Boron nitride nanotubes are noncytotoxic and can be functionalized for interaction with proteins and cells

We report the discovery that boron nitride nanotubes (BNNTs), isosteres of CNTs with unique physical properties, are inherently noncytotoxic. Furthermore, we developed a biomemetic coating strategy to interface BNNTs with proteins and cells. Finally, we showed that BNNTs can deliver DNA oligomers to the interior of cells with no apparent toxicity. This work suggests that BNNTs may be superior to CNTs for use as biological probes and in biomaterials.

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.

General, reproductive, developmental, and endocrine toxicity of boronated compounds

Boric acid and inorganic borates are abundant in nature. They are widely used in industrial, agricultural, cosmetic, and numerous smaller applications. These compounds are toxic to all species tested at high doses, but they are not carcinogenic or mutagenic. The major toxicities are reproductive and developmental. Testicular effects occurred at approximately 26 mg boron equivalents/kg body weight (bw)/d (26 mg boron equivalent (BE)/kg bw/d). New data on endocrine toxicity includes altered follicle stimulating hormone and testosterone within 14 d of treatment. Because these hormonal changes may be secondary effects of testicular toxicity, borates are not suspect as endocrine disrupters. The most sensitive of all the endpoints are prenatal growth and morphologic development in the rat; these changes occurred at a dose of 12.9 mg BE/kg bw/d. The no observed adverse effect level for rat fetal development was 9.6 mg/kg BE. Considering the estimated human exposure levels and a safety factor of 30, humans are not at significant risk of reproductive failure due to borates from environmental sources. The margin of exposure is estimated at 72 for males and 129 for females. Thus, the likelihood of human toxicity caused by boric acid and inorganic borates from exposure during normal activities is remote.

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].

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.

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.

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.

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.

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.

Selective tumor kill of cerebral glioma by photodynamic therapy using a boronated porphyrin photosensitizer

The prognosis for patients with the high-grade cerebral glioma glioblastoma multiforme is poor. The median survival for primary tumors is < 12 months, with most recurring at the site of the original tumor, indicating that a more aggressive local therapy is required to eradicate the unresectable "nests" of tumor cells invading into adjacent brain. Two adjuvant therapies with the potential to destroy these cells are porphyrin-sensitized photodynamic therapy (PDT) and boron-sensitized boron neutron capture therapy (BNCT). The ability of a boronated porphyrin, 2,4-(alpha, beta-dihydroxyethyl) deuteroporphyrin IX tetrakiscarborane carboxylate ester (BOPP), to act as a photosensitizing agent was investigated in vitro with the C6 rat glioma cell line and in vivo with C6 cells grown as an intracerebral tumor after implantation into Wistar rats. These studies determined the doses of BOPP and light required to achieve maximal cell kill in vitro and selective tumor kill in vivo. The data show that BOPP is more dose effective in vivo by a factor of 10 than the current clinically used photosensitizer hematoporphyrin derivative and suggest that BOPP may have potential as a dual PDT/BNCT sensitizer.

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.

Evaluation of carborane-containing porphyrins as tumour targeting agents for boron neutron capture therapy

A number of carborane-containing porphyrins were administered to mice bearing subcutaneously transplanted mammary carcinomas. Administration was via serial intraperitoneal (i.p.) injections to assess their relative toxicities and tumour affinities. Three analogues of the natural porphyrin heme and four tetraphenylporphyrins (TPPs) were given at total doses of 78-245 micrograms g-1 body weight. The water-insoluble TPPs were less toxic to mice, and delivered greater amounts of boron to tumour than did the water-soluble TPPS and the heme analogues. One such compound, NiTCP-H, delivered more than 100 micrograms B g-1 to tumour tissue with a tumour:blood boron concentration ratio greater than 500:1 and a tumour: brain boron concentration ratio greater than 50:1, 4 days after the last of six i.p. injections given over 2 days. Another TPP analogue, NiTCP, delivered approximately 50 micrograms B g-1 to tumour with similar boron concentrations in normal tissues. Neither compound was toxic to mice at total doses of approximately 200 micrograms g-1 body weight. In contrast, the heme analogues were toxic and, with the exception of VCDP, delivered less boron to tumour than NiTCP and NiTCP-H. The two porphyrins with the greatest potential for application to boron neutron capture therapy (BNCT), NiTCP and NiTCP-H, yielded higher tumour:blood and tumour:brain boron concentration ratios in mice than could be achieved with p-boronophenylalanine (BPA) and sodium mercaptoundecahydrododecaborate (BSH), the compounds which are currently being used in clinical trials of BNCT in the treatment of glioblastoma. The boron delivered by each of the porphyrins tested remained in tumour tissue longer than did boron delivered by either BPA or BSH. The copper and nickel chelates of these porphyrins behave identically in vivo. The former offer the potential for imaging by 67Cu-mediated single photon emission computed tomography (SPECT) to aid BNCT treatment planning.

