Determination of unbound docetaxel and paclitaxel in plasma by ultrafiltration and liquid chromatography–tandem mass spectrometry

Development of an hollow fiber solid phase microextraction method for the analysis of unbound fraction of imatinib and N-desmethyl imatinib in human plasma

Therapeutic drug monitoring (TDM) of imatinib (IM) in cancer therapy offers the potential to improve treatment efficacy while minimizing toxicity. There was a significant correlation between unbound concentration and clinical response and toxicity, compared with total plasma concentrations, and the quantification of unbound IM and its metabolite, N-desmethyl imatinib (NDI) are of interest for TDM. However, traditional unbound drug separation methods have shortcomings, especially are susceptible to non-specific binding (NSB) of drugs to the polymer-constructed components of filter membranes, which are difficult to avoid at present. Hence it is necessary to developed a reliable separation method for the analysis of the unbound fraction of IM and NDI in TDM. We developed and validated an hollow fiber solid phase microextraction (HF-SPME) method coupled with high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) that to measure unbound IM and NDI concentration in human plasma. It used the NSB phenomenon and solve the NSB problem. The preparation procedure only involves a common vortex and ultrasonication without dilution of samples and modification of membrane. A total of 50 chronic myeloid leukemia (CML) patients were enrolled in our study. The relationship between the unbound and total concentrations for IM and NDI, as well as the concentration ratios of NDI to IM in 50 clinical plasma samples were investigated. The extraction recovery is high to 95.5-106 % with validation parameters for the methodological results were all excellent. There were both a poor linear relationship between the unbound and total concentrations for IM (r2=0.504) and NDI (r2=0.201) in 50 clinical plasma samples. The unbound concentration ratios of NDI to IM varied widely in CML patients. The determination of unbound IM and NDI concentration is meaningful and necessary. The developed HF-SPME method is simple, accurate and precise that could be used to measure unbound IM and NDI concentration in clinical TDM.

A Sensitive Assay for Unbound Docetaxel Using Ultrafiltration plus HPLC-MS and Its Application to a Clinical Study

INTRODUCTION

Docetaxel, a taxane used in the treatment of solid tumours, exerts pharmacological activity when in its unbound form. We report a sensitive assay to quantify unbound docetaxel after oral administration of docetaxel plus encequidar (oDox+E). Unbound drug quantification is important due to its direct correlation with drug-related toxicity and therapeutic efficacy. We improve on the sensitivity of current assay methods and demonstrate the utility of the assay on a novel formulation of oral docetaxel.

METHODS

Ultrafiltration followed by high-performance liquid chromatography and tandem mass spectrometry (HPLC-MS/MS) was utilized. Long-term stability, precision, accuracy, and recovery experiments were conducted to validate the assay. Additionally, patient samples from a Phase I dose-escalation pharmacokinetic study were analyzed using the developed assay.

RESULTS

The assay method exhibited long-term stability with an observed change between 0.8 and 6.9% after 131 days of storage at -60 °C. Precision and accuracy quality controls met the FDA acceptance criteria. An average recovery of 88% was obtained. Patient sample analysis demonstrated successful implementation of the assay.

CONCLUSION

A validated sensitive assay was developed with an LLOQ of 0.084 ng/mL using 485 µL of human plasma. The sensitivity of the assay allowed quantification of unbound docetaxel concentrations in an early-phase oDox+E clinical study to compare it against IV docetaxel using pharmacokinetic modelling. Successful development of oDox+E represents an opportunity to replace the current IV docetaxel regimen with an oral regimen with lower cost, decreased side effects, and improve patient quality of life and experience.

Prostate artery chemoembolization in prostate cancer: A proof of concept study in spontaneous prostate cancer in a canine model

PURPOSE

The purpose of this study was to assess the feasibility and efficacy of docetaxel-loaded bead chemoembolization in spontaneous prostate cancer in a canine model.

MATERIALS AND METHODS

Five pet dogs with histopathologically proven prostate cancer were referred for prostate artery chemoembolization (PACE). After PACE, all animals were followed, including pharmacokinetic study and clinical and biological evolution, until death. Pelvic contrast-enhanced computed tomography examination was performed at one and two months. Animals were subjected to pathological examination after death.

