Cellular Accumulation and Pharmacodynamic Evaluation of the Intracellular Activity of CEM-101, a Novel Fluoroketolide, againstStaphylococcus aureus,Listeria monocytogenes, andLegionella pneumophilain Human THP-1 Macrophages

Abstract

CEM-101 is a novel fluoroketolide with lower MICs than those of telithromycin and macrolides. Our aim was to assess the cellular accumulation and intracellular activity of CEM-101 using models developed for analyzing the pharmacokinetics and pharmacological properties of antibiotics against phagocytized bacteria. We used THP-1 macrophages and Staphylococcus aureus (ATCC 25923 [methicillin (meticillin) sensitive]), Listeria monocytogenes (strain EGD), and Legionella pneumophila (ATCC 33153). CEM-101 reached cellular-to-extracellular-concentration ratios of about 350 within 24 h (versus approximately 20, 30, and 160 for telithromycin, clarithromycin, and azithromycin, respectively). This intracellular accumulation was suppressed by incubation at a pH of <6 and by monensin (proton ionophore) and was unaffected by verapamil (P-glycoprotein inhibitor; twofold accumulation increase for azithromycin) or gemfibrozil. While keeping with the general properties of the macrolide antibiotics in terms of maximal efficacy (E max ; approximately 1-log 10 -CFU decrease compared to the postphagocytosis inoculum after a 24-h incubation), CEM-101 showed significantly greater potency against phagocytized S. aureus than telithromycin, clarithromycin, and azithromycin (for which the 50% effective concentration [EC 50 ] and static concentrations were about 3-, 6-, and 15-fold lower, respectively). CEM-101 was also about 50-fold and 100-fold more potent than azithromycin against phagocytized L. monocytogenes and L. pneumophila, respectively. These differences in EC 50 s and static concentrations between drugs were minimized when data were expressed as multiples of the MIC, demonstrating the critical role of intrinsic drug activity (MIC) in eliciting the antibacterial intracellular effects, whereas accumulation per se was unimportant. CEM-101 should show enhanced in vivo potency if used at doses similar to those of the comparators tested here.

In Vitro Activity of CEM-101 against Streptococcus pneumoniae and Streptococcus pyogenes with Defined Macrolide Resistance Mechanisms

“…1) is a novel fluoroketolide that demonstrates enhanced potency compared to telithromycin, with activity against telithromycin-intermediate and telithromycin-resistant organisms (11). CEM-101 has shown significantly greater potency against phagocytized Staphylococcus aureus than telithromycin, azithromycin, and clarithromycin; CEM-101 was also about 50-fold and 100-fold more potent than azithromycin against phagocytized Listeria monocytogenes and Legionella pneumophila (17). CEM-101 exhibits the widest spectrum of activity against respiratory tract pathogens, includ- ing multidrug-resistant pneumococcus type 19A, compared to azithromycin, clarithromycin, erythromycin, telithromycin, clindamycin, and quinupristin-dalfopristin (11).…”

Contrasting Effects of Acidic pH on the Extracellular and Intracellular Activities of the Anti-Gram-Positive Fluoroquinolones Moxifloxacin and Delafloxacin againstStaphylococcus aureus

“…We used the general protocol described in our previous publications (6,26) for uninfected cells. For pH dependence studies, cells were incubated with media adjusted to specific pH values, ranging from 5.0 to 7.4, using 5 mM phosphate buffer.…”

“…This could be an advantage with respect to S. aureus infections, since this bacterium, which shows a high tolerance to low pH, survives and multiplies in mild acidic environments (47), such as the skin, the vagina, or the urinary tract, and within the phagolysosomes of infected cells (6), where the pH is about 5 to 5.5 (19). Thus, delafloxacin contrasts with what is observed for many of the current antistaphylococcal antibiotics for which activity is reduced when the pH is lowered, as seen for other fluoroquinolones (e.g., norfloxa-cin, ciprofloxacin, or moxifloxacin [6,48]), macrolides (26), clindamycin (37), and gentamicin (7).…”

Renaissance of antibiotics against difficult infections: Focus on oritavancin and new ketolides and quinolones

“…Despite the tremendous number of molecules produced, only a few of them were brought on the market, among which some were withdrawn or have seen their use restricted because in telithromycin, may possibly account for the higher intrinsic activity of solithromycin as compared to telithromycin (57). As for other macrolides and ketolides, solithromycin's pharmacokinetic profile is characterized by a broad tissue distribution and high cellular accumulation (58,59), reaching elevated concentrations in alveolar macrophages (24-h AUC: 1500 mg.h/L; ratio to serum concentration: 180) and epithelial lining fluid (24-h AUC: 80 mg.h/L; ratio to serum concentration: 10). Its half-life of 6.65 h related to a high protein binding (85%) (60) allows for a once-a-day administration, with a proposed therapeutic scheme by oral route consisting in a loading dose of 800 mg followed by a 4-day treatment with a daily dose of 400 mg.…”

“…Taken together, these properties are advantageous for the treatment of respiratory or genital infections. They also rationalize activity against intracellular pathogens like S. aureus, Listeria monocytogenes, L. pneumophila, and N. gonorrhoeae (58,67), against which solithromycin proves at least as effective but more potent than other macrolides, based essentially on its lower MICs and not on its higher accumulation level. In the clinics, solithromycin has, at this stage, already proven as effective as levofloxacin with a more favorable safety profile in a phase II trial for the treatment of community-acquired bacterial pneumonia, where patients were randomized to receive either 800 mg solithromycin orally on day 1, followed by 400 mg daily on days 2 to 5, or 750 mg levofloxacin during 5 days (75).…”