Identification of Entacapone as a Novel β-Arrestin 1 Biased Antagonist of CXCR7

Background: The C-X-C chemokine receptor type 7 (CXCR7), also known as atypical chemokine receptor 3 (ACKR3), primarily signals through β-arrestin and plays a pivotal role in tumor progression, inflammation, and neurodegenerative diseases. CXCR7 antagonists block chemokine binding and dampen β-arrestin signaling. Accordingly, identification of such antagonists is highly desirable for therapeutic development against CXCR7 driven pathologies. Methods: Through microscale thermophoresis (MST) screening of a Food and Drug Administration (FDA)-approved drug library, entacapone was identified as a CXCR7 binder. The NanoBit complementation assay was employed to evaluate the effect of entacapone on CXCR7 mediated β-arrestin 1/2 recruitment. Molecular docking was performed to predict the binding pocket and binding sites. Results: Entacapone specifically bound to CXCR7 with a Kd value of 6.04 µM. Although entacapone did not directly activate CXCR7, it selectively inhibited CXCL12 and VUF11207 induced β-arrestin 1 recruitment with no significant effect on β-arrestin 2 recruitment. Molecular docking suggested that entacapone interacted with key residues via hydrophobic contacts, including Trp100, Phe124, Gln301, and Leu305, and formed hydrogen bonds with Ser103, Asn108, and Tyr51 in the transmembrane core, collectively suggesting a possible binding mode compatible with stabilizing the receptor in an inactive conformation. Conclusions: Entacapone, a clinically well established COMT inhibitor, is reported for the first time as a novel biased antagonist of CXCR7, providing a new candidate molecule for drug repurposing.