Cicletanine binding to human plasma proteins and erythrocytes, a particular HSA-drug interaction

Species differences in plasma protein binding of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease inhibitor nirmatrelvir

Plasma protein binding (PPB) studies on the SARS-CoV-2 main protease inhibitor nirmatrelvir revealed considerable species differences primarily in dog and rabbit, which prompted further investigations into the biochemical basis for these differences.The unbound fraction (f_u) of nirmatrelvir in dog and rabbit plasma was concentration (2-200 µM)-dependent (dog f_u,p 0.024-0.69, rabbit f_u,p 0.010-0.82). Concentration (0.1-100 µM)-dependent binding in serum albumin (SA) (f_u,SA 0.040-0.82) and alpha-1-acid glycoprotein (AAG) (f_u,AAG 0.050-0.64) was observed in dogs. Nirmatrelvir showed minimal binding to rabbit SA (1-100 µM: f_u,SA 0.70-0.79), while binding to rabbit AAG was concentration-dependent (0.1-100 µM: f_u,AAG 0.024-0.66). In contrast, nirmatrelvir (2 µM) revealed minimal binding (f_u,AAG 0.79-0.88) to AAG from rat and monkeys. Nirmatrelvir showed minimal-to-moderate binding to SA (1-100 µM; f_u,SA 0.70-1.0) and AAG (0.1-100 µM; f_u,AAG 0.48-0.58) from humans across tested concentrations.Nirmatrelvir molecular docking studies using published crystal structures and homology models of human and preclinical species SA and AAG were used to rationalise the species differences to plasma proteins. This suggested that species differences in PPB are primarily driven by molecular differences in albumin and AAG resulting in differences in binding affinity.

Studies on the interaction between HSA and new halogenated metformin derivatives: influence of lipophilic groups in the binding ability

In the type II diabetes mellitus, Metformin hydrochloride is recommended as a common FAD approved drug. Synthesis of novel metformin series has been widely explored, mainly due to its biological importance and to improve their pharmacokinetic profile. Generally, human serum albumin (HSA) is the main protein used to study drug viability in vitro analysis. Thus, the present study reports the synthesis of three new halogenated metformin derivatives (MFCl, MFBr and MFCF₃) and its interaction toward HSA by multiple spectroscopic techniques (UV-Vis, circular dichroism, steady-state, time-resolved and synchronous fluorescence), combined to computational methods (molecular docking and quantum chemical calculation). The interaction between each halogenated metformin derivative and HSA is spontaneous (ΔG°<0), entropically driven (ΔS°>0), moderate (K_a and K_b ≈ 10⁴ M^-1) and occurs preferentially in the subdomain IIA (close to Trp-214 residue). Molecular docking results suggested hydrogen bonding, van der Waals and hydrophobic interactions as the main binding forces. Quantum chemical calculations suggested imino groups as the most intense electrostatic negative potentials, while the positive electrostatic potential is located at the hydrogen atoms on N,N-dimethyl and the phenyl systems which can help the hydrophobic interactions. [Formula: see text]Communicated by Ramaswamy H. Sarma.

Photoactive assemblies of organic compounds and biomolecules: drug–protein supramolecular systems

Modification of the drug excited state properties within proteins provides information on binding and may result in a different photoreactivity.

Stability of the Hsp90 inhibitor 17AAG hydroquinone and prevention of metal-catalyzed oxidation

