Determination of drug-plasma protein binding using human serum albumin chromatographic column and multiple linear regression model

A Fully Integrated Assay Panel for Early Drug Metabolism and Pharmacokinetics Profiling

Evaluation and optimization of physicochemical and metabolic properties of compounds are a crucial component of the drug development process. Continuous access to this information during the design-make-test-analysis cycle enables identification of chemical entities with suitable properties for efficient project progression. In this study, we describe an integrated and automated assay panel (DMPK Wave 1) that informs weekly on lipophilicity, solubility, human plasma protein binding, and metabolic stability in rat hepatocytes and human liver microsomes. All assays are running in 96-well format with ultraperformance liquid chromatography-mass spectrometry (MS)/MS as read-out. A streamlined overall workflow has been developed by optimizing all parts of the process, including shipping of compounds between sites, use of fit-for-purpose equipment and information systems, and technology for compound requesting, data analysis, and reporting. As a result, lead times can be achieved that well match project demands across sites independently of where compounds are synthesized. This robust screening strategy is run on a weekly basis and enables optimization of structure-activity relationships in parallel with DMPK properties to allow efficient and informed decision making.

Lipophilicity and biomimetic properties to support drug discovery

INTRODUCTION

Lipophilicity, expressed as the octanol-water partition coefficient, constitutes the most important property in drug action, influencing both pharmacokinetic and pharmacodynamics processes as well as drug toxicity. On the other hand, biomimetic properties defined as the retention outcome on HPLC columns containing a biological relevant agent, provide a considerable advance for rapid experimental - based estimation of ADME properties in early drug discovery stages. Areas covered: This review highlights the paramount importance of lipophilicity in almost all aspects of drug action and safety. It outlines problems brought about by high lipophilicity and provides an overview of the drug-like metrics which incorporate lower limits or ranges of logP. The fundamental factors governing lipophilicity are compared to those involved in phospholipophilicity, assessed by Immobilized Artificial Membrane Chromatography (IAM). Finally, the contribution of biomimetic properties to assess plasma protein binding is evaluated. Expert opinion: Lipophilicity and biomimetic properties have important distinct and overlapping roles in supporting the drug discovery process. Lipophilicity is unique in early drug design for library screening and for the identification of the most promising compounds to start with, while biomimetic properties are useful for the experimentally-based evaluation of ADME properties for the synthesized novel compounds, supporting the prioritization of drug candidates and guiding further synthesis.

In vitro metabolism of specific CYP2D and CYP3A opioid substrates using rat liver S9 fractions and mass spectrometry reveal a severe metabolic impairment with increasing age

Codeine and oxycodone are opioids used to alleviate pain. The outcome of the treatment is ultimately related to their metabolism by Cytochromes P450 (CYPs). Depending on the drugs used, alterations in the metabolism of drugs by CYPs can lead to severe consequences including alterations in their efficacy, safety and toxicity. The objectives of this study were to develop a novel HPLC-MS/MS method capable of quantifying codeine and oxycodone along with specific metabolites using an isotopic dilution strategy and study the rate of formation of morphine (CYP2D), norcodeine (CYP3A), oxymorphone (CYP2D) and noroxycodone (CYP3A). The chromatographic separation was achieved using a Biobasic C₁₈ 100 × 1 mm column combined with an isocratic mobile phase composed of methanol and 10 mm ammonium acetate (40:60) at a flow rate of 75 μL/min. The mass spectrometer was operating in scan mode MS/MS and the analytical range was set at 10-10 000 nm. The precision (RSD) and accuracy (RE) observed were 4.4-11.5 and -9.1-6.1% respectively. Liver S9 fractions from 3-, 6-, 12- and 18-month-old male Sprague-Dawley rats were prepared and Michaelis-Menten parameters were determined. The derived maximum enzyme velocity suggested a rapid saturation of the CYP2D and CYP3A active sites in the liver S9 fractions of 18-month-old rats. Moreover, metabolic stabilities of codeine and oxycodone in rat liver S9 fractions were significantly greater for the 18-month-old rats. This study suggests that there is an impairment of CYP2D and CYP3A metabolism in aging rats.

