Tumor Targeting Properties of Indium-111 Labeled Genetically Engineered Fab′ and F(ab′)2 Constructs of Chimeric Tumor Necrosis Treatment (chTNT)-3 Antibody

Genetic engineering techniques have allowed the construction of Fab′ and F(ab′)2 constructs of chimeric tumor necrosis treatment antibody (chTNT-3), a chimeric monoclonal antibody (MAb) that targets necrotic regions of solid tumors. The purpose of this study is to evaluate the in vitro and in vivo properties of Fab′ and F(ab′)2 constructs radiolabeled with indium-111 (111In) using diethylentriamine pentaacetic acid (DTPA) conjugation to develop a clinically useful imaging agent for the detection of necrosis in solid tumors. Optimization of the MAb-to-DTPA ratio showed that a 1:2 ratio gave the best immunoreactivity while providing good radiolabeling efficiency and high specific activity for all three DPTA conjugates. In addition, 111In-labeled Fab′ and F(ab′)2 conjugates were found to have faster whole body clearance times and better biodistribution profiles compared to parental 111In-labeled chTNT-3 in tumor-bearing mice. Although radiolabeled Fab′ and F(ab′)2 constructs showed lower tumor uptake than radiolabeled chTNT-3, biodistribution results showed that these constructs had significantly lower uptake in liver, spleen, and other normal organs (except the kidney), and therefore had higher tumor-to-organ ratios. In addition, a comparison of all derivatives showed that the F(ab′)2 reagent gave the best results in tumor imaging studies. These results demonstrate that stable, a genetically engineered F(ab′)2 construct can be successfully radiolabeled with 111In to produce potential imaging reagents for the imaging and monitoring of tumor necrosis.