In vivo Evaluation of 177Lu- and 67/64Cu-Labeled Recombinant Fragments of Antibody chCE7 for Radioimmunotherapy and PET Imaging of L1-CAM-Positive Tumors

Purpose: 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 67/64 Cu and 177 Lu 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. Experimental Design: 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 67 Cu and 177 Lu. 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 64 Cu-3-( p -nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycine-chCE7F(ab′) 2 . Results: The 177 Lu- and 67 Cu-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 177 Lu fragment and 2.3%ID/g for the 67 Cu fragment at 24 hours. The most striking difference concerned radioactivity present in the kidneys, being 34.5%ID/g for the 177 Lu fragment and 16.0%ID/g for the 67 Cu 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: 67/64 Cu- and 177 Lu-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 67 Cu- and 177 Lu-labeled immunoconjugates showed different in vivo behavior, with 67/64 Cu-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.