Pulmonary Toxicity of Boron Nitride Nanomaterials Is Aspect Ratio Dependent

Boron nitride (BN) nanomaterials have drawn a lot of interest in the material science community. However, extensive research is still needed to thoroughly analyze their safety profiles. Herein, we investigated the pulmonary impact and clearance of two-dimensional hexagonal boron nitride (h-BN) nanosheets and boron nitride nanotubes (BNNTs) in mice. Animals were exposed by single oropharyngeal aspiration to h-BN or BNNTs. On days 1, 7, and 28, bronchoalveolar lavage (BAL) fluids and lungs were collected. On one hand, adverse effects on lungs were evaluated using various approaches (e.g., immune response, histopathology, tissue remodeling, and genotoxicity). On the other hand, material deposition and clearance from the lungs were assessed. Two-dimensional h-BN did not cause any significant immune response or lung damage, although the presence of materials was confirmed by Raman spectroscopy. In addition, the low aspect ratio h-BN nanosheets were internalized rapidly by phagocytic cells present in alveoli, resulting in efficient clearance from the lungs. In contrast, high aspect ratio BNNTs caused a strong and long-lasting inflammatory response, characterized by sustained inflammation up to 28 days after exposure and the activation of both innate and adaptive immunity. Moreover, the presence of granulomatous structures and an indication of ongoing fibrosis as well as DNA damage in the lung parenchyma were evidenced with these materials. Concurrently, BNNTs were identified in lung sections for up to 28 days, suggesting long-term biopersistence, as previously demonstrated for other high aspect ratio nanomaterials with poor lung clearance such as multiwalled carbon nanotubes (MWCNTs). Overall, we reveal the safer toxicological profile of BN-based two-dimensional nanosheets in comparison to their nanotube counterparts. We also report strong similarities between BNNTs and MWCNTs in lung response, emphasizing their high aspect ratio as a major driver of their toxicity.

Influence of Impurities from Manufacturing Process on the Toxicity Profile of Boron Nitride Nanotubes

The toxicity of boron nitride nanotubes (BNNTs) has been the subject of conflicting reports, likely due to differences in the residuals and impurities that can make up to 30-60% of the material produced based on the manufacturing processes and purification employed. Four BNNTs manufactured by induction thermal plasma process with a gradient of BNNT purity levels achieved through sequential gas purification, water and solvent washing, allowed assessing the influence of these residuals/impurities on the toxicity profile of BNNTs. Extensive characterization including infrared and X-ray spectroscopy, thermogravimetric analysis, size, charge, surface area, and density captured the alteration in physicochemical properties as the material went through sequential purification. The material from each step is screened using acellular and in vitro assays for evaluating general toxicity, mechanisms of toxicity, and macrophage function. As the material increased in purity, there are more high-aspect-ratio particulates and a corresponding distinct increase in cytotoxicity, nuclear factor-κB transcription, and inflammasome activation. There is no alteration in macrophage function after BNNT exposure with all purity grades. The cytotoxicity and mechanism of screening clustered with the purity grade of BNNTs, illustrating that greater purity of BNNT corresponds to greater toxicity.

Phototoxicity of BODIPY in long-term imaging can be reduced by intramolecular motion

For long-term live-cell fluorescence imaging and biosensing, it is crucial to work with a dye that has high fluorescence quantum yield and photostability without being detrimental to the cells. In this paper, we demonstrate that neutral boron-dipyrromethene (BODIPY)-based molecular rotors have great properties for high-light-dosage demanding live-cell fluorescence imaging applications that require repetitive illuminations. In molecular rotors, an intramolecular rotation (IMR) allows an alternative route for the decay of the singlet excited state (S₁) via the formation of an intramolecular charge transfer state (CT). The occurrence of IMR reduces the probability of the formation of a triplet state (T₁) which could further react with molecular oxygen (³O₂) to form cytotoxic reactive oxygen species, e.g., singlet oxygen (¹O₂). We demonstrate that the oxygen-related nature of the phototoxicity for BODIPY derivatives can be significantly reduced if a neutral molecular rotor is used as a probe. The studied neutral molecular rotor probe shows remarkably lower phototoxicity when compared with both the non-rotating BODIPY derivative and the cationic BODIPY-based molecular rotor in different light dosages and dye concentrations. It is also evident that the charge and localization of the fluorescent probe are as significant as the IMR in terms of the phototoxicity in a long-term live-cell imaging.

A Comparison of the Photophysical, Electrochemical and Cytotoxic Properties of meso-(2-, 3- and 4-Pyridyl)-BODIPYs and Their Derivatives

Boron dipyrromethene (BODIPY) dyes bearing a pyridyl moiety have been used as metal ion sensors, pH sensors, fluorescence probes, and as sensitizers for phototherapy. A comparative study of the properties of the three structural isomers of meso-pyridyl-BODIPYs, their 2,6-dichloro derivatives, and their corresponding methylated cationic pyridinium-BODIPYs was conducted using spectroscopic and electrochemical methods, X-ray analyses, and TD-DFT calculations. Among the neutral derivatives, the 3Py and 4Py isomers showed the highest relative fluorescence quantum yields in organic solvents, which were further enhanced 2-4-fold via the introduction of two chlorines at the 2,6-positions. Among the cationic derivatives, the 2catPy showed the highest relative fluorescence quantum yield in organic solvents, which was further enhanced by the use of a bulky counter anion (PF₆^-). In water, the quantum yields were greatly reduced for all three isomers but were shown to be enhanced upon introduction of 2,6-dichloro groups. Our results indicate that 2,6-dichloro-meso-(2- and 3-pyridinium)-BODIPYs are the most promising for sensing applications. Furthermore, all pyridinium BODIPYs are highly water-soluble and display low cytotoxicity towards human HEp2 cells.

Ex Vivo and In Vivo Evaluation of Dodecaborate-Based Clusters Encapsulated in Ferumoxytol Nanoparticles

Host-guest interactions represent a growing research area with recent work demonstrating the ability to chemically manipulate both host molecules as well as guest molecules to vary the type and strength of bonding. Much less is known about the interactions of the guest molecules and hybrid materials containing similar chemical features to typical macrocyclic hosts. This work uses in vitro and in vivo kinetic analyses to investigate the interaction of closo-dodecahydrododecaborate derivatives with ferumoxytol, an iron oxide nanoparticle with a carboxylated dextran coating. We find that several boron cluster derivatives can become encapsulated into ferumoxytol, and the lack of pH dependence in these interactions suggests that ion pairing, hydrophobic/hydrophilic interaction, and hydrogen bonding are not the driving force for encapsulation in this system. Biodistribution experiments in BALB/c mice show that this system is nontoxic at the reported dosage and demonstrate that encapsulation of dodecaborate-based clusters in ferumoxytol can alter the biodistribution of the guest molecules.

Selective Detection of Cu+ Ions in Live Cells via Fluorescence Lifetime Imaging Microscopy

Copper is an essential trace element in living organisms with its levels and localisation being carefully managed by the cellular machinery. However, if misregulated, deficiency or excess of copper ions can lead to several diseases. Therefore, it is important to have reliable methods to detect, monitor and visualise this metal in cells. Herein we report a new optical probe based on BODIPY, which shows a switch-on in its fluorescence intensity upon binding to copper(I), but not in the presence of high concentration of other physiologically relevant metal ions. More interestingly, binding to copper(I) leads to significant changes in the fluorescence lifetime of the new probe, which can be used to visualize copper(I) pools in lysosomes of live cells via fluorescence lifetime imaging microscopy (FLIM).

