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Olga Lomovskaya

Publications and source records attributed to Olga Lomovskaya.

13 recordsLinked to original sources
PubMed2006

Waltzing transporters and 'the dance macabre' between humans and bacteria.

Multidrug-resistance efflux pumps - in particular those belonging to the resistance-nodulation-cell-division (RND) family of transporters, with their unusually high degree of substrate promiscuity - significantly restrict the effectiveness of antibacterial therapy. Recent years have heralded remarkable insights into the structure and mechanisms of these fascinating molecular machines. Here, we review recent advances in the field and describe various approaches used in combating efflux-mediated resistance.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2006

Practical applications and feasibility of efflux pump inhibitors in the clinic--a vision for applied use.

The world of antibiotic drug discovery and development is driven by the necessity to overcome antibiotic resistance in common Gram-positive and Gram-negative pathogens. However, the lack of Gram-negative activity among both recently approved antibiotics and compounds in the developmental pipeline is a general trend despite the fact that the plethora of covered drug targets are well-conserved across the bacterial kingdom. Such intrinsic resistance in Gram-negative bacteria is largely attributed to the activity of multidrug resistance (MDR) efflux pumps. Moreover, these pumps also play a significant role in acquired clinical resistance. Together, these considerations make efflux pumps attractive targets for inhibition in that the resultant efflux pump inhibitor (EPI)/antibiotic combination drug should exhibit increased potency, enhanced spectrum of activity and reduced propensity for acquired resistance. To date, at least one class of broad-spectrum EPI has been extensively characterized. While these efforts indicated a significant potential for developing small molecule inhibitors against efflux pumps, they did not result in a clinically useful compound. Stemming from the continued clinical pressure for novel approaches to combat drug resistant bacterial infections, second-generation programs have been initiated and show early promise to significantly improve the clinical usefulness of currently available and future antibiotics against otherwise recalcitrant Gram-negative infections. It is also apparent that some changes in regulatory decision-making regarding resistance would be very helpful in order to facilitate approval of agents aiming to reverse resistance and prevent its further development.

Anti-Bacterial Agents↗
PubMed2006

Pharmacodynamics of levofloxacin against Pseudomonas aeruginosa with reduced susceptibility due to different efflux pumps: do elevated MICs always predict reduced in vivo efficacy?

The Pseudomonas aeruginosa efflux pumps MexAB-OprM, MexCD-OprJ, and MexEF-OprN play an important role in susceptibility to fluoroquinolones in vitro. To determine if levofloxacin MICs arising from different levels of expression of efflux pumps result in a proportional reduction in the response to levofloxacin in vivo, isogenic strains of P. aeruginosa were tested with levofloxacin in two mouse models of infection (sepsis and neutropenic mouse thigh models). The levofloxacin 50% effective doses (ED(50)s) increased proportionally with the MICs for most strains. Similarly, the 24-h area under the concentration-time curve (AUC)/MIC ratio that resulted in 90% of the maximum bactericidal activity (90% E(max)) exceeded 75 for all strains except those with elevated MICs due to MexEF-OprN overexpression. In these strains, levofloxacin ED(50)s were 2- to 10-fold lower than the ED(50)/MIC ratios in the other strains and 90% E(max) AUC/MIC ratios were 2- to 4-fold lower than those predicted from pharmacodynamic modeling of efficacy against other strains. These data show that while the MexEF-OprN efflux pump can provide P. aeruginosa resistance to levofloxacin in vitro, it appears to be less efficient in providing resistance to levofloxacin in animal models of infection.

Animals↗
PubMed2005

Use of an efflux pump inhibitor to determine the prevalence of efflux pump-mediated fluoroquinolone resistance and multidrug resistance in Pseudomonas aeruginosa.

Fluoroquinolone-resistance in Pseudomonas aeruginosa may be due to efflux pump overexpression (EPO) and/or target mutations. EPO can result in multidrug resistance (MDR) due to broad substrate specificity of the pumps. MC-04,124, an efflux pump inhibitor (EPI) shown to significantly potentiate activity of levofloxacin in P. aeruginosa, was used to examine the prevalence of EPO in clinical isolates. MICs were determined for ciprofloxacin, levofloxacin, moxifloxacin, and gatifloxacin with or without EPI and for other antipseudomonal agents by using broth microdilution against P. aeruginosa isolates from adults (n = 119) and children (n = 24). The prevalence of the EPO phenotype (>/=8-fold MIC decrease when tested with EPI) was compared among subgroups with different resistance profiles. The EPO phenotype was more prevalent among levofloxacin-resistant than levofloxacin-sensitive strains (61%, 48/79 versus 9%, 6/64). EPO was present in 60% of fluoroquinolone-resistant strains without cross-resistance, while it was present at variable frequencies among strains with cross-resistance to other agents: piperacillin-tazobactam (86%), ceftazidime (76%), cefepime (65%), imipenem (56%), gentamicin (55%), tobramycin (48%), and amikacin (27%). The magnitude of MIC decrease with an EPI paralleled the frequency of which the EPO phenotype was observed in different subgroups. EPI reduced the levofloxacin MIC by as much as 16-fold in eight strains for which MICs were 128 microg/ml. Efflux-mediated resistance appears to contribute significantly to fluoroquinolone resistance and MDR in P. aeruginosa. Our data support the fact that increased fluoroquinolone usage can negatively impact susceptibility of P. aeruginosa to multiple classes of antipseudomonal agents.

