In vivo pharmacokinetic screening in cassette dosing experiments; the use of on-line Pprospekt liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry technology in drug discovery

“Cocktail” Approaches and Strategies in Drug Development: Valuable Tool or Flawed Science?

There is an increasing interest in the simultaneous administration of several probe substrates to characterize the activity of multiple drug-metabolizing enzymes, the so-called "cocktail" approach. However, this method remains controversial and is being investigated more extensively. No general consensus has emerged on the applicability of this approach in clinical investigation and during drug development. The objective of the article is to review this important yet specialized technique, as well as its merits, drawbacks, and potential application in drug development. Among the two-, three-, four-, five-, and six-drug in vivo cocktails previously evaluated in humans, a variety of substrate probe combinations have been studied. Some probe combinations have been validated not to interact in vivo and have been useful in characterizing drug-drug interaction potential and metabolic enzyme induction in humans. For drug candidates that affect two or more in vitro pathways or are potential gene inducers, the use of a cocktail approach may facilitate the rapid delineation of the drug candidate's drug interaction potential. It may also offer the potential of providing clear guidance on safely conducting larger clinical studies and limiting comedication restrictions to only those likely to be clinically relevant.

High-throughput liquid chromatography/mass spectrometry method for the quantitation of small molecules using accurate mass technologies in supporting discovery drug screening

RATIONALE

Drug discovery samples are routinely analyzed using liquid chromatography/tandem mass spectrometry (LC/MS/MS) methods on triple quadrupole mass spectrometers employing multiple reaction monitoring (MRM). In order to improve analysis throughput, quantitation of small molecules on a quadrupole time-of-flight (QqTOF) instrument using TOF scan and high-resolution MRM (MRM-HR) modes was evaluated in this study.

METHODS

Cassette dosed plasma and brain samples from nine compounds were extracted using a protein precipitation method. Separation was achieved by reversed-phase liquid chromatography. Mass spectrometric analysis was performed using TOF scan and high-resolution MRM approaches on a QqTOF mass spectrometer with turbo-ionspray ionization. Results were compared to those obtained on a triple quadrupole mass spectrometer.

RESULTS

The dynamic range varied depending on compounds and instruments and was similar between the MRM on QqQ and full TOF scan mode on QqTOF. Linear or quadratic regression and 1/x(2) weighting were used. Resolution on the QqTOF instrument was around 32000 and mass accuracy was within 4.4 ppm. The MRM-HR method showed better sensitivity compared to the TOF scan method, and was comparable to the MRM on a QqQ mass spectrometer. Assay accuracy was within ±25%.

CONCLUSIONS

A TOF scan method allowed the use of the generic method without compound-specific optimization and was an alternative choice for routine high-throughput quantitation of small molecules. The MRM-HR method on the QqTOF showed good sensitivity which was comparable to that obtained by the MRM method on the triple quadrupole mass spectrometer.

Turbulent flow bioanalysis in drug metabolism and pharmacokinetics

Turbulent flow chromatography (TFC) as an analytical technique was introduced in the mid-1990s for online sample processing in bioanalysis. Turbulent flow columns are packed with large particles permitting the use of high mobile phase linear velocities. Solute molecules travel in a uniform concentrated band in which large matrix biomolecules are effectively separated from lower molecular weight analytes by differential mass transfer effects. In addition, the use of various bonded stationary phases enhances selectivity in TFC separations. Originally, the turbulent flow column was used for both online sample processing and the analytical separation. This mode of operation has largely been replaced with a dual column arrangement, in which sample processing is done online with the turbulent flow column and a second analytical column is employed for separation. Within the pharmaceutical industry, certain laboratories now use TFC routinely for bioanalytical support of in vivo drug discovery pharmacokinetic studies. Validated TFC methods are also used to support GLP-compliant preclinical toxicokinetic studies and clinical trials. TFC has been shown to simplify bioanalytical sample preparation and reduce sample processing costs when compared with offline techniques such as SPE. TFC may be combined with multiplexing up to four HPLC systems to a single mass spectrometer to increase analytical throughput.

N-in-1 dosing pharmacokinetics in drug discovery: experience, theoretical and practical considerations

N-in-1 (or cassette) dosing pharmacokinetics (PK) has been used in drug discovery for rapid assessment of PK properties of new chemical entities. However, because of potential for drug-drug interactions this procedure is still controversial. This study was to retrospectively evaluate the N-in-1 dosing approach in drug discovery with an emphasis on the potential for drug-drug interactions. The systemic clearance, volume of distribution, oral bioavailability, and renal excretion of the 31 lead compounds in rats, dogs or chimpanzees were significantly correlated between the N-in-1 dosing and discrete studies with r values of 0.69, 0.91, 0.53, and 0.83 (p < 0.005 for all), respectively. PK parameters for 11 quality control compounds which were involved in 194 N-in-1 studies for screening approximately 1000 compounds had coefficient of variations of less than 70%. The intrinsic microsomal clearances generated from the N-in-1 and discrete incubations were nearly identical (r = 0.97, p < 0.0001). The intrinsic clearances of quality control compound from the N-in-1 incubations were consistent with its discrete CL(int) estimate (cv: 5.4%). Therefore, N-in-1 dosing is a useful approach in drug discovery to quickly obtain initial PK estimates. Potential drug-drug interactions that result in confounding PK estimates do not occur as frequently as expected.

Snapshot PK: a rapid rodent in vivo preclinical screening approach

Described in this article are strategies implemented to increase the throughput of in vivo rodent pharmacokinetic (PK) studies using the snapshot PK study design and automated methods for compound submission, sample processing, data analysis and reporting. Applying snapshot PK studies to categorize the oral exposure of >1300 discovery compounds as low, moderate or high resulted in an attrition rate of 86%. The follow up full PK studies on the remaining compounds found that 98% of the compounds were predicted in the correct (69%) or adjacent (29%) oral exposure category by the snapshot PK studies. These results demonstrate that the snapshot PK screen in rodents can serve as an effective and efficient in vivo tool in the compound selection process in drug discovery.

