Studies on Synthesis and Biodistribution of ¹³¹I-labeled 4-iodine-L-phenylalanine

L-type amino acid transporter protein(LAT1) is one of the hotspots in cancer research as a target for cancer visualization and therapy. In this study, ¹³¹I-labeled 4-iodo-L-phenylalanine(¹³¹IPA) tracer was synthesized by aqueous-phase one-step radiosubstitution reaction using 4-boron-L-phenylalanine(BPA) as a reactant and initially evaluated for tumor diagnostic studies. The results showed that the radiochemical purity(RCP) of the synthesized ¹³¹IPA was 96.33%, and the radiochemical yield(RCY) reached 92±0.3%. The intake of ¹³¹IPA in non-small-cell lung cancer A549 cells reached the highest value at 3 h; whereas the intake in glioma GL261 cell to peak value was at 8 h. In mice, ¹³¹IPA was mainly metabolized and excreted through the liver and kidney, with almost no residue in the body after 24 h. In addition, in vivo imaging in small animals showed that ¹³¹IPA had high intake and long residence time in A549 tumor model from 2 to 12 h. In the in situ GL261 tumor model, ¹³¹IPA could be observed to reach brain tumors through the blood-brain barrier at 2 h. Imagings at 8 h and 12 h showed better brain tumor specificity, with a target-to-benefit ratio of T/M≈3.4.