Non-invasive estimation of BPA-derived boron concentration in tumors by 18F-FBPA PET

Abstract

In boron neutron capture therapy (BNCT), ¹⁰B-4-borono-L-phenylalanine (BPA) is commonly used as a ¹⁰B carrier. Positron emission tomography using 4-borono-2-¹⁸F-fluoro-phenylalanine (¹⁸F-FBPA PET) has been performed to estimate boron concentration and predict the therapeutic effects of BNCT; however, the association between tumor uptake of ¹⁸F-FBPA and boron concentration in tumors remains unclear. The present study investigated the transport mechanism of ¹⁸F-FBPA and BPA, and evaluated the utility of ¹⁸F-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 ¹⁸F-FBPA and ¹⁴C-BPA uptake in FaDu and LN-229 human cancer cells. ¹⁸F-FBPA uptake strongly correlated with ¹⁴C-BPA uptake in seven human tumor cell lines (r = 0.93; p <0.01). PET experiments demonstrated that tumor uptake of ¹⁸F-FBPA was independent of the administration method, and uptake of ¹⁸F-FBPA by bolus injection correlated well with BPA uptake by continuous intravenous infusion. The results of this study revealed that evaluating tumor uptake of ¹⁸F-FBPA by PET was useful for estimating ¹⁰B concentration in tumors.

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