Detection of Endogenous Ligand Bias: A Case Study Using the Chemokine Receptor Family

A Green1, TS Wehrman1, DL Bassoni1, JJ Campbell2, NP Gerard3, C Gerard3, S Rajagopal4. 1DiscoveRx Corporation, Fremont, California, USA, 2Department of Dermatology, Brigham and Women’s Hospital, Boston, MA, USA, 3Division of Respiratory Diseases, Department of Pediatrics, Children’s Hospital, Boston, MA, USA, 4Department of Medicine, Duke University Medical Center, Durham, NC, USA

The pattern of intracellular signaling downstream of GPCR activation is now known to be specific to the ligand-receptor pair as opposed to an inherent, rigid property of the receptor. In a drug discovery setting, this property of GPCRs is now being exploited to develop designer molecules that have tailored intracellular responses. Although pathway bias is typically associated with synthetic molecules, we hypothesized that receptors having multiple endogenous ligands could use the same principles to tailor their cellular responses. The chemokine receptor family was selected due to the ability of several ligands to activate multiple targets and vice versa. The receptor responses were profiled in second messenger, β-arrestin and internalization assays. Although many ligands signal equally well in all three systems, a surprising number of ligands exhibited significant bias. Importantly, these biased molecules also had differential effects when assayed on primary cells, confirming the differences observed using the recombinant systems. Taken together these results suggest that functional selectivity is a generally applicable phenomenon of synthetic as well as endogenous ligands.