RESULTS

Both prostate arteries were successfully chemoembolized in all dogs. A median dose of 18 mg (Q1, Q3; 11.8, 20 mg) docetaxel loaded in 3 mL of 50-100 µm super absorbent polymer beads was injected into each dog. At one month, four of the five dogs were still alive and the median prostate volume was 51% lower (prePACE median prostate volume, 18.4 mL [Q1, Q3; 12, 32.1 mL] vs. postPACE median prostate volume, 6.2 mL [Q1, Q3; 6.2, 11 mL]). At two months, three dogs died because of disease progression. The two remaining dogs showed a 70% median decrease in prostate volume. Prostate pathological examination showed 73% of necrosis. No worsening of urinary symptoms was observed. Pharmacokinetic analysis showed limited systemic passage of docetaxel. All dogs died of metastatic spread at nine months.

CONCLUSION

This study suggests that PACE is feasible and safe for the treatment of spontaneous prostate cancer in a canine model and may provide a new approach to treat selected patients with prostate cancer.

Barriers and opportunities for the clinical implementation of therapeutic drug monitoring in oncology

There are few fields of medicine in which the individualisation of medicines is more important than in the area of oncology. Under-dosing can have significant ramifications due to the potential for therapeutic failure and cancer progression; by contrast, over-dosing may lead to severe treatment-limiting side effects, such as agranulocytosis and neutropenia. Both circumstances lead to poor patient prognosis and contribute to the high mortality rates still seen in oncology. The concept of dose individualisation tailors dosing for each individual patient to ensure optimal drug exposure and best clinical outcomes. While the value of this strategy is well recognised, it has seen little translation to clinical application. However, it is important to recognise that the clinical setting of oncology is unlike that for which therapeutic drug monitoring (TDM) is currently the cornerstone of therapy (e.g. antimicrobials). Whilst there is much to learn from these established TDM settings, the challenges presented in the treatment of cancer must be considered to ensure the implementation of TDM in clinical practice. Recent advancements in a range of scientific disciplines have the capacity to address the current system limitations and significantly enhance the use of anticancer medicines to improve patient health. This review examines opportunities presented by these innovative scientific methodologies, specifically sampling strategies, bioanalytics and dosing decision support, to enable optimal practice and facilitate the clinical implementation of TDM in oncology.

Pretreatment and non-specific binding in ultrafiltration device: Impact on protease inhibitor quantification

INTRODUCTION

Ultrafiltration (UF) is used to separate unbound drugs; however, non-specific binding (NSB) may be a limiting factor of this technique. Pretreatment of UF devices has been suggested to reduce NSB. Therefore, the pretreatment methodologies for UF devices were evaluated in order to test their effectiveness in reducing NSB of protease inhibitors (PIs).

METHODOLOGY

Two PIs (lopinavir-LPV and ritonavir-RTV) were tested. UF devices were pretreated with ultrapure water, Tween-20 or Tween-80. To evaluate the NSB, after UF devices being pretreated, ultrafiltrate solutions containing the analytes at two concentrations (low and high) were used. Samples were quantified by LC-MS/MS.

RESULTS

UF devices pretreated with Tween-5% had the lowest NSB for both analytes. NSB values varied between 7 and 11% at low concentration 16-34% at high LPV concentration, respectively. For RTV, NSB was approximately 6% for low concentration and 18% for high concentration. Failure to completely remove Tween in UF devices could results in an overestimation of NSB.

CONCLUSION

Pretreatment of UF device with Tween and subsequent removal proved to be effective in reducing NSB of PI.

