Ultrafast liquid chromatography-tandem mass spectrometry determination of donepezil in human plasma: application to a bioequivalence study

A liquid chromatography equipped with tandem mass spectrometric method using multi-stage flow rates was developed for the determination of donepezil in human plasma to support a randomized, crossover bioequivalence (BE) study in which healthy volunteers each received a single oral dose of the reference and test formulations of 10 mg donepezil hydrochloride. This integrated liquid chromatography with tandem mass spectrometry (LC-MS/MS) system with electrospray ionization and a deuterium-labeled internal standard (IS) were employed for the positive multiple-reaction-monitoring (MRM) analyses. The baseline separation using a high-resolution monolithic column under gradient and flexible flowrate conditions between donepezil and multiple interfering peaks from the extracted quality control, calibration standard and study plasma samples following simple protein precipitation extraction procedures was accomplished within 1.5 minutes. The ultrafast monolithic column performance in terms of chromatographic separation efficiency, peak asymmetry and resolution and retention time reproducibility was found to be sustainable. The linear dynamic range was detected over a concentration range of 0.2–50 ng/mL. The intra- and inter-day assay accuracy and precision were within 15% for the analyte in individual biological fluids. A positive correlation coefficient (r) greater than 0.995 for donepezil concentrations in study plasma samplers measured by the proposed and the other validated LC-MS/MS methods in support of a bioequivalence study was observed.

Himbacine-derived thrombin receptor antagonists: c7-spirocyclic analogues of vorapaxar

We have synthesized several C7-spirocyclic analogues of vorapaxar and evaluated their in vitro activities against PAR-1 receptor. Some of these analogues showed activities and rat plasma levels comparable to vorapaxar. Compound 5c from this series showed excellent PAR-1 activity (K i = 5.1 nM). We also present a model of these spirocyclic compounds docked to the PAR-1 receptor based on the X-ray crystal structure of vorapaxar bound to PAR-1 receptor. This model explains some of the structure-activity relationships in this series.

Himbacine-derived thrombin receptor antagonists: c7-aminomethyl and c9a-hydroxy analogues of vorapaxar

We have synthesized several C7-aminomethyl analogues of vorapaxar that are potent PAR-1 antagonists. Many of these analogues showed excellent in vitro binding affinity and pharmacokinetics profile in rats. Compound 6a from this series showed excellent PAR-1 activity (K i = 5 nM). We have also synthesized a C9a-hydroxy analogue of vorapaxar, which showed very good PAR-1 affinity (K i = 19.5 nM) along with excellent rat pharmacokinetic profile and ex vivo efficacy in the cynomolgus monkey.

Discovery of SCH 900271, a Potent Nicotinic Acid Receptor Agonist for the Treatment of Dyslipidemia

Structure-guided optimization of a series of C-5 alkyl substituents led to the discovery of a potent nicotinic acid receptor agonist SCH 900271 (33) with an EC50 of 2 nM in the hu-GPR109a assay. Compound 33 demonstrated good oral bioavailability in all species. Compound 33 exhibited dose-dependent inhibition of plasma free fatty acid (FFA) with 50% FFA reduction at 1.0 mg/kg in fasted male beagle dogs. Compound 33 had no overt signs of flushing at doses up to 10 mg/kg with an improved therapeutic window to flushing as compared to nicotinic acid. Compound 33 was evaluated in human clinical trials.

Targeting the replication checkpoint using SCH 900776, a potent and functionally selective CHK1 inhibitor identified via high content screening

