title: Intermolecular complementation achieves high-specificity tumor targeting by anthrax toxin.
abstract: Anthrax toxin protective antigen (PrAg) forms a heptamer in which the binding site for lethal factor (LF) spans two adjacent monomers. This suggested that high cell-type specificity in tumor targeting could be obtained using monomers that generate functional LF-binding sites only through intermolecular complementation. We created PrAg mutants with mutations affecting different LF-binding subsites and containing either urokinase plasminogen activator (uPA) or matrix metalloproteinase (MMP) cleavage sites. Individually, these PrAg mutants had low toxicity as a result of impaired LF binding, but when administered together to uPA- and MMP-expressing tumor cells, they assembled into functional LF-binding heteroheptamers. The mixture of two complementing PrAg variants had greatly reduced toxicity in mice and was highly effective in the treatment of aggressive transplanted tumors of diverse origin. These results show that anthrax toxin, and by implication other multimeric toxins, offer excellent opportunities to introduce multiple-specificity determinants and thereby achieve high therapeutic indices.
authors.affiliation: Microbial Pathogenesis Section, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Shihui
authors.initials: S
authors.lastname: Liu
authors.forename: Vivien
authors.initials: V
authors.lastname: Redeye
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Kuremsky
authors.forename: Marissa
authors.initials: M
authors.lastname: Kuhnen
authors.forename: Alfredo
authors.initials: A
authors.lastname: Molinolo
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Bugge
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Leppla
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000942:Antigens, Bacterial / Q000737:chemistry* / Q000494:pharmacology*; D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000737:chemistry* / Q000494:pharmacology*; D001665:Binding Sites; D045744:Cell Line, Tumor; D016503:Drug Delivery Systems / Q000379:methods*; D004354:Drug Screening Assays, Antitumor; D005260:Female; D006801:Humans; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D011485:Protein Binding; D015202:Protein Engineering
chemical_list: D000942:Antigens, Bacterial; D000970:Antineoplastic Agents; D001427:Bacterial Toxins; C030325:anthrax toxin