Boron Neutron Capture Therapy Drug Research Articles

Self-assembling A6K peptide nanotubes as a mercaptoundecahydrododecaborate (BSH) delivery system for boron neutron capture therapy (BNCT)

Boron neutron capture therapy (BNCT) is a tumor selective therapy, the effectiveness of which depends on sufficient 10B delivery to and accumulation in tumors. In this study, we used self-assembling A6K peptide nanotubes as boron carriers and prepared new boron agents by simple mixing of A6K and BSH. BSH has been used to treat malignant glioma patients in clinical trials and its drug safety and availability have been confirmed; however, its contribution to BNCT efficacy is low. A6K nanotube delivery improved two major limitations of BSH, including absence of intracellular transduction and non-specific drug delivery to tumor tissue. Varying the A6K peptide and BSH mixture ratio produced materials with different morphologies—determined by electron microscopy—and intracellular transduction efficiencies. We investigated the A6K/BSH 1:10 mixture ratio and found high intracellular boron uptake with no toxicity. Microscopy observation showed intracellular localization of A6K/BSH in the perinuclear region and endosome in human glioma cells. The intracellular boron concentration using A6K/BSH was almost 10 times higher than that of BSH. The systematic administration of A6K/BSH via mouse tail vein showed tumor specific accumulation in a mouse brain tumor model with immunohistochemistry and pharmacokinetic study. Neutron irradiation of glioma cells treated with A6K/BSH showed the inhibition of cell proliferation in a colony formation assay. Boron delivery using A6K peptide provides a unique and simple strategy for next generation BNCT drugs.

Suitability of boric acid as a boron drug for boron neutron capture therapy for hepatoma

Hepatoma is the second leading cause of cancer death worldwide. Due to the poor outcomes of patients with late diagnosis, newer treatments for hepatoma are still needed. As an emerging therapy, boron neutron capture therapy (BNCT) may be an effective solution in hepatoma management. In this study, boric acid (BA) was used as the boron drug for in vivo analysis of action mechanism. The N1S1 single liver tumor-bearing rat and the VX2 multifocal liver tumor-bearing rabbit models were used to investigate the retention status of BA in the tumor regions during BNCT. The autoradiographic examination showed BA can localize specifically not only in the hepatoma cells but also in tumor blood vessels. Our findings indicate that superior hepatoma targeting could be achieved in BA-mediated BNCT, which supports BA to be a suitable boron drug for BNCT for hepatoma.

Electrosprayed chitosan/alginate/polyvinyl alcohol nanoparticles as boric acid carriers for 10Boron neutron capture therapy.

Aim: To improve the killing efficacy of head and neck squamous cells (SAS) by boric acid-mediated boron neutron capture therapy (BNCT).Materials & methods:Boric acid-containing chitosan/alginate/polyvinyl alcohol nanoparticles (B-capNPs) were manufactured using the nano-electrospray process.Results: Less than 10% of the boric acid leaked from the B-capNPs over 2days. The B-capNPs killed up to 2.8-fold more SAS cells and reduced cytotoxicity tenfold when compared with pure boric acid alone. B-capNPs show selective uptake in tumor cells with tumor/normal ratios of SAS to normal (NIH 3T3) and macrophage (RAW 264.7) cells of 4.0 and 3.5, respectively, which are greater than the minimum acceptable tumor/normal ratio for BNCT of 2.5. Conclusion: These findings illustrate that B-capNPs may be more superior as BNCT drugs than pure boric acid.

Microdistribution and quantification of the boron neutron capture therapy drug BPA in primary cell cultures of human glioblastoma tumour by NanoSIMS.