Probing Variations of Reduction Activity at the Plasma Membrane Using a Targeted Ratiometric FRET Probe

Plasma membrane (PM) is the turntable of various reactions that regulate essential functionalities of cells. Among these reactions, the thiol disulfide exchange (TDE) reaction plays an important role in cellular processes. We herein designed a selective probe, called membrane reduction probe (MRP), that is able to report TDE activity at the PM. MRP is based on a green emitting BODIPY PM probe connected to rhodamine through a disulfide bond. MRP is fluorogenic as it is turned off in aqueous media due to aggregation-caused quenching, and once inserted in the PM, it displays a bright red signal due to an efficient fluorescence energy resonance transfer (FRET) between the BODIPY donor and the rhodamine acceptor. In the PM model, the MRP can undergo TDE reaction with external reductive agents as well as with thiolated lipids embedded in the bilayer. Upon TDE reaction, the FRET is turned off and a bright green signal appears allowing a ratiometric readout of this reaction. In cells, the MRP quickly labeled the PM and was able to probe variations of TDE activity using ratiometric imaging. With this tool in hand, we were able to monitor variations of TDE activity at the PM under stress conditions, and we showed that cancer cell lines presented a reduced TDE activity at the PM compared to noncancer cells.

Hexagonal boron nitride nanoparticles trigger oxidative stress by modulating thiol/disulfide homeostasis

BACKGROUND

Hexagonal boron nitride nanoparticles (hBN NPs) are encouraging nanomaterials with unique chemical properties in medicine and biomedical fields. Until now, the optimal hBN NP's dosage and biochemical mechanism that can be used for in vivo systems has not been fully revealed. The main aim of this article is to reveal characteristics, serum and tissue interactions and any acute cytotoxic effect of different dose of hBN NPs for the first time.

METHODS

hBN NPs at concentrations varying between 50-3200 µg/kg was administered by intravenous injection to Wistar albino rats (n = 80) divided into seven dosage and control groups. Blood and tissue samples were taken after 24 hours.

RESULTS

Our findings suggested that higher doses hBN NPs caused oxidative stress on the serum of rats dose-dependently. However, hBN NPs did not affect thiol/disulfide homeostasis on kidney, liver, spleen, pancreas and heart tissue of rats. Furthermore, hBN NPs increased serum disulfide formation by disrupting the thiol/disulfide balance in rats. Also, LOOH and MPO levels increased at high doses, while CAT levels decreased statistically.

CONCLUSION

The results revealed that hBN NPs induce oxidative stress in a dose-dependent manner by modulating thiol/disulfide homeostasis in rats at higher concentrations.

Bioorthogonal Turn-On BODIPY-Peptide Photosensitizers for Tailored Photodynamic Therapy

Photodynamic therapy (PDT) leads to cancer remission via the production of cytotoxic species under photosensitizer (PS) irradiation. However, concomitant damage and dark toxicity can both hinder its use. With this in mind, we have implemented a versatile peptide-based platform of bioorthogonally activatable BODIPY-tetrazine PSs. Confocal microscopy and phototoxicity studies demonstrated that the incorporation of the PS, as a bifunctional module, into a peptide enabled spatial and conditional control of singlet oxygen (1 O2 ) generation. Comparing subcellular distribution, PS confined in the cytoplasmic membrane achieved the highest toxicities (IC50 =0.096±0.003 μm) after activation and without apparent dark toxicity. Our tunable approach will inspire novel probes towards smart PDT.

Robust Strategy for Antibody-Polymer-Drug Conjugation: Significance of Conjugating Orientation and Linker Charge on Targeting Ability

Antibody-drug conjugates have shown great promise in active targeting for cancer therapy. The existing chemical techniques for antibody conjugation generally lack efficiency or universality. In this article, a site-specific antibody conjugation was developed by using a mild reaction between a benzoboroxole (BB) functionality and cis-diol moiety of sugar units in the antibody fragment crystallizable region under neutral pH conditions. A BB/PEG/ICG-grafted poly(aspartic acid) comb-like functional polymer was first synthesized and conjugated with transferrin (Tf) to form a transferrin-polymer-drug conjugate [Tf-P(BB)], which showed 120% increase in HepG2 hepatoma (Tf receptor overexpression) cell uptake compared to a nontargeting protein-polymer-drug conjugate [HRP-P(BB)]. The universality of this method was further demonstrated by the enhanced uptake of trastuzumab (anti-Her2 antibody)-polymer-drug conjugates in MCF-7 (295%) and MDA-MB-435S (66.4%) (Her2 positive) cells. The positive charge of the linker had great influence on the targeting ability of the antibody-polymer-drug conjugates. The in vivo studies demonstrated the distinct targeting ability of Tf-P(BB) in the HepG2 xenograft tumor, and the tumor accumulation of the Tf-P(BB) testing group increased by 92% with respect to the control group [HRP-P(BB)]. More significantly, the HepG2 cell uptake amount of the antibody-oriented conjugate [Tf-P'(BB)] was 2.4-fold higher than that of the controlled group [Tf-P'(Hex)]. On the basis of this facile site-specific conjugation method, the conjugates are able to change the antibody species easily against various cancers, while maintaining the antibody integrity and targeting ability.

In vivo toxicity evaluation of boron nitride nanosheets in Bombyx mori silkworm model

Boron nitride nanosheets (BN NSs), a novel material with a structure similar to graphene, have attracted much attention due to their extraordinary properties. A deep in vivo study of the toxicity of BN NSs is indispensable, which can help to understand their potential risk and provide useful information for their safe application. However, so far as we know, the systematic in vivo toxicity evaluation of BN NSs hasn't been reported. In this study, silkworm (Bombyx mori) was used as a model to investigate the toxicity of BN NSs, by continuously feeding silkworm larvae with BN NSs at various mass concentrations (1%, 2%, 3%, 4%). The toxicity was evaluated from the levels of animal entirety (mortality, silkworm growth, cocoons and silk properties), tissues (pathological examination) and genes (transcriptomic profiling). The results show that the exposure to BN NSs causes no obvious adverse effects on the growth, silk properties or tissues of silkworm, but the expressions of genes in midgut concerned with some specific functions and pathways are significantly changed, indicating that BN NSs may have potential danger to lead to dysfunction. This study has performed in vivo toxicity evaluation of BN NSs and provided useful safety information for the application of BN NSs.

Effects of boron-containing compounds on cardiovascular disease risk factors - A review

Boron is considered to be a biological trace element but there is substantial and growing support for it to be classified as an essential nutrient for animals and humans, depending on its speciation. Boron-containing compounds have been reported to play an important role in biological systems. Although the exact biochemical functions of boron-containing compounds have not yet been fully elucidated, previous studies suggest an active involvement of these molecules in the mediation of inflammation and oxidative stress. Chronic inflammation and oxidative stress are known to amplify the effects of the main cardiovascular risk factors: smoking, diet, obesity, arterial hypertension, dyslipidemia, type 2 diabetes (as modifiable risk factors), and hyperhomocysteinemia and age (as independent risk factors). However, the role of boron-containing compounds in cardiovascular systems and disease prevention has yet to be established. This paper is a review of boron-containing compounds' existence in nature and their possible functions in living organisms, with a special focus on certain cardiovascular risk factors that may be diminished by intake of these compounds, leading to a reduction of cardiovascular morbidity and/or mortality.

Assessing and Mitigating the Hazard Potential of Two-Dimensional Materials

The family of two-dimensional (2D) materials is comprised of a continually expanding palette of unique compositions and properties with potential applications in electronics, optoelectronics, energy capture and storage, catalysis, and nanomedicine. To accelerate the implementation of 2D materials in widely disseminated technologies, human health and environmental implications need to be addressed. While extensive research has focused on assessing the toxicity and environmental fate of graphene and related carbon nanomaterials, the potential hazards of other 2D materials have only recently begun to be explored. Herein, the toxicity and environmental fate of postcarbon 2D materials, such as transition metal dichalcogenides, hexagonal boron nitride, and black phosphorus, are reviewed as a function of their preparation methods and surface functionalization. Specifically, we delineate how the hazard potential of 2D materials is directly related to structural parameters and physicochemical properties and how experimental design is critical to the accurate elucidation of the underlying toxicological mechanisms. Finally, a multidisciplinary approach for streamlining the hazard assessment of emerging 2D materials is outlined, thereby providing a pathway for accelerating their safe use in a range of technologically relevant contexts.

