Another gene pathway deals with the VEGF gene, Vascular Endothelial Growth Factor, which remains involved in the process of angiogenesis or the formation of new blood vessels. The formation of an intramolecular G-quadruplex structure has been shown through studies on the polypurine tract of the promoter region of the VEGF gene. Through recent research on the role of G-quadruplex function in vivo, the stabilization of G-quadruplex structures was shown to regulate VEGF gene transcription, with inhibition of transcription factors in this pathway. The intramolecular G-quadruplex structures are formed mostly through the abundant guanine sequence in the promoter region of this specific pathway. The cyclin-dependent cell cycle checkpoint kinase inhibitor-1 CDKN1A (also known as p21) gene harbours promoter G-quadruplex. Interaction of this G-quadruplex with TRF2 (also known as TERF2) resulted in epigenetic regulation of p21, which was tested using the G-quadruplex-binding ligand 360A.