17-(allylamino)-17-demethoxygeldanamycin (17AAG) is a benzoquinone ansamycin Hsp90 inhibitor which has promising anticancer activity in vitro, in animal models and in clinical trials. 17AAG has poor water-solubility which is a potential problem for clinical formulation. The hydroquinone derivative of 17AAG, 17AAG hydroquinone (17AAGH(2)), is considerably more water soluble and since we previously demonstrated that 17AAGH(2) was a more potent Hsp90 inhibitor than its parent quinone, it is a good candidate for clinical use and is currently in clinical trials. However, 17AAGH(2) can be oxidized back to 17AAG under aerobic conditions so we tested the relative stability of 17AAGH(2) and the effect of different metal ions and metal chelators on the oxidation of 17AAGH(2). We found that copper could accelerate 17AAGH(2) oxidation while copper chelators such as D-penicillamine could inhibit oxidation. Human serum albumin (HA) has copper-binding ability and we found that HA diminished the rate of 17AAGH(2) oxidation. Although we found that 17AAG could associate with HA, no association was observed between 17AAGH(2) and HA. In summary, our data demonstrates that copper chelators can prevent 17AAGH(2) oxidation and suggests that HA prevents 17AAGH(2) oxidation via a copper chelation mechanism. Agents that prevent oxidation may be useful in clinical formulations of 17AAGH(2.)

Toxicokinetics and metabolisms of benzophenone-type UV filters in rats

Sunscreens containing UV filters are recommended to reduce damage caused by solar UV radiation. Recently, benzophenone (BP)-type UV filters have become widely used as UV stabilizers in skin-moisturizing products and sunscreen lotions; however, very little information is available regarding the potential harmful effects of prolonged exposure to these compounds. Therefore, we investigated the toxicokinetics and metabolism of BP-type UV filters in rats using gas chromatography-mass spectrometry (GC-MS). To examine the metabolism of BP-type UV filters, we analyzed the parent compounds BP and 2-hydroxy-4-methoxybenzophenone (HMB). In rats, BP was mainly converted to benzhydrol (BH) and 4-hydroxybenzophenone (HBP) (i.e., type A UV filters). In contrast, HMB was converted into at least three intermediates, including 2,4-dihydroxybenzophenone (DHB), which was formed via o-demethylation and subsequently converted into 2,3,4-trihydroxybenzophenone (THB), and 2,2'-dihydroxy-4-methoxybenzophenone (DHMB), which formed via the aromatic hydroxylation of HMB (i.e., type B UV filters). Next, the toxicokinetic curve for BP showed a peak concentration (Cmax) of 2.06+/-0.46 microg/ml at approximately 4h after BP administration. After a single oral dose of HMB, the Cmax of HMB reached 21.21+/-11.61 microg/ml within 3h (Tmax), and then declined rapidly compared to the kinetic curve of BP. The concentration of these metabolites in rat blood decreased much more slowly over time compared to the parent compounds. Thus, our results indicate that such metabolites might have more significant adverse effects than the parent compounds over the long term.

Use of Triplet Excited States for the Study of Drug Binding to Human and Bovine Serum Albumins

The triplet excited states of (S)- and (R)-flurbiprofen (FBP) have been used as reporters for the microenvironments experienced within the binding sites of human and bovine serum albumins. Regression analysis of triplet decay provides valuable information on the degree of protection that these excited states are afforded from attack by a second FBP molecule, oxygen, or other reagents. The multiexponential fitting of these decays can be satisfactorily correlated with the distribution of the drug among the two binding sites and its presence as the noncomplexed form in the bulk solution. This assignment has been confirmed by using (S)-ibuprofen or capric acid as selective site II replacement probes. Triplet lifetimes and site occupancy are sensitive to the type of serum albumin employed (human versus bovine). Finally, the binding behaviour of (S)- and (R)-FBP exhibits little stereoselectivity.

