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PubMed1993

NMR studies of the alpha-chymotrypsin-(R)-1-acetamido-2-(4- fluorophenyl)ethane-1-boronic acid complex.

The interaction of (R)-1-acetamido-2-(4-fluorophenyl)ethane-1-boronic acid with alpha-chymotrypsin at pH 4 was studied by a variety of 19F-NMR experiments. It was demonstrated that this compound forms a complex with a 1:1 stoichiometry, probably because the boronic acid acts as a 'transition state' inhibitor of the enzyme. Analysis of fluorine T1 relaxation behavior and 19F[1H] NOE data shows that the rate constant for dissociation of the complex is 1.3 s-1 and that the motion of the 4-fluoroaromatic ring within the complex can be characterized by an overall rotational correlation time of 13 ns and a correlation time for rotation about its local C2 axis of 110 ns. Enzyme-induced fluorine chemical shifts, fluorine relaxation times, line width data and 2D 19F[1H] NOE results suggest that the structure of the complex in the vicinity of the fluoroaromatic ring is similar to that found in a closely similar acylated enzyme. However, the dynamics of 4-fluoroaromatic ring motions are different in the two systems, with the ring being slightly more mobile in the boronic acid complex than in the acylenzyme.

Binding Sites↗
PubMed1994

Boron neutron capture therapy (BNCT): a radiation oncology perspective.

Boron neutron capture therapy (BNCT) offers considerable promise in the search for the ideal cancer therapy, a therapy which selectively and maximally damages malignant cells while sparing normal tissue. This bimodal treatment modality selectively concentrates a boron compound in malignant cells, and then "activates" this compound with slow neutrons resulting in a highly lethal event within the cancer cell. This article will review this treatment modality from a radiation oncology, biology, and physics perspective. The remainder of the articles in this special issue of the Journal will provide a survey of the current "state-of-the-art" in this rapidly expanding field, including information with regard to boron compounds and their localization.

Boron Neutron Capture Therapy↗
PubMed1990

A review of techniques for the analysis of boron in the development of neutron capture therapy agents.

The resurgence of interest in neutron capture therapy, which uses boron-10 labelled compounds and neutron irradiation as a technique for the treatment of cancer, has been accompanied by the application of a new generation of techniques for the analysis and imaging of boron in biological matrices. In this review, a description is given of the requirements for boron neutron capture agents and the achievements to date of the analytical techniques.

Animals↗
PubMed1996

A dosimetry system for boron neutron capture therapy based on the dual counter microdosimetric technique.

A dosimetric technique based on proportional counter microdosimetry has been developed for the dosimetry of mixed radiation fields employed in boron neutron capture therapy (BNCT). The technique has been successfully used to measure the gamma, fast neutron and the boron dose rates in the mixed radiation field from a 252Cf source. The measured fast neutron and boron dose rates are in good agreement with the calculations and the measurements reported by other researchers. A systematic discrepancy is observed in the gamma dose rate measurements, with the present measurements being approximately 35% lower than those reported elsewhere.

Boron Neutron Capture Therapy↗
PubMed2006

Boron impregnation treatment of Eucalyptus grandis wood.

Eucalyptus grandis is suitable for small timber purposes, but its wood is reported to be non-durable and difficult to treat. Boron compounds being diffusible, and the vacuum-pressure impregnation (VPI) method being more suitable for industrial-scale treatment, the possibility of boron impregnation of partially dry to green timber was investigated using a 6% boric acid equivalent (BAE) solution of boric acid and borax in the ratio 1:1.5 under different treatment schedules. It was found that E. grandis wood, even in green condition, could be pressure treated to desired chemical dry salt retention (DSR) and penetration levels using 6% BAE solution. Up to a thickness of 50mm, in order to achieve a DSR of 5 kg/m(3) boron compounds, the desired DSR level as per the Indian Standard for perishable timbers for indoor use, it was found that neither the moisture content of wood nor the treatment schedule posed any problem as far as the treatability of E. grandis wood was concerned.

Boron↗
PubMed2005

Boronic acid fluorescent sensors for monosaccharide signaling based on the 6-methoxyquinolinium heterocyclic nucleus: progress toward noninvasive and continuous glucose monitoring.