The ability of secondary ion mass spectrometry (SIMS) to provide high sensitivity imaging of elements and small-medium mass molecules in biological tissues and cells, makes it a very powerful tool for drug distribution studies. Here we report on the application of a high-resolution dynamic SIMS instrument for the quantification and localisation of therapeutic levels of the BNCT agent l-para-(dihydroxyboryl)-phenylalanine (BPA) in primary cell cultures from human patients exhibiting glioblastoma multiform tumours. Boron uptake and distribution was determined quantitatively as a function of cell-sampling location and different treatment regimes. Importantly, BPA was found to accumulate in cancer cells invading the 'brain around tumour' tissue in addition to the main tumour site. Pre-treatment of samples with l-tyrosine was found not to increase the uptake of BPA, nor change the intracellular drug distribution. In cultured cells from the tumour core and brain around tumour, with and without l-tyrosine pre-treatment, normalised boron-related signals were higher from cell nuclei than from cytoplasm. An efflux treatment was found to reduce BPA levels, but at a rate slower than the original uptake, and did not affect the intracellular drug distribution. To the best of our knowledge, these data represent the first published study of BPA uptake and l-amino acid pre-treatment in cultured primary human cells using dynamic SIMS, and the most detailed, subcellular distribution study of a BNCT agent in any cellular system.

Tracing Boron with Fluorescence and Positron Emission Tomography Imaging of Boronated Porphyrin Nanocomplex for Imaging-Guided Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) induces high-energy radiation within cancer cells while avoiding damage to normal cells without uptake of BNCT drugs, which is holding great promise to provide excellent control over locally invasive malignant tumors. However, lack of quantitative imaging technique to determine local boron concentration has been a great challenge for nuclear physicians to apply accurate neutron irradiation during the treatment, which is a key factor that has limited BNCT's application in clinics. To meet this challenge, this study describes coating boronated porphyrins with a biocompatible poly(lactide- co-glycolide)-monomethoxy-poly(polyethylene-glycol) (PLGA-mPEG) micelle for selective tumor accumulation and reduced toxicity comparing with the previously reported boronated porphyrin drugs. Fluorescence imaging and positron emission tomography (PET) imaging were performed, unveiling the potential imaging properties of this boronated porphyrin nanocomplex (BPN) to locate tumor region and to determine tissue-localized boron concentration which facilitates treatment planning. By studying the pharmacokinetics of BPN with Cu-64 PET imaging, the treatment plan was adjusted from single bolus injection to multiple times of injections of smaller doses. As expected, high tumor uptake of boron (125.17 ± 13.54 ppm) was achieved with an extraordinarily high tumor to normal tissue ratio: tumors to liver, muscle, fat, and blood were 3.24 ± 0.22, 61.46 ± 20.26, 31.55 ± 10.30, and 33.85 ± 5.73, respectively. At last, neutron irradiation with BPN showed almost complete tumor suppression, demonstrating that BPN holds a great potential for being an efficient boron delivery agent for imaging-guided BNCT.

Structural Insight Into Protein Binding of Boron Tracedrug UTX-97 Revealed by the Co-Crystal Structure With Lysozyme at 1.26 Å Resolution

Boron neutron capture therapy (BNCT) is one of the numbers of radiotherapies for treatment of certain cancers. The ability of low-dose irradiation with neutrons or radioactive beams to provide an acceptable quality of life is an objective which has not yet been achieved; therefore it will be necessary to increase the efficiency of the neutron capture reaction by lower dose irradiation and by achieving higher drug concentrations in living cells. Drug selectivity in targeting the affected cellular compartment is most important. Molecular design and synthesis of drugs should be based on high resolution structures and analysis of specific compounds and host molecules; however, it is necessary to obtain crystals for X-ray structural analysis. Because compounds containing bulky functional groups are difficult to crystalize due to their flexibility, the method described here makes it possible to stabilize these compounds by complexing them with protein molecules. We have first solved the three-dimensional structure of a BNCT drug-protein molecule combination at 1.26 Å resolution, and discuss the nature of the interaction between a BNCT drug and the protein molecule residues.

