Loss of apelin blocks the emergence of sprouting angiogenesis in experimental tumors
Angiogenesis-inhibitor (AI) drugs targeting vascular endothelial growth factor (VEGF) signalling to the endothelial cell (EC) are used to treat various cancers types. However, primary or secondary resistance to therapy is common. Clinical and pre-clinical studies suggest that other alternative pro-angiogenic factors are up-regulated after VEGF-pathway inhibition. Therefore, identification alternative pro-angiogenic pathway(s) is critical for the development of more effective anti-angiogenic therapy. Here we study the role of apelin as a pro-angiogenic G-protein coupled receptor (GPCR) ligand in tumor growth and angiogenesis. We applied single-cell RNA-sequencing to Mouse Lewis lung carcinoma (LLC1) or B16F10 mouse melanoma cell lines (1 X 106)  implanted subcutaneously into the flanks of 12 weeks old Apln-/y or littermate control mice in combination with sunitinib or control (vehicle) treatment. We found apelin loss reduced angiogenic sprouting and tip cell marker gene expression in comparison to the sunitinib-alone treated mice and prevented EC tip cell differentiation.