Bioequivalence of paclitaxel protein-bound particles in patients with breast cancer: determining total and unbound paclitaxel in plasma by rapid equilibrium dialysis and liquid chromatography-tandem mass spectrometry

Background and objective: Paclitaxel protein-bound particles for injectable suspension (nab-paclitaxel) showed many advantages in safety, effectiveness, and convenience. Different from conventional formulations, the bioequivalence evaluation of nab-paclitaxel formulations requires to determine the total amount of paclitaxel in plasma and the unbound paclitaxel to reflect their in vivo disposition. This study aimed to develop an analytical method to quantify the total and unbound paclitaxel in plasma and evaluate the bioequivalence of two formulations of nab-paclitaxel in patients with breast cancer. Materials and methods: An open-label, randomized, two-period crossover study was completed among 24 Chinese patients with breast cancer. The patients were randomized to receive either the test formulation on cycle 1 day 1 and after 21 days in cycle 2 day 1 by the reference formulation (Abraxane®), or vice versa. Rapid equilibrium dialysis was adopted to separate the unbound paclitaxel in human plasma. Total and unbound paclitaxel concentrations were measured by the validated liquid chromatography-tandem mass spectrometry methods over the range of 5.00-15,000 and 0.200-200 ng/mL, respectively. The bioequivalence of the test formulation to the reference formulation was assessed using the Food and Drug Administration and European Medicines Agency guidelines. Results: All the 90% confidence intervals (CIs) of the geometric mean ratios fell within the predetermined acceptance range. The 90% CIs for the area under the concentration-time curve (AUC) from 0 h to 72 h (AUC0-t), AUC from time zero to infinity (AUC0-∞), and peak plasma concentrations (Cmax) for total paclitaxel were 92.03%-98.05%, 91.98%-99.37%, and 91.37%-99.36%, respectively. The 90% CIs of AUC0-t, AUC0-∞, and Cmax for unbound paclitaxel were 86.77%-97.88%, 86.81%-97.88%, and 87.70%-98.86%, respectively. Conclusion: Bioequivalence between the two nab-paclitaxel formulations was confirmed for total and unbound paclitaxel at the studied dose regimen.

Methods and Study Designs for Characterizing the Pharmacokinetics and Pharmacodynamics of Carrier-Mediated Agents

Major advances in carrier-mediated agents (CMAs), which include nanoparticles, nanosomes, and conjugates, have revolutionized drug delivery capabilities over the past decade. While providing numerous advantages, such as greater solubility, duration of exposure, and delivery to the site of action over their small molecule counterparts, there is substantial variability in systemic clearance and distribution, tumor delivery, and pharmacologic effects (efficacy and toxicity) of these agents. In this chapter, we focus on the analytical and phenotypic methods required to design a study that characterizes the pharmacokinetics (PK) and pharmacodynamics (PD) of all forms of these nanoparticle-based drug agents. These methods include separation of encapsulated and released drugs, ultrafiltration for measurement of non-protein bound active drug, microdialysis to measure intra-tumor drug concentrations, immunomagnetic separation and flow cytometry for sorting cell types, and evaluation of spatial distribution of drug forms relative to tissue architecture by mass spectrometry imaging and immunohistochemistry.

Determination of total and unbound docetaxel in plasma by ultrafiltration and UPLC-MS/MS: application to pharmacokinetic studies

A sensitive and specific liquid chromatographic/tandem mass spectrometric (LC-MS/MS) method was developed and validated for quantifying total and unbound docetaxel drug concentrations in plasma. Calibration curves for unbound and total docetaxel were linear over the respective ranges of 0.108~10.8 and 0.54~216 ng/mL. The intra- and interday assay accuracy and precision did not exceed 15%. The methods were validated to show the standard range linearity, sensitivity, selectivity, accuracy, precision, and stability of docetaxel in the matrices tested. In addition, this method is fast and simple with a short run time of 4.5 min and a small plasma sample volume (500 µL). The validated method was successfully applied to a pharmacokinetic study of a docetaxel micelle formulation in rat plasma after intravenous administration at a dose of 10 mg/kg. Docetaxel micelles slowly released their drug payload, and protein-bound, unbound, and micellar drug pools existed simultaneously. These various forms in plasma pools were also measured in the study. We confirmed that most of the docetaxel in plasma was micelle-associated (96.52% at 24 h and 83.14% at 72 h) after micellar docetaxel administration, as a result of sequestration of the drug in long-circulating micelles.

