Prediction of the permeability of neutral drugs inferred from their solvation properties

Determination of drug absorption is an important component of the drug discovery and development process in that it plays a key role in the decision to promote drug candidates to clinical trials. We have developed a method that, on the basis of an analysis of the dynamic distribution of water molecules around a compound obtained by molecular dynamics simulations, can compute a parameter-free value that correlates very well with the compound permeability measured using the human colon adenocarcinoma (Caco-2) cell line assay

EXPERIMENTAL AND MOLECULAR DYNAMICS SIMULATION STUDIES OF PARTITIONING AND TRANSPORT ACROSS LIPID BILAYER MEMBRANES

Most drugs undergo passive transport during absorption and distribution in the body. It is desirable to predict passive permeation of future drug candidates in order to increase the productivity of the drug discovery process. Unlike drug-receptor interactions, there is no receptor map for passive permeability because the process of transport across the lipid bilayer involves multiple mechanisms. This work intends to increase the understanding of permeation of drug-like molecules through lipid bilayers. Drug molecules in solution typically form various species due to ionization, complexation, etc. Therefore, species specific properties must be obtained to bridge the experiment and simulations. Due to the volume contrast between intra- and extravesicular compartments of liposomes, minor perturbations in ionic and binding equilibria become significant contributors to transport rates. Using tyramine as a model amine, quantitative numerical models were developed to determine intrinsic permeability coefficients. The microscopic ionization and binding constants needed for this were independently measured. The partition coefficient in 1,9-decadiene was measured for a series of compounds as a quantitative surrogate for the partitioning into the hydrocarbon region of the bilayer. These studies uncovered an apparent long-range interaction between the two polar substituents that caused deviations in the microscopic pKa values and partition coefficient of tyramine from the expected values. Additionally the partition coefficients in the preferred binding region of the bilayer were also measured by equilibrium uptake into liposomes. All-atom molecular dynamics simulations of lipid bilayers containing tyramine, 4- ethylphenol, or phenylethylamine provided free energies of transfer of these solutes from water to various locations on the transport path. The experimentally measured partition coefficients were consistent with the free energy profiles in showing the barrier in the hydrocarbon region and preferred binding region near the interface. The substituent contributions to these free energies were also quantitatively consistent between the experiments and simulations. Specific interactions between solutes and the bilayer suggest that amphiphiles are likely to show preferred binding in the head group region and that the most of hydrogen bonds involving solutes located inside the bilayer are with water molecules. Solute re-orientation inside the bilayer lowers the partitioning barrier by allowing favorable interactions

Physicochemical Properties Of 131I-Rutin Under Acidic Labeling Condition As A Radiolabeled Compound For The Diagnosis Of Cancer

Radiolabeled rutin (131I-rutin) has potential use in future diagnosis of cancer. The physicochemical characteristics of 131I-rutin are essential in regard to its distribution and accumulation in the body. Therefore, to ensure successful delivery of a labeled compound, it is necessary to evaluate its physicochemical properties. The labeling of 131I-rutin was accomplished using the oxidation method assisted by Chloramine-T under acidic conditions. Radiochemical purity value was measured by thin-layer chromatography (TLC-SG F254) using 100% methanol as the mobile phase. The electrical charge of 131I-rutin was determined by the paper electrophoresis. Moreover, the lipophilicity (P) was evaluated by the partition coefficient in the organic-water liquid. Plasma protein binding was determined in vitro by precipitation method using a 5% trichloroacetic acid (TCA) solution. The results showed that 131I-rutin has a neutral charge and a lipophilicity value (Log P) of 0.395 ± 0.203 (hydrophilic), and was bound to human blood plasma proteins with a percentage of 69.36% ± 1.88%.Radiolabeled rutin (131I-rutin) has potential use in future diagnosis of cancer. The physicochemical characteristics of 131I-rutin are essential in regard to its distribution and accumulation in the body. Therefore, to ensure successful delivery of a labeled compound, it is necessary to evaluate its physicochemical properties. The labeling of 131I-rutin was accomplished using the oxidation method assisted by Chloramine-T under acidic conditions. Radiochemical purity value was measured by thin-layer chromatography (TLC-SG F254) using 100% methanol as the mobile phase. The electrical charge of 131I-rutin was determined by the paper electrophoresis. Moreover, the lipophilicity (P) was evaluated by the partition coefficient in the organic-water liquid. Plasma protein binding was determined in vitro by precipitation method using a 5% trichloroacetic acid (TCA) solution. The results showed that 131I-rutin has a neutral charge and a lipophilicity value (Log P) of 0.395 ± 0.203 (hydrophilic), and was bound to human blood plasma proteins with a percentage of 69.36% ± 1.88%

Thermodynamics of the Abraham General Solvation Model: Solubility and Partition Aspects

