A new bifunctional chelating agent conjugated with monoclonal antibody and labelled with technetium-99m for targeted scintigraphy: 6-(4-isothiocyanatobenzyl)-5,7-dioxo-1,11-(carboxymethyl)-1,4,8,11-tetraazacyclotridecane.
OBJECTIVE
The purpose of this study was to obtain the convenient, synthetically useful bifunctional chelating agent, 6-(4-isothiocyanatobenzyl)-5,7-dioxo-1,11-(carboxymethyl)-1,4,8,11-tetraazacyclotridecane, and to apply it to stable (99m)Tc-labelling of monoclonal antibodies (mAbs).


METHODS
The chelate was synthesised by reaction of nitrobenzyl malonate and triethylenetetramine followed by alkylation by reacting with bromoacetic acid at pH 10. The amino group was converted to isothiocyanato derivative by reacting with thiophosgene at pH 2.0. Conjugation with mAbs [(anti-carcinoembryonic antigen (CEA) and anti-epidermal growth factor receptor (EGFr)] was performed at pH 8.4 using trisodium phosphate solution by incubating at 37 degrees C for 1 h and subjected to purification on size exclusion chromatography.


RESULTS
When radioimmunoconjugates were labelled with (99m)Tc, the specific activity of immunoconjugates was 20-30 mCi/mg of protein and their immunoreactivity exceeded 80%. The stability in serum indicated that the metal remained bound to antibodies. Biodistribution studies in athymic mice grafted with U-87 human glioblastoma multiforme and MDA-MB-468 human breast carcinoma tumours revealed significant localisation of (99m)Tc-labelled antibodies in tumours and reduced accumulation in normal organs.


CONCLUSIONS
This bifunctional chelating agent is promising for immunoscintigraphy because of good tumour-to-normal organ contrast.
Mishra
Anil Kumar
AK
Department of Radiopharmaceutical Chemistry, Institute of Nuclear Medicine and Allied Science, Brig. S.K Mazumdar Road, Delhi 110054, India. akmishra@inmas.org
Panwar
Puja
P
Hosono
Makoto
M
Chuttani
Krishna
K
Mishra
Pushpa
P
Sharma
Rakesh Kumar
RK
Chatal
Jean-Francois
JF
D000473:Alkanes / Q000032:analysis* / Q000737:chemistry; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism*; D002614:Chelating Agents / Q000378:metabolism*; D016503:Drug Delivery Systems / Q000379:methods; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D011877:Radionuclide Imaging / Q000379:methods*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013194:Staining and Labeling / Q000379:methods; D013667:Technetium / Q000378:metabolism*; D023041:Xenograft Model Antitumor Assays / Q000379:methods
D000473:Alkanes; D000911:Antibodies, Monoclonal; D002614:Chelating Agents; D013667:Technetium; C094074:tridecane