Mass spectrometry in the pharmacokinetic studies of anticancer natural products

In the history of medicine, nature has represented the main source of medical products. Indeed, the therapeutic use of plants certainly goes back to the Sumerian and Hippocrates and nowadays nature still represents the major source for new drugs discovery. Moreover, in the cancer treatment, drugs are either natural compounds or have been developed from naturally occurring parent compounds firstly isolated from plants and microbes from terrestrial and marine environment. A critical element of an anticancer drug is represented by its severe toxicities and, after administration, the drug concentrations have to remain in an appropriate range to be effective. Anyway, the drug dosage defined during the clinical studies could be inappropriate for an individual patient due to differences in drug absorption, metabolism and excretion. For this reason, personalized medicine, based on therapeutic drug monitoring (TDM), represents one of most important challenges in cancer therapy. Mass spectrometry sensitivity, specificity and fastness lead to elect this technique as the Golden Standard for pharmacokinetics and drug metabolism studies therefore for TDM. This review focuses on the mass spectrometry-based methods developed for pharmacokinetic quantification in human plasma of anticancer drugs derived from natural sources and already used in clinical practice. Particular emphasis was placed both on the pre-analytical and analytical steps, such as: sample preparation procedures, sample size required by the analysis and the limit of quantification of drugs and metabolites to give some insights on the clinical practice applicability. © 2015 Wiley Periodicals, Inc. Mass Spec Rev. 36:213-251, 2017.

The significance of a new parameter – plasma protein binding – in therapeutic drug monitoring and its application to carbamazepine in epileptic patients

The primary cause of the variability of C_f in pharmacology is the change in plasma protein binding (PPB), thus PPB monitoring should be applied to a better individualization of drug dosage regimens in clinical patients.

A Comparison of LC-MS/MS and a Fully Integrated Autosampler/Solid-Phase Extraction System for the Analysis of Protein Binding Samples

A new analysis approach was evaluated for measuring plasma protein binding (PPB) of small molecules using the Agilent RapidFire high-throughput system coupled with a Sciex API 4000 mass spectrometer (RF-MS/MS). Thirty-three proprietary and 12 literature compounds were subjected to rapid equilibrium dialysis (RED) and evaluated in parallel using RF-MS/MS at 16.4 s/sample and traditional liquid chromatography–tandem mass spectrometry (LC-MS/MS) at 3.5 min/sample, thus making the RF-MS/MS analysis over 12 times faster than LC-MS/MS. The high-throughput analysis method that was developed demonstrated excellent correlation with the traditional LC-MS/MS analysis method with an r2 value of 0.96. The RF-MS/MS analysis method was implemented to increase sample throughput, decrease turnaround time for PPB data, and decrease time burden on existing LC-MS/MS instruments.

Application of a UPLC-MS/MS method to the protein binding study of TM-2 in rat, human and beagle dog plasma

TM-2 known as a potential antitumor drug is a novel semi-synthetic taxane derivative. As drug–protein interactions contribute to insights into pharmacokinetic and pharmacodynamic properties, we elucidated the binding of TM-2 to plasma protein. In this study, a simple, rapid and reliable method was developed and validated employing equilibrium dialysis for the separation of bound and unbound drugs and ultra-performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) for the quantitation. Protein binding reached equilibrium within 24 h of incubation at 37 °C. After liquid–liquid extraction with methyl tert-butyl ether, the samples were separated on Thermo Syncronis UPLC^® C₁₈ (2.1 mm×50 mm, 1.7 µm), and acquisition of mass spectrometric data was performed in multiple reaction monitoring (MRM) mode via positive electrospray ionization. The assay was linear over the concentration rang of 5–2000 ng/mL. The intra- and inter-day precisions were 0.1%–14.8%, and the accuracy was from −6.4% to 7.0%. This assay has been successfully applied to a protein binding study of TM-2 in rat, human and beagle dog plasma. TM-2 showed high protein binding of 81.4%±6.5% (rat), 87.9%±3.6% (human) and 79.4%±4.0% (beagle dog). The results revealed that there was an insignificant difference among the three species.

