Practical Synthesis of [18F]Pitavastatin and Evaluation of Hepatobiliary Transport Activity in Rats by Positron Emission Tomography

We developed a practical synthetic method for fluorine-18 (F-18)-labeled pitavastatin ([F-18]PTV) as a positron emission tomography (PET) tracer to assess hepatobiliary transporter activity and conducted a PET scan as a preclinical study for proof-of-concept in rats. This method is a one-pot synthesis involving aromatic F-18-fluorination of an arylboronic acid ester followed by deprotection under acidic conditions, which can be reproduced in general clinical sites equipped with a standard radiolabeling system due to the simplified procedure. PET imaging confirmed that intravenously administered [F-18]PTV was rapidly accumulated in the liver and gradually transferred into the intestinal lumen through the bile duct. Radiometabolite analysis showed that [F-18]PTV was metabolically stable, and 80% of the injected dose was detected as the unchanged form in both blood and bile. We applied integration plot analysis to assess tissue uptake clearance (CLuptake, (liver) and CLuptake, kidney) and canalicular efflux clearance (CLint, bile), and examined the effects of inhibitors on membrane transport. Treatment with rifampicin, an organic anion transporting polypeptide inhibitor, significantly reduced CL(uptake, liver )and CLuptake, ktdney. to 44% and 64% of control, respectively. In contrast, Ko143, a breast cancer resistance protein inhibitor, did not affect CLuptake, liver but significantly reduced CLint, bile to 39% of control without change in [F-18]PTV blood concentration. In addition, we found decreased CLuptake, liver and increased CLint, bile in Eisai hyperbilirubinemic rats in response to altered expression levels of transporters. We expect that [F-18]PTV can be translated into clinical application, as our synthetic method does not need special apparatus in the radiolabeling system and PET scan with [F-18]PTV can quantitatively evaluate transporter activity in vivo.