Tandem mass spectrometry of small-molecule signal transduction inhibitors: Accurate-m/z data to adapt structure proposals of product ions.

Protein kinases inhibitors or, more generally, signal transduction inhibitors (STIs) can be used to treat diseases in which deregulation of the protein kinase activity plays a role, such as in cancer. A wide variety of drugs has been developed and/or is under investigation to act as protein kinase inhibitors, especially in tyrosine kinase inhibition. The bioanalysis of STIs has received considerable attention in the past 20 years. Liquid chromatography-tandem mass spectrometry (LC-MS-MS) in selected-reaction monitoring (SRM) mode is the method-of-choice in such studies. In several of these studies from us and others, structures are proposed for the product ions applied in SRM. A critical review of these proposed structures is presented using accurate-m/z data, which we have now generated with a linear-ion-trap-Orbitrap hybrid mass spectrometer. This led to adaptation and new structural proposals of 18 product ions for 13 STIs. Our investigation endorses the power of accurate-m/z analysis in structure elucidation of product ions in bioanalytical LC-MS-MS studies and for which the SRM mode in tandem-quadrupole instruments is apparently less suitable.

Development and validation of a UPLC-MS/MS method with a broad linear dynamic range for the quantification of morphine, morphine-3-glucuronide and morphine-6-glucuronide in mouse plasma and tissue homogenates.

The aim of this study was to develop and to validate a UPLC-MS/MS method for the quantification of morphine, morphine-3-glucuronide, and morphine-6-glucuronide in mouse plasma and tissue homogenates to support preclinical pharmacokinetic studies. The sample preparation consisted of protein precipitation with cold (2-8 °C) methanol:acetonitrile (1:1, v/v), evaporation of the supernatant to dryness, and reconstitution of the dry-extracts in 4 mM ammonium formate pH 3.5. Separation was achieved on a Waters UPLC HSS T3 column (150 × 2.1 mm, 1.8 µm) maintained at 50 °C and using gradient elution with a total runtime of 6.7 min. Mobile phase A consisted of 4 mM ammonium formate pH 3.5 and mobile phase B of 0.1% formic acid in methanol:acetonitrile (1:1, v/v). Detection was carried out by tandem mass spectrometry with electrospray ionization in the positive ion mode. The method was validated within a linear range of 1-2,000 ng/mL, 10-20,000 ng/mL, and 0.5-200 ng/mL for morphine, morphine-3-glucuronide, and morphine-6-glucuronide, respectively. In human plasma, the intra- and inter-run precision of all analytes, including the lower limit of quantification levels, were ≤ 15.8%, and the accuracies were between 88.1 and 111.9%. It has been shown that calibration standards prepared in control human plasma can be used for the quantification of the analytes in mouse plasma and tissue homogenates. The applicability of the method was successfully demonstrated in a preclinical pharmacokinetic study in mice.

Metabolite profiling of the novel anti-cancer agent, plitidepsin, in urine and faeces in cancer patients after administration of 14C-plitidepsin.

PURPOSE: Plitidepsin absorption, distribution, metabolism and excretion characteristics were investigated in a mass balance study, in which six patients received a 3-h intravenous infusion containing 7 mg 14C-plitidepsin with a maximum radioactivity of 100 µCi. METHODS: Blood samples were drawn and excreta were collected until less than 1% of the administered radioactivity was excreted per matrix for two consecutive days. Samples were pooled within-patients and between-patients and samples were screened for metabolites. Afterwards, metabolites were identified and quantified. Analysis was done using Liquid Chromatography linked to an Ion Trap Mass Spectrometer and offline Liquid Scintillation Counting (LC-Ion Trap MS-LSC). RESULTS: On average 4.5 and 62.4% of the administered dose was excreted via urine over the first 24 h and in faeces over 240 h, respectively. Most metabolites were found in faeces. CONCLUSION: Plitidepsin is extensively metabolised and it undergoes dealkylation (demethylation), oxidation, carbonyl reduction, and (internal) hydrolysis. The chemical formula of several metabolites was confirmed using high resolution mass data.

Ultra-sensitive LC-MS/MS method for the quantification of gemcitabine and its metabolite 2',2'-difluorodeoxyuridine in human plasma for a microdose clinical trial.