Flexible Automated Approach for Quantitative Liquid Handling of Complex Biological Samples

A fully automated protein precipitation technique for biological sample preparation has been developed for the quantitation of drugs in various biological matrixes. All liquid handling during sample preparation was automated using a Hamilton MicroLab Star Robotic workstation, which included the preparation of standards and controls from a Watson laboratory information management system generated work list, shaking of 96-well plates, and vacuum application. Processing time is less than 30 s per sample or approximately 45 min per 96-well plate, which is then immediately ready for injection onto an LC-MS/MS system. An overview of the process workflow is discussed, including the software development. Validation data are also provided, including specific liquid class data as well as comparative data of automated vs manual preparation using both quality controls and actual sample data. The efficiencies gained from this automated approach are described.

A monolithic-phase based on-line extraction approach for determination of pharmaceutical components in human plasma by HPLC–MS/MS and a comparison with liquid–liquid extraction

An automated procedure using monolithic-phase based on-line extraction is described for pharmaceutical component analysis in plasma by LC-MS/MS. In this approach, a short monolithic C(18) 4.6 mm x 10 mm cartridge is used for high flow extraction at 4 mL/min. Plasma samples were subjected to protein precipitation first with acetonitrile, and the supernatant was diluted and loaded onto a monolithic cartridge. Sample elution was accomplished with narrow-bore LC-MS/MS system. A method for determination of Amprenavir (APV) and Atazanavir (AZV) in human plasma was developed with this approach. After 0.1 mL of plasma was transferred into each well of a 96-well plate by a liquid handler, the rest of sample preparation time typically only takes about 20 min. A Phenomenex Luna C18(2) 2.0 mm x 150 mm analytical column was used for the separation at a flow rate of 0.3 mL/min. The run time for each sample was 4 min. The standard curve range was 2.77-1520 ng/mL for Atazanavir, and 4.50-2560 ng/mL for Amprenavir. The accuracy (%bias) at the lower limit of quantitation (LLOQ) for Atazanavir was 2.7% and the precision (%CV) at the LLOQ was 7.9%, while the accuracy at LLOQ for Amprenavir was -1.3% and the precision at LLOQ was 7.8%. The inter-day %bias and %CV of the quality control samples of Atazanavir were < or = 4.5% and < or = 6.5%, respectively. The inter-day %bias and %CV of the quality control samples of Amprenavir were < or = 1.1% and < or = 7.2%, respectively. Coefficients of determination, a measure of linearity, ranged from 0.993 to 0.999. Very low carry-over (0.006%) even after high standard sample was demonstrated in the monolithic-phase based method. Other characteristics of such method include high recovery and good tolerance to matrix effect, which was demonstrated by 12 lots of plasma. The back pressure of the monolithic extraction cartridge remained the same after 450 samples injected. The performance of the monolithic-phased on-line extraction method was compared with that done by an automated 96-well liquid-liquid extraction procedure, which was carried out using hexane:ethyl acetate as the extraction solvent. The results showed that similar precision and accuracy were achieved by both methods.

Quantitative determination method for trace amount of penicillin contaminants in commercially available drug product by HPLC coupled with tandem mass spectrometry

A quantitative determination method for trace amount of penicillin contaminants in an active pharmaceutical ingredient (API) has been developed. Selective extraction of penicillin contaminants from the matrix containing API and specific separation among penicillin contaminants were achieved through an on-line column switching technique with gradient elution, followed by tandem mass spectrometric determination. Validation was conducted on the developed method in terms of specificity, linearity, accuracy, precision, and detection limit, and appeared reasonable. The detection limit was estimated as 0.03 ng/ml or lower of the concentration of penicillin contaminants in the preparation, corresponding to 4 parts par billion (ppb) against the API. This fulfilled the regulatory requirement by the authorities.

A novel on-line solid-phase extraction approach integrated with a monolithic column and tandem mass spectrometry for direct plasma analysis of multiple drugs and metabolites

An on-line solid-phase extraction liquid chromatography/tandem mass spectrometry (SPE LC/MS/MS) assay using a newly developed SPE column and a monolithic column was developed and validated for direct analysis of plasma samples containing multiple analytes. This assay was developed in an effort to increase bioanalysis throughput and reduce the complexity of on-line SPE LC/MS/MS systems. A simple column-switching configuration that requires only one six-port valve and one HPLC pumping system was employed for on-line plasma sample preparation and subsequent gradient chromatographic separation. The resulting analytical method couples the desired sensitivity with ease of use. The method was found to perform satisfactorily for direct plasma analysis with respect to assay linearity, specificity, sensitivity, precision, accuracy, carryover, and short-term stability of an eight-analyte mixture in plasma. A gradient LC condition was applied to separate the eight analytes that cannot be distinctly differentiated by MS/MS. With a run time for every injection of 2.8 min, a minimum of 300 direct plasma injections were made on one on-line SPE column without noticeable changes in system performance. Due to the ruggedness and simplicity of this system, generic methods can be easily developed and applied to analyze a wide variety of compounds in a high-throughput manner without laborious off-line sample preparation.

