Determination of the kinetic rate constant of cyclodextrin supramolecular systems by high performance affinity chromatography

Immobilization of M3 Muscarinic Receptor to Rapidly Analyze Drug-Protein Interactions and Bioactive Components in a Natural Plant

Despite its increasing application in pursing potential ligands, the capacity of receptor affinity chromatography is greatly challenged as most current research studies lack a comprehensive characterization of the ligand-receptor interaction, particularly when simultaneously determining their binding thermodynamics and kinetics. This work developed an immobilized M3 muscarinic receptor (M3R) affinity column by fixing M3R on amino polystyrene microspheres via the interaction of a 6-chlorohexanoic acid linker with haloalkane dehalogenase. The efficiency of the immobilized M3R was tested by characterizing the binding thermodynamics and kinetics of three known drugs to immobilized M3R using a frontal analysis and the peak profiling method, as well as by analyzing the bioactive compounds in Daturae Flos (DF) extract. The data showed that the immobilized M3R demonstrated good specificity, stability, and competence for analyzing drug-protein interactions. The association constants of (-)-scopolamine hydrochloride, atropine sulfate, and pilocarpine to M3R were determined to be (2.39 ± 0.03) × 10⁴, (3.71 ± 0.03) × 10⁴, and (2.73 ± 0.04) × 10⁴ M^-1, respectively, with dissociation rate constants of 27.47 ± 0.65, 14.28 ± 0.17, and 10.70 ± 0.35 min^-1, respectively. Hyoscyamine and scopolamine were verified as the bioactive compounds that bind to M3R in the DF extract. Our results suggest that the immobilized M3R method was capable of determining drug-protein binding parameters and probing specific ligands in a natural plant, thus enhancing the effectiveness of receptor affinity chromatography in diverse stages of drug discovery.

Mechanism and optimization of supramolecular complexation-enhanced fluorescence spectroscopy for the determination of SN-38 in plasma and cells

Quantitative detection of two different forms of SN-38 in biological samples is, currently, cumbersome and difficult. A revisit to the mechanism of supramolecular complexation-enhanced fluorescence spectroscopy helps to optimize the determination of SN-38 in plasma and the cellular pharmacokinetics in A549 cells based on the supramolecular complexation. Firstly, the inclusion mechanism dominated by thermodynamic constants was determined by measuring kinetic/thermodynamic parameters (k_on , k_off , ΔG, ΔH, ΔS). On this basis, the best effect of fluorescence sensitization was optimized through screening the interaction conditions (cyclodextrin species and concentrations, drug levels, temperature, pH of the buffer, and reaction time). Furthermore, the proportional relationship between the concentration of the inclusion complex and the fluorescence intensity was confirmed. Finally, a highly sensitive, selective spectrofluorimetric method was established and validated for quantitative analysis of the lactone and carboxylate molecular states of SN-38 plasma levels in rats and cell membrane transfer kinetics in A549 cell lines. The limits of detection for the lactone and carboxylate forms in plasma were found to be 0.44 ng·ml^-1 and 0.28 ng·ml^-1 , respectively. Precision and accuracy met the requirements of biological samples analysis. The proposed detection method provided a reference for elucidating the biodistribution of SN-38.

Kinetic Analysis by Affinity Chromatography

Important information on chemical processes in living systems can be obtained by the rates at which these biological interactions occur. This review will discuss several techniques based on traditional and high-performance affinity chromatography that may be used to examine the kinetics of biological reactions. These methods include band-broadening measurements, techniques for peak fitting, split-peak analysis, peak decay studies, and ultrafast affinity extraction. The general principles and theory of each method, as applied to the determination of rate constants, will be discussed. The applications of each approach, along with its advantages and limitations, will also be considered.

Solubility of Cyclodextrins and Drug/Cyclodextrin Complexes

Cyclodextrins (CDs), a group of oligosaccharides formed by glucose units bound together in a ring, show a promising ability to form complexes with drug molecules and improve their physicochemical properties without molecular modifications. The stoichiometry of drug/CD complexes is most frequently 1:1. However, natural CDs have a tendency to self-assemble and form aggregates in aqueous media. CD aggregation can limit their solubility. Through derivative formation, it is possible to enhance their solubility and complexation capacity, but this depends on the type of substituent and degree of substitution. Formation of water-soluble drug/CD complexes can increase drug permeation through biological membranes. To maximize drug permeation the amount of added CD into pharmaceutical preparation has to be optimized. However, solubility of CDs, especially that of natural CDs, is affected by the complex formation. The presence of pharmaceutical excipients, such as water-soluble polymers, preservatives, and surfactants, can influence the solubilizing abilities of CDs, but this depends on the excipients' physicochemical properties. The competitive CD complexation of drugs and excipients has to be considered during formulation studies.

