[Acute poisoning with boric acid].
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Boric Acids↗
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Results for “Boron Compounds”
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Action of phenyl-mercuric borate on experimentally infected cultures of epithelial cells.
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Borates↗
Potent and selective inhibitors of the proteasome: dipeptidyl boronic acids.
Potent and selective dipeptidyl boronic acid proteasome inhibitors are described. As compared to peptidyl aldehyde compounds, boronic acids in this series display dramatically enhanced potency. Compounds such as 15 are promising new therapeutics for treatment of cancer and inflammatory diseases.
Boronic Acids↗
Microanalytical techniques for boron analysis using the 10B(n,alpha)7Li reaction.
In order to predict the efficacy of boronated compounds for neutron capture therapy (NCT), it is mandatory that the boron concentration in tissues be known. Various techniques for measurement of trace amounts of boron (1-100 ppm) are available, including chemical and physical procedures. Experience has shown that, with the polyhedral boranes and carboranes in particular, the usual colorimetric and spark emission spectroscopic methods are not reliable. Although these compounds may be traced with additional radiolabels, direct physical detection of boron by nondestructive methods is clearly preferable. Boron analysis via detection of the prompt-gamma ray from the 10B(n, alpha)7Li reaction has been shown to be a reliable technique. Two prompt-gamma facilities developed at Brookhaven National Laboratory are described. One, at the 60-MW high flux beam reactor, uses sophisticated beam extraction techniques to enhance thermal neutron intensity and reduce fast neutron and gamma contamination. The other was constructed at Brookhaven's 5-MW medical research reactor and uses conventional shielding and electronics to provide an "on-line" boron analysis facility adjacent to beams designed for NCT, thus satisfying one of the requisites for clinical application of this procedure. Technical restrictions attendant upon the synthesis and testing of boronated biomolecules often require the measurement of trace amounts of boron in extremely small (mg) samples. A track-etching technique capable of detecting ng amounts of boron in mg liquid or cell samples is described. Thus it is possible to measure the boron content in small amounts (mg samples) of antibodies, or boron uptake in cells grown in tissue culture.
Biopsy, Needle↗
Synthesis of boron-containing heterocyclic compounds.
The synthesis of boron-containing 1,3,5-triazines and 1,2,4-triazines is described. Derivatives of 1,3,5-triazine containing the o-carborane cluster have been obtained by reacting the corresponding propargyl derivatives with B(10)H(14). Derivatives of 1,2,4-triazine containing the B(12)H(12)(2-) cluster have been obtained by nucleophilic substitution of ethylsulfone derivatives with B(12)H(11)SH(2-). They have been isolated in their ring-protonated form. Reaction of RNH(2)-B(8)H(11)NH-R with stericly demanding heterocycles failed, either for steric or for solubility reasons.
Journal Article↗
Hydrocarbon analogues of boron clusters--planarity, aromaticity and antiaromaticity.
An interesting feature of elemental boron and boron compounds is the occurrence of highly symmetric icosahedral clusters. The rich chemistry of boron is also dominated by three-dimensional cage structures. Despite its proximity to carbon in the periodic table, elemental boron clusters have been scarcely studied experimentally and their structures and chemical bonding have not been fully elucidated. Here we report experimental and theoretical evidence that small boron clusters prefer planar structures and exhibit aromaticity and antiaromaticity according to the Hückel rules, akin to planar hydrocarbons. Aromatic boron clusters possess more circular shapes whereas antiaromatic boron clusters are elongated, analogous to structural distortions of antiaromatic hydrocarbons. The planar boron clusters are thus the only series of molecules other than the hydrocarbons to exhibit size-dependent aromatic and antiaromatic behaviour and represent a new dimension of boron chemistry. The stable aromatic boron clusters may exhibit similar chemistries to that of benzene, such as forming sandwich-type metal compounds.
Boron↗
Selective boron drug delivery to brain tumors for boron neutron capture therapy.
