Abstract

Here we describe the pharmacologic properties of a series of clinically relevant chemoattractant receptor-homologous molecules expressed on T-helper type 2 (CRTh2) receptor antagonists, including fevipiprant (NVP-QAW039 or QAW039), which is currently in development for the treatment of allergic diseases. [³H]-QAW039 displayed high affinity for the human CRTh2 receptor (1.14 ± 0.44 nM) expressed in Chinese hamster ovary cells, the binding being reversible and competitive with the native agonist prostaglandin D₂ (PGD₂). The binding kinetics of QAW039 determined directly using [³H]-QAW039 revealed mean kinetic on (k_on) and off (k_off) values for QAW039 of 4.5 × 10⁷ M^-1min⁻¹ and 0.048 minute⁻¹, respectively. Importantly, the k_off of QAW039 (half-life = 14.4 minutes) was >7-fold slower than the slowest reference compound tested, AZD-1981. In functional studies, QAW039 behaved as an insurmountable antagonist of PGD₂-stimulated [³⁵S]-GTPγS activation, and its effects were not fully reversed by increasing concentrations of PGD₂ after an initial 15-minute incubation period. This behavior is consistent with its relatively slow dissociation from the human CRTh2 receptor. In contrast for the other ligands tested this time-dependent effect on maximal stimulation was fully reversed by the 15-minute time point, whereas QAW039’s effects persisted for >180 minutes. All CRTh2 antagonists tested inhibited PGD₂-stimulated human eosinophil shape change, but importantly QAW039 retained its potency in the whole-blood shape-change assay relative to the isolated shape change assay, potentially reflective of its relatively slower off rate from the CRTh2 receptor. QAW039 was also a potent inhibitor of PGD₂-induced cytokine release in human Th2 cells. Slow CRTh2 antagonist dissociation could provide increased receptor coverage in the face of pathologic PGD₂ concentrations, which may be clinically relevant.