The synthesis, characterization, and spectral properties of strategically designed boronic acid containing fluorescent sensors, o-, m-, p-BMOQBA, for the potential detection of tear glucose concentrations when immobilized in plastic disposable contact lenses is described. The new probes, BMOQBAs, consist of the 6-methoxyquinolinium nucleus as a fluorescent indicator, and the boronic acid moiety as a glucose chelating group. A control compound BMOQ, which has no boronic acid group and therefore does not bind monosaccharides has also been prepared. In this paper, we show that structural design considerations of the new probes have afforded for their compatibility within the lenses, with reduced probe sugar-bound pK(a) favorable with the mildly acidic lens environment. In addition, the new probes are readily water soluble, have high quantum yields, and can be prepared by a simple one-step synthetic procedure.

Boronic Acids↗
PubMed2005

Novel boronated derivatives of 5,10,15,20-tetraphenylporphyrin: synthesis and toxicity for drug-resistant tumor cells.

We have developed the synthesis of boronated porphyrins for potential application in cancer treatment, based on the functional derivatives of 5,10,15,20-tetraphenylporphyrin. Boronated amide derivatives starting from 5,10,15,20-tetra(p-aminophenyl)porphyrin and 9-o- and 9-m-carborane carboxylic acid chlorides were prepared. Also, the reaction of 2-formyl-5,10,15,20-tetraphenylporphyrin with closo-C-lithium-o- and m-carboranes, as well as with closo-C-lithium monocarbon carborane, yielded neutral and anionic boronated hydroxy derivatives of 5,10,15,20-tetraphenylporphyrin, respectively. Water-soluble forms of neutral compounds were prepared by deboronation of closo-polyhedra with Bu4NF into nido-7,8- and nido-7,9-dicarbaundecaborate anions. Monocarbon carborane conjugated with copper (II) complex of 5,10,15,20-tetraphenylporphyrin was active for a variety of tumor cell lines (IC50 approximately 5 microM after 48-72 h of exposure) but was inert for non-malignant fibroblasts at up to 100 microM. At low micromolar concentrations, this compound caused the death of cells that express P-glycoprotein and other mechanisms of resistance to conventional anticancer drugs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2006

Comparative molecular field analysis and comparative molecular similarity indices analysis of boron-containing human thymidine kinase 1 substrates.

Three-dimensional quantitative structure-activity relationship (3D-QSAR) using CoMFA and CoMSIA techniques was applied to evaluate 56 pyrimidine nucleosides as substrates of human thymidine kinase 1 (hTK1), 27 of them containing a carborane substituent either at the 3-, 5-, or 3'-position of the 2'-deoxyuridine scaffold. This is the first report describing 3D-QSAR studies of compounds containing boron atoms. Both CoMFA and CoMSIA models were derived from a training set of 47 molecules and the predictive capacity of the CoMSIA model was successfully validated by accurately calculating known phosphorylation rates of both boronated and non-boron hTK1 substrates that were not included in the training set. The optimal CoMSIA model provided the following values: q(2) 0.622, r(2) 0.983, s 0.165, and F 187.5. Contour maps obtained from the CoMSIA model were in agreement with the experimentally determined biological data.

Boron↗
PubMed2004

Aza-boronic acids as non-beta-lactam inhibitors of AmpC-beta-lactamase.

With the aim of improving the ability of non-beta-lactam inhibitors to inhibit AmpC-beta-lactamase, a series of 3-aza-phenyl-boronic acid derivatives was obtained using in parallel synthesis. The molecules were tested against Escherichia coli AmpC-beta-lactamase. The best inhibitors, 3-(2-hydroxy-naphthalen-1-ylazo)-phenyl-boronic acid (12) and 3-(2,4-dihydroxy-naphthalen-1-ylazo)-phenyl-boronic acid (14), showed apparent inhibition constant values (K(i)) of 0.3 and 0.45 microM and increased the potency of the semi-synthetic cephalosporin antibiotic, ceftazidime, lowering its minimum inhibitory concentration (MIC) value of 50%, against Gram-negative bacteria strains, producing high levels of AmpC-beta-lactamase.

