Construction and Preclinical Evaluation of a 124/131I-Labeled Radiotracer for the Detection of Mesothelin-Overexpressing Cancer.

Mesothelin is a molecular biomarker of many types of solid cancers, which may represent a highly promising new target in the development of cancer-targeted diagnostic agents. A human anti-mesothelin antibody with a low molecular weight, ET210sc, was applied; this antibody has potent affinity and can penetrate tissue quickly and stably without causing immunoreactions. We developed a new 124/131I-labeled radiotracer of ET210sc. The 124/131I-labeled ET210sc radiotracer showed excellent radiochemical quality (with over 99% radiolabeling yield, 0.07 GBq/μmol specific activity) and remarkable stability in phosphate-buffered saline (>95% at 3 days). The radiotracer retained its potent affinity (dissociation constant, Kd = 0.101 nM). The radiotracer specifically bound to mesothelin-positive cells in vitro. Interestingly, the radiotracer exhibited significant positive-to-negative tumor uptake ratios (1.5:1) 3 days postinjection. The estimated absorbed doses of each organ (e.g., 0.704 mGy/MBq for the rectum; 0.341 mGy/MBq for the spleen) met the medical safety standards for further clinical applications. Our findings provide an initial proof of concept for the potential use of 124/131I-labeled ET210sc radiotracers to detect mesothelin-overexpressing cancer. 124I-ET210sc is proposed to be an ideal imaging agent for further clinical applications.