Interaction of the New Ketolide ABT-773 (Cethromycin) with Human Polymorphonuclear Neutrophils and the Phagocytic Cell Line PLB-985 In Vitro

Abstract

Whatever the cell type and in contrast to the results obtained with HMR 3004, ABT-773 was mainly located in the cytosol (about 75%) and was rapidly released from loaded cells (about 40% at 5 min), followed by a plateau, likely owing to avid reuptake. Verapamil and H89, an inhibitor of protein kinase A, increased drug efflux. Uptake was sensitive to external pH, and the activation energy was moderate (about 50 kJ/mol). The existence of an active transport system on the PMN membrane was suggested by the following findings: concentrationdependent and saturable uptake (V max , about 10 000 ng/2.5 ؋ 10 6 PMNs/5 min; K m , about 60 g/ml) the inhibitory effects of PMN activators or inhibitors (phorbol myristate acetate, verapamil, Ni 2؉ ) and the significantly decreased levels of accumulation by killed cells and cells treated at low temperatures. In addition, various macrolides impaired ABT-773 uptake, contrary to the findings for the quinolone levofloxacin. ND-and D-PLB also presented saturation kinetics that defined an active transport system (V max and K m values were similar to those obtained with PMNs), but the activation pathway of the carrier system did not seem to be fully functional in ND-PLB. As has been observed with other erythromycin A derivatives, ABT-773 impaired oxidant production by phagocytes in a time-and concentration-dependent manner. These data extend our previous results on the existence of an active transport system common to all macrolides and ketolides, at least in PMNs.Ketolides are a new class of semisynthetic erythromycin A derivatives that are particularly designed to combat respiratory tract pathogens that have acquired resistance to macrolides (32). They are characterized by a 3-keto group instead of the usual ␣-L-cladinose moiety on the erythronolide A ring (6). Telithromycin (HMR 3647) is the first member of this new class to be approved for clinical use. Ketolides possess a broad antibacterial spectrum similar to that of erythromycin A, with additional activity against inducible macrolide-lincosamidestreptogramin B-resistant pathogens (4, 5). Activity against intracellular pathogens is the hallmark of macrolides and ketolides, but cellular uptake is required for these drugs to exhibit their activities (13,14). Contrary to macrolides, for which an extended literature on cellular uptake is available, few data are available on the uptake of ketolides (2,3,20,(29)(30)(31). The uptake of the ketolides HMR 3004 (formerly RU 64004) (30) and HMR 3647 (telithromycin) (31) and the fluoroketolides HMR 3562 and HMR 3787 (2) have been analyzed previously.ABT-773 (cethromycin), a new ketolide developed by Abbott, possesses good activity against gram-positive organisms, some gram-negative organisms, and intracellular bacteria (8,11,18). ABT-773 is active in vitro (9,19,24,27) and in vivo (12, 21) against penicillin-resistant and inducibly erythromycin-resistant staphylococci, streptococci, and pneumococci. No data are yet available, however, on its uptake by phagocytes. In the study described here w...

Cellular Uptake and Efflux of Azithromycin, Erythromycin, Clarithromycin, Telithromycin, and Cethromycin

“…This observation can be explained by the different cellular locations of the two ketolides tested. Unlike telithromycin, which accumulates in the granular compartment of PMNs (22,36), cethromycin is mainly located in the cytosol (18).…”

Posaconazole-Loaded Leukocytes as a Novel Treatment Strategy Targeting Invasive Pulmonary Aspergillosis

“…We therefore sought to investigate the utility of posaconazole-loaded neutrophils as therapeutics for invasive aspergillosis. We concentrations of these agents were observed in undifferentiated precursor cells (191,194). These high intracellular antimicrobial concentrations within PMNs have been linked to their enhanced therapeutic efficacy against intracellular pathogens.…”

Macrolides and Ketolides

“…Generally speaking, however, azithromycin and ketolides accumulate to the highest levels, probably related to the dicationic character of azithromycin on the one side and to the greater lipophilicity of ketolides on the other side. These drugs distribute mainly in lysosomes, with a smaller proportion found in the cytosol (Carlier et al 1987(Carlier et al , 1994Labro et al 2004 ;Togami et al 2010b ;Villa et al 1988 ). Infl ux transporters have been suggested to play a role in the uptake of ketolides in white blood cells (Labro et al 2004 ;Togami et al 2010b ;Vazifeh et al 1998 ), but the kinetics of their accumulation and their subcellular distribution are fully coherent with a passive mechanism of diffusion-segregation.…”

“…These drugs distribute mainly in lysosomes, with a smaller proportion found in the cytosol (Carlier et al 1987(Carlier et al , 1994Labro et al 2004 ;Togami et al 2010b ;Villa et al 1988 ). Infl ux transporters have been suggested to play a role in the uptake of ketolides in white blood cells (Labro et al 2004 ;Togami et al 2010b ;Vazifeh et al 1998 ), but the kinetics of their accumulation and their subcellular distribution are fully coherent with a passive mechanism of diffusion-segregation. Effl ux from the cells is usually slow, but it can be facilitated by the activity of the multidrug transporter P-glycoprotein (Munic et al 2010 ;Pachot et al 2003 ;Seral et al 2003b ).…”