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bioRxiv · 10.1101/2025.11.27.690635

L-Phenylalanine restriction amplifies boron neutron capture therapy efficacy through increased L-boronophenylalanine uptake and induces activating transcription factor 4 stress response in tumor cell lines

Tamari, Y.·Saba, R.·Takata, T.·Kimura, H.·Takita, M.·Yashiro, K.·Suzuki, M.·Yamazaki, H.·Yamada, K.
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Abstract

Boron neutron capture therapy (BNCT) relies on the selective uptake of boron-10 compounds by tumor cells. L-boronophenylalanine (BPA) serves as a key carrier, and enhancing its accumulation is critical for improving BNCT efficacy. In this study, we investigated the effects of L-phenylalanine (Phe) restriction on the tumor cell lines SAS, U87-MG, PANC-1, and A375, and the immortalized keratinocyte line HaCaT on modulating BPA uptake and associated cellular responses. Quantitative analysis using inductively coupled plasma atomic emission spectroscopy (ICP-AES) showed that 24 h Phe restriction increased BPA uptake in the SAS, U87-MG, and PANC-1 cell lines. Colony formation assays confirmed enhanced sensitivity to neutron irradiation in these cells. RNA sequencing indicated that Phe restriction activated the integrated stress response downstream of activating transcription factor 4 (ATF4), although this pathway was not directly linked to increased BPA uptake. The L-type amino acid transporter 1 (LAT1)/4F2 heavy chain (4F2HC) complex was identified as the exclusive transport route for BPA. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis showed that Phe restriction altered intracellular levels of amino acids that serve as LAT1/4F2HC exchange substrates, suggesting a metabolic basis for enhanced BPA transport. Our results reveal that Phe restriction enhances BPA uptake and BNCT efficacy in a cell line-dependent manner, likely through the modulation of amino-acid metabolism. Therefore, targeted amino-acid manipulation prior to BNCT may represent a promising strategy to improve therapeutic outcomes.

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Tamari, Y., Saba, R., Takata, T., Kimura, H., Takita, M., Yashiro, K., Suzuki, M., Yamazaki, H., Yamada, K.. 2025-12-01. L-Phenylalanine restriction amplifies boron neutron capture therapy efficacy through increased L-boronophenylalanine uptake and induces activating transcription factor 4 stress response in tumor cell lines. https://doi.org/10.1101/2025.11.27.690635

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