Synthesis and evaluation of 18F-labeled carbonic anhydrase IX inhibitors for imaging with positron emission tomography.

Two carbonic anhydrase IX (CA IX) inhibitors were radiolabeled with (18)F, and evaluated for imaging CA IX expression. Despite good affinity for CA IX and excellent plasma stability, uptake of both tracers in CA IX-expressing HT-29 tumor xenografts in mice was low. (18)F-FEC accumulated predominately in the liver and nasal cavity, whereas a significant amount of (18)F-U-104 was retained in blood. Due to minimal uptake in HT-29 tumors compared to other organs/tissues, these two tracers are not suitable for use for CA IX-targeted imaging.