Synthesis of novel ¹⁸F[FDG] labeled rhodamine: A potential PET myocardial perfusion imaging agent

Objectives Myocardial perfusion imaging (MPI) is usually performed using single-photon radiopharmaceuticals like ^99mTc-MIBI, ^99mTc-tetrofosmin and ²⁰¹Tl-chloride. Unlike SPECT, PET imaging offers several advantages in MPI. The currently used PET tracers for MPI studies (¹³NH₃, ⁸²Rb and ¹⁵O-water) have limitations. Rhodamine dyes are known to accumulate in the heart; thus several ¹⁸F-labeled rhodamine B were reported recently as potential MPI agents. Due to the clinical importance of [¹⁸F]-FDG and its availability we here report the synthesis and preclinical evaluation of new [¹⁸F]-FDG-rhodamine

Methods [¹⁸F]-FDG (300 MBq) was reacted with oxime-rhodamine conjugate in 1%HoAc/EtOH at 60^oC for 10 min. Work up of this reaction gave [¹⁸F]-FDG-rhodamine conjugate in quantitative radiochemical yield and purity as assessed by TLC/HPLC in less than 20 min. [¹⁸F]-FDG-rhodamine conjugate was incubated with human plasma in duplicate at 37^oC for 2 h and supernatant layers were analyzed by HPLC. Rats were injected via the lateral tail vein with the radiotracer. Animals were sacrificed after 60 min and tissues of interest were dissected, weighed and assayed for radioactivity

Results The synthetic approaches hold considerable promise as rapid and simple method for radiolabeling of rhodamine with [¹⁸F]-FDG in high radiochemical yield and in short time. The stability studies of [¹⁸F]-FDG-rhodamine plasma revealed that this radioconjugate remained stable. In vivo biological studies in rats at 60 min p.i., demonstrated fast and efficient clearance of [¹⁸F]-FDG-rhodamine from the blood and most of the organs and tissues. The target organ heart showed highest uptake (11.24±1.97%) of the %ID/g. This result demonstrates that [¹⁸F]-FDG-rhodamine may be useful PET for MPI.

Conclusions [¹⁸F]-FDG-rhodamine was prepared in quantitative radiochemical yields and purities in less than 20 min. Biodistribution in rats showed high myocardial uptake and favorable pharmacokinetics. These results demonstrate that this radioconjugate may be useful for MPI studies using PET.