Malignant glioma is one of the most deadly forms of cancer in humans and remains refractory to presently available treatments. Boron neutron capture therapy (BNCT) is a promising therapeutic modality for the treatment of malignant brain tumors. For successful BNCT, a sufficient quantity of boron atoms must be selectively delivered to individual brain tumor cells while at the same time the boron concentration in the normal brain tissue should be kept low to minimize the damage to normal brain tissue. However, the brain entry of drugs is restricted by the blood-brain barrier (BBB), even though the permeability of the pathological area of this barrier may be partially increased due to the present of brain tumors. Therefore, selective delivery of boron to tumor cells across the BBB is a major challenge to the BNCT of brain tumors. This review briefly discusses four main mechanisms responsible for drug transport across the BBB. Brain tumor-localizing boron compounds are described, such as borocaptate sodium, p-boronophenylalanine, boronated porphyrins and boronated nucleosides. Strategies employed to selectively deliver boron drug into brain tumors are reviewed including hyperosmotic BBB modification, biochemical opening of BBB, electropermeabilization and direct intracerebral delivery of boron drugs. Conjugation of boron drugs to macromolecules like monoclonal antibodies and epidermal growth factor are discussed for active tumor targeting. Boron delivery via microparticles such as liposomes, high density lipoproteins and nanoparticles is also covered for their potential utilization in BNCT of brain tumors.
Journal Article↗
An assessment of boric acid and borax using the IEHR Evaluative Process for Assessing Human Developmental and Reproductive Toxicity of Agents. Expert Scientific Committee.
BACKGROUND: Boron is a ubiquitous element widely distributed in nature in the form of borates at low concentrations in soils and rocks. Boron is released from these minerals by the natural weathering processes in the form of boric acid, which is water soluble and biologically available. High levels of boric acid are naturally found in sea water. Boric acid and borax are used in the greatest quantities and represent the major boron chemical exposures to humans and the environment. The principal use of boric acid and borax is in the manufacture of various types of glass products that do not result in exposure to the consumer. Boric acid and borax are also found in an array of consumer goods including fireproofing for fabrics and wood, insecticides, and in many cosmetics and personal care products as well. Boron may be an essential element for higher animals including humans. HUMAN EXPOSURE: Boric acid and borax are considered to be completely absorbed by the oral route of exposure. Absorption through intact skin is considered negligible, although absorption can occur through denuded or irritated skin. Boron levels in the body do not persist upon cessation of exposure. People may be exposed to boron through three primary sources: 1) consumption of private, municipal, or commercial (bottled) sources of drinking water; 2) dietary consumption of crops and other foodstuffs (including dietary supplements for body building); and 3) inhalation of boron compounds during their mining, manufacturing, and other industrial processing. While boron has been detected in 81.8% of the municipal water systems, it is a minor source of boron in most parts of the U.S. The mean boron concentration is reported as 0.2 mg B/L. However, residents of California and other western states with boron-rich geologic deposits may be regularly exposed to higher levels in drinking water. Individuals who drink bottled mineral water may also increase their exposure to boron. An EPA health advisory, recommends boron concentrations in drinking water not exceed 0.6 mg B/L [0.06 mM B] over a lifetime of exposure. Dietary exposure to boron for an adult typically ranges from ranges from 0.25 to 3.1 mg B/d with an average of 1.5 mg B/d. The high end of the exposure range, 3.1 mg B/d, was selected by the Expert Committee as best estimate of exposure. It should be noted that a diet high in fruits, vegetables, grains, legumes, and other food stuffs with high boron contents may lead to daily exposures as high as 10 mg B/d from diet alone. Some body building supplements contain boron at levels ranging from 1.5 to 10 mg B, with a median of 4 mg B. Use of the supplements containing the median concentration of boron could equal the daily intake an individual receives from diet and drinking water combined. Adults in the U.S. at the high end of the food exposure range may typically ingest up to 3.5 mg B/d, or a daily dose of 0.005 mmol B/kg b.wt., through exposure from diet (3.1 mg B/d) and drinking water (0.4 mg B/d). Individuals who also use body-building supplements may have a total daily boron intake of 7.5 mg B resulting in a daily dose of 0.01 mmol B/kg b.wt./d. Occupational exposure to boron is mainly through inhalation of borate containing dust during mining and manufacturing processes. Current occupational exposures to boron are reported to result in a daily dose of < 0.0001 to 0.2 mmol B/kg b.wt./d. Current U.S. OSHA permissible exposure limit (PEL) for sodium tetraborates is 10 mg/m3, and the California Occupational Safety and Health Administration PEL is 5 mg/m3. An exposure of 5 mg B/m3 translates to approximately 0.01 mmol B/kg b.wt./d that, coincidentally, is the same as exposure levels associated with combined municipal drinking water, diet, and body building supplement consumption. Infants may receive exposures to boric acid when it is used as a household insecticide for cockroach control. Exposure from boric acid-containing cosmetic and personal care products applie
Animals↗
A theoretical model for event statistics in microdosimetry. II: Nonuniform distribution of heavy ion tracks.
