Cellular processing of copper-67-labeled monoclonal antibody chCE7 by human neuroblastoma cells.
Monoclonal antibody chCE7, an internalizing neuroblastoma-specific chimeric antibody, was derivatized with the macrocyclic amine ligand 4-[(1,4,8,11-tetraazacyclotetradec-1-yl)-methyl] benzoic acid tetrahydrochloride and labeled with the potential therapeutic nuclide 67Cu. Using pulse labeling and an acid elution endocytosis assay, 67Cu-chCE7 was found to be internalized into human neuroblastoma (SKN-AS) cells at a similar rate and to a similar extent as 125I-labeled chCE7. Uptake of 67Cu-chCE7 and 125I-chCE7 into the acid stable (intracellular) pool proceeded with similar kinetics during the first 2 h of internalization. However, in contrast to 125I-chCE7-loaded cells, at later times intracellular radioactivity kept increasing in the case of 67Cu-chCE7-loaded cells. It was shown that this effect is due to the intracellular accumulation of a low M(r) degradation product consisting of the 67Cu-4[(1,4,8,11-tetraazacyclotetradec-1-yl)-methyl] benzoic acid complex, possibly with a short peptide attached to it. Degradation of both 125I-chCE7 and 67Cu-chCE7 was inhibited by chloroquine, indicating endosomal or lysosomal degradation, and a 43,000 M(r) fragment was found to be the major high M(r) degradation product in both cases. Although at times between 4 and 6 h of internalization intracellular breakdown of 67Cu-chCE7 was found to proceed more slowly, the major difference between the two immunoconjugates resides in the prolonged cellular retention of the 67Cu-chCE7 metabolite.
Novak-Hofer
I
I
Radiopharmacy Division, Paul Scherrer Institute, Bern, Switzerland.
Amstutz
H P
HP
Mäcke
H R
HR
Schwarzbach
R
R
Zimmermann
K
K
Morgenthaler
J J
JJ
Schubiger
P A
PA
D000911:Antibodies, Monoclonal / Q000008:administration & dosage / Q000378:metabolism*; D003301:Copper Radioisotopes / Q000008:administration & dosage / Q000378:metabolism*; D004705:Endocytosis; D006801:Humans; D018796:Immunoconjugates / Q000378:metabolism* / Q000627:therapeutic use; D009447:Neuroblastoma / Q000276:immunology* / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D003301:Copper Radioisotopes; D018796:Immunoconjugates