Automated 96-well liquid–liquid back extraction liquid chromatography–tandem mass spectrometry method for the determination of ABT-202 in human plasma

A high-throughput bioanalytical method using automated sample transferring, automated liquid-liquid back extraction and liquid chromatography-tandem mass spectrometry was developed in a GLP regulated environment for the determination of ABT-202 in human plasma. Samples of 0.30 ml were transferred into 96-well plate using an automatic liquid handler. Automated liquid-liquid extraction (LLE) was carried out on a 96-channel programmable liquid handling workstation using methyl tert-butyl ether as the extraction solvent. A dual-HPLC with single mass spectrometer configuration was utilized to provide a reliable and routine means to increase sample throughput. The standard curve range was 0.38-95.02 ng/ml. There was no interference from endogenous components in the blank plasma tested. The accuracy (% bias) at the lower limit of quantitation (LLOQ) was 7.7% and the precision (% CV) for samples at the LLOQ was 4.7%. The inter-day % CV and % bias of the quality control samples were < or = 6.8 and < or = 7.6%, respectively. Coefficients of determination, a measure of linearity, ranged from 0.994 to 0.997. The method was accurate and reproducible and was successfully applied to generate plasma concentration-time profiles for human subjects after low oral doses of the compound.

Cassette dosing pharmacokinetics of a library of 2,6,9-trisubstituted purine cyclin-dependent kinase 2 inhibitors prepared by parallel synthesis

Determination of pharmacokinetic properties in the intact animal remains a major bottleneck in drug discovery. Cassette dosing involves administration of a cocktail of drugs to individual animals. Here we describe the cassette dosing properties of a 107-membered library of 2,6,9-trisubstituted purine cyclin-dependent kinase 2 (CDK2) inhibitors. A three-step parallel synthesis approach produced compounds with purity ranging from 63% to 100%. Cassette dosing was validated by comparing the pharmacokinetic parameters obtained following i.v. administration of a mixture of olomoucine, R-roscovitine (CYC202), and bohemine, each at 16.6 mg/kg, with results for administration of single agents at 50 mg/kg. No significant difference was observed between the pharmacokinetic parameters of agents when dosed in combination compared with those of individual compounds. CYC202 showed the highest area under the curve (AUC) and the longest elimination half-life (t1/2). Further cassettes evaluated the library of trisubstituted purines with CYC202 and purvalanol A included as pharmacokinetic standards in a validated limited sampling strategy. The ratios of pharmacokinetic parameters to that of CYC202 [AUC, maximum concentration (Cmax), and t1/2] remained similar when compounds were tested in two different cassettes or as individual compounds. Following dosing of the same cassette on three different days, there was less than 20% variation in pharmacokinetic parameters between days. The structure-pharmacokinetics relationship showed that the favored purine substituents are benzylamine and veratrylamine at position 6, amino-2 propanol at position 2, and methylpropyl or hydroxyethyl at position 9. Without cassette dosing, this study would have used 3 times as many animals and would have taken 4 times longer, illustrating the power of this method in lead optimization.

The effect of eluent pH and compound acid–base character on the design of generic-gradient reversed-phase high-performance liquid chromatography (RP-HPLC) methods for use in drug discovery

The design of generic reversed-phase high-performance liquid chromatography (RP-HPLC) gradient methods for the analysis of compound mixtures or 'cocktails' has been investigated with particular reference to the eluent pH and the type of compound (acid, base or neutral) analysed. The use of eluents with an acidic eluent pH, an approach which is widely employed, can lead to non-retention of polar bases resulting in 'failure' of the method. This problem is aggravated where the majority of compounds submitted for analysis are bases, which is typical of many drug discovery programs. The problem can be ameliorated through the use of eluents with near neutral pH. Although these neutral pH eluents can lead to co-elution when cocktails are analysed and possibly ion-suppression where mass spectrometry (MS) is the detection method, this can be avoided through optimisation of the gradient shape.

Synthesis and Evaluation of PEG414, a Novel Formulating Agent that Avoids Analytical Problems Associated with Polydisperse Vehicles such as PEG400

Polyethylene glycol (PEG) 400 is widely used as a formulating agent for both intravenous and oral studies during drug discovery. It is a polydisperse material containing more than 16 oligomers, which can cause significant problems for high-performance liquid chromatography-mass spectrometry analysis due to ion suppression and isobaric interference. To overcome these difficulties, we have synthesized the single oligomer PEG414. The material has been characterized with a range of diverse drug compounds and shown to be comparable to PEG400 and superior to propylene glycol in terms of its solubilization power. The toxicological and metabolic properties of PEG414 should be similar to PEG400. It suffers none of the analytical problems associated with polydisperse agents and we expect it to be a useful alternative for the formulation of test compounds for intravenous and oral dosing during drug discovery.

Validation of a sensitive and automated 96-well solid-phase extraction liquid chromatography-tandem mass spectrometry method for the determination of desloratadine and 3-hydroxydesloratadine in human plasma

To support clinical development, a liquid chromatographic-tandem mass spectrometric (LC-MS-MS) method was developed and validated for the determination of desloratadine (descarboethoxyloratadine) and 3-OH desloratadine (3-hydroxydescarboethoxyloratadine) concentrations in human plasma. The method consisted of automated 96-well solid-phase extraction for sample preparation and liquid chromatography/turbo ionspray tandem mass spectrometry for analysis. [2H(4)]Desloratadine and [2H(4)]3-OH desloratadine were used as internal standards (I.S.). A quadratic regression (weighted 1/concentration(2)) gave the best fit for calibration curves over the concentration range of 25-10000 pg/ml for both desloratadine and 3-OH desloratadine. There was no interference from endogenous components in the blank plasma tested. The accuracy (%bias) at the lower limit of quantitation (LLOQ) was -12.8 and +3.4% for desloratadine and 3-OH desloratadine, respectively. The precision (%CV) for samples at the LLOQ was 15.1 and 10.9% for desloratadine and 3-OH desloratadine, respectively. For quality control samples at 75, 1000 and 7500 pg/ml, the between run %CV was </=7.5% for desloratadine and </=6.3% for 3-OH desloratadine. Between run %bias ranged from 4.1 to 8.0% for desloratadine and -11.5 to -4.8% for 3-OH desloratadine. Desloratadine and 3-OH desloratadine were stable in human plasma for 401 days at -22 degrees C, after five freeze/thaw cycles, up to 24 h at room temperature, and in reconstituted sample extracts (up to 185 h at 5 degrees C). This LC-MS-MS method for the determination of desloratadine and 3-OH desloratadine in human plasma met regulatory requirements for selectivity, sensitivity, goodness of fit, precision, accuracy and stability.