Pretreatment of plasma samples by a novel hollow fiber centrifugal ultrafiltration technique for the determination of plasma protein binding of three coumarins using acetone as protein binding releasing agent

A novel and practical sample pretreatment method based on hollow fiber centrifugal ultrafiltration (HFCF-UF) was developed to determine plasma protein binding by using HPLC. The samples for analyzing unbound and total concentrations could be prepared in parallel simultaneously by the same device. It only required centrifugation for a short time and the filtrate could be injected directly for HPLC analysis without further treatment. Coumarins were selected as the model drugs. Acetone was chosen as the releasing agent to free the binding drug from the drug-protein complex for the total drug concentration determination. Non-specific bindings (NSBs) between the analytes and hollow fiber membrane materials were investigated. The type and volume of protein binding releaser were optimized. Additionally, centrifugal speed and centrifugal time were considered. Under the optimized conditions, the absolute recovery rates of the unbound and total concentrations were in the range of 97.5-100.9% for the three analytes. The limits of detection were in the range of 0.0135-0.0667μgmL(-1). In vitro plasma protein binding of the three coumarins was determined at three concentrations using the validated method and the relative standard deviations (RSDs) were less than 3.4%. Compared with traditional method, the HFCF-UF method is simple to run, no specialized equipment requirement and is a more accurate plasma pretreatment procedure with almost excellent drug-protein binding equilibrium. Therefore, this method can be applied to determine the plasma protein binding in clinical practice. It also provides a reliable alternative for accurate monitoring of unbound or total drug concentration in therapeutic drug monitoring (TDM).

Rapid and sensitive liquid chromatography coupled with electrospray ionization tandem mass spectrometry method for the analysis of paclitaxel, docetaxel, vinblastine, and vinorelbine in human plasma

BACKGROUND

A rapid and sensitive analytical method using liquid chromatography coupled with electrospray ionization tandem mass spectrometry (LC-MS/MS) was developed for the determination of paclitaxel, docetaxel, vinblastine, and vinorelbine in human plasma.

METHODS

A simple liquid-liquid extraction procedure was applied using only 100-μL plasma. Chromatographic separation of these anticancer drugs was achieved with an isocratic mobile phase consisting of acetonitrile/aqueous buffer (10 mmol/L ammonium acetate and 0.1% formic acid in 70:30, vol/vol) at a flow rate of 0.25 mL/min in a short time (4.5 minutes).

RESULTS

The calibration curves for paclitaxel, docetaxel, vinblastine, and vinorelbine in spiked human plasma ranged from 25 to 2500, 10 to 1000, 10 to 1000, and 10 to 1000 ng/mL, respectively. The squares of the linear correlation coefficients were all more than 0.99. The intraday and interday relative standard deviations across 3 validation runs over the entire concentration range were less than 9.2%.

CONCLUSIONS

The established method should be helpful for the pharmacokinetic monitoring of paclitaxel, docetaxel, vinblastine, and vinorelbine in the human plasma of non-small cell lung cancer patients.

Quantification of taxanes in biological matrices: a review of bioanalytical assays and recommendations for development of new assays

Since the isolation of paclitaxel and its approval for the treatment of breast cancer, various taxanes and taxane formulations have been developed. To date, almost 100 bioanalytical assays have been published with the method development and optimization often extensively discussed by the authors. This Review presents an overview of assays published between January 1970 and September 2013 that described method development and validation of assays used to quantify taxanes in biological matrices such as plasma, urine, feces and tissue samples. For liquid chromatography assays, sample pretreatment, chromatographic separation and assay performance are compared. Since this Review discusses the limitations of previously developed liquid chromatography assays and gives recommendations for future assay development, it can be used as a reference for future development of liquid chromatography assays for the quantification of taxanes in various biological matrices to support preclinical and clinical studies.

