The increasing prevalence of serious infections caused by gram-positive bacteria, including those caused by methicillin (meticillin)-resistant Staphylococcus aureus (MRSA), highlights the need for new agents with enhanced antimicrobial properties (2,10,21,26,35). One promising approach has been the development of lipoglycopeptide antibiotics, semisynthetic derivatives of glycopeptides that contain hydrophobic substituents and that possess improved antimicrobial properties (1,4,13,32,39). Telavancin, a lipoglycopeptide derivative of vancomycin, exhibits enhanced potency in vitro, concentration-dependent bactericidal activity, and activity both in vitro and in vivo against organisms that display reduced susceptibility to vancomycin (17,18,23,24,28,31,33,36,42). Telavancin has been evaluated in phase III clinical trials for the treatment of complicated skin and skin structure infections and hospitalacquired pneumonia (46,53).The bactericidal action of telavancin results from a mechanism that includes the inhibition of cell wall synthesis and the disruption of essential membrane barrier functions (25). Telavancin possesses the glycopeptide core of vancomycin, which binds with a high affinity to the acyl-D-alanyl-D-alanine (DAla-D-Ala) terminus of cell wall precursors through a network of hydrogen bonds and hydrophobic packing interactions (3, 45). Inhibition of cell wall synthesis by telavancin therefore involves binding to late-stage peptidoglycan precursors, including membrane-embedded lipid II. These interactions prevent both the polymerization of the precursor into peptidoglycan and subsequent cross-linking events. Telavancin also binds to bacterial membranes and causes membrane depolarization and increased membrane permeability. The mechanism by which telavancin binds to and disrupts the function of the bacterial membrane has not been determined.The present study was undertaken to further explore the interaction of telavancin with the bacterial membrane. Using a flow cytometry assay optimized for the accurate measurement of membrane potential in bacteria, we demonstrate that telavancin causes pronounced, concentration-dependent depolarization in S. aureus cells. Isolates of S. aureus expressing important and emerging resistance phenotypes, such as MRSA, heterogeneous vancomycin-intermediate S. aureus (hVISA), vancomycin-intermediate S. aureus (VISA), and daptomycinnonsusceptibile MRSA, are equally susceptible to depolarization by telavancin. We provide evidence, through multiple lines of investigation, that membrane disruption by telavancin requires binding to the bacterial specific target, lipid II. Finally, we demonstrate that telavancin does not lyse bacteria during the time course that membrane effects are assayed. Importantly, the latter observation indicates that telavancin-induced membrane depolarization is not a consequence of a weakened * Corresponding author. Mailing address:

Remarkable selectivity enhancements of exceptionally small inhibitors are achieved toward the uPA target over the highly similar tPA anti-target through a single atom substitution on an otherwise relatively non-selective scaffold. Overall selectivities for uPA over tPA as high as 980-fold at physiological pH were realized. The increase in selectivity results from the displacement of a single bound water molecule common to the S1 site of both the uPA target and the tPA anti-target because of the ensuing deficit in hydrogen bonding of the arylamidine inhibitor when bound in the Ala190 protease anti-target.

The monocyclic beta-lactam antibiotic nocardicin A is related structurally and biologically to the bicyclic beta-lactams comprised of penicillins/cephalosporins, clavams, and carbapenems. Biosynthetic gene clusters are known for each of the latter, but not for monocyclic beta-lactams. A previously cloned gene encoding an enzyme specific to the biosynthetic pathway was used to isolate the nocardicin A cluster from Nocardia uniformis. Sequence analysis revealed the presence of 14 open reading frames involved in antibiotic production, resistance, and export. Among these are a two-protein nonribosomal peptide synthetase system, p-hydroxyphenylglycine biosynthetic genes, an S-adenosylmethionine-dependent 3-amino-3-carboxypropyl transferase (Nat), and a cytochrome P450. Gene disruption mutants of Nat, as well as an activation domain of the NRPS system, led to loss of nocardicin A formation. Several enzymes involved in antibiotic biosynthesis were heterologously overproduced, and biochemical characterization confirmed their proposed activities.

No abstract

We have prepared a series of achiral aminoacetonitriles, bearing tri-ring benzamide moieties and an aminocyclohexanecarboxylate residue at P2. This combination of binding elements resulted in sub-250 pM, reversible, selective, and orally bioavailable cathepsin K inhibitors. Lead compounds displayed single digit nanomolar inhibition in vitro (of rabbit osteoclast-mediated degradation of bovine bone). The best compound in this series, 39n (CRA-013783/L-006235), was orally bioavailable in rats, with a terminal half-life of over 3 h. 39n was dosed orally in ovariectomized rhesus monkeys once per day for 7 days. Collagen breakdown products were reduced by up to 76% dose-dependently. Plasma concentrations of 39n above the bone resorption IC50 after 24 h indicated a correlation between functional cellular and in vivo assays. Inhibition of collagen breakdown by cathepsin K inhibitors suggests this mechanism of action may be useful in osteoporosis and other indications involving bone resorption.