In microdose clinical trials a maximum of 100 µg of drug substance is administered to participants, in order to determine the pharmacokinetic properties of the agents. Measuring low plasma concentrations after administration of a microdose is challenging and requires the use of ulta-sensitive equipment. Novel liquid chromatography-mass spectrometry (LC-MS/MS) platforms can be used for quantification of low drug plasma levels. Here we describe the development and validation of an LC-MS/MS method for quantification of gemcitabine and its metabolite 2',2'-difluorodeoxyuridine (dFdU) in the low picogram per milliliter range to support a microdose trial. The validated assay ranges from 2.5-500 pg/mL for gemcitabine and 250-50,000 pg/mL for dFdU were linear, with a correlation coefficient (r2) of 0.996 or better. Sample preparation with solid phase extraction provided a good and reproducible recovery. All results were within the acceptance criteria of the latest US FDA guidance and EMA guidelines. In addition, the method was successfully applied to measure plasma concentrations of gemcitabine in a patient after administration of a microdose of gemcitabine.

Development and validation of a high-performance liquid chromatography-tandem mass spectrometry assay for the quantification of Dexamphetamine in human plasma.

Dexamphetamine is registered for the treatment of attention deficit hyperactivity disorder and narcolepsy. Current research has highlighted the possible application of dexamphetamine in the treatment of cocaine addiction. To support clinical pharmacologic trials a new simple, fast, and sensitive assay for the quantification of dexamphetamine in human plasma using liquid chromatography tandem mass spectrometry (LC-MS/MS) was developed. Additionally, it is the first reported LC-MS assay with these advantages to be fully validated according to current US FDA and EMA guidelines. Human plasma samples were collected on an outpatient basis and stored at nominally -20°C. The analyte and the internal standard (stable isotopically labeled dexamphetamine) were extracted using double liquid-liquid extraction (plasma-organic and organic-water) combined with snap-freezing. The aqueous extract was filtered and 2µL was injected on a C18-column with isocratic elution and analyzed with triple quadrupole mass spectrometry in positive ion mode. The validated concentration range was from 2.5-250ng/mL and the calibration model was linear. A weighting factor of 1 over the squared concentration was applied and correlation coefficients of 0.997 or better were obtained. At all concentrations the bias was within ±15% of the nominal concentrations and imprecision was ≤15%. All results were within the acceptance criteria of the latest US FDA guidance and EMA guidelines on method validation. In conclusion, the developed method to quantify dexamphetamine in human plasma was fit to support a clinical study with slow-release dexamphetamine.

Development and Validation of an LC-MS/MS Method for the Simultaneous Quantification of Abiraterone, Enzalutamide, and Their Major Metabolites in Human Plasma.

BACKGROUND: Abiraterone acetate and enzalutamide are 2 novel drugs for the treatment of metastatic castration-resistant prostate cancer. The metabolism of these drugs is extensive. Major metabolites are N-desmethyl enzalutamide, enzalutamide carboxylic acid, abiraterone N-oxide sulfate, and abiraterone sulfate; of which N-desmethyl enzalutamide is reported to possess antiandrogen capacities. A liquid chromatography-tandem mass spectrometry method for simultaneous quantification of abiraterone, enzalutamide, and the main metabolites has been developed and validated to support therapeutic drug monitoring. METHODS: Human plasma samples of patients treated with abiraterone or enzalutamide were harvested at the clinic and stored at -20°C. Proteins were precipitated by acetonitrile, and the final extract was injected on a Kinetex C18 column and separated with gradient elution. Analytes were detected by liquid chromatography-mass spectrometry (Triple Quad 6500). RESULTS: The method was validated over various linear ranges: 1-100 ng/mL for abiraterone, 5-500 ng/mL for enzalutamide and enzalutamide carboxylic acid, 10-1000 ng/mL for N-desmethyl enzalutamide, 30-3000 ng/mL for abiraterone N-oxide sulfate, and 100-10,000 ng/mL for abiraterone sulfate. Intra-assay and interassay variabilities were within ±15% of the nominal concentrations for quality control samples at medium and high concentrations and within ±20% at the lower limit of quantification, respectively. CONCLUSIONS: The described method for simultaneous determination of abiraterone and enzalutamide was validated successfully and provides a useful tool for therapeutic drug monitoring in patients treated with these agents.