Aza Compounds↗
PubMed2006

Removal of boron from aqueous solution by using neutralized red mud.

The adsorptive removal of boron from aqueous solution by using the neutralized red mud was studied in batch equilibration technique. The effects of pH, adsorbent dosage, initial boron concentration and contact time on the adsorption were investigated. The experiments demonstrated that boron removal was of a little fluctuation in pH range of 2-7 and it takes 20 min to attain equilibrium. The adsorption data was analyzed using the Langmuir and the Freundlich isotherm models and it was found that the Freundlich isotherm model represented the measured sorption data well.

Adsorption↗
PubMed2005

Why boron?

It is now more than 80 years since boron was convincingly demonstrated to be essential for normal growth of higher plants. However, its biochemical role is not well understood at the moment. Several recent reviews propose that B is implicated in three main processes: keeping cell wall structure, maintaining membrane function, and supporting metabolic activities. However, in the absence of conclusive evidence, the primary role of boron in plants remains elusive. Besides plants, growth of specific bacteria, such as heterocystous cyanobacteria and the recently reported actinomycetes of the genus Frankia, requires B, particularly for the stability of the envelopes that control the access of the nitrogenase-poisoning oxygen when they grow under N2-fixing conditions. Likewise, a role for B for animal embryogenesis and other developmental processes is being established. Finally, a new feature of the role of boron comes from signaling mechanisms for communication among bacteria and among legumes and rhizobia leading to N2-fixing symbiosis, and it is possible that new roles for B, based on its special chemistry and its interaction with Ca would appear in the world of signal transduction pathways. In conclusion, the diversity of roles played by B might indicate that either the micronutrient is involved in numerous processes or that its deficiency has a pleiotropic effect. The arising question is why such an element? Since all of the roles clearly established for B are related to its capacity to form diester bridges between cis-hydroxyl-containing molecules, we propose that the main reason for B essentiality is the stabilization of molecules with cis-diol groups turning them effective, irrespectively of their function.

Boron↗
PubMed2006

Mobilisation and attenuation of boron during coal mine rehabilitation, Wangaloa, New Zealand.

Environmental mobility and fate of boron has been traced from source to discharge waters through the rehabilitated Wangaloa coal mine in southern New Zealand. The boron is derived initially from coal, which has up to 450 mg/kg B. The coal also contains pyrite (2-5 wt.% S), which oxidizes to yield a low-pH environment (typical pH 2-5). Weathering of coal-bearing waste rock liberates B into rainwater that infiltrates into waste rock or evaporates to leave a gypsum crust enriched in B, possibly as boric acid or colemanite as inferred from geochemical modelling. Surface waters dissolve this evaporative material periodically, yielding total B concentrations up to 6 mg/L, at pH<4.5. Some of the available B is taken up by plants that have been established on the waste rock, resulting in foliage B concentrations of up to 230 mg/kg (dry weight). Partial attenuation of dissolved B by adsorption to iron oxyhydroxide occurs as groundwater passes through waste rock, but this is inhibited by adsorption competition with dissolved sulphate (up to 600 mg/L). Groundwater flows from the mine through a pit lake and wetland, with total dissolved B near 1 mg/kg after dilution and limited adsorption attenuation has occurred. Despite the widespread B mobility throughout the rehabilitated mine, there is little evidence of B toxicity in plants. The B concentrations in discharging waters are in the environmentally safe range for most aquatic organisms, being neither deficient in B as a micronutrient, nor boron-toxic.

Boron↗
PubMed2006

A versatile synthesis of 17-heteroaryl androstenes via palladium-mediated Suzuki cross-coupling with heteroaryl boronic acids.

Suzuki coupling of 17-iodoandrosta-5,16-dien-3beta-ol (1) and 17-iodoandrosta-4,16-dien-3-one (2) with nine heteroaryl boronic acids (mainly 2- or 3-furanyl, thienyl, benzofuranyl and benzothienyl boronic acid derivatives) were carried out under normal Suzuki condition (Pd(PPh(3))(4), 2M Na(2)CO(3) and MeOH), generally yielded C(17)-heteroaryl steroids in moderate (10-60%) yields, but furanyl-2- and 5-chlorothienyl-2-boronic acid did not give any coupling product.

