Improving the In Vivo Efficacy of an Anti-Tac (CD25) Immunotoxin by Pseudomonas Exotoxin A Domain II Engineering

• Published in: Molecular cancer therapeutics Vol. 17; no. 7; pp. 1486 - 1493
• Main Authors: Kaplan, Gilad, Mazor, Ronit, Lee, Fred, Jang, Youjin, Leshem, Yasmin, Pastan, Ira
• Format: Journal Article
• Language: English
• Published: United States American Association for Cancer Research Inc 01.07.2018
• Subjects: ADP Ribose Transferases - administration & dosage; ADP Ribose Transferases - genetics; ADP Ribose Transferases - immunology; Animals; Antibodies; Antibodies, Monoclonal - administration & dosage; Antibodies, Monoclonal - genetics; Antibodies, Monoclonal - immunology; Anticancer properties; Antitumor activity; Bacterial Toxins - administration & dosage; Bacterial Toxins - genetics; Bacterial Toxins - immunology; Biocompatibility; Cancer; CD22 antigen; CD25 antigen; Cell Line, Tumor; Cell Proliferation - drug effects; Cleavage; Clinical trials; Conformation; Cytotoxicity; Cytotoxicity, Immunologic - genetics; Effectiveness; Exotoxin A; Exotoxins - administration & dosage; Exotoxins - genetics; Exotoxins - immunology; Furin; Hematologic Neoplasms - drug therapy; Hematologic Neoplasms - genetics; Hematologic Neoplasms - immunology; Humans; Immunogenicity; Immunotoxins; Interleukin-2 Receptor alpha Subunit - antagonists & inhibitors; Interleukin-2 Receptor alpha Subunit - immunology; Lymphocytes T; Medical research; Mesothelin; Mice; Mutation; Point Mutation - genetics; Protein Domains - genetics; Protein Domains - immunology; Protein Engineering; Pseudomonas; Pseudomonas aeruginosa Exotoxin A; Sialic Acid Binding Ig-like Lectin 2 - antagonists & inhibitors; Sialic Acid Binding Ig-like Lectin 2 - immunology; T-Lymphocytes - drug effects; T-Lymphocytes - immunology; Toxicity; Virulence Factors - administration & dosage; Virulence Factors - genetics; Virulence Factors - immunology; Xenograft Model Antitumor Assays
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.mct-17-1041

Tac (CD25) is expressed on multiple hematologic malignancies and is a target for cancer therapies. LMB-2 is an extremely active anti-Tac recombinant immunotoxin composed of an Fv that binds to Tac and a 38-kDa fragment of exotoxin A (PE38). Although LMB-2 has shown high cytotoxicity toward Tac-expressing cancer cells in clinical trials, its efficacy was hampered by the formation of anti-drug antibodies against the immunogenic bacterial toxin and by dose-limiting off-target toxicity. To reduce toxin immunogenicity and nonspecific toxicity, we introduced six point mutations into domain III that were previously shown to reduce T-cell immunogenicity and deleted domain II from the toxin, leaving only the 11aa furin cleavage site, which is required for cytotoxic activity. Although this strategy has been successfully implemented for mesothelin and CD22-targeting immunotoxins, we found that removal of domain II significantly lowered the cytotoxic activity of anti-Tac immunotoxins. To restore cytotoxic activity in the absence of PE domain II, we implemented a combined rational design and screening approach to isolate highly active domain II-deleted toxin variants. The domain II-deleted variant with the highest activity contained an engineered disulfide-bridged furin cleavage site designed to mimic its native conformation within domain II. We found that this approach restored 5-fold of the cytotoxic activity and dramatically improved the MTD. Both of these improvements led to significantly increased antitumor efficacy We conclude that the next-generation anti-Tac immunotoxin is an improved candidate for targeting Tac-expressing malignancies. .