In vitro plasma protein binding determination of flunarizine using equilibrium dialysis and liquid chromatography-tandem mass spectrometry

A highly sensitive method was developed and validated for determining the free fraction of flunarizine in human plasma. Equilibrium dialysis was used for the separation of free (unbound) drug and liquid chromatography/tandem mass spectrometry (LC-MS/MS) was used for quantitation. Post-dialysis plasma or buffer samples of 0.2 mL were extracted using a liquid-liquid extraction procedure and analyzed using a high performance liquid chromatography electrospray tandem mass spectrometer system. The compounds were eluted isocratically on a Supelco Supelcosil ABZ+Plus column, ionized using a positive ion atmospheric pressure electrospray ionization source, and analyzed using multiple reaction monitoring. The ion transitions monitored were m/z 405-->203 for flunarizine and m/z 409-->207 for flunarizine-d4 (internal standard, IS). The chromatographic run time was 3.5 min per injection, with retention times of 2.1 min for both flunarizine and IS. The calibration curve for flunarizine was linear over the concentration range of 0.25-2000 ng/mL (r(2)>0.9989) in the combined matrix of human plasma and isotonic sodium phosphate buffer (1:1, v/v) with the lower limit of quantitation of 0.25 ng/mL. The inter-assay coefficient of variability (CV) for the quality control samples was less than 13.5%, and the inter-assay percent nominal was greater than 98.2%. In vitro protein binding of flunarizine was determined at concentrations of 5, 10 and 100 microg/mL using the validated method. Flunarizine was extensively bound to plasma protein with a 0.083+/-0.005% overall percent free drug in plasma and a CV value less than 7.8%. This validated method will be used for the ex vivo assessment of flunarizine protein binding in human plasma from a drug-drug interaction clinical study.

Simultaneous determination of unbound thyroid hormones in human plasma using high performance frontal analysis with electrochemical detection

A direct injection HPLC method in combination with high-performance frontal analysis (HPFA) and electrochemical detection (ECD) was developed for the simultaneous and sensitive determination of unbound thyroid hormones (thyroxine, triiodothyronine, and reverse triiodothyronine) in human plasma. The present on-line HPLC/HPFA system consists of an HPFA column, an extraction column and an analytical HPLC column connected through a column-switching device, and the eluent from the analytical column was monitored by ECD. The calibration lines showed good linearity (rsq.>0.999) within 7.4-148.2 pM for T4 and 1.5-74.1 pM for T3 and rT3. Unbound T4 and T3 concentrations determined by the present system were 16.4+/-2.4 pM (n=15) and 7.14+/-1.04 pM (n=15), which were in agreement with those determined by the EIA method. The unbound rT3 concentration was 2.30+/-0.27 pM (n=15). The CV% values of intra-day and inter-day assays (n=15) were less than 14.9% for T4, 14.5% for T3 and 13.2% for rT3. The present system was also applied to a competitive binding study of these thyroid hormones in human plasma.

High-Throughput Solution-Based Medicinal Library Screening against Human Serum Albumin

High-throughput screening of combinatorial libraries has evolved from studying large diverse libraries to analyzing small, structurally similar, focused libraries. This paradigm shift has generated a need for rapid screening technologies to screen both diverse and focused libraries in a simple, efficient, and inexpensive manner. We have proactively addressed these needs by developing a high-throughput, solution-based method combining size exclusion (SEC), two-dimensional liquid chromatography (2-D LC), and mass spectrometry (MS) for determining the relative binding of drug candidates in small, focused medicinal libraries against human serum albumin (HSA). Two types of libraries were used to evaluate the performance of the system. The first consisted of five diverse ligands with a wide range of hydrophobicities and whose association constants to HSA cover 3 orders of magnitude. A beta-lactam library composed of structurally similar compounds was used to further confirm the validity of the methodology. The ability to distinguish site-specific interactions of drugs competing for individual domains of the HSA receptor is also demonstrated. Comparison of chromatographic profiles of the library components before and after incubation with the receptor using multiple reaction monitoring allowed a ranking of the ligands according to their relative binding affinities. The observed rankings correlate closely with literature values of the association constants between the respective ligands and HSA. This simple, rugged methodology can screen a wide spectrum of chemical entities from combinatorial mixtures in less than 6 min.

