AZD8797 is an allosteric non-competitive modulator of the human CX3CR1 receptor

The chemokine receptor CX(3)CR1 has been implicated as an attractive therapeutic target in several diseases, including atherosclerosis and diabetes. However, there has been a lack of non-peptide CX(3)CR1 inhibitors to substantiate these findings. A selective small-molecule inhibitor of CX(3)CR1, AZD8797, was recently reported and we present here an in-depth in vitro characterization of that molecule. In a flow adhesion assay, AZD8797 antagonized the natural ligand, fractalkine (CX(3)CL1), in both human whole blood (hWB) and in a B-lymphocyte cell line with IC(50) values of 300 and 6 nM respectively. AZD8797 also prevented G-protein activation in a [(35)S]GTPγS (guanosine 5′-[γ-thio]triphosphate) accumulation assay. In contrast, dynamic mass redistribution (DMR) experiments revealed a weak G(αi)-dependent AZD8797 agonism. Additionally, AZD8797 positively modulated the CX(3)CL1 response at sub-micromolar concentrations in a β-arrestin recruitment assay. In equilibrium saturation binding experiments, AZD8797 reduced the maximal binding of (125)I-CX(3)CL1 without affecting K(d). Kinetic experiments, determining the k(on) and k(off) of AZD8797, demonstrated that this was not an artefact of irreversible or insurmountable binding, thus a true non-competitive mechanism. Finally we show that both AZD8797 and GTPγS increase the rate with which CX(3)CL1 dissociates from CX(3)CR1 in a similar manner, indicating a connection between AZD8797 and the CX(3)CR1-bound G-protein. Collectively, these data show that AZD8797 is a non-competitive allosteric modulator of CX(3)CL1, binding CX(3)CR1 and effecting G-protein signalling and β-arrestin recruitment in a biased way.