Abstract

CC chemokine receptor (CCR) 3 is a chemokine receptor implicated in recruiting cells, particularly eosinophils (EΦ), to the lung in episodes of allergic asthma. To investigate the efficacy of selective, small molecule antagonists of CCR3, we developed a murine model of EΦ recruitment to the lung. Murine eotaxin was delivered intranasally to mice that had previously received i.p. injections of ovalbumin (OVA), and the effects were monitored by bronchoalveolar lavage. A selective eosinophilic influx was produced in animals receiving eotaxin but not saline. Furthermore, the number of EΦ was concentration- and time-dependent. Although anti-CCR3 antibody reduced the number of EΦ, the effect of eotaxin in OVA-sensitized mice was not a direct chemotactic stimulus because mast cell deficiency (in WBB6F₁-Kit^w/Kit^w-v mice) significantly reduced the response. Two representative small molecule CCR3 antagonists from our program were characterized as being active at mouse CCR3. They were administered p.o. to wild-type mice and found to reduce eotaxin-elicited EΦ selectively in a dose-dependent manner. Pump infusion of one of the inhibitors to achieve steady-state levels showed that efficacy was not achieved at plasma concentrations equivalent to the in vitro chemotaxis IC₉₀ but only at much higher concentrations. To extend the results from our recruitment model, we tested one of the inhibitors in an allergenic model of airway inflammation, generated by adoptive transfer of OVA-sensitive murine T helper 2 cells and aerosolized OVA challenge of recipient mice, and found that it inhibited EΦ recruitment. We conclude that small molecule CCR3 antagonists reduce pulmonary eosinophilic inflammation elicited by chemokine or allergenic challenge.