Lipophilicity and biomimetic properties measured by HPLC to support drug discovery

HPLC methods that use chromatographic retention times for gaining information about the properties of compounds for the purpose of designing drug molecules are reviewed. Properties, such as lipophilicity, protein binding, phospholipid binding, and acid/base character can be incorporated in the design of molecules with the right biological distribution and pharmacokinetic profile to become an effective drug. Standardization of various methodologies is suggested in order to obtain data suitable for inter-laboratory comparison. The published HPLC methods for lipophilicity, acid/base character, protein and phospholipid binding are critically reviewed and compared with each other using the solvation equation approach. One of the most important discussion points is how these data can be used in models and how they can influence the drug discovery process. Therefore, the published models for volume of distribution, unbound volume of distribution and drug efficiency are also discussed. The general relationships between the chemical structure and biomimetic HPLC properties are described in view of ranking and selecting putative drug molecules.

Optimization of sphingosine-1-phosphate-1 receptor agonists: effects of acidic, basic, and zwitterionic chemotypes on pharmacokinetic and pharmacodynamic profiles

The efficacy of the recently approved drug fingolimod (FTY720) in multiple sclerosis patients results from the action of its phosphate metabolite on sphingosine-1-phosphate S1P1 receptors, while a variety of side effects have been ascribed to its S1P3 receptor activity. Although S1P and phospho-fingolimod share the same structural elements of a zwitterionic headgroup and lipophilic tail, a variety of chemotypes have been found to show S1P1 receptor agonism. Here we describe a study of the tolerance of the S1P1 and S1P3 receptors toward bicyclic heterocycles of systematically varied shape and connectivity incorporating acidic, basic, or zwitterionic headgroups. We compare their physicochemical properties, their performance in in vitro and in vivo pharmacokinetic models, and their efficacy in peripheral lymphocyte lowering. The campaign resulted in the identification of several potent S1P1 receptor agonists with good selectivity vs S1P3 receptors, efficacy at <1 mg/kg oral doses, and developability properties suitable for progression into preclinical development.

Analysis of biomolecular interactions using affinity microcolumns: a review

Affinity chromatography has become an important tool for characterizing biomolecular interactions. The use of affinity microcolumns, which contain immobilized binding agents and have volumes in the mid-to-low microliter range, has received particular attention in recent years. Potential advantages of affinity microcolumns include the many analysis and detection formats that can be used with these columns, as well as the need for only small amounts of supports and immobilized binding agents. This review examines how affinity microcolumns have been used to examine biomolecular interactions. Both capillary-based microcolumns and short microcolumns are considered. The use of affinity microcolumns with zonal elution and frontal analysis methods are discussed. The techniques of peak decay analysis, ultrafast affinity extraction, split-peak analysis, and band-broadening studies are also explored. The principles of these methods are examined and various applications are provided to illustrate the use of these methods with affinity microcolumns. It is shown how these techniques can be utilized to provide information on the binding strength and kinetics of an interaction, as well as on the number and types of binding sites. It is further demonstrated how information on competition or displacement effects can be obtained by these methods.

Biopartitioning micellar chromatography with sodium dodecyl sulfate as a pseudo α(1)-acid glycoprotein to the prediction of protein-drug binding

A simple and fast method is of urgent need to measure protein-drug binding affinity in order to meet the rapid development of new drugs. Biopartitioning micellar chromatography (BMC), a mode of micellar liquid chromatography (MLC) using micellar mobile phases in adequate experimental conditions, can be useful as an in vitro system in mimicking the drug-protein interactions. In this study, sodium dodecyl sulfate-micellar liquid chromatography (SDS-MLC) was used for the prediction of protein-drug binding based on the similar property of SDS micelles to α(1)-acid glycoprotein (AGP). The relationships between the BMC retention data of a heterogeneous set of 14 basic and neutral drugs and their plasma protein binding parameter were studied and the predictive ability of models was evaluated. Modeling of logk(BMC) of these compounds was established by multiple linear regression (MLR) and second-order polynomial models obtained in two different concentrations (0.07 and 0.09M) of SDS. The developed MLR models were characterized by both the descriptive and predictive ability (R(2)=0.882, R(CV)(2)=0.832 and R(2)=0.840, R(CV)(2)=0.765 for 0.07 and 0.09M SDS, respectively). The p values <0.01 also indicated that the relationships between the protein-drug binding and the logk(BMC) values were statistically significant at the 99% confidence level. The standard error of estimation showed the standard deviation of the regression to be 11.89 and 13.87 for 0.07 and 0.09M, respectively. The application of the developed model to a prediction set demonstrated that the model was also reliable with good predictive accuracy. The external and internal validation results showed that the predicted values were in good agreement with the experimental value.