Simultaneous determination of glipizide and rosiglitazone unbound drug concentrations in plasma by equilibrium dialysis and liquid chromatography-tandem mass spectrometry

Glipizide and rosiglitazone are widely used to treat Type 2 diabetes. In order to investigate drug-drug protein binding interaction between glipizide and rosiglitazone, a method was developed and validated for simultaneously determining the free (unbound) fraction of glipizide and rosiglitazone in plasma employing equilibrium dialysis for the separation of free drug and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for quantitation. Post-dialysis human plasma or buffer samples of 0.2 ml were extracted using a liquid-liquid extraction procedure and analyzed by a high performance liquid chromatography electrospray tandem mass spectrometer system. The compounds were eluted isocratically on a Zorbax SB-Phenyl column, ionized using an atmospheric pressure electrospray ionization source and analyzed in positive ion mode with multiple reaction monitoring. The ion transitions monitored were m/z 446-->321 for glipizide, m/z 358-->135 for rosiglitazone, and m/z 271-->155 for tolbutamide (internal standard, IS). The chromatographic run time was 5 min per injection, with retention times of 2.3, 3.4 and 2.3 min for glipizide, rosiglitazone and IS, respectively. The calibration curves of glipizide and rosiglitazone were over the range of 1-2000 ng/ml (r(2)>0.9969) in the combined matrix of human plasma and isotonic sodium phosphate buffer (1:1, v/v). The inter-assay precision and accuracy of the quality control samples were <10.9% of coefficient of variability and >93.5% and 94.5% of nominal concentration for glipizide and rosiglitazone, respectively. The lower limit of quantitation of both glipizide and rosiglitazone was 1.0 ng/ml. Both glipizide and rosiglitazone bound to plasma protein extensively (>99% bound). Glipizide and rosiglitazone free fraction averaged 0.678+/-0.071 and 0.389+/-0.061%, respectively, at plasma concentration of 1000 ng/ml. This developed method proves reproducible and sensitive and its application to clinical samples is also reported.

Predicting plasma protein binding of drugs: a new approach

In spite of the large amount of plasma protein binding data for drugs, it is not obvious and there is no clear consensus among different disciplines how to deal with this parameter in multidimensional lead optimization strategies. In this work, we have made a comprehensive study on the importance of plasma protein binding and the influencing factors in order to get new insights for this molecular property. Our analysis of the distribution of percentage plasma protein binding among therapeutic drugs showed that no general rules for protein binding can be derived, except for the class of chemotherapeutics, where a clear trend towards lower binding could be observed. For the majority of indication areas, however, empirical rules are missing. We present here an extensive list of multiply determined primary association constants for binding to human serum albumin (HSA) for 138 compounds from the literature. Correlating these binding constants with the percentage fraction of protein bound showed that the percentage data above 90%, corresponding to a binding constant below 6 microM, are of insufficient accuracy. Furthermore, it could be demonstrated that the lipophilicity of drugs, traditionally felt to dominate binding to HSA, is not the only relevant descriptor. Here, we report a generic model for the prediction of drug association constants to HSA, which uses a pharmacophoric similarity concept and partial least square analysis (PLS) to construct a quantitative structure-activity relationship. It is able to single out the submicromolar to nanomolar binders, i.e. to differentiate between 99.0 and 99.99% plasma protein binding. Depending on the system, this can be important in medicinal chemistry programs and may together with other computed physicochemical and ADME properties assist in the prioritization of synthetic strategies.

Determination of protein-drug binding constants by pressure-assisted capillary electrophoresis (PACE)/frontal analysis (FA)