Development and validation of an ultrafiltration-UPLC-MS/MS method for rapid quantification of unbound docetaxel in human plasma

Docetaxel lipid microsphere (DT-LM) is a novel formulation of docetaxel without Tween-80. A sensitive, robust and reproducible ultrafiltration (UF) followed by UPLC-MS/MS method was developed and validated for the quantification of unbound docetaxel in human plasma using paclitaxel as IS. Ultrafiltrate samples were chromatographed on Acquity UPLC BEH C18 column (50 mm × 2.1 mm, 1.7 μm). The mobile phase was a mixture of 10mM ammonium formate in water containing 0.2% formic acid (A) and acetonitrile containing 0.2% formic acid (B). The volume of plasma utilized was only 450 μL. The calibration curve was linear over the range of 0.2-200 ng/mL, with LLOQ of 0.2 ng/mL. The method was shown to be reliable and reproducible with intra- and inter-day precision and accuracy <±15%, and extraction recovery of 98.1-104.8%. Docetaxel was stable during stability studies, e.g., short term, post-preparation and freeze-thaw cycles. The validated method was utilized to support the pharmacological study of DT-LM in patients with advanced cancer.

Combined quantification of paclitaxel, docetaxel and ritonavir in human feces and urine using LC-MS/MS

A combined assay for the determination of paclitaxel, docetaxel and ritonavir in human feces and urine is described. The drugs were extracted from 200 μL urine or 50 mg feces followed by high-performance liquid chromatography analysis coupled with positive ionization electrospray tandem mass spectrometry. The validation program included calibration model, accuracy and precision, carry-over, dilution test, specificity and selectivity, matrix effect, recovery and stability. Acceptance criteria were according to US Food and Drug Administration guidelines on bioanalytical method validation. The validated range was 0.5-500 ng/mL for paclitaxel and docetaxel, 2-2000 ng/mL for ritonavir in urine, 2-2000 ng/mg for paclitaxel and docetaxel, and 8-8000 ng/mg for ritonavir in feces. Inter-assay accuracy and precision were tested for all analytes at four concentration levels and were within 8.5% and <10.2%, respectively, in both matrices. Recovery at three concentration levels was between 77 and 94% in feces samples and between 69 and 85% in urine samples. Method development, including feces homogenization and spiking blank urine samples, are discussed. We demonstrated that each of the applied drugs could be quantified successfully in urine and feces using the described assay. The method was successfully applied for quantification of the analytes in feces and urine samples of patients.

A pulsed tangential-flow ultrafiltration technique for studying protein-drug binding

We describe a pulsed tangential-flow ultrafiltration technique for rapid analysis of protein-drug binding. A protein-drug pulse was injected into a tangential-flow membrane device and made to flow parallel to the surface of a protein-retaining ultrafiltration membrane. The protein and protein-drug complexes were flushed out of the device in the retentate stream, whereas the free drug present in the permeate stream was quantified using on-line UV detector. The height of the permeate drug peak and its area under the curve were both found to be proportional to the free drug concentration in the injected sample. The fraction of bound drug was determined by comparison with peak obtained with protein-free drug sample. The characteristics of the permeate drug peak such as residence time, peak width, and peak height depended on both feed and permeate flow rates. The proposed technique in addition to being fast was "self-priming" in nature because the injected samples were flushed out of the module along with the retentate and permeate. This feature makes this technique particularly suitable for automated sample analysis. The technique was validated using three-model protein-drug combinations: bovine serum albumin (BSA)-antipyrine, BSA-tryptophan, and BSA-aspirin.

Effect of volume ratio of ultrafiltrate to sample solution on the analysis of free drug and measurement of free carbamazepine in clinical drug monitoring

Traditional ultrafiltration (UF) usually has a large volume ratio of ultrafiltrate to sample solution, and this ratio cannot be well controlled. It can break the balance of protein-binding equilibrium and exert an influence on the analysis of free drug. In the present study, we evaluated the influence of volume ratio of ultrafiltrate to sample solution on the analysis of free drug in human plasma. We used carbamazepine as a model drug and studied the effect of different centrifugation times on ultrafitrate volume and the related effects on unbound carbamazepine measurement. Moreover, we compared the hollow fiber centrifugal ultrafiltration (HFCF-UF) with traditional UF. Our results showed that the ultrafiltrate volume was changed from 40 to 400 μL with the increase of centrifugation time for the traditional UF, and the related changes in unbound concentration were significant. The rate of protein binding (BP) was changed from 40% to 70%. In contrast, a tiny and invariant ultrafiltrate yield (40 μL) was obtained using the HFCF-UF method, and the BP rate was around 72%. In addition, with the HFCF-UF method, the volume ratio of ultrafiltrate to sample solution could be also well controlled by the inner diameters of both the glass tube and hollow fiber. The HFCF-UF method was a more accurate plasma pretreatment procedure, by which the in vivo balance of protein-binding equilibrium was hardly broken. Therefore, this method was successfully employed to quantify the free fraction of carbamazepine in clinical samples.

