Abstract
1859
Objectives: Unlike conventionally labeled monoclonal antibodies (mAbs), pretargeting results in extremely rapid tumor accretion and whole-body clearance of radioactivity, causing substantial increases in tumor:blood ratios and potential for imaging and therapeutic efficacy. In order to develop a new system for pretargeting carcinoembryonic antigen (CEA), expressed in numerous cancers, a streptavidin (SA) conjugate of the mAb cT84.66 was synthesized. We evaluated the biodistribution of SA-cT84.66-pretargeted In-111-DOTA-biotin in nude mice bearing LS174T human colon cancer xenografts.
Methods: Antibody interchain disulfides were reduced with 1,4-dithiothreitol, and the resulting thiols were reacted with SMCC-SA. The desired SA-cT84.66 conjugate was purified by iminobiotin affinity chromatography and size exclusion HPLC. LS174T-bearing nude mice were injected with 4 μg of SA-cT84.66, followed 48 h later by 10 μCi of In-111-DOTA-biotin. Biodistributions were obtained from 15 min to 96 h post-injection.
Results: The molecular weight of the SA-cT84.66 conjugate (210 kDa) and immounoreactivity (100%) were confirmed by size exclusion HPLC, and the conjugate bound 3 equivalents of In-111-DOTA-biotin. LS174T tumor uptake of In-111-DOTA-biotin peaked at 3.32% ID/g after 15 min. Clearance from blood and normal organs was extremely rapid, and tumor:blood ratios were >20:1 after 24 h.
Conclusions: SA-cT84.66 was prepared with quantitative immunoreactivity and efficient radiobiotin binding. The specific tumor targeting and rapid whole body clearance of SA-cT84.66-pretargeted In-111-DOTA-biotin indicated that this system is promising for imaging and therapy of CEA-positive cancers.
Research Support (if any): Department of Veterans Affairs Merit Review Type I Award
- Society of Nuclear Medicine, Inc.