Publications by authors named "Karen L Leach"

10 Publications

  • Page 1 of 1

Intracellular concentrations determine the cytotoxicity of adefovir, cidofovir and tenofovir.

Toxicol In Vitro 2015 Feb;29(1):251-8

Compound Safety Prediction, Pfizer Inc., Groton, CT 06340, USA.

Lack of in vitro to in vivo translation is a major challenge in safety prediction during early drug discovery.One of the most common in vitro assays to evaluate the probability of a compound to cause adverse effects is a cytotoxicity assay. Cytotoxicity of a compound is often measured by dose–response curves assuming the administered doses and intracellular exposures are equal at the time of measurement.However, this may not be true for compounds with low membrane permeability or those which are substrates for drug transporters as intracellular concentrations are determined both by passive permeability and active uptake through drug transporters. We show here that three antiviral drugs, adefovir, cidofovir and tenofovir exhibit significantly increased cytotoxicity in HEK293 cells transfected with organic anion transporter (OAT) 1 and 3 compared to a lack of cytotoxicity in HEK293 wildtype cells. A further look at the media and intracellular drug concentrations showed that 24 h after dosing, all three drugs had higher intracellular drug concentrations than that of media in the HEK-OAT1 cells whereas the intracellular drug concentrations in the wildtype cells were much lower than the administered doses. Comparing cytotoxicity IC(50) values of adefovir, cidofovir and tenofovir based on administered doses and measured intracellular concentrations in HEK-OAT1 cells revealed that intracellular drug concentrations have significant impact on calculated IC(50) values. Tenofovir showed much less intrinsic cytotoxicity than adefovir and cidofovir using intracellular concentrations rather than media concentration. Our data suggest that for low permeable drugs or drugs that are substrates for drug transporters, the choice of cellular model is critical for providing an accurate determination of cytotoxicity.
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http://dx.doi.org/10.1016/j.tiv.2014.10.019DOI Listing
February 2015

Discovery of Dap-3 polymyxin analogues for the treatment of multidrug-resistant Gram-negative nosocomial infections.

J Med Chem 2013 Jun 18;56(12):5079-93. Epub 2013 Jun 18.

Pfizer Worldwide Research & Development, Pfizer, Inc., Groton, Connecticut 06340, USA.

We report novel polymyxin analogues with improved antibacterial in vitro potency against polymyxin resistant recent clinical isolates of Acinetobacter baumannii and Pseudomonas aeruginosa . In addition, a human renal cell in vitro assay (hRPTEC) was used to inform structure-toxicity relationships and further differentiate analogues. Replacement of the Dab-3 residue with a Dap-3 in combination with a relatively polar 6-oxo-1-phenyl-1,6-dihydropyridine-3-carbonyl side chain as a fatty acyl replacement yielded analogue 5x, which demonstrated an improved in vitro antimicrobial and renal cytotoxicity profiles relative to polymyxin B (PMB). However, in vivo PK/PD comparison of 5x and PMB in a murine neutropenic thigh model against P. aeruginosa strains with matched MICs showed that 5x was inferior to PMB in vivo, suggesting a lack of improved therapeutic index in spite of apparent in vitro advantages.
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http://dx.doi.org/10.1021/jm400416uDOI Listing
June 2013

Pyridone methylsulfone hydroxamate LpxC inhibitors for the treatment of serious gram-negative infections.

J Med Chem 2012 Feb 8;55(4):1662-70. Epub 2012 Feb 8.

Worldwide Medicinal Chemistry, Pfizer Worldwide Research and Development, 445 Eastern Point Road, Groton, Connecticut 06340, United States.

The synthesis and biological activity of a new series of LpxC inhibitors represented by pyridone methylsulfone hydroxamate 2a is presented. Members of this series have improved solubility and free fraction when compared to compounds in the previously described biphenyl methylsulfone hydroxamate series, and they maintain superior Gram-negative antibacterial activity to comparator agents.
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http://dx.doi.org/10.1021/jm2014875DOI Listing
February 2012

Potent inhibitors of LpxC for the treatment of Gram-negative infections.

J Med Chem 2012 Jan 11;55(2):914-23. Epub 2012 Jan 11.

Worldwide Medicinal Chemistry, Pfizer Global Research and Development, Eastern Point Road, Groton, Connecticut 06340, United States.

In this paper, we present the synthesis and SAR as well as selectivity, pharmacokinetic, and infection model data for representative analogues of a novel series of potent antibacterial LpxC inhibitors represented by hydroxamic acid.
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http://dx.doi.org/10.1021/jm2014748DOI Listing
January 2012

Linezolid, the first oxazolidinone antibacterial agent.

Ann N Y Acad Sci 2011 Mar;1222:49-54

Pfizer Global Research and Development, Groton, Connecticut 06340, USA.

Linezolid (Zyvox) is the first member of an entirely new class of antibiotics to reach the market in over 35 years; it was approved for use in 2000. A member of the oxazolidinone class of antibiotics, linezolid is highly effective for the treatment of serious Gram-positive infections and has activity that compares favorably with vancomycin for most clinically relevant pathogens. Zyvox is approved for use against serious Gram-positive infections, including those caused by Streptococcus pneumoniae, and the very challenging methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium organisms. Zyvox inhibits bacterial protein synthesis by binding to 23S rRNA in the catalytic site of the 50S ribosome. It can be administered both orally and intravenously and has good tissue distribution. Recent results have demonstrated that oxazolidinone analogs related to linezolid are effective in treating pulmonary tuberculosis caused by resistant Mycobacterium tuberculosis in animal infection models and suggest additional new therapeutic applications for these antibiotics.
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http://dx.doi.org/10.1111/j.1749-6632.2011.05962.xDOI Listing
March 2011

A distal methyl substituent attenuates mitochondrial protein synthesis inhibition in oxazolidinone antibacterials.

