TUMOR UPTAKE AND METABOLISM OF COPPER-67-LABELED MONOCLONAL-ANTIBODY CHCE7 IN NUDE-MICE BEARING NEUROBLASTOMA XENOGRAFTS

Methods: ChCE7, an internalizing, neuroblastoma-specific monoclonal an tibody (MAb), and its F(ab')(2) fragments were derived with the bifunc tional ligand 4-(1,4,8,11-tetraazacyclotetradec-1-yl)methyl benzoic ac id tetrahydrochloride (CPTA) and labeled with the potential therapeuti c nuclide Cu-67. After internalization and degradation of these immuno conjugates in SKN-AS human neuroblastoma cells, the terminal degradati on product was found to be the lysine adduct of the copper complex, In vivo distributions in nude mice bearing neuroblastoma xenografts were studied and extracts from tumor and tissue samples were analyzed. Res ults: The intact MAb showed high tumor uptake, stable over 4 days post injection (33.7% +/- 2.8% ID/g), with tumor/blood ratios increasing fr om 4.4 on Day 1 to 23.0 on Day 7 postinjection and low levels of radio activity in other tissues. Analysis of tumor extracts by gel filtratio n chromatography and high-pressure liquid chromatography (HPLC) showed that over the period of 4 days radioactivity was present both in a hi gh M(r) form, consisting of the MAb/antigen complex, as well as in a l ow M(r) form, consisting of the copper complex attached to short pepti des, including the lys-CPTA complex. There was no evidence of aggregat es or MAb/antigen complexes in the blood, radioactivity being exclusiv ely in the form of intact MAb, and radioactivity in the liver was foun d to consist of intact MAb, MAb fragments and the lys-CPTA metabolite. In the case of the F(ab')(2) fragments, high accumulation of radioact ivity in the kidneys was observed and analysis of kidney extracts show ed it to be due to rapid accumulation of the lys-CPTA complex. When ki dney uptake and retention of the CPTA complex as well as of its lysine and glycine adducts was investigated, the lysine complex was taken up more strongly and retained longer in the kidneys than the other compo unds. Conclusion: Copper-67-labeled MAb chCE7 F(ab')(2) fragments were prepared using a novel bifunctional copper ligand yl)-1,4,7,10-tetraa zacyclodecane-4,7,10-triacetate (DO3A). Compared with MAb-chCE7 F(ab') (2) fragments labeled by the CPTA ligand, labels using the DO3A ligand showed improved biodistributions resulting, 48 hr postinjection, in a 4-fold increase in tumor uptake and a 4-fold reduction of radioactivi ty in the kidneys.