A Carborane-Derivative “Click” Reaction under Heterogeneous Conditions for the Synthesis of a Promising Lipophilic MRI/GdBNCT Agent

Development of a Gadolinium-Boron-Conjugated Albumin for MRI-Guided Neutron Capture Therapy

Noninvasive monitoring of boron agent biodistribution is required in advance of neutron capture therapy. In this study, we developed a gadolinium-boron-conjugated albumin (Gd-MID-BSA) for MRI-guided neutron capture therapy. Gd-MID-BSA was prepared by labeling bovine serum albumin with a maleimide-functionalized gadolinium complex and a maleimide-functionalized closo-dodecaborate orthogonally. The accumulation of Gd-MID-BSA in tumors in CT26 tumor-bearing mice reached a maximum at 24 h after the injection, as confirmed by T1-based MRI and biodistribution analysis using inductively coupled plasma optical emission spectrometry. The concentrations of boron and gadolinium in the tumors exceeded the thresholds required for boron neutron capture therapy (BNCT) and gadolinium neutron capture therapy (GdNCT), respectively. The boron concentration ratios of tumor to blood and tumor to normal tissues satisfied the clinical criteria, indicating the reduction of undesired nuclear reactions of endogenous nuclei. The molar ratio of boron to gadolinium in the tumor was close to that of Gd-MID-BSA, demonstrating that the accumulation of Gd-MID-BSA in the tumor can be evaluated by MRI. Thermal neutron irradiation with Gd-MID-BSA resulted in significant suppression of tumor growth compared to the group injected with a boron-conjugated albumin without gadolinium (MID-BSA). The neutron irradiation with Gd-MID-BSA did not cause apparent side effects. These results demonstrate that the conjugation of gadolinium and boron within the albumin molecule offers a novel strategy for enhancing the therapeutic effect of BNCT and the potential of MRI-guided neutron capture therapy as a promising treatment for malignant tumors.

Imidazolium salts as an alternative for anti-Leishmania drugs: Oxidative and immunomodulatory activities

In this study we explored the previously established leishmanicidal activity of a complementary set of 24 imidazolium salts (IS), 1-hexadecylimidazole (C₁₆Im) and 1-hexadecylpyridinium chloride (C₁₆PyrCl) against Leishmania (Leishmania) amazonensis and Leishmania (Leishmania) infantum chagasi. Promastigotes of L. amazonensis and L. infantum chagasi were incubated with 0.1 to 100 μM of the compounds and eight of them demonstrated leishmanicidal activity after 48 h - C₁₀MImMeS (IC_{50 L. amazonensis} = 11.6), C₁₆MImPF₆(IC_{50 L. amazonensis} = 6.9), C₁₆MImBr (IC_{50 L. amazonensis} = 6), C₁₆M₂ImCl (IC_{50 L. amazonensis} = 4.1), C₁₆M₄ImCl (IC_{50 L. amazonensis} = 1.8), (C₁₀)₂MImCl (IC_{50 L. amazonensis} = 1.9), C₁₆Im (IC_{50 L. amazonensis} = 14.6), and C₁₆PyrCl (IC_{50 L. amazonensis} = 4).The effect of IS on reactive oxygen species production, mitochondrial membrane potential, membrane integrity and morphological alterations of promastigotes was determined, as well as on L. amazonensis-infected macrophages. Their cytotoxicity against macrophages and human erythrocytes was also evaluated. The IS C₁₀MImMeS, C₁₆MImPF₆, C₁₆MImBr, C₁₆M₂ImCl, C₁₆M₄ImCl and (C₁₀)₂MImCl, and the compounds C₁₆Im and C₁₆PyrCl killed and inhibited the growth of promastigote forms of L. amazonensis and L. infantum chagasi in a concentration-dependent manner, contributing to a better understanding of the structure-activity relationship of IS against Leishmania. These IS induced ROS production, mitochondrial dysfunction, membrane disruption and morphological alterations in infective forms of L. amazonensis and killed intracellular amastigote forms in very low concentrations (IC_{50 amastigotes} ≤ 0.3), being potential drug candidates against L. amazonensis.

