Boronophenylalanine, a boron delivery agent for boron neutron capture therapy, is transported by ATB^0,+, LAT1 and LAT2

Abstract

The efficacy of boron neutron capture therapy relies on the selective delivery of boron carriers to malignant cells. p-Boronophenylalanine (BPA), a boron delivery agent, has been proposed to be localized to cells through transporter-mediated mechanisms. In this study, we screened aromatic amino acid transporters to identify BPA transporters. Human aromatic amino acid transporters were functionally expressed in Xenopus oocytes and examined for BPA uptake and kinetic parameters. The roles of the transporters in BPA uptake were characterized in cancer cell lines. For the quantitative assessment of BPA uptake, HPLC was used throughout the study. Among aromatic amino acid transporters, ATB0,+, LAT1 and LAT2 were found to transport BPA with Km values of 137.4 ± 11.7, 20.3 ± 0.8 and 88.3 ± 5.6 μM, respectively. Uptake experiments in cancer cell lines revealed that the LAT1 protein amount was the major determinant of BPA uptake at 100 μM, whereas the contribution of ATB0,+ became significant at 1000 μM, accounting for 20–25% of the total BPA uptake in MCF-7 breast cancer cells. ATB0,+, LAT1 and LAT2 transport BPA at affinities comparable with their endogenous substrates, suggesting that they could mediate effective BPA uptake in vivo. The high and low affinities of LAT1 and ATB0,+, respectively, differentiate their roles in BPA uptake. ATB0,+, as well as LAT1, could contribute significantly to the tumor accumulation of BPA at clinical dose.

Specific transport of 3‐fluoro‐l‐α‐methyl‐tyrosine by LAT1 explains its specificity to malignant tumors in imaging

“…Because LAT1 is a potential therapeutic target as well as a diagnosis biomarker of cancer, the inhibitors of LAT1 have been developed to suppress tumor growth . LAT1 can also be used for tumor‐targeted delivery of anti‐tumor agents such as melphalan and para‐boronophenylalanine in boron neutron capture therapy . Therefore, the LAT1‐specific probe established in the present study could also be useful for the selection of subjects and the monitoring of therapeutic effects in the LAT1‐targeting therapies.…”

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

“…Detta et al demonstrate that LAT1 is involved in the transport of BPA. Wongthai et al reveal that BPA is transported by LAT2 and LAT1, but not LAT3 or LAT4. Although this study did not provide evidence for the involvement of LAT2 and LAT4 in the uptake of 18 F‐FBPA and 14 C‐BPA, inhibition analysis using short interfering RNA would directly elucidate the role that system L isoforms serve in their uptake.…”

“…To estimate BPA accumulation and the T/N ratios, PET using 4-borono-2-18 F-fluoro-phenylalanine ( 18 F-FBPA PET) has been performed. [3][4][5][6][7] Previously, we reported that 18 F-FBPA was predominantly transported by L-type amino acid transporter (system L). 8 In rat 9L gliosarcoma cells, 2-aminobicyclo-(2.2.1)-heptane-2-carboxylic acid (BCH) inhibited BPA uptake, which suggested that system L played a role in this phenomenon.…”

“…8 In rat 9L gliosarcoma cells, 2-aminobicyclo-(2.2.1)-heptane-2-carboxylic acid (BCH) inhibited BPA uptake, which suggested that system L played a role in this phenomenon. 9 However, the transport and uptake of 18 F-FBPA have not been compared with those of BPA in detail.…”

Novel therapeutic approaches targeting L-type amino acid transporters for cancer treatment

“…This difficult task could be achieved by the synthesis of a boron compound that is selectively delivered by LAT1. Indeed, p-boronophenylalanine (BPA), a boron compound commonly used in BNCT, is incorporated by LAT1[38-40], suggesting that LAT1 is an optimal mediator for delivery of boron in BNCT. However, since we cannot still completely rule out the possibility of BPA uptake by other transporters, it is necessary to develop compounds that exhibit strict selectivity to LAT1.…”