In vitro activity: SCH 563705 is a novel potent and orally active antagonist of CXCR2 and CXCR1 with good oral pharmacokinetic profiles in rat, mouse, monkey, and dog. It has IC50 values of 1.3 nM, 7.3 nM and Kis of 1 and 3 nM for CXCR2 and CXCR1, respectively. Targeting neutrophil migration with the CXCR2/CXCR1 antagonist SCH563705 led to a dose-dependent decrease in clinical disease scores and paw thickness measurements and clearly reduced inflammation and bone and cartilage degradation based on histopathology and paw cytokine analyses. In contrast, targeting monocyte migration with the CCR2 antagonist MK0812 had no effect on arthritis disease severity. The pharmacodynamic activities of both SCH563705 and MK0812 were verified by assessing their effects on the peripheral blood monocyte and neutrophil populations. SCH563705 selectively reduced the peripheral blood neutrophil frequency, and caused an elevation in the CXCR2 ligand CXCL1. MK0812 selectively reduced the peripheral blood monocyte frequency, and caused an elevation in the CCR2 ligand CCL2. The much greater impact of CXCR2/CXCR1 antagonism relative to CCR2 antagonism in this model of arthritis highlights the therapeutic potential for targeting CXCR2/CXCR1 in human arthritides.

Kinase Assay: SCH 563705 is a potent and orally available CXCR2 and CXCR1 antagonist, with IC50s of 1.3 nM, 7.3 nM and Kis of 1 and 3 nM, respectively. SCH 563705 shows potent inhibition against both Gro-a and IL-8 induced human neutrophil migration (chemotaxis IC50 = 0.5 nM, against 30 nM of Gro-a; chemotaxis IC50 = 37 nM, against 3 nM of IL-8). SCH 563705 potently inhibits mouse CXCR2 (IC50 = 5.2 nM)

Cell Assay: In contrast, targeting monocyte migration with the CCR2 antagonist MK0812 had no effect on arthritis disease severity. The pharmacodynamic activities of both SCH563705 and MK0812 were verified by assessing their effects on the peripheral blood monocyte and neutrophil populations. SCH563705 selectively reduced the peripheral blood neutrophil frequency, and caused an elevation in the CXCR2 ligand CXCL1. MK0812 selectively reduced the peripheral blood monocyte frequency, and caused an elevation in the CCR2 ligand CCL2. The much greater impact of CXCR2/CXCR1 antagonism relative to CCR2 antagonism in this model of arthritis highlights the therapeutic potential for targeting CXCR2/CXCR1 in human arthritides.