Biotinylation of a MRI/Gd BNCT theranostic agent to access a novel tumour-targeted delivery system

A new biotin based BNCT (Boron Neutron Capture Therapy)-MRI theranostic is here reported (Gd-AL01) in order to exploit the high tumour specificity of biotin and the selectivity of BNCT in a synergistic manner. The key is the preparation of an intermediate where an o-carborane is linked to two amino groups orthogonally protected via the exploitation of two consecutive Mitsunobu reactions. The aim is its functionalisation in two different steps with biotin as the biological vector and Gd-DOTA as the MRI probe and GdNCT agent. Cell uptake was evaluated on HeLa tumour cells overexpressing biotin receptors. The internalised boron is proportional to the concentration of the theranostic agent incubated in the presence of cells. A maximum value of 77 ppm is reached and a well detectable signal intensity increase in the T₁ weighted image of HeLa cells was observed, differently from clinically used GdHPDO3A, where no contrast is detected. These excellent results indicate that Gd-AL01 can be applied as a theranostic probe in BNCT studies.

The anti-tumor effects of imidazolium salts on oral squamous cell carcinoma

BACKGROUND

Imidazolium salts (IS), ionic derivatives of neutral imidazoles, have properties that can be adjusted by structural modifications to their cations and anions, which makes this particular class of compounds a promising option for developing biologically active compounds. The anti-tumor effects of the IS 1-n-butyl-3-methylimidazolium chloride (C₄ MImCl), 1-n-decyl-3-methylimidazolium chloride (C₁₀ MImCl), 1-n-hexadecyl-3-methylimidazolium chloride (C₁₆ MImCl), 1-n-hexadecyl-2,3-dimethylimidazolium chloride (C₁₆ M₂ ImCl), 1-n-octadecyl-3-methylimidazolium chloride (C₁₈ MImCl), 1-n-hexadecyl-3-methylimidazolium methanesulfonate (C₁₆ MImMeS), and 1-n-hexadecyl-2,3- dimethylimidazolium methanesulfonate (C₁₆ M₂ ImMeS) on oral squamous cell carcinoma (OSCC) have been studied here.

METHODS

Oral squamous cell carcinoma cells (CAL27) were incubated with increasing IS doses and then submitted to proliferation (2D), cell death (2D) and spheroid assay (3D).

RESULTS

The IS anti-tumor effect was dependent on both its N-alkyl chain length and anion, whereby C₁₆ MImCl proved to be more effective in combination for inhibiting cell proliferation and cell-cell adhesion, outperforming the methylated C₁₆ M₂ ImCl derivative and, most importantly, the gold standard-cisplatin. In addition, C₁₆ MImCl had little effect on keratinocytes and more pronounced effects on more aggressive tumor cells. It also exhibited similar effects on inducing cell death when compared to Cisplatin. This compound spread to a greater area of the tumor sphere and produced an enhanced number of apoptotic and necrotic cells in the tumor cell line, demonstrating only a small rise in the healthy cells.

CONCLUSION

These data indicate that the effect of C₁₆ MlmCl on OSCC is promising, as it is selective for cancer cells.

In Vitro Amoebicidal Activity of Imidazolium Salts Against Trophozoites

INTRODUCTION

Several strains of the free-living genus Acanthamoeba can cause granulomatous amoebic encephalitis (GAE), a rare chronic and slowly progressive infection of the central nervous system (CNS), and Acanthamoeba keratitis (AK), a sight-threatening eye infectious disease. AK incidence has increased with the popularization of the contact lens wear and its treatment is currently limited and frequently unsuccessful. As imidazolium salts (IS), cationic imidazole derivatives, have promising antimicrobial potential.

MATERIALS AND METHODS

The present study evaluated the amoebicidal activity of four IS; 1-n-hexadecyl-3-methylimidazolium methanesulfonate (C₁₆MImMeS), chloride (C₁₆MImCl) and bis (triluoromethylsulfonyl) imide (C₁₆MImNTf2 ), and 1-methyl-3-n-octadecylimidazolium chloride (C₁₈MImCl), against the Acanthamoeba castellanii (ATCC30010) environmental strain and a clinical isolate (genotype T4).

RESULTS

Three IS showed being lethal to 100% of the Acanthamoeba trophozoites at the minimum inhibitory concentrations of 125 and 62.5 μg/mL (C₁₆MImMeS), 31.25 and 62.5 μg/mL (C₁₆MImCl), and 125 and 125 μg/mL (C₁₈MImCl) for ATCC30010 and isolate T4, respectively. C₁₆MImNTf2 did not demonstrate amoebicidal activity. All active IS caused the hemolysis of erythrocytes. The cytotoxic effect of the IS was tested in RAW macrophages and human brain microvascular endothelial cells, which demonstrated cytotoxicity in all concentrations tested against both cell lines. As a consequence, these IS with amoebicidal activity presented low selectivity index values (SI) (SI < 1.0), demonstrating lack of parasite selectivity.

CONCLUSION

Thus, C₁₆MImMeS, C₁₆MImCl, and C18MImCl seem to hold greater promise as components for contact lens cleaning and disinfection solutions, instead of direct human application.