High performance affinity chromatography (HPAC) as a high-throughput screening tool in drug discovery to study drug-plasma protein interactions

Drug-plasma protein binding is an important parameter that, together with other physicochemical properties such as lipophilicity and pK(a), greatly influences drug absorption, distribution, metabolism, and excretion (ADME). Therefore, it is important for pharmaceutical companies to develop a rapid screening assay to examine plasma protein binding during the early stages of the drug discovery process. Human serum albumin (HSA) and α(1)-acid glycoprotein (AGP) are the most important plasma proteins that are capable of binding drugs. In this work, an automated and high-throughput (<3 min/compound) strategy was developed using high performance affinity chromatography (HPAC) with commercial HSA and AGP columns to evaluate drug-plasma protein interactions for drug screening. A generic gradient was used throughout the study to separate drugs that were weakly and tightly bound to HSA and AGP. To accelerate the analysis time, the system was calibrated in a single run by pooling reference compounds without overloading the column. For both HSA and AGP studies, the developed methods were successfully transferred from HPAC-UV to HPAC-MS with single quadrupole MS detection and ammonium acetate, pH 7.0 as a volatile mobile phase. The MS detection enhanced the sensitivity, selectivity, and throughput of the method by pooling unknown compounds. For HSA analyses, the binding percentages obtained using HPAC were well correlated with the binding percentages from the literature. This method was also able to rank compounds based on their affinity for HSA. Concerning the AGP analyses, the quality of the correlation between the binding percentages obtained in HPAC and those from the literature was weaker. However, the method was able to classify compounds into weak, medium, and strong binders and rank compounds based on their affinity for AGP.

CHROMATOGRAPHIC ANALYSIS OF DRUG INTERACTIONS IN THE SERUM PROTEOME

The binding of drugs with serum proteins and binding agents such as human serum albumin, α1-acid glycoprotein, and lipoproteins is an important process in determining the activity and fate of many pharmaceuticals in the body. A variety of techniques have been used to study drug interactions with serum proteins, but there is still a need for faster or better methods for such work. High-performance liquid chromatography (HPLC) is one tool that has been utilized in many formats for these types of measurements. Advantages of using HPLC for this application include its speed and precision, its ability to be automated, its good limits of detection, and its compatibility with a wide range of assay formats and detectors. This review will discuss various approaches in which HPLC can be employed for the study of drug-protein interactions. These techniques include the use of soluble proteins in zonal elution and frontal analysis methods or vacancy techniques such as the Hummel-Dreyer method. Zonal elution and frontal analysis methods that make use of immobilized proteins and high-performance affinity chromatography will also be presented. A variety of applications will be examined, ranging from the determination of free drug fractions to the measurement of the strength or rate of a drug-protein interaction. Newer developments that will be discussed include recent work in the creation of novel mathematical approaches for HPLC studies of drug-protein binding, the use of HPLC methods for the high-throughput screening of drug-protein binding, and the creation and use of affinity monoliths or affinity microcolumns for examining drug-protein systems.

Drug-protein binding: a critical review of analytical tools

The extent of drug binding to plasma proteins, determined by measuring the free active fraction, has a significant effect on the pharmacokinetics and pharmacodynamics of a drug. It is therefore highly important to estimate drug-binding ability to these macromolecules in the early stages of drug discovery and in clinical practice. Traditionally, equilibrium dialysis is used, and is presented as the reference method, but it suffers from many drawbacks. In an attempt to circumvent these, a vast array of different methods has been developed. This review focuses on the most important approaches used to characterize drug-protein binding. A description of the principle of each method with its inherent strengths and weaknesses is outlined. The binding affinity ranges, information accessibility, material consumption, and throughput are compared for each method. Finally, a discussion is included to help users choose the most suitable approach from among the wealth of methods presented.

