title: Tumor cell-selective cytotoxicity of matrix metalloproteinase-activated anthrax toxin.
abstract: Matrix metalloproteinases (MMPs) are overexpressed in a variety of tumor tissues and cell lines, and their expression is highly correlated to tumor invasion and metastasis. To exploit these characteristics in the design of tumor cell-selective cytotoxins, we constructed two mutated anthrax toxin protective antigen (PA) proteins in which the furin protease cleavage site is replaced by sequences selectively cleaved by MMPs. These MMP-targeted PA proteins were activated rapidly and selectively on the surface of MMP-overexpressing tumor cells. The activated PA proteins caused internalization of a recombinant cytotoxin, FP59, consisting of anthrax toxin lethal factor residues 1-254 fused to the ADP-ribosylation domain of Pseudomonas exotoxin A. The toxicity of the mutated PA proteins for MMP-overexpressing cells was blocked by hydroxamate inhibitors of MMPs, including BB94, and by a tissue inhibitor of matrix metalloproteinases (TIMP-2). The mutated PA proteins killed MMP-overexpressing tumor cells while sparing nontumorigenic normal cells when these were grown together in a coculture model, indicating that PA activation occurred on the tumor cell surface and not in the supernatant. This method of achieving cell-type specificity is conceptually distinct from, and potentially synergistic with, the more common strategy of retargeting a protein toxin by fusion to a growth factor, cytokine, or antibody.
authors.affiliation: Oral Infection and Immunity Branch, National Institute of Dental and Craniofacial Research, NIH, Bethesda, Maryland 20892-4350, USA.
authors.forename: S
authors.initials: S
authors.lastname: Liu
authors.forename: S
authors.initials: S
authors.lastname: Netzel-Arnett
authors.forename: H
authors.initials: H
authors.lastname: Birkedal-Hansen
authors.forename: S H
authors.initials: SH
authors.lastname: Leppla
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000942:Antigens, Bacterial; D001427:Bacterial Toxins / Q000235:genetics / Q000493:pharmacokinetics* / Q000633:toxicity*; D001665:Binding Sites; D001711:Biotransformation; D001943:Breast Neoplasms / Q000188:drug therapy / Q000201:enzymology; D019556:COS Cells / Q000201:enzymology; D002522:Chlorocebus aethiops; D018920:Coculture Techniques; D005354:Fibrosarcoma / Q000188:drug therapy / Q000201:enzymology; D006801:Humans; D020778:Matrix Metalloproteinase 2 / Q000096:biosynthesis / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000096:biosynthesis / Q000378:metabolism; D020782:Matrix Metalloproteinases / Q000096:biosynthesis / Q000378:metabolism*; D053504:Matrix Metalloproteinases, Membrane-Associated; D008545:Melanoma / Q000188:drug therapy / Q000201:enzymology; D008666:Metalloendopeptidases / Q000096:biosynthesis / Q000378:metabolism; D009154:Mutation; D014407:Tumor Cells, Cultured; D014709:Vero Cells / Q000201:enzymology
chemical_list: D000942:Antigens, Bacterial; D001427:Bacterial Toxins; C030325:anthrax toxin; D020782:Matrix Metalloproteinases; D053504:Matrix Metalloproteinases, Membrane-Associated; D008666:Metalloendopeptidases; D020778:Matrix Metalloproteinase 2; D020780:Matrix Metalloproteinase 9