Comparative analysis of the interaction of capecitabine and gefitinib with human serum albumin using 19 F nuclear magnetic resonance-based approach

Modulation of the photobehavior of gefitinib and its phenolic metabolites by human transport proteins

The photobiological damage that certain drugs or their metabolites can photosensitize in proteins is generally associated with the nature of the excited species that are generated upon interaction with UVA light. In this regard, the photoinduced damage of the anticancer drug gefitinib (GFT) and its two main photoactive metabolites GFT-M1 and GFT-M2 in cellular milieu was recently investigated. With this background, the photophysical properties of both the drug and its metabolites have now been studied in the presence of the two main transport proteins of human plasma, i.e., serum albumin (HSA) and α1-acid glycoprotein (HAG) upon UVA light excitation. In general, the observed photobehavior was strongly affected by the confined environment provided by the protein. Thus, GFT-M1 (which exhibits the highest phototoxicity) showed the highest fluorescence yield arising from long-lived HSA-bound phenolate-like excited species. Conversely, locally excited (LE) states were formed within HAG, resulting in lower fluorescence yields. The reserve was true for GFT-M2, which despite being also a phenol, led mainly to formation of LE states within HSA, and phenolate-like species (with a minor contribution of LE) inside HAG. Finally, the parent drug GFT, which is known to form LE states within HSA, exhibited a parallel behavior in the two proteins. In addition, determination of the association constants by both absorption and emission spectroscopy revealed that the two metabolites bind stronger to HSA than the parent drug, whereas smaller differences were observed for HAG. This was further confirmed by studying the competing interactions between GFT or its metabolites with the two proteins using fluorescence measurements. These above experimental findings were satisfactorily correlated with the results obtained by means of molecular dynamics (MD) simulations, which revealed the high affinity binding sites, the strength of interactions and the involved amino acid residues. In general, the differences observed in the photobehavior of the drug and its two photoactive metabolites in protein media are consistent with their relative photosensitizing potentials.

[Advances in chromatography in the study of drug-plasma protein interactions]

After entering human blood circulation, small-molecule drugs interact extensively with various plasma proteins, such as human serum albumin and α1-acid glycoprotein. These interactions profoundly affect the distribution of drugs in vivo and the binding of drugs to targets, thus affecting the efficacy of drugs. In-depth investigation of drug-plasma protein interactions is of great significance for the optimization of drug properties, the development of new drugs, risk assessment, and combination therapy of drugs. Therefore, it is essential to develop highly efficient, sensitive, and accurate methods for elucidating drug-plasma protein interactions. Chromatography is a powerful tool with high throughput, high separation performance, and high sensitivity in the characterization of drug-protein interactions. High-performance affinity chromatography (HPAC) and capillary electrophoresis (CE) have been widely utilized in this field. These methods include the determination of the effects of the posttranslational modification of proteins on binding and the competitive binding of multiple drugs. In addition, various chromatographic methods are used to obtain interaction information such as the binding constant, binding-site number, and dissociation rate constant. In this review, the common strategies and recent advances in HPAC and CE in the study of drug-plasma protein interactions are briefly reviewed. The immobilization methods of proteins, the principles and applications of frontal analysis, zonal elution, ultrafast affinity extraction, peak profiling, and peak decay analysis are discussed for HPAC and affinity capillary electrophoresis (ACE) and capillary electrophoresis frontal analysis (CE-FA) for CE. HPAC relies on the fixation of proteins on the surfaces of chromatographic stationary phases by covalent linking or physical adsorption, followed by obtaining the drug-protein interaction information through a variety of chromatographic methods. In the frontal chromatography analysis, mobile phases with different concentrations of drugs are passed through the HPAC column to obtain different breakthrough times. The process can determine the number of drug binding sites and the binding constant of each site in the affinity protein with high accuracy. The zonal elution method can detect the drug binding sites on proteins using site-specific probes to determine whether there is competition between drugs and probes. The sample consumption and analysis time of the zonal elution method are much less than those in frontal chromatography analysis. The ultrafast affinity extraction method can inject complex samples, such as serum, into affinity columns to determine the free drug components. It can measure the combination and dissociation constants of drug-protein interactions by changing the chromatography flow rate. Peak profiling and peak decay analyses are both effective methods for investigating the dissociation of drugs and proteins. In CE analysis, the drug and protein samples are dissolved in an electrophoresis buffer, and their interactions are measured during electrophoresis with high accuracy and low sample consumption. However, the adsorption of proteins on the capillary wall can compromise CE performance. Common CE methods in drug-protein interaction analysis are ACE and CE-FA. ACE is usually performed by changing the effective mobility of drugs via the addition of different concentrations of proteins. This method has been widely used, and several variant techniques have been developed recently. CE-FA involves the sampling of a drug premixed at a known concentration with a target protein. Compared with other CE methods, CE-FA exhibits the unique advantages of high throughput, automatic online analysis, and the ability to determine high-order drug-protein interactions. Finally, the shortcomings of current chromatography methods are summarized, and the application prospects and development direction of chromatography technology in the field of drug-plasma protein interaction research are discussed.

