Enhancement of Cancer Cell-Killing Effects of Boron Neutron Capture Therapy by Manipulating the Expression of L-Type Amino Acid Transporter 1

In this study, we examined whether the cancer cell-killing effects of boron neutron capture therapy (BNCT) are enhanced by manipulating the expression levels of l-type amino acid transporter 1 (LAT1) of human cancer cells, which transports boronophenylalanine into cells. We transfected pCMV/LAT1-GFP plasmids into a T98G glioblastoma cell line and selected several clones. Confocal laser microscopic observation was performed to confirm the stable overexpression of LAT1 in the plasma membranes of the clones. Western blot was used to analyze the cellular accumulation of LAT1 protein in the clones. Relative intracellular uptake of boronophenylalanine (BPA) was determined by measuring the radioactivity of 14C-BPA using a radioactive iodine (RI) tracer method. Sensitivity to neutron and gamma (γ)-ray fluences generated by a research reactor facility at Kyoto University was assayed using colony formation assay. Green fluorescent protein (GFP)-tagged LAT1 was observed in the plasma membranes of the LAT1-overexpressing clones and the cellular accumulation of GFP-tagged LAT1 was largely increased in these clones. Intracellular uptake of BPA was 1.5-5.0 times greater among the clones than that in a control clone. The LAT1-overexpressing clones and transiently LAT1-lipofected T98G cells showed clearly enhanced sensitivity to neutron and γ-ray fluences compared to the control clone when they were treated with 10BPA. The sensitivity of cancer cells to the fluences was well correlated with the expression level of LAT1 in the cells and the level of BPA uptake. These results suggest that overexpression of LAT1 in cancer cells results in enhanced anticancer effects of BNCT, and BNCT combined with gene therapy is beneficial for tumors with low LAT1 expression.