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.

2-µm fused-core column ultra-high-performance liquid chromatography/tandem mass spectrometric determination of donepezil in human plasma: Application to a bioequivalence study.

Ultra-high-performance liquid chromatography (UHPLC) hyphenated to tandem mass spectrometric methods using the dimethylpentafluorophenylpropyl stationary phase with polar and nonpolar characteristics of a 2-µm fused-core silica particle packing were evaluated to perform efficient separation for the analysis of donepezil in human plasma. The fused-core silica particle design providing the shorter diffusional mass transfer path for the analytes is less affected in resolving power by increasing mobile-phase velocity for faster chromatographic resolution between the administered compound and multiple interfering peaks from the extracted quality control, calibration standard and study samples following simple protein precipitation extraction procedures. In this work, two UHPLC-MS/MS approaches requiring 1.2 min per sample run time and neither expensive ultra-high-pressure instrumentation nor new laboratory protocols were applied and compared for determination of donepezil in human plasma at sub-nanograms per milliliter region to support a randomized, crossover bioequivalence (BE) study in which healthy volunteers each received a single oral dose of the test and reference formulations of 10 mg donepezil hydrochloride. The column performance in terms of chromatographic separation efficiency, peak asymmetry and resolution and retention time reproducibility was found to be sustainable over a thousand extracted plasma injections. 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. Positive correlation coefficients (r) greater than 0.98 and 0.99 for donepezil concentrations in study plasma samplers measured by the proposed UHPLC-MS/MS approaches and another validated HPLC-MS/MS method were observed.

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.

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.

Discovery of nor-seco himbacine analogs as thrombin receptor antagonists.

Discovery of a novel nor-seco himbacine analog as potent thrombin receptor (PAR-1) antagonist is described. Despite low plasma level, these new analogs showed excellent ex vivo efficacy in the monkey platelet aggregation assay. A potent hydroxy metabolite generated in vivo was identified as the agent responsible for the ex vivo efficacy. Following this discovery, the metabolite series was optimized to obtain analogs that showed very good ex vivo efficacy along with excellent pharmacokinetic profile in c. 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.

Discovery of a vorapaxar analog with increased aqueous solubility.

An analog of the thrombin receptor antagonist vorapaxar (SCH 530348) with increased aqueous solubility, compound 9c (SCH 602539), was discovered through incorporation of polar substituents on the pyridine ring of the himbacine-derived lead series. This analog retained the excellent potency, pharmacokinetic and safety properties of vorapaxar while increasing the aqueous solubility by 20-fold. Also presented are in vivo evaluations of this compound in a cynomolgus monkey platelet aggregation assay and in a Folts model of thrombosis in anesthetized monkeys.

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.

Chrysanthemum morifolium Ramat. reduces the oxidized LDL-induced expression of intercellular adhesion molecule-1 and E-selectin in human umbilical vein endothelial cells.

ETHNOPHARMACOLOGICAL RELEVANCE: The flower of Chrysanthemum morifolium Ramat. (CM) with antioxidant, cardiovascular protective and anti-inflammatory functions, has been widely used in China for hundreds of years as a healthy beverage and medicine. AIMS OF THE STUDY: The purpose of the present study is to investigate the effects of HCM (a hot water extract of the flower of Chrysanthemum morifolium Ramat. [CM]), ECM (an ethanol extract of CM), and the abundant flavonoids apigenin and luteolin in CM on the oxidized LDL (oxLDL)-induced expression of ICAM-1 and E-selectin in human umbilical vein endothelial cells (HUVECs). The possible mechanism of these effects was also determined. MATERIALS AND METHODS: MTT assay was for cell viability. Western blot was used for ICAM-1 and E-selection protein expression, and for activation of protein kinase B (PKB) and cAMP responsive element binding protein (CREB) proteins. Fluorescence flow cytometry was for ICAM-1 and E-selectin expression on cell surface. DCF-DA flow cytometric assay was used for reactive oxygen species (ROS) production. RESULTS: HCM, ECM, apigenin, and luteolin dose-dependently inhibited ICAM-1 and E-selectin expression and adhesion of HL-60 by oxLDL. HCM, ECM, apigenin, and luteolin reversed the inhibition of phosphorylation of Akt and CREB by oxLDL; however, this reversion was abolished by wortmannin. In addition, wortmannin abrogated the inhibitory effects of CM extracts, apigenin and luteolin on adhesion molecule expression. The ROS scavenging capability of HCM, ECM, apigenin, and luteolin proceeded dose-dependently in the presence of oxLDL. CONCLUSION: CM is a plant with cardiovascular-protective potential and the inhibitory effects of CM on ICAM-1 and E-selectin expression are, at least partially, attributed to its antioxidant activity and modulation of the PI3K/Akt signaling pathway.

The role of exploratory drug metabolism and pharmacokinetics in new drug research: case study-selection of a thrombin receptor antagonist for development.

The rising costs and time associated with bringing new medicines to the market have created a need for a new paradigm for reducing the attrition rates of drug candidates in both preclinical and clinical development stages. Early appraisal of drug metabolism and pharmacokinetic (DMPK) parameters is now possible due to several higher throughput in vitro and in vivo screens. This knowledge of DMPK properties should not only shorten the timelines for the selection of drug candidates but also enhance the probability of their success for development. The role of DMPK researchers in the drug research paradigm should not be limited to screening a large array of compounds during the lead optimization process but should include a strive for an understanding of the absorption, distribution, metabolism, excretion, and potential drug-related toxicities of a chemical series. As an example, in this article we present a specific DMPK research screening paradigm and describe a case study using the Thrombin Receptor Antagonist program. This screening paradigm followed by the extensive lead optimization process culminated in the selection of SCH 530348, a potent, selective and orally active thrombin receptor antagonist for the treatment of thrombosis.

The role of hyphenated chromatography-mass spectrometry techniques in exploratory drug metabolism and pharmacokinetics.

The advances in high-speed synthesis technologies have produced a large number of biologically active new chemical entities (NCEs) for developability assessment. Current drug discovery efforts have been focused on identifying drug metabolism and pharmacokinetic (DMPK) issues at the earliest possible stage in order to reduce the attrition rate of drug candidates during the development phase. Mass spectrometry (MS) has proven a powerful tool in providing rapid qualitative and quantitative measurements of drug molecules for DMPK studies in both drug discovery and development. Although mass spectrometers can serve as separation devices, for most pharmaceutical applications, some form of chromatography is combined with MS. For most MS-based methods, tandem mass spectrometry (MS/MS) utilizes atmospheric pressure ionization (API) and chromatographic techniques. This review describes the major hyphenated chromatography-mass spectrometry techniques and their applications in supporting exploratory DMPK studies including various in vitro and in vivo PK and metabolite identification profiles.

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.

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.

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.