Quantification of farnesylmethylcysteine in lysates of peripheral blood mononuclear cells using liquid chromatography coupled with electrospray tandem mass spectrometry: pharmacodynamic assay for farnesyl transferase inhibitors

Biological effectiveness is an important parameter in determining optimal dosages of molecular targeted drugs, such as farnesyl transferase inhibitors. To determine concentration-effect relationships, robust and quantitative biological assays are a prerequisite. Here, we present a novel assay for protein farnesylation that is based on generation of the biomarker farnesylmethylcysteine (FmC). Quantification was performed with liquid chromatography coupled to tandem mass spectrometry. The assay has been validated based on the most recent FDA guidelines for bioanalytical validation, and all results were within requirements. FmC is formed under the action of an endogenous protease that is activated upon cell lysis. The biomarker could be detected in A549 human lung cancer cells as well as in human peripheral blood mononuclear cells. Incubation of A549 cells with AZD3409, a novel prenyl transferase inhibitor, resulted in a significant decrease of the FmC concentration in the lysates. These findings provide a very good starting point for use of this assay in preclinical and clinical dose finding studies with FTIs.

Method for internal standard introduction for quantitative analysis using on-line solid-phase extraction LC-MS/MS

A novel approach for on-line introduction of internal standard (IS) for quantitative analysis using LC-MS/MS has been developed. In this approach, analyte and IS are introduced into the sample injection loop in different steps. Analyte is introduced into the injection loop using a conventional autosampler (injector) needle pickup from a sample vial. IS is introduced into the sample injection loop on-line from a microreservoir containing the IS solution using the autosampler. As a result, both analyte and IS are contained in the sample loop prior to the injection into the column. Methodology allowed to reliably introduce IS and demonstrated injection accuracy and precision comparable to those obtained using off-line IS introduction (i.e., IS and analyte are premixed before injection) while maintaining chromatographic parameters (i.e., analyte and IS elution time and peak width). This new technique was applied for direct analysis of model compounds in rat plasma using on-line solid-phase extraction (SPE) LC-MS/MS quantification. In combination with on-line SPE, IS serves as a surrogate IS and compensates for signal variations attributed to sample preparation and instrumentation factors including signal suppression. The assays yielded accuracy (85-119%), precision (2-16%), and analyte recovery comparable to those obtained using off-line IS introduction. Furthermore, on-line IS introduction allows for nonvolumetric sample (plasma) collection and direct analysis without the need of measuring and aliquoting a fixed sample volume prior to the on-line SPE LC-MS/MS analysis. Therefore, this methodology enables direct sample (plasma) analysis without any sample manipulation and preparation.

Direct quantification in bioanalytical LC–MS/MS using internal calibration via analyte/stable isotope ratio

The possibility to rationalize and simplify bioanalysis, without compromising the analytical quality, by omitting the calibration curves was studied. Using mass spectrometry (MS) and a stable isotope labeled internal standard it was possible to get equally good results by calculating the results directly from the analyte/internal standard area ratio and a predetermined response factor as by the traditional way, using a calibration curve run at the same occasion. To be able to use this simplified quantification method, that we call internal calibration, in its most simple form there are some prerequisites that must be considered: (1) The relative response should not be concentration dependent. (2) The relative response should be constant between batches/days. (3) The level of analyte in the internal standard should not be detectable. (4) There should be no influence from naturally occurring isotopes of the analyte on the internal standard peak area. A bioanalytical LC-MS/MS method for a research compound was validated both with and without calibration curves and no significant differences were found regarding precision and accuracy. It was shown that all four prerequisites above were fulfilled. Validation data were very good for the whole concentration range, 0.010-30 micromol/L. Long-term data for QC samples showed excellent precision and accuracy.

Liquid chromatography–tandem mass spectrometric assay for the nucleoside reverse transcriptase inhibitor emtricitabine in human plasma

A liquid chromatography-tandem mass spectrometric assay for the determination of the antiretroviral nucleoside emtricitabine in human plasma was developed and validated using a simple sample pre-treatment procedure. After addition of 5'-deoxy-5-fluorocytidine as the internal standard and protein precipitation with acetonitrile, the supernatant was directly injected in the isocratic chromatographic system using a polar embedded reversed-phase column and formic acid in water-methanol as the eluent. The eluate was completely led into an electrospray interface with positive ionization and the analytes were quantified using triple quadrupole mass spectrometry. The assay was validated in the range 5-5000 ng/mL. Intra-day precisions were <or=7% and inter-day precisions were <or=10%. Accuracies between 92 and 99% were found. The analytes were chemically stable under all relevant conditions and the assay was applied in the analysis of plasma samples of HIV-infected patients treated with the drug.

