Non-invasive estimation of B-4-borono-L-phenylalanine-derived boron concentration in tumors by PET using 4-borono-2- F-fluoro-phenylalanine.

In boron neutron capture therapy (BNCT), B-4-borono-L-phenylalanine (BPA) is commonly used as a B carrier. PET using 4-borono-2- F-fluoro-phenylalanine ( F-FBPA PET) has been performed to estimate boron concentration and predict the therapeutic effects of BNCT; however, the association between tumor uptake of F-FBPA and boron concentration in tumors remains unclear. The present study investigated the transport mechanism of F-FBPA and BPA, and evaluated the utility of F-FBPA PET in predicting boron concentration in tumors. The transporter assay revealed that 2-aminobicyclo-(2.2.1)-heptane-2-carboxylic acid, an inhibitor of the L-type amino acid transporter, significantly inhibited F-FBPA and C-4-borono-L-phenylalanine ( C-BPA) uptake in FaDu and LN-229 human cancer cells. F-FBPA uptake strongly correlated with C-BPA uptake in 7 human tumor cell lines (r = .93; P < .01). PET experiments demonstrated that tumor uptake of F-FBPA was independent of the administration method, and uptake of F-FBPA by bolus injection correlated well with BPA uptake by continuous intravenous infusion. The results of this study revealed that evaluating tumor uptake of F-FBPA by PET was useful for estimating B concentration in tumors.