Structure elucidation of three isomeric metabolites of SYN-2836, a novel antifungal agent, in dogs via liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry methodologies

In-vitro metabolic profiling study of potential topoisomerase inhibitors 'pyrazolines' in RLMs by mass spectrometry

Taking into consideration of the cytotoxicity and topo-IIα inhibitory activity of pyrazoline derivatives (1-3) against HCT15 cells, and known topo-IIα inhibitor, etoposide, respectively, the compounds were biotransformed in rat liver microsomes. LC-MS/MS and MALDI mass spectrometric techniques has been used for analysis. All three compounds were biotransformed into demethylated metabolites. Among three compounds, compounds 1 and 2 were biotransformed into mono-hydroxylated metabolites and compound 3 biotransformed into reduced and epoxidized metabolites. Reduced and reduced along with demethylation metabolites were identified from MALDI Orbitrap spectrometric analysis. Without NADPH or microsomes no compounds (1-3) were generated metabolites, it shows CYP450 enzymes involvement in the presence of NADPH in the metabolisms.

In vitro investigation of metabolic profiling of newly developed topoisomerase inhibitors (ethyl fluorescein hydrazones, EtFLHs) in RLMs by LC-MS/MS

Metabolic profiling of newly reported five topoisomerase inhibitors namely ethyl fluorescein hydrazones (EtFLHs) were studied in rat liver microsomes (RLMs) and the data were acquired in a liquid chromatography (LC) ion trap mass spectrometry. Hydroxyl group containing EtFLHs derivatives (1-3) were bio-transformed into hydrolyzed, mono-hydroxylated and hydrolyzed together with mono-hydroxylated metabolites. On the other hand, nitro and methoxy groups containing EtFLHs derivatives (4-5) were bio-transformed into hydrolyzed, hydrolyzed together with mono-hydroxylated and azo-reductive metabolites in the presence of NADPH. No metabolites were observed in the absence of either NADPH or microsomes for the compounds (1-5), indicating a likely involvement of CYP450 enzymes and cofactor NADPH in the metabolisms.

Characterization of imatinib metabolites in rat and human liver microsomes: differentiation of hydroxylation from N-oxidation by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry

In vitro metabolism of imatinib was investigated in rat and human liver microsomes. Atmospheric pressure chemical ionization (APCI) mass spectrometry (MS) was applied in differentiating hydroxyl metabolites from N-oxides of imatinib because N-oxides are known to undergo deoxygenation during APCI. In addition, the major oxidative metabolite (M9, N-oxidation on the piperazine ring) was observed to undergo in-source fragmentation by elimination of formaldehyde. This fragment ion resulted from Meisenheimer rearrangement with migration of the N-methyl group to the corresponding N-methoxyl piperazine, followed by elimination of formaldehyde due to thermal energy activation at the vaporizer of APCI source. The presence of this fragment ion distinguished not only N-oxide from isomeric hydroxylated metabolite, but also unambiguously indicated that oxidation occurred on the N-4 of the piperazine ring where the methyl group was attached.

Even-electron ions: a systematic study of the neutral species lost in the dissociation of quasi-molecular ions

The collision-induced dissociations of the even-electron [M + H](+) and/or [M - H](-) ions of 121 model compounds (mainly small aromatic compounds with one to three functional groups) ionized by electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) have been studied using an ion trap instrument, and the results are compared with the literature data. While some functional groups (such as COOH, COOCH(3), SO(3)H in the negative ion mode, or NO(2) in both the positive and negative ion modes) generally promote the loss of neutrals that are characteristic as well as specific, other functional groups (such as COOH in the positive ion mode) give rise to the loss of neutrals that are characteristic, but not specific. Finally, functional groups such as OH and NH(2) in aromatic compounds do not lead to the loss of a neutral that reflects the presence of these substituents. In general, the dissociation of [M + H](+) and [M - H](-) ions generated from aliphatic compounds or compounds containing an aliphatic moiety obeys the even-electron rule (loss of a molecule), but deviations from this rule (loss of a radical) are sometimes observed for aromatic compounds, in particular for nitroaromatic compounds. Thermochemical data and ab initio calculations at the CBS-QB3 level of theory provide an explanation for these exceptions. When comparing the dissociation behaviour of the even-electron [M + H](+) and/or [M - H](-) ions (generated by ESI or APCI) with that of the corresponding odd-electron [M](+) ions (generated by electron ionization, EI), three cases may be distinguished: (1) the dissociation of the two ionic species differs completely; (2) the dissociation involves the loss of a common neutral, yielding product ions differing in mass by one Da, or (3) the dissociations lead to a common product ion.

