Non-invasive imaging of Toll-like receptor 5 expression using 131I-labeled mAb in the mice bearing H22 tumors

Toll-like receptor 5 (TLR5) is overexpressed in several cancers and metastases, and presents an enticing target for molecular imaging of primary tumors. In the present study, 131I-anti-TLR5 monoclonal antibody (mAb) was evaluated for its use as a novel radiotracer for imaging hepatocarcinoma in mice bearing H22 tumors. The expression of TLR5 was analyzed by quantitative polymerase chain reaction and immunohistochemistry. The anti-TLR5 mAb and isotype immunoglobulin G (IgG) were radiolabeled with iodine-131 by the Iodogen method. The in vitro stability of iodinalized probes was determined in serum or saline for a series of times, and then evaluated with radio-thin-layer chromatography. The biodistribution study and autoradiography were performed in H22 tumor-bearing mice. It was found that H22-xenografted tumor tissue exhibited a higher level of TLR5 expression compared with normal liver tissues. 131I-anti-TLR5 mAb and 131I-IgG were obtained subsequent to purification, with high radiochemical purity (>95%), and remained stable for 48 h in human serum. The target-to-non-target ratio in the 131I-anti-TLR5 mAb group was significantly higher compared with the 131I-IgG group. The biodistribution study and autoradiography demonstrated that 131I-anti-TLR5 mAb was specifically retained in hepatocarcinoma with a high tumor uptake. Altogether, these results show that 131I-anti-TLR5 mAb is capable of detecting lesions in a TLR5-expressing tumor, with high target selectivity, and may offer a promising agent for hepatocarcinoma diagnosis and encourage further investigation.