A microdosimetry model, described in Part I, applies to the case of a convex site immersed in a uniform distribution of heavy particle tracks, and assumes no restrictions in site geometry or the kind of randomness. In Part II, this model is extended to include nonuniform distributions of particle tracks. This situation is relevant to the study of microdosimetry, for example, in boron neutron capture, in irradiation experiments using heavy ion particle beams, where the sources of particle tracks are external to the cell, or in irradiation from internally incorporated particle-emitting radionuclides, such as environmental radon or occupational exposure to radioactive materials. The formalism developed permits the calculation of statistical properties, track length distributions, and microdosimetric spectra for convex sites where the "inner" and "outer" concentrations of sources may be different, or for tracks originating on the surface of a convex site. Expressions applicable to the case of surface-distributed sources of tracks are presented that may represent situations such as boron compounds bound to the membrane of a cellular nucleus in boron neutron capture. A series of Monte Carlo calculations and analytical solutions, illustrating the case of spherical site geometry, are presented and compared. Finally, microdosimetric spectra and specific energy averages are calculated for alpha and lithium particles originating from thermal neutron capture in 10B, showing their dependence on 10B localization (extra-site, uniform, intra-site, or surface-distributed).
Biophysical Phenomena↗
Cataractogenic effects of a boron hydride disulfide compound.
The disulfide form but not the sulfhydryl form of a boron hydride compound was found to be cataractogenic. Apparently this compound attaches to the sulfhydryl group of Na-K ATPase in the lens epithelium inactivating this crucial enzyme. The consequence is that a defect in the cation pump activity arises, leading to a rapid influx of Na ions and loss of K ions and marked increase in hydration. These changes are thought to lead to opacification.
Acute Disease↗
Synthesis and in vitro evaluation of the phenylboric acid derivative entrapped lipiodol in boron neutron capture therapy for hepatoma.
BACKGROUND: Hepatoma, a common cancer in Taiwan, responds poorly to conventional therapies. Boron neutron capture therapy (BNCT) may provide a promising approach for hepatoma therapy. In this study, a pharmaceutical composition, phenylboric acid derivative entrapped lipiodol (PBAD-lipiodol), was synthesized and characterized. In vitro study was used for evaluation of PBAD-lipiodol for the BNCT of hepatoma. MATERIALS AND METHODS: alpha Track observation was used to identify the boron compound in the TLC plate and to evidence the uniform distribution of boron in the PBAD-lipiodol. Inductively coupled plasma-atomic emission spectroscopy and neutron activation analysis were used to determine the concentrations of boron and lipiodol, respectively. Human hepatoma HepG2 cells were used for in vitro experiments. A Nomarski optical microscope was used to investigate the uptake of PBAD-lipiodol globules in individual hepatoma cells. RESULTS: PBAD-lipiodol was stable in human serum. The boron source, PBAD, was uniformly distributed in PBAD-lipiodol. Many of the PBAD-lipiodol globules were internalized and retained in HepG2 cells, and the boron concentration of HepG2 cells reached 269 ppm after 72 hours of PBAD-lipiodol treatment. CONCLUSION: In vitro studies revealed that PBAD-lipiodol could deliver a therapeutically effective amount of PBAD as a boron source for the BNCT of hepatoma. PBAD-lipiodol is a potential new boron drug for the BNCT of hepatoma.