Cytotoxicity and Efflux Pump Inhibition Induced by Molybdenum Disulfide and Boron Nitride Nanomaterials with Sheetlike Structure

Sheetlike molybdenum disulfide (MoS₂) and boron nitride (BN) nanomaterials have attracted attention in the past few years due to their unique material properties. However, information on adverse effects and their underlying mechanisms for sheetlike MoS₂ and BN nanomaterials is rare. In this study, cytotoxicities of sheetlike MoS₂ and BN nanomaterials on human hepatoma HepG2 cells were systematically investigated at different toxic end points. Results showed that MoS₂ and BN nanomaterials decreased cell viability at 30 μg/mL and induced adverse effects on intracellular ROS generation (≥2 μg/mL), mitochondrial depolarization (≥4 μg/mL), and membrane integrity (≥8 μg/mL for MoS₂ and ≥2 μg/mL for BN). Furthermore, this study first found that low exposure concentrations (0.2-2 μg/mL) of MoS₂ and BN nanomaterials could increase plasma membrane fluidity and inhibit transmembrane ATP binding cassette (ABC) efflux transporter activity, which make both nanomaterials act as a chemosensitizer (increasing arsenic toxicity). Damage to plasma membrane and release of soluble Mo or B species might be two reasons that both nanomaterials inhibit efflux pump activities. This study provides a systematic understanding of the cytotoxicity of sheetlike MoS₂ and BN nanomaterials at different exposure levels, which is important for their safe use.

The protective study about alleviation of simvastatin on the damages of PEG-BNs in mice

Boron nitride nanoparticles have been proved to cause various toxicities, damages or inflammations after entering into in vivo in previous reports. However, up to now, there are rare investigations about the alleviation of damages caused by nanoparticles in vivo through natural small molecule drugs. Therefore, in this work, PEG-BNs with high solubility was successfully synthesized, and then their biodistribution in mice were studied using radiolabeling technique. And the heart, lung, liver, spleen, kidney tissues and blood samples were done for histology and biochemical analysis. The results showed that PEG-BNs were mainly distributed in lung, liver, kidney and spleen with an obviouse decreasing distribution as the experimental time was increasing. Besides, significantly serum biochemical and tissue pathological changes induced by PEG-BNs were confirmed. Moreover, after simvastatin (SST) exposure to the PEG-BNs model mice, the damages and biochemical indexes were recovered significantly as compared to the single exposure group mice in serum, which indicates a good treatment effect on the toxicity of PEG-BNs in vivo in mice. This study provides some basic data and useful information for the treatment of damages caused by the nanoparticles in mice in the future.

Current data regarding the structure-toxicity relationship of boron-containing compounds

Boron is ubiquitous in nature, being an essential element of diverse cells. As a result, humans have had contact with boron containing compounds (BCCs) for a long time. During the 20th century, BCCs were developed as antiseptics, antibiotics, cosmetics and insecticides. Boric acid was freely used in the nosocomial environment as an antiseptic and sedative salt, leading to the death of patients and an important discovery about its critical toxicology for humans. Since then the many toxicological studies done in relation to BCCs have helped to establish the proper limits of their use. During the last 15 years, there has been a boom of research on the design and use of new, potent and efficient boron containing drugs, finding that the addition of boron to some known drugs increases their affinity and selectivity. This mini-review summarizes two aspects of BCCs: toxicological data found with experimental models, and the scarce but increasing data about the structure-activity relationship for toxicity and therapeutic use. As is the case with boron-free compounds, the biological activity of BCCs is related to their chemical structure. We discuss the use of new technology to discover potent and efficient BCCs for medicinal therapy by avoiding toxic effects.

Tavaborole, a Novel Boron-Containing Small Molecule Pharmaceutical Agent for Topical Treatment of Onychomycosis: I. Reproductive and Developmental Toxicity Studies

Tavaborole is a topical antifungal agent approved by the US Food and Drug Administration for the treatment of toenail onychomycosis. As part of the nonclinical development program, reproductive and developmental toxicity studies were conducted (rat oral fertility and early embryonic development, rat (oral) and rabbit (dermal) embryo-fetal development). There were no effects on fertility or reproductive performance at doses up to 300 mg/kg/d (107 times the maximum recommended human dose [MRHD] based on mean area under the plasma concentration-time curve comparisons). In the rat embryo-fetal development toxicity studies, teratogenicity was not observed at doses up to 100 mg/kg/d (29 times the MRHD). However, several treatment-related skeletal malformations and variations were observed at 300 mg/kg/d (570 times the MRHD). In rabbit embryo-fetal development toxicity studies dosed via oral or dermal administration, the no observable adverse effect level for maternal toxicity and embryo-fetal toxicity was 50 mg/kg/d (16 times the MRHD) and 5% (26 times the MRHD), respectively.

Dual Functioning Thieno-Pyrrole Fused BODIPY Dyes for NIR Optical Imaging and Photodynamic Therapy: Singlet Oxygen Generation without Heavy Halogen Atom Assistance

We discovered a rare phenomenon wherein a thieno-pyrrole fused BODIPY dye (SBDPiR690) generates singlet oxygen without heavy halogen atom substituents. SBDPiR690 generates both singlet oxygen and fluorescence. To our knowledge, this is the first example of such a finding. To establish a structure-photophysical property relationship, we prepared SBDPiR analogs with electron-withdrawing groups at the para-position of the phenyl groups. The electron-withdrawing groups increased the HOMO-LUMO energy gap and singlet oxygen generation. Among the analogs, SBDPiR688, a CF3 analog, had an excellent dual functionality of brightness (82290 m(-1)  cm(-1) ) and phototoxic power (99170 m(-1)  cm(-1) ) comparable to those of Pc 4, due to a high extinction coefficient (211 000 m(-1)  cm(-1) ) and balanced decay (Φflu =0.39 and ΦΔ =0.47). The dual functionality of the lead compound SBDPiR690 was successfully applied to preclinical optical imaging and for PDT to effectively control a subcutaneous tumor.

Boron-containing compounds: chemico-biological properties and expanding medicinal potential in prevention, diagnosis and therapy

INTRODUCTION

Although the medicinal use of boron-containing compounds (BCCs) had long been limited to antiseptics, in the last few decades, these compounds have been used as antibiotics or chemotherapeutic agents. In the last few years, boron has been included in the moieties of many known drugs to improve their capacity in binding to their respective target receptors.

AREAS COVERED

The current review focuses on research and patent literature of the last decade related to the development of BCCs as preventive, diagnostic and therapeutic tools. It explores the possible mechanisms of action of these compounds as well as the advantageous features of their structure and chemico-pharmacological properties.

EXPERT OPINION

Although uncertainties exist about the mechanism of action of BCCs, increasing evidence about their toxicological profile strongly suggests that many can be safely administered to humans. Even stronger evidence exists regarding the capacity of BCCs to reach multiple targets that are involved in the treatment of common diseases. It seems fair to say that some BCCs will reach the market for medicinal use in the near future, not only for targeting microbial or neoplastic systems but also for acting on cell-signaling processes involved in many other disorders.

