Enhancing the Specificity of the CAIX-Targeted Radionuclide Probe via the Optimization Cyclic Peptide Cyclization Linker

Carbonic anhydrase IX (CAIX) is a key biomarker for clear cell renal cell carcinoma (ccRCC) PET imaging. The reported probe 68Ga-DPI-4452 strongly targets both hCAIX and hCAII, therefore hindering its clinical applications. This study developed two optimized probes, 68Ga-WF1 and 68Ga-WF2. They have nanomolar affinity for hCAIX but far weaker binding to hCAII compared with that of 68Ga-DPI-4452. In OS-RC-2 tumor-bearing mice, the tumor uptake of 68Ga-WF1 and 68Ga-WF2 was comparable to that of 68Ga-DPI-4452. However, since 68Ga-WF2 exhibited the lowest affinity for mCAII and mCAIX, its gastrointestinal uptake was the lowest. The autoradiography result revealed that three probes strongly bound human ccRCC tissues, while 68Ga-WF1 and 68Ga-WF2 bound far less to digestive tract tissues. Due to the lowest affinity of 68Ga-WF1 for hCAII, it effectively reduces uptake in the human gastrointestinal tract, holding promise for high tumor contrast and low gastrointestinal tract toxicity for ccRCC PET imaging.