Generic solid phase extraction-liquid chromatography-tandem mass spectrometry method for fast determination of drugs in biological fluids

A generic method was developed for the fast determination of a wide range of drugs in serum or plasma. The methodology comprises generic solid-phase extraction, on-line coupled to gradient HPLC with tandem mass spectrometric detection (SPE-LC-MS/MS). The individual components of the SPE-LC-MS/MS system were optimized in an integrated approach to maximize the application range and minimize the method development time. The optimized generic SPE-LC-MS/MS protocol was evaluated for 11 drugs with different physicochemical properties. Good quantification for 10 out of 11 of the pharmaceuticals in serum or plasma could be readily achieved. The quantitative assays gave recoveries better than 95%, lower quantification limits of 0.2-2.0 ng/ml, acceptable precision and accuracy and good linearity over 2-4 orders of magnitude. Carry-over was determined to be in the range of 0.02-0.10%, without optimization.

A new generic column switching system for quantitation in cassette dosing using LC/MS/MS

Cassette dosing is a method in which multiple drugs are administered to a single animal at the same time, and the plasma concentrations of the individual compounds are simultaneously determined. This method enables high-throughput rapid screening for pharmacokinetic assessment of new drug candidates. An available gradient method was modified for cassette dosing analysis to attain the advantages of high sensitivity and applicability to a wide range of compounds. However, two problems arose; (1). the time-consuming optimization of mobile phases for each compound group, which limited applicability and (2). the remarkable suppression of ionization by polyethyleneglycol, which is commonly used in intravenous administration. To resolve these problems, a new column switching method was established to attain wider applicability and avoid the ionization suppression. This column switching system is very simple because the trap column and the analytical column are specified and the mobile phase is selected from only two species. Method optimization requires only the selection of the mobile phase and takes only a few hours. About 200 compounds, which were administered as about 50 cassettes, were analyzed using this column switching system. Assay validation of one cassette was carried out, and good accuracy and precision were obtained. About 90% of the compounds could be determined within 20% bias. These results showed that this new column switching system for cassette dosing is accurate enough for the screening of drug candidates and offers wide applicability for various compounds. This system was shown to be very useful for the determination of cassette dosing samples, containing multiple compounds.

Rapid analysis of metabolic stability of dopamine receptor antagonists and detection of their metabolites by liquid chromatography/tandem mass spectrometry

In vitro metabolic stability of dopamine D(3)/D(4) receptor antagonists and identification of their metabolites by high-performance liquid chromatography (HPLC) coupled with ion-trap mass spectrometry (ITMS) were assessed in rat liver microsomes. The compounds were divided into three cassette groups for rapid quantitative analysis of multiple drugs and simultaneous detection of their metabolites. The samples from incubation with rat liver microsomes were pooled into designed cassette groups and analyzed by HPLC/electrospray ITMS in full-scan mode. The metabolic stability of the drugs was determined by comparing their signals after incubation for 0 and for 30min. The metabolic stability of the examined dopamine receptor antagonists was in the range of 9.9-84.4%. In addition, the present cassette analysis allowed the simultaneous detection of metabolites formed during the same incubation without having to reanalyze the samples. The metabolites were first characterized by nominal mass measurement of the corresponding protonated molecules. Subsequent multistage tandem mass spectrometry on the ion-trap instrument allowed characterization of the structure of the detected metabolites. N,O-dealkylation and ring hydroxylation reactions were identified as major metabolic reactions in piperazinylalkylisoxazole derivatives. These results suggested that the present approach is useful for the rapid evaluation of metabolic stability and structural characterization of metabolites within a short period in new drug discovery.

Quantitative characterization of differential ion suppression on liquid chromatography/atmospheric pressure ionization mass spectrometric bioanalytical methods

Ion suppression is a known phenomenon in atmospheric pressure ionization mass spectrometry. These suppression effects have been shown to adversely affect the accuracy and precision of quantitative bioanalytical methods. This paper presents a simple procedure for determining the impact of differential ion suppression on bioanalytical methods that utilize atmospheric pressure ionization mass spectrometric (APIMS) detection. This procedure was applied to the assessment of two potential internal standards, and to determine selectivity issues for another analyte which was to be measured in multiple species.

Product ion scanning using a Q-q-Q linear ion trap (Q TRAP) mass spectrometer

The use of a Q-q-Q(linear ion trap) instrument to obtain product ion spectra is described. The instrument is based on the ion path of a triple quadrupole mass spectrometer with Q3 operable as either a conventional RF/DC quadrupole mass filter or a linear ion trap mass spectrometer with axial ion ejection. This unique ion optical arrangement allows de-coupling of precursor ion isolation and fragmentation from the ion trap itself. The result is a high sensitivity tandem mass spectrometer with triple quadrupole fragmentation patterns and no inherent low mass cut-off. The use of the entrance RF-only section of the instrument as accumulation ion trap while the linear ion trap mass spectrometer is scanning enhances duty cycles and results in increased sensitivities by as much as a factor of 20. The instrument is also capable of all of the triple quadrupole scans including multiple-reaction monitoring (MRM) as well as precursor and constant neutral loss scanning. The high product ion scanning sensitivity allows the recording of useful product ion spectra near the MRM limit of quantitation.

