Single-step radiosynthesis and in vivo evaluation of a novel fluorine-18 labeled hippurate for use as a PET renal agent.

The objective of this study was to investigate a new fluorine-18 labeled hippurate, m-cyano-p-[(18)F]fluorohippurate ([(18)F]CNPFH), as a potential radiopharmaceutical for evaluating renal function by PET. [(18)F]CNPFH was synthesized by a direct one-step nucleophilic aromatic substitution using an (18)F-for-[N(CH(3))(3)](+)-reaction. In vivo stability was determined by HPLC analysis of urine collected from a healthy rat at 30min p.i. of [(18)F]CNPFH. The plasma protein binding (PPB) and erythrocyte uptake of [(18)F]CNPFH were determined using blood collected from healthy rats at 5min p.i. Biodistribution studies were conducted in healthy rats at 10min and 1h p.i. of [(18)F]CNPFH. Dynamic PET/CT imaging data were acquired in normal rats. For comparison, the same rats underwent an identical imaging study using the previously reported p-[(18)F]fluorohippurate ([(18)F]PFH) renal agent. [(18)F]CNPFH demonstrated high in vivo stability with no metabolic degradation. The in vivo PPB and erythrocyte uptake of [(18)F]CNPFH were found to be comparable to those of [(18)F]PFH. Biodistribution and dynamic PET/CT imaging studies revealed a rapid clearance of [(18)F]CNPFH primarily through the renal-urinary pathway. However, unlike [(18)F]PFH, a minor (about 12%) fraction was eliminated via the hepatobiliary route. The PET-derived [(18)F]CNPFH renograms revealed an average time-to-peak (T(max)) of 3.2±0.4min which was similar to [(18)F]PFH, but the average time-to-half-maximal activity (11.4±2.8min) was found to be higher than that of [(18)F]PFH (7.1±1.3min). Our in vivo results indicate that [(18)F]CNPFH has renogram characteristics similar to those of [(18)F]PFH, however, the unexpected hepatobiliary elimination is adding undesirable background signal in the PET images.