AMD3100 Is a CXCR7 Ligand with Allosteric Agonist Properties

The bicyclam AMD3100 is known as a small synthetic inhibitor of the CXCL12-binding chemokine receptor CXCR4. Here, we show that AMD3100 also binds to the alternative CXCL12 receptor CXCR7. CXCL12 or AMD3100 alone activate beta-arrestin recruitment to CXCR7, which we identify as a previously unreported signaling pathway of CXCR7. In addition, AMD3100 increases CXCL12 binding to CXCR7 and CXCL12-induced conformational rearrangements in the receptor dimer as measured by bioluminescence resonance energy transfer. Moreover, small but reproducible increases in the potency of CXCL12-induced arrestin recruitment to CXCR7 by AMD3100 are observed. Taken together, our data suggest that AMD3100 is an allosteric agonist of CXCR7. The finding that AMD3100 not only binds CXCR4, but also to CXCR7, with opposite effects on the two receptors, calls for caution in the use of the compound as a tool to dissect CXCL12 effects on the respective receptors in vitro and in vivo.