Imidazolium salts as alternative compounds to control diseases caused by plant pathogenic bacteria

AIMS

To evaluate the inhibitory effect of five structurally different imidazolium salts on the in vitro growth of plant pathogenic bacteria that belong to divergent taxonomic genera as well as their ability to reduce the severity of common bacterial blight of common bean caused by Xanthomonas axonopodis pv. phaseoli and bacterial speck of tomato caused by Pseudomonas syringae pv. tomato.

METHODS AND RESULTS

Growth inhibition of Xanthomonas, Pseudomonas, Erwinia, Pectobacterium and Dickeya strains by imidazolium salts was assessed in vitro by radial diffusion on agar medium and by ressazurin reduction in liquid medium. The reduction of common bacterial blight and bacterial speck symptoms and the area under de disease progress curves were determined by spraying two selected imidazolium salts on healthy plants 48 h prior to inoculation with virulent strains of the bacterial pathogens. All imidazolium salts inhibited the growth of all plant pathogenic bacteria when tested by radial diffusion on agar medium. The strength of inhibition differed among imidazolium salts when tested on the same bacterial strain and among bacterial strains when tested with the same imidazolium salt. In liquid medium, most imidazolium salts presented the same minimum inhibitory concentration (MIC) and minimum bactericidal concentration values (200 µmol l^-1 ), the most notable exception of which was the MIC (at least 1000 µmol l^-1 ) for the dicationic MImC₁₀ MImBr₂ . The imidazolium salts C₁₆ MImBr and C₁₆ MImCl caused significant reductions in the severity of common bacterial blight symptoms when compared with nontreated plants.

CONCLUSION

Imidazolium salts inhibit the in vitro growth of plant pathogenic bacteria and reduce plant disease symptoms to levels comparable to an authorized commercial antibiotic product.

SIGNIFICANCE AND IMPACT OF THE STUDY

New compounds exhibiting broad-spectrum antibacterial activity with potential use in agriculture were identified.

Microbiota potentialized larvicidal action of imidazolium salts against Aedes aegypti (Diptera: Culicidae)

Mosquitoes are important vectors of pathogens due to their blood feeding behavior. Aedes aegypti (Diptera: Culicidae) transmits arboviruses, such as dengue, Zika, and Chikungunya. This species carries several bacteria that may be beneficial for its biological and physiological development. Therefore, studying the response of its microbiota to chemical products could result in vector control. Recently, imidazolium salts (IS) were identified as effective Ae. aegypti larvicides. Considering the importance of the mosquito microbiota, this study addressed the influence of IS on the bacteria of Ae. aegypti larvae. After exposition of larvae to different IS concentrations, the cultured microbiota was identified through culturomics and mass spectrometry, and the non-cultivated microbiota was characterized by molecular markers. In addition, the influence of the IS on axenic larvae was studied for comparison. There was an alteration in both cultivable species and in their diversity, including modifications in bacterial communities. The axenic larvae were less susceptible to the IS, which was increased after exposing these larvae to bacteria of laboratory breeding water. This highlights the importance of understanding the role of the larval microbiota of Ae. aegypti in the development of imidazolium salt-based larvicides. Such effect of IS towards microbiota of Ae. aegypti larvae, through their antimicrobial action, increases their larvicidal potential.

Modular triazine-based carborane-containing carboxylic acids - synthesis and characterisation of potential boron neutron capture therapy agents made of readily accessible building blocks

Based on a modular combination of s-triazine, the well-known 9-mercapto-1,7-dicarba-closo-dodecaborane(12) and commercially available carboxylic acids, namely thioglycolic acid, glycine, and N_α-Boc-l-lysine, several carboxylic acid derivatives were synthesised and fully characterised. The thioglycolic acid derivative was introduced into a peptide hormone by solid phase peptide synthesis. High activity and selective internalisation into peptide receptor-expressing cells was observed. With a very high boron content of twenty boron atoms, these derivatives are interesting as selective Boron Neutron Capture Therapy (BNCT) agents.

Lipoproteins and lipoprotein mimetics for imaging and drug delivery

Lipoproteins are a set of natural nanoparticles whose main role is the transport of fats within the body. While much work has been done to develop synthetic nanocarriers to deliver drugs or contrast media, natural nanoparticles such as lipoproteins represent appealing alternatives. Lipoproteins are biocompatible, biodegradable, non-immunogenic and are naturally targeted to some disease sites. Lipoproteins can be modified to act as contrast agents in many ways, such as by insertion of gold cores to provide contrast for computed tomography. They can be loaded with drugs, nucleic acids, photosensitizers or boron to act as therapeutics. Attachment of ligands can re-route lipoproteins to new targets. These attributes render lipoproteins attractive and versatile delivery vehicles. In this review we will provide background on lipoproteins, then survey their roles as contrast agents, in drug and nucleic acid delivery, as well as in photodynamic therapy and boron neutron capture therapy.