Checkpoint kinase 1 (CHK1) is an essential serine/threonine kinase that responds to DNA damage and stalled DNA replication. CHK1 is essential for maintenance of replication fork viability during exposure to DNA antimetabolites. In human tumor cell lines, ablation of CHK1 function during antimetabolite exposure led to accumulation of double-strand DNA breaks and cell death. Here, we extend these observations and confirm ablation of CHK2 does not contribute to these phenotypes and may diminish them. Furthermore, concomitant suppression of cyclin-dependent kinase (CDK) activity is sufficient to completely antagonize the desired CHK1 ablation phenotypes. These mechanism-based observations prompted the development of a high-content, cell-based screen for γ-H2AX induction, a surrogate marker for double-strand DNA breaks. This mechanism-based functional approach was used to optimize small molecule inhibitors of CHK1. Specifically, the assay was used to mechanistically define the optimal in-cell profile with compounds exhibiting varying degrees of CHK1, CHK2, and CDK selectivity. Using this approach, SCH 900776 was identified as a highly potent and functionally optimal CHK1 inhibitor with minimal intrinsic antagonistic properties. SCH 900776 exposure phenocopies short interfering RNA-mediated CHK1 ablation and interacts synergistically with DNA antimetabolite agents in vitro and in vivo to selectively induce dsDNA breaks and cell death in tumor cell backgrounds.

Discovery of a potent nicotinic Acid receptor agonist for the treatment of dyslipidemia

Nicotinic acid has been used clinically for decades to control serum lipoproteins. Nicotinic acid lowers very low-density lipoprotein (VLDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, and lipoprotein-a (LPa), and it is also effective in raising high-density lipoprotein (HDL)-cholesterol. However, nicotinic acid has several side effects in clinical use. The most notable is intense cutaneous vasodilation "flushing" on the upper body and face. We discovered a pyranopyrimidinedione series to be nicotinic acid receptor agonists. A potent nicotinic acid receptor agonist from this series {5-(3-cyclopropylpropyl)-2-(difluoromethyl)-3H-pyrano[2,3-d]pyrimidine-4,7-dione}with reduced flushing side effect in dogs was identified.

Role of matrix metalloproteinase-8 in the modulation of systemic 5-fluorouracil pharmacokinetics by local irradiation

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Background: Concurrent chemoradiation with 5-fluorouracil (5-FU) is widely accepted for cancer treatment. However, the interactions between radiation and 5-FU remain unclear. We evaluated the influence of local irradiation on the pharmacokinetics of 5-FU in rats.

Methods: The single-fraction radiation was delivered to the whole pelvic fields of Sprague-Dawley rats from a linear accelerator after computerized tomography-based planning. 5-FU at 100 mg/kg was intravenously infused 24 hours after radiation. A high-performance liquid chromatography system equipped with a UV detector was used to measure 5-FU in the blood. Matrix metalloproteinase-8 (MMP-8) inhibitor I was administered to the rats to examine whether or not RT modulation of 5-FU pharmacokinetic parameters could be blocked.

Results: Compared with sham-irradiated controls, whole pelvic irradiation reduced the area under the concentration versus time curve (AUC) of 5-FU in plasma and, in contrast, increased the AUC in bile in a radiation dose-dependent manner. Based on protein array analysis, the amount of plasma MMP-8 was increased by whole pelvic irradiation (2.8-fold by 0.5 Gy and 5.3-fold by 2 Gy) in comparison with controls. Pretreatment with MMP-8 inhibitor reversed the effect of irradiation on AUC of 5-FU in plasma.

Conclusions: Local irradiation may modulate the systemic pharmacokinetics of 5-FU through stimulating the release of MMP-8. This unexpected influence is worthy of further investigation and for consideration in clinical practice of radiotherapy for cancer.

No significant financial relationships to disclose.

Hydrophilic interaction liquid chromatography-tandem mass spectrometry for drug development

Hydrophilic interaction chromatography (HILIC) offers a difference in selectivity as compared to traditional normal phase and reversed-phase liquid chromatography and therefore has great potential for the separation of a variety of pharmaceuticals. This review is devoted to summarizing HILIC coupled to tandem mass spectrometric (MS/MS) methods for the rapid, sensitive and accurate determinations of small molecules employed for supporting drug discovery. The perspectives and challenges on performing HILIC-MS/MS assays are also presented.

