Mechanisms of cell association of chloroquine to leucocytes

One approach currently being used to get more insight into the molecular mechanisms of action of drugs and their (micro)pharmacokinetic events is to perform cellular association studies. We have examined the association of the antimalarial and antirheumatic drug chloroquine (CQ) to isolated human blood cells. This study dealt with the hypothesis that inflammatory cells such as the leucocytes are the mediators of the anti-inflammatory activity of drugs, both as target cells and as potential vehicles for the transport of drugs to inflamed tissues. A suitable ligand-binding assay was developed to measure the cellular association of CQ. The polymorphonuclear leucocytes (PMNs) accumulated CQ to a greater extent than mononuclear leucocytes and red blood cells; this can be explained by the presence of a lot of acidic cellular organelles as lysosomes in the PMS, which trap the weak base CQ. The accumulation in the PMNs was dependent on temperature, cellular intactness and the extracellular pH. The apparent temperature dependency indicates that one or more energy delivery steps are involved in the entire process of cellular association. Scatchard analysis of the association of CQ to human PMNs revealed two different sites, with KD values of 1.7 microM and 0.12 mM for the low and high affinity site, respectively. The cellular association of CQ is inhibited by supratherapeutic concentrations of some nonsteroidal anti-inflammatory drugs. This is possibly due to an interaction at the level of the cellular transport pathways and emphasizes the value of micropharmacokinetic studies.