Inhibitors of bacterial efflux pumps as adjuvants in antibiotic treatments and diagnostic tools for detection of resistance by efflux.

Active efflux is a widespread mechanism for bacterial resistance to antibiotics, which contributes to poor intrinsic susceptibility, cross-resistance to structurally diverse classes of drugs, or selection of other mechanisms of resistance. Thus, inhibition of efflux pumps appears to be (i) a promising strategy for restoring the activity of existing antibiotics, and (ii) a useful method to detect the presence of efflux determinants in clinical isolates. Structurally dissimilar classes of inhibitors have been patented in the last decade, some are analogs of antibiotic substrates [tetracyclines, quinolones or aminoglycosides] and others, new chemical entities [including substituted indoles, ureas, aromatic amides, piperidinecarboxylic acids, alkylamino- or alkoxyquinolines, peptidomimetics, and pyridopyrimidines].

MexAB-OprM specific efflux pump inhibitors in Pseudomonas aeruginosa. Part 7: highly soluble and in vivo active quaternary ammonium analogue D13-9001, a potential preclinical candidate.

A series of 4-oxo-4H-pyrido[1,2-a]pyrimidine derivatives, substituted at the 2-position with piperidines bearing quaternary ammonium salt side chains, were synthesized and evaluated for their ability to potentiate the activity of the fluoroquinolone levofloxacin (LVFX) and the beta-lactam aztreonam (AZT) in Pseudomonas aeruginosa. Attachment of the charged entity using an N-ethylcarbamoyloxy linker led to the discovery of the highly soluble compound 22 (D13-9001), which maintained good potency in vitro and displayed excellent activity in vivo in a rat pneumonia model of P. aeruginosa.

MexAB-OprM specific efflux pump inhibitors in Pseudomonas aeruginosa. Part 6: exploration of aromatic substituents.

A series of 4-oxo-4H-pyrido[1,2-a]pyrimidine derivatives, derivatized at the 2-position with aromatic substituents, were synthesized by the Suzuki cross-coupling method and evaluated for their ability to potentiate the activity of the fluoroquinolone levofloxacin (LVFX) and the anti-pseudomonas beta-lactam aztreonam (AZT) in Pseudomonas aeruginosa. By incorporating hydrophilic substituents onto the aryl nucleus, we found a morpholine analogue that possessed improved solubility, retained activity in vitro, and displayed potentiation activity in vivo in a rat model of P. aeruginosa pneumonia.

MexAB-OprM specific efflux pump inhibitors in Pseudomonas aeruginosa. Part 5: Carbon-substituted analogues at the C-2 position.

A series of 4-oxo-4H-pyrido[1,2-a]pyrimidine derivatives, derivatized at the 2-position with carbon-linked substituents, were synthesized and evaluated for their ability to potentiate the activity of the fluoroquinolone levofloxacin (LVFX) and the anti-pseudomonas beta-lactam aztreonam (AZT) in Pseudomonas aeruginosa. Palladium-catalyzed cross-coupling methods were applied for the incorporation of aliphatic and aromatic substituents.

MexAB-OprM specific efflux pump inhibitors in Pseudomonas aeruginosa. Part 4: Addressing the problem of poor stability due to photoisomerization of an acrylic acid moiety.

Exchange of the ethylene tether in a series of pyridopyrimidine-based MexAB-OprM specific efflux pump inhibitors to an amide bond stabilized the olefin of the acrylic acid moiety, preventing facile photoisomerization to the Z-isomer. Furthermore, the activity was drastically improved in the amide tether variants, providing extremely potent acrylic acid and vinyl tetrazole analogues.

Biowarfare Pathogens. Is the Research Flavor Different Than That of Clinically Relevant Pathogens?

This chapter introduces four chemical warfare agents: bacillus anthracis (anthrax), yersinia pestis (plague), variola major (smallpox), and francesella tularensis (tularemia). Anthrax is a dimorphic bacterium that normally exists as spores. The clinical presentation can be as cutaneous, inhalational or gastrointestinal forms that are fortuitously not transmissible from person to person.

MexAB-OprM specific efflux pump inhibitors in Pseudomonas aeruginosa. Part 3: Optimization of potency in the pyridopyrimidine series through the application of a pharmacophore model.

The addition of substituents to the pyridopyrimidine scaffold of MexAB-OprM specific efflux pump inhibitors was explored. As predicted by a pharmacophore model, the incorporation substituents at the 2-position improved potency. Piperidines were found to be optimal, and further introduction of polar groups without compromising the activity was shown to be feasible.

MexAB-OprM specific efflux pump inhibitors in Pseudomonas aeruginosa. Part 2: achieving activity in vivo through the use of alternative scaffolds.

Problems of low solubility, high serum protein binding, and lack of efficacy in vivo in first generation MexAB-OprM specific efflux pump inhibitors were addressed. Through the use of pharmacophore modelling, the key structural elements for pump inhibition were defined. Use of alternative scaffolds upon which the key elements were arrayed gave second generation leads with greatly improved physical properties and activity in the potentiation of antibacterial quinolones (levofloxacin and sitafloxacin) versus Pseudomonas aeruginosa in vivo.

MexAB-OprM-specific efflux pump inhibitors in Pseudomonas aeruginosa. Part 1: discovery and early strategies for lead optimization.

The identification of a series of compounds that specifically inhibit efflux by the MexAB-OprM pump system in Pseudomonas aeruginosa is described. Synthesis and in vitro structure-activity relationships (SARs) are outlined. Early leads lacked activity in animal models, and efforts to improve solubility and reduce serum protein binding by the introduction of polar groups are discussed.

Synthetic dihydropacidamycin antibiotics: a modified spectrum of activity for the pacidamycin class.

Dihydropacidamycins having an antibacterial spectrum modified from that of the natural product pacidamycins and mureidomycins have been synthesized. Synthetic dihydropacidamycins with noteworthy antibacterial activity against wild-type and resistant Escherichia coli have been identified (MIC=4-8 microg/mL). Some dihydropacidamycins are shown to have activity against multi-resistant clinical strains of Mycobacterium tuberculosis.

Conformationally-restricted analogues of efflux pump inhibitors that potentiate the activity of levofloxacin in Pseudomonas aeruginosa.

Conformational restriction of the ornithine residue of the efflux pump inhibitor D-ornithine-D-homophenylalanine-3-aminoquinoline (MC-02,595, 2) furnished bioisosteric proline derivatives that were less toxic in vivo and as active as the lead in potentiating the activity of the fluoroquinolone levofloxacin via the inhibition of efflux pumps in Pseudomonas aeruginosa.

In vivo antibacterial activity of RWJ-54428, a new cephalosporin with activity against gram-positive bacteria.

RWJ-54428 (MC-02,479) is a new cephalosporin with activity against resistant gram-positive organisms, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and penicillin-resistant Streptococcus pneumoniae. The in vivo efficacy of RWJ-54428 was evaluated against gram-positive bacteria in four mouse models of infection. RWJ-54428 was effective in vivo against methicillin-susceptible and -resistant S.

Peptidomimetics of efflux pump inhibitors potentiate the activity of levofloxacin in Pseudomonas aeruginosa.

Several classes of peptidomimetics of the efflux pump inhibitor D-ornithine-D-homophenylalanine-3-aminoquinoline (MC-02,595) have been prepared and evaluated for their ability to potentiate the activity of the fluoroquinolone levofloxacin in Pseudomonas aeruginosa. A number of the new analogues were as active or more active than the lead, demonstrating that a peptide backbone is not essential for activity.