PLAU and cancer: Another approach is to insert the natural ligand of special receptor that is enriched in cancer cells to the surface of the virus, for example interleukin-13 receptor α2 chain (IL-13Rα2) and N-terminal fragment of urokinase-type plasminogen activator are in enriched in some kind of cancer cells (Debinski et al., 1999; Zhou et al., 2002; Kamiyama et al., 2006).