Simultaneous high-throughput determination of interaction kinetics for drugs and cyclodextrins by high performance affinity chromatography with mass spectrometry detection

The individual determination of the apparent dissociation rate constant (kd,app) using high performance affinity chromatography (HPAC) is a tedious process requiring numerous separate tests and massive data fitting, unable to provide the apparent association rate constant (ka) and equilibrium binding constant (Ka). In this study, a HPAC with mass spectrometry detection (HPAC-MS/MS) was employed to determine the drug-cyclodextrin (CD) interaction kinetics with low sample loading quantity (<10 ng per injection for single compound) and high-throughput yield as twenty drugs determined in one injection. The kd,app measured by HPAC-MS/MS approach were 0.89 ± 0.07, 4.34 ± 0.01, 1.48 ± 0.01 and 7.77 ± 0.04 s(-1) for ketoprofen, trimethoprim, indapamide and acetaminophen, with kd,app for acetaminophen consistent with that from the HPAC method with UV detector in our previous studies. For twenty drugs with diverse structures and chemical properties, good correlationship was found between kd,app measured by single compound analysis method and high-throughput HPAC-MS/MS approach, with the correlation coefficient of 0.987 and the significance F less than 0.001. Comprehensive quantification of ka,app, kd,app and Ka values was further performed based on the measurement of kd,app by peak profiling method and Ka by the peak fitting method. And the investigation of the drug-CD interaction kinetics under different conditions indicated that the column temperature and mobile phase composition significantly affected the determination of ka,app, kd,app and Ka while also dependent on the acidity and basicity of drugs. In summary, the high-throughput HPAC-MS/MS approach has been demonstrated high efficiency in determination of the drug-CD primary interaction kinetic parameter, especially, kd,app, being proven as a novel tool in screening the right CD for the solubilization of the right drug.

High-throughput measurement of drug–cyclodextrin kinetic rate constants by a small molecule microarray using surface plasmon resonance imaging

A high-throughput methodology for the measurement of drug–CD kinetic rate constants.

Analytical methods for kinetic studies of biological interactions: A review

The rates at which biological interactions occur can provide important information concerning the mechanism and behavior of these processes in living systems. This review discusses several analytical methods that can be used to examine the kinetics of biological interactions. These techniques include common or traditional methods such as stopped-flow analysis and surface plasmon resonance spectroscopy, as well as alternative methods based on affinity chromatography and capillary electrophoresis. The general principles and theory behind these approaches are examined, and it is shown how each technique can be utilized to provide information on the kinetics of biological interactions. Examples of applications are also given for each method. In addition, a discussion is provided on the relative advantages or potential limitations of each technique regarding its use in kinetic studies.

Determination of the kinetic rate constant of cyclodextrin supramolecular systems by high-performance affinity chromatography

The kinetics of the association and dissociation are fundamental kinetic processes for the host-guest interactions (such as the drug-target and drug-excipient interactions) and the in vivo performance of supramolecules. With advantages of rapid speed, high precision and ease of automation, the high-performance affinity chromatography (HPAC) is one of the best techniques to measure the interaction kinetics of weak to moderate affinities, such as the typical host-guest interactions of drug and cyclodextrins by using a cyclodextrin-immobilized column. The measurement involves the equilibration of the cyclodextrin column, the upload and elution of the samples (non-retained substances and retained solutes) at different flow rates on the cyclodextrin and control column, and data analysis. It has been indicated that cyclodextrin-immobilized chromatography is a cost-efficient high-throughput tool for the measurement of (small molecule) drug-cyclodextrin interactions as well as the dissociation of other supramolecules with relatively weak, fast, and extensive interactions.

Multianalyte determination of the kinetic rate constants of drug-cyclodextrin supermolecules by high performance affinity chromatography

The kinetics of the dissociation is fundamental to the formation and the in vivo performance of cyclodextrin supramolecules. The individual determination of the apparent dissociation rate constant (kd,app) using high performance affinity chromatography (HPAC) is a tedious process requiring numerous separate studies and massive data fitting. In this study, the multianalyte approach was employed to simultaneously measure the kd,app values of three drugs through one injection based on the investigation of the dependence of drug-cyclodextrin interaction kinetics on the mobile phase composition. As a result, the kd,app values increased when decreasing the ion strength, increasing the ionization of drugs and adding extra organic solvents. The values of kd,app for acetaminophen, phenacetin and S-flurbiprofen estimated by the multianalyte approach were 8.54±1.81, 5.36±0.94 and 0.17±0.02s(-1), respectively, which were in good agreement with those determined separately (8.31±0.58, 5.01±0.42 and 0.15±0.01s(-1)). For both of the single and multiple flow rate peak profiling methods, the results of the multianalyte approach were statistically equivalent with that of the single compound analysis for all of the three drugs (p>0.05). The multianalyte approach can be employed for the efficient evaluation of the drug-cyclodextrin kinetics with less variance caused by cyclodextrin column bleeding.