Fragmentation study of imatinib and characterization of new imatinib metabolites by liquid chromatography-triple-quadrupole and linear ion trap mass spectrometers

Imatinib (Gleevec) is an anticancer drug that inhibits specific protein kinases involved in cell proliferation. Whereas this drug is considered to have opened a new era, various mechanisms of resistance have been associated with imatinib relapse. Drug disposition in cancer cells including influx, efflux and drug metabolism is one mechanism that remains to be more thoroughly investigated. Moreover, recent genomic studies have revealed that some isozymes of cytochrome P450 (CYP) are possibly associated with the treatment outcome. Therefore, this research paper investigates the role of the activity of CYP1A1, 1A2, 1B1, 3A4, 4F2 and 4F3A/B on the fate of imatinib. First, a study of imatinib fragmentation was effected using electrospray triple-quadrupole and linear ion trap tandem mass spectrometers (MSn). Accurate mass determinations were performed at enhanced mass resolution for the identification of some product ions that were not predicted by two fragmentation softwares. Whereas the quadrupole MS was not designed for accurate mass measurement, delta mass errors were below 20 ppm. Then, a biotransformation study was effected in vitro. Imatinib metabolites were produced in microsomal incubations containing CYP isozymes. Imatinib and metabolites were extracted from incubation mixtures by protein precipitation, and supernatants were injected into a liquid chromatography equipment coupled with MS(n). Hydrophobic interaction liquid chromatography resolved one demethylated-, two hydroxy- and three N-oxide metabolites. Various rates of metabolite formation were observed between CYP isozymes. Liquid chromatography with deuterium oxide-containing mobile phase (H/D exchange) or incorporation of (18)O from H(2) (18)O added in the incubations was performed to elucidate the metabolite structure. Various MS(n) product scans (n < or = 4) were acquired on the linear ion trap or on the triple-quadrupole MS. Postulated structures of new metabolites are addressed.

Prediction of MS/MS data. 1. A focus on pharmaceuticals containing carboxylic acids

Metabolite identification is a necessary step in developing safe and effective drugs. Metabolite analysis typically involves rapid identification of the chemical composition of the metabolite by automated HPLC-MS methods, followed by the laborious process of identifying the structure of the metabolite. Since MS is typically utilized to identify the metabolite, it is logical to utilize MS/MS to structurally characterize the sample. However, interpretation of MS/MS data may not provide sufficient information, as fragmentation pathways are not well understood or predictable. Therefore, other more time-consuming methods of analysis are often undertaken. If the dissociation rules for low-energy MS/MS experiments were clearly defined for all classes of compounds, more information would be obtained from MS/MS data, and metabolite identification would proceed more rapidly. We are currently developing methods to define these fragmentation rules. By screening approximately 100 carboxylic acids at a time and applying knowledge of physical-organic chemistry, predictive rules are under development that describe how compounds dissociate under low-energy collision-induced dissociation conditions. Studies of carboxylic acid dissociation demonstrate that this approach is practical and reliable. Dissociation rules were predicted with a 90% success rate, when tested on acid-containing pharmaceuticals. This predictive power cannot be matched by any commercially available software. This study, and others like it, will be used to develop algorithms that more rapidly identify drug metabolites and degradation products, based on MS/MS data. Such algorithms will benefit drug development for all types of pharmaceuticals.

High-throughput screening for stability and inhibitory activity of compounds toward cytochrome P450-mediated metabolism

With the advent of combinatorial chemistry and high-throughput screening technology, thousands of molecules can now be rapidly synthesized and screened for biological activity against large numbers of protein targets, greatly increasing the speed with which lead compounds are identified during the early stages of drug discovery. However, rapid optimization of parameters that determine whether a high-affinity ligand or a potent inhibitor will become a successful drug remains a challenge in improving the efficiency of the drug discovery process. Parameters that define absorption, distribution, metabolism, and excretion properties of drug candidates are important determinants of therapeutic efficacy, and thus should be optimized during early stages of drug discovery. Although the speed with which drugs are screened for properties such as absorption, cytochrome P450 (CYP) inhibition, and metabolic stability has increased over the past several years, the screening rate/capacity is still several orders of magnitude lower than those for high-throughput methods used in lead identification, resulting in a bottleneck in the drug discovery process. This review discusses current methods used in the in vitro screening of drugs for their stability toward CYP-mediated oxidative metabolism. This is a critical screen in the drug discovery process because metabolism by CYP represents an important clearance mechanism for the vast majority of compounds, thus affecting their oral bioavailability and/or duration of action.

Mass spectrometry innovations in drug discovery and development

This review highlights the many roles mass spectrometry plays in the discovery and development of new therapeutics by both the pharmaceutical and the biotechnology industries. Innovations in mass spectrometer source design, improvements to mass accuracy, and implementation of computer-controlled automation have accelerated the purification and characterization of compounds derived from combinatorial libraries, as well as the throughput of pharmacokinetics studies. The use of accelerator mass spectrometry, chemical reaction interface-mass spectrometry and continuous flow-isotope ratio mass spectrometry are promising alternatives for conducting mass balance studies in man. To meet the technical challenges of proteomics, discovery groups in biotechnology companies have led the way to development of instruments with greater sensitivity and mass accuracy (e.g., MALDI-TOF, ESI-Q-TOF, Ion Trap), the miniaturization of separation techniques and ion sources (e.g., capillary HPLC and nanospray), and the utilization of bioinformatics. Affinity-based methods coupled to mass spectrometry are allowing rapid and selective identification of both synthetic and biological molecules. With decreasing instrument cost and size and increasing reliability, mass spectrometers are penetrating both the manufacturing and the quality control arenas. The next generation of technologies to simplify the investigation of the complex fate of novel pharmaceutical entities in vitro and in vivo will be chip-based approaches coupled with mass spectrometry.

