ABSTRACT
New drugs with novel mechanisms of resistance are desperately needed to address both community and nosocomial infections due to Gram-negative bacteria. One such potential target is LpxC, an essential enzyme that catalyzes the first committed step of lipid A biosynthesis. Achaogen conducted an extensive research campaign to discover novel LpxC inhibitors with activity against Pseudomonas aeruginosa We report here the in vitro antibacterial activity and pharmacodynamics of ACHN-975, the only molecule from these efforts and the first ever LpxC inhibitor to be evaluated in phase 1 clinical trials. In addition, we describe the profiles of three additional LpxC inhibitors that were identified as potential lead molecules. These efforts did not produce an additional development candidate with a sufficiently large therapeutic window and the program was subsequently terminated.
Subject(s)
Anti-Bacterial Agents/pharmacology , Bacterial Proteins/antagonists & inhibitors , Drug Resistance, Multiple, Bacterial/drug effects , Enzyme Inhibitors/pharmacology , Pseudomonas aeruginosa/drug effects , Catalysis/drug effects , Humans , Pseudomonas aeruginosa/metabolismABSTRACT
UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a Zn2+ deacetylase that is essential for the survival of most pathogenic Gram-negative bacteria. ACHN-975 (N-((S)-3-amino-1-(hydroxyamino)-3-methyl-1-oxobutan-2-yl)-4-(((1R,2R)-2-(hydroxymethyl)cyclopropyl)buta-1,3-diyn-1-yl)benzamide) was the first LpxC inhibitor to reach human clinical testing and was discovered to have a dose-limiting cardiovascular toxicity of transient hypotension without compensatory tachycardia. Herein we report the effort beyond ACHN-975 to discover LpxC inhibitors optimized for enzyme potency, antibacterial activity, pharmacokinetics, and cardiovascular safety. Based on its overall profile, compound 26 (LPXC-516, (S)-N-(2-(hydroxyamino)-1-(3-methoxy-1,1-dioxidothietan-3-yl)-2-oxoethyl)-4-(6-hydroxyhexa-1,3-diyn-1-yl)benzamide) was chosen for further development. A phosphate prodrug of 26 was developed that provided a solubility of >30â mg mL-1 for parenteral administration and conversion into the active drug with a t1/2 of approximately two minutes. Unexpectedly, and despite our optimization efforts, the prodrug of 26 still possesses a therapeutic window insufficient to support further clinical development.
Subject(s)
Amidohydrolases/antagonists & inhibitors , Anti-Bacterial Agents/pharmacology , Diynes/pharmacology , Enzyme Inhibitors/pharmacology , Heart/drug effects , Hydroxamic Acids/pharmacology , Animals , Anti-Bacterial Agents/chemical synthesis , Anti-Bacterial Agents/pharmacokinetics , Anti-Bacterial Agents/toxicity , Bacterial Proteins/antagonists & inhibitors , Cardiotoxicity , Diynes/chemical synthesis , Diynes/pharmacokinetics , Diynes/toxicity , Enzyme Inhibitors/chemical synthesis , Enzyme Inhibitors/pharmacokinetics , Enzyme Inhibitors/toxicity , Hydroxamic Acids/chemical synthesis , Hydroxamic Acids/pharmacokinetics , Hydroxamic Acids/toxicity , Male , Molecular Structure , Prodrugs/chemical synthesis , Prodrugs/pharmacokinetics , Prodrugs/pharmacology , Prodrugs/toxicity , Pseudomonas aeruginosa/drug effects , Rats, Sprague-Dawley , Structure-Activity RelationshipABSTRACT
A major challenge for new antibiotic discovery is predicting the physicochemical properties that enable small molecules to permeate Gram-negative bacterial membranes. We have applied physicochemical lessons from previous work to redesign and improve the antibacterial potency of pyridopyrimidine inhibitors of biotin carboxylase (BC) by up to 64-fold and 16-fold against Escherichia coli and Pseudomonas aeruginosa, respectively. Antibacterial and enzyme potency assessments in the presence of an outer membrane-permeabilizing agent or in efflux-compromised strains indicate that penetration and efflux properties of many redesigned BC inhibitors could be improved to various extents. Spontaneous resistance to the improved pyridopyrimidine inhibitors in P. aeruginosa occurs at very low frequencies between 10-8 and 10-9. However, resistant isolates had alarmingly high minimum inhibitory concentration shifts (16- to >128-fold) compared to the parent strain. Whole-genome sequencing of resistant isolates revealed that either BC target mutations or efflux pump overexpression can lead to the development of high-level resistance.
Subject(s)
Anti-Bacterial Agents/pharmacology , Bacterial Proteins/antagonists & inhibitors , Carbon-Nitrogen Ligases/antagonists & inhibitors , Escherichia coli/drug effects , Pseudomonas aeruginosa/drug effects , Anti-Bacterial Agents/chemical synthesis , Anti-Bacterial Agents/chemistry , Bacterial Outer Membrane/drug effects , Bacterial Outer Membrane/metabolism , Bacterial Proteins/genetics , Bacterial Proteins/metabolism , Carbon-Nitrogen Ligases/genetics , Carbon-Nitrogen Ligases/metabolism , Chemical Phenomena , Drug Resistance, Multiple, Bacterial/drug effects , Drug Resistance, Multiple, Bacterial/genetics , Escherichia coli/enzymology , Escherichia coli/genetics , Microbial Sensitivity Tests , Models, Chemical , Molecular Structure , Mutation , Pseudomonas aeruginosa/enzymology , Pseudomonas aeruginosa/geneticsABSTRACT
Intracellular pathogens subvert the host cell cytoskeleton to promote their own survival, replication, and dissemination. Study of these microbes has led to many discoveries about host cell biology, including the identification of cytoskeletal proteins, regulatory pathways, and mechanisms of cytoskeletal function. Actin is a common target of bacterial pathogens, but recent work also highlights the use of microtubules, cytoskeletal motors, intermediate filaments, and septins. The study of pathogen interactions with the cytoskeleton has illuminated key cellular processes such as phagocytosis, macropinocytosis, membrane trafficking, motility, autophagy, and signal transduction.