Lessons from the crystallographic analysis of small molecule binding to human serum albumin

SUMMARY

Human serum albumin (HSA) is an abundant and highly soluble plasma protein with the capacity to bind a remarkably diverse set of lipophilic anionic compounds so that it fulfils important roles in the transport of nutrients, hormones and toxins. The protein attracts great interest from the pharmaceutical industry since it can also bind a variety of drug molecules, impacting their delivery and efficacy. Our understanding of the binding and transport properties of albumin has been transformed by structural studies of the protein, in which crystallographic analysis has played a leading role. This review summarises the main insights to have accrued from this work, highlighting the significant advances that have been made but also pointing out some of the challenges ahead. Since further progress is likely to benefit from increased structural scrutiny of HSA, methodological developments instrumental to the success of crystallographic analysis of the protein are discussed in some detail.

Characterization of drug-protein interactions in blood using high-performance affinity chromatography

The binding of drugs with proteins in blood, serum, or plasma is an important process in determining the activity, distribution, rate of excretion, and toxicity of drugs in the body. High-performance affinity chromatography (HPAC) has received a great deal of interest as a means for studying these interactions. This review examines the various techniques that have been used in HPAC to examine drug-protein binding and discusses the types of information that can be obtained through this approach. A comparison of these techniques with traditional methods for binding studies (e.g., equilibrium dialysis and ultrafiltration) will also be presented. The use of HPAC with specific serum proteins and binding agents will then be discussed, including HSA and alpha(1)-acid glycoprotein (AGP). Several examples from the literature are provided to illustrate the applications of such research. Recent developments in this field are also described, such as the use of improved immobilization techniques, new data analysis methods, techniques for working directly with complex biological samples, and work with immobilized lipoproteins. The relative advantages and limitations of the methods that are described will be considered and the possible use of these techniques in the high-throughput screening or characterization of drug-protein binding will be discussed.

Quantitative structure-(chromatographic) retention relationships

Since the pioneering works of Kaliszan (R. Kaliszan, Quantitative Structure-Chromatographic Retention Relationships, Wiley, New York, 1987; and R. Kaliszan, Structure and Retention in Chromatography. A Chemometric Approach, Harwood Academic, Amsterdam, 1997) no comprehensive summary is available in the field. Present review covers the period of 1996-August 2006. The sources are grouped according to the special properties of kinds of chromatography: Quantitative structure-retention relationship in gas chromatography, in planar chromatography, in column liquid chromatography, in micellar liquid chromatography, affinity chromatography and quantitative structure enantioselective retention relationships. General tendencies, misleading practice and conclusions, validation of the models, suggestions for future works are summarized for each sub-field. Some straightforward applications are emphasized but standard ones. The sources and the model compounds, descriptors, predicted retention data, modeling methods and indicators of their performance, validation of models, and stationary phases are collected in the tables. Some important conclusions are: Not all physicochemical descriptors correlate with the retention data strongly; the heat of formation is not related to the chromatographic retention. It is not appropriate to give the errors of Kovats indices in percentages. The apparently low values (1-3%) can disorient the reviewers and readers. Contemporary mean interlaboratory reproducibility of Kovats indices are about 5-10 i.u. for standard non polar phases and 10-25 i.u. for standard polar phases. The predictive performance of QSRR models deteriorates as the polarity of GC stationary phase increases. The correlation coefficient alone is not a particularly good indicator for the model performance. Residuals are more useful than plots of measured and calculated values. There is no need to give the retention data in a form of an equation if the numbers of compounds are small. The domain of model applicability of models should be given in all cases.

Micellar liquid chromatography with dodecyl dimethyl betaine as an in vitro method for prediction of protein-drug binding

With the accelerating development of new drugs, there is a high need for rapid and simple screening technologies. In this paper, a new in vitro method, dodecyl dimethyl betaine (BS-12) micellar liquid chromatography (MLC) was presented for prediction of protein-drug binding based on the similar property of BS-12 micelles to protein. The predictive possibility of this method was validated by comparing the retention factors of drugs (antidiabetic and antibacterial drugs) on C18 modified by different surfactants with those on the protein column. Through the investigation of the concentration and pH effect on the retention of the drugs in BS-12 MLC, quantitative retention-protein binding relationships were established according to the retention factors in 0.2 M BS-12 (pH 7.4) MLC and those on the protein column. According to the relationships established, the protein binding of seven drugs for psychiatric disorders, six potential drugs for antibiotics and four commercial antibiotics were predicted. The results were consistent with those on the BSA column very well. This indicated, BS-12 MLC was a simple, fast and reproducible method to predict protein-drug binding.

