title: Mik-beta 1(Fv)-PE40, a recombinant immunotoxin cytotoxic toward cells bearing the beta-chain of the IL-2 receptor.
abstract: Mik-beta 1 is a mAb that binds to the beta subunit of the IL-2R. We have constructed a recombinant single chain immunotoxin Mik-beta 1(Fv)-PE40 by genetically fusing the H and L V domains of Mik-beta 1 to each other via a peptide linker, and then to PE40, a derivative of Pseudomonas exotoxin. Mik-beta 1(Fv)-PE40 was selectively cytotoxic for cells expressing high levels of IL-2R beta (p75) subunit. Mik-beta 1(Fv)-PE40 was cytotoxic to the NK cell line YT-S, which expresses p75 but not p55 subunits, with an IC50 of 6 ng/ml. The ATL line HUT-102 was less sensitive, with an IC50 of 200 ng/ml. However, the IC50 could be lowered to 11 ng/ml when Mik-beta 1(Fv)-PE40 was allowed to bind to HUT-102 cells at 4 degrees C for 4 h before overnight incubation at 37 degrees C. An excess of Mik-beta 1 but not of anti-Tac, the anti-p55 mAb, prevented the cytotoxicity of Mik-beta 1(Fv)-PE40. We constructed a more active version of Mik-beta 1(Fv)-PE40, designated Mik-beta 1(Fv)-PE40KDEL, by converting the carboxyl-terminus of the toxin from -REDLK to -KDEL. Mik-beta 1(Fv)-PE40KDEL showed an IC50 of 2 ng/ml toward YT-S cells and 35 ng/ml toward HUT-102 cells. Binding studies using radioiodinated Mik-beta 1 showed that Mik-beta 1(Fv)-PE40 bound to the p75 receptor subunit with 11% of the affinity of the native Mik-beta 1 antibody. Mik-beta 1(Fv)-PE40 may be a useful reagent to study cells that express IL-2R, and it deserves further study as a possible treatment for cancers in which the malignant cells express high numbers of p75 subunit.
authors.affiliation: Laboratory of Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892.
authors.forename: R J
authors.initials: RJ
authors.lastname: Kreitman
authors.forename: W P
authors.initials: WP
authors.lastname: Schneider
authors.forename: C
authors.initials: C
authors.lastname: Queen
authors.forename: M
authors.initials: M
authors.lastname: Tsudo
authors.forename: D J
authors.initials: DJ
authors.lastname: Fitzgerald
authors.forename: T A
authors.initials: TA
authors.lastname: Waldmann
authors.forename: I
authors.initials: I
authors.lastname: Pastan
mesh_terms: D036002:ADP Ribose Transferases; D000595:Amino Acid Sequence; D001427:Bacterial Toxins; D001483:Base Sequence; D002460:Cell Line; D005098:Exotoxins / Q000494:pharmacology*; D006801:Humans; D000922:Immunotoxins / Q000737:chemistry / Q000235:genetics / Q000494:pharmacology*; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D015375:Receptors, Interleukin-2 / Q000276:immunology*; D011994:Recombinant Proteins / Q000494:pharmacology; D013696:Temperature; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A
chemical_list: D036002:ADP Ribose Transferases; D001427:Bacterial Toxins; D005098:Exotoxins; D000922:Immunotoxins; D015375:Receptors, Interleukin-2; D011994:Recombinant Proteins; D037521:Virulence Factors; D000097668:Pseudomonas aeruginosa Exotoxin A