Quantitative determination of the cytidine deaminase inhibitor tetrahydrouridine (THU) in mouse plasma by liquid chromatography/electrospray ionization tandem mass spectrometry

A number of anticancer drugs are cytidine analogues that undergo metabolic deactivation catalyzed by cytidine deaminase (CD). 3,4,5,6-Tetrahydrouridine (THU) is a potent inhibitor of CD, by acting as a transition-state analogue of its natural substrate cytidine. However, to date its pharmacokinetic properties have not been fully characterized, which has impaired its optimal preclinical evaluation and clinical use. We report a liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay for the sensitive, accurate and precise quantitation of THU in mouse plasma. Validation was performed according to FDA guidelines. The assay employed deuterated THU as the internal standard and an acetonitrile protein precipitation step. Separation, based on hydrophilic interaction chromatography, was achieved with an amino column and an isocratic mobile phase of 0.1% formic acid in acetonitrile and water followed by a wash. Chromatographic separation was followed by positive-mode electrospray ionization MS/MS detection in the multiple reaction monitoring (MRM) mode. The assay was accurate (92.5-109.9%) and precise (2.1-9.0%) in the concentration range of 0.2-50 microg/mL. Recovery from plasma was near-complete (92.9-119.3%) and ion suppression was negligible (-17.5 to -0.2%). Plasma freeze/thaw stability (93.1-102.1%), stability for 3 months at -80 degrees C (99.5-110.9%), and stability for 4 h at room temperature (92.1-102.4%) were all in order. This assay is currently being used to quantitate THU in ongoing pharmacokinetic studies. In addition, the assay is expected to be a useful tool in any future studies involving co-administration of THU with cytidine analogues.

Validated assay for the simultaneous determination of the anti-cancer agent gemcitabine and its metabolite 2',2'-difluorodeoxyuridine in human plasma by high-performance liquid chromatography with tandem mass spectrometry

A sensitive and specific high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) assay for the quantitative determination of gemcitabine (dFdC) and its metabolite 2',2'-difluorodeoxyuridine (dFdU) is presented. A 200-microL aliquot of human plasma was spiked with a mixture of internal standards, didanosine, lamivudine and fludarabine, and extracted using solid-phase extraction. Dried extracts were reconstituted in 1 mM ammonium acetate/acetonitrile (97:3, v/v) and 10-microL volumes were injected onto the HPLC system. Separation was achieved on a 150 x 2.1 mm C18 bonded phase endcapped with polar groups (Synergi Hydro-RP column) using an eluent composed of 1 mM ammonium acetate (pH 6.8)/acetonitrile (94:6, v/v). Detection was performed by positive ion electrospray ionization followed by MS/MS. The assay quantifies a range from 0.5 to 1000 ng/mL for gemcitabine and from 5 to 10,000 ng/mL for dFdU using 200 microL of human plasma sample. Validation results demonstrate that gemcitabine and dFdU concentrations can be accurately and precisely quantified in human plasma. This assay is used to support clinical pharmacologic studies with gemcitabine.

Stability experiments in human urine with EO9 (apaziquone): A novel anticancer agent for the intravesical treatment of bladder cancer

EO9 (apaziquone) is a novel, promising anticancer agent, which is currently being investigated for the intravesical treatment of bladder cancer. EO9 contains a highly reactive aziridine ring in its structure that limits its chemical stability in acidic aqueous solutions. The stability of the pharmaceutically formulated EO9 in human urine, including the effects of several parameters such as temperature, buffer strength and pH have been investigated. Urine extracts were analyzed by high-performance liquid chromatography coupled to electrospray tandem mass spectrometry (HPLC-MS/MS) using a TurboIonspray interface and positive-ion multiple reaction monitoring. EO9 was unstable in urine at 43 degrees C during the instillation for longer than 1 h. However, the drug was stable in human urine for 3 h at 37 degrees C. EO9 is stable in urine stabilized with TRIS buffer (pH 9.0; 5 mM) for up to three freeze/thaw cycles at -20 and -70 degrees C and 3 months of storage at -70 degrees C. The results also illustrated that with the lower pH in urine, EO9 became more unstable. Furthermore, a new degradation product of EO9 was discovered and successfully identified as EO9-Cl. The outcomes of these stability experiments will be implemented to insure proper sample handling at the clinical sites, transport, storage, and sample handling during analysis in the forthcoming preclinical studies of EO9 in superficial bladder cancer, supported by bioanalysis and pharmacokinetic monitoring.

Quantitative analysis of EO9 (apaziquone) and its metabolite EO5a in human plasma by high-performance liquid chromatography under basic conditions coupled to electrospray tandem mass spectrometry

A sensitive and specific LC-MS/MS assay for the quantitative determination of EO9 and its metabolite EO5a is presented. A 200-microl human plasma aliquot was spiked with a mixture of deuterated internal standards EO9-d3 and EO5a-d4 and extracted with 1.25 ml ethyl acetate. Dried extracts were reconstituted in 0.1 M ammonium acetate-methanol (7 : 3, v/v) and 25 microl-volumes were injected into the HPLC system. Separation was achieved on a 150 x 2.1 mm C18 column using an alkaline eluent (1 mM ammonium hydroxide-methanol (gradient system)). Detection was performed by positive ion electrospray followed by tandem mass spectrometry. The assay quantifies a range from 5 to 2500 ng/ml for EO9 and from 10 to 2500 ng/ml EO5a using 200 microl of human plasma samples. Validation results demonstrate that EO9 and EO5a concentrations can be accurately and precisely quantified in human plasma. This assay will be used to support clinical pharmacologic studies with EO9.

