LATE-BREAKING ABSTRACT: A novel role for CCR3 in promoting airways hyperreactivity; Role for CCR3-muscarinic M3 receptor heterodimers

We have developed a novel therapeutic inhibitor against the chemokine receptor CCR3 for allergic asthma that significantly inhibited the MCh PC 20 response in a Phase IIa trial in mild-to-moderate asthmatics. In vivo , AXP1275 had shown significant efficacy in reducing inflammatory mediators and cellular infiltrates in non-human primate models of allergic asthma, and, surprisingly, had also inhibited airways hyperreactivity and methacholine constriction responses (PC 150 ). In addition, inhibition was seen with ex-vivo carbachol (CCh)-induced constriction in human lung tissue. In order to discern pharmacologically-relevant mechanisms for inhibition of CCh-induced lung constriction by AXP1275, we have investigated the receptor pharmacology of CCR3 in human lung tissue. Immunohistochemically, CCR3 is present on epithelium and smooth muscle, and is co-localized with the muscarinic M3 receptor. In receptor transfectants, CCL11 and CCh cross-sensitize agonist-induced calcium mobilization, suggesting cooperativity between CCR3 and M3. AXP1275 and muscarinic receptor antagonists inhibit responses in a similarly-cooperative manner. Bioluminescence resonance energy transfer (BRET) assays demonstrated that CCR3 and M3 heterodimerize, and this was further supported by receptor co-immunoprecipitation assays. Receptor heterodimerization of CCR3 and M3 on non-leukocytic cells in vivo may provide a plausible explanation for the efficacy of CCR3-selective inhibitors on the hyperreactivity response in asthma.