A simple method for the determination of binding constants of drugs to human serum albumin (HSA) and alpha(1)-acid glycoprotein (AGP) was developed by pressured-assisted capillary electrophoresis (PACE) based on the principle of frontal analysis (FA). The free drug concentration was measured from the height of the frontal peak and calculated based on the external drug standard in the absence of protein. With a known concentration of total drug, the percentage of drug bound to HSA or AGP was then determined. The binding constants of drug to HSA or AGP were obtained from non-linear curve fitting of the percentage of bound drug as a function of total protein concentration or total drug concentration. The sample was prepared by mixing known concentrations of drug and protein in phosphate buffered saline (PBS) and equilibrated for 30 min. A large volume of sample solution (approximately 80 nl) was injected at 1.0 psi for 40 s into the fused silica capillary, which was filled with PBS buffer. Due to the difference in charge/size ratio, the free drug was separated from the protein/protein-drug complex when 15-25 kV voltage and 0.5-1.5 psi air pressure were applied. External air pressure was used to improve the throughput, prevent protein loss, and achieve a better drug plateau. By modifying experimental conditions, a wide range of binding constants could be measured. This PACE/FA method works well for basic, neutral, and weakly acidic compounds.

1H-NMR study of the effect of acetonitrile on the interaction of ibuprofen with human serum albumin

The effect of acetonitrile (ACN) on the low-affinity interaction between human serum albumin (HSA) and ibuprofen (IBP) was studied using 1H-NMR techniques. Both chemical shift and relaxation measurements showed the addition of ACN to the solutions decreased the binding affinity of IBP to HSA and reduced the hydrophobic interaction between them. The self-diffusion coefficients of IBP were measured as a function of the drug concentration at different ACN concentrations. The association constant, K(a), for ligand-HSA complexes and the number of binding sites, n, are evaluated by the application of Langmuir isotherm. The results indicated that the value of n was about 38 without ACN, and about 26 with ACN concentration 12% (v/v%). The decreased binding capacity of IBP to HSA in the presence of ACN was mainly attributed to the competition of ACN with IBP to the low-affinity binding sites of HSA molecule.

NMR study on the low-affinity interaction of human serum albumin with diclofenac sodium

The low-affinity interaction between human serum albumin (HSA) and Diclofenac sodium (DCF) was studied using NMR techniques. Both 13C-NMR chemical shift and linewidth show that the dichlorophenyl ring in DCF molecule plays a primary role in its interaction with HSA. Langmuir adsorption isotherm was applied to evaluate the association constant K and the number of binding sites n of the drug/HSA complex through (1)H-NMR spin-lattice relaxation measurement. The results indicate that Langmuir isotherm can perfectly explain the capacity of low-affinity binding of proteins for the ligands.

Human alpha-1-glycoprotein and its interactions with drugs

For about half a century, the binding of drugs to plasma albumin, the "silent receptor," has been recognized as one of the major determinants of drug action, distribution, and disposition. In the last decade, the binding of drugs, especially but not exclusively basic entities, to another plasma protein, alpha 1-acid glycoprotein (AAG), has increasingly become important in this regard. The present review points out that hundreds of drugs with diverse structures bind to this glycoprotein. Although plasma concentration of AAG is much lower than that of albumin, AAG can become the major drug binding macromolecule in plasma with significant clinical implications. Also, briefly reviewed are the physiological, pathological, and genetic factors that influence binding, the role of AAG in drug-drug interactions, especially the displacement of drugs and endogenous substances from AAG binding sites, and pharmacokinetic and clinical consequences of such interactions. It can be predicted that in the future, rapid automatic methods to measure binding to albumin and/or AAG will routinely be used in drug development and in clinical practice to predict and/or guide therapy.

Determination of the binding of a beta 2-blocker drug, frusemide and ceftriaxone to serum proteins by capillary zone electrophoresis

A modified Hummel-Dreyer method was used to study the binding of drugs with serum proteins by high performance capillary electrophoresis. The study was carried out to check the possible interaction between serum proteins and a highly selective beta 2-blocker, ICI 118551 (ICI). To prove the suitability of the method the protein binding of frusemide and ceftriaxone, drugs previously investigated, was also studied. The analyses were carried out by injecting a solution of s alpha(1)-acidic glycoprotein (alpha(1)-AGP) or human serum albumin in 70 mM NaH2PO4/Na2HPO4(pH 7.4) buffer into an uncoated fused silica capillary filled with the same buffer. In the capillary, maintained at a working temperature of 35 degrees C, a known amount of the ICI, frusemide or ceftriaxone was added. The method allows the bound drug to be determined directly.