Human mass balance study and metabolite profiling of 14C-niraparib, a novel poly(ADP-Ribose) polymerase (PARP)-1 and PARP-2 inhibitor, in patients with advanced cancer.

Niraparib is an investigational oral, once daily, selective poly(ADP-Ribose) polymerase (PARP)-1 and PARP-2 inhibitor. In the pivotal Phase 3 NOVA/ENGOT/OV16 study, niraparib met its primary endpoint of improving progression-free survival (PFS) for adult patients with recurrent, platinum sensitive, ovarian, fallopian tube, or primary peritoneal cancer in complete or partial response to platinum-based chemotherapy. Significant improvements in PFS were seen in all patient cohorts regardless of biomarker status. This study evaluates the absorption, metabolism and excretion (AME) of 14C-niraparib, administered to six patients as a single oral dose of 300 mg with a radioactivity of 100 µCi. Total radioactivity (TRA) in whole blood, plasma, urine and faeces was measured using liquid scintillation counting (LSC) to obtain the mass balance of niraparib. Moreover, metabolite profiling was performed on selected plasma, urine and faeces samples using liquid chromatography - tandem mass spectrometry (LC-MS/MS) coupled to off-line LSC. Mean TRA recovered over 504 h was 47.5% in urine and 38.8% in faeces, indicating that both renal and hepatic pathways are comparably involved in excretion of niraparib and its metabolites. The elimination of 14C-radioactivity was slow, with t1/2 in plasma on average 92.5 h. Oral absorption of 14C-niraparib was rapid, with niraparib concentrations peaking at 2.49 h, and reaching a mean maximum concentration of 540 ng/mL. Two major metabolites were found: the known metabolite M1 (amide hydrolysed niraparib) and the glucuronide of M1. Based on this study it was shown that niraparib undergoes hydrolytic, and conjugative metabolic conversions, with the oxidative pathway being minimal.

Validation and Clinical Evaluation of a Novel Method To Measure Miltefosine in Leishmaniasis Patients Using Dried Blood Spot Sample Collection.

To facilitate future pharmacokinetic studies of combination treatments against leishmaniasis in remote regions in which the disease is endemic, a simple cheap sampling method is required for miltefosine quantification. The aims of this study were to validate a liquid chromatography-tandem mass spectrometry method to quantify miltefosine in dried blood spot (DBS) samples and to validate its use with Ethiopian patients with visceral leishmaniasis (VL). Since hematocrit (Ht) levels are typically severely decreased in VL patients, returning to normal during treatment, the method was evaluated over a range of clinically relevant Ht values. Miltefosine was extracted from DBS samples using a simple method of pretreatment with methanol, resulting in >97% recovery. The method was validated over a calibration range of 10 to 2,000 ng/ml, and accuracy and precision were within ±11.2% and ≤7.0% (≤19.1% at the lower limit of quantification), respectively. The method was accurate and precise for blood spot volumes between 10 and 30 µl and for Ht levels of 20 to 35%, although a linear effect of Ht levels on miltefosine quantification was observed in the bioanalytical validation. DBS samples were stable for at least 162 days at 37°C. Clinical validation of the method using paired DBS and plasma samples from 16 VL patients showed a median observed DBS/plasma miltefosine concentration ratio of 0.99, with good correlation (Pearson'sr= 0.946). Correcting for patient-specific Ht levels did not further improve the concordance between the sampling methods. This successfully validated method to quantify miltefosine in DBS samples was demonstrated to be a valid and practical alternative to venous blood sampling that can be applied in future miltefosine pharmacokinetic studies with leishmaniasis patients, without Ht correction.

Quantification of miltefosine in peripheral blood mononuclear cells by high-performance liquid chromatography-tandem mass spectrometry.