Spectroscopic, computational modeling and cytotoxicity of a series of meso-phenyl and meso-thienyl-BODIPYs

A series of twenty-two BODIPY compounds were synthesized, containing various meso-phenyl and meso-thienyl groups, and their spectroscopic and structural properties were investigated using both experimental and computational methods. Further functionalization of the BODIPY framework via iodination at the 2,6-pyrrolic positions was explored in order to determine the effect of these heavy atoms on the photophysical and cytotoxicity of the meso-aryl-BODIPYs. BODIPYs bearing meso-thienyl substituents showed the largest red-shifted absorptions and emissions and reduced fluorescence quantum yields. The phototoxicity of the BODIPYs in human carcinoma HEp2 cells depends on both the presence of iodines and the nature of the meso-aryl groups. Six of the eleven 2,6-diiodo-BODIPYs investigated showed at least a sevenfold enhancement in phototoxicity (IC50 = 3.5-28 μM at 1.5 J/cm(2)) compared with the non-iodinated BODIPYs, while the others showed no cytotoxicity, while their singlet oxygen quantum yields ranged from 0.02 to 0.76. Among the series investigated, BODIPYs 2a and 4a bearing electron-donating meso-dimethoxyphenyl substituents showed the highest phototoxicity and dark/phototoxicity ratio, and are therefore the most promising for application in PDT.

An assessment of the genetic toxicology of novel boron-containing therapeutic agents

Boron-containing compounds are being studied as potential therapeutic agents. As part of the safety assessment of these therapeutic agents, a battery of genetic toxicology studies was conducted. The battery included a bacterial reverse mutation (Ames) assay, an in vitro chromosome aberration assay in peripheral human lymphocytes, and an in vivo rat micronucleus study. The following compounds represent some of the boron-containing compounds that have been advanced to human clinical trials in various therapeutic areas. The borinic picolinate, AN0128, is an antibacterial compound with anti-inflammatory activity that has been studied in clinical trials for acne and the treatment of mild to moderate atopic dermatitis. AN2690 (tavaborole) is a benzoxaborole in Phase 3 clinical trials for the topical treatment of onychomycosis, a fungal infection of the toenails and fingernails. Another benzoxaborole derivative, AN2728, a phosphodiesterase-4 (PDE4) inhibitor, is in Phase 2 clinical trials for the treatment of atopic dermatitis. AN2898, also a PDE4 inhibitor, has been studied in clinical trials for atopic dermatitis and psoriasis. AN3365 is a leucyl-tRNA synthetase inhibitor that has been in clinical development for the treatment of various Gram-negative bacterial infections. These five representative compounds were negative in the three genotoxicity assays. Furthermore, AN2690 has been studied in mouse and rat 2-year bioassays and was not found to have any carcinogenic potential. These results demonstrate that it is possible to design boron-based therapeutic agents with no genetic toxicology liabilities.

In vitro investigation of the cellular toxicity of boron nitride nanotubes

Nanotubes present one of the most promising opportunities in nanotechnology with a plethora of applications in nanoelectronics, mechanical engineering, as well as in biomedical technology. Due to their structure and some physical properties, boron nitride (BN) nanotubes (BNNTs) possess several advantages over carbon nanotubes (CNTs), and they are now commercially produced and used on a large scale. The human and environmental exposure to BN nanomaterials is expected to increase in the near future, and their biological responses need to be examined. Using complementary assays, we have extensively investigated the effects of BNNTs on the viability and metabolic status of different cell types: on the one hand, the effects on cells present in the lung alveoli, and on the other hand, on human embryonic kidney (HEK) cells. Our results indicate that BNNTs are cytotoxic for all cell types studied and, in most cases, are more cytotoxic than CNTs in their pristine (p-CNT) and functionalized (f-CNT) form. However, the level of toxicity and the prominent morphological alterations in the cell populations withstanding BNNT exposure are cell-type-dependent. For instance, BNNTs induced extensive multinucleated giant cell formation in macrophages and increased levels of eosinophilia in fibroblasts. Finally, our results point the toxicity of tubular nanomaterials to be strongly correlated with the cellular accumulation enhanced for straight nanotubes.

Effects assessment: boron compounds in the aquatic environment

In previous studies, boron compounds were considered to be of comparatively low toxicity in the aquatic environment, with predicted no effect concentration (PNEC) values ranging around 1 mg B/L (expressed as boron equivalent). In the present study, we describe an evaluation of toxicity data for boron available for the aquatic environment by different methods. For substances with rich datasets, it is often possible to perform a species sensitivity distribution (SSD). The typical outcome of an SSD is the Hazardous Concentration 5% (HC5), the concentration at which 95% of all species are protected with a probability of 95%. The data set currently available on the toxic effects of boron compounds to aquatic organisms is comprehensive, but a careful evaluation of these data revealed that chronic data for aquatic insects and plants are missing. In the present study both the standard assessment factor approach as well as the SSD approach were applied. The standard approach led to a PNEC of 0.18 mg B/L (equivalent to 1.03 mg boric acid/L), while the SSD approach resulted in a PNEC of 0.34 mg B/L (equivalent to 1.94 mg boric acid/L). These evaluations indicate that boron compounds could be hazardous to aquatic organisms at concentrations close to the natural environmental background in some European regions. This suggests a possible high sensitivity of some ecosystems for anthropogenic input of boron compounds. Another concern is that the anthropogenic input of boron could lead to toxic effects in organisms adapted to low boron concentration.

Intracellular uptake and trafficking of difluoroboron dibenzoylmethane-polylactide nanoparticles in HeLa cells

In this study, nanoparticles based on difluoroboron dibenzoylmethane-poly(lactic acid) (BF(2)dbmPLA) are prepared. Polylactic acid or polylactide is a commonly used degradable polymer, while the boron dye possesses a large extinction coefficient, high emission quantum yield, two-photon absorption, and sensitivity to the surrounding environment. BF(2)dbmPLA exhibits molecular-weight-dependent emission properties and can be formulated as stable nanoparticles, suggesting that its unique optical properties may be useful in multiple contexts for probing intracellular environments. Here we show that BF(2)dbmPLA nanoparticles are internalized into cultured HeLa cells by endocytosis, and that within the cellular milieu, they retain their fluorescence properties. BF(2)dbmPLA nanoparticles are photostable, resisting laser-induced photobleaching under conditions that destroy the fluorescence of a common photostable probe, LysoTracker Blue. Their endocytosis is also lipid-raft-dependent, as evidenced by their significant colocalization with cholera toxin B subunit in membrane compartments after uptake and their sensitivity of uptake to methyl-beta-cyclodextrin. Additionally, BF(2)dbmPLA nanoparticle endocytosis utilizes microtubules and actin filaments. Internalized BF(2)dbmPLA nanoparticles do not accumulate in acidic late endosomes and lysosomes but within a perinuclear nonlysosomal compartment. These findings demonstrate the feasibility of using novel BF(2)dbmPLA nanoparticles exhibiting diverse emission properties for in situ, live cell imaging and suggest that their endogenous uptake occurs through a lipid-raft-dependent endocytosis mechanism.

Intracellular uptake of a new boronated porphyrin EC032

We measured the toxicity and intracellular uptake of a newly developed boronated porphyrin EC032, and verified the fluorescence-based boron concentration measuring methods. Toxicity study showed that concentration required to produce a 50% reduction in viability (IC(50)) of EC032 was more than 0.25 mM. Fluorescence study showed the intracellular uptake of EC032 increased up until 24 h after its exposure to C6, 9L, U87, and U251 cells. There was also a linear correlation between ICP-AES and fluorescence intensity as an arbitrary unit about measurement of boron concentration. Fluorescence-based boron concentration measuring methods are very simple and useful methods, especially for screening of slight test dose of porphyrin compounds.

