Retroviral gene delivery system activatable by plasmin

In the current study, the construction of a plasmin-activatable epidermal growth factor (EGF)receptor targeted vector is described. The 52 amino acid EGF-receptor binding domain was linked to codon + 1 of the N- terminus of the 4070A envelope glycoprotein (SU) via a PSIQYRGL (single letter amino acid code) plasmin-sensitive linker. The plasmin-cleavable vector gave low background infectivity on EGF-receptor positive human epithelial carcinoma A431 cells but was efficiently activated by endogenous proteases on EGF-receptor positive human fibrosarcoma HT1080 cells. Addition of exogenous plasminogen to the A431 cells increased the infectivity of the Er-.WSN.A vector up to 12-fold and this plasmin-dependent increase in infectivity of the vector could be suppressed by addition of aprotinin, a serine protease inhibitor.