Phagocytes, the physiological compartment in which Leishmania parasites reside, are the main site of action of the drug miltefosine, but the intracellular pharmacokinetics of miltefosine remain unexplored. We developed a bioanalytical method to quantify miltefosine in human peripheral blood mononuclear cells (PBMCs), expanding from an existing high performance liquid chromatography-tandem mass spectrometry method for the quantification of miltefosine in plasma. The method introduced deuterated miltefosine as an internal standard. Miltefosine was extracted from PBMC pellets by addition of 62.5% methanol. Supernatant was collected, evaporated and reconstituted in plasma. Chromatographic separation was performed on a reversed phase C18 column and detection with a triple-quadrupole mass spectrometer. Miltefosine was quantified using plasma calibration standards ranging from 4 to 1000ng/mL. This method was validated with respect to its PBMC matrix effect, selectivity, recovery and stability. No matrix effect could be observed from the PBMC content (ranging from 0.17 to 26.3×10(6)PBMCs) reconstituted in plasma, as quality control samples were within 3.0% of the nominal concentration (precision less than 7.7%). At the lower limit of quantitation of 4 ng/mL plasma, corresponding to 0.12ng/10(6) PBMCs in a typical clinical sample, measured concentrations were within 8.6% of the nominal value. Recovery showed to be reproducible as adding additional pre-treatment steps did not increase the recovery with more than 9%. This method was successfully applied to measure intracellular miltefosine concentrations in PBMC samples from six cutaneous leishmaniasis patients up to one month post-treatment.

Stability of oxaliplatin in chloride-containing carrier solutions used in hyperthermic intraperitoneal chemotherapy.

PURPOSE: Oxaliplatin is increasingly becoming the chemotherapeutic drug of choice for the treatment of peritoneal malignancies using cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS-HIPEC). Oxaliplatin is unstable in chloride-containing media, resulting in the use of 5% dextrose as the carrier solution in these procedures. Exposure of the peritoneum to 5% dextrose during perfusion times varying from 30 min to 90 min is associated with serious hyperglycemias and electrolyte disturbances. This can result in significant postoperative morbidity and mortality. In order to find out whether safer, chloride-containing carrier solutions can be used, we report the results of in-vitro analysis of oxaliplatin stability in both chloride-containing and choride-deficient carrier solutions and discuss the implications for oxaliplatin-based CRS-HIPEC procedures. METHODS: 5 mg of oxaliplatin was added to 50 mL of various carrier solutions at 42 °C: 5% dextrose, 0.9% sodium chloride, Ringer lactate, Dianeal(®) PD4 glucose 1.36% solution for peritoneal dialysis and 0.14 M sterile phosphate buffer pH 7.4. Samples were collected at standardized intervals and oxaliplatin concentration was determined using a stability indicating high-performance liquid chromatographic method, coupled to an UV detector (HPLC-UV); oxaliplatin degradation products were identified using HPLC-mass spectometry. RESULTS: In 5% dextrose, oxaliplatin concentration remained stable over a 2-hour period. Increasing chloride concentrations were associated with increasing degradation rates; however, this degradation was limited to <10% degradation after 30 min (the standard peritoneal perfusion time in most clinical CRS-HIPEC protocols) and <20% degradation after 120 min at 42 °C. In addition, oxaliplatin degradation was associated with the formation of its active drug form [Pt(dach)Cl2]. CONCLUSIONS: The use of chloride-containing carrier solutions for oxaliplatin does not relevantly affect its concentrations under the tested in-vitro conditions. Chloride seems to promote formation of the active cytotoxic drug form of oxaliplatin and therefore could enhance its cytotoxic effect. These data show that more physiological, chloride-containing carrier solutions can be used safely and effectively as a medium for oxaliplatin in CRS-HIPEC procedures.

Quantification of cabazitaxel, its metabolite docetaxel and the determination of the demethylated metabolites RPR112698 and RPR123142 as docetaxel equivalents in human plasma by liquid chromatography-tandem mass spectrometry.

We present a sensitive validated LC-MS/MS assay for the simultaneous determination of cabazitaxel and docetaxel in human plasma, with calibration ranges of 1.0-150 ng/mL for cabazitaxel and 0.1-15 ng/mL for docetaxel. Sample pretreatment consisted of liquid-liquid extraction with tert-butyl methyl ether. Chromatographic separation was achieved on a Zorbax Extend C18 column using a gradient mixture of 10mM ammonium hydroxide and methanol. Mass detection was carried out by turbo ion spray ionization in positive ion multiple reaction monitoring mode. All inter-day accuracies and precisions were within ±15% of the nominal value and within ±20% at the lower limit of quantitation. Demethylations of cabazitaxel yielding the metabolites RPR112698 and RPR123142 were monitored semi-quantitatively and quantified as ng docetaxel equivalents. Plasma samples of a prostate cancer patient treated with cabazitaxel were analyzed to demonstrate the usefulness of the presented assay for clinical drug monitoring. In conclusion, this method can be applied to support clinical pharmacokinetic studies with the novel anticancer drug cabazitaxel.