Mapping pharmaceuticals in rat brain sections using MALDI imaging mass spectrometry

Matrix-assisted laser desorption/ionization-tandem mass spectrometric method (MALDI-MS/MS) has proven to be a reliable tool for direct measurement of the disposition of small molecules in animal tissue sections. As example, MALDI-MS/MS imaging system was employed for visualizing the spatial distribution of astemizole and its primary metabolite in rat brain tissues. Astemizole is a second-generation antihistamine, a block peripheral H1 receptor, which was introduced to provide comparable therapeutic benefit but was withdrawn in most countries due to toxicity risks. Astemizole was observed to be heterogeneously distributed to most parts of brain tissue slices including cortex, hippocampus, hypothalamic, thalamus, and ventricle regions while its major metabolite, desmethylastemizole, was only found around ventricle sites. We have shown that astemizole alone is likely to be responsible for the central nervous system (CNS) side effects when its exposures became elevated.

Continuous and intermittent dosing of lonafarnib potentiates the therapeutic efficacy of docetaxel on preclinical human prostate cancer models

Lonafarnib is a potent, selective farnesyltransferase inhibitor (FTI) undergoing clinical studies for the treatment of solid tumors and hematological malignancies. Preclinically, a number of FTIs, including lonafarnib, interact with taxanes to inhibit cancer cell growth in an additive/synergistic manner. These observations provided rationale for investigating the effects of combining lonafarnib and docetaxel on preclinical prostate cancer models. To date, docetaxel is the only chemotherapeutic agent in clinical use for hormone-refractory prostate cancer. In vitro experiments with 22Rv1, LNCaP, DU-145, PC3 and PC3-M prostate cancer cell lines showed significantly enhanced inhibition of cell proliferation and apoptosis when lonafarnib was added to docetaxel. In human tumor xenograft models, continuous coadministration of lonafarnib with docetaxel caused marked tumor regressions (24-47%) in tumors from all of the cell types as well as parental CWR22 xenografts. Intermittent dosing of lonafarnib (5 days on then 5 days off) coadministered with docetaxel produced similar regressions in hormone-refractory 22Rv1 tumors. 22Rv1 tumors progressing on docetaxel treatment also responded to treatment with intermittent lonafarnib (5 days on then 5 days off). Moreover, animals did not exhibit any signs of toxicity during coadministration of lonafarnib and docetaxel. In conclusion, coadministration of continuous and intermittent lonafarnib enhanced the antitumor activity of docetaxel in a panel of prostate cancer models. An intermittent dosing schedule of lonafarnib coadministered with docetaxel may allow enhanced efficacy to that of continuous dosing by improving the tolerability of higher doses of lonafarnib.

Ultra-performance hydrophilic interaction liquid chromatography/tandem mass spectrometry for the determination of everolimus in mouse plasma

Ultra-performance hydrophilic interaction liquid chromatography (UPHILIC) interfaced with the electrospray ionization (ESI) source of a tandem mass spectrometer (MS/MS) was developed for the simultaneous determination of everolimus in mouse plasma samples. UPHILIC was performed on a sub-2 microm bare silica particle packing with the column pressure under traditional high-performance liquid chromatography (HPLC) to allow fast separation of pharmaceutical compounds within a chromatographic analysis time of 1 min. This UPHILIC technology is comparable with reversed-phase ultra-performance liquid chromatography (RPUPLC) in terms of chromatographic efficiency but demands neither expensive ultra-high-pressure instrumentation nor new laboratory protocols. With the ESI source, multiple reaction monitoring (MRM) of the ammoniated adduct ions of the analyte was used for tandem mass spectrometric detection. The retention mechanism profiles of the test compounds under HILIC conditions were explored. The influences of experimental factors such as the compositions of mobile phases on the chromatographic performance and the ionization efficiency of the test compounds in positive ion mode were investigated. A UPHILIC/MS/MS approach following a protein precipitation procedure was applied for the quantitative determination of everolimus at the low ng/mL region in support of a pharmacodynamic study. The analytical results obtained by the UPHILIC/MS/MS approach were fond to be in good agreement with those obtained by the RPUPLC/MS/MS method in terms of assay sample throughput, sensitivity and accuracy.

