title: Stability of a metabolizable ester bond in radioimmunoconjugates.
abstract: Ester bonds have been used as metabolizable linkages to reduce radioactivity levels in non-target tissues following the administration of antibodies labeled with metallic radionuclides. In this radiochemical design of antibodies, while the ester bonds should be cleaved rapidly in non-target tissues, high stability of the ester bonds in plasma is also required to preserve target radioactivity levels. To assess the structural requirements to stabilize the ester bond, a new benzyl-EDTA-derived bifunctional chelating agent with an ester bond, (1-[4-[4-(2- maleimidoethoxy)succinamido]benzyl]ethylenediamine-N,N,N',N' -tetraacetic acid; MESS-Bz-EDTA), was developed. MESS-Bz-EDTA was coupled with a thiolated monoclonal antibody (OST7, IgG1) prepared by reducing its disulfide bonds to introduce the ester bond close and proximal to the antibody molecule. For comparison, 1-[4-(5- maleimidopentyl)aminobenzyl]ethylenediamine-N,N,N',N'-tetraacetic acid (EMCS-Bz-EDTA) and meleimidoethyl 3-[131I]iodohippurate (MIH) was coupled to OST7 under the same conjunction chemistry. When incubated in 50% murine plasma or a buffered-solution of neutral pH, OST7-MESS-Bz-EDTA-111In rapidly released the radioactivity, and more than 95% of the initial radioactivity was liberated after a 24 h incubation in both solutions, due to a cleavage of the ester bond. On the other hand, only about 20% of the radioactivity was released from OST7-MIH-131I in both solutions during the same incubation period. In mice biodistribution studies, while a slightly faster radioactivity clearance from the blood with less radioactivity levels in the liver and kidneys was observed with OST7-MIH-131I than with OST7-EMCS-Bz-EDTA-111In, OST7-MESS-Bz-EDTA-111In indicated radioactivity clearance from the blood much faster than and almost comparable to that of OST7-MIH-131I and succinamidobenzyl-EDTA-111In, respectively. These findings as well as previous findings on radiolabeled antibodies with ester bonds suggested that while an introduction of an ester bond close to an antibody molecule stabilized the ester bond against esterase access, chemical structures of the linkages and radiolabels attached to the ester bonds play a significant role in the chemical stability of the ester bond. This may explain the different stability of the ester bonds in radioimmunoconjugates so far reported.
authors.affiliation: Faculty of Pharmaceutical Sciences, Kyoto University, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Arano
authors.forename: K
authors.initials: K
authors.lastname: Wakisaka
authors.forename: T
authors.initials: T
authors.lastname: Mukai
authors.forename: T
authors.initials: T
authors.lastname: Uezono
authors.forename: H
authors.initials: H
authors.lastname: Motonari
authors.forename: H
authors.initials: H
authors.lastname: Akizawa
authors.forename: C
authors.initials: C
authors.lastname: Kairiyama
authors.forename: Y
authors.initials: Y
authors.lastname: Ohmomo
authors.forename: C
authors.initials: C
authors.lastname: Tanaka
authors.forename: M
authors.initials: M
authors.lastname: Ishiyama
authors.forename: H
authors.initials: H
authors.lastname: Sakahara
authors.forename: J
authors.initials: J
authors.lastname: Konishi
authors.forename: A
authors.initials: A
authors.lastname: Yokoyama
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry* / Q000493:pharmacokinetics; D002850:Chromatography, Gel; D002855:Chromatography, Thin Layer; D004492:Edetic Acid / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D004952:Esters / Q000737:chemistry / Q000378:metabolism; D018796:Immunoconjugates / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics; D007205:Indium Radioisotopes; D051379:Mice; D008815:Mice, Inbred Strains; D051381:Rats; D014018:Tissue Distribution
chemical_list: D000911:Antibodies, Monoclonal; D004952:Esters; D018796:Immunoconjugates; D007205:Indium Radioisotopes; C103216:OST7-(1-(4-(4-(2-maleimidoethoxy)succinamido)benzyl)ethylenediamine-N,N,N',N'-tetraacetic acid); D004492:Edetic Acid