RESUMO
Multidrug resistance in Gram-negative bacteria has become so threatening to human health that new antibacterial platforms are desperately needed to combat these deadly infections. The concept of siderophore conjugation, which facilitates compound uptake across the outer membrane by hijacking bacterial iron acquisition systems, has received significant attention in recent years. While standard in vitro MIC and resistance frequency methods demonstrate that these compounds are potent, broad-spectrum antibacterial agents whose activity should not be threatened by unacceptably high spontaneous resistance rates, recapitulation of these results in animal models can prove unreliable, partially because of the differences in iron availability in these different methods. Here, we describe the characterization of MB-1, a novel siderophore-conjugated monobactam that demonstrates excellent in vitro activity against Pseudomonas aeruginosa when tested using standard assay conditions. Unfortunately, the in vitro findings did not correlate with the in vivo results we obtained, as multiple strains were not effectively treated by MB-1 despite having low MICs. To address this, we also describe the development of new in vitro assays that were predictive of efficacy in mouse models, and we provide evidence that competition with native siderophores could contribute to the recalcitrance of some P. aeruginosa isolates in vivo.
Assuntos
Antibacterianos/farmacologia , Farmacorresistência Bacteriana/efeitos dos fármacos , Monobactamas/farmacologia , Infecções por Pseudomonas/tratamento farmacológico , Pseudomonas aeruginosa/efeitos dos fármacos , Piridonas/farmacologia , Sideróforos/farmacologia , Adaptação Fisiológica/efeitos dos fármacos , Adaptação Fisiológica/genética , Animais , Antibacterianos/química , Bioensaio , Farmacorresistência Bacteriana/genética , Feminino , Ferro/metabolismo , Camundongos , Camundongos Endogâmicos ICR , Testes de Sensibilidade Microbiana , Monobactamas/química , Mutagênese Sítio-Dirigida , Oligopeptídeos/genética , Oligopeptídeos/metabolismo , Infecções por Pseudomonas/microbiologia , Pseudomonas aeruginosa/genética , Pseudomonas aeruginosa/crescimento & desenvolvimento , Piridonas/química , Sideróforos/genética , Sideróforos/metabolismo , Falha de TratamentoRESUMO
The incidence of hospital-acquired infections with multidrug-resistant (MDR) Gram-negative pathogens is increasing at an alarming rate. Equally alarming is the overall lack of efficacious therapeutic options for clinicians, which is due primarily to the acquisition and development of various antibiotic resistance mechanisms that render these drugs ineffective. Among these mechanisms is the reduced permeability of the outer membrane, which prevents many marketed antibiotics from traversing this barrier. To circumvent this, recent drug discovery efforts have focused on conjugating a siderophore moiety to a pharmacologically active compound that has been designed to hijack the bacterial siderophore transport system and trick cells into importing the active drug by recognizing it as a nutritionally beneficial compound. MC-1, a novel siderophore-conjugated ß-lactam that promotes its own uptake into bacteria, has exquisite activity against many Gram-negative pathogens. While the inclusion of the siderophore was originally designed to facilitate outer membrane penetration into Gram-negative cells, here we show that this structural moiety also renders other clinically relevant antibiotic resistance mechanisms unable to affect MC-1 efficacy. Resistance frequency determinations and subsequent characterization of first-step resistant mutants identified PiuA, a TonB-dependent outer membrane siderophore receptor, as the primary means of MC-1 entry into Pseudomonas aeruginosa. While the MICs of these mutants were increased 32-fold relative to the parental strain in vitro, we show that this resistance phenotype is not relevant in vivo, as alternative siderophore-mediated uptake mechanisms compensated for the loss of PiuA under iron-limiting conditions.
Assuntos
Antibacterianos/farmacologia , Farmacorresistência Bacteriana/fisiologia , Bactérias Gram-Negativas/efeitos dos fármacos , Bactérias Gram-Negativas/genética , beta-Lactamas/farmacologia , Animais , Proteínas da Membrana Bacteriana Externa/genética , Proteínas da Membrana Bacteriana Externa/metabolismo , Western Blotting , Clonagem Molecular , Infecção Hospitalar/microbiologia , Farmacorresistência Bacteriana/genética , Farmacorresistência Bacteriana Múltipla/genética , Escherichia coli/genética , Biblioteca Gênica , Camundongos , Porinas/genética , Pseudomonas aeruginosa/efeitos dos fármacos , Pseudomonas aeruginosa/genética , Sepse/tratamento farmacológico , Sepse/microbiologia , Sideróforos , beta-Lactamases/biossíntese , beta-Lactamases/genéticaRESUMO
Novel siderophore-linked monobactams with in vitro and in vivo anti-microbial activity against MDR Gram-negative pathogens are described.
Assuntos
Farmacorresistência Bacteriana Múltipla/efeitos dos fármacos , Bactérias Gram-Negativas/efeitos dos fármacos , Infecções por Bactérias Gram-Negativas/tratamento farmacológico , Monobactamas/farmacologia , Animais , Sítios de Ligação/efeitos dos fármacos , Proteínas Sanguíneas/química , Cristalografia por Raios X , Relação Dose-Resposta a Droga , Infecções por Bactérias Gram-Negativas/microbiologia , Humanos , Camundongos , Testes de Sensibilidade Microbiana , Modelos Moleculares , Estrutura Molecular , Monobactamas/síntese química , Monobactamas/química , Ratos , Relação Estrutura-AtividadeRESUMO
A novel series of monocarbam compounds exhibiting promising antibacterial activity against multidrug resistant Gram-negative microorganisms is reported, along with the synthesis of one such molecule MC-1 (1). Also reported are structure-activity relationships associated with the in vitro and in vivo efficacy of 1 and related analogues in addition to the hydrolytic stability of such compounds and possible implications thereof.
RESUMO
Respiratory tract bacterial strains are becoming increasingly resistant to currently marketed macrolide antibiotics. The current alternative telithromycin (1) from the newer ketolide class of macrolides addresses resistance but is hampered by serious safety concerns, hepatotoxicity in particular. We have discovered a novel series of azetidinyl ketolides that focus on mitigation of hepatotoxicity by minimizing hepatic turnover and time-dependent inactivation of CYP3A isoforms in the liver without compromising the potency and efficacy of 1.