Hydrophilic interaction liquid chromatography/tandem mass spectrometry for the simultaneous determination of dasatinib, imatinib and nilotinib in mouse plasma

Hydrophilic interaction liquid chromatography (HILIC) interfaced with atmospheric pressure ionization (API) sources and a tandem mass spectrometer (MS/MS) was developed for the simultaneous determination of dasatinib, imatinib and nilotinib in mouse plasma samples. The retention profiles of all analytes on several silica stationary phases under HILIC conditions were explored. The influences of experimental factors such as the compositions of mobile phases on the chromatographic performance and the ionization efficiency of all analytes in positive ion mode were investigated. The applicability of the proposed HILIC/MS/MS approach following a protein precipitation procedure for the quantitative determination of dasatinib, imatinib and nilotinib at low nano-mole levels was examined with respect to assay specificity and linearity. The analytical results obtained by various HILIC/MS/MS approaches were found to be in good agreement with those obtained by reversed-phase liquid chromatography/tandem mass spectrometry (RPLC/MS/MS) methods in terms of assay sample throughputs, sensitivity and accuracy. Furthermore, the potential of matrix ionization suppression on the proposed HILIC/MS/MS systems was investigated using the post-column infusion technique.

Visualization of first-pass drug metabolism of terfenadine by MALDI-imaging mass spectrometry

The aim of this article is to focus on the implementation and the application of matrix-assisted laser desorption/ionization-imaging mass spectrometric system (MALDI-IMS) to determine the disposition or biotransformation pathway of terfenadine and its active metabolite, fexofenadine in mouse and rat whole-body tissue sections. Whole-body MALDI-IMS data showed that the poor oral bioavailability of terfenadine was largely due to high first-pass metabolism in the intestines and the liver before the compound reached systemic circulation.

Heterotricyclic himbacine analogs as potent, orally active thrombin receptor (protease activated receptor-1) antagonists

Pursuing our earlier efforts in the himbacine-based thrombin receptor antagonist area, we have synthesized a series of compounds that incorporate heteroatoms in the C-ring of the tricyclic motif. This effort has resulted in the identification of several potent heterocyclic analogs with excellent affinity for the thrombin receptor. Several of these compounds demonstrated robust inhibition of platelet aggregation in an ex vivo model in cynomolgus monkeys following oral administration. A detailed profile of 28b, a benchmark compound in this series, with a Ki of 4.3 nM, is presented.

Fused-Core Silica Column High-Performance Liquid Chromatography/Tandem Mass Spectrometric Determination of Rimonabant in Mouse Plasma

A high-performance liquid chromatography (HPLC) method using a fused-core silica particle packing was evaluated to allow fast and efficient separation for the analysis of pharmaceutical compounds. Fused-core particles are produced by "fusing" a porous silica layer onto a solid silica particle. The efficiencies of columns packed with 2.7 microm "fused-core" particles (a 0.5 microm porous shell fused to a solid 1.7 microm silica core particle) and 1.7 microm porous particles were compared in reversed-phase HPLC using rimonabant as an analyte. The fused-core silica materials providing the shorter diffusional mass transfer path for solutes are less affected in resolving power by increases in mobile-phase velocity than the sub-2 microm porous silica packings resulting in faster separations and higher sample throughput. This fast HPLC technology is comparable with ultrahigh-pressure liquid chromatography (UHPLC) in terms of chromatographic performance but demands neither expensive ultra-high-pressure instrumentation nor new laboratory protocols. The column effluent was directly connected to the atmospheric pressure chemical ionization (APCI) source prior to tandem mass spectrometric detection. In this work, the described fast HPLC-MS/MS and UHPLC-MS/MS approaches requiring approximately 1.5 min per sample were applied and compared for the determination of the rimonabant in mouse plasma samples at the low nanograms per milliliter region in support of a pharmacodynamic study.

Himbacine derived thrombin receptor (PAR-1) antagonists: SAR of the pyridine ring

The structure-activity relationship (SAR) of the vinyl pyridine region of himbacine derived thrombin receptor (PAR-1) antagonists is described. A 2-vinylpyridyl ring substituted with an aryl or a heteroaryl group at the 5-position showed the best overall PAR-1 affinity and pharmacokinetic properties. One of the newly discovered analogs bearing a 5-(3-pyridyl) substituent showed excellent PAR-1 affinity (Ki = 22 nM) and oral activity with reduced ClogP and improved off-target selectivity compared to an earlier development candidate.

