Cellular Uptake of Two Fluoroketolides, HMR 3562 and HMR 3787, by Human Polymorphonuclear Neutrophils In Vitro

Abstract

We analyzed the cellular accumulation of two new fluoroketolides, HMR 3562 and HMR 3787, by human polymorphonuclear neutrophils (PMN) in vitro. Both compounds were rapidly taken up by PMN, with a cellular-to-extracellular concentration ratio (C/E) of about 141 (HMR 3562) and 117 (HMR 3787) at 5 min, and this was followed by a plateau at 60 to 180 min, with a C/E of >300 at 180 min. Both ketolides were mainly located in PMN granules (about 75%) and egressed slowly from loaded cells (about 40% at 60 min), owing to avid reuptake. Uptake was moderately sensitive to external pH, and activation energy was also moderate (about 70 kJ/mol). As with other macrolides and ketolides, the existence of an active transport system was suggested by (i) the strong interindividual variability in uptake kinetics, suggesting variability in the number or activity of a transport protein; (ii) the saturation kinetics characteristic of a carrier-mediated transport system (V max , about 2,300 ng/2.5 ؋ 10 6 PMN/5 min; K m , about 50 g/ml); (iii) the inhibitory effects of Ni 2؉ (a blocker of the Na ؉ -Ca 2؉ exchanger), phorbol myristate acetate (a protein kinase C activator), and H89 (a protein kinase A inhibitor). Although these two ketolides are more related to HMR 3647 (telithromycin), it is interesting that the presence of a fluoride gave these molecules a cellular pharmacokinetics more like those of HMR 3004 than those of HMR 3647. The macrolide transport system has not been yet elucidated, but our data confirm that, despite variations in chemical structure, all erythromycin A derivatives share a transmembrane transport system.

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

“…Among the recent areas of progress that has been made with this antibiotic family, much interest has been shown in the development of the ketolide class. Interestingly, this new group of erythromycin A derivatives seems to share with classical macrolides the use of an active transport system responsible for their accumulation, at least in phagocytic cells (2,30,31). The model of human neutrophils has widely been used to study the cellular uptake of macrolides and ketolides.…”

“…We also recently developed a model of a phagocytic cell line, PLB-985, a human myeloid leukemia cell line which can undergo granulocytic differentiation under specific conditions (3). We have been able to compare all available ketolides by use of these two models (2,3,(29)(30)(31). To extend our data on structure-activity relationships, we have investigated in the present study the accumulation of a new ketolide, ABT-773, for which no data have yet been published.…”

“…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.…”

Accumulation and activity of cethromycin (ABT-773) within human polymorphonuclear leucocytes

“…6 However, the kinetic profiles of other ketolides evaluated cannot be included in any group, showing intermediate kinetic characteristics. [1][2][3][4] Although these com-pounds have been shown to be strongly incorporated and accumulated by human PMNs, achieving high intracellular concentrations, they display a lower intraphagocytic activity than expected from the intracellular concentrations obtained. 3,5,7 Cethromycin is a new ketolide, a semisynthetic derivative of macrolide erythromycin A.…”

“…Erythromycin Aderivatives (macrolides and ketolides) are able to penetrate and concentrate intracellularly, reaching high intracellular concentrations. [1][2][3][4][5][6] Macrolide uptake by human polymorphonuclear leucocytes (PMNs) shows two patterns of intracellular pharmacokinetics, related to their chemical structure. Monobasic macrolides display saturable accumulation kinetics, characteristic of a carrier-mediated transport system and a rapid efflux, whereas the uptake of dibasic macrolides, such as azithromycin, is characterized by a progressive accumulation, without saturation and a slow efflux.…”