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 penta-acetic 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 radio-labeled 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.