The feasibility of boron neutron capture therapy (BNCT) greatly depends on the selective accumulation of B in tumors. The p-boronophenylalanine-fructose (BPA-f) complex has been established as a conventional BNCT agent due to its preferential uptake into tumors, which is driven by amino acid transporters. However, the retention of BPA-f in tumors is highly limited because of an antiport mechanism, which is regulated by a gradient of amino acid concentration across the cancer cell membrane. Thus, to preserve a high B concentration in tumors, patients are inevitably subjected to a constant intravenous infusion. To this end, we employed a phenylboronic acid (PBA)-decorated polymeric nanoparticle (Nano) as a sialic acid-targeting BNCT agent. In this manner, the PBA can exhibit dual functionalities, i.e., exhibiting a neutron capture capacity and hypersialyated cancer cell targeting effect. Our developed Nano possesses a supramolecular structure composed of a core and shell comprised of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) segments, respectively. The PBA moiety is installed at the PEG end, providing an unusually strong targeting effect, supposedly via multivalent binding onto the cancer cell membrane. As in BNCT, we verified the feasibility of Nano against a B16 melanoma-bearing mouse model. By virtue of efficient tumor targeting, even at a 100-fold lower dose than BPA-f, the Nano achieved a potent antitumor effect.
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