In vivo evaluation of 177Lu- and 67/64Cu-labeled recombinant fragments of antibody chCE7 for radioimmunotherapy and PET imaging of L1-CAM-positive tumors.
OBJECTIVE
The L1 cell adhesion protein is overexpressed in tumors, such as neuroblastomas, renal cell carcinomas, ovarian carcinomas, and endometrial carcinomas, and represents a target for tumor diagnosis and therapy with anti-L1-CAM antibody chCE7. Divalent fragments of this internalizing antibody labeled with 67/64Cu and 177Lu were evaluated to establish a chCE7 antibody fragment for radioimmunotherapy and positron emission tomography imaging, which combines high-yield production with improved clearance and biodistribution properties.


METHODS
chCE7F(ab')2 fragments were produced in high amounts (0.2 g/L) in HEK-293 cells, substituted with the peptide-linked tetraazamacrocycle 3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycyl-L-p-isothiocyanato-phenylalanine, and labeled with 67Cu and 177Lu. In vivo bioevaluation involved measuring kinetics of tumor and tissue uptake in nude mice with SK-N-BE2c xenografts and NanoPET (Oxford Positron Systems, Oxford, United Kingdom) imaging with 64Cu-3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycine-chCE7F(ab')2.


RESULTS
The 177Lu- and 67Cu-labeled immunoconjugates reached maximal tumor accumulation at 24 hours after injection with similar levels of 12%ID/g to 14%ID/g. Blood levels dropped to 1.0%ID/g for the 177Lu fragment and 2.3%ID/g for the 67Cu fragment at 24 hours. The most striking difference concerned radioactivity present in the kidneys, being 34.5%ID/g for the 177Lu fragment and 16.0%ID/g for the 67Cu fragment at 24 hours. Positron emission tomography imaging allowed clear visualization of s.c. xenografts and peritoneal metastases and a detailed assessment of whole-body tracer distribution.


CONCLUSIONS
67/64Cu- and 177Lu-labeled recombinant chCE7F(ab')2 revealed suitable in vivo characteristics for tumor imaging and therapy but displayed higher kidney uptake than the intact monoclonal antibody. The 67Cu- and 177Lu-labeled immunoconjugates showed different in vivo behavior, with 67/64Cu-3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycine-F(ab')2 appearing as the more favorable conjugate due to superior tumor/kidney ratios.
Grünberg
Jürgen
J
Center for Radiopharmaceutical Science ETH-PSI-USZ, Paul Scherrer Institute, Villigen, Switzerland.
Novak-Hofer
Ilse
I
Honer
Michael
M
Zimmermann
Kurt
K
Knogler
Karin
K
Bläuenstein
Peter
P
Ametamey
Simon
S
Maecke
Helmut R
HR
Schubiger
P August
PA
D000818:Animals; D003301:Copper Radioisotopes; D006801:Humans; D018796:Immunoconjugates; D007128:Immunoglobulin Fragments; D008187:Lutetium; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000000981:diagnostic imaging; D039842:Neural Cell Adhesion Molecule L1 / Q000737:chemistry / Q000276:immunology* / Q000493:pharmacokinetics*; D009447:Neuroblastoma / Q000473:pathology; D049268:Positron-Emission Tomography / Q000379:methods; D011868:Radioisotopes; D014018:Tissue Distribution; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
D003301:Copper Radioisotopes; D018796:Immunoconjugates; D007128:Immunoglobulin Fragments; D039842:Neural Cell Adhesion Molecule L1; D011868:Radioisotopes; D008187:Lutetium