 8.5+/-0.2) receptor variants and the rat native receptor (pK(i) 8.8+/-0.2). The compound displayed at least 30-fold selectivity for the human 5-HT(7(a)) receptor versus other human cloned 5-HT receptors apart from the 5-HT(1D) receptor ( approximately 10-fold selective). 2 SB-656104-A antagonised competitively the 5-carboxamidotryptamine (5-CT)-induced accumulation of cyclic AMP in h5-HT(7(a))/HEK293 cells with a pA(2) of 8.5. 3 Following a constant rate iv infusion to steady state in rats, SB-656104 had a blood clearance (CL(b)) of 58+/-6 ml min(-1) kg(-1) and was CNS penetrant with a steady-state brain : blood ratio of 0.9 : 1. Following i.p. administration to rats (10 mg kg(-1)), the compound displayed a t(1/2) of 1.4 h with mean brain and blood concentrations (at 1 h after dosing) of 0.80 and 1.0 micro M, respectively. 4 SB-656104-A produced a significant reversal of the 5-CT-induced hypothermic effect in guinea pigs, a pharmacodynamic model of 5-HT(7) receptor interaction in vivo (ED(50) 2 mg kg(-1)). 5 SB-656104-A, administered to rats at the beginning of the sleep period (CT 0), significantly increased the latency to onset of rapid eye movement (REM) sleep at 30 mg kg(-1) i.p. (+93%) and reduced the total amount of REM sleep at 10 and 30 mg kg(-1) i.p. with no significant effect on the latency to, or amount of, non-REM sleep. SB-269970-A produced qualitatively similar effects in the same study. 6 In summary, SB-656104-A is a novel 5-HT(7) receptor antagonist which has been utilised in the present study to provide further evidence for a role for 5-HT(7) receptors in the modulation of REM sleep.
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http://dx.doi.org/10.1038/sj.bjp.0705290DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1573887PMC
June 2003

SB-656104-A: a novel 5-HT(7) receptor antagonist with improved in vivo properties.

Bioorg Med Chem Lett 2002 Nov;12(22):3341-4

GlaxoSmithKline, New Frontiers Science Park, Harlow, Essex, UK.

A focused SAR study around the previously reported selective 5-HT(7) receptor antagonist, SB-269970-A has resulted in the identification of a structurally related analogue having an improved pharmacokinetic profile. Replacement of the phenolic group in SB-269970-A with an indole moiety, and replacement of the piperidinyl 4-methyl group with a heterocyclic ring system proved to be the key changes leading to the identification of SB-656104-A.
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http://dx.doi.org/10.1016/s0960-894x(02)00690-xDOI Listing
November 2002