Boronotyrosine, a Borylated Amino Acid Mimetic with Enhanced Solubility, Tumor Boron Delivery, and Retention for the Re-emerging Boron Neutron Capture Therapy Field

A novel quantitative method for the determination of 10B-carrier boronophenylalanine in rat plasma by UHPLC-MS/MS and comparison with ICP-MS

L-Boronophenylalanine (BPA), a widely used 10B carrier for clinical boron neutron capture therapy (BNCT), was quantified in rat plasma through a simple, effective and stable ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method. Chromatographic separation was performed on an ACQUITY UPLC HSS T3 (100 mm × 2.1 mm, 1.8 μm) column with the mobile phase of 0.5 % formic acid aqueous solution and acetonitrile. For the detector, the m/z ion pairs used for quantification were 209.1→120.1 for BPA and 210.1→120.1 for internal standard in a positive mode by electrospray ionization (ESI) using multiple reaction monitoring (MRM). The method is specific and robust with rare affection by endogenous substances in the matrix. A good linear relationship was observed over 80-80000 ng/mL (r2 = 0.9993). The values of inter- and intra-day accuracy and precision were within the acceptance criteria of ±15 %. BPA was found to be stable under different experimental conditions. This developed method was successfully applied on a pharmacokinetic experiment on Sprague-Dawley rats (intravenous injection, 125 mg/kg) and a comparation between UHPLC-MS/MS and ICP-MS for BPA was carried out.

A Bis-Boron Amino Acid for Positron Emission Tomography and Boron Neutron Capture Therapy

Trifluoroborate boronophenylalanine (BBPA) is a boron amino acid analog of 4-boronophenylalanine (BPA) but with a trifluoroborate group (-BF3 -) instead of a carboxyl group (-COOH). Clinical studies have shown that 18F-labeled BBPA ([18F]BBPA) can produce high-contrast tumor images in positron emission tomography (PET). Beyond PET imaging, BBPA is a theranostic agent for boron neutron capture therapy (BNCT). Because BBPA possesses an identical chemical structure to BNCT and PET, it can potentially predict the boron concentration for BNCT using [18F]BBPA-PET. The synthesis of BBPA was achieved by selectively fluorinating the α-aminoborate compound, taking advantage of the varying rates of solvolysis of the B-F bond. The study showcased the high-contrast [18F]BBPA-PET imaging in various tumor models, highlighting its broad applicability for both [18F]BBPA-PET and BBPA-BNCT. [18F]BBPA-PET tumor uptake remains consistent across various doses, including those used in BNCT. This enables accurate estimation of the boron concentration in tumors using [18F]BBPA-PET. With its dual boron structure, BBPA increases boron concentration in tumor cells and tumor tissues compared to BPA. Thus, less boron carrier is needed. This study introduces a new theranostic boron carrier that enhances boron accumulation in tumors, predicts boron concentration, and enhances the accuracy and effectiveness of BNCT.

Early Stage In Vitro Bioprofiling of Potential Low-Molecular-Weight Organoboron Compounds for Boron Neutron Capture Therapy (BNCT)-Proposal for a Guide

Given the renewed interest in boron neutron capture therapy (BNCT) and the intensified search for improved boron carriers, as well as the difficulties of coherently comparing the carriers described so far, it seems necessary to define a basic set of assays and standardized methods to be used in the early stages of boron carrier development in vitro. The selection of assays and corresponding methods is based on the practical experience of the authors and is certainly not exhaustive, but open to discussion. The proposed tests/characteristics: Solubility, lipophilicity, stability, cytotoxicity, and cellular uptake apply to both low molecular weight (up to 500 Da) and high molecular weight (5000 Da and more) boron carriers. However, the specific methods have been selected primarily for low molecular weight boron carriers; in the case of high molecular weight compounds, some of the methods may need to be adapted.

Amino Acid-Based Boron Carriers in Boron Neutron Capture Therapy (BNCT)

Interest in the design of boronated amino acids has emerged, partly due to the utilization of boronophenylalanine (BPA), one of the two agents employed in clinical Boron Neutron Capture Therapy (BNCT). The boronated amino acids synthesized thus far for BNCT investigations can be classified into two categories based on the source of boron: boronic acids or carboranes. Amino acid-based boron carriers, employed in the context of BNCT treatment, demonstrate significant potential in the treatment of challenging tumors, such as those located in the brain. This review aims to shed light on the developmental journey and challenges encountered over the years in the field of amino acid-based boron delivery compound development. The primary focus centers on the utilization of the large amino acid transporter 1 (LAT1) as a target for boron carriers in BNCT. The development of efficient carriers remains a critical objective, addressing challenges related to tumor specificity, effective boron delivery, and rapid clearance from normal tissue and blood. LAT1 presents an intriguing and promising target for boron delivery, given its numerous characteristics that make it well suited for drug delivery into tumor tissues, particularly in the case of brain tumors.