Blood vessels in tumors express higher level of aminopeptidase N (APN) than normal tissues. Evidence suggests that the CNGRC motif is an APN ligand which targets tumor vasculature. Increased expression of APN in tumor vascular endothelium, therefore, offers an opportunity for targeted delivery of NGR peptide-linked drugs to tumors.
Jiang, W., Jin, G., Ma, D., Wang, F., Fu, T., Chen, X., … Hua, Z. (2012). Modification of cyclic NGR tumor neovasculature-homing motif sequence to human plasminogen kringle 5 improves inhibition of tumor growth. PLoS ONE, 7(5). https://doi.org/10.1371/journal.pone.0037132