(10)B-NMR determination of (10)B-BPA, (10)B-BPA-fructose complex and total (10)B in blood for BNCT

4-Iodobenzonitrile as a fluorogenic derivatization reagent for chromatographic analysis of L-p-boronophenylalanine in whole blood samples using Suzuki coupling reaction

BACKGROUND

L-p-Boronophehylalanine (BPA) is used in boron neutron capture therapy (BNCT), which is a novel selective cancer radiotherapy technique. It is important to measure BPA levels in human blood for effective radiotherapy; a prompt gamma-ray spectrometer, ICP-AES, and ICP-MS have been used for this purpose. However, these methods require sophisticated and expensive apparatuses as well as experienced analysts. Herein, we propose an HPLC-FL method for the determination of BPA after precolumn derivatization. A new fluorogenic reagent for aryl boronic acid derivatives, namely, 4-iodobenzonitrile, was employed for the fluorogenic derivatization of BPA based on the Suzuki coupling reaction.

RESULTS

After the fluorogenic derivatization, a fluorescent cyanobiphenyl derivative is formed with maximum fluorescence at 335 nm after excitation at 290 nm. The developed method showed good linearity (r2=0.997) over the concentration range of 0.5-1000 nmol/L, and the detection limit (S/N = 3) was 0.26 nmol/L. The proposed method is more sensitive than previously reported methods for the determination of BPA, including the ICP-MS. Finally, the proposed method was successively applied to the measurement of BPA in human whole blood samples with a good recovery rate (≥95.7 %) using only 10 μL of blood sample. The proposed method offers a simple and efficient solution for monitoring BPA levels in BNCT-treated patients.

SIGNIFICANCE

4-Iodobenzonitrile was investigated as a new fluorogenic reagent for BPA based on Suzuki coupling. A new HPLC-FL method for BPA in whole blood samples with ultrasensitivity was developed. The developed method is superior in sensitivity to all previously reported methods for BPA. The method requires only a very small sample volume, making it suitable for micro-blood analysis of BPA via fingerstick sampling.

Boron analysis and imaging of cells with 2-hr BPA exposure by using micro-proton particle-induced gamma-ray emission (PIGE)

Particle-induced gamma-ray emission (PIGE), which measures prompt gamma rays at 428 keV from ¹⁰B (p, p'γ) ⁷Be, was used to confirm the boron distribution within 2hr-BPA-exposed cells. Distribution images of potassium, phosphate, and boron and the whole spectrum showed the ratios of boron counts to total (%) as follows: control group: 1.35 ± 0.073%; 2hr boron exposure group: 2.33 ± 0.35%; and boron exposure/wash group: 1.58 ± 0.095%. Micro-beam PIXE/PIGE can be a promising tool for visualization of intracellular Boron.

Difference in BPA uptake between glioma stem-like cells and their cancerous cells

Tumor sphere-forming (TS) glioma stem cells and cancerous TS cells were analyzed in vivo and in vitro. The boron concentration in murine TS tumors was higher than normal tissue. The boron concentration at 24 h was 0.80 ± 0.09 μg/10⁷ in the TS cells, and 1.08 ± 0.08 μg/10⁷ in the cancerous cells. The LAT-1 amino-acid transporter positive rate was 35.4% in the TS cells and 100% in the cancerous cells. These results suggested the relation between LAT-1 expression and boronophenylalanine concentration in vitro.