A liquid chromatography/tandem mass spectrometry assay to quantitate MS-275 in human plasma

A rapid, sensitive and selective method was developed and validated using LC/MS/MS for determination of MS-275 in human plasma. Sample preparation involved a single step liquid-liquid extraction by the addition of 0.2 ml of plasma with 5 ml acetonitrile/n-butyl-chloride. Separation of the compounds of interest, including the internal standard paclitaxel, was achieved on a Waters X-Terra C(18) (50 mm x 2.1mm i.d., 3.5 microm) analytical column using a mobile phase consisting of acetonitrile/ammonium acetate (pH 2.9; 2mM)(60:40, v/v) containing 0.1% formic acid and isocratic flow at 0.15 ml/min for 3 min. The analytes were monitored by tandem-mass spectrometry with electrospray positive ionization. Linear calibration curves were generated over the range of 0.5-100 ng/ml with values for the coefficient of determination of >0.99. The values for both within day and between day precision and accuracy were well within the generally accepted criteria for analytical methods (<15%). This method was subsequently used to measure concentrations of MS-275 in cancer patients receiving an oral weekly dose of 4 mg/m(2).

Determination of didanosine in maternal plasma, amniotic fluid, fetal and placental tissues by high-performance liquid chromatography-tandem mass spectrometry

A rapid and efficient high-performance liquid chromatography (HPLC)-tandem mass spectrometry method for the determination of didanosine concentrations in maternal rat plasma, amniotic fluid, placental and fetal tissue samples has been developed and validated. Tissue samples were homogenized in optima water and centrifuged. The supernatant was subjected to solid-phase extraction (SPE) prior to analysis. Plasma and amniotic fluid samples were extracted without pretreatment. An Agilent 1100 Series HPLC coupled with a Micromass Quattro II triple quadrupole mass spectrometer was used for all analyses. Chromatographic resolution was achieved on a Nova-Pak phenyl analytical column (2.0 x 150 mm, 4 microm particle size) equipped with a Phenomenex Security-guard phenyl guard cartridge (2.0 x 4.0 mm) using 60% methanol in 10 mm ammonium acetate buffer mobile phase for all matrices at a flow rate of 0.15 mL/min. The method yields retention times of 2.9 min for didanosine and 3.0 min for the internal standard, stavudine. Limits of detection were 1 ng/mL for all matrices. Recoveries were 70% or greater for both compounds in the different matrices. Within- and between-run precision (%RSD) and accuracy (%error) was less than 15% for all matrices.

Liquid chromatography–tandem mass spectrometric assay for the analysis of uracil, 5,6-dihydrouracil and β-ureidopropionic acid in urine for the measurement of the activities of the pyrimidine catabolic enzymes

A liquid chromatography-tandem mass spectrometric assay for the determination of uracil, 5,6-dihydrouracil and beta-ureidopropionic acid in urine was developed to measure the activities of enzymes involved in pyrimidine breakdown. The assay was required to investigate the relation between the uracil-dihydrouracil ratio and toxicities observed after treatment with fluoropyrimidines drugs. After addition of stable isotopically labelled internal standards, the analytes were isolated from a 100-microl urine sample using liquid-liquid extraction with ethyl acetate-2-propanol. Compounds were separated on an Atlantis dC18 column, using ammonium acetate-formic acid in water as the eluent. The eluate was totally led into an electrospray interface with positive ionisation and the analytes were quantified using triple quadrupole mass spectrometry. The assay was validated in the range 1.6-1600 microM, using both, artificial urine and pooled urine as matrices. Intra-day precisions were < or = 8% and inter-day precisions were < or = 10%. Accuracies between 91 and 108% were found. The analytes were chemically stable under all relevant conditions and the assay was successfully applied in two clinical studies of cancer patients treated with 5-fluorouracil or capecitabine.

Quantitative determination of zebularine (NSC 309132), a DNA methyltransferase inhibitor, and three metabolites in murine plasma by high-performance liquid chromatography coupled with on-line radioactivity detection

The metabolism of zebularine (NSC 309132), a novel agent that inhibits DNA methyltransferases, is still uncharacterized. To examine the in vivo metabolism of zebularine, an analytical method was developed and validated (based on FDA guidelines) to quantitate 2-[(14)C]-zebularine and its major metabolites in murine plasma. Zebularine and its metabolites uridine, uracil and dihydrouracil were baseline-separated based on hydrophilic interaction chromatography by using an amino column. The assay was accurate and precise in the concentration ranges of 5.0-100 microg/mL for zebularine, 2.5-50 microg/mL for uridine, 1.0-10 microg/mL for uracil and 0.5-5.0 microg/mL for dihydrouracil. This assay is being used to quantitate zebularine and its metabolites in ongoing pharmacokinetic studies of zebularine.

