Engineering Native-like GPCR Antigens Enables Discovery of an LPA2-Blocking Antibody for Ovarian Cancer

G-protein-coupled receptors (GPCRs) are high-value therapeutic targets, yet antibody discovery remains limited by difficulties in preparing antigens that preserve native conformations. Here, we engineered a native-like, full-length human LPA2 antigen by combining N-terminal P9* fused with amphipathic poly-γ-glutamate (APG) stabilization, affording an antigen suitable for the selection of antibodies with therapeutic efficacy. By screening a large synthetic human scFv library, we isolated an antagonistic antibody against LPA2 that bound LPA2 selectively over LPA1 (EC₅₀: 4.5 nM for IgG; 30 nM for scFv). The discovered antibody inhibited the growth of SKOV-3, an ovarian cancer cell line, <i>in vitro</i> by reducing the phosphorylation of multiple signaling pathways, including p38, protein kinase B (Akt), and signal transducer and activator of transcription 3 (STAT3), with particularly strong suppression of extracellular signal regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). <i>In vivo</i>, the antibody suppressed tumor growth in SKOV-3 xenografted BALB/c nude mice without affecting body weight. Furthermore, computational docking revealed that the anti-LPA2 antibody blocked LPA-mediated downstream signaling by masking the ligand-binding pocket of LPA2. Collectively, these results validate an engineering-first strategy for generating native-like GPCR antigens that enable the discovery of functional anti-GPCR antibodies with therapeutic efficacy and is readily generalizable to other challenging membrane targets.