Biomolecular interactions and binding dynamics of tyrosine kinase inhibitor erdafitinib, with human serum albumin

Erdafitinib is an approved tyrosine kinase inhibitor that inhibits fibroblast growth factor receptor. It has been described as one of the potent anti-tumor drugs especially for the treatment of urothelial carcinoma. In this study, we have investigated the binding dynamics of erdafitinib with human serum albumin (HSA) using multiple spectroscopic techniques. The outcome of the results suggests the occurrence of static quenching during the interaction of HSA with erdafitinib which leads to the formation of non-fluorescent HSA-erdafitinib ground state complex. Formation of HSA-erdafitinib complex was also confirmed from the findings of absorption spectral analysis. The changes in microenvironment around hydrophobic domains (especially tryptophan and tyrosine) were deciphered from fluorescence spectroscopy which was further confirmed by synchronous spectral analysis. In order to gain insight into the binding site of erdafitinib in HSA, molecular docking combined with competitive displacement assay was performed. The modified form of Stern Volmer equation was used to estimate various binding parameters including number of binding sites. The findings are indicative of a single binding site (n = 1) with binding constant in the order of 10⁴. The negative values of thermodynamic parameters like ΔG, ΔH and ΔS were suggestive of the binding reaction being spontaneous and exothermic, while the hydrogen bonds and Van der Waals interactions being the major forces present between HSA and erdafitinib. Circular dichroism spectral analysis revealed the alterations in the conformation of HSA structure and reduction in its α-helical content.Communicated by Ramaswamy H. Sarma[Formula: see text].

Probing the binding mechanism of capecitabine to human serum albumin using spectrometric methods, molecular modeling, and chemometrics approach

Capecitabine as a prodrug of 5-Fluorouracil plays an important role in the treatment of breast and gastrointestinal cancers. Herein, in view of the importance of this drug in chemotherapy, interaction mechanism between Capecitabine (CAP) and human serum albumin (HSA) as a major transport protein in the blood circulatory system has been investigated by using a combination of spectroscopic and molecular modeling methods. The fluorescence spectroscopic results revealed that capecitabine could effectively quench the intrinsic fluorescence of HSA through a static quenching mechanism. Evaluation of the thermodynamic parameters suggested that the binding process was spontaneous while hydrogen bonds and van der Waals forces played a major role in this interaction. The value of the binding constant (K_b = 1.820 × 10⁴) suggested a moderate binding affinity between CAP and HSA which implies its easy diffusion from the circulatory system to the target tissue. The efficiency of energy transfer and the binding distance between the donor (HSA) and acceptor (CAP) were determined according to forster theory of nonradiation energy transfer as 0.410 and 4.135 nm, respectively. Furthermore, UV-Vis spectroscopic results confirmed that the interaction was occurred between HSA and CAP and caused conformational and micro-environmental changes of HSA during the interaction. Multivariate curve resolution-alternating least square (MCR-ALS) methodology as an efficient chemometric tool was used to separate the overlapped spectra of the species. The MCR-ALS result was exploited to estimate the stoichiometry of interaction and to provide concentration and structural information about HSA-CAP interactions. Molecular docking studies suggested that CAP binds mainly to the subdomain IIA of HSA, which were compatible with those obtained by experimental data. Finally, molecular dynamics simulation (MD) was performed on the best docked complex by considering the permanence and flexibility of HSA-CAP complex in the binding site. MD result showed that CAP could steadily bind to HSA in the site I based on the formation of hydrogen bond and π-π stacking interaction in addition to hydrophobic force.

Computational and spectroscopic analysis of interaction between food colorant citrus red 2 and human serum albumin

The main aim of this work was to gain insight into the binding properties between a food colorant, citrus red 2 (CR), and human serum albumin (HSA), which is the predominant protein in blood plasma. Here, computer simulations and multiple spectroscopies were applied to predict and characterize the interaction between CR and HSA. Docking and molecular dynamics presented a stable binding configuration with low fluctuations. Fluorescence spectroscopy and lifetime results suggested that the CR–HSA combination undergoes static quenching mechanism with binding constant of 10⁵ L/mol. Displacement analysis showed the binding of CR at site I of HSA, which agrees with the docking results. The binding process occured spontaneously and was mainly driven by electrostatic interactions. Synchronous fluorescence and circular dichroism measurements demonstrate the changes in the microenvironment residues and α-helix contents of HSA induced by CR. The computational and experimental techniques are complementary to clearly understand the food colorant transportation and bioaccumulative toxicity in the human body.

