Boron Accumulation in Brain Tumor Cells through Boc-Protected Tryptophan as a Carrier for Boron Neutron Capture Therapy

Fluorine-18 labeling PEGylated 6-boronotryptophan for PET scanning of mice for assessing the pharmacokinetics for boron neutron capture therapy of brain tumors

Two tryptophan compound classes 5- and 6-borono PEGylated boronotryptophan derivatives have been prepared for assessing their aqueous solubility as formulation of injections for boron neutron capture therapy (BNCT). The PEGylation has improved their aqueous solubility thereby increasing their test concentration in 1 mM without suffering from toxicity. In-vitro uptake assay of PEGylated 5- and 6-boronotryptophan showed that the B-10 concentration can reach 15-50 ppm in U87 cell whereas the uptake in LN229 cell varies. Shorter PEG compound 6-boronotryptophanPEG200[18F] was obtained in 1.7 % radiochemical yield and the PET-derived radioradioactivity percentage in 18 % was taken up by U87 tumor at the limb of xenograft mouse. As high as tumor to normal uptake ratio in 170 (T/N) was obtained while an inferior radioactivity uptake of 3 % and T/N of 8 was observed in LN229 xenografted mouse.

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.

Next generation of boron neutron capture therapy (BNCT) agents for cancer treatment

Boron neutron capture therapy (BNCT) is one of the most promising treatments among neutron capture therapies due to its long-term clinical application and unequivocally obtained success during clinical trials. Boron drug and neutron play an equivalent crucial role in BNCT. Nevertheless, current clinically used l-boronophenylalanine (BPA) and sodium borocaptate (BSH) suffer from large uptake dose and low blood to tumor selectivity, and that initiated overwhelm screening of next generation of BNCT agents. Various boron agents, such as small molecules and macro/nano-vehicles, have been explored with better success. In this featured article, different types of agents are rationally analyzed and compared, and the feasible targets are shared to present a perspective view for the future of BNCT in cancer treatment. This review aims at summarizing the current knowledge of a variety of boron compounds, reported recently, for the application of BCNT.

Polyphenolic Boronates Inhibit Tumor Cell Proliferation: Potential Mitigators of Oxidants in the Tumor Microenvironment

Boronate-based compounds have been used in brain cancer therapy, either as prodrugs or in combination with other modalities. Boronates containing pro-luminescent and fluorescent probes have been used in mouse models of cancer. In this study, we synthesized and developed polyphenolic boronates and mitochondria-targeted polyphenolic phytochemicals (e.g., magnolol [MGN] and honokiol [HNK]) and tested their antiproliferative effects in brain cancer cells. Results show that mitochondria-targeted (Mito) polyphenolic boronates (Mito-MGN-B and Mito-HNK-B) were slightly more potent than Mito-MGN and Mito-HNK in inhibiting proliferation of the U87MG cell line. Similar proliferation results also were observed in other cancer cell lines, such as MiaPaCa-2, A549 and UACC-62. Independent in vitro experiments indicated that reactive nitrogen species (e.g., peroxynitrite) and reactive oxygen species (e.g., hydrogen peroxide) stoichiometrically react with polyphenolic boronates and Mito-polphenolic boronates, forming polyphenols and Mito-polyphenols as major products. Previous reports suggest that both Mito-MGN and Mito-HNK activate cytotoxic T cells and inhibit immunosuppressive immune cells. We propose that Mito-polyphenolic boronate-based prodrugs may be used to inhibit tumor proliferation and mitigate oxidant formation in the tumor microenvironment, thereby generating Mito-polyphenols in situ, as well as showing activity in the tumor microenvironment.

Cell-free expression of NO synthase and P450 enzyme for the biosynthesis of an unnatural amino acid L-4-nitrotryptophan

Cell-free system has emerged as a powerful platform with a wide range of in vitro applications and recently has contributed to express metabolic pathways for biosynthesis. Here we report in vitro construction of a native biosynthetic pathway for L-4-nitrotryptophan (L-4-nitro-Trp) synthesis using an Escherichia coli-based cell-free protein synthesis (CFPS) system. Naturally, a nitric oxide (NO) synthase (TxtD) and a cytochrome P450 enzyme (TxtE) are responsible for synthesizing L-4-nitro-Trp, which serves as one substrate for the biosynthesis of a nonribosomal peptide herbicide thaxtomin A. Recombinant coexpression of TxtD and TxtE in a heterologous host like E. coli for L-4-nitro-Trp production has not been achieved so far due to the poor or insoluble expression of TxtD. Using CFPS, TxtD and TxtE were successfully expressed in vitro, enabling the formation of L-4-nitro-Trp. After optimization, the cell-free system was able to synthesize approximately 360 μM L-4-nitro-Trp within 16 h. Overall, this work expands the application scope of CFPS for study and synthesis of nitro-containing compounds, which are important building blocks widely used in pharmaceuticals, agrochemicals, and industrial chemicals.

Fused 1,2-Diboraoxazoles Based on closo-Decaborate Anion-Novel Members of Diboroheterocycle Class

The novel members of the 1,2-diboraoxazoles family have been obtained. In the present work, we have carried out the intramolecular ring-closure reaction of borylated iminols of general type [B₁₀H₉N=C(OH)R]⁻ (R = Me, Et, ⁿPr, ⁱPr, ^tBu, Ph, 4-Cl-Ph). This process is conducted in mild conditions with 83–87% yields. The solid-state structures of two salts of 1,2-diboraoxazoles were additionally investigated by X-ray crystallography. In addition, the phenomena of bonding interactions in the 1,2-diboraoxazole cycles have been theoretically studied by the Quantum Theory of Atoms in Molecules analysis. Several local and integral topological properties of the electron density involved in these interactions have been computed.