Adult↗
PubMed2004

Quinazolinone-based fungal efflux pump inhibitors. Part 1: Discovery of an (N-methylpiperazine)-containing derivative with activity in clinically relevant Candida spp.

The discovery of a series of quinazolinone-based fungal efflux pump inhibitors by high-throughput screening for potentiation of fluconazole in C. albicans is described. Attempts to improve the aqueous solubility of screening hits led to the discovery of an analog with greatly improved physical properties and activity against clinically-relevant Candida spp.

ATP-Binding Cassette Transporters↗
PubMed2003

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.

Aminobutyrates↗
PubMed2003

MexXY-OprM efflux pump is necessary for a adaptive resistance of Pseudomonas aeruginosa to aminoglycosides.

Exposure of Pseudomonas aeruginosa to aminoglycosides frequently selects for recalcitrant subpopulations exhibiting an unstable, "adaptive" resistance to these antibiotics. In this study, we investigated the implication in the phenomenon of MexXY-OprM, an active efflux system known to export aminoglycosides in P. aeruginosa. Immunoblotting experiments demonstrated that the transporter MexY, but not the outer membrane pore OprM, was overproduced during the post-drug exposure adaptation period in wild-type strain PAO1. Furthermore, MexY production was dependent upon the degree of bacterial exposure to gentamicin (drug concentration). In contrast to parental strain PAO1, mutants defective in MexXY or in OprM were unable to develop adaptive resistance. Altogether, these results indicate that the resistance process requires the rapid production of MexXY and the interaction of these proteins with the constitutively produced component OprM.

Adaptation, Physiological↗
PubMed2002

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.

Anti-Infective Agents↗
PubMed2002

On the mechanism of substrate specificity by resistance nodulation division (RND)-type multidrug resistance pumps: the large periplasmic loops of MexD from Pseudomonas aeruginosa are involved in substrate recognition.

Tripartite efflux systems of Gram-negative bacteria that contain an inner membrane transporter belonging to the resistance nodulation division (RND) superfamily can extrude a large variety of structurally diverse compounds. To gain an insight into the molecular mechanisms of substrate recognition by these multidrug resistance (MDR) transporters, we isolated spontaneous mutations that altered the substrate specificity of the MexCD-OprJ pump from Pseudomonas aeruginosa. These mutations enabled the pump to extrude the normally non-transported beta-lactam antibiotic carbenicillin. All amino acid substitutions were mapped to the large periplasmic loops (LPLs) of the RND proper, MexD. Q34K, E89K, A292V and P328L were found in the first LPL, located between transmembrane domains (TMD) 1 and 2, whereas F608S and N673K were contained in the second LPL, located between TMD7 and TMD8. These mutations also had a substantial impact on the MexCD-OprJ-mediated transport of numerous other substrates. Subsequent replacement of amino acid residues identified above by cysteines rendered MexCD-OprJ susceptible to inhibition by a thiol-reactive agent, MIANS. Interestingly, MIANS inhibited the transport of some (pyronin, EtBr) but not other (ANS, Leu-Nap) substrates of the pump. Our results suggest that the precise structure of the periplasmic loops of MexD determines the rate of transport of individual substrates. These results are consistent with the hypothesis that, in the case of RND transporters, the LPLs are directly implicated in substrate recognition and contain multiple sites of interaction for various structurally diverse compounds.

Amino Acid Substitution↗
PubMed2002

Multidrug pump inhibitors uncover remarkable activity of plant antimicrobials.

Plant antimicrobials are not used as systemic antibiotics at present. The main reason for this is their low level of activity, especially against gram-negative bacteria. The reported MIC is often in the range of 100 to 1,000 micro g/ml, orders of magnitude higher than those of common broad-spectrum antibiotics from bacteria or fungi. Major plant pathogens belong to the gram-negative bacteria, which makes the low level of activity of plant antimicrobials against this group of microorganisms puzzling. Gram-negative bacteria have an effective permeability barrier, comprised of the outer membrane, which restricts the penetration of amphipathic compounds, and multidrug resistance pumps (MDRs), which extrude toxins across this barrier. It is possible that the apparent ineffectiveness of plant antimicrobials is largely due to the permeability barrier. We tested this hypothesis in the present study by applying a combination of MDR mutants and MDR inhibitors. A panel of plant antimicrobials was tested by using a set of bacteria representing the main groups of plant pathogens. The human pathogens Pseudomonas aeruginosa, Escherichia coli, and Salmonella enterica serovar Typhimurium were also tested. The results show that the activities of the majority of plant antimicrobials were considerably greater against the gram-positive bacteria Staphylococcus aureus and Bacillus megaterium and that disabling of the MDRs in gram-negative species leads to a striking increase in antimicrobial activity. Thus, the activity of rhein, the principal antimicrobial from rhubarb, was potentiated 100- to 2,000-fold (depending on the bacterial species) by disabling the MDRs. Comparable potentiation of activity was observed with plumbagin, resveratrol, gossypol, coumestrol, and berberine. Direct measurement of the uptake of berberine, a model plant antimicrobial, confirmed that disabling of the MDRs strongly increases the level of penetration of berberine into the cells of gram-negative bacteria. These results suggest that plants might have developed means of delivering their antimicrobials into bacterial cells. These findings also suggest that plant antimicrobials might be developed into effective, broad-spectrum antibiotics in combination with inhibitors of MDRs.

Anti-Bacterial Agents↗