Enantioselective synthesis of adamantylalanine and carboranylalanine and their incorporation into the proteasome inhibitor bortezomib

The incorporation of adamantylalanine and carboranylalanine at the P2 site of bortezomib is well tolerated and provided potent cell permeable proteasome inhibitors with increased off-rates compared to bortezomib. Adamantylalanine and carboranylalanine were synthesized enantioselectively by an asymmetric Strecker reaction on Ellmans tert-butyl sulfinimines.

Insights into the use of gadolinium and gadolinium/boron-based agents in imaging-guided neutron capture therapy applications

Gadolinium neutron capture therapy (Gd-NCT) is currently under development as an alternative approach for cancer therapy. All of the clinical experience to date with NCT is done with (10)B, known as boron neutron capture therapy (BNCT), a binary treatment combining neutron irradiation with the delivery of boron-containing compounds to tumors. Currently, the use of Gd for NCT has been getting more attention because of its highest neutron cross-section. Although Gd-NCT was first proposed many years ago, its development has suffered due to lack of appropriate tumor-selective Gd agents. This review aims to highlight the recent advances for the design, synthesis and biological testing of new Gd- and B-Gd-containing compounds with the task of finding the best systems able to improve the NCT clinical outcome.

When CuAAC 'Click Chemistry' goes heterogeneous

Within the green chemistry context, heterogeneous catalysis is more and more applied to organic synthesis. The well known ‘click chemistry’ and especially its flagship, the copper-catalyzed azide–alkyne cycloaddition reaction (CuAAC), is now catch up by such heterogenisation process and copper ions or metals have been grafted or deposited on or into various solids, such as (bio)polymers, charcoal, silica, zeolites, POM or MOF.

A novel SWCNT platform bearing DOTA and β-cyclodextrin units. "One shot" multidecoration under microwave irradiation

The functionalization of single-walled carbon nanotubes (SWCNTs) via microwave-assisted grafting reactions enables efficient multidecoration in a single step. A novel water-soluble SWCNT platform was prepared via the simple 1,3-dipolar cycloaddition of azomethine ylides under dielectric heating. Thanks to a single grafting reaction the CNT surface binds in a 1 : 1 ratio an amino acidic β-cyclodextrin (β-CD) derivative and the DOTAMA moiety (1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid monoamide). This novel "one shot" synthesis, compared with multistep functionalizations, preserves the SWCNT's structural integrity (TEM images). Besides thermogravimetric analyses, the determination of the amount of β-CD and DOTA moieties grafting onto the SWCNT's surface was performed on the basis of phenolphthalein and gadolinium complexation, respectively.

A theranostic approach based on the use of a dual boron/Gd agent to improve the efficacy of Boron Neutron Capture Therapy in the lung cancer treatment

This study aims at developing an innovative theranostic approach for lung tumor and metastases treatment, based on Boron Neutron Capture Therapy (BNCT). It relies on to the use of low density lipoproteins (LDL) as carriers able to maximize the selective uptake of boron atoms in tumor cells and, at the same time, to quantify the in vivo boron distribution by magnetic resonance imaging (MRI). Tumor cells uptake was initially assessed by ICP-MS and MRI on four types of tumor (TUBO, B16-F10, MCF-7, A549) and one healthy (N-MUG) cell lines. Lung metastases were generated by intravenous injection of a Her2+ breast cancer cell line (i.e. TUBO) in BALB/c mice and transgenic EML4-ALK mice were used as primary tumor model. After neutron irradiation, tumor growth was followed for 30-40 days by MRI. Tumor masses of boron treated mice increased markedly slowly than the control group. From the clinical editor: In this article, the authors described an improvement to existing boron neutron capture therapy. The dual MRI/BNCT agent, carried by LDLs, was able to maximize the selective uptake of boron in tumor cells, and, at the same time, quantify boron distribution in tumor and in other tissues using MRI. Subsequent in vitro and in vivo experiments showed tumor cell killing after neutron irradiation.

The hydroboration reaction as a key for a straightforward synthesis of new MRI-NCT agents

A new lipophilic NCT/MRI agent has been synthesised in only four steps and characterised from the relaxometric point of view. This compound shows a high affinity for LDLs that can be loaded with 300 complexes per particle.

