pyrimidinones and Helicobacter-Infections

Two independent series of inhibitors of Helicobacter pylori glutamate racemase (MurI) were characterized for their kinetic mechanism, and one was used to generate resistant mutants in vitro. Mutant MurI enzymes from these strains were characterized by structural, genetic, kinetic and biophysical methods. Both inhibitor series, pyrazolopyrimidinediones and benzodiazepines, are uncompetitive with respect to the glutamate substrate, and the resistance mutations were found to act by reducing the affinity of MurI for substrate, thereby reducing the pool of enzyme-substrate complex available for binding inhibitor, while still allowing sufficient glutamate racemase activity for peptidoglycan construction. Uncompetitive inhibitors of a single-substrate, single-product enzyme are rare, and this work gives insight into an remarkable resistance mechanism. This article will discuss the projected clinical impact of H. pylori MurI resistance on these types of inhibitors.

Topics: Amino Acid Isomerases; Amino Acid Sequence; Anti-Bacterial Agents; Bacterial Proteins; Benzodiazepines; Binding Sites; Catalytic Domain; Cell Wall; Drug Resistance, Bacterial; Helicobacter Infections; Helicobacter pylori; Humans; Kinetics; Molecular Sequence Data; Muramidase; Mutation; Peptidoglycan; Protein Binding; Pyrimidinones; Sequence Alignment; Substrate Specificity

Structure-activity relationships are presented around a series of pyrazolopyrimidinediones that inhibit the growth of Helicobacter pylori by targeting glutamate racemase, an enzyme that provides d-glutamate for the construction of N-acetylglucosamine-N-acetylmuramic acid peptidoglycan subunits assimilated into the bacterial cell wall. Substituents on the inhibitor scaffold were varied to optimize target potency, antibacterial activity and in vivo pharmacokinetic stability. By incorporating an imidazole ring at the 7-position of scaffold, high target potency was achieved due to a hydrogen bonding network that occurs between the 3-position nitrogen atom, a bridging water molecule and the side chains Ser152 and Trp244 of the enzyme. The lipophilicity of the scaffold series proved important for expression of antibacterial activity. Clearances in vitro and in vivo were monitored to identify compounds with improved plasma stability. The basicity of the imidazole may contribute to increased aqueous solubility at lower pH allowing for improved oral bioavailability.

Topics: Administration, Oral; Amino Acid Isomerases; Animals; Anti-Bacterial Agents; Biological Availability; Helicobacter Infections; Helicobacter pylori; Humans; Imidazoles; Mice; Models, Molecular; Pyrazoles; Pyrimidinones; Structure-Activity Relationship

Topics: Breath Tests; Carbon Isotopes; False Negative Reactions; Helicobacter Infections; Helicobacter pylori; Humans; Peptic Ulcer; Proton Pump Inhibitors; Pyrimidinones; Tetrahydroisoquinolines; Urea

Revaprazan (Revanex(R)) is a novel proton pump inhibitor (PPI) that has a somewhat different effect on proton pump compared with the other PPI's, also (called as 'acid pump antagonist'). We aimed to examine the false negative rate of 13C-urea breath test (UBT) in the patients with Helicobacter pylori (H. pylori) associated peptic ulcer disease who were treated with revaprazan and evaluate the anti-urease activity of revaprazan.. Total 55 patients were enrolled in this study. They received EGD examination between January 2009 and December 2009 and diagnosed histologically as H. pylori associated peptic ulcer disease. All patients took revaprazan only. Three patients were excluded because of underlying chronic disease and inappropriate breath sampling. The remaining 52 patients had UBT at 0, 2 and 4 weeks of revaprazan use. After 2 weeks of the cessation of revaprazan, they had the fourth UBT.. At 2 and 4 weeks, the false negative rates of UBT were 5.8% and 23.1%, respectively (p=0.05). After 2 weeks of the cessation, the cases of the false negative result were five. Four out of five patients had prolonged negative results on two or three successive tests, and baseline 13C difference value did not predict the false negative results.. False negative results of UBT were common and increased with prolonged use of acid pump antagonist. As PPI, it had also anti-urease activity and most patients (47/52, 90.4%) reverted to positive results by 2 weeks after the cessation of taking the medication.

Topics: Breath Tests; Carbon Isotopes; False Negative Reactions; Female; Helicobacter Infections; Helicobacter pylori; Humans; Male; Middle Aged; Peptic Ulcer; Proton Pump Inhibitors; Pyrimidinones; Tetrahydroisoquinolines; Urea