In Vivo Application of Carboranes for Boron Neutron Capture Therapy (BNCT): Structure, Formulation and Analytical Methods for Detection

Carboranes have emerged as one of the most promising boron agents in boron neutron capture therapy (BNCT). In this context, in vivo studies are particularly relevant, since they provide qualitative and quantitative information about the biodistribution of these molecules, which is of the utmost importance to determine the efficacy of BNCT, defining their localization and (bio)accumulation, as well as their pharmacokinetics and pharmacodynamics. First, we gathered a detailed list of the carboranes used for in vivo studies, considering the synthesis of carborane derivatives or the use of delivery system such as liposomes, micelles and nanoparticles. Then, the formulation employed and the cancer model used in each of these studies were identified. Finally, we examined the analytical aspects concerning carborane detection, identifying the main methodologies applied in the literature for ex vivo and in vivo analysis. The present work aims to identify the current strengths and weakness of the use of carboranes in BNCT, establishing the bottlenecks and the best strategies for future applications

Exploiting Blood Transport Proteins as Carborane Supramolecular Vehicles for Boron Neutron Capture Therapy

Carboranes are promising agents for applications in boron neutron capture therapy (BNCT), but their hydrophobicity prevents their use in physiological environments. Here, by using reverse docking and molecular dynamics (MD) simulations, we identified blood transport proteins as candidate carriers of carboranes. Hemoglobin showed a higher binding affinity for carboranes than transthyretin and human serum albumin (HSA), which are well-known carborane-binding proteins. Myoglobin, ceruloplasmin, sex hormone-binding protein, lactoferrin, plasma retinol-binding protein, thyroxine-binding globulin, corticosteroid-binding globulin and afamin have a binding affinity comparable to transthyretin/HSA. The carborane@protein complexes are stable in water and characterized by favorable binding energy. The driving force in the carborane binding is represented by the formation of hydrophobic interactions with aliphatic amino acids and BH-π and CH-π interactions with aromatic amino acids. Dihydrogen bonds, classical hydrogen bonds and surfactant-like interactions also assist the binding. These results (i) identify the plasma proteins responsible for binding carborane upon their intravenous administration, and (ii) suggest an innovative formulation for carboranes based on the formation of a carborane@protein complex prior to the administration

Interaction of Au(iii) with amino acids: a vade mecum for medicinal chemistry and nanotechnology

Au(iii) is highly reactive. At odds with its reduced counterpart, Au(i), it is hardly present in structural databases. And yet, it is the starting reactant to form gold nanoclusters (AuNCs) and the constitutive component of a new class of drugs. Its reactivity is a world apart from that of the iso-electronic Pt(ii) species. Rather than DNA, it targets proteins. Its interaction with amino acid residues is manifold. It can strongly interact with the residue backbones, amino acid side chains and protein ends, it can form appropriate complexes whose stabilization energy reaches up to more than 40 kcal mol−1, it can affect the pKa of amino acid residues, and it can promote charge transfer from the residues to the amount that it is reduced. Here, quantum chemical calculations provide quantitative information on all the processes where Au(iii) can be involved. A myriad of structural arrangements are examined in order to determine the strongest interactions and quantify the amount of charge transfer between protonated and deprotonated residues and Au(iii). The calculated interaction energies of the amino acid side chains with Au(iii) quantitatively reproduce the experimental tendency of Au(iii) to interact with selenocysteine, cysteine and histidine and negatively charged amino acids such as Glu and Asp. Also, aromatic residues such as tyrosine and tryptophan strongly interact with Au(iii). In proteins, basic pH plays a role in the deprotonation of cysteine, lysine and tyrosine and strongly increases the binding affinity of Au(iii) toward these amino acids. The amino acid residues in the protein can also trigger the reduction of Au(iii) ions. Sulfur-containing amino acids (cysteine and methionine) and selenocysteine provide almost one electron to Au(iii) upon binding. Tyrosine also shows a considerable tendency to act as a reductant. Other amino acids, commonly identified in Au-protein adducts, such as Ser, Trp, Thr, Gln, Glu, Asn, Asp, Lys, Arg and His, possess a notable reducing power toward Au(iii). These results and their discussion form a vade mecum that can find application in medicinal chemistry and nanotech applications of Au(iii)

