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Objective: The application of monoclonal antibodies targeting biomarkers expressed on tumor cells for imaging plays a pivotal role in the early detection and prognosis of cancer.3H11 is a monoclonal antibody that targets gastric cancer with high specificity and affinity.In this study, we for the first time investigated 111In-labeled 3H11 for the diagnosis of colon cancer.Method: The expression level of 3H11 antigen on HT29 human colon cancer was detected by ELISA and fluoroimmunoassay.3H11 was coupled with bifunctional chelator CHX-A"-DTPA and the conjugate was labeled with 111In.In vitro and in vivo characterizations of the radiotracer were carried out.Biodistribution and gamma imaging studies of 111In-labeled 3H11 were performed in HT29 colon cancer xenograft model.Results: High expression level of 3H11 antigen on HT29 human colon cancer cells was detected,which was comparable to positive control BGC823 gastric cancer cells.The Kd and Bmax values were determined by Receptor Radioligand Binding Assay with 125I-3H11, which showed 3H11 had high affinity to HT29 colon cancer cells.Furthermore, it is suggested by in vitro studies that 3H11 is able to retain high immunoreactivity and stability in vivo after labeling with 111In.111In-CHX-A"-DTPA-3H11 had the highest tumor uptake (16.71±0.78 %ID/g) at 120 h postinjection.The tumor uptake was higher than any of the other organs, which led to the high T/NT ratios (4.96 for tumor to blood, 30.02 for tumor to muscle, 10.29 for tumor to bone, 2.55 for tumor to kidney, 1.04 for tumor to liver, 19.42 for tumor to stomach, 8.52 for tumor to intestine, at 120 h postinjection, respectively).Clear images of HT29 xenografts were obtained at 24 h postinjection with high tumor-to-background contrast.Conclusion: 3H11 antigen is specifically expressed on colon cancer with high level, making it a new target for diagnosis and therapy of colon cancer.111In-CHX-A"-DTPA-3H11 is able to target the tumor with high affinity while maintaining good stability in vivo.It is believed that 111 In-labeled 3H 11 is a promising imaging agent for colon cancer.