A simple and sensitive assay for the quantitative analysis of rivastigmine and its metabolite NAP 226-90 in human EDTA plasma using coupled liquid chromatography and tandem mass spectrometry

A sensitive and specific high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) assay for the determination of rivastigmine and its major metabolite NAP 226-90 is presented. A 100 microL plasma aliquot was spiked with a structural analogue of rivastigmine as internal standard (PKF214-976-AE-1) and proteins were precipitated by adding 200 microL of methanol. After centrifugation a volume of 100 microL of the clear supernatant was mixed with 100 microL of methanol/water (30:70, v/v) and volumes of 25 microL were injected onto the HPLC system. Separation was acquired on a 150 x 2.0 mm i.d. Gemini C18 column using a gradient system with 10 mM ammonium hydroxide and methanol. Detection was performed by using a turboionspray interface and positive ion multiple reaction monitoring by tandem mass spectrometry. The assay quantifies rivastigmine from 0.25 to 50 ng/mL and its metabolite NAP 226-90 from 0.50 to 25 ng/mL, using human plasma samples of 100 microL. Validation results demonstrate that rivastigmine and metabolite concentrations can be accurately and precisely quantified in human EDTA plasma. This assay is now used to support clinical pharmacologic studies with rivastigmine.

Liquid chromatographic assay for the non-peptidic protease inhibitor tipranavir in plasma

Tipranavir is the most recently introduced protease inhibitor for the suppression of the human immunodeficiency virus (HIV). A selective reversed-phase liquid chromatographic assay, previously developed for atazanavir, has been extended and validated for tipranavir in plasma. Compounds were isolated from a 500 microL plasma sample using liquid-liquid extraction with dichloromethane. After evaporation and reconstitution of the extract the sample was analysed using reversed-phase liquid chromatography and ultra violet detection at 280 nm. In the evaluated concentration range (0.2-50 microg/mL tipranavir), intra-day precisions were <or=8% and inter-day precisions were <or=10%. Accuracies between 95 and 108% were found. The clinical applicability of the assay was demonstrated in an HIV-infected patient who ingested 500 mg tipranavir bid in combination with 100 mg ritonavir.

Liquid chromatography-mass spectrometry for the quantitative bioanalysis of anticancer drugs

The monitoring of anticancer drugs in biological fluids and tissues is important during both pre-clinical and clinical development and often in routine clinical use. Traditionally, liquid chromatography (LC) in combination with ultraviolet (UV), fluorescence, or electrochemical detection is employed for this purpose. The successful hyphenation of LC and mass spectrometry (MS), however, has dramatically changed this. MS detection provides better sensitivity and selectivity than UV detection and, in addition, is applicable to a significantly larger group of compounds than fluorescence or electrochemical detection. Therefore, LC-MS has now become the method of first choice for the quantitative bioanalysis of many anticancer agents. There are still, however, a lot of new developments to be expected in this area, such as the introduction of more sensitive and robust mass spectrometers, high-throughput analyses, and further optimization of the coupled LC systems. Many articles have appeared in this field in recent years and are reviewed here. We conclude that LC-MS is an extremely powerful tool for the quantitative analysis of anticancer drugs in biological samples.

Development and validation of an LC–UV method for the quantification and purity determination of the novel anticancer agent C1311 and its pharmaceutical dosage form

C1311 (5-[[2-(diethylamino)ethyl]amino]-8-hydroxyimidazo [4,5,1-de]-acridin-6-one-dihydrochloride trihydrate) is the lead compound from the group of imidazoacridinones, a novel group of rationally designed anticancer agents. The pharmaceutical development of C1311 necessitated the availability of an assay for the quantification and purity determination of C1311 active pharmaceutical ingredient (API) and its pharmaceutical dosage form. A reversed-phase liquid chromatographic method (RP-LC) with ultraviolet (UV) detection was developed, consisting of separation on a C18 column with phosphate buffer (60 mM; pH 3 with 1 M citric acid)-acetonitrile-triethylamine (83:17:0.05, v/v/v) as the mobile phase and UV-detection at 280 nm. The method was found to be linear over a concentration range of 2.50-100 microg/mL, precise and accurate. Accelerated stress testing showed degradation products, which were well separated from the parent compound, confirming its stability-indicating capacity. Moreover, the use of LC-MS and on-line photo diode array detection enabled us to propose structures for four degradation products. Two of these products were also found as impurities in the API and more abundantly in an impure lot of API.

LC–UV method development and validation for the investigational anticancer agent imexon and identification of its degradation products

Imexon (4-imino-1,3-diazabicyclo[3,1,0]-hexan-2-one) is a member of the class of 2-cyanoaziridine derivatives, which have been of interest as immunomodulators and anticancer agents since the late 1970s. The pharmaceutical development of imexon necessitated the availability of an assay for the quantification and purity determination of imexon active pharmaceutical ingredient (API) and the drug in its pharmaceutical dosage form. A liquid chromatographic (LC) method with ultraviolet (UV) detection was developed, using a reverse phase column with phosphate buffer (pH 6; 50 mM) as mobile phase and UV detection at 230 nm. Although retention capacity for imexon was small (capacity factor of 0.5), the method was found to be linear over the concentration range of interest of 1.0-25 microg/mL, precise, accurate, and stability-indicating. Moreover, the use of LC-mass spectrometry (MS) and on-line photodiode array (PDA) detection enabled us to propose structures for four degradation products. Two of these products were also found as impurities in the API. The degradation products, including chloro- and hydroxy-derivatised products were shown to arise from nucleophilic reactions with the activated aziridine moiety of imexon. The developed LC-UV method was found suitable for the pharmaceutical quality control of imexon API and the drug in its pharmaceutical dosage form.