Subject(s)
Bacteria/metabolism , Bacterial Infections/metabolism , Bacterial Physiological Phenomena , Cytoskeleton/metabolism , Host-Pathogen Interactions/physiology , Animals , Autophagy/physiology , Biological Transport, Active/physiology , Cell Membrane/metabolism , Cell Membrane/microbiology , Cell Movement/physiology , Cytoskeleton/microbiology , Humans , Phagocytosis/physiology , Signal Transduction/physiologyABSTRACT
Diverse intracellular pathogens subvert the host actin-polymerization machinery to drive movement within and between cells during infection. Rickettsia in the spotted fever group (SFG) are Gram-negative, obligate intracellular bacterial pathogens that undergo actin-based motility and assemble distinctive 'comet tails' that consist of long, unbranched actin filaments. Despite this distinct organization, it was proposed that actin in Rickettsia comet tails is nucleated by the host Arp2/3 complex and the bacterial protein RickA, which assemble branched actin networks. However, a second bacterial gene, sca2, was recently implicated in actin-tail formation by R. rickettsii. Here, we demonstrate that Sca2 is a bacterial actin-assembly factor that functionally mimics eukaryotic formin proteins. Sca2 nucleates unbranched actin filaments, processively associates with growing barbed ends, requires profilin for efficient elongation, and inhibits the activity of capping protein, all properties shared with formins. Sca2 localizes to the Rickettsia surface and is sufficient to promote the assembly of actin filaments in cytoplasmic extract. These results suggest that Sca2 mimics formins to determine the unique organization of actin filaments in Rickettsia tails and drive bacterial motility, independently of host nucleators.
Subject(s)
Actins/metabolism , Bacterial Proteins/metabolism , Rickettsia/metabolism , MovementABSTRACT
Many Rickettsia species are intracellular bacterial pathogens that use actin-based motility for spread during infection. However, while other bacteria assemble actin tails consisting of branched networks, Rickettsia assemble long parallel actin bundles, suggesting the use of a distinct mechanism for exploiting actin. To identify the underlying mechanisms and host factors involved in Rickettsia parkeri actin-based motility, we performed an RNAi screen targeting 115 actin cytoskeletal genes in Drosophila cells. The screen delineated a set of four core proteins-profilin, fimbrin/T-plastin, capping protein, and cofilin--as crucial for determining actin tail length, organizing filament architecture, and enabling motility. In mammalian cells, these proteins were localized throughout R. parkeri tails, consistent with a role in motility. Profilin and fimbrin/T-plastin were critical for the motility of R. parkeri but not Listeria monocytogenes. Our results highlight key distinctions between the evolutionary strategies and molecular mechanisms employed by bacterial pathogens to assemble and organize actin.
Subject(s)
Actin Capping Proteins/metabolism , Actin Depolymerizing Factors/metabolism , Membrane Glycoproteins/metabolism , Microfilament Proteins/metabolism , Motion , Profilins/metabolism , Rickettsia/pathogenicity , Actin Capping Proteins/antagonists & inhibitors , Actin Capping Proteins/genetics , Actin Depolymerizing Factors/antagonists & inhibitors , Actin Depolymerizing Factors/genetics , Animals , Cell Line , Chlorocebus aethiops , Drosophila , Gene Silencing , Membrane Glycoproteins/antagonists & inhibitors , Membrane Glycoproteins/genetics , Microfilament Proteins/antagonists & inhibitors , Microfilament Proteins/genetics , Models, Biological , Profilins/antagonists & inhibitors , Profilins/genetics , RNA, Small Interfering/genetics , RNA, Small Interfering/metabolismABSTRACT
The unicellular green alga Chlamydomonas reinhardtii is a widely used model organism for studies of oxygenic photosynthesis in eukaryotes. Here we describe the development of a resource for functional genomics of photosynthesis using insertional mutagenesis of the Chlamydomonas nuclear genome. Chlamydomonas cells were transformed with either of two plasmids conferring zeocin resistance, and insertional mutants were selected in the dark on acetate-containing medium to recover light-sensitive and nonphotosynthetic mutants. The population of insertional mutants was subjected to a battery of primary and secondary phenotypic screens to identify photosynthesis-related mutants that were pigment deficient, light sensitive, nonphotosynthetic, or hypersensitive to reactive oxygen species. Approximately 9% of the insertional mutants exhibited 1 or more of these phenotypes. Molecular analysis showed that each mutant line contains an average of 1.4 insertions, and genetic analysis indicated that approximately 50% of the mutations are tagged by the transforming DNA. Flanking DNA was isolated from the mutants, and sequence data for the insertion sites in 50 mutants are presented and discussed.