The two PA mutants, PA-L1 and PA-U2, were programmed to be specific for several cancer cell lines in vitro by changing the cleavage site from furin to matrix metalloproteases (MMPs) and urokinase plasminogen activator (uPA), respectively [52,53], which are overexpressed in many cancer types while not very abundant at the surface of normal cells. Here, PLAU is linked to cancer.