Bioanalysis of HIV protease inhibitors in samples from sanctuary sites

The human immunodeficiency virus (HIV) is present in several sites inside the human body, which are hardly accessible to antiretroviral drugs, the so-called sanctuary sites. The most important sanctuary sites are cerebrospinal fluid (CSF), peripheral blood mononuclear cells (PBMCs) and seminal plasma. The determination of drug concentrations in these sanctuary sites may form an important step in treatment optimisation of HIV-infected individuals. However, bioanalysis in these sites is hampered by several factors with regard to sample preparation, chromatography and detection. In this review, we will discuss these issues and give an overview of published methods using high-performance liquid chromatography (HPLC) for the bioanalysis of HIV protease inhibitors in CSF, PBMCs and seminal plasma.

Determination of thiamine and its phosphorylated forms in human plasma, erythrocytes and urine by HPLC and fluorescence detection: a preliminary study on cancer patients

In man, neurotoxicity associated to ifosfamide treatment can be reversed by intravenous thiamine administration. Trying to explain this clinical finding, we decided to study possible changes in thiamine availability and activation in patients exposed to ifosfamide. Free thiamine and its phosphate esters levels were measured in plasma, erythrocytes and urine by an ion-pair HPLC method with pre-column derivatization, which allowed separation of the fluorescent compounds in less than 10 min. The method was validated by linearity, sensitivity and reproducibility studies, whose values met the demands for bioanalytical assays. This method was applied to assess thiamine status in cancer patients exposed to ifosfamide therapy for advanced disease.

Liquid chromatographic assay for the protease inhibitor atazanavir in plasma

Atazanavir is the most recently introduced protease inhibitor for the suppression of the anti-human immunodeficiency virus. A sensitive and selective reversed-phase liquid chromatographic assay for this drug in human plasma has been developed and validated. Atazanavir was isolated from a 500 microL plasma sample using liquid-liquid extraction with dichloromethane. After evaporation and reconstitution of the extract the sample was analysed using liquid chromatography and ultraviolet detection at 280 nm. In the evaluated concentration range (44-4395 ng/mL atazanavir), intra-day precisions were < or =7% and inter-day precisions were < or =14%. Accuracies between 96 and 106% were found. The lower limit of quantification was 44 ng/mL with an intra-day precision of 7%, an inter-day precision of 14% and an accuracy of 87%. There was no interference from 32 tested potentially co-administrated drugs and metabolites. The usefulness of the assay was demonstrated for samples obtained from an HIV-infected patient treated with atazanavir.

Chemical derivatization and mass spectral libraries in metabolic profiling by GC/MS and LC/MS/MS

An overview is presented of gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS), the two major hyphenated techniques employed in metabolic profiling that complement direct 'fingerprinting' methods such as atmospheric pressure ionization (API) quadrupole time-of-flight MS, API Fourier transform MS, and NMR. In GC/MS, the analytes are normally derivatized prior to analysis in order to reduce their polarity and facilitate chromatographic separation. The electron ionization mass spectra obtained are reproducible and suitable for library matching, mass spectral collections being readily available. In LC/MS, derivatization and library matching are at an early stage of development and mini-reviews are provided. Chemical derivatization can dramatically increase the sensitivity and specificity of LC/MS methods for less polar compounds and provides additional structural information. The potential of derivatization for metabolic profiling in LC/MS is demonstrated by the enhanced analysis of plant extracts, including the potential to measure volatile acids such as formic acid, difficult to achieve by GC/MS. The important role of mass spectral library creation and usage in these techniques is discussed and illustrated by examples.

A simple and sensitive assay for the quantitative analysis of paclitaxel and metabolites in human plasma using liquid chromatography/tandem mass spectrometry

A sensitive and specific LC-MS/MS assay for the determination of paclitaxel and its 3'p- and 6-alpha-hydroxy metabolites is presented. A 200 microL plasma aliquot was spiked with a 13C6-labeled paclitaxel internal standard and extracted with 1.0 mL tert-butylmethylether. Dried extracts were reconstituted in 0.1 M ammonium acetate-acetonitrile (1:1, v/v) and 25 microL volumes were injected onto the HPLC system. Separation was performed on a 150 x 2.1 mm C18 column using an alkaline eluent (10 mm ammonium hydroxide-methanol, 30:70, v/v). Detection was performed by positive ion electrospray followed by tandem mass spectrometry. The assay quantifies a range for paclitaxel from 0.25 to 1000 ng/mL and metabolites from 0.25 to 100 ng/mL using 200 microL human plasma samples. Validation results demonstrate that paclitaxel and metabolite concentrations can be accurately and precisely quantified in human plasma. This assay is now used to support clinical pharmacologic studies with paclitaxel.