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.

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.

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.

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.

A review: CNS effects and normal tissue tolerance in dogs

Large animal studies have been utilized to define tolerance of normal brain to irradiation and verify treatment planning programs with two recently installed epithermal neutron beams. The normal brain tolerance studies utilized two biological endpoints, magnetic resonance visible damage only and neurologic signs progressing to death. The studies focused on defining the proton RBE for the contaminant fast neutrons, and from nitrogen capture of thermal neutrons and boron capture reaction biologic effect. The proton RBE was approximately 3.0 to 6.7, depending on whether a dose reduction factor for the low gamma dose rate was employed. The microscopic distribution of the boron compounds, coupled with the extremely short length of the fission fragments from thermal neutron capture by 10B yields an observed biologic effect much less than would be expected from such high LET irradiation. This observed biologic effect, which is a product of the microdistribution of the boron atom and the relative biologic effect of the fission fragments has been termed compound factor. The compound factor was based on the calculated physical dose from the fission fragment in blood based on measured blood 10B concentration. The approximate compound factor for BSH was studied at the two institutions and it ranged from 0.27 to 0.55, depending on the site and the endpoint chosen. The mean compound factor for BPA was only studied at one site and was found to be 1.1 for both endpoints. The increase in the compound factor for BPA is in keeping with previous calculations based on the differences in compound distribution. Results of these studies has helped the initiation of phase I and phase II clinical trials at Brook haven National Laboratory and the planned European clinical trials at Petten, The Netherlands.

Enhanced survival of glioma bearing rats following boron neutron capture therapy with blood-brain barrier disruption and intracarotid injection of boronophenylalanine

Boronophenylalanine (BPA) has been used for boron neutron capture therapy (BNCT) of brain tumors in both experimental animals and humans. The purpose of the present study was to determine if the efficacy of BNCT could be enhanced by means of intracarotid (i.c.) injection of BPA with or without blood-brain barrier disruption (BBB-D) and neutron irradiation using a rat brain tumor model. For biodistribution studies, F98 glioma cells were implanted stereotactically into the brains of Fischer rats, and 12 days later BBB-D was carried out by i.c. infusion of 25% mannitol (1.373 mOsmol/ml), followed immediately by i.c. administration of 300, 500 or 800 mg of BPA/kg body weight (b.w.). At the 500 mg dose a fourfold increase in tumor boron concentration (94.5 micrograms/g) was seen at 2.5 hours after BBB-D. compared to 20.8 micrograms/g in i.v. injected animals. The best composite tumor to normal tissue ratios were observed at 2.5 hours after BBB-D, at which time the tumor: blood (T: Bl) ratio was 10.9, and the tumor: brain (T:Br) ratio was 7.5, compared to 3.2 and 5.0 respectively for i.v. injected rats. In contrast, animals that had received i.c. BPA without BBB-D had T : Bl and T:Br ratios of 8.5 and 5.9, respectively, and the tumor boron concentration was 42.7 micrograms/g. For therapy experiments, initiated 14 days after intracerebral implantation of F98 glioma cells, 500 mg/kg b.w. of BPA were administered i.v. or i.c. with or without BBB-D, and the animals were irradiated 2.5 hours later at the Brook-haven Medical Research Reactor with a collimated beam of thermal neutrons delivered to the head. The mean survival time for untreated control rats was 24 +/- 3 days, 30 +/- 2 days for irradiate controls, 37 +/- 3 days for those receiving i.v. BPA, 52 +/- 15 days for rats receiving i.c. BPA without BBB-D, and 95 +/- 95 days for BBB-D followed by i.c. BPA and BNCT. The latter group had a 246% increase in life span (ILS) compared to untreated controls and a 124% ILS compared to that of i.v. injected animals. These survival data are the best ever obtained with the F98 glioma model and suggest that i.c. administration of BPA with or without BBB-D may be useful as a means to increase the efficacy of BNCT.