Method development and validation for the quantification of dasatinib, erlotinib, gefitinib, imatinib, lapatinib, nilotinib, sorafenib and sunitinib in human plasma by liquid chromatography coupled with tandem mass spectrometry.

To support pharmacokinetic-guided dosing in individual patients, a fast and accurate method for simultaneous determination of anticancer tyrosine kinase inhibitors (TKIs) dasatinib, erlotinib, gefitinib, imatinib, lapatinib, nilotinib, sorafenib and sunitinib in human plasma was developed using high-performance liquid chromatography and detection with tandem mass spectrometry (HPLC-MS/MS). Stable isotopically labeled compounds of the eight different TKIs were used as internal standards. Plasma proteins were precipitated and an aliquot of supernatant was directly injected onto a reversed phase chromatography system consisting of a Gemini C18 column (50 × 2.0 mm i.d., 5.0 µm particle size) and then compounds were eluted with a gradient. The outlet of the column was connected to a triple quadrupole mass spectrometer with electrospray interface. Ions were detected in the positive multiple reaction monitoring mode. This method was validated over a linear range from 20.0 to 10,000 ng/mL for erlotinib, gefitinib, imatinib, lapatinib, nilotinib and sorafenib, and from 5.00 to 2500 ng/mL for dasatinib and sunitinib. Results from the validation study demonstrated good intra- and inter-assay accuracy (<13.1%) and precision (10.0%) for all analytes. This method was successfully applied for routine therapeutic drug monitoring purposes in patients treated with the investigated TKIs.

A validated assay for the quantitative analysis of vatalanib in human EDTA plasma by liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

A sensitive and accurate method for the determination of vatalanib in human EDTA plasma was developed using high-performance liquid chromatography and detection with tandem mass spectrometry. Stable isotopically labeled imatinib was used as internal standard. Plasma proteins were precipitated and an aliquot of the supernatant was directly injected onto a Phenomenex Gemini C18 analytical column (50 mm x 2.0 mm ID, 5.0 microm particle size) and then compounds were eluted with a linear gradient. The outlet of the column was connected to a Sciex API 365 triple quadrupole mass spectrometer and ions were detected in positive multiple reaction monitoring mode. The lower limit of quantification was 10 ng/mL (S/N approximately 10, CV < or = 8.4%). This method was validated over a linear range from 10 to 2500 ng/mL, and results from the validation study demonstrated a good intra- and inter-assay accuracy (inaccuracy < or = 9.57%) and precision (CV < or = 8.81%). This method has been used to determine plasma vatalanib concentrations in patients with advanced solid tumor, enrolled in a phase I pharmacokinetic trial with the drug.

Identification and profiling of circulating metabolites of atazanavir, a HIV protease inhibitor.

Atazanavir is a commonly prescribed protease inhibitor for treatment of HIV-1 infection. Thus far, only limited data are available on the in vivo metabolism of the drug. Three systemic circulating metabolites have been reported, but their chemical structures have not been released publicly. Atazanavir metabolites may contribute to its effectiveness but also to its toxicity and interactions. Thus, there is a need for extensive metabolic profiling of atazanavir. Our goals were to screen and identify previously unknown atazanavir metabolites and to develop a sensitive metabolite profiling method in plasma. Five atazanavir metabolites were detected and identified in patient samples using liquid chromatography coupled to linear ion trap mass spectrometry: one N-dealkylation product (M1), two metabolites resulting from carbamate hydrolysis (M2 and M3), a hydroxylated product (M4), and a keto-metabolite (M5). For sensitive semiquantitative analysis of the metabolites in plasma, the method was transferred to liquid chromatography coupled to triple quadrupole mass spectrometry. In 12 patient samples, all the metabolites could be detected, and possible other potential atazanavir keto-metabolites were found. Atazanavir metabolite levels were positively correlated with atazanavir levels, but interindividual variability was high. The developed atazanavir metabolic screening method can now be used for further clinical pharmacological research with this antiretroviral agent.

Quantification of the HIV-integrase inhibitor raltegravir and detection of its main metabolite in human plasma, dried blood spots and peripheral blood mononuclear cell lysate by means of high-performance liquid chromatography tandem mass spectrometry.

