Publications by authors named "Martijn Hilhorst"

8 Publications

  • Page 1 of 1

Method transfer: a CRO perspective.

Bioanalysis 2017 Aug 1;9(15):1131-1134. Epub 2017 Aug 1.

PRA Health Sciences Bioanalytical Laboratory, Amerikaweg 18, Assen, The Netherlands.

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http://dx.doi.org/10.4155/bio-2017-0078DOI Listing
August 2017

Stabilization of clinical samples collected for quantitative bioanalysis--a reflection from the European Bioanalysis Forum.

Bioanalysis 2015 ;7(3):333-43

Bioanalytical Laboratory, PRA Health Sciences, Westerbrink 3, 9405 BJ Assen, The Netherlands.

In bioanalysis of small molecules, the analyte concentration in the measured samples should reflect the concentration during sample collection. Precautions may be needed to prevent over- or under-estimation of the obtained result. This might require the addition of stabilizers to prevent degradation or nonspecific binding. For unstable drugs, it is essential to know how analytes can be stabilized before the start of the clinical study. Although the stabilization methods are well documented, the impact of the stabilization on the clinical workflow is not properly addressed. Already during method development, the clinical implications in terms of personnel safety, ease of use, training possibilities and staff capacity should be taken into account, and validation of the bioanalytical method should reflect collection procedures.
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http://dx.doi.org/10.4155/bio.14.290DOI Listing
November 2015

Sense and nonsense of miniaturized LC-MS/MS for bioanalysis.

Bioanalysis 2014 ;6(24):3263-5

PRA Health Sciences, Westerbrink, The Netherlands.

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http://dx.doi.org/10.4155/bio.14.263DOI Listing
August 2015

Pharmacodynamics, pharmacokinetics, safety, and tolerability of encenicline, a selective α7 nicotinic receptor partial agonist, in single ascending-dose and bioavailability studies.

Clin Ther 2015 Feb 14;37(2):311-24. Epub 2014 Oct 14.

Forum Pharmaceuticals, Boston, Massachusetts. Electronic address:

Purpose: Encenicline (EVP-6124) is a selective α7 nicotinic acetylcholine receptor partial agonist being developed for cognitive impairment in Alzheimer's disease and schizophrenia. We report on 2 single-dose studies to assess the relative bioavailability, pharmacokinetic profile, tolerability, and cognitive effects of encenicline in healthy volunteers.

Methods: A single ascending-dose study assessed the safety, tolerability, pharmacokinetic, and pharmacodynamic profiles of encenicline in healthy male volunteers. Subjects received a single 1-, 3.5-, 7-, 20-, 60-, or 180-mg oral solution dose of encenicline or placebo. A second single-dose, randomized, open-label, 3-period, crossover study in healthy male and female subjects compared the relative bioavailability of a 1-mg oral capsule versus a 1-mg oral solution dose of encenicline and evaluated the effects of food and sex on encenicline pharmacokinetic profile.

Findings: In the first study, encenicline was well tolerated and dose-proportional increases in C(max) (mean range 0.59-100 ng/mL) and AUC0-∞ (mean range 45.6-8890 ng·h/mL) were observed over a 1- to 180-mg dose range. Procognitive effects on the Digit Symbol Substitution Test were maximal at the 20-mg dose. In the second study, encenicline 1-mg oral capsules and oral solution were bioequivalent and there was no observed food effect on encenicline pharmacokinetic profile with the 90% confidence intervals of the treatment ratios for both comparisons (ie, capsule to solution and fed to fasted) for Cmax and AUC being within 80% to 125%. A 30% to 40% higher encenicline exposure in female subjects than respective values in male subjects was consistent with a 33% higher weight of the male subjects. No clinically relevant safety profile or tolerability effects of encenicline were observed.

Implications: Encenicline was well tolerated at single doses up to 180 mg, and doses as low as 1 mg had dose- and time-dependent pharmacodynamic effects on the central nervous system. Oral capsule and solution were bioequivalent and were not affected by food. Although a sex effect on pharmacokinetic profile was observed, it was attributable to weight differences. Clinical Trial Registration at EudraCT: 2006-005623-42 and EudracT: 2008-000029-20.
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http://dx.doi.org/10.1016/j.clinthera.2014.09.013DOI Listing
February 2015

HPLC-MS/MS method for the determination of cytarabine in human plasma.

