Contrasting Eect of Acidic pH on the Extracellular and Intracellular Activities of Delaf loxacin (DFX) vs Moxif loxacin (MXF) Towards S. aureus (2010)

RESULTS Structural formulae: The open arrows point to the acidic function of f luoroquinolones and the plain arrow, to the basic function of moxif loxacin that is protonated at physiological pH. CONCLUSIONS Delaf loxacin is highly intrinsically active against S. aureus. In contrast to moxif loxacin, it shows enhanced potency and e cacy at acidic pH against both extracellular and intracellular bacteria, in relation with its higher accumulation in both procaryotic and eucaryotic cells. This may confer an advantage to delaf loxacin for the treatment of staphylococcal infections in territories where pH is acidic, including those involving intracellular reservoirs. A) Inf luence of acidic pH on the accumulation of moxif loxacin and dela oxacin STUDY AIM Contrasting E ect of Acidic pH on the Extracellular and Intracellular Activities of Delaf loxacin (DFX) vs Moxif loxacin (MXF) Towards S. aureus Sandrine Lemaire, Paul M. Tulkens, and Francoise Van Bambeke Unite de Pharmacologie cellulaire et moleculaire, Louvain Drug Research Institute, Universite catholique de Louvain, Brussels, Belgium Poster A1-677 Mailing address: F. Van Bambeke UCL 73.70 av. Mounier 73, 1200 Brussels, Belgium francoise.vanbambeke@uclouvain.be Bacteria, susceptibility testing, and extracellular activity: S. aureus strain ATCC 25923 was used for all experiments. MICs were determined in pH-adjusted Mueller Hinton Broth by microdilution. Extracellular activity was determined as previously described (4). Cell line: Experiments were performed with THP-1 cells (ATCC TIB-202), a human myelomonocytic cell line displaying macrophage-like activity. Determination of antibiotic accumulation in S. aureus and THP-1 cells: Antibiotic accumulation was measured after 30 min. incubation. The content in antibiotic was determined by microbiological assay (disc-plate). The cellular concentration of uoroquinolones was expressed by reference to the total cell protein, as determined using the Folin-Ciocalteu/biuret method. Cellular accumulation in THP-1 cells was calculated using a conversion factor of 5 μL per mg of cell protein. Cell infection and assessment of intracellular activity: Cell infection was performed exactly as described previously (4) with a starting inoculum of ~ 1 to 2 x 106 CFU/mg protein. Antibiotic activities was examined after 24 hours in the presence of xed concentration of antibiotics in media at pH 7.4 or 5.5, and results were expressed as the change in the inoculum at 24 hours compared to time zero. pH 7.4 pH 5.5 pH 7.4 pH 5.5 Accumulation in S. aureus a 100.0 ± 4.1 57.8 ± 4.7 100.0 ± 9.7 1100.2 ± 180.7 MICs (mg/L) 0.03 0.125 0.0075 0.0002 Accumulation in THP-1 cells 5.8 ± 0.5 1.5 ± 0.0 1.7 ± 0.4 19.8 ± 4.7 Intracell. activity c at 0.1 mg/L 0.7 ± 0.2 0.5 ± 0.0 -0.5 ± 0.01 -1.3 ± 0.0 at 1 mg/L -1.5 ± 0.1 0.1 ± 0.1 -0.6 ± 0.0 -3.0 ± 0.1 b Cellular to extracellular concentration ratio (30 min.) c ∆log cfu from time 0 (24 h) Parameters studied Moxifloxacin Delafloxacin a Antibiotic uptake within S. aureus (30 min.; % of control value [pH 7.4]) Delaf loxacin (DFX) is an investigational quinolone demonstrating potent intrinsic activity, especially against Grampositive bacteria (including MRSA isolates)1-2. From a chemical point of view, delaf loxacin di ers from other currently used quinolones by the absence of a protonable substituant, which confers a weak acid character to the molecule. This property further increases its potency in acidic environments. This could be advantageous for S. aureus infections, as this bacterium has ability to survive and thrive in mildly acidic compartments3-4 (such as the skin, the vagina, the urinary tract, or the phagolysosomes of infected cells [pH 5-5.5]). BACKGROUND