Bioorg Med Chem Lett 2007 Sep 13;17(18):5036-40. Epub 2007 Jul 13.

Pfizer Global Research and Development, 34790 Ardentech Ct., Fremont, CA 94555, USA.

Oxazolidinone analogs bearing substituted piperidine or azetidine C-rings are described. Analogs with a methyl group at the 3-position of the azetidine ring or the 4-position of the piperidine ring exhibited reduced mitochondrial protein synthesis inhibition while retaining good antibacterial potency.
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http://dx.doi.org/10.1016/j.bmcl.2007.07.022DOI Listing
September 2007

The site of action of oxazolidinone antibiotics in living bacteria and in human mitochondria.

Mol Cell 2007 May;26(3):393-402

Pfizer Inc., 2800 Plymouth Road, Ann Arbor, MI 48105, USA.

The oxazolidinones are one of the newest classes of antibiotics. They inhibit bacterial growth by interfering with protein synthesis. The mechanism of oxazolidinone action and the precise location of the drug binding site in the ribosome are unknown. We used a panel of photoreactive derivatives to identify the site of action of oxazolidinones in the ribosomes of bacterial and human cells. The in vivo crosslinking data were used to model the position of the oxazolidinone molecule within its binding site in the peptidyl transferase center (PTC). Oxazolidinones interact with the A site of the bacterial ribosome where they should interfere with the placement of the aminoacyl-tRNA. In human cells, oxazolidinones were crosslinked to rRNA in the PTC of mitochondrial, but not cytoplasmic, ribosomes. Interaction of oxazolidinones with the mitochondrial ribosomes provides a structural basis for the inhibition of mitochondrial protein synthesis, which is linked to clinical side effects associated with oxazolidinone therapy.
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http://dx.doi.org/10.1016/j.molcel.2007.04.005DOI Listing
May 2007

Oxazolidinones inhibit cellular proliferation via inhibition of mitochondrial protein synthesis.

Antimicrob Agents Chemother 2005 Sep;49(9):3896-902

Department of Antibacterial Pharmacology, Pfizer, Ann Arbor, MI 48105, USA.

The oxazolidinones are a relatively new structural class of antibacterial agents that act by inhibiting bacterial protein synthesis. The oxazolidinones inhibit mitochondrial protein synthesis, as shown by [35S]methionine incorporation into intact rat heart mitochondria. Treatment of K562 human erythroleukemia cells with the oxazolidinone eperezolid resulted in a time- and concentration-dependent inhibition of cell proliferation. The cells remained viable, but an increase in doubling time was observed with eperezolid treatment. Inhibition was reversible, since washing and refeeding of cells in the absence of compound resulted in a resumption of growth. The growth-inhibitory effect of the oxazolidinones did not appear to be cell type specific, and inhibition of CHO and HEK cells also was demonstrated. Treatment of cells resulted in a decrease in mitochondrial cytochrome oxidase subunit I levels, consistent with an inhibition of mitochondrial protein synthesis. Eperezolid caused no growth inhibition of rho zero (rho0) cells, which contain no mitochondrial DNA; however, the growth of the parent 143B cells was inhibited. These results provide a direct demonstration that the inhibitory effect of eperezolid in mammalian cells is the result of mitochondrial protein synthesis inhibition.
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http://dx.doi.org/10.1128/AAC.49.9.3896-3902.2005DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1195406PMC
September 2005

3-Aminopyrazole inhibitors of CDK2/cyclin A as antitumor agents. 1. Lead finding.

J Med Chem 2004 Jun;47(13):3367-80

Chemistry Department, Pharmacia Italia, Viale Pasteur 10, 20014 Nerviano (MI), Italy.

Abnormal proliferation mediated by disruption of the normal cell cycle mechanisms is a hallmark of virtually all cancer cells. Compounds targeting complexes between cyclin-dependent kinases (CDK) and cyclins, such as CDK2/cyclin A and CDK2/cyclin E, and inhibiting their kinase activity are regarded as promising antitumor agents to complement the existing therapies. From a high-throughput screening effort, we identified a new class of CDK2/cyclin A/E inhibitors. The hit-to-lead expansion of this class is described. X-ray crystallographic data of early compounds in this series, as well as in vitro testing funneled for rapidly achieving in vivo efficacy, led to a nanomolar inhibitor of CDK2/cyclin A (N-(5-cyclopropyl-1H-pyrazol-3-yl)-2-(2-naphthyl)acetamide (41), PNU-292137, IC50 = 37 nM) with in vivo antitumor activity (TGI > 50%) in a mouse xenograft model at a dose devoid of toxic effects.
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http://dx.doi.org/10.1021/jm031145uDOI Listing
June 2004

A catch-and-release strategy for the combinatorial synthesis of 4-acylamino-1,3-thiazoles as potential CDK5 inhibitors.

Bioorg Med Chem Lett 2003 Oct;13(20):3491-5

Medicinal Chemistry Research, Pharmacia Corporation, 333 Portage St., Kalamazoo, MI 49007, USA.

Two-dimensional libraries of 4-acylamino-1,3-thiazoles 9 were prepared via Curtius rearrangement of 1,3-thiazole-4-carbonyl azides 6, trapping of the intermediate isocyanates with oxime resin, and thermal regeneration of the isocyanates from the washed resin in the presence of nucleophiles. Several compounds proved to be selective inhibitors of CDK5/p25 versus the closely homologous CDK2/cyclin A enzyme, with the best analogue (43) possessing over 100-fold selectivity.
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http://dx.doi.org/10.1016/s0960-894x(03)00726-1DOI Listing
October 2003