In Vitro and In Vivo Antagonism of a G Protein-Coupled Receptor (S1P3) with a Novel Blocking Monoclonal Antibody

Background S1P 3 is a lipid-activated G protein-couple receptor (GPCR) that has been implicated in the pathological processes of a number of diseases, including sepsis and cancer. Currently, there are no available high-affinity, subtype-selective drug compounds that can block activation of S1P 3 . We have developed a monoclonal antibody (7H9) that specifically recognizes S1P 3 and acts as a functional antagonist. Methodology/Principal Findings Specific binding of 7H9 was demonstrated by immunocytochemistry using cells that over-express individual members of the S1P receptor family. We show, in vitro, that 7H9 can inhibit the activation of S1P 3 -mediated cellular processes, including arrestin translocation, receptor internalization, adenylate cyclase inhibiton, and calcium mobilization. We also demonstrate that 7H9 blocks activation of S1P 3 in vivo, 1) by preventing lethality due to systemic inflammation, and 2) by altering the progression of breast tumor xenografts. Conclusions/Significance We have developed the first-reported monoclonal antibody that selectively recognizes a lipid-activated GPCR and blocks functional activity. In addition to serving as a lead drug compound for the treatment of sepsis and breast cancer, it also provides proof of concept for the generation of novel GPCR-specific therapeutic antibodies.