Development of a fluorescence immunoassay for measurement of paclitaxel in human plasma

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.

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.

Fluorescence immunoassay using an optical fiber for determination of Dermatophagoides farinae (Der f1)

Immunoassay methods are generally used for measuring of allergenic substances. However, they need special facilities, skilled handling, and time-consuming procedure. In this work, a fiber-optic immunoassay system which could measure allergen by fluorescent intensities of immune complexes formed by allergens and fluorescently labeled antibodies was established. Immune complexes absorbed on the optical fiber probe surface, and excitation light was injected into the probe, then evanescent field is created in the proximity of the probe. The fluorophores were excited by the evanescent light, and fluorescence was detected by a photo diode. The target allergen detected by our system was Der f1 derived from Dermatophagoides farinae that is one of the house dust mite and major source of inhaled allergens. The fluorophore used labeling on detecting antibody was cyanine 5. The system enabled to detect and quantitatively determine of Der f1. The measurement range was from 0.24 to 250 ng/ml, and the result competes with ELISA. The measurement time was 16 min/sample. The immunoassay system was applied to measurement of Der f1 from actual dust samples. Calculated values of Der f1 showed good correlations between the fiber-optic fluoroimmunoassay and ELISA.

Quantitative analysis of nucleic Acid hybridization on magnetic particles and quantum dot-based probes

In the present study we describe sandwich design hybridization probes consisting of magnetic particles (MP) and quantum dots (QD) with target DNA, and their application in the detection of avian influenza virus (H5N1) sequences. Hybridization of 25-, 40-, and 100-mer target DNA with both probes was analyzed and quantified by flow cytometry and fluorescence microscopy on the scale of single particles. The following steps were used in the assay: (i) target selection by MP probes and (ii) target detection by QD probes. Hybridization efficiency between MP conjugated probes and target DNA hybrids was controlled by a fluorescent dye specific for nucleic acids. Fluorescence was detected by flow cytometry to distinguish differences in oligo sequences as short as 25-mer capturing in target DNA and by gel-electrophoresis in the case of QD probes. This report shows that effective manipulation and control of micro- and nanoparticles in hybridization assays is possible.

Single-bead immunoassays using magnetic microparticles and spectral-shifting quantum dots

This paper reports a single-bead immunoassay method based on the combined use of magnetic microparticles (MMPs) for target capturing/enrichment and antibody-conjugated semiconductor quantum dots (QDs) for fluorescence detection. In comparison with organic dyes and fluorescent proteins, QDs exhibit unique optical properties such as size-tunable fluorescence emission (spectral shifting), large absorption coefficients, improved brightness, and superior photostability. Magnetic beads, composed of iron oxide nanoparticles embedded in polymeric matrices, provide a platform for rapid capturing and enrichment of biomolecules and pathogens in dilute biological and environmental samples. However, a major problem in using magnetic beads for fluorescence immunoassays is that the bead's autofluorescence strongly interferes with the target detection signal. This spectral overlapping problem can be overcome by using semiconductor QDs as a new class of spectral-shifting labels. By shifting the QD emission signals away from the bead autofluorescence, it is possible to detect biomolecular antigens such as tumor necrosis factor (TNF-alpha) at femtomolar (10-15 M) concentrations when the target molecules are captured and enriched on the magnetic bead surface. This sensitivity is almost 1000 times higher that that of traditional immunoabsorbent assays and more than 100 times higher than immunofluorescent assays using organic dyes.

Self-aligned immobilization of proteins utilizing PEG patterns

A novel self-aligned method to selectively immobilize proteins on a silicon dioxide surface is developed in conjunction with a standard lift-off patterning technique of a PEG layer. The approach is designed to photolithographically pattern regions that specifically bind target proteins and particles, surrounded by regions that suppress non-specific attachment of bio-species. The physical and biological properties of the derivatized surfaces at the end of the fabrication process are characterized.

