A group of novel VEGF splice variants as alternative therapeutic targets in renal cell carcinoma

The efficacy of anti‐angiogenic treatment by targeting VEGF/VEGF receptors in metastatic clear cell renal cell carcinoma (ccRCC) varies from patient to patient. Discovering the reasons behind this variability could lead to the identification of relevant therapeutic targets. Thus, we investigated the novel splice variants of VEGF that are less efficiently inhibited by anti‐VEGF/VEGFR targeting than the conventional isoforms. By in silico analysis, we identified a novel splice acceptor in the last intron of the VEGF gene resulting in an insertion of 23 bp in VEGF mRNA. Such an insertion can shift the open‐reading frame in previously described splice variants of VEGF (VEGF XXX ), leading to a change in the C‐terminal part of the VEGF protein. Next, we analysed the expression of these alternatively spliced VEGF new isoforms (VEGF XXX/NF ) in normal tissues and in RCC cell lines by qPCR and ELISA, and we investigated the role of VEGF 222/NF (equivalent to VEGF 165 ) in physiological and pathological angiogenesis. Our in vitro data demonstrated that recombinant VEGF 222/NF stimulated endothelial cell proliferation and vascular permeability by activating VEGFR2. In addition, VEGF 222/NF overexpression enhanced proliferation and metastatic properties of RCC cells, whereas downregulation of VEGF 222/NF resulted in cell death. We also generated an in vivo model of RCC by implanting RCC cells overexpressing VEGF 222/NF in mice, which we treated with polyclonal anti‐VEGF XXX/NF antibodies. VEGF 222/NF overexpression enhanced tumour formation with aggressive properties and a fully functional vasculature, while treatment with anti‐VEGF XXX/NF antibodies slowed tumour growth by inhibiting tumour cell proliferation and angiogenesis. In a patient cohort from the NCT00943839 clinical trial, we investigated the relationship between plasmatic VEGF XXX/NF levels, resistance to anti‐VEGFR therapy and survival. High plasmatic VEGF XXX/NF levels correlated with shorter survival and lower efficacy of anti‐angiogenic drugs. Our data confirmed the existence of new VEGF isoforms that could serve as novel therapeutic targets in patients with RCC that are resistant to anti‐VEGFR therapy.