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

Abstract

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.

A novel CD44v6 targeting antibody fragment with improved tumor-to-blood ratio

“…The kidneys exhibited a relatively high uptake of 125 I-Fab'. High uptake of antibody fragments in the kidneys has been reported before (26,27) and is probably a result of reabsorption by the renal tubular cells and catabolism (38).…”

“…This has, to our knowledge, never before been reported for CD44v6-binding radioimmunotargeting molecules. For other targets, enzymatically derived divalent F(ab') 2 and monovalent Fab' fragments have shown promising results in animal studies (24)(25)(26)(27)(28) and clinical studies (29,30) and F(ab') 2 fragments against a different target in HNSCC (E48) has been shown to be equally effective as the parent antibody, in tumor and lymph node detection with planar gamma camera (31).…”

NHS76/PEP2, a Fully Human Vasopermeability-Enhancing Agent to Increase The Uptake and Efficacy of Cancer Chemotherapy

“…The whole-body activity immediately after injection and at selected times thereafter was measured with a CRC-7 microdosimeter (Capintec). The data were analyzed to calculate the whole-body half-lives as described previously (32). Significance levels (Ps) in whole-body radioactivity of 125 I-NHS76 and 125 I-NHS76/PEP 2 were determined using the Wilcoxon rank sum test (33).…”

PET of Hypoxia with89Zr-Labeled cG250-F(ab′)2in Head and Neck Tumors

“…In several studies, uptake of F(ab9) 2 antibody fragments in murine kidneys has been reported to be higher than that of intact antibodies (15,33). A high uptake of F(ab9) 2 in the kidneys likely results from fragment reabsorption by the renal tubular cells.…”

“…Uptake of whole antibody was much higher (25.2 6 6.2 %ID/g), as compared with uptake of 89 Zr-cG250-F(ab9) 2 in our study (2.68 6 1.30 %ID/g). Tumor uptake of intact IgG is usually higher than that of its fragmented form (32,33). This is due to the much longer circulatory half-life of IgG, because high blood levels are the driving force for tumor accumulation.…”