ABSTRACT
The resistance of methicillin-resistant Staphylococcus aureus (MRSA) to all ß-lactam classes limits treatment options for serious infections involving this organism. Our goal is to discover new agents that restore the activity of ß-lactams against MRSA, an approach that has led to the discovery of two classes of natural product antibiotics, a cyclic depsipeptide (krisynomycin) and a lipoglycopeptide (actinocarbasin), which potentiate the activity of imipenem against MRSA strain COL. We report here that these imipenem synergists are inhibitors of the bacterial type I signal peptidase SpsB, a serine protease that is required for the secretion of proteins that are exported through the Sec and Tat systems. A synthetic derivative of actinocarbasin, M131, synergized with imipenem both in vitro and in vivo with potent efficacy. The in vitro activity of M131 extends to clinical isolates of MRSA but not to a methicillin-sensitive strain. Synergy is restricted to ß-lactam antibiotics and is not observed with other antibiotic classes. We propose that the SpsB inhibitors synergize with ß-lactams by preventing the signal peptidase-mediated secretion of proteins required for ß-lactam resistance. Combinations of SpsB inhibitors and ß-lactams may expand the utility of these widely prescribed antibiotics to treat MRSA infections, analogous to ß-lactamase inhibitors which restored the utility of this antibiotic class for the treatment of resistant Gram-negative infections.
Subject(s)
Anti-Bacterial Agents/pharmacology , Bacterial Proteins/antagonists & inhibitors , Biphenyl Compounds/pharmacology , Depsipeptides/pharmacology , Glycopeptides/pharmacology , Glycosides/pharmacology , Lipopeptides/pharmacology , Membrane Proteins/antagonists & inhibitors , Methicillin-Resistant Staphylococcus aureus/drug effects , Oligopeptides/pharmacology , Staphylococcal Infections/drug therapy , beta-Lactams/pharmacology , Animals , Anti-Bacterial Agents/isolation & purification , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Biological Transport , Biphenyl Compounds/chemical synthesis , Depsipeptides/isolation & purification , Drug Synergism , Drug Therapy, Combination , Female , Glycopeptides/chemical synthesis , Glycopeptides/isolation & purification , Glycosides/isolation & purification , Humans , Lipopeptides/isolation & purification , Membrane Proteins/genetics , Membrane Proteins/metabolism , Methicillin-Resistant Staphylococcus aureus/genetics , Methicillin-Resistant Staphylococcus aureus/growth & development , Mice , Mice, Inbred BALB C , Microbial Sensitivity Tests , Multigene Family , Oligopeptides/chemical synthesis , Serine Endopeptidases/genetics , Serine Endopeptidases/metabolism , Staphylococcal Infections/microbiology , beta-Lactam Resistance/drug effects , beta-Lactam Resistance/genetics , beta-Lactamases/genetics , beta-Lactamases/metabolismABSTRACT
Novel water-soluble amide analogs were synthesized from nocathiacin I (1) through the formation of the carboxylic acid intermediate followed by coupling to primary or secondary amines. Several compounds with potent antibacterial activity and adequate water solubility were identified. Of these, compound 19 was selected for more extensive evaluation because of its excellent in vitro antibacterial activity and in vivo efficacy, as well as clean off-target screening.
Subject(s)
Amides/chemistry , Anti-Bacterial Agents/chemical synthesis , Peptides/chemistry , Piperazines/chemical synthesis , Amides/chemical synthesis , Animals , Anti-Bacterial Agents/chemistry , Anti-Bacterial Agents/pharmacology , Intercellular Signaling Peptides and Proteins , Mice , Microbial Sensitivity Tests , Piperazines/chemistry , Piperazines/pharmacokinetics , Solubility , Structure-Activity Relationship , Water/chemistryABSTRACT
Parasite cGMP-dependent protein kinase (PKG) is one of the validated biochemical targets for the treatment of coccidiosis. We screened our library of natural product extracts for inhibitors of parasite PKG for the discovery of anticoccidial leads. Terferol (1) and three new terphenyls (2, 3, and 4) were isolated using bioassay-guided fractionation of the microbial extract of a Phoma sp. by a high-throughput two-step isolation method employing LH-20 and reversed-phase HPLC. These compounds inhibited parasite PKG with IC(50) values in the range 0.9-5.8 microM.
Subject(s)
Ascomycota/chemistry , Coccidiosis/drug therapy , Cyclic GMP-Dependent Protein Kinases/antagonists & inhibitors , Eimeria tenella/drug effects , Enzyme Inhibitors , Terphenyl Compounds , Animals , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/isolation & purification , Enzyme Inhibitors/pharmacology , France , Molecular Structure , Terphenyl Compounds/chemistry , Terphenyl Compounds/isolation & purification , Terphenyl Compounds/pharmacologyABSTRACT
Compounds 10a (IC50 110 pM) and 21 (IC50 40 pM) are the most potent inhibitors of Eimeria tenella cGMP-dependent protein kinase activity reported to date and are efficacious in the in vivo antiparasitic assay when administered to chickens at 12.5 and 6.25 ppm levels in the feed. However, both compounds are positive in the Ames microbial mutagenesis assay which precludes them from further development as antiprotozoal agents in the absence of negative lifetime rodent carcinogenicity studies.
Subject(s)
Antiprotozoal Agents/chemical synthesis , Cyclic GMP-Dependent Protein Kinases/antagonists & inhibitors , Eimeria tenella/drug effects , Enzyme Inhibitors/chemical synthesis , Imidazoles/chemical synthesis , Pyridines/chemical synthesis , Animal Feed , Animals , Antiprotozoal Agents/chemistry , Antiprotozoal Agents/pharmacology , Chickens , Coccidiosis/drug therapy , Eimeria tenella/enzymology , Enzyme Inhibitors/chemistry , Enzyme Inhibitors/pharmacology , Imidazoles/chemistry , Imidazoles/pharmacology , Male , Molecular Structure , Mutagenicity Tests , Oocysts/drug effects , Parasitic Sensitivity Tests , Pyridines/chemistry , Pyridines/pharmacology , Rats , Rats, Sprague-Dawley , Stereoisomerism , Structure-Activity RelationshipABSTRACT
Parasite cGMP-dependent protein kinase (PKG) has been recently validated as a biochemical target for the treatment of coccidiosis. To discover new anticoccidial leads, we have screened our library of natural product extracts for inhibitors of parasite PKG. Bioassay-guided fractionation of the microbial extracts has led to the discovery of tenellones A (2) and B (3), two new highly substituted benzophenones. The isolation, structure, and activity of these compounds are described.