Synthesis, Liposomal Preparation, and in Vitro Toxicity of Two Novel Dodecaborate Cluster Lipids for Boron Neutron Capture Therapy

A new class of lipids, containing the closo-dodecaborate cluster, has been synthesized. Two lipids, S-(N, N-(2-dimyristoyloxyethyl)acetamido)thioundecahydro-closo-dodecaborate (2-) (B-6-14) and S-(N, N-(2-dipalmitoyloxyethyl)acetamido)thioundecahydro-closo-dodecaborate (2-) (B-6-16) are described. Both of them have a double-tailed lipophilic part and a headgroup carrying two negative charges. Differential scanning calorimetry shows that B-6-14 and B-6-16 bilayers have main phase transition temperatures of 18.8 and 37.9 degrees C, respectively. Above the transition temperature of 18.8 degrees C, B-6-14 can form liposomal vesicles, representing the first boron-containing lipid with this capability. Upon cooling below the transition temperature, stiff bilayers are formed. When incorporated into liposomal formulations with equimolar amounts of distearoyl phosphatidylcholine (DSPC) and cholesterol, stable liposomes are obtained. The zeta-potential measurements indicate that both B-6-14- and B-6-16-containing vesicles are negatively charged, with the most negative potential described of any liposome so far. The liposomes are of high potential value as transporters of boron to tumor cells in treatments based on boron neutron capture therapy (BNCT). Liposomes prepared from B-6-14 were slightly less toxic in V79 Chinese hamster cells (IC50 5.6 mM) than unformulated Na2B12H11SH (IC50 3.9 mM), while liposomes prepared from B-6-16 were not toxic even at 30 mM.

Hyaluronan as carrier of carboranes for tumor targeting in boron neutron capture therapy

Boron neutron capture therapy (BNCT) represents a promising approach for tumor therapy. A critical requirement for BNCT is tumor targeting, a goal that is currently addressed with the development of low and high molecular weight agents capable of interacting with receptors expressed by cancer cells. Here, we describe a new bioconjugate (HApCB) composed by n-propyl carborane linked to hyaluronan (HA) via an ester linkage for a degree of substitution of approximately 30%, leading to a water-soluble derivative. The structure and main physicochemical characteristics of the new HA derivative were determined by means of Fourier transform infrared, fluorescence, and 1H, 13C, and 10B NMR analysis and are herein reported in detail. As HA is recognized by the CD44 antigen, densely populating the surface of many tumor cells, HApCB is expected to deliver boron atoms from the locally released carborane cages directly to target cells for antitumor application in BNCT. In vitro biological experiments showed that HApCB was not toxic for a variety of human tumor cells of different histotypes, specifically interacted with CD44 as the native unconjugated HA, and underwent uptake by tumor cells, leading to accumulation of amounts of boron atoms largely exceeding those required for a successful BNCT approach. Thus, HApCB may be regarded as a promising new BNCT agent for specific targeting of cancer cells overexpressing the CD44 receptor.

Synthesis of Boron Cluster Lipids: closo-Dodecaborate as an Alternative Hydrophilic Function of Boronated Liposomes for Neutron Capture Therapy

We succeeded in the synthesis of the double-tailed boron cluster lipids 4a-c and 5a-c, which have a B12H11S moiety as a hydrophilic function, by S-alkylation of B12H11SH (BSH) with bromoacetyl and chloroacetocarbamate derivatives of diacylglycerols for a liposomal boron delivery system on neutron capture therapy. Calcein encapsulation experiments revealed that the liposomes, prepared from the boron cluster lipid 4b, DMPC, PEG-DSPE, and cholesterol, are stable at 37 degrees C in FBS solution for 24 h. [reaction: see text].

Cytotoxic evaluation of cubic boron nitride in human origin cultured cells

The aim of this study was to evaluate the cytotoxicity of cubic boron nitride (cBN), a component of surgical cutting tools. The small quantities of cBN that typically remain on implants as a result of the manufacturing process may act as abrasives, injuring tissues surrounding the implant. To determine how cBN affects cells, we treated human neuroblastoma cells (NB-1) and human articular chondrocytes (nHAC-kn) with different concentrations of cBN powder and assessed cell growth and cell survival using the methyl-thiazol-tetrazolium (MTT) assay and a fluorescence probe assay. We also assessed the effects of tungsten carbide (WC) and cobalt (Co), two common components of joint implants, on cell growth and cell survival. Both cBN and WC moderately inhibited NB-1 and nHAC-kn cell growth. However, cBN and WC did not affect cell survival, even at high concentrations (40 microg/ml). By contrast, Co affected cell survival, inducing cell death in both cell types at increasing concentrations. These results suggest that cBN may be less toxic than WC alloys containing Co.

Synthesis, cellular uptake and animal toxicity of a tetra(carboranylphenyl)-tetrabenzoporphyrin

A water-soluble nido-carboranyl-tetrabenzoporphyrin has been synthesized in 43% overall yield, by condensation of butanopyrrole with a carboranylbenzaldehyde, followed by metal insertion, oxidation, demetallation and deboronation reactions. This compound accumulated within human glioblastoma T98G cells to a significant higher extent than a structurally related nido-carboranylporphyrin, and localized preferentially in the cell lysosomes. Animal toxicity studies using male and female BALB/c mice revealed that both compounds are non-toxic even at a dose of 160 mg/kg, administered intraperitoneally as a single injection at a concentration of 4 mg/mL. It is concluded that the tetra(carboranylphenyl)-tetrabenzoporphyrin is a promising new sensitizer for the treatment of malignant tumors.

Toxicity, biodistribution, and convection-enhanced delivery of the boronated porphyrin BOPP in the 9L intracerebral rat glioma model

PURPOSE

To investigate the toxicity, biodistribution, and convection-enhanced delivery (CED) of a boronated porphyrin (BOPP) that was designed for boron neutron capture therapy and photodynamic therapy.

METHODS AND MATERIALS

For the toxicity study, Fischer 344 rats were injected with graded concentrations of BOPP (35-100 mg/kg) into the tail vein. For boron biodistribution studies, 9L tumor-bearing rats received BOPP either systematically (intravenously) or locally.

RESULTS

All rats that received 70 mg/kg BOPP and 70% of rats that received < or = 60 mg/kg BOPP i.v. either had to be euthanized or died within 4 days of injection. In the biodistribution study, boron levels were relatively high in liver, kidney, spleen, and adrenal gland tissue, and moderate levels were found in all other organs. The maximum tumor boron concentration was 21.4 mug/g at 48 h after i.v. injection; this concentration of boron in brain tumors is at the low end of the range considered optimal for therapy. In addition, the tumor/blood ratio (approximately 1.2) was not optimal. When BOPP was delivered directly into intracerebral 9L tumors with CED, we obtained tumor boron concentrations much greater than those obtained by i.v. injection. Convection-enhanced delivery of 1.5 mg BOPP produced an average tumor boron level of 519 mug/g and a tumor/blood ratio of approximately 1850:1.

CONCLUSIONS

Our study demonstrates that changing the method of BOPP delivery from i.v. to CED significantly enhances the boron concentration in tumors and produces very favorable tumor/brain and tumor/blood ratios.

[Development of the method of magnetic neutron capture therapy of cancer]

The method of magnetic neutron capture therapy (MNTC) of cancer can be described as a combination of two methods: the targeted delivery of drugs using magnetic carriers and the proper neutron capture therapy which consists in tumor irradiation with thermal neutrons following the delivery of 10B compounds to the tumor site. Two-component ultradispersed particles containing Fe and C were tested as magnetic adsorbents of boron phenylalanine and borax. The quantities of absorbed borax proved sufficient for high concentration of boron atoms at the tumor site. The kinetics of boron release to saline substantiates the application of Fe-B (10%) ultradispersed particles for efficient MNTC. Both particle types have high magnetization and magnetic homogeneity, can form stable magnetic suspensions, and have low toxicity.