Biocompatibility of functionalized boron phosphate (BPO4) nanoparticles for boron neutron capture therapy (BNCT) application

Boron neutron capture therapy (BNCT) is a radiotherapy treatment based on the accumulation in the tumor of a 10B-containing drug and subsequent irradiation with low energy neutrons, which bring about the decay of 10B to 7Li and an α particle, causing the death of the neoplastic cell. The effectiveness of BNCT is limited by the low delivery and accumulation of the used boron-containing compounds. Here we report the development and the characterization of BPO4 nanoparticles (NPs) as a novel possible alternative drug for BNCT. An extensive analysis of BPO4 NP biocompatibility was performed using both mature blood cells (erythrocytes, neutrophils and platelets) and a model of hematopoietic progenitor cells. A time- and concentration-dependent cytotoxicity study was performed on neoplastic coloncarcinoma and osteosarcoma cell lines. BPO4 functionalization with folic acid, introduced to improve the uptake by tumor cells, appeared to effectively limit the unwanted effects of NPs on the analyzed blood components. From the Clinical EditorBoron neutron capture therapy (BNCT) is a radiotherapy treatment modality based on the accumulation of a 10B-containing drug and subsequent irradiation with low energy neutrons, inducing the decay of 10B to 7Li and an α particle, causing neoplastic cell death. This team of authors reports on a folic acid functionalized BPO4 nanoparticle with improved characteristics compared with conventional BNCT approaches, as demonstrated in tumor cell lines, and hopefully to be followed by translational human studies.

Potential of using boric acid as a boron drug for boron neutron capture therapy for osteosarcoma

Osteosarcoma is a malignant tumor commonly found in human and animals. The ability of boric acid (BA) to accumulate in osteosarcoma due to the mechanism of the bone formation of cancer cells would make boron neutron capture therapy (BNCT) an alternative therapy for osteosarcoma. This study evaluated the feasibility of using BA as the boron drug for BNCT of bone cancer. The cytotoxicity of BA to L929 cells exceeded that of UMR-106 cells. With 25 μg (10)B/mL medium of BA treatment, the boron concentration in UMR-106 cells was higher than that in L929 cells. The biodistribution and pharmacokinetics of BA in Sprague-Dawley (SD) rats were studied by administrating 25 mg (10)B/kg body weight to SD rats. Blood boron level decreased rapidly within one hour after BA injection. Boron concentration in the long bone was 4-6 time higher than that of blood. Results of this study suggest that BA may be a potential drug for BNCT for osteosarcoma.

Carborane Derivatives Loaded into Liposomes as Efficient Delivery Systems for Boron Neutron Capture Therapy

Boron neutron capture therapy (BNCT) is an anticancer therapy based on the incorporation of (10)B in tumors, followed by neutron irradiation. Recently, the synthesis and delivery of new boronated compounds have been recognized as some of the main challenges in BNCT application. Here, we report on the use of liposomes as carriers for BNCT active compounds. Two carborane derivatives, i.e., o-closocarboranyl beta-lactoside (LCOB) and 1-methyl-o-closocarboranyl-2-hexylthioporphyrazine (H(2)PzCOB), were loaded into liposomes bearing different surface charges. The efficacy of these formulations was tested on model cell cultures, that is, DHD/K12/TRb rat colon carcinoma and B16-F10 murine melanoma. These induce liver and lung metastases, respectively, and are used to study the uptake of standard BNCT drugs, including borophenylalanine (BPA). Boron concentration in treated cells was measured by alpha spectrometry at the TRIGA mark II reactor (University of Pavia). Results showed high performance of the proposed formulations. In particular, the use of cationic liposomes increased the cellular concentration of (10)B by at least 30 times more than that achieved by BPA.

Incorporation and characterization of boron neutron capture therapy agents into mesoporous silicon and silicon nanowires

The tunable pore size, biodegradability, and surface chemis- try of mesoporous silicon (BioSilicon ™ ) are important to a broad spectrum of uses for drug delivery. For the case of Boron Neutron Capture Therapy (BNCT), encapsulation of a given boron-containing drug molecule within a porous BioSilicon ™ microparticle provides a vehicle for a brachytherapy method that avoids the necessity of drug modification. In this work, the loading and characterization of three clinically approved BNCT drugs into mesoporous Si is demonstrated. Because of difficulties associated with light element detection, a method based on a Beer's Law analysis of selected FTIR vibrational bands has been developed to estimate boron-containing drug loading in these materials. As a complementary nanostructural platform, a cathodic deposition process for the surface enriched growth of selected drugs onto the surface of silicon nanowires is also described.