Practical aspects of liquid chromatography/electrospray tandem mass spectrometry for rapid identification of metabolites of a new antifungal agent SYN-2836 in dog urine

This report presents the structural elucidation of 12 urinary metabolites of SYN-2836, a new antifungal agent showing extensive metabolism in beagle dogs, using complementary liquid chromatography/tandem mass spectrometry (LC/MS/MS) methodologies. The 12 SYN-2836 metabolites were readily divided into four groups by considering that all three members of each group, although differing in masses, exhibited highly similar product ion mass spectra. This suggests that the metabolites within each group share a common major substructure. Therefore, all the grouped SYN-2836 metabolites were strategically identified by characterization of the major substructures followed by determination of the additional small substructures. This grouping strategy greatly facilitated the structural elucidation of these metabolites. Other strategies were also employed to achieve as rapid and unambiguous characterization of the SYN-2836 metabolites as possible.

Liquid chromatography-mass spectrometry in the study of the metabolism of drugs and other xenobiotics

The application of liquid chromatography-mass spectrometry (LC/MS) to the study of metabolism of drugs and other xenobiotics is reviewed. Original research papers covering the period from 1998 to early 2000 and concerning the use of LC/MS in the study of xenobiotic metabolism in humans and other mammalian species are reviewed. LC/MS interfaces, sample preparation steps, column types, mobile phases and additives, and the type of metabolites detected are summarized and discussed in an attempt to identify the current and future trends in the use of LC/MS for metabolism studies. Applications are listed according to the parent xenobiotic type and include substances used in therapeutics, drug candidates, compounds being evaluated in clinical trials, environmental pollutants, adulterants and naturally occurring substances.

Interspecies comparison of pharmacokinetics of the novel triazole antifungal agent SYN-2869 and its derivatives

The pharmacokinetics and distribution in tissue of several novel triazole antifungal agents were studied in different animal species in order to select an appropriate lead compound. The purpose of the study was also to determine species differences in pharmacokinetics for SYN azoles to select the most appropriate species for secondary efficacy and toxicological evaluation of the selected compound. SYN-2836, SYN-2869, SYN-2903, and SYN-2921 were rapidly absorbed into the systemic circulation and reached maximum concentrations (C(max)s) of 7.31 +/- 2.53, 6.29 +/- 0.85, 6.16 +/- 0.39, and 3.41 +/- 0.34 microg/ml, respectively, in BALB/c mice after administration of an oral dose of 50 mg/kg of body weight, with bioavailability being greater than 45% in all mice. The areas under the concentration-time curve from time zero to infinity (AUC(0-infinity)s) after administration of a single intravenous dose of 20 mg/kg to mice varied between 25.0 and 63.6 microg. h/ml. The half-life was in the range of 4.5 to 6 h. In Sprague-Dawley rats there was no significant difference in AUC(0-infinity) after administration of a single intravenous dose of 20 mg/kg, but on oral administration, the bioavailability of SYN-2836 was extremely low, while that of SYN-2869 was only 14.7%. In New Zealand White rabbits the C(max) and the time to reach C(max) for SYN-2836 and SYN-2869 after administration of a single oral dose of 50 mg/kg were similar. There were significant differences in AUC(0-infinity) and half-life between SYN-2836 and SYN-2869. On the other hand, in beagle dogs the C(max) and AUC(0-infinity) of SYN-2836 after administration of a single oral dose of 30 mg/kg were 4.82 +/- 1.54 microg/ml and 41.8 +/- 15.7 microg. h/ml, respectively, which were threefold higher than those of SYN-2869. The concentrations of the SYN compounds in tissue indicated that the AUC(0-infinity)s of SYN-2836, SYN-2869, SYN-2903, and SYN-2921 in mouse lungs were significantly different from each other. The ratios of the concentrations of the SYN azoles in lungs to those in plasma were also significantly different from those for itraconazole. Among the SYN azoles the highest concentration in the lungs was found for SYN-2869. The higher level of distribution of SYN-2869 into lung tissue was considered to contribute to the potent efficacy in respiratory tract infection models compared with the potency of itraconazole. Significant differences in the pharmacokinetics of these compounds were observed in different animal species, and selection of an animal model for further evaluation was based on results obtained from these studies.

Novel sample preparation method facilitating identification of urinary drug metabolites by liquid chromatography-tandem mass spectrometry

A simple, efficient procedure was developed for the preparation of urine samples, which greatly facilitated the identification of the urinary metabolites of a new antifungal agent SYN-2836. The urine samples following dilution with acetonitrile (ACN) formed distinct upper (ACN) and lower (aqueous) solution phases. The SYN-2836 metabolites were concentrated in the upper solution except that two glucuronides were concentrated in the lower solution. The upper solutions, containing concentrated metabolites and significantly reduced endogenous polar species, were ideally suitable for the metabolite identification. This novel sample preparation procedure would be applicable in identification of urinary metabolites of other drugs and drug candidates.