Cytotoxicities of a 4-META/MMA-TBBO resin against human pulp fibroblasts

This study was designed to investigate the cytotoxicity of MMA (methyl methacrylate) and 4-META (4-methacryloyloxyethoxycarbonylphthalic anhydride)/MMA with or without TBBO (tri-n-butylborane partially oxide), an initiator and TBBO alone against human pulp fibroblasts (HPF). Cell viabilities were measured by MTT assay. The cytotoxicity of 4-META/MMA-TBBO was comparable with that of MMA-TBBO. TBBO showed higher cytotoxicity than 4-META/MMA. The cytotoxicity induction of a 4-META/MMA-TBBO resin may be preferably associated with TBBO.

Synthesis of New Boron-Rich Building Blocks for Boron Neutron Capture Therapy or Energy-Filtering Transmission Electron Microscopy

The synthesis of a new ortho-carborane derivative, tetracarboranylketone 4, is reported here. Ketone 4 was prepared from a tetraalkynylated ketone by the addition of decaborane. The keto group was then easily modified to yield the glycosides 17alpha and 18beta, which contain glucose or galactose, respectively, and the nucleotide 13b. In addition to ketone 4, which is acyclic, cyclic ketone 8 was also synthesised. X-ray diffraction analysis of compound 4 indicated the presence of two toluene guest molecules per molecule of the host compound. Furthermore, compound 4 displays a rather low cytotoxicity. These novel products can be used as building blocks to create a new class of biomolecules containing high-density carborane clusters. Such molecules may constitute powerful tools for applications like Boron Neutron Capture Therapy or Energy-Filtering Transmission Electron Microscopy.

Stereospecific activity of two glutamate analogs

Two glutamic acid analogs, (+)-(S)- and (-)-(R)-4-(2,2-diphenyl-1,3,2-oxazaborolidin-5-oxo)propionic acid ((+)-(S)- and (-)-(R)-Trujillon, respectively), were prepared. The stereospecific activity of their pharmacological properties was studied. The median convulsant dose (CD(50)) and median lethal dose (LD(50)) were analyzed in female Swiss Webster mice and their effects in vivo on unitary electrical activity in globus pallidus neurons were elucidated in male Wistar rats. Compounds were characterized by (1)H, (13)C, and (11)B nuclear magnetic resonance. The LD(50) of (+)-(S)-Trujillon was 449.08 mg/kg and it increased spontaneous motor activity, while with (-)-(R)-Trujillon there was no mortality up to 1,000 mg/kg and it decreased spontaneous motor activity. The CD(50) in experiments with (+)-(S)-Trujillon was 199.34 mg/kg. Unitary recording in globus pallidus neurons showed i.v. administration (+)-(S)-Trujillon (50 mg/kg) increased frequency 79.0 +/- 23.0% in relation to basal response. (-)-(R)-Trujillon and (+)-(S)-glutamate (50 mg/kg each) did not provoke changes in spontaneous basal firing. Local infusion of (+)-(S)-Trujillon (1 nMol) increased spontaneous firing in most neurons tested by 269.0 +/- 83.0% in relation to basal values. Intrapallidal infusion of (-)-(R)-Trujillon (1 nMol) and saline solution did not cause statistically significant changes in globus pallidus spiking. Results showed that (+)-(S)-Trujillon crosses the blood-brain barrier and has stereospecific activity.

Mutagenic effect of borocaptate sodium and boronophenylalanine in neutron capture therapy

PURPOSE

To investigate the mutagenic effect in boron neutron capture therapy (BNCT), Chinese hamster ovary cells were incubated with 10 B-enriched borocaptate sodium (BSH) or para-boronophenylalanine (BPA) before exposure to thermal neutrons, and the occurrence of mutations at the hypoxanthine-guanine phosphoribosyl transferase (HPRT) locus was measured.

METHODS AND MATERIALS

BSH or BPA was added to cells 20 h or 2 h before irradiation and removed before irradiation. Cells were irradiated with thermal neutrons. The biologic end point of cell survival was measured by colony formation assay. The mutagenicity was calculated from the mutation frequency at the HPRT locus.

RESULTS

The mutagenicity of BSH and BPA was similar to that of 10B boric acid when the cells were irradiated with neutrons at an isosurvival dose after 2-h preincubation. Preincubation with BSH for 20 h, compared with preincubation for just 2 h, had no effect on either cytotoxicity or mutagenicity in BNCT. However, with BPA, 20-h preincubation, compared with 2-h preincubation, caused an increase in the cell killing effect, but a decrease in the mutagenic effect of the BNCT.

CONCLUSION

After 20-h incubation, BPA was less mutagenic than BSH. The mutagenic study of electroporated BPA or BSH revealed a reduced mutagenicity. These results suggest that the retention of these boron compounds in the cells causes a more accurate assault on the cell and lessens the chance of misrepair after neutron irradiation.

Evaluation of the genotoxic effects of the boron neutron capture reaction in human melanoma cells using the cytokinesis block micronucleus assay

The present work reports on the genotoxicity of the boron neutron capture (BNC) reaction in human metastatic melanoma cells (A2058) assessed by the cytokinesis block micronucleus assay (CBMN) using p-borono-L-phenylalanine (BPA) as the boron delivery agent. Different concentrations of BPA (0.48, 1.2 and 2.4 mM) and different fluences of thermal neutrons were studied. Substantial genotoxic potential of alpha and lithium particles generated inside or near the malignant cell by the BNC reaction was observed in a dose-response manner as measured by the frequency of micronucleated binucleated melanoma cells and by the number of micronuclei (MN) per binucleated cell. The distribution of the number of MN per micronucleated binucleated cell was also studied. The BNC reaction clearly modifies this distribution, increasing the frequency of micronucleated cells with 2 and, especially, > or =3 MN and conversely decreasing the frequency of micronucleated cells with 1 MN. A decrease in cell proliferation was also observed which correlated with MN formation. A discrete genotoxic and anti-proliferative contribution from both thermal neutron irradiation and BPA was observed and should be considered secondary. Additionally, V79 Chinese hamster cells (chromosomal aberrations assay) and human lymphocytes (CBMN assay) incubated with different concentrations of BPA alone did not show any evidence of genotoxicity. The presented results reinforce the usefulness of the CBMN assay as an alternative method for assessment of the deleterious effects induced by high LET radiation produced by the BNC reaction in human melanoma cells.

Carboranyl bisglycosides for the treatment of cancer by boron neutron capture therapy

Boron neutron capture therapy is a special type of radiotherapy for the treatment of cancer by using boron compounds. Problems often arise from the low water solubility of these compounds, their unselective uptake into the cancer cells, and their toxicity. Here we describe the novel water-soluble ortho-carboranyl bisglycosides 7 and 10 containing either lactose or glucose and the mixed bisglycosides 1 and 28 containing glucose, mannose, and galactose. The carboranyl bisglycosides show almost no toxicity toward bronchial carcinoma cells of line A549 up to a concentration of 0.50 mM. As anticipated, these compounds exhibit nearly no uptake into C6 glioma cells; they can therefore be used for a selective delivery into malignant cells by using conjugates of glycohydrolases and monoclonal antibodies which bind to tumor-associated antigens, since by enzymatic hydrolysis the bisglycosides are transformed into lipophilic compounds.

Relationship between amine-carboxyboranes and TNF alpha for the regulation of cell growth in different tumor cell lines

The amine-carboxyboranes were shown to be synergistic with tumor necrosis factor alpha (TNF alpha) in cytotoxicity and inhibition of DNA synthesis in select types of cancer cells depending on the presence of a TNF alpha high affinity receptor on the membrane of the cell. Initially both TNF alpha and the amine-carboxyboranes reduce the influx of calcium but later cause a significant increase intracellularly. This influx is not linked with the amine-carboxyborane activating the calcitonin receptor in the tumor cells. Neither the agents nor TNF alpha directly inhibits DNA topoisomerase II activity but both did cause decreased phosphorylation of the enzyme by protein kinase C (PKC). The two agents caused synergistic inhibition. This event correlated with increased DNA protein linked breaks, DNA fragmentation and cell death. These protein linked breaks are additive with etoposide's effects but the latter agent's mechanism is different than phosphorylation of topoisomerase II. There was no evidence that the DNA fragmentation was caused by a calcium induced endonuclease enzyme in these cancer cells. The low-molecular weight amine-carboxyboranes appear to play an identical function as TNF alpha in its role to cause DNA breaks and fragmentation to cause apoptosis.

