Assay and Drug Development Technologies - 7

ADVANCES IN HIGH CONTENT SCREENING
parameters that are automatically produced. Third, BioApplication
software offers programmed management of large
data sets by coupling the production of information on drug
responses from multiparameter image data with a concurrent
data archiving application. Finally, interactive and automated
bioinformatics tools are used to build and provide access to
knowledge from cellular information. This knowledge results
from making crucial connections between the hypotheses
used to design screening assays and the enormous amount of
information HCS assays generate. The generation of cellular
knowledge through investigative results leading to the discovery
of new molecular interactions, detection of unexpected
compound activities, or prediction of new activities,
thus becomes the foundation of the next round of HCS assay
design and cellular analysis. ''Cellome factories,'' where several
components of the workflow schematic shown in Fig. 1
are scaled to run in parallel, can now bring the fields of genomics
and proteomics to life by doing large-scale cellomics
studies.
HCS started with the development of instrumentation designed
to meet specifications ranging from speed of reading
microplates, number ofdistinct fluorescent probes to measure,
analyzing fixed versus living cells, and optical sectioning of
thick cell preparations. The early stages of the field of HCS
were thus instrument-centric. However, the real advances in
HCS have been made recently by recognizing that the amount
ofcomplex data generated by any of the instruments requires
the integration of sample preparation, instrumentation,
BioApplication software, reagents, and informatics/bioinformatics
tools. HCS is a systems engineering challenge, and the
seamless integration of its key components will produce the
most efficient and rapid workflow from data to information to
new knowledge that is the key to smart drug discovery. Before
discussing the integration of the components in a real-world
use case, it is worth exploring the characteristics and issues
with the components of optimal HCS.
SAMPLE PREPARATION
Preparation of cells for analysis is the most timeconsuming,
complex, and yet important part of HCS. The
capacity of the detector is only one part of the screening
equation, and ample consideration must be given to assay
preparation, including cell plating, compound addition, incubation,
and post-assay processing. Regardless of how fast
an instrument can collect images, if the cells being analyzed
are in suboptimal condition, the results ofthe analysis must be
questioned. Furthermore, sophisticated image processing and
analysis algorithms can provide variable results if sample
quality is not uniform.
Unlike homogeneous assays designed for high-throughput
screening, the performance of most HCS assays is dependent
on the ability to maintain monolayers of cells in the sample
array. Because many biological processes are also dependent
on cell density, biological responses of cells in senescent,
over-cultured, or confluent cultures can be drastically different
from those obtained from cells in log-phase growth.
Clumping and piling of cells can adversely affect assay performance,
by interfering with the system's ability to distinguish
individual cells for analysis as well as altering the
responsiveness of the cells. Therefore, care must be exercised
in setup of the appropriate HCS assay systems.
One solution to the complexity and time-consuming nature
FIG. 1. HCS workflow schematic. Depicted on the left are the
design, implementation, interpretation, and knowledge building
steps involved in HCS. On the right, solutions for each of these
steps that have been integrated into a complete HCS platform.
of manual HCS sample preparation is the use of automated
sample preparation systems. When using these systems, care
must be taken to ensure cellular integrity. Aggressive compound
addition, plate washing, or postassay handling can
adversely affect sample quality. Extra care must also be
exercised when cell samples are prepared manually. Sample
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Assay and Drug Development Technologies

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