Biomedical and biological mass spectrometry

This review focuses on biological and biomedical mass spectrometry, and covers a selection of publications in this area included in the MEDLINE database for the period 1987-2001. Over the last 15 years, biological and biomedical mass spectrometry has progressed out of all recognition. The development of soft ionization methods, such as electrospray ionization and matrix-assisted laser desorption ionization, has mainly contributed to the remarkable progress, because they can easily produce gas-phase ions of large, polar, and thermally labile biomolecules, such as proteins, peptides, nucleic acids and others. The innovations of ionization methods have led to remarkable progress in mass spectrometric technology and in biochemistry, biotechnology and molecular biology research. In addition, mass spectrometry is one of the powerful and effective technologies for drug discovery and development. It is applicable to studies on structural determination, drug metabolism, including pharmacokinetics and toxicokinetics, and de novo drug discovery by applying post-genomic approarches. In the present review, the innovative soft ionization methods are first discussed along with their features. Also, the characteristics of the mass spectrometers which are active in the biological and biomedical research fields are also described. In addition, examples of the applications of biological and biomedical mass spectrometry are provided.

Cassette dosing approach and quantitative structure-pharmacokinetic relationship study of antifungal N-myristoyltransferase inhibitors

Pharmacokinetic (PK) parameters of N-myristoyltransferase (Nmt) inhibitors were measured, and a multivariate quantitative structure-pharmacokinetic relationship (QSPKR) model for predicting rat elimination half-life (t(1/2)) values was constructed. One hundred seven benzofuran derivatives have been selected as the data set for QSPKR analysis. The correlation between the t(1/2) values and 30 physicochemical descriptors was examined by a stepwise multiple linear regression method. The statistical analysis gives a significant QSPKR model (r = 0.843) with the following three variables: partial negative surface area (PNSA), atomic-based octanol/water partition coefficient (AlogP), and the number of rotational bonds (Rotlbonds). The QSPKR model obtained is predictive and simple, and would give a direction for designing new Nmt inhibitors having good PK profiles.

Direct cocktail analysis of drug discovery compounds in pooled plasma samples using liquid chromatography-tandem mass spectrometry

Direct plasma injection technology coupled with a LC-MS/MS assay provides fast and straightforward method development and greatly reduces the time for the tedious sample preparation procedures. In this work, a simple and sensitive bioanalytical method based on direct plasma injection using a single column high-performance liquid chromatography (HPLC) and tandem mass spectrometry (MS/MS) was developed for direct cocktail analysis of double-pooled mouse plasma samples for the quantitative determination of small molecules. The overall goal was to improve the throughput of the rapid pharmacokinetic (PK) screening process for early drug discovery candidates. Each pooled plasma sample was diluted with working solution containing internal standard and then directly injected into a polymer-coated mixed-function column for sample clean-up, enrichment and chromatographic separation. The apparent on-column recovery of six drug candidates in mouse plasma samples was greater than 90%. The single HPLC column was linked to either an atmospheric pressure chemical ionization (APCI) or electrospray ionization (ESI) source as a part of MS/MS system. The total run cycle time using single column direct injection methods can be achieved within 4 min per sample. The analytical results obtained by the described direct injection methods were comparable with those obtained by semi-automated protein precipitation methods within +/- 15%. The advantages and challenges of using direct single column LC-MS/MS methods with two ionization sources in combination of sample pooling technique are discussed.

An intelligent data acquisition system for simultaneous screening of microsomal stability and metabolite profiling by liquid chromatography/mass spectrometry

This paper describes the development of a mass spectrometer-based, intelligent, programmable, sample-selection data acquisition system with two unique features. One is that the system allows automatic determination of the mass to charge ratio (m/z) of an unknown compound and the utilization of the molecular ion information to perform selective ion monitoring (SIM) experiments for quantitation. The other is its decision-making capability to select intelligently different samples and perform different experiments during data acquisition. These features were demonstrated by the application of the system to simultaneous screening for the microsomal stability and metabolite profiling of adatanserin. In this application, the data acquisition system continuously calculated the peak areas of adatanserin from SIM analyses of a batch of microsomal incubates stopped at various time points. Once the peak area of adatanserin had dropped to an arbitrarily predefined 60% of the initial value, the system made a decision to perform metabolite profiling of the sample. This decision initiated a series of automated operations, such as selecting a sample for re-analysis, changing the data acquisition time and liquid chromatographic gradient and switching the SIM mode to the data-dependent product ion scanning mode. The completed analysis of the batch of samples provided information both on the microsomal stability and on the metabolic profile of adatanserin. This simultaneous approach to investigating microsomal stability and metabolite profiling significantly increases the throughput for drug discovery support.

Applications of new liquid chromatography-tandem mass spectrometry technologies for drug development support

We have evaluated (i) a multiplexed electrospray interface, (ii) serial sample introduction, and (iii) a quadrupole time-of-flight mass spectrometer for quantitative bioanalysis in compliance with good laboratory practice. These evaluations were done using a 96-well plate liquid chromatography-tandem mass spectrometry method for the quantitation of loratadine and its metabolite, descarboethoxyloratadine. The assay has a dynamic range of 1-1000 ng/ml with 5.56 pg of each analyte being injected on-column at the limit of quantitation. For the four-channel multiplexed electrospray experiments, one-run validations were performed simultaneously in rat, rabbit, mouse and dog plasma. In the four-stream serial experiments, the total run time of the assay was reduced from 3.5 to 0.35 min, resulting in a net acquisition time of 11 s. Four simulated validation runs with standard and quality control solutions were analyzed. Precision and accuracy for standards and quality control samples met US Food and Drug Administration recommended criteria for both the drug and the metabolite using those two approaches. In addition, a quadrupole time-of-flight mass spectrometer was used as a detector in the tandem mass spectrometry mode for the loratadine assay. Our results demonstrated that a dynamic range of three orders of magnitude could be achieved using the quadrupole time-of-flight mass spectrometer, making it useful for quantitation in preclinical toxicology studies.