For the quantification of the HIV-integrase inhibitor raltegravir in human plasma, dried blood spots and peripheral blood mononuclear cell (PBMC) lysate, an assay was developed and validated, using liquid chromatography coupled with tandem mass spectrometry. The assay also allowed detection, but no quantification due to absence of reference substance, of the main metabolite, raltegravir-glucuronide. Raltegravir was extracted from plasma by means of protein precipitation with a mixture of methanol and acetonitrile using only 50microL plasma. Extraction from dried blood spots was performed with a simple one-step extraction with a mixture of methanol, acetonitrile and 0.2M zincsulphate in water (1:1:2, v/v/v) and extraction from cell lysate was performed in 50% methanol in water. Chromatographic separation was performed on a reversed phase C18 column (150mmx2.0mm, particle size 5microm) with a quick stepwise gradient using an acetate buffer (pH 5) and methanol, at a flow rate of 0.25mL/min. The analytical run time was 10min. The triple quadrupole mass spectrometer was operated in the positive ion-mode and multiple reaction monitoring was used for drug quantification. The method was validated over a range of 50-10,000ng/mL in plasma and dried blood spots and a range of 1-500ng/mL in PBMC lysate. Dibenzepine was used as the internal standard. The method was proven to be specific, accurate, precise and robust. Accuracies ranged from 104% to 105% in plasma, from 93% to 105% in dried blood spots and from 82% to 113% in PBMC lysate. Precision over the complete concentration range was less than 6%, 11% and 13% in plasma, dried blood spots and PBMC lysate, respectively. The method is now applied for therapeutic drug monitoring and pharmacological research in HIV-infected patients treated with raltegravir.

Quantitative analysis of gemcitabine triphosphate in human peripheral blood mononuclear cells using weak anion-exchange liquid chromatography coupled with tandem mass spectrometry.

Gemcitabine triphosphate (dFdCTP) is a highly active metabolite of gemcitabine. It is formed intra-cellularly via the phosphorylation of gemcitabine by deoxycytidine kinase. The monitoring of dFdCTP in human peripheral blood mononuclear cells (PBMCs), in addition to plasma concentrations of gemcitabine and its metabolite 2',2'-difluorodeoxyuridine, is considered very useful in determining pharmacokinetic-pharmacodynamic relationships. We describe a novel sensitive assay for the quantification of dFdCTP in human PBMCs. The method is based on weak anion-exchange liquid chromatography and detection with tandem mass spectrometry (LC-MS/MS). The assay has been validated from 1 ng/ml (lower limit of quantification, LLOQ) to 25 ng/ml (upper limit of quantification, ULOQ) using 180 microl aliquots of PBMC extracts containing approximately 0.648 mg protein or 3.8 x 10(6) lysed PBMCs. The LLOQ is equivalent to 94 fmol/10(6) cells (1 ng/ml = 0.18 ng/180 microl or 0.18 ng/0.648 mg protein = 0.047 ng/10(6) cells or 94 fmol/10(6) cells). This highly sensitive assay is capable of quantifying about 200-fold lower concentrations of dFdCTP in human PBMCs than currently available methods.

Sensitive inductively coupled plasma mass spectrometry assay for the determination of platinum originating from cisplatin, carboplatin, and oxaliplatin in human plasma ultrafiltrate.

We present a highly sensitive, rapid method for the determination of platinum originating from the anticancer agents cisplatin, carboplatin, and oxaliplatin in human plasma ultrafiltrate. The method is based on the quantification of platinum by inductively coupled plasma mass spectrometry and allows quantification of 7.50 ng l-1 platinum in only 150 microl of matrix. Sample pretreatment involves dilution of samples with 1% HNO3. Validation fulfilled the most recent FDA guidelines for bioanalytical method validation. Validated ranges of quantification were 7.50 ng l-1 to 1.00x10(5) ng l-1 in plasma ultrafiltrate for all three platinum compounds. The assay is now successfully used to support pharmacokinetic studies in cancer patients treated with cisplatin, carboplatin, or oxaliplatin.

