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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.

SUBMITTER: Liu S

PROVIDER: S-EPMC2405912 | biostudies-literature | 2005 Jun

REPOSITORIES: biostudies-literature

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Intermolecular complementation achieves high-specificity tumor targeting by anthrax toxin.

Liu Shihui S Redeye Vivien V Kuremsky Jeffrey G JG Kuhnen Marissa M Molinolo Alfredo A Bugge Thomas H TH Leppla Stephen H SH

Nature biotechnology 20050515 6

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) cleava ...[more]

PMID: 15895075

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Project description:UnlabelledThe actions of many bacterial toxins depend on their ability to bind to one or more cell-surface receptors. Anthrax toxin acts by a sequence of events that begins when the protective-antigen (PA) moiety of the toxin binds to either one of two cell-surface proteins, ANTXR1 and ANTXR2, and is proteolytically activated. The activated PA self-associates to form oligomeric pore precursors, which, in turn, bind the enzymatic moieties of the toxin and transport them to the cytosol. We introduced a double mutation into domain 4 of PA to ablate its native receptor-binding function and fused epidermal growth factor (EGF) to the C terminus of the mutated protein. The resulting fusion protein transported enzymatic effector proteins into a cell line that expressed the EGF receptor (A431 cells), but not into a line lacking this receptor (CHO-K1 cells). Addition of excess free EGF blocked transport of effector proteins into A431 cells via the fusion protein, but not via native PA. We also showed that fusing the diphtheria toxin receptor-binding domain to the C terminus of the mutated PA channeled effector-protein transport through the diphtheria toxin receptor. PA fusion proteins with altered receptor specificity may be useful in biological research and could have practical applications, including ablation or perturbation of selected populations of cells in vivo.ImportanceBacterial toxins that act within mammalian cells have receptor-dependent mechanisms to transport their enzymatic components to the cytoplasmic compartment. By inactivating or otherwise modifying their respective intracellular targets, these intracellular effectors disrupt metabolic pathways and in some cases cause death of the cell. Our results show that the receptor specificity of the transport protein of anthrax toxin may be readily changed, raising the possibility that receptor-redirected forms of protective antigen (PA) and PA homologs may be useful for research and medical applications requiring modification or ablation of designated populations of cells.

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Intermolecular complementation achieves high-specificity tumor targeting by anthrax toxin.

Publications

Intermolecular complementation achieves high-specificity tumor targeting by anthrax toxin.

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