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.

Synthesis of carboranes containing an azulene framework and in vitro evaluation as boron carriers

3-(o-Carboranylhydroxymethyl)-7-isopropylazulene sodium carboxylate (1) and 3-(o-carboranylmethyl)-7-isopropylazulene sodium sulfonate (2) were synthesized from the palladium-catalyzed addition reaction of 1-carboranyltributylstannane (4) to azulene aldehydes (3 and 9). Although the water solubility of 1 was of the order of 10(-6) M, that of 2 was of the order of 10(-3) M and was enough for clinical use. The cytotoxicity of 1 (IC50) toward B-16 melanoma cells was of the order of 10(-5) M, whereas that of 2 was of the order of 10(-4) M. This value was close to that of BPA (approximately 9 x 10(-3) M) which is utilized for clinical use. The boron uptake by B-16 cells was 0.17 microgram of B/10(6) cells for 1 and 0.25 microgram of B/10(6) cells for 2. It is clear that compound 2 accumulates in B-16 melanoma cells with a significantly high level although it is highly water soluble and its cytotoxicity is significantly low.

Specific inhibition of plasma kallikrein modulates chronic granulomatous intestinal and systemic inflammation in genetically susceptible rats

The kallikrein-kinin (K-K) (contact) system is activated during acute and chronic relapsing phases of enterocolitis induced in genetically susceptible Lewis rats by intramural injection of peptidoglycan-polysaccharide (PG-APS). Using the selective plasma kallikrein inhibitor P8720, we investigate whether activation of the K-K system plays a primary role in chronic granulomatous intestinal and systemic inflammation in this model. Group I (negative control) received human serum albumin intramurally. Group II (treatment) received PG-APS intramurally and P8720 orally. Group III (positive control) received PG-APS intramurally and albumin orally. P8720 attenuated the consumption of the contact proteins, high molecular weight kininogen (P<0.03), and factor XI (P<0.04) in group II vs. group III. P8720 decreased chronic intestinal inflammation measured by blinded gross (P<0.01) and histologic (P<0.0005) scores as well as systemic complications (arthritis, splenomegaly, hepatomegaly, leukocytosis, and acute-phase reaction) (P<0.01) in group II as compared with group III. We conclude that relapsing chronic enterocolitis and systemic complications are in part due to plasma K-K system activation, and that inhibition of this pathway is a potential therapeutic approach to human inflammatory bowel disease and associated extraintestinal manifestations.

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.

Biodistribution and toxicity of 2,4-divinyl-nido-o-carboranyldeuteroporphyrin IX in mice

BALB/c mice with transplanted subcutaneous KHJJ mammary carcinomas were given 2,4-divinyl-nido-o-carboranyldeuteroporphyrin IX (VCDP), a prospective boron carrier for boron neutron-capture therapy, to determine the dose schedule that results in maximal boron uptake in tumor. A total dose of 270 +/- 10 micrograms/g body weight given in a 4-day multiple intraperitoneal injection schedule (3/day) resulted in 30-50 micrograms boron/g tumor. After such a dose, thrombocytopenia, granulocytosis and altered liver enzyme levels were measured in the blood. Blood boron clearance was followed for an 18 hr to 6 day post-injection period. Toxic effects of VCDP subsided within 4-6 days after the last injection. In view of the greater than 30 micrograms/g peak accumulation of boron in tumor from VCDP and the subsequent rapid reversal of VCDP toxicity, further studies of VCDP in small mammals relevant to its distribution, toxicity and potential clinical use for neutron-capture therapy of tumors appear warranted.

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.