Bioanalytical method validation: a risk-based approach?

Bioanalysis frequently involves the measurement of very low analyte concentrations in complex and potentially variable matrices. It is not possible to test in validation every possible circumstance that may be encountered when analyzing study samples; logically, therefore, some risk of obtaining erroneous results exists when validated methods are applied to study samples. An initial attempt has been made to apply a risk management tool to the bioanalytical situation, with the hope that this will stimulate further discussion on the idea of more formally addressing "risk" with regards to bioanalytical method validation.

Simultaneous determination of cefatrizine and clavulanic acid in dog plasma by HPLC

A rapid and specific high-performance liquid chromatographic method was developed and validated for the simultaneous determination of cefatrizine and clavulanic acid in the plasma of beagle dog. The sample pretreatment procedure involved reaction of clavulanic acid with 1,2,4-triazole, which readily produced a derivative with its maximum UV absorption at 314 nm. This derivative was separated in a reverse-phase C-18 column without being interfered by other components present in plasma. Cefatrizine, however, was not derivatized and, therefore determined directly at 269 nm. Sulfanilamide was used as an internal standard. The retention times of sulfanilamide, the derivative, and cefatrizine were, 3.5, 4.9, and 6.0 min, respectively. The assay showed linearity from 2 to 100 microg/ml for cefatrizine and from 1 to 50 microg/ml for clavulanic acid. Precision expressed as R.S.D. ranged from 4.2 to 18.2% for cefatrizine and 5.5 to 15.8% for clavulanic acid. Accuracy ranged from 97.9 to 120% (lower limit of quantitation) for cefatrizine and from 97.7 to 119.2% for clavulanic acid. Extraction efficiencies for cefatrizine, clavulanic acid, and internal standard from dog plasma averaged 79.8+/-5.8%, 84.8+/-6.2%, and 89.0+/-3.8%, respectively. This method was employed successfully to follow the time course of the concentration of cefatrizine and clavulanic acid in beagle dogs following oral administration of cefatrizine and clavulanic acid.

Quantitative determination of the novel anticancer drug E7070 (indisulam) and its metabolite (1,4-benzenedisulphonamide) in human plasma, urine and faeces by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry

E7070 (indisulam) is a novel anticancer drug currently undergoing clinical investigation. We present a sensitive and specific method for the quantitative determination of E7070 and its metabolite M1 (1,4-benzenedisulphonamide) in human plasma, urine and faeces. The analytes and their tetra-deuterated analogues, which were used as internal standards, were isolated from the biological matrix by solid-phase extraction with OASIS cartridges (0.5 mL plasma or 1 mL urine) and by liquid-liquid extraction with ethyl acetate at pH 5 (1 mL faecal homogenate). The analytes were separated on a C8 reversed-phase chromatographic column and analyzed using electrospray ionization and tandem mass spectrometric detection in the negative ion mode. The validated concentration ranges in plasma were 0.1-20 microg/mL for E7070 and 0.01-2 microg/mL for M1. In urine and faecal homogenate, a concentration range from 0.05-10 microg/mL or microg/g, respectively, was validated for both analytes. Validation of the plasma assay was performed according to the most recent FDA guidelines. The assay fulfilled all generally accepted requirements for linearity (r > 0.99, residuals between -8 and 10%), accuracy (-13.5 to 1.4%) and precision (all less than 11%) in the tested matrices. We investigated recovery, stability (working solutions at -20 degrees C and at room temperature, biological matrices at -20 degrees C, room temperature and after 3 freeze/thaw cycles; final extracts at room temperature) and robustness. All these parameters were found acceptable. This method is suited for mass balance studies or therapeutic drug monitoring, as demonstrated by a case example showing plasma concentrations and cumulative excretion of E7070 and M1 in urine and faeces. Furthermore, we show the presence of E7070 metabolites in patient urine.

Development and validation of a method to determine the unbound paclitaxel fraction in human plasma

Paclitaxel is pharmaceutically formulated in a mixture of Cremophor EL and ethanol (1:1, v/v). The unbound fraction of the anticancer drug paclitaxel in plasma is dependent on both plasma protein binding and entrapment in Cremophor EL micelles. We have developed a simple and reproducible method for the quantification of the unbound paclitaxel fraction in human plasma. Human plasma was spiked with [3H]paclitaxel and [14C]glucose (unbound reference) and incubated at 37 degrees C for 30 min. Plasma ultrafiltrate was prepared by a micropartition system (MPS-1) and collected in a sample cup containing 100 microl of plasma to prevent the loss of paclitaxel due to adsorption. The radionuclides were separated after combustion of the biological samples using a sample oxidizer and the radioactivity was determined by liquid scintillation counting. The unbound fraction of paclitaxel was calculated by dividing the ratios of 3H and 14C in plasma ultrafiltrate and in plasma. The method was thoroughly validated using human plasma spiked with pharmacologically relevant concentrations of paclitaxel (10-1000 ng/ml) and Cremophor EL (0.25-2.0%). The method was precise, with a within-day precision ranging from 3.9 to 11.0% and a between-day precision ranging from 5.8 to 13.1%. In patient plasma with low serum albumin values containing 1% of Cremophor EL, the unbound fraction appeared to be significantly higher than that in plasma with normal albumin values. The determination of the unbound fraction of paclitaxel proved to be stable during a 10-week storage at -20 degrees C. Furthermore, the assay was applicable in patient samples. This assay can be used to determine the unbound fraction of paclitaxel in plasma. Moreover, its design should allow the determination of the unbound concentrations of other hydrophobic drugs.

