Abstract
We tested efficacy of a urokinase‐activated recombinant anthrax toxin (PrAgU2/FP59) on 11 human AML cell lines. PrAgU2/FP59 consists of PrAgU2, the cell binding domain in which the furin activation site is replaced by a urokinase plasminogen activator (uPA) activation site and FP59, the catalytic domain, consisting of Pseudomonas aeruginosa exotoxin A. PrAgU2 binds cells, is cleaved by uPA, heptamerizes, binds 3 molecules of FP59 and undergoes endocytosis releasing FP59 in the cytosol. FP59 ADP ribosylates EF2 causing protein synthesis inhibition and cell death. Introduction of the uPA activation site selectively targets this toxin to tumor cells expressing an active uPA system.7/11 AML cell lines were highly sensitive to PrAgU2/FP59 (IC50 = 0.5–33 pM, % cell kill > 95%) while 4/11 cell lines were moderately sensitive to PrAgU2/FP59 (IC50 = 160–410 pM, % cell kill > 70%). Addition of pro‐uPA increased AML sensitivity to PrAgU2/FP59 by an average of 40 fold. Addition of a neutralizing anti‐uPA antibody decreased toxicity of PrAgU2/FP59 to AML cells by an average of 14 fold, demonstrating requirement for active uPA for selective activation of PrAgU2/FP59.AML cells are sensitive to the cytotoxic effects of a urokinase‐targeted recombinant anthrax toxin with sensitivity depending on the expression of active uPA. PrAgU2/FP59 is a promising tumor selective therapeutic for the potential treatment of AML.
Published Version
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