Chloroquine Interferes with Lipopolysaccharide-Induced TNF-α Gene Expression by a Nonlysosomotropic Mechanism

Abstract

Chloroquine (CQ) is a lysosomotropic weak base with over 60 years of clinical use for the treatment of malaria and rheumatologic disorders. Consistent with its anti-inflammatory properties, CQ has been shown to interfere with TNF-α release from mononuclear phagocytes. Because it is unclear how CQ mediates these immunomodulatory effects, we set out to elucidate its mechanism of action. CQ exhibited dose-dependent inhibition of LPS-induced TNF-α release from human PBMC at therapeutically attainable concentrations. Additional studies to determine the specificity of this effect showed that although CQ reduced IL-1β and IL-6 release, secretion of RANTES was unaffected. CQ acted by reducing TNF-α mRNA accumulation without destabilizing its mRNA or interfering with NF-κB nuclear translocation or p50/p65 isoform composition of DNA-binding complexes. Intracellular cytokine staining indicated that CQ reduced TNF-α production pretranslationally without interfering with TNF-α processing or release. We utilized bafilomycin A1 pretreatment to block the pH-dependent trapping of CQ in endosomes and lysosomes. Although bafilomycin A1 alone did not interfere with TNF-α expression, preincubation augmented the ability of CQ to reduce TNF-α mRNA levels, suggesting that CQ did not act by a lysosomotropic mechanism. Using confocal microscopy, we showed that bafilomycin A1 pretreatment resulted in a dramatic redistribution of quinacrine, a fluorescent congener of CQ, from cytoplasmic vacuoles to the nucleus. These data indicate that CQ inhibits TNF-α gene expression without altering translocation of NF-κB p50/p65 heterodimers. This dose-dependent effect occurs over a pharmacologically relevant concentration range and does not require pH-dependent lysosomotropic accumulation of CQ.