Session: Inhibitors of Bacterial and Fungal Efflux Pumps
Location:
Exhibit Hall
Session Date:
Monday, 9/27/99
Session Time:
3:00 pm - 4:30 pm
Targeting Efflux Pumps in Pseudomonas aeruginosa
O. Lomovskaya1, A. Lee1, M. Warren1, J. Galazzo1, R. Fronko1, M. Lee1, S.
Chamberland1, S. Hecker1, V. Lee1, H. Ishida2, K. Hoshino2
1Microcide Pharmaceuticals, Inc.: Mountain View, CA; 2Daiichi Pharmaceutical
Co, Ltd.: Tokyo, Japan
We present the first report on identification and characterization of bacterial multi-drug
resistance (MDR) pump inhibitors through high-throughput screening of small molecule
libraries. Whole-cell assays were implemented to search for efflux pump inhibitors (EPIs)
of the three MDR pumps (MexAB-OprM, MexCD-OprJ, MexEF-OprN) that
contribute to fluoroquinolone resistance in clinical isolates of P. aeruginosa. Secondary
assays were developed to identify leads with exquisite activity as inhibitors. Both
pump-selective and broad-spectrum EPIs, which are active against all three known Mex
pumps from P. aeruginosa and their close E. coli pump homolog (AcrAB-TolC), were
discovered. Broad-spectrum EPIs decreased significantly the intrinsic resistance of P.
aeruginosa to fluoroquinolones [16-fold for levofloxacin (LVFX)]. Acquired resistance
due to overexpression of efflux pumps was also decreased (32 to 64-fold reduction in
MIC for LVFX). Similarly, 32 to 64-fold reduction in MICs in the presence of EPIs was
observed for strains with overexpressed pumps and various target mutations conferring
resistance to LVFX (e.g., gyrA, parC). We also compared the frequencies of
emergence of LVFX-resistant variants in the wild-type strain at 4xMIC of LVFX (1
mg/ml) when LVFX was used alone or in combination with EPI. In case of LVFX alone,
the frequency was 10-6-10-7 cfu/ml. In contrast, with an EPI, the frequency is below the
level of detection (<10-11). In summary, the inhibition of efflux pumps 1) decreased
intrinsic resistance significantly, 2) reversed acquired resistance, and 3) resulted in
decreased frequency of emergence of P. aeruginosa strains that are highly resistant to
fluoroquinolones. |
