Synthesis and Biological Evaluation of O-[3-¹⁸F-fluoropropyl]-α-methyl Tyrosine in Mesothelioma-Bearing Rodents

Abstract

Radiolabeled tyrosine analogs enter cancer cells via upregulated amino acid transporter system and have been shown to be superior to 18F-fluoro-2-deoxy-D-glucose (18F-FDG) in differential diagnosis in cancers. In this study, we synthesized O-[3-19F-fluoropropyl]-α-methyl tyrosine (19F-FPAMT) and used manual and automated methods to synthesize O-[3-18F-fluoropropyl]-α-methyl tyrosine (18F-FPAMT) in three steps: nucleophilic substitution, deprotection of butoxycarbonyl, and deesterification. Manual and automated synthesis methods produced 18F-FPAMT with a radiochemical purity >96%. The decay-corrected yield of 18F-FPAMT by manual synthesis was 34% at end-of-synthesis (88 min). The decay-corrected yield of 18F-FPAMT by automated synthesis was 15% at end-of-synthesis (110 min). 18F-FDG and 18F-FPAMT were used for in vitro and in vivo studies to evaluate the feasibility of 18F-FPAMT for imaging rat mesothelioma (IL-45). In vitro studies comparing 18F-FPAMT with 18F-FDG revealed that 18F-FDG had higher uptake than that of 18F-FPAMT, and the uptake ratio of 18F-FPAMT reached the plateau after being incubated for 60 min. Biodistribution studies revealed that the accumulation of 18F-FPAMT in the heart, lungs, thyroid, spleen, and brain was significantly lower than that of 18F-FDG. There was poor bone uptake in 18F-FPAMT for up to 3 hrs suggesting its in vivo stability. The imaging studies showed good visualization of tumors with 18F-FPAMT. Together, these results suggest that 18F-FPAMT can be successfully synthesized and has great potential in mesothelioma imaging.