NRP1 and neoplasm: To show the synergy between the two peptides, Sugahara et al. (2009) constructed a cyclic fusion sequence of c(CRGDK/RGPD/EC) that triggers tissue penetration of drugs through three processes: The RGD motif targets integrin αvβ3 to accumulate at tumor endothelium cells, then exposes the cryptic CendR motif, RGDK/R, by proteolytic cleavage, and finally induces tumor penetration following interaction with neuropilin-1.