Suitability of boron carriers for BNCT: Accumulation of boron in malignant and normal liver cells after treatment with BPA, BSH and BA

Hepatocellular carcinoma remains widely prevalent in tropical Africa and south-east Asia. At present, there are no effective treatments for hepatoma and its prognosis is extremely poor unless the tumor was diagnosed in an early stage and resected before metastasis. Therefore, boron neutron capture therapy (BNCT) may provide an alternative therapy for treatment of hepatocellular carcinoma. In this study, the intracellular concentrations of l-boronophenylalanine (BPA), sodium borocaptate (BSH) and boric acid (BA) were examined in human hepatoma HepG2 and liver Clone 9 cell cultures. With the use of 25 μg B/mL media of BPA, BSH and BA, the intracellular uptake of boron in HepG2 and Clone 9 cells was compared. The suitability of BPA, BSH and BA were further evaluated on the basis of organ-specific boron distribution in normal rat tissues. BPA, BSH and BA were administered via intraperitoneal injection into rats with corresponding boron concentrations of 7, 25, and 25 mg/kg body weight, respectively. The accumulation rates of BPA, BSH and BA in HepG2 cells were higher than that of Clone 9 cells. Boron concentration in BPA, BSH and BA treated HepG2 cells were 1.8, 1.5, and 1.6-fold of Clone 9 cells at 4 h, respectively. In both HepG2 and Clone 9 cells, although the concentration of boron in BPA-treated cells exceeded that in BA-treated ones, however, cells treated with BPA had similar surviving fraction as those treated with BA after neutron irradiation. The accumulation ratios of boron in liver, pancreas and kidney to boron in blood were 0.83, 4.16 and 2.47, respectively, in BPA treated rats, and 0.75, 0.35 and 2.89, respectively, in BSH treated rats at 3 h after treatment. However, boron does not appear to accumulate specifically in soft tissues in BA treated rats. For in situ BNCT of hepatoma, normal organs with high boron concentration and adjacent to liver may be damaged in neutron irradiation. BPA showed high retention in pancreas and may not be a good drug for BNCT of hepatoma. BSH had higher retention in liver but low level in pancreas and spleen appears to be a better candidate BNCT drug for hepatoma. These preliminary results provide useful information on future application of BNCT for hepatoma.

Dynamic secondary ion mass spectrometry analysis of boron from boron neutron capture therapy drugs in co-cultures: single-cell imaging of two different cell types within the same ion microscopy field of imaging.

A co-culture, cryogenic SIMS methodology is presented for the quantitative analysis of cell type-dependent accumulation of boron delivered by BPA-F and BSH, two clinically approved drugs used in boron neutron capture therapy of cancer. T98G human glioblastoma cells were co-cultured with morphologically different normal LLC-PK1 epithelial cells or GM3348 human skin fibroblasts. Our freeze-fracture method of cryogenic sample preparation successfully fractured the different cell types grown together in co-cultures. Quantitative observations revealed an active uptake of boron from BPA-F in both T98G and LLC-PK1 cells but did not show cell type-dependent differences. Accumulation of BSH in all three cell types examined also did not reveal any cell type-dependent differences in co-cultures. As this method relies on the analysis, within the same field of SIMS imaging, of two different cell types that have been maintained under identical conditions of growth, drug exposure, sample preparation, and instrumental analysis, it provides the most effective approach for comparing cell type-specific differences in boron concentrations. The most effective applications of this method will be realized in testing the selectivity of experimental boronated compounds designed to specifically target tumor cells.