Androstenes↗
PubMed1998

Interaction of mercaptoundecahydrododecaborate (BSH) with phosphatidylcholine: relevance to boron neutron capture therapy.

The interaction of mercaptoundecahydrododecaborate (B12H11SH2-, BSH) with phosphatidylcholine was investigated in this study in order to illuminate possible uptake mechanisms of BSH in tumor cells. BSH has been used clinically in Japan as a boron containing agent in patients with malignant brain tumors for boron neutron capture therapy (BNCT). After infusion, BSH accumulates selectively in tumor tissue. Little is known for the mechanism of boron uptake to tumor cells. Fourier transform infrared (FTIR) spectrometry was used to quantify BSH (at wavenumber 2490 cm-1) and phosphatidylcholine (at wavenumber 2850-2970 cm-1). After extraction into carbon tetrachloride (CCl4), we could find an absorbance maximum at 2490 cm-1 as a B-H band in the mixture of BSH with phosphatidylcholine, which is attributed to a BSH-phosphatidylcholine complex, which could dissolve well in CCl4. The molar ratio of BSH to phosphatidylcholine in the CCl4 solution was at most one mole of BSH to two moles of phosphatidylcholine independent of the excess BSH. The doubly negatively charged BSH can interact with two phosphatidylcholine molecules through their singly positively charged choline residues. These ion pairs could be responsible for membrane binding and penetration, and for cell internalization.

Borohydrides↗
PubMed1999

Boronated protoporphyrin (BOPP): localization in lysosomes of the human glioma cell line SF-767 with uptake modulated by lipoprotein levels.

PURPOSE: Boronated protoporphyrin (BOPP) is a candidate for use in both boron neutron capture therapy (BNCT) and photodynamic therapy (PDT) of glioblastoma multiforme (GBM). Our objectives are to identify factors that influence the uptake and retention of BOPP in vitro and to determine BOPP distribution in a human glioma cell line in vitro. This information will aid the development of compounds and treatment strategies that increase the effectiveness of BNCT therapy for GBM. METHODS AND MATERIALS: The amount, distribution pattern, and site of internalization of BOPP were assessed using fluorescence microscopy. Living human glioma (SF-767) cells were imaged after a 24-h exposure to BOPP (20-135.6 microg/ml, normal serum). Dose-dependent uptake of BOPP was determined using both fluorescence microscopy of individual living cells and inductively-coupled plasma-atomic emission spectroscopy (ICP-AES) analysis of cell pellets. Lysosome- or mitochondria-specific fluorescent probes were used to identify the cellular compartment containing BOPP. Two human fibroblast cell lines, AG-1522 (LDL receptor-positive) and GM019-15C (LDL receptor-deficient), were used to investigate LDL receptor-dependent BOPP uptake. The dependence of BOPP uptake on lipoproteins in the media was determined by exposing each of the three cell types to BOPP in medium containing either normal (NS) or lipoprotein deficient serum (LPDS). RESULTS: BOPP accumulated in the lysosomes of human glioma cells in vitro, and not in the mitochondria, as reported for C6 rat glioma cells in vitro. BOPP uptake was concentration-dependent and was also dependent on the amount of lipoproteins in the medium. Over the range of incubation concentrations studied and at the single exposure duration time point investigated (24 h), all cells retained a similar amount of BOPP. At the lowest incubation concentration (20 microg/ml, NS), the amount of boron retained was near 10(9) atoms per cell (15 microg B/g cells). Lysosomes containing high concentrations of BOPP were randomly distributed throughout the cytoplasm; however, larger lysosomes containing BOPP were concentrated around the cell nucleus. Little or no BOPP accumulated in the cell nucleus. At incubation concentrations of 20 and 40 microg/ml (24-h time point), BOPP uptake in SF-767 cells was reduced in LPDS compared with NS (66% reduction). A similar result was observed for normal human fibroblasts (AG-1522 cells, 40 microg/ml, 24 h). At 40 microg/ml, in both NS and LPDS at 24 h, BOPP accumulation in LDL receptor-deficient human fibroblasts (GM019-15C cells) was reduced relative to AG-1522 cells. BOPP accumulation in GM019-15C cells (40 microg/ml, 24 h) was not affected by serum lipoprotein levels. CONCLUSION: In cell culture, BOPP is taken up by human glioma cells via the LDL pathway and is compartmentalized into cellular lysosomes. Knowledge of this mechanism of BOPP uptake and retention will be important in attempts to modify toxicity and efficacy of this drug.

