title: A recombinant immunotoxin against the tumor-associated antigen mesothelin reengineered for high activity, low off-target toxicity, and reduced antigenicity.
abstract: SS1P is a recombinant immunotoxin (RIT) engineered for the targeted elimination of malignant cells that express the tumor-associated antigen mesothelin. It is composed of an antimesothelin antibody variable fragment (Fv) linked to a cytotoxic fragment of Pseudomonas exotoxin A (PE) that includes domains II and III of native PE. The clinical use of SS1P is limited by its propensity to induce neutralizing antibodies and to cause a dose-limiting capillary leak syndrome (CLS) in patients. In this article, we describe a reengineered SS1P with improved properties that overcome these deficits. The redesign of SS1P consists of (i) removing the bulk of PE domain II (residues 251-273 and 284-394 of native PE), leaving only an 11-residue furin cleavage site, (ii) adding a Gly-Gly-Ser peptide linker after the furin cleavage site, and (iii) replacing eight highly solvent-exposed residues in the catalytic domain of PE. The new molecule, SS1-LR/GGS/8M, has cytotoxic activity comparable with SS1P on several mesothelin-expressing cell lines and remarkably improved activity on primary cells from patients with mesothelioma. In a mouse xenograft tumor model, high doses of SS1-LR/GGS/8M elicit antitumor activity superior to the activity of SS1P at its maximum-tolerated dose. In addition, SS1-LR/GGS/8M has greatly decreased ability to cause CLS in a rat model and reduced antigenicity or reactivity with antibodies to the sera of patients previously treated with SS1P.
authors.affiliation: Laboratory of Molecular Biology, Center for Cancer Research, National Cancer Institute, NIH, Bethesda, MD 20892, USA.
authors.forename: John E
authors.initials: JE
authors.lastname: Weldon
authors.forename: Laiman
authors.initials: L
authors.lastname: Xiang
authors.forename: Jingli
authors.initials: J
authors.lastname: Zhang
authors.forename: Richard
authors.initials: R
authors.lastname: Beers
authors.forename: Dawn A
authors.initials: DA
authors.lastname: Walker
authors.forename: Masanori
authors.initials: M
authors.lastname: Onda
authors.forename: Raffit
authors.initials: R
authors.lastname: Hassan
authors.forename: Ira
authors.initials: I
authors.lastname: Pastan
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents / Q000009:adverse effects / Q000276:immunology / Q000494:pharmacology*; D019559:Capillary Leak Syndrome / Q000139:chemically induced; D045744:Cell Line, Tumor; D005260:Female; D058851:GPI-Linked Proteins / Q000276:immunology / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D020128:Inhibitory Concentration 50; D020714:Maximum Tolerated Dose; D000090204:Mesothelin; D008654:Mesothelioma / Q000188:drug therapy* / Q000473:pathology; D051379:Mice; D008819:Mice, Nude; D016297:Mutagenesis, Site-Directed; D051381:Rats; D017208:Rats, Wistar; D011993:Recombinant Fusion Proteins / Q000009:adverse effects / Q000235:genetics / Q000276:immunology / Q000494:pharmacology*; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D058851:GPI-Linked Proteins; C000715528:Msln protein, mouse; D011993:Recombinant Fusion Proteins; C581921:SS1-LR-GGS-8M immunotoxin; D000090204:Mesothelin