Effects of boron derivatives on extracellular matrix formation

Boric acid solution (3%) dramatically improves wound healing through action on the extracellular matrix, a finding that has been obtained in vitro. Consequently, investigations are presently underway to produce boronated compounds having a therapeutical effectiveness similar to that of boric acid. On the basis of experimental results obtained with boric acid, we examined the effects of boron derivatives on extracellular matrix formation and degradation and analyzed their potential toxicity by using two biological models (chick embryo cartilage and human fibroblasts). The four boron derivatives tested in this study (triethanolamine borate; N-diethyl-phosphoramidate-propylboronique acid; 2,2 dimethylhexyl-1,3-propanediol-aminopropylboronate and 1,2 propanediol-aminopropylboronate) mimicked the effects of boric acid. They induced a decrease of intracellular concentrations in extracellular matrix macromolecules (proteoglycans, proteins)-associated with an increase of their release in culture medium and stimulated the activity of intra- and extracellular proteases. Similarly to boric acid, these actions occurred after exposure of the cells to concentrations of all boron derivatives without apparent toxic effects. The compounds were found to be more toxic than boric acid itself when concentrations were calculated according to their molecular weight. Nevertheless, these in vitro preliminary results demonstrate effects of boron derivatives that may be of therapeutic benefit in wound repair.

The influence of lipophilicity on binding of boronated DNA-intercalating compounds in human glioma spheroids

Five boronated DNA-intercalating compounds [5-ortho-carboranyl phenanthridinium (5-o-CP), 5-para-carboranyl phenanthridinium (5-p-CP), 6-para-carboranyl phenanthridinium, water-soluble boronated phenanthridinium and water-soluble boronated acridine (WSA1)], primarily developed for boron neutron capture therapy (BNCT), were analysed regarding their binding in cultured human malignant glioma spheroids. Comparisons were made with the corresponding DNA intercalators ethidium bromide and acridine orange. Octanol/phosphate buffered saline-water coefficients were determined for all compounds, and it was found that the most lipophilic (5-o-CP and 5-p-CP) were most toxic and accumulated high amounts of boron in monolayer cells. These compounds bound primarily in the outermost part of spheroids with poor penetration into the inner region, even after 2 days of continuous exposure. On the other hand, the most hydrophilic compound (WSA1) showed lower toxicity and lower boron accumulation in monolayer cells, and rapid binding in the inner region of spheroids. A reasonable explanation for this observation is that the lipophilic compounds interact mainly with lipophilic parts of the cells, like cellular membranes, and therefore rapidly binds to cells, preventing penetration and binding to cells in the deeper region of the spheroids. The possibility of using these compounds for BNCT are discussed.

Boron neutron capture therapy of brain tumors: functional and neuropathologic effects of blood-brain barrier disruption and intracarotid injection of sodium borocaptate and boronophenylalanine

Sodium borocaptate (BSH) and boronophenylalanine (BPA) are two drugs that have been used clinically for boron neutron capture therapy (BNCT) of brain tumors. We previously have reported that hyperosmotic mannitol-induced disruption of the blood-brain barrier (BBB-D), followed by intracarotid (i.c.) administration of BPA or BSH, either individually or in combination, significantly enhanced tumor boron delivery and the efficacy of BNCT in F98 glioma bearing rats. The purpose of the present study was to determine the short-term neuropathologic consequences of this treatment and the long-term effects on motor and cognitive function, as well as the neuropathologic sequelae 1 year following neutron capture irradiation. BBB-D was carried out in non-tumor bearing Fischer rats by infusing a 25% solution of mannitol i.c. followed by i.c. injection of BPA or BSH, either individually or in combination, immediately thereafter. Animals were euthanized 2 days after compound administration, and their brains were processed for neuropathologic examination, which revealed sporadic, mild, focal neuronal degeneration, hemorrhage, and necrosis. To assess the long-term effects of such treatment followed by neutron capture irradiation, non-tumor bearing rats were subjected to BBB-D after which they were injected i.c. with BPA (25 mg B/kg body weight (b.w)) or BSH (30 mg B/kg b.w.) either individually or in combination (BPA 12.5 mg and BSH 14 mg B/kg b.w.). Two and a half hours later they were irradiated at the Medical Research Reactor, Brookhaven National Laboratory, Upton, NY, with the same physical radiation doses (5.79, 8.10 or 10.06 Gy), delivered to the brain, as those that previously had been used for our therapy experiments. The animals tolerated this procedure well, after which they were returned to Columbus, Ohio where their clinical status was monitored weekly. After 1 year, motor function was assessed using a sensitive and reliable locomotor rating scale for open field testing in rats and cognitive function was evaluated by their performance in the Morris water maze, the results of which were similar to those obtained with age matched controls. After functional evaluation, the rats were euthanized, their brains were removed, and then processed for neuropathologic examination. Subtle histopathologic changes were seen in the choroid plexuses of irradiated animals that had received BPA, BSH or saline. Radiation related ocular changes consisting of keratitis, blepharitis, conjunctivitis and cataract formation were seen with similar frequency in most rats in each treatment group. Based on these observations, and the previously reported significant therapeutic gain associated with BBB-D and i.c. injection of BSH and BPA, the present observations establish its safety in rats and suggest that further studies in large animals and humans are warranted.

Pharmacokinetics and effects after intravenous administration of high-dose boron to rat

Boron (B) compounds have been widely used in the chemical industry, agriculture, and environmental science. The kinetics and toxicity of B were studied by analyzing several serum and urine parameters after a single intravenous injection of sodium tetraborate solution (B: 85.7 mg/kg) in Wistar male rats. Blood samples were removed at 0, 1, 2, 4, and 6 h after injection. The serum parameters studied included: B, Na, Ca, K, P, Mg, gamma-GTP, AST, ALT, BUN, Cr, CK, LDH and ALD. Plasma concentration-time profiles of B were evaluated by a nonlinear least-squares method for fitting data to polyexponential equations and calculation of relevant pharmacokinetic parameters. Urine samples were collected from the bladder following infusion. The urinary parameters that were studied included urine volume and excretion of B, Cr and NAG. Results indicated that a two-compartment model could describe the elimination of B from plasma after intravenous administration. Urine volume significantly increased. A diuretic effect of B was noted.

Treatment of isografted 9L rat brain tumors with beta-5-o-carboranyl-2'-deoxyuridine neutron capture therapy

beta-5-o-Carboranyl-2'-deoxyuridine (D-CDU) is a nontoxic pyrimidine nucleoside analogue designed for boron neutron capture therapy of brain tumors. In vitro studies indicated that D-CDU accumulates to levels 92- and 117-fold higher than the extracellular concentration in rat 9L and human U-251 glioma cells, respectively, and persists for several hours at levels 5-fold higher than the extracellular concentration. Furthermore, D-CDU was not toxic to rats injected i.p. with up to 150 mg/kg. On the basis of these studies, D-CDU was evaluated as a neutron capture therapy agent using rats bearing stereotactically implanted intracranial 9L tumors at single i.p. doses of 30 mg/kg and 150 mg/kg of D-CDU (20% 10B enriched), given 2 h before irradiation with thermal neutrons. Boron concentrations in tumors 2 h after dosing were 2.3 +/- 1.6 and 7.4 +/- 1.3 micrograms boron/g tissue (mean +/- SD), corresponding to tumor/brain ratios of 11.5 +/- 3.6 and 6.8 +/- 2.0 micrograms boron/g tissue for the low and high doses, respectively. All untreated animals died within 28 days, whereas half survived at days 32, 55, and 38 for groups receiving neutrons only, 30 mg/kg D-CDU, and 150 mg/kg D-CDU, respectively. Odds ratios of all treatment groups differed significantly from the untreated group (P < 0.002; logrank test). The median survival time for the 30 mg/kg-treated group but not for the 150 mg/kg-treated group was significantly longer than for rats treated with neutrons only (P = 0.036), which may correlate with the decreased tumor selectivity for D-CDU observed at the higher dose. Additional pharmacodynamic studies are warranted to determine optimal dosing strategies for D-CDU.

