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Current
Drug Metabolism
ISSN: 1389-2002
Current Drug Metabolism
Volume 7, Number 5, June 2006
Contents
Use of Mass Spectrometry for Drug Metabolism Studies
Guest Editor: Walter A. Korfmacher
Editorial: Pp. 455
Utility of Mass Spectrometry for Pharmaceutical Profiling
Applications Pp. 457-466
E.H. Kerns and L. Di
[Abstract]
Utility of Mass Spectrometry for In-Vitro
ADME Assays Pp. 467-477
I. Chu and A.A. Nomeir
[Abstract]
Increasing Speed and Throughput When Using HPLC-MS/MS Systems
for Drug Metabolism and Pharmacokinetic Screening Pp.
479-489
Y. Hsieh and W.A. Korfmacher
[Abstract]
LC-MS Development Strategies for Quantitative
Bioanalysis Pp. 491-502
M. Jemal and Y.-Q. Xia
[Abstract]
Application of Mass Spectrometry for Metabolite
Identification Pp. 503-523
S. Ma, S.K. Chowdhury and K.B. Alton
[Abstract]
The Role of Mass Spectrometry in Biomarker Discovery
and Measurement Pp. 525-539
B.L. Ackermann, J.E. Hale and K.L. Duffin
[Abstract]
The Use of Qtrap Technology in Drug Metabolism Pp.
541-545
R. King and C. Fernandez-Metzler
[Abstract]
Utility of the Hybrid LTQ-FTMS for Drug Metabolism
Applications Pp. 547-555
M. Sanders, P.A. Shipkova, H. Zhang and B.M. Warrack
[Abstract]
Use of Nano-Electrospray for Metabolite Identification
and Quantitative Absorption, Distribution, Metabolism and
Excretion Studies Pp. 557-563
C.E.C.A. Hop
[Abstract]
Abstracts
[Back to top]
Editorial
The impetus for this special edition stems from the realization
that mass spectrometry is now an indispensable tool that is
needed for all the phases of new drug discovery and development.
Mass spectrometry is first used for the structural characterization
of all new compounds and then for their pharmaceutical profiling.
The new compounds that show activity in a high throughput
screening assay are then brought to a discovery drug metabolism
group for further evaluation. It can be stated that at least
one mass spectrometry group is an essential requirement for
a successful drug metabolism department. Mass spectrometry
has become the premier analytical tool for the multiple in
vitro and in vivo absorption, distribution, metabolism and
excretion (ADME) assays. These assays use mass spectrometry
for both quantitative and qualitative applications. One of
the most common uses of HPLC-MS/MS systems is for bioanalytical
assays of both preclinical and clinical pharmacokinetic (PK)
samples. Another important application area is the identification
of drug metabolites; new software tools and new MS instrumentation
has been developed to improve our ability to both detect and
identify these metabolites. In addition, the new application
area of biomarker discovery and measurement is becoming a
very important part of the new drug development process. Furthermore,
mass spectrometry is continuing to evolve as evidenced by
new ionization sources (nano-ESI) and new types of hybrid
mass spectrometers (e.g., the Q-Trap MS and the LTQ-FTMS systems)
that have become available in the last few years. I have selected
experts in various fields of mass spectrometry to write the
reviews and mini-reviews that you will find in this special
edition. I want to thank Chandra Prakash for suggesting this
special edition and thank the authors of these reviews and
mini-reviews for their excellent manuscripts. Together these
papers and their references provide a good overview of the
use of mass spectrometry in current drug metabolism applications.
Walter A. Korfmacher, Ph.D.
Director
Exploratory Drug Metabolism
K-15-2880
Schering-Plough Research Institute
2015 Galloping Hill Rd.
Kenilworth, NJ 07033, USA
E-mail: walter.korfmacher@spcorp.com
[Back to top]
Utility of Mass Spectrometry for Pharmaceutical Profiling
Applications
E.H. Kerns and L. Di
MS has great utility for pharmaceutical profiling, the measurement
of physicochemical and metabolic properties that are crucial
to the discovery and development of new drug candidates. An
evaluation of the capabilities of MS to improve the speed,
specificity, sensitivity and cost per compound of method in
development indicates when MS technologies have utility compared
to other analytical techniques. MS has been used successfully
for methods that profile the critical properties: permeability,
lipophilicity, plasma and solution stability, solubility,
plasma protein binding and integrity. In general, MS has utility
in these methods using analytical strategies involving unique
MS technologies (e.g., parallel multiplexed interfaces, trap-and-elute),
orthogonal detection to UV, high sensitivity for low LOQs,
low concentration studies, highly specific MS/MS SRM, combinatorial
analysis, use of internal standards, providing initial structural
data in addition to quantitative and facile integration with
HPLC autosamplers and other hardware that allow enhanced on-line
experiments. Ultimately, it is important to evaluate the appropriateness
of any technique that is being considered for use in a method,
to insure that it best meets all of the criteria for the organization’s
needs.