Simple and rapid method for the simultaneous determination of the non-nucleoside reverse transcriptase inhibitors efavirenz and nevirapine in human plasma using liquid chromatography

Efavirenz and nevirapine are non-nucleoside reverse transcriptase inhibitors for the treatment of HIV-1-infected individuals. A simple and rapid high-performance liquid chromatographic method for the simultaneous quantification of efavirenz and nevirapine in human plasma suitable for therapeutic drug monitoring is described. Sample pre-treatment consisted of protein precipitation with acetonitrile and subsequently dilution with distilled water. The drugs were separated from endogenous compounds by isocratic reversed-phase high-performance liquid chromatography with ultraviolet detection at 275 nm. The method was validated over the therapeutically relevant concentration range of 0.05-15.0 mg l(-1) and 0.25-15.0 mg l(-1) for efavirenz and nevirapine, respectively, using a volume of 100 microl of plasma. The calibration curves were linear over this concentration range. Carbamazepine was used as internal standard. The assay proved to be accurate (accuracies varied between -12.7 and 8.5%) and precise (intra- and inter-assay precisions were less then 5.9%). The tested batches of control human plasma and frequently co-administered drugs did not interfere with the described methodology. Efavirenz and nevirapine were stable under various relevant storage conditions. This validated assay is suited for use in pharmacokinetic studies with efavirenz and nevirapine and can readily be implemented in the setting of a hospital laboratory for the monitoring of efavirenz and nevirapine concentrations.

Liquid chromatographic assay for the antiviral nucleotide analogue tenofovir in plasma using derivatization with chloroacetaldehyde

A sensitive and selective reversed-phase liquid chromatographic assay for tenofovir in human plasma has been developed and validated. Tenofovir was isolated from a 200 microl plasma sample using protein precipitation with trichloroacetic acid. The fluorescent 1,N(6)-etheno derivative is formed at 98 degrees C in the buffered extract with chloroacetaldehyde. This derivative was analysed using gradient ion-pair liquid chromatography and fluorescence detection at 254 nm for excitation and 425 nm for emission. In the evaluated concentration range (20-1000 ng/ml), the intra-day precision was 4% and the inter-day precision was 5-6%. An accuracy of between 97 and 110% was determined. The lower limit of quantification was 20 ng/ml with an inter-day precision of 11%, an intra-day precision of 12% and an accuracy of 103%. The assay is subject to interference from co-administered abacavir. The usefulness of the assay was demonstrated for samples obtained from an HIV-infected patient treated with tenofovir.

Quantitative analysis of ES-285, an investigational marine anticancer drug, in human, mouse, rat, and dog plasma using coupled liquid chromatography and tandem mass spectrometry

A method was developed for the quantitative analysis of the novel anticancer agent ES-285 (spisulosine; free base) in human, mouse, rat, and dog plasma using high-performance liquid chromatography/electrospray ionization tandem mass spectrometry in order to support pre-clinical and clinical studies with the drug. Sample preparation was carried out by protein precipitation with acetonitrile, containing isotopically labeled (d(3)) ES-285 as internal standard. Aliquots of 10 micro l of the supernatant were injected directly on to an Inertsil ODS-3 column (50 x 2.0 mm i.d., 5 micro m). Elution was carried out using methanol-10 mM ammonium formate (pH 4) in water (80 : 20, v/v) pumped at a flow-rate of 0.2 ml min(-1) with a run time of 8 min. Multiple reaction monitoring chromatograms obtained on an API365 triple-quadrupole mass spectrometer were used for quantification. The lower limit of quantitation (LLOQ) was 10 ng ml(-1) in human, mouse, rat, and dog plasma and the linear dynamic range extended to 500 ng ml(-1). A full validation of the method was performed in human plasma, and partial validations were performed in mouse, rat and dog plasma. Accuracies and precisions were <20% at the LLOQ concentration and <15% for all other concentrations in all matrices. ES-285 was stable during all steps of the assay. Thus far this method has been used successfully to analyze over 500 samples in pre-clinical trials, and will be implemented in the planned clinical phase I studies.

High-performance liquid chromatographic analysis of the anticancer drug irinotecan (CPT-11) and its active metabolite SN-38 in human plasma

A rapid, sensitive, and specific high-performance liquid chromatography (HPLC) method for the simultaneous determination of irinotecan (CPT-11) and its active metabolite SN-38 in human plasma is described. The analytes are quantified as the totals of their carboxylate and lactone form. The sample pretreatment consisted of a simple protein precipitation with acetonitrile-methanol (1:1, v/v), after which CPT-11 and SN-38 were quantitatively converted to their carboxylate form by adding 0.01 mol/L sodium tetraborate (pH, 9). Chromatography was carried out on a Zorbax SB-C18 column with fluorescence detection. The method has been validated, and stability tests under various clinically relevant conditions have been performed. The lower limit of quantification (LLOQ) was 5.0 ng/mL for CPT-11 and 0.5 ng/mL for SN-38. Standard concentration ranges were linear between 5 and 1,500 ng/mL for CPT-11 and between 0.5 and 100 ng/mL for SN-38. This assay is simple, rapid, and very useful for therapeutic monitoring of CPT-11 and SN-38.