Antineoplastic Agents↗
PubMed1988

Kinetic properties of the binding of alpha-lytic protease to peptide boronic acids.

The kinetic parameters for peptide boronic acids in their interaction with alpha-lytic protease were determined and found to be similar to those of other serine proteases [Kettner, C., & Shenvi, A. B. (1984) J. Biol. Chem. 259, 15106-15114]. alpha-Lytic protease hydrolyzes substrates with either alanine or valine in the P1 site and has a preference for substrate with a P1 alanine. The most effective inhibitors are tri- and tetrapeptide analogues that have a -boroVal-OH residue in the P1 site. At pH 7.5, MeOSuc-Ala-Ala-Pro-boroVal-OH has a Ki of 6.4 nM and Boc-Ala-Pro-boroVal-OH has a Ki of 0.35 nM. Ac-boroVal-OH and Ac-Pro-boroVal-OH are 220,000- and 500-fold less effective, respectively, than the tetrapeptide analogue. The kinetic properties of the tri- and tetrapeptide analogues are consistent with the mechanism for slow-binding inhibition, E + I in equilibrium EI in equilibrium EI*, while the less effective inhibitors are simple competitive inhibitors. MeO-Suc-Ala-Ala-Pro-boroAla-OH is a simple competitive inhibitor with a Ki of 67 nM at pH 7.5. Other peptide boronic acids, which are analogues of nonsubstrates, are less effective than substrate analogues but still are effective competitive inhibitors. For example, MeOSuc-Ala-Ala-Pro-boroPhe-OH has a Ki of 0.54 microM although substrates with a phenylalanine in the P1 position are not hydrolyzed. Binding for boronic acid analogues of both substrate and nonsubstrate analogues is pH dependent with higher affinity near pH 7.5. Similar binding properties have been observed for pancreatic elastase. Both enzymes have almost identical requirements for an extended peptide inhibitor sequence in order to exhibit highly effective binding and slow-binding characteristics.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed2006

Occurrence and fate of nitrosamines and nitrosamine precursors in wastewater-impacted surface waters using boron as a conservative tracer.

Using boron as a conservative tracer of municipal wastewater effluents, a mass balance was developed to determine river flowrates that requires only wastewater discharge flowrates and boron concentrations in wastewater effluents and in the river upstream and downstream of these discharges. Furthermore, this method permits calculation of the percentage of the river deriving from wastewater. This method could be useful within river sections featuring no independent data regarding river discharge. We assessed the decay of nitrate and N-nitrosodimethylamine (NDMA) precursors within an engineered treatment wetland and, using our boron analysis technique to account for dilution, within the Quinnipiac River (CT). Although both decayed with several day half-lives, their slow decay indicates they can persist to impact downstream drinking water supplies. Concentrations of NDMA and N-nitrosomorpholine (NMOR) were measurable within the river, but concentrations of four other nitrosamines, their precursors, and NMOR precursors were not detectable.

Boron↗
PubMed1991

Boron-containing thiouracil derivatives for neutron-capture therapy of melanoma.

Boron-containing derivatives of 2-thiouracil and 2,4-dithiouracil and the corresponding 6-propyl compounds, containing a dihydroxyboryl group in the 5-position, have been prepared. These compounds accumulate in B16 melanoma in mice in concentrations up to 30 micrograms of boron per gram tissue. The uptake persists. The toxicity of both 2-thiouracil derivatives is low. These compounds are therefore good candidates for boron neutron-capture therapy of malignant melanoma.

Animals↗