Measurement of drug–protein binding by immobilized human serum albumin-HPLC and comparison with ultrafiltration

An HPLC method employing CHIRAL-I (150 mm x 3 mm), 5 microm column from Chrom. Tech., immobilized with human serum albumin (HSA), was used to determine in vitro protein binding of several compounds. Experimentally obtained plasma protein data exhibited good correlation with the reported values. The method was compared with the conventional ultra filtration technique and both yielded similar results. Proprietary compounds that could not be analyzed by ultra filtration due to high non-specific binding to filter membrane were successfully analyzed by HSA-HPLC method. On the other hand, two proprietary compounds did not elute from HSA column due to strong binding, but were successfully analyzed by ultra filtration. This proves that both the techniques have their own merits and demerits and should be exploited judiciously as per the requirement. The plasma protein binding studies conducted on four gyrase inhibitors in rat and human plasma exhibited no interspecies difference via ultra filtration method. Further, it was also observed that the protein binding obtained for the four gyrase inhibitors by HSA-HPLC method was not only similar to that obtained by ultra filtration in human plasma but was also in accordance with ex vivo and in vitro protein binding obtained for rat plasma after ultra filtration because these compounds predominantly bind to HSA The binding of several compounds to alpha1-acid glycoprotein (AGP), another important plasma protein, was also examined using AGP immobilized column. However, the data could not be relied upon since some anti-bacterials and non-steroidal anti-inflammatory drugs (NSAIDS), which are known to predominantly bind to HSA, were also found to bind to AGP.

Structural basis of the drug-binding specificity of human serum albumin

Human serum albumin (HSA) is an abundant plasma protein that binds a remarkably wide range of drugs, thereby restricting their free, active concentrations. The problem of overcoming the binding affinity of lead compounds for HSA represents a major challenge in drug development. Crystallographic analysis of 17 different complexes of HSA with a wide variety of drugs and small-molecule toxins reveals the precise architecture of the two primary drug-binding sites on the protein, identifying residues that are key determinants of binding specificity and illuminating the capacity of both pockets for flexible accommodation. Numerous secondary binding sites for drugs distributed across the protein have also been identified. The binding of fatty acids, the primary physiological ligand for the protein, is shown to alter the polarity and increase the volume of drug site 1. These results clarify the interpretation of accumulated drug binding data and provide a valuable template for design efforts to modulate the interaction with HSA.

Fast Gradient HPLC Method to Determine Compounds Binding to Human Serum Albumin. Relationships with Octanol/Water and Immobilized Artificial Membrane Lipophilicity

A fast gradient HPLC method (cycle time 15 min) has been developed to determine Human Serum Albumin (HSA) binding of discovery compounds using chemically bonded protein stationary phases. The HSA binding values were derived from the gradient retention times that were converted to the logarithm of the equilibrium constants (logK HSA) using data from a calibration set of molecules. The method has been validated using literature plasma protein binding data of 68 known drug molecules. The method is fully automated, and has been used for lead optimization in more than 20 company projects. The HSA binding data obtained for more than 4000 compounds were suitable to set up global and project specific quantitative structure binding relationships that helped compound design in early drug discovery. The obtained HSA binding of known drug molecules were compared to the Immobilized Artificial Membrane binding data (CHI IAM) obtained by our previously described HPLC-based method. The solvation equation approach has been used to characterize the normal binding ability of HSA, and this relationship shows that compound lipophilicity is a significant factor. It was found that the selectivity of the "baseline" lipophilicity governing HSA binding, membrane interaction, and octanol/water partition are very similar. However, the effect of the presence of positive or negative charges have very different effects. It was found that negatively charged compounds bind more strongly to HSA than it would be expected from the lipophilicity of the ionized species at pH 7.4. Several compounds showed stronger HSA binding than can be expected from their lipophilicity alone, and comparison between predicted and experimental binding affinity allows the identification of compounds that have good complementarities with any of the known binding sites.

