Liver background uptake of [F]FLT in PET imaging.

High liver uptake presents a problem for 3'-deoxy-3'-[F]fluorothymidine ([F]FLT) as a radiotracer for imaging cellular proliferation in the liver with positron emission tomography (PET). This investigation re-visited some issues related to the high liver background uptake of [F]FLT with an animal model of woodchucks. Several enzymes involved in the hepatic catabolism of FLT, thymidine phosphorylase (TP, TYMP), uridine 5'-diphospho-glucuronosyl-transferases (UDP-GTs, short for UGTs), and β-glucuronidase (GUSB), their homology as well as hepatic expression between the human and the woodchuck was examined.