A mixed-mode liquid chromatography-tandem mass spectrometric method for the determination of cytarabine in mouse plasma

A novel mixed-mode high performance liquid chromatographic system (HPLC) interfaced with an atmospheric pressure chemical ionization (APCI) source and a tandem mass spectrometer (MS/MS) was developed for the determination of cytarabine (ara-C) in mouse plasma to support pharmacodynamic studies. The mixed-mode reversed-phase ion-exchange chromatography column was adapted for sufficient retention and separation of a small and polar analyte. The impact of the mobile phase composition on both chromatographic separation and the ionization efficiency of the test compound in the positive mode was investigated. The potential of ionization suppression from endogenous biological matrices on the mixed-mode LC-APCI/MS/MS method was evaluated using the post-column infusion technique. Furthermore, the feasibility of using the mixed-mode HPLC-MS/MS method for the determination of the plasma concentrations of cytarabine in mice was demonstrated by comparing those obtained by the ion-pairing HPLC-MS/MS method.

Ultra-performance liquid chromatography/tandem mass spectrometric determination of diastereomers of SCH 503034 in monkey plasma

This paper describes the development and qualification of a fast, sensitive and specific ultra-performance liquid chromatography/tandem mass spectrometric (UPLC/MS/MS) method for the determination of diastereomers of SCH 503034 in monkey plasma. The analytical method involves direct protein precipitation with a mixture of methanol/acetonitrile (10/90) containing an internal standard, followed by separation of the stereoisomers on an Acquity UPLC C(18) column and detected by selected reaction monitoring (SRM) in positive ionization mode using atmospheric pressure chemical ionization (APCI). The effects of ion-pairing agents on separation and ionization efficiency were investigated. The two diastereomers were well separated (R=1.3) with a runtime of 5 min under an isocratic condition. The method was qualified. The linear concentration range was 1-2500 ng/ml for the both stereoisomers. Inter-assay mean bias and relative standard deviation (R.S.D.) were in the range of -1.2% to 3.6% and 2.8-10%, respectively. Intra-assay mean bias and R.S.D. were in the range of -1.3% to 5.5% and 2.3-7.8%, respectively. Recoveries of the stereoisomers at concentration levels of 2.5, 50 and 1000 ng/ml were 87.2-90.0%, 89.1-90.4% and 92.3-94.3%, respectively. The LLOQ for this assay was 1 ng/ml. No matrix interferences were observed in six different sources of blank monkey plasma.

Supercritical Fluid Chromatography and High-Performance Liquid Chromatography/Tandem Mass Spectrometric Methods for the Determination of Cytarabine in Mouse Plasma

The separation of cytarabine (ara-C) from the endogenous compounds in mouse plasma by packed-column supercritical fluid chromatography (pSFC) was achieved on bare silica stationary phase with an isocratic mobile phase composed of CO2/methanol solvent with addition of ammonium acetate. SFC is commonly assumed to be only applicable to nonpolar and relatively low-polarity compounds. In this work, a broader range of compound polarities amenable to pSFC with appropriate mobile-phase modifiers and additives under normal-phase retention mechanism was demonstrated. The pSFC was integrated with an atmospheric pressure chemical ionization source and a tandem mass spectrometer (MS/MS) to enhance the sensitivity, selectivity, and speed of the assay. The influence of mobile-phase components on chromatographic performance and ionization efficiency of the test compounds was investigated for improving the sensitivity and separation for the analyte and the internal standard. The pSFC-MS/MS approach requiring approximately 2.5 min/sample for the determination of ara-C at nanograms per milliliter in mouse plasma was partially validated with respect to stability, linearity, and reproducibility. The mouse plasma levels of ara-C obtained by the pSFC-MS/MS method were found to be consistent with those determined by various reversed-phase, high-performance liquid chromatography methods using a porous graphite carbon column, a mixed-mode column, or a C18 column in conjunction with an ion-pairing agent coupled to a tandem mass spectrometer.