Drug affinity to immobilized target bio-polymers by high-performance liquid chromatography and capillary electrophoresis

This review addresses the use of high-performance liquid chromatography (HPLC) and capillary electrophoresis (CE) as affinity separation methods to characterise drugs or potential drugs-bio-polymer interactions. Targets for the development of new drugs such as enzymes (IMERs), receptors, and membrane proteins were immobilized on solid supports. After the insertion in the HPLC system, these immobilized bio-polymers were used for the determination of binding constants of specific ligands, substrates and inhibitors of pharmaceutical interest, by frontal analyses and zonal elution methods. The most used bio-polymer immobilization techniques and methods for assessing the amount of active immobilized protein are reported. Examples of increased stability of immobilized enzymes with reduced amount of used protein were shown and the advantages in terms of recovery for reuse, reproducibility and on-line high-throughput screening for potential ligands are evidenced. Dealing with the acquisition of relevant pharmacokinetic data, examples concerning human serum albumin binding studies are reviewed. In particular, papers are reported in which the serum carrier has been studied to monitor the enantioselective binding of chiral drugs and the mutual interaction between co-administered drugs by CE and HPLC. Finally CE, as merging techniques with very promising and interesting application of microscale analysis of drugs' binding parameters to immobilized bio-polymers is examined.

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.

Evaluation of the human serum albumin column as a discovery screening tool for plasma protein binding

A total of 69 compounds with a variety of chemical structures were assayed using a human serum albumin column in combination with UV and mass spectrometric detection. A moderate correlation, R(2)=0.661, between the plasma protein binding, determined by traditional techniques of equilibrium dialysis or ultrafiltration, and chromatographic retention factor (k'/k'+1) was observed. Disparity between the regression line and numerous samples was observed across the entire range of plasma protein binding. Attempts to discriminate between compounds from the data set to achieve better correlation based physico-chemical properties were unsuccessful. Good agreement was observed for retention times obtained with UV detection with mobile phase containing phosphate buffer and mass spectrometric detection with mobile phase containing acetate buffer. Essentially identical data were obtained for compounds analyzed in singlet or cassette for minimally or highly bound (>90% bound) compounds. Analysis of cassettes containing compounds with plasma protein binding greater than 90% did not cause column overload, even at analyte concentrations up to 100 microg/ml. Diverse results were obtained when chromatographic retention was used to rank order various classes of compounds. Better correlation with ordering from known binding was obtained when a compound class contained a wide range of protein binding, in contrast to when compounds within a given class were all highly bound.

Quantitative structure-retention relationships in affinity high-performance liquid chromatography

In this report the affinity high-performance liquid chromatography data, which were determined on silica-based human serum albumin, alpha1-acid glycoprotein, keratin, collagen, melanin, amylose tris(3,5-dimethylphenylcarbamate), and basic fatty acid binding protein columns, are discussed. Using a quantitative structure-retention relationship (QSRR) approach the affinity data were interpreted in terms of structural requirements of specific binding sites on biomacromolecules. The unique chromatographic properties of immobilized artificial membrane and cholesterol stationary phases were also analyzed from the point of view of mimicking biological processes. It has been demonstrated that chemometric processing of appropriately designed sets of chromatographic data derived in systems comprising biomolecules provides information of relevance for molecular pharmacology and rational drug design.

High-performance affinity chromatography: a powerful tool for studying serum protein binding

High-performance affinity chromatography (HPAC) is a method in which a biologically-related ligand is used as a stationary phase in an HPLC system. This approach is a powerful means for selectively isolating or quantitating agents in complex samples, but it can also be employed to study the interactions of biological systems. In recent years there have been numerous reports in which HPAC has been used to examine the interactions of drugs, hormones and other substances with serum proteins. This review discusses how HPAC has been used in such work. Particular attention is given to the techniques of zonal elution and frontal analysis. Various applications are provided for these techniques, along with a list of factors that need to be considered in their optimization and use. New approaches based on band-broadening studies and rapid immunoextraction are also discussed.

Quantitative structure/retention relationships in affinity chromatography

Affinity chromatography (AC) followed by quantitative structure/retention relationships (QSRR) analysis provides information on both the analytes and the macromolecules forming the stationary phases. QSRR equations derived for test series of analytes (often drugs) are interpreted in terms of structural requirements of the specific binding sites on macromolecules. Chromatographically demonstrated differences in analyte/macromolecule interactions may be relevant to molecular pharmacology and rational drug design. Multiple regression analysis of appropriately designed sets of affinity-chromatographic data may help increase the speed and efficiency of search as for new drugs and reduce the need for in vivo screening. Specific high-performance affinity-chromatographic separations can be optimized by rational selection of chiral columns, the characteristics of which are provided by QSRR.