Boron Neutron Capture Therapy↗
Synthesis and biological evaluation of boronic acid containing cis-stilbenes as apoptotic tubulin polymerization inhibitors.
A series of boronic acid containing cis-stilbenes as potent inhibitors of tubulin polymerization was synthesized by the introduction of boronic acid as an acceptor-type functional group into the aromatic ring B of the combretastatin framework. High cell-growth inhibition was observed with boron compounds 13 c and 13 d, in which a hydroxy group on the aromatic ring B of combretastatin A-4 was replaced with boronic acid; IC50 values toward B-16 and 1-87 cell lines are 0.48-2.1 microM. Compounds 13 c and 13 d exhibited significant inhibitory activity toward tubulin polymerization (IC50=21-22 microM). The carboxylic acid derivative 17, which can be considered as a mimic of boronic acid 13 c, did not show significant inhibition of cell growth or tubulin polymerization. According to the FACScan analysis using Jurkat cells, apoptosis was induced after incubation for 8 h with 13 c at a concentration of >10(-8) M. Growth inhibitory experiments against a panel of 39 human cancer cell lines revealed 13 c to inhibit growth differently than combretastatin A-4; the correlation coefficient (r) between the two compounds was 0.553 in the COMPARE analysis.
Animals↗
Analysis of 10B by PIGE with factor analytical gamma-ray peak identification.
Studying the biodistribution of boronated compounds for B neutron capture therapy (BNCT) requires the accurate detection of low levels of boron (10B) in biological samples. Proton induced gamma-ray emission analysis (PIGE) of 10B was found to be viable in a study of low density lipoprotein (LDL), in tissue and blood samples. However, the method is sensitive to Na present in the samples and can therefore not be used for accurate measurements of 10B concentrations below 5 ppm in samples containing Na. PIGE can be considered to be an appropriate reference method for chemical B analysis. The factor analytical method presented here is the most objective way to separate Na and B peaks from each other, and the factorizing method can be applied in different forms of spectral analysis.
Boron↗
Toward clinical application of prompt gamma spectroscopy for in vivo monitoring of boron uptake in boron neutron capture therapy.
In boron neutron capture therapy (BNCT) the absorbed dose to the tumor cells and healthy tissues depends critically on the boron uptake. Pronounced individual variations in the uptake patterns have been observed for two boron compounds currently used in clinical trials. This implies a high uncertainty in the determination of the boron dose component. In the present work a technique known as prompt gamma spectroscopy (PGS) is studied that potentially can be used for in vivo and noninvasive boron concentration determination at the time of the treatment. The technique is based upon measurement of gamma rays promptly emitted in the 10B(n,alpha)7Li and 1H(n,gamma)2D reactions. The aim of this work is to prepare the present setup for clinical application as a monitor of boron uptake in BNCT patients. Therefore, a full calibration and a set of phantom experiments were performed in a clinical setting. Specifically, a nonuniform boron distribution was studied; a skin/ dura, a larger blood vessel, and tumor within a head phantom was simulated. The results show that it is possible to determine a homogeneous boron concentration of 5 microg/g within +/-3% (1 standard deviation). In the nonuniform case, this work shows that the boron concentration can be determined through a multistep measurement procedure, however, with a somewhat higher uncertainty (approximately 10%). The present work forms the basis for a subsequent clinical application of the PGS setup aimed at in vivo monitoring of boron uptake.
Blood Vessels↗
International Symposium on the Health Effects of Boron and its Compounds. Proceedings. Irvine, California, September 16-17, 1992.