[Back to top]
Utility of Mass Spectrometry for In-Vitro
ADME Assays
I. Chu and A.A. Nomeir
A balance between pharmacological activity, safety and drug
metabolism and pharmacokinetics (DMPK) attributes determines
the fate of a new chemical entity (NCE) in drug discovery.
Because of the increased number of NCEs requiring DMPK evaluation,
several in vitro higher-throughput screens and counter
screens designed to evaluate DMPK attributes have been introduced
in drug discovery. The DMPK screens evaluate NCEs for potential
absorption, metabolism, drug-drug interactions, brain penetration,
protein binding and pharmacokinetics. Higher-throughput analytical
methodologies for the determination of either a common end
product of a screen or the parent compound (and/or possible
metabolites) are essential for successful DMPK screens. Because
of its speed, sensitivity and specificity, liquid chromatography-tandem
mass spectrometry (LC-MS/MS) has become the technology of
choice for sample analysis. In this review, several in
vitro screening assays that we employ in drug discovery
are discussed with an emphasis on LC-MS/MS role in accelerating
them.
[Back to top]
Increasing Speed and Throughput When Using HPLC-MS/MS
Systems for Drug Metabolism and Pharmacokinetic Screening
Y. Hsieh and W.A. Korfmacher
Both combinatorial chemistry and parallel synthesis provide
a valuable means for the production of large numbers of compounds
with diverse molecular architectures that become available
for various drug discovery experiments. In both the lead optimization
and lead selection stages, one requirement that is common
for many processes is the need for bioanalytical support.
This review summarizes current high throughput strategies
and efficient methodologies that are employed for drug metabolism
and pharmacokinetic (DMPK) screens for a series of drug discovery
compounds. For these types of assays, high performance liquid
chromatography coupled to a tandem mass spectrometer (HPLC-MS/MS)
has now become the technique of choice. The major high throughput
strategies including sample reduction and cassette dosing
are discussed. The methods for increasing the speed of HPLC-MS/MS-based
analyses, such as fast chromatography, direct sample injection,
parallel technologies and combined ionization interfaces are
also presented in this review. In addition, the special challenges
when performing HPLC-MS/MS bioanalysis, such as the choice
of ionization sources, matrix ionization suppression and the
potential for endogenous interferences, are addressed.
[Back to top]
LC-MS Development Strategies for Quantitative Bioanalysis
M. Jemal and Y.-Q. Xia
Although quantitative bioanalysis using liquid chromatography
in conjunction with atmospheric pressure ionization tandem
mass spectrometry (LC-MS/MS) has been in use for approximately
fifteen years, new concepts and technologies are continuously
being introduced to enhance the multiple steps of quantitative
LC-MS/MS bioanalysis. In this review article, we have focused
on concepts and technologies that have recently been introduced
to achieve further improvements in biological sample collection/storage
and extraction, chromatography and mass spectrometric detection.
Under these major headings, a number of specific topics are
presented, summarizing the most recent findings in these areas.
Included among the topics discussed are: off-line plasma extraction,
on-line plasma extraction, enhanced mass resolution, atmospheric
pressure photoionization, high-field asymmetric waveform ion
mobility spectrometry, electron capture atmospheric pressure
chemical ionization, enhancing MS detection via formation
of anionic and cationic adducts, chemical derivatization,
ultra-performance chromatography, hydrophilic interaction
chromatography, and MS-friendly ion-pair reversed-phase chromatography.
In the end, we discuss potential pitfalls in LC-MS/MS bioanalysis
and the means to avoid them. Such pitfalls may occur due to
mass spectral interference from metabolites or prodrugs, due
to the use of inappropriate calibration standard and quality
control samples for analysis involving unstable drugs or metabolites,
and due to the wild card phenomenon commonly known as the
matrix effect.
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Application of Mass Spectrometry for Metabolite Identification
S. Ma, S.K. Chowdhury and K.B. Alton
Metabolism studies play a pivotal role in drug discovery
and development. Characterization of metabolic “hot-spots”
as well as reactive and pharmacologically active metabolites
is critical to designing new drug candidates with improved
metabolic stability, toxicological profile and efficacy. Metabolite
identification in the preclinical species used for safety
evaluation is required in order to determine whether human
metabolites have been adequately tested during non-clinical
safety assessment. From an instrumental standpoint, high performance
liquid chromatography (HPLC) coupled with mass spectrometry
(MS) dominates all analytical tools used for metabolite identification.
The general strategies employed for metabolite identification
in both drug discovery and drug development settings together
with sample preparation techniques are reviewed herein. These
include a discussion of the various ionization methods, mass
analyzers, and tandem mass spectrometry (MS/MS) techniques
that are used for structural characterization in a modern
drug metabolism laboratory. Mass spectrometry-based techniques,
such as stable isotope labeling, on-line H/D exchange, accurate
mass measurement to enhance metabolite identification and
recent improvements in data acquisition and processing for
accelerating metabolite identification are also described.
