Non‐invasive estimation of (10)B‐4‐borono‐L‐phenylalanine‐derived boron concentration in tumors by PET using 4‐borono‐2‐(18)F‐fluoro‐phenylalanine

In boron neutron capture therapy (BNCT), (10)B‐4‐borono‐L‐phenylalanine (BPA) is commonly used as a (10)B carrier. PET using 4‐borono‐2‐(18)F‐fluoro‐phenylalanine ((18)F‐FBPA PET) has been performed to estimate boron concentration and predict the therapeutic effects of BNCT; however, the association between tumor uptake of (18)F‐FBPA and boron concentration in tumors remains unclear. The present study investigated the transport mechanism of (18)F‐FBPA and BPA, and evaluated the utility of (18)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 (18)F‐FBPA and (14)C‐4‐borono‐L‐phenylalanine ((14)C‐BPA) uptake in FaDu and LN‐229 human cancer cells. (18)F‐FBPA uptake strongly correlated with (14)C‐BPA uptake in 7 human tumor cell lines (r = .93; P < .01). PET experiments demonstrated that tumor uptake of (18)F‐FBPA was independent of the administration method, and uptake of (18)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 (18)F‐FBPA by PET was useful for estimating (10)B concentration in tumors.