Experimental mole fraction solubilities of several carboxylic acids (2-methoxybenzoic acid, 4-methoxybenzoic acid, 4-nitrobenzoic acid, 4-chloro-3-nitrobenzoic acid, 2-chloro-5-nitrobenzoic acid,2-methylbenzoic acid and ibuprofen) and 9-fluorenone, thianthrene and xanthene were measured in a wide range of solvents of varying polarity and hydrogen-bonding characteristics. Results of these measurements were used to calculate gas-to-organic solvent and water-to-organic solvent solubility ratios, which were then substituted into known Abraham process partitioning correlations. The molecular solute descriptors that were obtained as the result of these computations described the measured solubility data to within an average absolute deviation of 0.2 log units. The calculated solute descriptors also enable one to estimate many chemically, biologically and pharmaceutically important properties for the ten solutes studied using published mathematical correlations

P-glycoprotein (ABCB1) - weak dipolar interactions provide the key to understanding allocrite recognition, binding, and transport

P-glycoprotein (ABCB1) is the first discovered mammalian member of the large family of ATP binding cassette (ABC) transporters. It facilitates the movement of compounds (called allocrites) across membranes, using the energy of ATP binding and hydrolysis. Here, we review the thermodynamics of allocrite binding and the kinetics of ATP hydrolysis by ABCB1. In combination with our previous molecular dynamics simulations, these data lead to a new model for allocrite transport by ABCB1. In contrast to previous models, we take into account that the transporter was evolutionarily optimized to operate within a membrane, which dictates the nature of interactions. Hydrophobic interactions drive lipid-water partitioning of allocrites, the transport process's first step. Weak dipolar interactions (including hydrogen bonding, π-π stacking, and π-cation interactions) drive allocrite recognition, binding, and transport by ABCB1 within the membrane. Increasing the lateral membrane packing density reduces allocrite partitioning but enhances dipolar interactions between allocrites and ABCB1. Allocrite flopping (or reorientation of the polar part towards the extracellular aqueous phase) occurs after hydrolysis of one ATP molecule and opening of ABCB1 at the extracellular side. Rebinding of ATP re-closes the transporter at the extracellular side and expels the potentially remaining allocrite into the membrane. The high sensitivity of the steady-state ATP hydrolysis rate to the nature and number of dipolar interactions, as well as to the dielectric constant of the membrane, points to a flopping process, which occurs to a large extent at the membrane-transporter interface. The proposed unidirectional ABCB1 transport cycle, driven by weak dipolar interactions, is consistent with membrane biophysics

The Different Faces of Ibuprofen-Based Ionic Liquids and Eutectic Systems: Promising Innovative Ionic-Liquid-Based Formulations of an Over-the-Counter Anti-Inflammatory Drug

