Assessment of chemokine receptor function on monocytes in whole blood: In vitro and ex vivo evaluations of a CCR2 antagonist

Inhibition of monocyte and macrophage function by targeting chemokine receptors represents an attractive strategy for therapeutic intervention in inflammatory diseases. We describe an assay to assess Chemokine Receptor function on whole blood monocytes by measuring chemokine stimulated change in cell shape as measured by flow cytometry. The relative potential of the chemokine receptors CCR1, CCR2, CCR5, CX(3)CR1, and CXCR4 to activate monocytes in whole blood was evaluated and compared. Analysis of MCP-1 response for monocytes in blood from numerous donors revealed that the assay method had excellent intra-donor reproducibility and sensitivity. Further, the utility of this assay to determine target engagement by Chemokine Receptor antagonists was demonstrated using a CCR2 Antagonist in rhesus monkeys. Blockade of CCR2 on whole blood monocytes was demonstrated ex vivo on blood samples collected from rhesus monkeys administered a small molecule CCR2 Antagonist (MK-0812). Using a delayed-type hypersensitivity reaction to elicit monocyte recruitment to the skin of rhesus monkeys, we also evaluated the ability of MK-0812 to block monocyte migration in vivo. Blockade of CCR2 stimulation of whole blood monocytes was correlated with the inhibition of monocyte recruitment to the skin, validating the potential to use this approach in the evaluation of dose selection for Chemokine Receptor antagonists clinically.