Pharmacokinetics of benzophenone-3 after oral exposure in male rats

Benzophenone-3 (BZ-3) is one of the UV-absorbing agents that has been used in industry and medicine for more than 30 years. Millions of consumers are exposed to benzophenones on a daily basis owing to the widespread use of these compounds in many of the products on the market, such as lipsticks, hair sprays, hair dyes, shampoo and detergent bars and sunscreen lotions. This study was performed to investigate the pharmacokinetics of BZ-3 after oral administration at 100 mg kg-1 body weight in male Sprague-Dawley rats. Absorption from the gastrointestinal tract was rapid because BZ-3 was detected in blood 5 min after administration. The peak plasma concentration (Cmax) was 25.6 +/- 4.6 micrograms ml-1 and the time of occurrence (tmax) was 3.0 +/- 0.4 h. The half-life of absorption of BZ-3 was 0.71 h. The elimination pattern was biphasic with alpha and beta half-lives of elimination of 0.88 and 15.90 h, respectively. The results of this study indicate the presence of strong binding between the plasma protein and BZ-3. Tissue distribution studies at 6 h indicate that the liver contained the highest concentration of free (58.9 +/- 23.8 micrograms) and total (free+bound or conjugated) BZ-3 (2087 +/- 60.1 micrograms), followed by kidney and testes, respectively. Urine and feces analysis indicate that urine was the major route of excretion, followed by feces. Further analysis of urine samples also indicates that conjugation of BZ-3 with glucuronic acid was the major systemic elimination route for the compound.

Study of protein-drug binding using capillary zone electrophoresis

CApillary zone electrophoresis was tested for its suitability for studying protein-drug binding. Three methods were investigated, viz., the Hummel-Dreyer method, the vacancy peak method and frontal analysis. Frontal analysis appeared to be the preferred method.

Separation procedures used to reveal and follow drug-protein binding

The review gives a critical evaluation of the different separation procedures used to study drug-protein interactions and describes their various fields of application. For pharmacological studies, the most widely used methods are dialysis and ultrafiltration, because they allow measurements with solutions of high protein concentrations, such as those found in therapeutic conditions. Both techniques use membrane devices, which may induce additional binding effects. Another drawback of these techniques is the need for radiolabelled compounds. Chromatographic methods, which now take advantage of the technology of high-performance liquid chromatography, are generally faster and do not use drug labelling because of the higher sensitivities of the detectors. Two different approaches are possible: either all the interacting species (protein and drug) are dissolved in the mobile phase, or one of them (protein or drug) is immobilized on the support. Several chromatographic methods are available for studies in solution that differ according to the sample injection mode (frontal or zonal elution) and the nature of the mobile phase used. They include quantitation of the drug-protein complex by zonal elution, the Hummel and Dreyer method, frontal elution, the vacancy peak method, and retention analysis by zonal elution. Frontal elution is the most rigorous method since all the species at equilibrium are present in the mobile phase with known and constant concentrations. The most promising one is the Hummel and Dreyer method, because of the very small amount of protein injected in the mobile phase containing the drug. Drug-protein interactions may be studied by affinity chromatography by immobilizing one of the interacting species on the support. Comparison of the constants obtained with methods when both the drug and the protein are in solution is questionable, since the immobilized species in affinity separations differ in their physical properties from those in solution. The main advantage with studies on immobilized proteins is the easy comparison of the binding properties of various drugs, especially when they are enantiomeric. The results of the binding constants measured by different separation methods are given for the albumin-phenylbutazone and albumin-warfarin systems. Good agreement is generally obtained, which proves the validity of using chromatography as a tool to study drug-protein interactions.