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Animals↗
Antineoplastic activity of a series of boron analogues of alpha-amino acids.
A series of amine cyanoboranes, amine carboxyboranes, and boron analogues of alpha-amino acids have been investigated for antineoplastic activity against the growth of Ehrlich ascites cells. Additional studies demonstrated that the boron analogues inhibited DNA and RNA synthesis at 300 microM. The suppression of DNA synthesis of Ehrlich ascites cells correlated with the reduction of DNA polymerase, 5-phosphoribosyl-1-pyrophosphate amidotransferase, and dihydrofolate reductase activities afforded by the boron compounds. These derivatives did not suppress protein synthesis, thymidylate synthetase, or thymidine monophosphate kinase activities as previously reported for some boron antineoplastic agents.
Amino Acids↗
Clinical considerations for neutron capture therapy of brain tumors.
The radiotherapeutic management of primary brain tumors and metastatic melanoma in brain has had disappointing clinical results for many years. Although neutron capture therapy was tried in the United States in the 1950s and 1960s, the results were not as hoped. However, with the newly developed capability to measure boron concentrations in blood and tissue both quickly and accurately, and with the advent of epithermal neutron beams obviating the need for scalp and skull reflection, it should now be possible to mount such a clinical trial of NCT again and avoid serious complications. As a prerequisite, it will be important to demonstrate the differential uptake of boron compound in brain tumor as compared with normal brain and its blood supply. If this can be done, then a trial of boron neutron capture therapy for brain tumors should be feasible. Because boronated phenylalanine has been demonstrated to be preferentially taken up by melanoma cells through the biosynthetic pathway for melanin, there is special interest in a trial of boron neutron capture therapy for metastatic melanoma in brain. Again, the use of an epithermal beam would make this a practical possibility. However, because any epithermal (or thermal) beam must contain a certain contaminating level of gamma rays, and because even a pure neutron beam causes gamma rays to be generated when it interacts with tissue, we think that it is essential to deliver treatments with an epithermal beam for boron neutron capture therapy in fractions in order to minimize the late-effects of low-LET gamma rays in the normal tissue. I look forward to the remainder of this Workshop, which will detail recent progress in the development of epithermal, as well as thermal, beams and new methods for tracking and measuring the uptake of boron in normal and tumor tissues.
Animals↗
Chemically stabilized phenylboranylidene groups having a dimethoxytrityl group as a colorimetrically detectable protecting group designed for cis-1,2-diol functions of ribonucleosides in the solid-phase synthesis of m2(2,2)G5'ppT.
To not only improve the inherently poor stability of the phenylboranylidene group as a protecting group of the 2',3'-cis-diol function of ribonucleosides but also introduce a colorimetrically detectable function into its mother structure, various 2-[(dialkylamino)methyl]phenylboronic acid derivatives having a [(4,4'-dimethoxytrityl)oxy]methyl group were synthesized. The reaction of uridine with these substituted phenylboronic acid derivatives gave the corresponding 2',3'-O-phenylboranylideneuridine derivatives. The stability of these phenylboranylidene groups was examined. As a result, it was shown that the steric hindrance around the amino group greatly influenced the stability of the 2-substituted phenylboranylidene groups. The 2-aminomethyl-5-[[(4,4'-dimethoxytrityl)oxy]methyl]phenylboranylidene group was the most stable. Its 2-dimethylamino counterpart, the 2-[(dimethylamino)methyl]-5-[[(4,4'-dimethoxytrityl)oxy]methyl]phenylboranylidene group, was the second most stable. When the most and second stable protecting groups were applied to the synthesis of m(2)(2,2)G(5)(')ppT on controlled pore glass, the second stable protecting group showed the best result. The use of this DMTr-containing protecting group enabled us to estimate colorimetrically the amount of the m(2)(2,2)G residue that was incorporated into the reactive site of the pT-loaded CPG resin.
Boron Compounds↗