Abstract
Immunotoxins based on Pseudomonas exotoxin A (PE) are promising anticancer agents that combine a variable fragment (Fv) from an antibody to a tumor-associated antigen with a 38-kDa fragment of PE (PE38). The intoxication pathway of PE immunotoxins involves receptor-mediated internalization and trafficking through endosomes/lysosomes, during which the immunotoxin undergoes important proteolytic processing steps but must otherwise remain intact for eventual transport to the cytosol. We have investigated the proteolytic susceptibility of PE38 immunotoxins to lysosomal proteases and found that cleavage clusters within a limited segment of PE38. We subsequently generated mutants containing deletions in this region using HA22, an anti-CD22 Fv-PE38 immunotoxin currently undergoing clinical trials for B-cell malignancies. One mutant, HA22-LR, lacks all identified cleavage sites, is resistant to lysosomal degradation, and retains excellent biologic activity. HA22-LR killed chronic lymphocytic leukemia cells more potently and uniformly than HA22, suggesting that lysosomal protease digestion may limit immunotoxin efficacy unless the susceptible domain is eliminated. Remarkably, mice tolerated doses of HA22-LR at least 10-fold higher than lethal doses of HA22, and these higher doses exhibited markedly enhanced antitumor activity. We conclude that HA22-LR advances the therapeutic efficacy of HA22 by using an approach that may be applicable to other PE-based immunotoxins.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, N.I.H., Intramural
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Research Support, Non-U.S. Gov't
MeSH terms
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ADP Ribose Transferases / adverse effects
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ADP Ribose Transferases / genetics
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ADP Ribose Transferases / pharmacokinetics
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ADP Ribose Transferases / pharmacology*
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Animals
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Antibodies, Monoclonal / adverse effects
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Antibodies, Monoclonal / genetics
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Antibodies, Monoclonal / pharmacokinetics
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Antibodies, Monoclonal / pharmacology*
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Bacterial Toxins / adverse effects
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Bacterial Toxins / genetics
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Bacterial Toxins / pharmacokinetics
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Bacterial Toxins / pharmacology*
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Clinical Trials as Topic
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Endosomes / metabolism
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Exotoxins / adverse effects
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Exotoxins / genetics
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Exotoxins / pharmacokinetics
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Exotoxins / pharmacology*
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Female
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Humans
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Immunoglobulin Variable Region / adverse effects
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Immunoglobulin Variable Region / genetics
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Immunoglobulin Variable Region / pharmacology*
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Immunotoxins / adverse effects
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Immunotoxins / genetics
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Immunotoxins / pharmacokinetics
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Immunotoxins / pharmacology*
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Leukemia, Lymphocytic, Chronic, B-Cell / drug therapy*
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Leukemia, Lymphocytic, Chronic, B-Cell / metabolism
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Lysosomes / metabolism
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Mice
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Mice, Inbred BALB C
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Mice, Nude
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Mutation
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Pseudomonas aeruginosa Exotoxin A
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Sialic Acid Binding Ig-like Lectin 2*
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Virulence Factors / adverse effects
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Virulence Factors / genetics
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Virulence Factors / pharmacokinetics
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Virulence Factors / pharmacology*
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Xenograft Model Antitumor Assays*
Substances
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Antibodies, Monoclonal
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Bacterial Toxins
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CD22 protein, human
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Cd22 protein, mouse
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Exotoxins
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Immunoglobulin Variable Region
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Immunotoxins
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Sialic Acid Binding Ig-like Lectin 2
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Virulence Factors
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ADP Ribose Transferases