Simultaneous quantification of fludarabine and cyclophosphamide in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

Fludarabine and cyclophosphamide are anticancer agents mainly used in the treatment of hematologic malignancies. We have developed and validated an assay using high-performance liquid chromatography (HPLC) coupled with electrospray ionization tandem mass spectrometry for the quantification of fludarabine in combination with cyclophosphamide in human heparin and human EDTA plasma. Sample pre-treatment consisted of a protein precipitation with cold acetonitrile (-20 degrees C) using 250 microL of plasma. Separation was performed on an Extend C18 column (150 x 2.1 mm i.d.; 5 microm) with a stepwise gradient using 1 mM ammonia solution and acetonitrile at a flow rate of 400 microL/min. The analytical run time was 12 min. The triple quadrupole mass spectrometer was operated in the positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over a concentration range of 1 to 100 ng/mL for fludarabine and cyclophosphamide in human heparin and human EDTA plasma. The coefficients of variation were <13.9% for inter- and intra-day precisions. Mean accuracies were also within the designated limits (+/-15%). The analytes were stable in plasma, processed extracts and in stock solution under all relevant conditions.

Simultaneous quantification of the new HIV protease inhibitors atazanavir and tipranavir in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

We have developed and validated an assay, using liquid chromatography coupled with electrospray tandem mass spectrometry (LC-MS/MS), for the quantification of the novel protease inhibitors (PIs) atazanavir and tipranavir. The sample pre-treatment consisted of protein precipitation with a mixture of methanol and acetronitrile using 100 microl plasma for atazanavir and 50 microl for tipranavir. Chromatographic separation was achieved on an Inertsil ODS3 column (50 mm x 2.0 mm i.d., particle size 5 microm), with a quick stepwise gradient using an acetate buffer (pH 5) and methanol, at a flow rate of 0.5 ml/min. The analytical run time was 5.5 min. The triple quadrupole mass spectrometer operated in the positive ion-mode and multiple reaction monitoring (MRM) was used for drug quantification. The assay was linear over a concentration range of 0.05-10 microg/ml for atazanavir and 0.1-75 microg/ml for tipranavir. Saquinavir-d5 was used as internal standard. The intra- and inter-day coefficients of variation were less than 3.8% for atazanavir and less than 10.4% for tipranavir. Accuracies were within +/-7.3 and +/-7.2% for atazanavir and tipranavir, respectively. Both drugs were stable under various relevant storage conditions. The validated concentration ranges proved to be adequate to measure concentrations of human immunodeficiency virus type-1 (HIV-1)-infected individuals. The developed method could easily be combined with a previously developed LC-MS/MS assay for the quantification of protease inhibitors.

Rapid quantification of HIV protease inhibitors in human plasma by high-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry.

HIV protease inhibitors are important antiretroviral drugs which have substantially reduced the morbidity and mortality associated with HIV-1 infection. Recent data have shown relationships between plasma concentrations of the protease inhibitors and clinical response, which makes therapeutic drug monitoring valuable. We have developed and validated an assay, using liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS), for the routine quantification of the six licensed protease inhibitors (amprenavir, indinavir, lopinavir, nelfinavir, ritonavir and saquinavir) and the pharmacologically active nelfinavir metabolite M8 in plasma. The sample pretreatment consisted of protein precipitation with a mixture of methanol and acetronitrile using only 100 microl of plasma. Chromatographic separation was performed on an Inertsil ODS3 column (50 x 2.0 mm i.d., particle size 5 microm), with a quick stepwise gradient using an acetate buffer (pH 5) and methanol, at a flow rate of 0.5 ml min(-1). The analytical run time was 5.5 min. The use of a 96-well plate autosampler allowed batch sizes up to 150 patient samples. The triple-quadrupole mass spectrometer was operated in the positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over the concentration ranges 0.01-10 microg ml(-1) for indinavir and saquinavir, 0.1-10 microg ml(-1) for amprenavir, 0.05-10 microg ml(-1) for nelfinavir and ritonavir, 0.1-20 microg ml(-1) for lopinavir and 0.01-5 microg ml(-1) for M8. Saquinavir-d(5) and indinavir-d(6) were used as internal standards. The coefficients of variation were always <10% for both intra-day and inter-day precisions for each compound. Mean accuracies were also between the designated limits (+/-15%). The validated concentration ranges proved to be adequate in daily practice. This robust and fast LC/MS/MS assay is now successfully applied for routine therapeutic drug monitoring and pharmacokinetic studies in our hospital.