Preparation and characterization of liposomal systems entrapping the boronated compound o-carboranylpropylamine

Boron neutron capture therapy (BNCT) is based on the nuclear reaction that occurs when the stable isotope, Boron-10, is irradiated with low-energy thermal neutrons to yield ionizing Helium and Lithium ions that are highly damaging and usually lethal to cells. The successful treatment of cancer by BNCT requires the selective concentration of Boron-10 within malignant tumours. Liposomes have been used as therapeutic compound delivery vehicles for in vivo application, including several anticancer agents. The ability of the boron-containing compound, o-carboranylpropylamine chloride, to accumulate within unilamellar liposomes in response to a transmembrane pH gradient is evaluated. Characterization of the systems obtained is performed for conventional and polyethylene glycol (PEG)-modified (stealth) liposomes, in terms of lipid and CPA contents, vesicle size and stability in detergent solutions. Results demonstrate that CPA loading and vesicle stability can be controlled by the experimental procedure. The loading of CPA into liposomes with average diameters of 100 nm is estimated at 13000 molecules per vesicle for the most stable systems. CPA toxicity to normal human peripheral blood lymphocytes and to adherent glioblastoma multiforme SK-MG-1 cells in vitro is observed to decrease as a result of the entrapment of CPA in liposomes.

Biopharmaceutics of boronated radiosensitizers: liposomal formulation of MnBOPP (manganese chelate of 2,4-(alpha, beta-dihydroxyethyl) deuterioporphyrin IX) and comparative toxicity in mice

Binary treatment modalities such as photodynamic therapy (PDT) and neutron capture therapy (NCT) combine low-toxicity electromagnetic irradiation with an appropriate radiation sensitizer to enhance selectivity for tumor targets. The porphyrin derivative tetrakiscarborane carboxylate ester of 2,4-(alpha, beta-dihydroxyethyl) deuterioporphyrin IX (BOPP) shows tumor-selective uptake and is active in both treatment modalities. BOPP also chelates paramagnetic ions such as Mn(2+), and therefore its tissue accumulation and selectivity can be detected noninvasively by using magnetic resonance imaging. However, local and systemic toxicity appears elevated for the Mn(2+) chelate (MnBOPP), but is poorly characterized. Here we have developed a liposomal formulation of MnBOPP and compared its toxicity with that of MnBOPP administered to mice in saline. The optimal liposome composition and maximal capacity to accommodate MnBOPP were investigated by differential scanning calorimetry and by encapsulation efficiency. MnBOPP was encapsulated quantitatively at up to 12 mol % (drug:lipid) in liposomes of varying composition, and remained incorporated during extended dialysis. Phase separation of drug- and lipid-rich domains was observed above 12% drug. MnBOPP in buffered saline was lethal to animals at 90 micromol/kg, and caused severe necrosis at the injection site at dose levels of 60 micromol/kg or greater. In contrast, MnBOPP formulated in liposomes was well tolerated at the highest tested dose of 135 micromol/kg, with the elimination of local toxicity.

Synthesis and biological evaluation of boron-containing polyamines as potential agents for neutron capture therapy of brain tumors

New boron-containing spermidine/spermine (SPD/SPM) analogues have been synthesized: N5-[4-(2-aminoethyl-o-carboranyl)butyl] and N5-{4-[(2,3-dihydroxypropyl)-o-carboranyl]butyl} SPD/SPM derivatives (ASPD-5, ASPM-5, DHSPD-5, and DHSPM-5) as well as N5-{[4-(dihydroxyboryl)phenyl]methyl}spermidine (BBSPD-5). These boronated polyamines retain their ability to displace ethidium bromide from calf thymus DNA and are rapidly taken up in vitro by F98 rat glioma cells. The in vitro toxicities of ASPD-5, ASPM-5, DHSPD-5, and DHSPM-5 are lower than those previously reported for N5-[4-(o-carboranyl)butyl] SPD/SPM derivatives (SPD-5 and SPM-5) but similar to those of native SPD and SPM. Very low toxicity was also observed for BBSPD-5. In vivo studies of ASPD-5 and BBSPD-5 were performed in mice bearing intracerebral implants of the GL261 glioma and subcutaneous implants of the B16 melanoma. The biodistribution data found in both tumor models suggest that the polyamines synthesized to date do not appear to be suitable boron agents for BNCT.

[Single and 2-week repeated intravenous dose toxicity studies of disodium mercaptoundecahydro-closo-dodecaborate in rats]

Disodium mercaptoundecahydro-closo-dodecaborate (BSH) is a boron compound used in Boron Neutron Capture Therapy for malignant brain tumors. Intravenous single and 2-week repeated dose toxicity studies of BSH were performed in Sprague-Dawley rats. In the single-dose study, BSH was administered at doses of 100, 300 or 600 mg/kg. Death occurred within 10 min (acute type) or from 5 hr to 2 days (delayed type) after dosing in the 600 mg/kg group. No differences in mortality by sex and dosing speed were observed. Major causes of death were considered to be circulatory disorder in acute death and renal injury in delayed death. The renal injury was observed in the 300 and 600 mg/kg groups. In the 2-week repeated dose study, BSH was administered at doses of 30, 100 or 300 mg/kg/day for 14 days. Body weight gain was suppressed in the 100 and 300 mg/kg groups. One male in the 300 mg/kg group died due to renal and pulmonary lesions at day 8. Slight anemia was observed in the 300 mg/kg group. Pathologically, the kidney showed tubular regeneration with increase of weight in the 300 mg/kg. From these results, the NOAEL of BSH is 30 mg/kg/day.

[Reverse mutation test of disodium mercaptoundecahydro-closo-dodecaborate with bacteria]

Disodium mercaptoundecahydro-closo-dodecaborate (BSH) was studied for mutgenic potential by reverse mutation test with bacteria. The test was carried out using five different tester strains, S. typhimurium TA100, TA1535, TA98 and TA1537, and E. coli WP2uvrA by the preincubation method. BSH was tested at concentrations ranging from 156 to 5000 micrograms per plate. The test substance did not induce revertants dose-dependently in any strains with or without a metabolic activation system. Therefore, it was concluded that BSH was not mutagenic in the present reverse mutation test.

Antitumor properties of boron complexes with hydroxy biguanide and salicyl hydroxamic acid against Ehrlich ascites carcinoma

A new derivative of hydroxamic acid, hydroxy biguanido hydrochloride monohydrate and its boron derivative, dihydroxy-oxybiguanido boron (III) hydrochloride monohydrate were synthesized. Another boron compound, hydroxo-salicyl-hydroxamato boron (III) was synthesized from known salicyl hydroxamic acid. Antitumor properties of all the compounds evaluated against Ehrlich ascites carcinoma in mice show enhanced survival time when boron is incorporated in the compounds. Hematological parameters, alkaline phosphatase in serum of the treated animals show minimum toxic effects after boron is coupled with their respective hydroxamic acids.