Joann Huber

Chemical genetic identification of peptidoglycan inhibitors potentiating carbapenem activity against methicillin-resistant Staphylococcus aureus.

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial and community-acquired pathogen for which few existing antibiotics are efficacious. Here we describe two structurally related synthetic compounds that potentiate beta-lactam activity against MRSA. Genetic studies indicate that these agents target SAV1754 based on the following observations: (i) it has a unique chemical hypersensitivity profile, (ii) overexpression or point mutations are sufficient to confer resistance, and (iii) genetic inactivation phenocopies the potentiating effect of these agents in combination with beta-lactams. Further, we demonstrate these agents inhibit peptidoglycan synthesis. Because SAV1754 is essential for growth and structurally related to the recently reported peptidoglycan flippase of Escherichia coli, we speculate it performs an analogous function in S. aureus. These results suggest that SAV1754 inhibitors might possess therapeutic potential alone, or in combination with beta-lactams to restore MRSA efficacy.

Dicationic 2-fluorenonylcarbapenems: Potent anti-MRS agents with improved solubility and pharmacokinetic properties

The synthesis and biological evaluation of a series of dicationic-substituted 2-fluorenonylcarbapenems is described. This class of compounds showed enhanced water solubility while maintaining potent activity against MRS. Introduction of a 1-beta-methyl substituent was found to improve pharmacokinetics.

Broadening the spectrum of β-lactam antibiotics through inhibition of signal peptidase type I

ABSTRACT The resistance of methicillin-resistant Staphylococcus aureus (MRSA) to all β-lactam classes limits treatment options for serious infections involving this organism. Our goal is to discover new agents that restore the activity of β-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 β-lactam antibiotics and is not observed with other antibiotic classes. We propose that the SpsB inhibitors synergize with β-lactams by preventing the signal peptidase-mediated secretion of proteins required for β-lactam resistance. Combinations of SpsB inhibitors and β-lactams may expand the utility of these widely prescribed antibiotics to treat MRSA infections, analogous to β-lactamase inhibitors which restored the utility of this antibiotic class for the treatment of resistant Gram-negative infections.

Discovery and antibacterial activity of glabramycin A–C from Neosartorya glabra by an antisense strategy

Treatment of drug-resistant bacteria is a significant unmet medical need. This challenge can be met only by the discovery and development of new antibiotics. Antisense technology is one of the newest discovery tools that provides enhanced sensitivity for detection of antibacterials, and has led to the discovery of a number of interesting new antibacterial natural products. Continued utilization of this technology led to the discovery of three new bicyclic lactones, glabramycins A–C, from a Neosartorya glabra strain. Glabramycin C showed strong antibiotic activity against Streptococcus pneumoniae (MIC 2 μg ml−1) and modest antibiotic activity against Staphylococcus aureus (MIC 16 μg ml−1). The isolation, structure, relative configuration and antibacterial activity, and plausible biogenesis of these compounds have been discussed.

Isolation, structure and antibacterial activity of pleosporone from a pleosporalean ascomycete discovered by using antisense strategy.

Protein synthesis is one of the best antibacterial targets that have led to the development of a number of highly successful clinical drugs. Protein synthesis is catalyzed by ribosome, which is comprised of a number of ribosomal proteins that help the catalysis process. Ribosomal protein S4 (RPSD) is one of the proteins that is a part of the ribosomal machinery and is a potential new target for the discovery of antibacterial agents. Screening of microbial extracts using antisense-sensitized rpsD Staphylococcus aureus strain led to the isolation of pleosporone, a new compound, with modest antibacterial activities with MIC ranging from 1 to 64 microg/mL. This compound showed the highest sensitivity for Streptococcus pneumoniae and Haemophilus influenzae, and exhibited MICs of 4 and 1 microg/mL, respectively. Pleosporone showed modest selectivity for the inhibition of RNA synthesis compared to DNA and protein synthesis, and showed activity against HeLa cells. Isolation, structure elucidation, and biological activity of pleosporone have been described.

Isolation, Structure, and Antibacterial Activity of Phaeosphenone from a Phaeosphaeria sp. Discovered by Antisense Strategy

Ribosomal protein S4 (RPSD), a part of the ribosomal small subunit, is one of the proteins that is a part of the ribosomal machinery and is a potential new target for the discovery of antibacterial agents. Continued screening of microbial extracts using antisense-sensitized rpsD Staphylococcus aureus strain led to the isolation of a new dimeric compound, phaeosphenone (2). Compound 2 showed broad-spectrum antibacterial activity against Gram-positive bacteria, exhibiting MIC values ranging from 8 to 64 microg/mL. Phaeosphenone showed the highest sensitivity for Streptococcus pneumoniae (8 microg/mL) and inhibited the growth of Candida albicans with an MIC of 8 microg/mL. Phaeosphenone showed a modest selectivity for the inhibition of RNA synthesis over DNA and protein synthesis in S. aureus.

Synthesis and properties of 2-(naphthosultamyl)methyl-carbapenems with potent anti-MRSA activity: discovery of L-786,392.

A series of 1beta-methyl-2-(naphthosultamyl)methyl-carbapenems bearing dicationic groups on the naphthosultamyl moiety was prepared and evaluated for activity against resistant gram-positive bacteria. Based on a combination of excellent in vitro antibacterial activity, acceptable mouse acute toxicity, and a desirable fragmentation pattern on beta-lactam ring opening, the analog 2g (L-786,392) was selected for extended evaluation.

Benzothiazolylthio carbapenems: potent anti-MRSA agents

Abstract A series of sulfur-linked benzothiazolyl carbapenems has been prepared and evaluated against a battery of microorganisms. Many of the compounds displayed good activity against methicillin-resistant Staphylococcus aureus (MRSA). Data is presented which delimits the pharmacophore and provides a preliminary SAR.

The synthesis and antibacterial activity of 2-carbolinyl-carbapenems: potent anti-MRSA/MRCNS agents

Abstract A series of 2-carbolinyl-carbapenems was prepared via the Stille stannane coupling reaction. This new class of antibiotics exhibited potent activity in vitro against methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase negative staphylococci (MRCNS) as well as a broad spectrum of antibacterial activity. A high resistance to the mammalian dehydropeptidase, DHP-1, was also observed.

The discovery and synthesis of 2-biphenylcarbapenems active against methicillin resistant staphylococci

Abstract The discovery and synthesis of the arylcarbapenem 2b possessing potent activity against highly resistant strains of methicillin resistant staphylococci are dislosed.