[18F]VM4-037 MicroPET Imaging and Biodistribution of Two In Vivo CAIX-Expressing Tumor Models

[F-18]VM4-037 was recently developed as a positron emission tomography (PET) tracer for the detection of carbonic anhydrase IX (CAIX), a tumor-specific protein upregulated under hypoxic conditions. In this study, the accumulation of [F-18]VM4-037 was determined in two CAIX-expressing preclinical human tumor models. U373 and HT29 tumor-bearing animals were injected with [F-18]VM4-037 and underwent microPET imaging up to 4 h post-injection (p.i.). Biodistribution throughout the different organs was assessed at 2 and 4 h p.i. using gamma counting. MicroPET imaging showed high [F-18]VM4-037 uptake in the abdominal region, and biodistribution revealed high radioactivity in the kidney, ileum, colon, liver, stomach, and bladder. Although high CAIX expression was confirmed in both tumor models, tumor uptake assessed with microPET and biodistribution experiments was comparable to background tissues. In this study, [F-18]VM4-037 does not specifically accumulate in CAIX-expressing tumors, indicating that the tracer is not suitable for the detection of CAIX.