Rounding out this review, we offer additional thoughts about
the potential of alternative and less frequently used techniques
such as LC-NMR/MS, CRIMS and ICPMS.
[Back to top]
The Role of Mass Spectrometry in Biomarker Discovery
and Measurement
B.L. Ackermann, J.E. Hale and K.L. Duffin
Recent advances in the biological and analytical sciences
have led to unprecedented interest in the discovery and quantitation
of endogenous molecules that serve as indicators of drug safety,
mechanism of action, efficacy, and disease state progression.
By allowing for improved decision-making, these indicators,
referred to as biomarkers, can dramatically improve the efficiency
of drug discovery and development. Mass spectrometry has been
a key part of biomarker discovery and evaluation owing to
several important attributes, which include sensitive and
selective detection, multi-analyte analysis, and the ability
to provide structural information. Because of these capabilities,
mass spectrometry has been widely deployed in search for new
markers both through the analysis of large molecules (proteomics)
and small molecules (metabonomics). In addition, mass spectrometry
is increasingly being used to support quantitative measurement
to assist in the evaluation and validation of biomarker leads.
In this review, the dual role of mass spectrometry for biomarker
discovery and measurement is explored for both large and small
molecules by examining the key technologies and methods used
along the continuum from drug discovery through clinical development.
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The Use of Qtrap Technology in Drug Metabolism
R. King and C. Fernandez-Metzler
Advances in mass spectrometry continue to bring new and exciting
capabilities to the study of drug metabolism. This review
covers the hybrid linear ion trap – triple quadrupole
mass spectrometer, the QTrap. While still a recent addition
to the arsenal of mass spectrometry techniques available to
the metabolism scientist, reports in the literature highlight
the advantages of the system for metabolite identification.
The system combines the selective scans of the triple quadrupole
with the high speed, high sensitivity of the ion trap allowing
metabolites to be found and characterized in a single scan.
Additionally, the system has MS3 and
time delayed fragmentation scans that aid in structure elucidation.
Since the fragmentation occurs in the collision cell of the
triple quadrupole, the traditionally rich fragmentation of
the collision cell fragmentation is preserved.
In addition to helping to make traditional processes more
efficient, work has been done that shows the potential of
the instrument to change traditional DMPK approaches. Researchers
have reported methods that allow for both qualitative analysis
of circulating metabolites and quantification of parent drug
within the same analysis. The approaches reported show how
the instrument can be used to collect more information from
every sample and potentially streamline typical drug metabolism
assays.
[Back to top]
Utility of the Hybrid LTQ-FTMS for Drug Metabolism
Applications
M. Sanders, P.A. Shipkova, H. Zhang and B.M. Warrack
Fourier Transform Ion Cyclotron Mass Spectrometry (FTMS)
provides the highest mass accuracy and mass resolving power
of the currently available mass spectrometers. One of the
main drawbacks in its use for absorption, distribution, metabolism
and excretion (ADME) applications has been its incompatibility
with standard HPLC columns and flow rates. Hybrid instruments,
such as the LTQ-FT, provide the much needed bridge between
the excellent performance and capabilities of the FT mass
spectrometers and the well-established, tested and validated
features of quadrupoles and ion traps. The hybrid instruments
are compatible with standard HPLC flow rates, have high-throughput
and automation compatibility, and also provide data dependant
MSn. The ability to maintain the fidelity of an
externally calibrated accurate mass measurement across an
HPLC peak, where the analyte concentrations are rapidly changing,
is a significant advance for this technology, as is the ability
to perform data dependent MS/MS experiments on the chromatographic
time scale. The MSn and accurate mass capabilities
are routinely utilized to rapidly confirm the identification
of expected metabolites or to elucidate the structures of
unusual or unexpected metabolites. The combination of traditional
high-flow chromatography and robust, externally calibrated
accurate mass determination for both parent and product ions
makes the LTQ-FTMS a very powerful analytical tool for the
characterization of metabolites, identification of metabolic
soft-spots and for metabonomics studies.
[Back to top]
Use of Nano-Electrospray for Metabolite Identification
and Quantitative Absorption, Distribution, Metabolism and
Excretion Studies
C.E.C.A. Hop
Determination of the pharmacokinetics and metabolite identification
have been an integral part of drug discovery and development
to ensure that drugs have appropriate absorption, distribution,
metabolism and excretion properties. Liquid chromatography
interfaced with a mass spectrometer has greatly facilitated
these studies. Nano-electrospray has distinct sensitivity
advantages and the increased amount of time available to perform
mass spectrometric experiments facilitates structural characterization
of metabolites. The recently developed silicon chip-based
nano-electrospray devices are more practical than pulled capillaries.
The use of these devices for the determination of pharmacokinetics
and metabolite identification will be described and particular
attention will be paid to the distinct advantages and disadvantages
these devices offer. |