Evaluation of a four-channel multiplexed electrospray triple quadrupole mass spectrometer for the simultaneous validation of LC/MS/MS methods in four different preclinical matrixes

A four-channel multiplexed electrospray interface on a triple quadrupole mass spectrometer was evaluated for the simultaneous validation of LC/MS/MS methods for the quantitation of loratadine and its metabolite, descarboethoxyloratadine, in four different biological matrixes. The assays were performed in rat, rabbit, mouse, and dog plasma from 1 to 1000 ng/mL using 96-well solid-phase extraction for sample preparation. The limit of quantitation of 1 ng/mL corresponded to 5.56 pg of each analyte injected on-column. For the drug, quality control samples (n = 6 at four concentrations) had precision ranging from 0.967 to 16.0% and accuracy ranging from -8.44 to 10.5% across all four species. For the metabolite, the precision ranged from 0.684 to 11.0% and the accuracy was between 6.36 and -9.06%. Intersprayer cross talk for the multiplexed electrospray ion source was evaluated as a function of analyte concentration and was less than 0.08% at concentrations as high as 1000 ng/mL. These results demonstrate the feasibility of using parallel analysis to reduce the time required for method validation and to increase sample throughput in drug development studies.

The development of a staggered parallel separation liquid chromatography/tandem mass spectrometry system with on-line extraction for high-throughout screening of drug candidates in biological fluids

A new parallel liquid chromatography/tandem mass spectrometry (LC/MS/MS) system has been developed, in which the mass detector was shared between two staggered parallel chromatographic runs. Since the chromatography for biofluids assay generally requires good analyte retention and thus tends to leave large blank chromatographic windows, this parallel system allowed the efficient use of the mass detector during these blank windows, resulting in significantly improved sample throughput. Also, in order to remove the bottleneck in sample extraction for this parallel separation system, a high-flow extraction device was used to perform on-line extraction. This allowed for the direct injection of biofluids onto the system. The performance and capability of this system was evaluated in tests that contained a single analyte (oxazepam) and multiple analytes (12-in-1). The results indicated that the data generated from this system were comparable to those obtained on a conventional single-column system. An application of the system for high-throughput pharmacokinetic screening of drug candidates was also demonstrated.

High-speed liquid chromatography/tandem mass spectrometry using a monolithic column for high-throughput bioanalysis

With the ever-increasing workload from a variety of in vitro and in vivo screening procedures, new analytical methodologies to perform bioanalysis in an accurate and high-throughput manner are in great demand. In this work, monolithic columns were used instead of conventional particulate HPLC columns to perform chromatographic separations. Because the pressure drop on a monolithic column was considerably lower than that on a particulate column, a high flow rate (6 mL/min) was used for a 4.6 x 50 mm monolithic column with a total backpressure of about 61 bar measured using acetonitrile/water (50:50). The capability of using a regular column length at high flow rates, combined with the extremely small dependency of separation efficiency on linear flow velocity, allowed for the generation of sufficient chromatographic resolving power in a significantly reduced runtime. As demonstrated in this work, a plasma extract of a mixture of tempazepam, tamoxifen, fenfluramine, and alprozolam were baseline separated within a total analysis time of one minute. An average peak width at half maximum of approximately one second was noted using a generic broad gradient. It was also found that the separation efficiency and signal/noise (S/N) ratios for this separation remained almost constant at flow rates of 1, 3, and 6 mL/min, respectively. The ruggedness of the separation was evaluated by injecting 600 plasma extracts containing the replicates of a standard curve of the above mixture during an overnight run. The chromatographic retention time, separation quality, peak response and sensitivity were highly reproducible throughout the run. This high-speed liquid chromatography/tandem mass spectrometry (LC/MS/MS) system has been used routinely in the authors' laboratory to support drug discovery programs.

Selected reaction monitoring LC-MS determination of idoxifene and its pyrrolidinone metabolite in human plasma using robotic high-throughput, sequential sample injection

The generation of large numbers of samples during early drug discovery has increased the demand for rapid and selective methods of analysis. Liquid chromatography-tandem mass spectrometry (LC-MS-MS), because of its sensitivity, selectivity, and robustness, has emerged as a powerful tool in the pharmaceutical industry for many analytical needs. This work presents a high-throughput selected reaction monitoring LC-MS bioanalytical method for the determination of idoxifene, a selective estrogen receptor modulator, and its pyrrolidinone metabolite in clinical human plasma samples. The described method uses short, small-bore columns, high flow rates, and elevated HPLC column temperatures to perform LC separations of idoxifene and its metabolite within 10 s/sample. Sequential injections were accomplished with a 215/889 multiple probe liquid handler (Gilson, Inc.), which aspirates eight samples simultaneously and performs its rinse cycle parallel to sample injection, resulting in minimum lag time between injections. This high-throughput method was applied to the determination of idoxifene and its metabolite in clinical human plasma samples. Sample preparation employed liquid/liquid extraction in the 96-well format. Method validation included determination of intra- and interassay accuracy and precision values, recovery studies, autosampler stability, and freeze-thaw stability. The LOQ obtained was 10 ng/mL for idoxifene and 30 ng/mL for the metabolite. Using idoxifene-d5 as an internal standard, idoxifene showed acceptable accuracy and precision values at QC level 1 (QC1, 15 ng/mL), level 2 (QC2, 100 ng/mL), and level 3 (QC3, 180 ng/mL) (85.0% accuracy +/- 12.0% precision, 95.1 +/- 4.9%, and 90.3 +/- 4.7%, respectively). The pyrrolidinone metabolite also showed acceptable accuracy and precision values (using no internal standard for quantitation) at QC1 (60 ng/mL), QC2 (100 ng/mL), and QC3 (180 ng/mL) (104.9 +/- 14.4%, 91.1 +/- 13.0%, and 90.8 +/- 12.2%, respectively). The validated method was applied to the analysis of 613 human clinical plasma samples. An average run time of 23 s/sample (approximately 37 min/ 96-well plate or over 3,700 sample/day) was achieved. The successful validation presented indicates that rapid methods of analysis can efficiently and reliably contribute to the fast sample turnaround required for high sample number generating processes.