Determination of docetaxel in rat plasma and its application in the comparative pharmacokinetics of Taxotere and SID530, a novel docetaxel formulation with hydroxypropyl-β-cyclodextrin

In this study, a sensitive, simple and reliable method for the quantification of docetaxel in rat plasma was developed and validated using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The plasma samples were prepared by protein precipitation, and paclitaxel was used as an internal standard (IS). Chromatographic separation was achieved using a Gemini C(18) column (2.0 × 150 mm, 5 µm) with a mobile phase consisting of 0.1% formic acid-acetonitrile (30:70, v/v). The precursor-product ion pairs used for multiple reaction monitoring were m/z 808.5 → 527.5 (docetaxel) and m/z 854.2 → 286.5 (IS, paclitaxel). A calibration curve for docetaxel was constructed over the range 1-1000 ng/mL. The developed method was specific, precise and accurate, and no matrix effect was observed. The validated method was applied in a comparative pharmacokinetic study in which two docetaxel formulations, SID530, a new parenteral formulation of docetaxel with hydroxypropyl-β-cyclodextrin (HP-β-CD), and Taxotere, were administered to rats at a dose of 5 mg/kg. For SID530 and Taxotere, the mean C(0) values were 1494 and 1818 ng/mL, respectively, and the AUC(last) values were 837 and 755 h ng/mL, respectively. These two formulations did not show any statistical differences with regard to the pharmacokinetic parameters, thus establishing that the SID530 and Taxotere products are pharmacokinetically comparable in male rats.

Rapid quantification of sucrose esters in oriental tobacco by liquid chromatography-ion trap mass spectrometry

A rapid and sensitive LC-MS/MS method was developed for the quantitative determination of sucrose esters (SEs) in Oriental tobacco samples. The sample preparation involved a 10-min sonication extraction procedure with acetone and five-fold dilution of the extract with methanol. The experiment was carried out in positive ion mode by ESI IT mass spectrometer. Because of lack of authentic standards of SEs, sucrose octa-acetate (internal standard, IS) was used as a surrogate to validate the proposed method. Matrix-matched standard calibration was used for quantification of IS in the spiked samples. Under optimized MS/MS conditions, an LOQ of 3.9 microg/g was achieved for IS, with an LOD of about 1.2 microg/g. Recoveries for IS were 95-97%. Among 19 monitored SEs, the contents of 11 SEs had RSDs lower than 13.7%. The method, with very little sample handling and good sensitivity, was applied to the rapid quantification of SEs in four Oriental tobacco samples. It appears that the sum of contents of the five SEs with MW 650, 664, and 678 Da occupied approximately 80% of the total content of SEs.

Development of a piezoelectric immunosensor for the measurement of paclitaxel

This paper describes the development of a piezoelectric immunosensor for the measurement of paclitaxel (taxol), a natural anti-cancer agent. An antibody specific for taxanes was immobilized onto the surface of quartz crystals by means of the layer-by-layer self-assembly technique. The immobilization was achieved using electrostatic interactions between a precursor layer and the antibody molecules. The assembly process was monitored by a quartz crystal microbalance (QCM) and the topography of the modified quartz crystals was investigated by means of atomic force microscopy. The specific interaction of the immobilized antibody with paclitaxel in solution at different concentrations was monitored as a change in resonant frequency of the modified crystal. Moreover, the influence of non-specific adsorption was also characterized. The results show that the proposed immunosensor offers a promising alternative to classical analytical methods for a fast and easy determination of paclitaxel.