title: Releasable PEGylation of mesothelin targeted immunotoxin SS1P achieves single dosage complete regression of a human carcinoma in mice.
abstract: Recombinant immunotoxins exhibit targeting and cytotoxic functions needed for cell-specific destruction. However, antitumor efficacy, safety, and pharmacokinetics of these therapeutics might be improved by further macromolecular engineering. SS1P is a recombinant anti-mesothelin immunotoxin in clinical trials in patients with mesothelin-expressing tumors. We have modified this immunotoxin using several PEGylation strategies employing releasable linkages between the protein and the PEG polymers, and observed superior performance of these bioconjugates when compared to similar PEG derivatives bearing permanent linkages to the polymers. PEGylated derivatives displayed markedly diminished cytotoxicity on cultured mesothelin-overexpressing A431-K5 cells; however, the releasable PEGylated immunotoxins exhibited increased antitumor activity in A431-K5 xenografts in mice, with a diminished animal toxicity. Most significantly, complete tumor regressions were achievable with single dose administration of the bioconjugates but not the native immunotoxin. Pharmacokinetic analysis of the releasable PEGylated derivatives in mice demonstrated an over 80-fold expansion of the area under the curve exposure of bioactive protein when compared to native immunotoxin. A correlation in degree of derivatization, release kinetics, and polymer size with potency was observed in vivo, whereas in vitro cytotoxicity was not predictive of efficacy in animal models. The potent antitumor efficacy of the releasable PEGylated mesothelin-targeted immunotoxins was not exhibited by similar untargeted PEG immunotoxins in this model. Since the bioconjugates can also exhibit the attributes of passive targeting via enhanced permeability and retention, this is the first demonstration of a pivotal role of active targeting for immunotoxin bioconjugate efficacy.
authors.affiliation: Enzon Pharmaceuticals, Incorporated, 20 Kingsbridge Road, Piscataway, New Jersey 08854, and Laboratory of Molecular Biology, National Cancer Institute, NIH, Bethesda, Maryland 20892, USA. david.filpula@enzon.com
authors.forename: David
authors.initials: D
authors.lastname: Filpula
authors.forename: Karen
authors.initials: K
authors.lastname: Yang
authors.forename: Amartya
authors.initials: A
authors.lastname: Basu
authors.forename: Raffit
authors.initials: R
authors.lastname: Hassan
authors.forename: Laiman
authors.initials: L
authors.lastname: Xiang
authors.forename: Zhenfan
authors.initials: Z
authors.lastname: Zhang
authors.forename: Maoliang
authors.initials: M
authors.lastname: Wang
authors.forename: Qing-cheng
authors.initials: QC
authors.lastname: Wang
authors.forename: Mitchell
authors.initials: M
authors.lastname: Ho
authors.forename: Richard
authors.initials: R
authors.lastname: Beers
authors.forename: Hong
authors.initials: H
authors.lastname: Zhao
authors.forename: Ping
authors.initials: P
authors.lastname: Peng
authors.forename: John
authors.initials: J
authors.lastname: Zhou
authors.forename: Xiguang
authors.initials: X
authors.lastname: Li
authors.forename: Gerald
authors.initials: G
authors.lastname: Petti
authors.forename: Ahsen
authors.initials: A
authors.lastname: Janjua
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Dechun
authors.initials: D
authors.lastname: Wu
authors.forename: Deshan
authors.initials: D
authors.lastname: Yu
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Zhang
authors.forename: Clifford
authors.initials: C
authors.lastname: Longley
authors.forename: David
authors.initials: D
authors.lastname: FitzGerald
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Kreitman
authors.forename: Ira
authors.initials: I
authors.lastname: Pastan
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000493:pharmacokinetics* / Q000627:therapeutic use; D002277:Carcinoma / Q000188:drug therapy* / Q000378:metabolism; D058851:GPI-Linked Proteins; D006801:Humans; D000922:Immunotoxins / Q000737:chemistry* / Q000493:pharmacokinetics* / Q000627:therapeutic use; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors*; D000090204:Mesothelin; D051379:Mice; D008807:Mice, Inbred BALB C; D011092:Polyethylene Glycols / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry / Q000493:pharmacokinetics / Q000627:therapeutic use; D023041:Xenograft Model Antitumor Assays
chemical_list: D000911:Antibodies, Monoclonal; D058851:GPI-Linked Proteins; D000922:Immunotoxins; D008562:Membrane Glycoproteins; C000715528:Msln protein, mouse; D011994:Recombinant Proteins; C474515:SS1(dsFv)PE38; D011092:Polyethylene Glycols; D000090204:Mesothelin