A rapid, automated approach to optimisation of multiple reaction monitoring conditions for quantitative bioanalytical mass spectrometry

An improvement to the procedure for the rapid optimisation of mass spectrometry (PROMS), for the development of multiple reaction methods (MRM) for quantitative bioanalytical liquid chromatography/tandem mass spectrometry (LC/MS/MS), is presented. PROMS is an automated protocol that uses flow-injection analysis (FIA) and AppleScripts to create methods and acquire the data for optimisation. The protocol determines the optimum orifice potential, the MRM conditions for each compound, and finally creates the MRM methods needed for sample analysis. The sensitivities of the MRM methods created by PROMS approach those created manually. MRM method development using PROMS currently takes less than three minutes per compound compared to at least fifteen minutes manually. To further enhance throughput, approaches to MRM optimisation using one injection per compound, two injections per pool of five compounds and one injection per pool of five compounds have been investigated. No significant difference in the optimised instrumental parameters for MRM methods were found between the original PROMS approach and these new methods, which are up to ten times faster. The time taken for an AppleScript to determine the optimum conditions and build the MRM methods is the same with all approaches.

Solid-phase trapping of solutes for further chromatographic or electrophoretic analysis

Because of its simplicity, speed and effectiveness, solid-phase extraction (SPE) has become the preferred technique for concentration of selected analytes prior to chromatographic or electrophoretic analysis. In this review the historical development of SPE is briefly traced. Then the principles of SPE are reviewed in some detail. Numerous references are given on the format, sorbents, elution conditions, online techniques and automation with special emphasis on relatively recent developments. The principles and recent advances in solid-phase microextraction (SPME) are also reviewed. The final section on selected recent applications includes an extensive list of references to work published within the last three years. Future trends and developments are discussed briefly.

Factors to consider in the development of generic bioanalytical high-performance liquid chromatographic-mass spectrometric methods to support drug discovery

Mass spectrometric detection is gradually replacing ultraviolet (UV) as the method of choice in bioanalysis, especially in the area of early drug discovery where high sensitivity and rapid sample throughput is required and where samples are frequently pooled or "cocktailed" prior to dosing or analysis. The change from UV to MS detection requires a significant change in approach since the use of MS poses a number of unexpected problems and limitations which relate to instrument design and the ionisation process. Whilst electrospray ionisation (ESI) allows the analyst to focus on the analyte of interest it is non-selective and blind to background effects which can in certain instances alter the response of the compound of interest, leading to inaccurate data. In addition, when analysing compound mixtures, a number of precautions need to be taken since adduct formation in the MS source, the highly ESI responsive nature of formulating agents and the effect of the isotopic distribution in organic drug molecules can all lead to the production of compromised data. Whilst many of these problems can be minimised or avoided this often results in a complex and inflexible analysis system. Ultimately the analyst has to assess the degree of risk involved and take actions which reflect the use the data.

High-throughput screening in drug metabolism and pharmacokinetic support of drug discovery

The application of rapid methods currently used for screening discovery drug candidates for metabolism and pharmacokinetic characteristics is discussed. General considerations are given for screening in this context, including the criteria for good screens, the use of counterscreens, the proper sequencing of screens, ambiguity in the interpretation of results, strategies for false positives and negatives, and the special difficulties encountered in drug metabolism and pharmacokinetic screening. Detailed descriptions of the present status of screening are provided for absorption potential, blood-brain barrier penetration, inhibition and induction of cytochrome P450, pharmacokinetics, biotransformation, and computer modeling. Although none of the systems currently employed for drug metabolism and pharmacokinetic screening can be considered truly high-throughput, several of them are rapid enough to be a practical part of the screening paradigm for modern, fast-moving discovery programs.

Integrated sample collection and handling for drug discovery bioanalysis

An integrated sample handling process for drug discovery bioanalysis is described. The streamlining of study design, sample collection and automatic bioanalytical sample processing is demonstrated. Specific details for the entire procedure regarding the time saved, ease of automation and integration are defined. Details of sample handling involved a sample collection map, sample collection formatting and volume, dilution schemes for high concentration samples, choice of biological fluid and evaluating the capabilities of two liquid-handling workstations. Numerous comparisons were conducted between the new approaches and the conventional sample handling approaches. The precision and accuracy obtained from the new integrated sample handling process were comparable to those obtained from a conventional approach, as were pharmacokinetic profiles and parameters. This new sampling process greatly improved the efficiency of drug discovery bioanalysis. The integration of pre-clinical protocol design, sample collection and bioanalysis processes was also achieved.

Automating solid-phase extraction: current aspects and future prospects

This paper reviews current trends and techniques in automated solid-phase extraction. The area has shown a dramatic growth the number of manuscripts published over the last 10 years, including applications in environmental science, food science, clinical chemistry, pharmaceutical bioanalysis, forensics, analytical biochemistry and organic synthesis. This dramatic increase of more that 100% per year can be attributed to the commercial availability of higher throughput 96-well workstations and extraction plates that allow numerous samples to be processed simultaneously. These so-called parallel-processing workstations represent the highest throughput systems currently available. The advantages and limitations of other types of systems, including discrete column systems and on-line solid-phase extraction are also discussed. Discussions of how automated solid-phase extractions can be developed, generic approaches to automated solid-phase extraction, and three noteworthy examples of automated extractions are given. The last part of the review suggests possible near- and long-term directions of automated solid-phase extraction.