Studies on the structure of the complex of the boron neutron capture therapy drug, L-p-boronophenylalanine, with fructose and related carbohydrates: Chemical and 13C NMR evidence for the β-D-fructofuranose 2,3,6-(p-phenylalanylorthoboronate) structure

Studies on the structure of the complex of the boron neutron capture therapy drug, L-p-boronophenylalanine, with fructose and related carbohydrates: Chemical and 13C NMR evidence for the β-D-fructofuranose 2,3,6-(p-phenylalanylorthoboronate) structure

Evidence for spontaneous, reversible paracyclophane formation. Aprotic solution structure of the boron neutron capture therapy drug, L-p-boronophenylalanine

The simple, straightforward 1H NMR spectrum of the neutron capture therapy drug, L-p-boronophenylalanine (L-p-BPA), in D2O changes to a more complex one in DMSO-d6 in which the ratio of new species observed is highly concentration dependent. The new species detected can only be explained by an additional stereocenter being formed at the boron center by intermolecular chelation of the amino acid of another molecule of L-p-BPA. This gives rise to the presence of an oligomeric species as well as another whose aromatic protons appear as a pair of sharp AB quartets centered further upfield at 6.66 and 6.84. Due to these shifts and couplings observed between the benzylic protons and the proton at the stereocenter of the amino acid, it is proposed that this species is a paracyclophane dimer of L-p-BPA in which one molecule of L-p-BPA chelates head-to-tail with another. This cyclophane dimer predominates in low concentrations ( 90 mM) concentrations. The formation of these two species is completely reversible, the addition of D2O completely regenerating L-p-BPA. Variable temperature 1H NMR found that the two pairs of aromatic protons of the cyclophane dimer coalesce at Tc = 141 °C, corresponding to a ΔG‡ = 20.6 kcal mol−1.

Imaging of boron in tissue at the cellular level for boron neutron capture therapy.

Glioblastoma multiforme, and other tumors involving the brain, are undergoing experimental treatment with a promising new technique: boron neutron capture therapy (BNCT). BNCT relies on the capture of thermal neutrons by boron deposited biochemically in the tumor and the subsequent fission of the boron into energetic lithium ions and alpha particles. An important requirement for improved BNCT is the development of more selective boron delivery mechanisms. The ability to image the boron concentration in tissue sections and even inside individual cells would be an important aid in the development of these delivery mechanisms. We have compared both sputter-initiated resonance ionization microprobe (SIRIMP), which combines resonance ionization with a high-energy pulsed focused sputter ion beam and mass spectrometric detection of ions, with laser atomization resonance ionization microprobe (LARIMP), which uses a laser pulse instead of an ion pulse for the atomization process, to determine their characteristics in locating and quantifying boron concentrations as a function of position in tissues obtained from a rat which had been infused with a BNCT drug. The data show that the SIRIMP/LARIMP techniques are well suited for quantitative and ultrasensitive imaging of boron trace element concentrations in biological tissue sections. The LARIMP mode could be used to quickly determine the spatial boron concentration with intercellular resolution over large areas down to the low nanograms-per-gram level, while the SIRIMP mode could be used to determine the spatial boron concentration and its variability in intracellular areas.

Intracellular boron localization and uptake in cell cultures using imaging secondary ion mass spectrometry (ion microscopy) for neutron capture therapy for cancer

Quantitative ion microscopy of freeze-fractured, freeze-dried cultured cells is a technique for single cell and subcellular elemental analysis [1–3]. This review describes the technique and its usefulness in determining the uptake and subcellular distribution of the boron from boron neutron capture therapy drugs.

Boron-11 magnetic resonance imaging and spectroscopy; tools for investigating pharmacokinetics for boron neutron capture therapy.

Boron neutron capture therapy (BNCT) is brachyradiotherapy by heavy charged particles from the l0B(n,α)7Li nuclear reaction.1,2 BNCT depends upon the delivery of boron-10 containing drugs to the targeted lesions; the non-invasive verification and quantification of the boron content is a difficult problem. Clearly, experimental and clinical investigations of BNCT drugs would be greatly improved by the development of a non-invasive method for measuring the boron distribution in vivo. For example, such a technique could be used to monitor the course of distribution of a BNCT drug in the liver, kidney, bladder, brain and other organs of a patient scheduled for BNCT of a brain tumor so as to predict the optimum time for neutron irradiation of the brain.3