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#immunotoxins

6 public questions tagged with this topic.

Immunological Applications

Which toxin is commonly used in immunotoxins?

Selecting optimal toxin component for immunoconjugate involves potency, intracellular stability, lack of mammalian cell surface receptors to avoid nonspecific uptake, and ability to produce recombinant fusion maintaining disulfide integrity. Diphtheria toxin secreted by toxigenic Corynebacterium diphtheriae, 58 kDa single polypeptide proteolytically cleaved into 21 kDa catalytic A fragment and 37 kDa binding-translocation B fragment linked by single disulfide Cys186-Cys201. Catalytic activity transfers ADP-ribose to elongation factor 2 with turnover number approximately 1000 per minute. Native

Ref: Weldon & Pastan FEBS J 2011 PE38 DT388 catalytic domain; Collier EF2 ADP-ribosylation translation arrest mechanism.

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Immunological Applications

Immunotoxins kill target cells mainly by:

Mechanism by which protein toxins arrest protein synthesis culminates in rapid programmed cell death via mitochondrial pathway capable of killing quiescent cells. Diphtheria toxin fragment A catalyzes ADP-ribosylation of unusual post-translationally modified histidine diphthamide at position 699 of eukaryotic elongation factor 2 present exclusively on domain IV, using oxidized NAD+ as ADP-ribose donor releasing nicotinamide. Modified elongation factor cannot mediate translocation step of peptidyl-tRNA from A site to P site on 60S ribosomal subunit, halting elongation after single round. Ricin

Ref: Collier Annu Rev Biochem 1975 diphtheria ADP-ribosyl EF2; Olsnes Pharmac Ther ribosome N-glycosidase ricin apoptosis.

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Immunological Applications

Immunotoxins are composed of:

Immunotoxins constructed to overcome lack of selectivity of conventional chemotherapy achieve tumor specific delivery of ultrapotent protein toxins that cannot enter mammalian cells unaided. Design consists of targeting moiety typically single-chain variable fragment scFv or disulfide stabilized Fab derived from murine or humanized antibody recognizing tumor antigen CD22 on hairy cell leukemia, CD25 on adult T cell leukemia, mesothelin on mesothelioma, linked via flexible glycine-serine peptide or reducible disulfide bond formed between engineered cysteines to effector toxin devoid of native r

Ref: Pastan et al Nature Rev Cancer 2006 6:559 immunotoxins PE38; Kreitman Clin Cancer Res 2009 fusion toxin de-immunized.

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Immunological Applications

Which toxin is commonly used in immunotoxins?

Diphtheria toxin produced Corynebacterium diphtheriae lysogenized temperate corynephage beta carrying tox gene regulated iron-dependent repressor DtxR provides ideal warhead immunotoxin because catalytic mechanism well characterized potency extreme one molecule sufficient kill cell enzymatic turnover inactivating millions ribosomes extensive clinical experience vaccine toxoid. AB architecture A domain catalytic 21 kDa active site Glu148 critical nucleophile performing NAD-dependent ADP-ribosylation EF2 B domain receptor-binding translocation B composed receptor-binding subdomain C-terminal 482

Ref: Pastan Diphtheria Toxin Immunotoxin Clinical Development 2009; FDA Ontak Tagraxofusp DT Fusion Mechanism Label; Collier Diphtheria Toxin Structure Function Catalysis Enzymology.

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Immunological Applications

Immunotoxins kill target cells mainly by:

Protein toxins employed immunotoxin design kill primarily through catalytic inactivation protein synthesis machinery requiring only few molecules cytosol triggering irreversible apoptosis. Diphtheria toxin fragment A 21 kDa ADP-ribosyltransferase modifies diphthamide residue unique post-translationally modified histidine 699 eukaryotic elongation factor 2 synthesized seven enzymes DPH1-7 adding 3-amino-3-carboxypropyl trimethylation diphthine amidation transferring ADP-ribose oxidized NAD imidazole inhibiting translocation peptidyl tRNA A site P site elongation cycle 80S ribosome mediated GTP

Ref: Collier 1967 Diphtheria Toxin ADP-ribosylation EF2 Discovery; Pastan PE38 Protein Synthesis Inhibition Mechanism; Lodish Protein Synthesis eEF2 Function Chapter 7.

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Immunological Applications

Immunotoxins are composed of:

Immunotoxins chimeric proteins integrating targeting domain derived monoclonal antibody and cytotoxic domain protein toxin to achieve picomolar potency against malignant cells expressing defined surface antigen. Antibody moiety typically Fab prime 50 kDa scFv 25 kDa composed heavy variable light variable domains connected glycine serine linker disulfide-stabilized Fv dsFv recognizing tumor antigens CD22 135 kDa hairy cell leukemia CD25 IL-2 receptor alpha cutaneous T-cell lymphoma mesothelin 40 kDa GPI-anchored mesothelioma pancreatic adenocarcinoma HER2 with affinity 1-10 nM. Toxin component

Ref: Pastan Annu Rev Med 2007 Immunotoxin Construction Principles Review; FDA Lumoxiti Moxetumomab Design Label; Janeway Immunotoxin Antibody Toxin Fusion Mechanism.

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