Fully automated determination of eserine N-oxide in human plasma using on-line solid-phase extraction with liquid chromatography coupled with electrospray ionization tandem mass spectrometry

A sensitive and entirely automated solid-phase extraction/liquid chromatography/electrospray ionization tandem mass spectrometric (SPE/LC/ESI-MS/MS) method was developed and validated for the determination of eserine N-oxide (ENO), a cholinesterase inhibitor-like physostigmine in human plasma, for use in pharmacokinetic studies. ENO is light-sensitive and the use of a fully on-line process increased the reliability of the assay. Plasma samples previously mixed with neostigmine bromide to prevent in vitro degradation, and tacrine as internal standard (IS), were directly injected into the SPE/LC/ESI-MS/MS system. MS software piloted the overall system. MS/MS detection of ENO and the IS was performed in the positive ion ESI mode using multiple reaction monitoring. The linear calibration curve for ENO ranged from 25 pg ml(-1) to 12.5 ng ml(-1). The limit of quantitation was 25 pg ml(-1) with 250 microl of plasma injected. Precision, accuracy and stability tests were within the acceptable range and just one analyst is required to analyze 50 unknown samples a day five days per week, from the preparation of the samples (i.e. thawing and centrifugation) to data processing. A pilot pharmacokinetic study in three healthy volunteers treated with 4.5 mg of ENO (Génésérine3((R))) showed that the method was suitable for pharmacokinetic studies in humans.

Higher throughput bioanalysis by automation of a protein precipitation assay using a 96-well format with detection by LC-MS/MS

Generic methodology for the automated preparation and analysis of drug levels in plasma samples within a drug discovery environment was achieved through the redesign of a protein precipitation assay to a microtiter (96-well) plate format and the application of robotic liquid handling for performance of all transfer and pipetting steps. Validation studies revealed that the application of robotics to sample preparation, in general, maintained the analytical accuracy and precision compared with preparing samples manually. The use of rapid gradient LC-MS/MS for analysis coupled with flow diversion of the solvent front allowed the introduction of protein-precipitated samples into the mass spectrometer without the necessity for source cleaning. The problem inherent in automatically pipetting plasma, caused by fibrinogen clots, was overcome by storing samples at -80 degrees C and thus precluding clot formation. The resulting methodology allowed sample preparation for a 96-well plate designed to accommodate 54 unknowns, duplicate 12-point calibration curves, and 6 sets of quality controls at three levels in approximately 2 h. This approach allowed an increase in throughput of sample preparation and analysis to >400 samples per day per LC-MS/MS instrument with minimal manual intervention. Overall, substantial time savings were realized, demonstrating that automation is an increasingly essential tool in a drug discovery bioanalytical environment.

High-throughput caco-2 cell permeability screening by cassette dosing and sample pooling approaches using direct injection/on-line guard cartridge extraction/tandem mass spectrometry

A method for high-throughput Caco-2 permeability screening of drug candidates has been developed using thirteen generic drugs as test compounds. The high throughput was achieved by either a sample pooling or a cassette dosing approach, along with the use of a rapid, simple and sensitive direct injection/on-line guard cartridge extraction/tandem mass spectrometric assay that was also developed in this study. It was of concern that possible drug-drug interactions (e.g., inhibition of P-glycoprotein-mediated transport of a drug by another, and/or competition of the drugs for transport pathways), when the cassette dosing regimen was implemented, may give rise to inconsistent results compared with those attained by a traditional single-drug dosing approach. However, the apparent permeability coefficients of the test drugs across Caco-2 monolayers measured by the sample pooling or cassette dosing (up to five drugs co-administered in this study) strategy were in good conformity with the data obtained by single-drug dosing followed by discrete sample analysis.

Approaches to higher-throughput pharmacokinetics (HTPK) in drug discovery

With pressure on pharmaceutical companies to reduce time-to-market and improve the success rate of new drug candidates, higher-throughput pharmacokinetic (HTPK) support has become an integral part of many drug discovery programmes. This report details the amalgamation of robotics, new sample preparation technologies and highly sensitive and selective mass spectrometric detection systems to deliver the promise of HTPK. A historical perspective on automated bioanalysis with the current approaches and future prospects for the discipline are described.

High-throughput approaches to the quantitative analysis of ketoconazole, a potent inhibitor of cytochrome P450 3A4, in human plasma

Ketoconazole, an imidazole-piperazine compound, is an orally active antimycotic agent. In addition, ketoconazole is a specific inhibitor of cytochrome P450 3A4. As about 60% of oxidized drugs are biotransformed by this isoform, the potential effect of a concomitant administration of ketoconazole on drug disposition may be of interest during drug development. The present paper describes three different approaches (methods A, B, and C) to attain high-throughput sample preparation and analysis in the quantification of ketoconazole in human plasma. Method A consisted of acetonitrile precipitation in a 96-well plate, transfer of the supernatant via a Tomtec Quadra 96 Model 320, and subsequent injection onto a 50 x 4.6 mm (i.d.) Develosil Combi-RP-5 column (packed with C30 bonded silica particles). Method B consisted of an identical sample preparation to method A with the exception that a Michrom Magic Bullet(trade mark) column, 2.0 --> 0.50 mm (i.d., tapered bore) x25 mm length, was used. Lastly, in method C, a turbulent-flow chromatography (TurboFlow LC/APCI-MS/MS) module was used for the direct analysis of ketoconazole in human plasma. A Sciex API 3000 was used in methods A and B, while a Micromass Quattro LC was employed in method C. Based on the values obtained for the calibrator (standard) and quality control samples, all three protocols yielded satisfactory accuracy, precision, and reduced manual sample preparation time.