The global goal of the current thesis is to demonstrate the feasibility of the ionic liquids (ILs) platform to boost “old” drugs efficiency. With this ground, cholinium- and imidazolium- based ILs were used to formulate pharmaceutically active ILs (API-ILs) and eutectic systems with ibuprofen (Ibu) as parent active pharmaceutical ingredient (API). The aqueous solubility, water and simulated biological fluids, of the IBU-based ILs and eutectics relatively to Ibu neutral and salt form (sodium ibuprofen) were assessed. Jointly, insights into task-specific fluorinated ILs that reduce the impact of the addition of water upon the IL’s H-bond acceptance ability, a key factor to obtain functionalized materials to be used in the dissolution of drugs or biomolecules, were attained. The cytotoxic profiles were characterized for both IBU-based ILs and eutectics, as well as for the parent API (Ibu), using two human cells lines, colon carcinoma cells (Caco-2) and hepatocellular carcinoma cells (HepG-2). The biocompatibility of all Ibu formulations was also evaluated through a hemolytic activity assay. Moreover, the anti-inflammatory properties of all Ibu formulations, ILs, eutectics, and parent API, were assessed through the inhibition of bovine serum albumin (BSA) denaturation and inhibition of cyclooxygenases (COX-1 and COX-2). The assessment of ionicity, through measurements of density, viscosity, and ionic conductivity, was carried out to evaluate the formation of ion-pairs or clusters that enhance membrane permeation. In the end, an in vitro skin permeation assay was attained through Skin Parallel Artificial Membrane Permeability Assays (Skin-PAMPA) to evaluate the Ibu-based ILs and eutectics skin permeability. The evaluation of the permeation potential allows to guide the design of transdermal drug delivery systems. The results of this thesis comprise a proof of concept for the feasibility of task-specific ILs and IL-based eutectics, namely API-ILs and API-based eutectics, in the development of novel drug delivery systems, and more broadly for biological, biochemical, and pharmaceutical applications.O objetivo global da presente tese é demonstrar a viabilidade do uso da plataforma de líquidos iónicos (LIs) para aumentar a eficiência de fármacos “antigos”. Desta forma, LIs à base de colínio e imidazólio foram usados para formular LIs farmacologicamente ativos (API- ILs) e sistemas eutécticos com ibuprofeno (Ibu) como princípio ativo (API) de origem. A solubilidade aquosa, em água e em fluidos biológicos simulados, dos LIs à base de Ibu e eutécticos em relação ao Ibu neutro e na forma de sal (ibuprofeno sódico) foi avaliada. Foram também obtidas informações sobre LIs fluorados que reduzem o impacto da adição de água devido à sua capacidade de aceitação de ligações de hidrogénio, um fator chave para se obter materiais funcionalizados para serem usados na dissolução de fármacos ou biomoléculas. Os perfis citotóxicos foram caracterizados tanto para ILs baseados em Ibu como para os sistemas eutécticos e o API de origem (Ibu), usando duas linhagens de células humanas, células de carcinoma de cólon (Caco-2) e células de carcinoma hepatocelular (HepG-2). A biocompatibilidade de todas as formulações de Ibu também foi avaliada através de um ensaio de atividade hemolítica. As propriedades anti-inflamatórias de todas as formulações de Ibu, ILs, eutéticos e API de origem, foram avaliadas através da inibição da desnaturação da albumina sérica bovina (BSA) e inibição das ciclooxigenases (COX-1 e COX-2). A avaliação da ionicidade através da medição de densidade, viscosidade e condutividade iónica, foi realizada para avaliar a formação de pares iónicos ou aglomerados que poderão aumentar a permeação nas membranas. Por fim, foi realizado um ensaio de permeação cutânea in vitro através do sistema Skin Parallel Artificial Membrane Permeability Assay (Skin-PAMPA) para avaliar a permeabilidade cutânea dos Lis e eutéticos à base de Ibu. A avaliação do potencial de permeação permite orientar a correta formulação de um novo sistema de entrega transdérmica de fármacos. Os resultados desta tese compreendem uma prova de conceito para a viabilidade do uso de LIs e eutécticos baseados em IL, nomeadamente API-ILs e eutécticos baseados em API, no desenvolvimento de novos sistemas de administração de fármacos e, mais amplamente, para aplicações biológicas, bioquímicas e aplicações farmacêuticas

In silico activity and ADMET profiling of phytochemicals from Ethiopian indigenous aloes using pharmacophore models

In silico profiling is used in identification of active compounds and guide rational use of traditional medicines. Previous studies on Ethiopian indigenous aloes focused on documentation of phytochemical compositions and traditional uses. In this study, ADMET and drug-likeness properties of phytochemicals from Ethiopian indigenous aloes were evaluated, and pharmacophore-based profiling was done using Discovery Studio to predict therapeutic targets. The targets were examined using KEGG pathway, gene ontology and network analysis. Using random-walk with restart algorithm, network propagation was performed in CODA network to find diseases associated with the targets. As a result, 82 human targets were predicted and found to be involved in several molecular functions and biological processes. The targets also were linked to various cancers and diseases of immune system, metabolism, neurological system, musculoskeletal system, digestive system, hematologic, infectious, mouth and dental, and congenital disorder of metabolism. 207 KEGG pathways were enriched with the targets, and the main pathways were metabolism of steroid hormone biosynthesis, lipid and atherosclerosis, chemical carcinogenesis, and pathways in cancer. In conclusion, in silico target fishing and network analysis revealed therapeutic activities of the phytochemicals, demonstrating that Ethiopian indigenous aloes exhibit polypharmacology effects on numerous genes and signaling pathways linked to many diseases

The Interaction of Temozolomide with Blood Components Suggests the Potential Use of Human Serum Albumin as a Biomimetic Carrier for the Drug

The interaction of temozolomide (TMZ) (the main chemotherapeutic agent for brain tumors) with blood components has not been studied at the molecular level to date, even though such information is essential in the design of dosage forms for optimal therapy. This work explores the binding of TMZ to human serum albumin (HSA) and alpha-1-acid glycoprotein (AGP), as well as to blood cell-mimicking membrane systems. Absorption and fluorescence experiments with model membranes indicate that TMZ does not penetrate into the lipid bilayer, but binds to the membrane surface with very low affinity. Fluorescence experiments performed with the plasma proteins suggest that in human plasma, most of the bound TMZ is attached to HSA rather than to AGP. This interaction is moderate and likely mediated by hydrogen-bonding and hydrophobic forces, which increase the hydrolytic stability of the drug. These experiments are supported by docking and molecular dynamics simulations, which reveal that TMZ is mainly inserted in the subdomain IIA of HSA, establishing -stacking interactions with the tryptophan residue. Considering the overexpression of albumin receptors in tumor cells, our results propose that part of the administered TMZ may reach its target bound to plasma albumin and suggest that HSA-based nanocarriers are suitable candidates for designing biomimetic delivery systems that selectively transport TMZ to tumor cells