Improved antitumor activity of a recombinant anti-Lewis(y) immunotoxin not requiring proteolytic activation

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 93; no. 3; pp. 974 - 978
• Main Authors: Kuan, C T, Pastan, I
• Format: Journal Article
• Language: English
• Published: United States National Acad Sciences 06.02.1996
• Subjects: Adenocarcinoma - drug therapy; ADP Ribose Transferases; Animals; Antibodies, Monoclonal; Antineoplastic Agents - therapeutic use; Antineoplastic Agents - toxicity; Bacterial Toxins; Base Sequence; Breast Neoplasms; Cell Survival - drug effects; DNA Primers; Exotoxins - biosynthesis; Exotoxins - therapeutic use; Exotoxins - toxicity; Female; Humans; Immunotoxins - therapeutic use; Immunotoxins - toxicity; L Cells; Leukemia, T-Cell; Lewis Blood Group Antigens - immunology; Male; Mice; Mice, Inbred BALB C; Mice, Nude; Molecular Sequence Data; Mutagenesis, Site-Directed; Polymerase Chain Reaction; Prostatic Neoplasms; Pseudomonas aeruginosa; Pseudomonas aeruginosa Exotoxin A; Recombinant Proteins - biosynthesis; Recombinant Proteins - therapeutic use; Recombinant Proteins - toxicity; Stomach Neoplasms; Transplantation, Heterologous; Tumor Cells, Cultured; Virulence Factors
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.93.3.974

B1(dsFv)-PE33 is a recombinant immunotoxin composed of a mutant form of Pseudomonas exotoxin (PE) that does not need proteolytic activation and a disulfide-stabilized Fv fragment of the anti-Lewis(y) monoclonal antibody B1, which recognizes a carbohydrate epitope on human carcinoma cells. In this molecule, amino acids 1-279 of PE are deleted and domain Ib (amino acids 365-394) is replaced by the heavy chain variable region (VH) domain of monoclonal antibody B1. The light chain (VL) domain is connected to the VH domain by a disulfide bond. This recombinant toxin, termed B1(dsFv)-PE33, does not require proteolytic activation and it is smaller than other immunotoxins directed at Lewis(y), all of which require proteolytic activation. Furthermore, it is more cytotoxic to antigen-positive cell lines. B1(dsFv)-PE38 has the highest antitumor activity of anti-Lewis(y) immunotoxins previously constructed. B1(dsFv)-PE33 caused complete regression of tumors when given at 12 micrograms/kg (200 pmol/kg) every other day for three doses, whereas B1(dsFv)-PE38 did not cause regressions at 13 micrograms/kg (200 pmol/kg). By bypassing the need for proteolytic activation and decreasing molecular size we have enlarged the therapeutic window for the treatment of human cancers growing in mice, so that complete remissions are observed at 2.5% of the LD50.