Evaluation Of ～(111)In-CHX-A"-DTPA-3H11 In Nude Mice Bearing HT29 Human Colon Cancer Xenograft

In this study, we attempted monoclonal antibody 3H11 (mAb 3H11) for the diagnosisof colon cancer first. The mAb 3H11 was labeled with ¹¹¹In, and in vitro and in vivoevaluation were performed.The expression level of 3H11 antigen on HT29 human colon cancer was detected byELISA and fluoroimmunoassay in vitro and ex vivo. The experiment results demonstratedhigh expression level of 3H11 antigen on HT29 human colon cancer, which wascomparable to positive control BGC823 gastric cancer cells. The Kd and Bmax weredetermined by Receptor Radioligand Binding Assay with ¹²⁵I-3H11, which showed HT29had good affinity to mAb 3H11.The bifunctional chelator CHX-A″-DTPA was conjugated to mAb 3H11. ELISAanalysis revealed that the conjugate CHX- A″-DTPA-3H11 had almost the sameimmunoreactivity as mAb 3H11. The labeling yield of ¹¹¹In-CHX-A″-DTPA-3H11 was84.26%, and the radiochemistry purity was more than 99% after PD-10 columnpurification. The preparation showed good stability in saline, PBS and nude mice serum(NMS) during 148 h incubation period. The radioimmunoactive fraction determined byLindmo method demonstrated that the radiotracer retained good immunoreactivity.The biodistribution andγimaging were performed in nude mice with HT29 humancolon cancer xenografts. Comparing to ¹¹¹In-CHX- A″-DTPA-mIgG control, the clearimages of xenograft tumors were obtained at 24 h postinjection. The tumor targenting wasobserved from biodistribution study. The tumor uptake of ¹¹¹In-CHX-A″-DTPA-3H11 washigher with 16.71±0.78 %ID/g at 120 h postinjection, and the T/NT ratios were 4.96 fortumor to blood, 30.02 for tumor to muscle, 10.29 for tumor to bone, 2.55 for tumor tokidney, 1.04 for tumor to liver, 19.42 for tumor to stomach, 8.52 for tumor to intestine, respectively.These results concludes that 3H11 antigen is expressed on colon cancer with highlevel, and this antigen may become a new promising target for diagnosis and therapy ofcolon cancer; ¹¹¹In-CHX-A″-DTPA-3H11 shows excellent in vitro and in vivo stability aswell as tumor targeting. It is a good candidate for radioimmunoimaging of colon cancer.