Dissecting the supramolecular dispersion of fullerenes by proteins/peptides: Amino acid ranking and driving forces for binding to c60

Molecular dynamics simulations were used to quantitatively investigate the interactions between the twenty proteinogenic amino acids and C60. The conserved amino acid backbone gave a constant energetic interaction ~5.4 kcal mol−1, while the contribution to the binding due to the amino acid side chains was found to be up to ~5 kcal mol−1 for tryptophan but lower, to a point where it was slightly destabilizing, for glutamic acid. The effects of the interplay between van der Waals, hydrophobic, and polar solvation interactions on the various aspects of the binding of the amino acids, which were grouped as aromatic, charged, polar and hydrophobic, are discussed. Although π–π interactions were dominant, surfactant‐like and hydrophobic effects were also observed. In the molecular dynamics simulations, the interacting residues displayed a tendency to visit configura-tions (i.e., regions of the Ramachandran plot) that were absent when C60 was not present. The amino acid backbone assumed a “tepee‐like” geometrical structure to maximize interactions with the fullerene cage. Well‐defined conformations of the most interactive amino acids (Trp, Arg, Met) side chains were identified upon C60 binding

Identification of Potential Drug Targets of Calix[4]arene by Reverse Docking

Calixarenes are displaying great potential for the development of new drug delivery systems, diagnostic imaging, biosensing devices and inhibitors of biological processes. In particular, calixarene derivatives are able to interact with many different enzymes and function as inhibitors. By screening of the potential drug target database (PDTD) with a reverse docking procedure, we identify and discuss a selection of 100 proteins that interact strongly with calix[4]arene. We also discover that leucine (23.5 %), isoleucine (11.3 %), phenylalanines (11.3 %) and valine (9.5 %) are the most frequent binding residues followed by hydrophobic cysteines and methionines and aromatic histidines, tyrosines and tryptophanes. Top binders are peroxisome proliferator-activated receptors that already are targeted by commercial drugs, demonstrating the practical interest in calix[4]arene. Nuclear receptors, potassium channel, several carrier proteins, a variety of cancer-related proteins and viral proteins are prominent in the list. It is concluded that calix[4]arene, which is characterized by facile access, well-defined conformational characteristics, and ease of functionalization at both the lower and higher rims, could be a potential lead compound for the development of enzyme inhibitors and theranostic platforms

Dissecting the Interactions between Chlorin e6 and Human Serum Albumin

Chlorin e6 (Ce6) is among the most used sensitizers in photodynamic (PDT) and sonodynamic (SDT) therapy; its low solubility in water, however, hampers its clinical exploitation. Ce6 has a strong tendency to aggregate in physiological environments, reducing its performance as a photo/sono-sensitizer, as well as yielding poor pharmacokinetic and pharmacodynamic properties. The interaction of Ce6 with human serum albumin (HSA) (i) governs its biodistribution and (ii) can be used to improve its water solubility by encapsulation. Here, using ensemble docking and microsecond molecular dynamics simulations, we identified the two Ce6 binding pockets in HSA, i.e., the Sudlow I site and the heme binding pocket, providing an atomistic description of the binding. Comparing the photophysical and photosensitizing properties of Ce6@HSA with respect to the same properties regarding the free Ce6, it was observed that (i) a red-shift occurred in both the absorption and emission spectra, (ii) a maintaining of the fluorescence quantum yield and an increase of the excited state lifetime was detected, and (iii) a switch from the type II to the type I mechanism in a reactive oxygen species (ROS) production, upon irradiation, took place

A multidisciplinary study of chemico-physical properties of different classes of 2-aryl-5(or 6)-nitrobenzimidazoles: NMR, electrochemical behavior, ESR, and DFT calculations

Continuing in our researches on the syntheses, reactivity, pharmacological/biological activities of heterocyclic compounds containing one or more nitrogen atoms we have examined some chemico-physical properties (1H and 13C NMR, electrochemical behavior, and ESR) of three series of 2-aryl-5(or 6)-nitrobenzimidazoles (1–3) variously substituted in the 2-aryl ring. The electrochemical behavior of the nitro group on the benzimidazole ring has been studied by cyclic voltammetry. This has allowed to point out both the reversibility, the formal potential, and the number of electrons involved in the electrochemical processes, and to evaluate the effect of the substituents present on the aryl ring. The data collected have been able to furnish a complete picture of electronic distribution and have been supported by DFT calculations

