Mast cells, neutrophils, and macrophages are important inflammatory cells that have been implicated in the pathogenesis of acute and chronic inflammatory diseases. To explore a novel antiinflammatory agent, we have synthesized two types of acridines, 9-anilinoacridine and 9-phenoxyacridine derivatives, for evaluation on the grounds that acridine is a versatile heterocycle possessing a wide variety of biological properties. The title compounds were synthesized by reaction of 9-chloroacridine with appropriate Ar-NH(2) and Ar-OH, and their antiinflammatory activities on inhibitory effects on the activation of mast cells, neutrophils, and macrophages were studied. Three acridine derivatives 4, 10, and 11 were proved to be more potent than the reference inhibitor mepacrine for the inhibition of rat peritoneal mast cell degranulation with similar IC(50) values (16-21 microM). Compound 3 also showed potent inhibitory activity (IC(50) = 8.2 and 4.4 microM, respectively) for the secretion of lysosomal enzyme and beta-glucuronidase from neutrophils. Moreover, compounds 5 and 9 were shown to be efficacious inhibitors of TNF-alpha production in macrophage-like cell lines RAW 264.7. Compounds 2 and 12 were the potent inhibitors of TNF-alpha production in murine microglial cell lines N9. To further explore the cytotoxic properties of these acridine derivatives, (E)-12 was selected for NCI's in vitro disease-oriented tumor cells screen. The results indicated that this compound had no significant cytotoxicity with a mean GI(50) of 58.0 microM. These results indicated that the antiinflammatory effects of acridine derivatives were mediated, at least in part, through the suppression of chemical mediators released from mast cells, neutrophils, and macrophages and that these compounds have the potential to be novel antiinflammatory agents with no significant cytotoxicity.