Construction of a I-124-Labeled Specific Antibody for the Noninvasive Detection of Mesothelin-Overexpressing Tumors

Mesothelin (MSLN) is a molecular biomarker of many types of solid tumors, such as mesothelioma, pancreatic cancer, and colon cancer. Owing to the significant difference in expression between cancer cells and normal cells, mesothelin has been widely used as a key target in cancer immunotherapy. In this study, we used iodine isotope (I-nat/124/125)-labeled mesothelin antibodies to noninvasively detect MSLN expression in mice with LS174T colon cancer. The I-124-labeled MSLN antibody showed a high radiochemical purity (RCP, > 99%) and specific activity (20.8-67.8 GBq/mu mol) after purification and was stable in 5% HSA and PBS (> 95% RCP at 8 days). Western blot analysis indicated that the LS174T cells showed a higher MSLN protein level than the HepG2 cells. The half maximal effective concentration (EC50) values of the MSLN antibody and I-nat-anti-MSLN were 34.77 +/- 3.72 ng/mL and 32.60 +/- 2.52 ng/mL (P = 0.63), respectively. The dissociation constant of I-124-anti-MSLN binding to MSLN protein was 16.0 nM. The radiotracer showed a significantly higher uptake in LS174T cells than in HepG2 tumor cells (1.56 +/- 0.09 vs 0.81 +/- 0.03, P = 0.0016) 2 days postinjection. The LS174T mouse models showed extremely low organ uptake and high tumor uptake 96 h after the injection of I-124-anti-MSLN, and the T/M values were much higher than those of the other imaging groups (10.56 +/- 1.20 for I-124-anti-MSLN in LS174T mice vs 3.27 +/- 0.20 for I-124-anti-MSLN in HepG2 mice vs 3.53 +/- 0.2 for I-124-IgG in LS174T mice). The immunochemical histology results showed that LS174T tumors were strongly positive (+++) for MSLN, while those in the HepG2 group showed slight expression (+). The dosimetry estimation study showed that the effective dose of I-124-anti-MSLN was 0.185 mSv/MBq, which is within the range of acceptable doses for further nuclear medicine translational research. Taken together, these results suggest that this radiotracer has the potential for detecting mesothelin-overexpressing tumors.