Selective ion transport in large-area graphene oxide membrane filters driven by the ionic radius and electrostatic interactions

Filters made of graphene oxide (GO) are promising for purification of water and selective sieving of specific ions; while some results indicate the ionic radius as the discriminating factor in the sieving efficiency, the exact mechanism of sieving is still under debate. Furthermore, most of the reported GO filters are planar coatings with a simple geometry and an area much smaller than commercial water filters. Here, we show selective transport of different ions across GO coatings deposited on standard hollow fiber filters with an area >10 times larger than typical filters reported. Thanks to the fabrication procedure, we obtained a uniform coating on such complex geometry with no cracks or holes. Monovalent ions like Na+ and K+ can be transported through these filters by applying a low electric voltage, while divalent ions are blocked. By combining transport and adsorption measurements with molecular dynamics simulations and spectroscopic characterization, we unravel the ion sieving mechanism and demonstrate that it is mainly due to the interactions of the ions with the carboxylate groups present on the GO surface at neutral pH

Amino acid modified graphene oxide for the simultaneous capture and electrochemical detection of glyphosate

Amino acid modified graphene oxide derivatives (GO-AA) are herein proposed as active materials for the capture and consequent electrochemical detection of organic pollutants in aqueous media. Glyphosate (GLY), an herbicide present in many water compartments, was chosen as benchmark species to test the effectiveness of these materials for its electroactive nature, allowing direct evidence of the capture event. L-Lysine, L-Arginine or LMethionine were grafted on GO surface through epoxide ring opening reaction, promoting the amino acids binding and the concomitant partial reduction of GO. The synthetic process results in a charge resistance drop from 8.1 KΩ for GO to 0.8–2.1 KΩ for the various GO-AA, supporting the applicability of these materials in electrochemical sensing. The resulting GO-Lysine, GO-Arginine and GO-Methionine were exploited for GLY adsorption from water. GO-Lysine was found to have the strongest interaction with GLY, with a removal efficiency of 76 % after 1 h, which is about two-fold higher than those of granular activated carbon, the industrial benchmark adsorbent. GO-AAs outperform the pristine unmodified material also when exploited as active materials for the capturing and following electrochemical detection of GLY. GO-Lysine showed the best sensitivity and allowed the recognition of GLY in water even when present at concentration levels down to 2 μg/L. Molecular dynamics simulations confirmed that the enhanced performance of this material can be ascribed to the hydrogen bond and salt bridge interactions between Lys moieties and GLY, originated from hydrogen bond and salt bridge interactions

Identification of Blood Transport Proteins to Carry Temoporfin: A Domino Approach from Virtual Screening to Synthesis and In Vitro PDT Testing

Temoporfin (mTHPC) is one of the most promising photosensitizers used in photodynamic therapy (PDT). Despite its clinical use, the lipophilic character of mTHPC still hampers the full exploitation of its potential. Low solubility in water, high tendency to aggregate, and low biocompatibility are the main limitations because they cause poor stability in physiological environments, dark toxicity, and ultimately reduce the generation of reactive oxygen species (ROS). Applying a reverse docking approach, here, we identified a number of blood transport proteins able to bind and disperse monomolecularly mTHPC, namely apohemoglobin, apomyoglobin, hemopexin, and afamin. We validated the computational results synthesizing the mTHPC-apomyoglobin complex (mTHPC@apoMb) and demonstrated that the protein monodisperses mTHPC in a physiological environment. The mTHPC@apoMb complex preserves the imaging properties of the molecule and improves its ability to produce ROS via both type I and type II mechanisms. The effectiveness of photodynamic treatment using the mTHPC@apoMb complex was then demonstrated in vitro. Blood transport proteins can be used as molecular “Trojan horses” in cancer cells by conferring mTHPC (i) water solubility, (ii) monodispersity, and (iii) biocompatibility, ultimately bypassing the current limitations of mTHPC