Comparative studies on the human serum albumin binding of the clinically approved EGFR inhibitors gefitinib, erlotinib, afatinib, osimertinib and the investigational inhibitor KP2187

Binding interactions between human serum albumin (HSA) and four approved epidermal growth factor receptor (EGFR) inhibitors gefitinib (GEF), erlotinib (ERL), afatinib (AFA), osimertinib (OSI), as well as the experimental drug KP2187, were investigated by means of spectrofluorometric and molecular modelling methods. Steady-state and time resolved spectrofluorometric techniques were carried out, including direct quenching of protein fluorescence and site marker displacement measurements. Proton dissociation processes and solvent dependent fluorescence properties were investigated as well. The EGFR inhibitors were predominantly presented in their single protonated form (HL⁺) at physiological pH except ERL, which is charge-neutral. Significant solvent dependent fluorescence properties were found for GEF, ERL and KP2187, namely their emission spectra show strong dependence on the polarity and the hydrogen bonding ability of the solvents. The inhibitors proved to be bound at site I of HSA (in subdomain IIA) in a weak-to-moderate fashion (logK' 3.9-4.9) using spectrofluorometry. OSI (logK' 4.3) and KP2187 can additionally bind in site II (in subdomain IIIA), while GEF, ERL and AFA clearly show no interaction here. Docking methods qualitatively confirmed binding site preferences of compounds GEF and KP2187, and indicated that they probably bind to HSA in their neutral forms. Binding constants calculated on the basis of the various experimental data indicate a weak-to-moderate binding on HSA, only OSI exhibits somewhat higher affinity towards this protein. However, model calculations performed at physiological blood concentrations of HSA resulted in high (ca. 90%) bound fractions for the inhibitors, highlighting the importance of plasma protein binding.

Glycation of human serum albumin impairs binding to the glucagon-like peptide-1 analogue liraglutide

The long-acting glucagon-like peptide-1 analogue liraglutide has proven efficiency in the management of type 2 diabetes and also has beneficial effects on cardiovascular diseases. Liraglutide's protracted action highly depends on its capacity to bind to albumin via its palmitic acid part. However, in diabetes, albumin can undergo glycation, resulting in impaired drug binding. Our objective in this study was to assess the impact of human serum albumin (HSA) glycation on liraglutide affinity. Using fluorine labeling of the drug and ¹⁹F NMR, we determined HSA affinity for liraglutide in two glycated albumin models. We either glycated HSA in vitro by incubation with glucose (G25- or G100-HSA) or methylglyoxal (MGO-HSA) or purified in vivo glycated HSA from the plasma of diabetic patients with poor glycemic control. Nonglycated commercial HSA (G0-HSA) and HSA purified from plasma of healthy individuals served as controls. We found that glycation decreases affinity for liraglutide by 7-fold for G100-HSA and by 5-fold for MGO-HSA compared with G0-HSA. A similarly reduced affinity was observed for HSA purified from diabetic individuals compared with HSA from healthy individuals. Our results reveal that glycation significantly impairs HSA affinity to liraglutide and confirm that glycation contributes to liraglutide's variable therapeutic efficiency, depending on diabetes stage. Because diabetes is a progressive disease, the effect of glycated albumin on liraglutide affinity found here is important to consider when diabetes is managed with this drug.

Multinuclear NMR Measurements and DFT Calculations for Capecitabine Tautomeric Form Assignment in a Solution

The molecular structure of capecitabine (a widely applied prodrug of 5-fluorouracil) was studied by multinuclear NMR measurements and DFT quantum mechanical calculations. One or two tautomeric forms in a solution were detected depending on the solvent used. In the organic solvents, a mixture of two forms of capecitabine was observed: carbamate and imine tautomers. In the aqueous solution, only the carbamate form was found. The methylation of capecitabine yields mainly two products in different proportions: N³-methylcapecitabine and N⁷-methylcapecitabine. The protonation of capecitabine in organic solvents with perchloric acid occurs at the N3 nitrogen atom. DFT calculations strongly support the results coming from the analysis of the NMR spectra.

Rapid analysis of interaction between six drugs and β2 -adrenergic receptor by injection amount-dependent method

Drug-protein interaction analysis has become a considerable topic in life science which includes clarifying protein functions, explaining drug action mechanisms and uncovering novel drug candidates. This work was to determine the association constants (K_A ) of six drugs to β₂ -adrenergic receptor by injection amount-dependent method using stationary phase containing the immobilized receptor. The values of K_A were calculated to be (25.85 ± 0.035) × 10⁴  m^-1 for clorprenaline, (42.51 ± 0.054) × 10⁴  m^-1 for clenbuterol, (6.67 ± 0.008) × 10⁴  m^-1 for terbutaline, (33.99 ± 0.025) × 10⁴  m^-1 for tulobuterol, (7.59 ± 0.011) × 10⁴  m^-1 for salbutamol and (78.52 ± 0.087) × 10⁴  m^-1 for bambuterol. This rank order agreed well with the data determined by zonal elution, frontal analysis and nonlinear chromatography, even using different batches of β₂ -AR column. A good correlation was found between the association constants by the current method and radio-ligand binding assay. Our data indicates that the injection amount-dependent method is a powerful alternative for rapid analysis of ligand-receptor interactions.