Role of CELSR2 in tumor progression and its targeting in triple negative breast cancer

Triple-negative breast cancer (TNBC) presents a significant public health challenge due to its molecular heterogeneity, high metastatic potential, and resistance to conventional therapies. Although targeted treatments such as PARP inhibitors and immune checkpoint inhibitors have been approved in recent years, the majority of patients derive limited benefit from these options. To identify novel therapeutic targets for TNBC, we investigated Cadherin EGF LAG seven-pass G-type receptor 2 (CELSR2)—an adhesion G-protein coupled receptor (GPCR) primarily studied in the context of neural development, coronary artery disease, scoliosis, and metabolic disorders. Our analyses revealed that CELSR2 overexpression correlates with significantly reduced metastasis-free and overall survival in TNBC patients. Furthermore, transcriptomic data showed increased CELSR2 expression in metastatic lesions compared to primary tumors. At the single-cell level, CELSR2 expression was largely confined to malignant cells within tumors, while normal tissues showed minimal expression, suggesting CELSR2 may represent a promising and selective therapeutic target. Functional studies using siRNA and shRNA-mediated knockdown of CELSR2 led to marked reductions in TNBC cell proliferation, migration, and invasion through the extracellular matrix. To elucidate the underlying mechanisms, we found that CELSR2 activates the cAMP/PKA/CREB signaling pathway, thereby promoting oxidative phosphorylation in TNBC cells. In vivo, xenografts of CELSR2-silenced TNBC cells in immunodeficient NSG mice exhibited impaired tumor growth and reduced Ki67 expression, confirming its tumor-promoting role. To assess CELSR2's druggability, we immunized a llama with cell membranes from MCF7 cells—a line with high CELSR2 expression. After constructing a nanobody library, we performed iterative screenings using CELSR2-expressing cells and the recombinant extracellular domain of CELSR2. Two nanobodies specific to CELSR2 were isolated. Treatment with these nanobodies significantly inhibited TNBC cell proliferation and migration, mirroring the phenotypes observed upon genetic knockdown. In summary, our study reveals a previously unrecognized role for CELSR2 in TNBC progression and provides a proof-of-concept for targeting this receptor with nanobody-based therapies. These findings support CELSR2 as a promising candidate for therapeutic intervention in triple-negative breast cancer.