Synthesis of a carborane-containing cholesterol derivative and evaluation as a potential dual agent for MRI/BNCT applications

In this study the synthesis and characterization of a new dual, imaging and therapeutic, agent is proposed with the aim of improving the efficacy of Boron Neutron Capture Therapy (BNCT) in cancer treatment. The agent (Gd-B-AC01) consists of a carborane unit (ten boron atoms) bearing a cholesterol unit on one side (to pursue the incorporation into the liposome bi-layer) and a Gd(iii)/1,4,7,10-tetraazacyclododecane monoamide complex on the other side (as a MRI reporter to attain the quantification of the B/Gd concentration). In order to endow the BNCT agent with specific delivery properties, the liposome embedded with the MRI/BNCT dual probes has been functionalized with a pegylated phospholipid containing a folic acid residue at the end of the PEG chain. The vector allows the binding of the liposome to folate receptors that are overexpressed in many tumor types, and in particular, in human ovarian cancer cells (IGROV-1). An in vitro test on IGROV-1 cells demonstrated that Gd-B-AC01 loaded liposomes are efficient carriers for the delivery of the MRI/BNCT probes to the tumor cells. Finally, the BNCT treatment of IGROV-1 cells showed that the number of surviving cells was markedly smaller when the cells were irradiated after internalization of the folate-targeted GdB10-AC01/liposomes.

Syntheses and structural characterization of o-carboranylamides with direct cage-amide bond

Reactions of lithio-o-carborane with isocyanates under various conditions were studied, and the structural features of the resulting carboranylamides are described. The reactions of o-carborane (o-C2B10H12), n-BuLi (two equiv.) and two equiv. of (substituted) phenylisocyanate, pentylisocyanate and p-ethylphenylthioisocyanate in diethyl ether, respectively, led, after workup, to the corresponding mono-substituted carboranylamide 2a-g and carboranylthioamide 5 in low to moderate yields, and only with RNCO (R = Ph, m-MeOC6H4, pentyl) could disubstituted products 3a-c be isolated. The reaction with phenylisocyanate afforded the mono-amide and di-amide products in a ratio of approximately 1 : 2, whereas in the other two reactions the ratios are approximately 4 : 1 and 3 : 2, respectively. In tetrahydrofuran all the reactions attempted with RNCO (R = Ph, p-IC6H4, m-NCC6H4 and pentyl) gave more monoamide products than those in diethyl ether. With phenylisocyanate no diamide product was isolated and with pentylisocyanate the ratio between monoamide and diamide is approximately 3.5 : 1. The new carboranylamides were characterized by means of elemental analyses, IR and NMR spectroscopy and mass spectrometry, as well as single-crystal X-ray diffraction analyses of 2a-f, 3a and 5.

High yielding synthesis of carboranes under mild reaction conditions using a homogeneous silver(I) catalyst: direct evidence of a bimetallic intermediate

Methods used to prepare functionalized carboranes generally require heating to high temperatures, and thus limits the range of derivatives which can be prepared directly from alkynes. We show here that by using a homogeneous silver(I) catalyst it is now possible to prepare carboranes in good to excellent yield at temperatures below 40 °C, including at room temperature. The process is general and provides an important new synthetic strategy for the preparation of functionalized boron clusters.

Cell cycle arrest, extracellular matrix changes and intrinsic apoptosis in human melanoma cells are induced by Boron Neutron Capture Therapy

Boron Neutron Capture Therapy (BNCT) involves the selective accumulation of boron carriers in tumor tissue followed by irradiation with a thermal or epithermal neutron beam. This therapy is therefore a cellular irradiation suited to treat tumors that have infiltrated into healthy tissues. BNCT has been used clinically to treat patients with cutaneous melanomas which have a high mortality. Human normal melanocytes and melanoma cells were treated with BNCT at different boronophenylalanine concentrations for signaling pathways analysis. BNCT induced few morphological alterations in normal melanocytes, with a negligible increase in free radical production. Melanoma cells treated with BNCT showed significant extracellular matrix (ECM) changes and a significant cyclin D1 decrease, suggesting cell death by necrosis and apoptosis and cell cycle arrest, respectively. BNCT also induced a significant increase in cleaved caspase-3 and a decrease in the mitochondrial electrical potential with selectivity for melanoma cells. Normal melanocytes had no significant differences due to BNCT treatment, confirming the data from the literature regarding the selectivity of BNCT. The results from this study suggest that some signaling pathways are involved in human melanoma treatment by BNCT, such as cell cycle arrest, ECM changes and intrinsic apoptosis.