Bioanalysis 2011 Jul;3(14):1603-11

PRA International Early Development Services, Assen, The Netherlands.

Background: Cytarabine is an anti-tumor drug that is currently under investigation for treatment in combination with other anticancer drugs for the chemotherapy of leukemia. The quantitative determination of cytarabine in plasma is challenging due to the required sensitivity, its in vitro instability and the presence of an isobaric endogenous compound, cytidine. Owing to the polarity of cytarabine, conventional chromatography cannot provide adequate separation of the analyte and the interfering compounds. A few analytical methods have been reported for the determination of cytarabine in plasma, but their sensitivity was not sufficient since most of these methods apply spectrophotometric detection.

Results: In this article, an LC-MS/MS method is described for the determination of cytarabine in human plasma down to the sub ng/ml level. To prevent conversion of cytarabine by cytidine deaminase, whole blood samples were stabilized with tetrahydrouridine directly after the collection of whole blood at the clinical site. Cation-exchange SPE was employed to extract cytarabine from 50 µl human plasma. UHPLC on high strength silica T3 column (100 × 2.1 mm × 1.8 µm) was applied to achieve adequate separation of cytarabine from cytidine within a reasonable run time of 5 min. A triple quad mass spectrometer equipped with an ESI source was used for detection.

Conclusion: The method was linear over the concentration ranges of 0.500-500 ng/ml. The intra- and inter-day relative standard deviation (precision) as well as the bias (accuracy) were well below 15%. In the presence of tetrahydrouridine, cytarabine was sufficiently stable under all relevant conditions. The method was successfully applied to support a clinical pharmacokinetic study with a low dose of cytarabine.
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http://dx.doi.org/10.4155/bio.11.140DOI Listing
July 2011

Selective isolation at the femtomole level of phosphopeptides from proteolytic digests using 2D-NanoLC-ESI-MS/MS and titanium oxide precolumns.

Anal Chem 2004 Jul;76(14):3935-43

Department of Biomolecular Mass Spectrometry, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands.

Selective detection of phosphopeptides from proteolytic digests is a challenging and highly relevant task in many proteomics applications. Often phosphopeptides are present in small amounts and need selective isolation or enrichment before identification. Here we report a novel automated method for the enrichment of phosphopeptides from complex mixtures. The method employs a two-dimensional column setup, with titanium oxide-based solid-phase material (Titansphere) as the first dimension and reversed-phase material as the second dimension. Phosphopeptides are separated from nonphosphorylated peptides by trapping them under acidic conditions on a TiO(2) precolumn. Nonphosphorylated peptides break through and are trapped on a reversed-phase precolumn after which they are analyzed by nanoflow LC-ESI-MS/MS. Subsequently, phosphopeptides are desorbed from the TiO(2) column under alkaline conditions, reconcentrated onto the reversed-phase precolumn, and analyzed by nanoflow LC-ESI-MS/MS. The selectivity and practicality of using TiO(2) precolumns for trapping phosphopeptides are demonstrated via the analysis of a model peptide RKISASEF, in a 1:1 mixture of a non- and a monophosphorylated form. A sample of 125 fmol of the phosphorylated peptide could easily be isolated from the nonphosphorylated peptide with a recovery above 90%. In addition, proteolytic digests of three different autophosphorylation forms of the 153-kDa homodimeric cGMP-dependent protein kinase are analyzed. From proteolytic digests of the fully autophosphorylated protein at least eight phosphorylation sites are identified, including two previously uncharacterized sites, namely, Ser-26 and Ser-44. Ser-26 is characterized as a minor phosphorylation site in purified PKG samples, while Ser-44 is identified as a novel in vitro autophosphorylation target. These results clearly show that TiO(2) has strong affinity for phosphorylated peptides, and thus, we conclude that this material has a high potential in the field of phosphoproteomics.
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http://dx.doi.org/10.1021/ac0498617DOI Listing
July 2004