Simple high-performance liquid chromatographic assay for melphalan in perfusate, rat liver and tumour tissue

A simple, sensitive and selective reversed-phase liquid chromatographic assay has been developed and validated for the anti-cancer agent melphalan in perfusate, liver and tumour tissue originating from isolated rat liver perfusion studies. Melphalan was extracted from the matrix using ice-cold methanol. The drug and the internal standard, propylparaben, were detected using ultraviolet absorbance at 262 nm. The assay has been validated in the 0.05-25 microg/mL range for perfusate; the lower limit of quantification (LLQ) is 0.05 microg/mL in perfusate and 0.25 ng/mg in liver and tumour tissues. Accuracies ranged from 89 to 110% and the inter-assay precisions were all below 15% (20% at the LLQ). Melphalan in a biological matrix has to be processed between 0 and 4 degrees C and is stable under all relevant processing and storage conditions tested. The assay has been exhaustively used in isolated liver perfusion studies with the drug demonstrating its applicability.

Isocratic ion-exchange chromatographic assay for the nucleotide gemcitabine triphosphate in human white blood cells

An isocratic bio-analytical assay for the nucleotide gemcitabine triphosphate (2',2'-difluorodeoxycytidine 5'-triphosphate, dFdCTP) in human white blood cells (leukocytes) has been developed and validated. The method is based on ion-exchange liquid chromatography and ultraviolet detection (275 nm). dFdCTP is isolated from the matrix by extraction with perchloric acid while the sample is chilled on ice. After neutralization with potassium hydroxide and removal of the potassium perchlorate precipitate, with the sample still chilled on ice, the mixture is injected into the chromatograph. The method has been validated in the range 0.4-20 microM, 0.4 microM (approximately 20 pmol/10(6) cells) being the lower limit of quantification, using erythrocytes as a substitute for leukocytes. Precisions and accuracies both meet the current requirements for a bioanalytical assay. The stability of dFdCTP in intact mononuclear blood cells on ice is strongly limited (half-life approximately 100 min) and after freezing the half-life of the analyte in the cellular lysate is approximately 30 min. On the other hand, no degradation was observed for dFdCTP for at least approximately 24 h in perchloric acid extracts on ice or in neutralized extracts at ambient temperature. The applicability of the assay was demonstrated in white blood cells of a patient with advanced non-small cell lung cancer receiving i.v. gemcitabine.

Selective high-performance liquid chromatographic assay for itraconazole and hydroxyitraconazole in plasma from human immunodeficiency virus-infected patients

A sensitive and selective reversed-phase liquid chromatographic assay for itraconazole and hydroxyitraconazole in human plasma has been developed and validated. Itraconazole and hydroxyitraconazole were extracted from the matrix using solid-phase extraction on a strong cation-exchange sorbent. All compounds were detected using fluorescence at 265 and 363 nm for excitation and emission, respectively. The assay has been validated over the range 10-1,000 ng/ml for both compounds, 10 ng/ml being the lower limit of quantification. Accuracies ranged from 104 to 113% for itraconazole and from 91 to 103% for hydroxyitraconazole. The intra-assay precisions were all below 9% for itraconazole and below 8% for hydroxyitraconazole. The selectivity has been evaluated with respect to all registered anti-human immunodeficiency virus (HIV) drugs and other potential co-medications and a few of their metabolites, commonly used by HIV-infected individuals. Both itraconazole and hydroxyitraconazole were stable under relevant conditions for HIV-inactivation and storage of samples. The applicability of the assay was demonstrated for samples collected from a treated HIV-infected patient.

Hydrophilic interaction liquid chromatography/electrospray mass spectrometry determination of acyclovir in pregnant rat plasma and tissues

Reversed-phase chromatography is the most common means of separation for small drug molecules. However, polar drugs may suffer from poor retention and peak shape in reversed-phase high-performance liquid chromatography (RP-HPLC). Hydrophilic interaction liquid chromatography (HILIC) provides a viable alternative to RP-HPLC and is an excellent way to separate polar compounds. This paper describes a HILIC/ESI-MS/MS assay for the determination of acyclovir from rat plasma, amniotic fluid, placental tissue, and fetal tissue. The isocratic separation utilizes an underivatized silica column with an acetonitrile/formate buffer mobile phase (80:20). The method is validated over a range of 50 ng/mL to 50 micro g/mL with % error and % relative standard deviation of <15% over 3 days. All samples are prepared by acetonitrile protein precipitation, which yields high recovery (>84% for acyclovir). This assay can be applied to the pharmacokinetic study of the placental transfer of acyclovir.