Genetically Engineered Elastin-Protein A Fusion as a Universal Platform for Homogeneous, Phase-separation Immunoassay

A simple and universal platform for competitive phase-separation immunoassay is reported based on a fusion protein composed of a temperature-responsive elastin-like polypeptide (ELP) and the antibody-binding staphylococcal protein A (SpA). The basic principle is to take advantage of the ability of SpA to bind a variety of antibodies with high affinity, allowing simple separation of antigen-antibody complex by thermal precipitation. The resulting ELP-SpA fusion was shown to preserve the ability to reversibly precipitate as well as its high affinity toward different IgGs and IgMs. As a model system, a competitive phase-separation immunoassay based on the ELP-SpA format was established for paclitaxel (taxol) with IC(50) (20.18 nM) and the lower detection limit (2.94 nM) very similar to those reported for the ELISA format. Unlike the heterogeneous interaction in ELISA, which decreases the antibody-binding activity, the reported homogeneous immunoassay not only alleviates this problem but also enables the potential for high-throughput automation. We believe that the reported ELP-SpA fusion will find applications not only as a powerful diagnostic tool for diverse analytes but also a potential useful tool for purification and immobilization of antibody.

A tubulin-based fluorescent polarization assay for paclitaxel

This paper reports the development, characterization, and application of a separation-free, homogeneous, and simple to perform fluorescence polarization bioassay for paclitaxel. The bioassay is based on the binding interaction of paclitaxel to tubulin, the receptor protein on which this drug acts. The bioassay was carried out in a competitive format where the paclitaxel and a synthetic fluorescent-labeled paclitaxel (Rh-Tx) competed for tubulin binding, causing a change in fluorescence polarization, which was an inverse function of the paclitaxel concentration. The bioassay had a dynamic range from 0.03 to 0.35 microM, which falls in the therapeutic range (0.01-10 microM), and a limit of detection of 23 nM. The bioassay was selective against other naturally occurring taxanes such as baccatin III and 10-deacetylbaccatin III. However, there was interference from cephalomannine. The excellent sensitivity, accuracy, reproducibility, and simplicity make this analytical technique suitable for routine and high-throughput analyses and might be helpful in providing better care for patients. The bioassay was successfully applied to the determination of paclitaxel in human plasma.

Continuous-flow fluoro-immunosensor for paclitaxel measurement

A fluorescence-based continuous-flow immunosensor for sensitive, precise, accurate and fast determination of paclitaxel was developed. The sensor utilizes anti-paclitaxel antibody immobilized through its Fc region and crosslinked by dimethylpimelimidate to protein A attached covalently onto the silanized inner walls of a glass capillary column followed by saturation of the paclitaxel-binding sites with rhodamine-labeled paclitaxel. The assay is based on the displacement and detection downstream of the rhodamine-labeled paclitaxel, by a flow-through spectrofluorometer, as a result of the competition with paclitaxel introduced as a pulse into the stream of carrier buffer flowing through the system. The peak height of the fluorescence intensity profile of the displaced rhodamine-labeled paclitaxel was directly proportional to the concentration of paclitaxel applied and was a function of the carrier buffer flow rate. The sensitivity of the immunosensor response ranged from 0.31 relative fluorescence units (RFU)/ng/ml at a flow rate 0.1 ml/min to 0.52 RFU/ng/ml at 1 ml/min, while the lower detection limit ranged from 1 ng/ml at 0.1 ml/min to 4 ng/ml at 1 ml/min. The immunosensor response was very reproducible (RSD=4.8%; n=10) and linear up to 100 ng/ml. The assay time ranged from 2 min at 1 ml/min to 8 min at 0.1 ml/min. A technique developed to resaturate the antigen binding sites of the immobilized antibody with rhodamine-labeled paclitaxel was successful in regenerating the capillary column without affecting its performance, thus enhancing the economic viability of the immunosensor. The immunosensor was successfully applied for the determination of paclitaxel in human plasma.