A novel derivative of the chelon desferrioxamine for site‐specific conjugation to antibodies

Abstract

We describe the preparation of the modified chelator aminooxyacetyl-ferrioxamine, and the replacement of its iron atom by 67Ga at high specific activity. The aminooxy function of this compound was allowed to react with the aldehyde groups generated by the periodate oxidation of the oligosaccharide of a mouse IgG1 monoclonal antibody (MAb) directed against carcino-embryonic antigen (CEA). The use of the aminooxy group allowed a stable bond to be formed between the chelon and the antibody with no need for reduction. Iron was removed from the ferrioxamine moiety and replaced by 67Ga either before or after conjugation of the chelon to the antibody. In either case the labelled antibody was injected into nude mice bearing a human colon carcinoma having the appropriate antigenicity. Unoxidized antibody, labelled with 125I by conventional methods, was co-injected as an internal control. Additional control experiments were carried out with a non-immune IgG using the same 67Ga-labelled modified chelon as above. The in vivo distribution of the modified antibodies was evaluated at various times between 24 and 96 hr after injection. The methods used were gamma-camera imaging and, more quantitatively, gamma-counting of the various organs after dissection. Interestingly, with the metal-chelon-labelled antibody, the intensity and specificity of tumor labelling was comparable and in some cases superior to the results obtained with radio-iodinated antibody. In particular, there was almost no increase in liver and spleen uptake of radioactive metal relative to radio-iodine, contrary to what has been observed with most antibodies labelled with 111In after conjugation with DTPA.

Clinical applications of Gallium-68

“…Several ligand systems, such as DFO (Koizumi et al, 1987; Koizumi et al, 1988; Pochon et al, 1989; Yokoyama et al, 1982), DTPA [(Wagner and Welch, 1979), (Hnatowich and Schlegel, 1981)] and N,N′-di(2-hydroxybenzyl) ethylene diamine,N,N′-diacetic acid derivative (HBED) (Schuhmacher et al, 1986) have been studied, but proved prohibitively unstable to warrant further investigation. Interestingly, Ga(III) is known to localize to sites of infection and inflammation and has been used for 67 Ga-based scintigraphy (El-Maghraby et al, 2006).…”

Synthesis Concepts for Peptides and Proteins

“…Oximeforming ligation [185,186] is based on the coupling of a O-peptidyl hydroxylamine as the amino component with a peptide aldehyde forming the peptide oxime 11. Oximeforming ligation [185,186] is based on the coupling of a O-peptidyl hydroxylamine as the amino component with a peptide aldehyde forming the peptide oxime 11.…”

CERN-MEDICIS (Medical Isotopes Collected from ISOLDE): A New Facility

“…University of Geneva, and ISOLDE was fully established [16]. The study of the possible use of radioactive ion beams for biomedical research was then extended to a bio-conjugate (chelator-antibody), which is known to have higher tumor specificity: aminooxyacetyl-ferrioxamine coupled to murine anti carcinoembryonic antigen (CEA) IgG1 monoclonal antibody MAB 35, synthesized by Pochon and co-workers [17]. The chelator-antibody conjugates were labelled by 2 h incubation in acetate solution with several different lanthanides ( 153 Gd, 169 Yb, 167 Tm, 141 Ce) and 225 Ac produced from U-carbide and Ta-foil targets and purified by cation-exchange chromatography column containing α-hydroxyisobutyric acid (HIB) [18].…”