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Oct 15, 2009 (Vol. 29, No. 18)

High-Content Screening Surges Ahead

Advances in Methodology Yield Functional and Mechanistic Data Earlier in Discovery Process

  • Vendors Roll Out Image-Analysis Solutions

    Versatility across application areas, from microscope-based imaging for detecting intracellular phenomena to high-speed scans at the cellular level to whole organism screening, is the focal point of instrument development at MDS Analytical Technologies. “With the options in our Complete Solution and the right infrastructure, you can use image-based assays for primary screening. We have tackled all the common bottlenecks,” said Michael Sjaastad, Ph.D., director of marketing for cellular imaging at MDS.

    The IsoCyte® DL laser-scanning cytometer complements the company’s ImageXpress® instrument platform as part of its overall HCS solution. MDS offers a high-throughput option that can screen and do image analysis on a 1,536-well plate in two to five minutes, according to Dr. Sjaastad. The instrument can image whole wells for accurate cell counting in cell-viability measurements, scan a microscope slide, or produce and analyze images of organisms such as zebrafish or worms when used in conjunction with the MetaXpress image-analysis software.

    For now, current systems “have the image resolution and acquisition speed researchers need,” and in Dr. Sjaastad’s view, future improvements will focus on “streamlining the data-analysis workflow and bringing the costs down per data point.”

    In a workshop at the meeting, Oliver Leven, Ph.D., head of screener professional services at Genedata, identified several ongoing challenges in HCS, including managing the volume and complexity of the data, improving the efficiency of data analysis, and creating an audit trail of results interpretation. As the throughput and scale of HCS increases, so too, do the difficulty and scope of these challenges.

    As researchers scale up an assay for high-throughput HCS, they need to select a defined set of parameters that represent the phenotype of interest and that allow them to assess the quality of both the assay and the data output. They also need to identify threshold values above or below which a result signifies a change in phenotype.

    The typical HCS image-analysis software that drives HCS systems routinely quantifies the cell images to yield a numerical description of the phenotypes. For large experiments, however, Dr. Leven described the researcher’s need to go back and view an image associated with an interesting or suspicious measurement as a persistent bottleneck.

    “The image is the experiment,” said Dr. Leven. A hit should signify a change in the cells, but it could also be an anecdotal finding or the result of an image out of focus. Distinguishing true hits from false positive results remains a challenge.

    Dr. Leven recounted the HCS projects  that Genedata has performed for its pharma customers emphasizing the ability of the company’s High Content Analyzer—a new addition to the Genedata Screener® enterprise solution—to retrieve immediately any desired image. The high-throughput HCS projects described by Dr. Leven were able to analyze 40,000 compounds on a daily basis, for a total campaign of more than two million compounds, generating multifeatured data sets for each well.

    PerkinElmer’s high-content screening portfolio includes the Opera confocal microplate image reader and Acapella™ image-analysis software, the compact Operetta HCS system, driven by Harmony™ software, and the Columbus™ data-management system and new Columbus 2.0 for use with the Opera platform.

    Gabriele Gradl, Ph.D., global product leader for HCS at PerkinElmer Cellular Technologies, emphasized the complexity involved in deriving robust, quantitative data from cellular measurements derived on image analysis of high-content screens. Whereas, fluorescence-based analysis typically relies on identifying objects in cells and measuring their fluorescence intensities, PerkinElmer has developed a computational strategy that is independent of absolute fluorescence intensity. It relies on texture analysis and quantitative pattern analysis for data generation.

    Texture-analysis tools can detect patterns and effects that would not be apparent on routine visual analysis, according to Dr. Gradl. Threshold adjacency statistics is one example of such a tool. It searches for differences in fluorescence intensity values between adjacent pixels over a defined distance. Dr. Gradl described the particular advantages of applying texture analysis for detecting subtle morphologic changes associated with cell viability or toxicity assays and in stem cell research. It can detect differences not visible to the eye and identify changes that the user might not even have known to look for in the data. She presented, as an example, the use of texture analysis to assess mitochondrial integrity, as loss of mitochondrial activity and enhanced mitochondrial biogenesis are early markers of cytotoxicity.

    Dr. Gradl also described the use of texture analysis in brightfield imaging and the ability to assess segmentation based on granularity, enabling label-free proliferation assays and analysis of cell differentiation in real time.

    The algorithms developed by PerkinElmer can apply texture analysis to whole cells or to specific intracellular compartments depending on the design of the assay. The company is exploring a range of applications for its texture-analysis software tools, including stem cell differentiation analysis, quality control of stem cells produced for therapeutic use, live-cell imaging over time, and 3-D tissue sample analysis.

    Earlier this year, GE Healthcare introduced the IN Cell Analyzer 2000 cell-imaging system, which incorporates several new features: preview scoring of a selected area of a sample before an acquisition run; a large chip CCD camera coupled with a widefield illumination source for twice the brightness of a conventional xenon lamp, according to GE; whole-well imaging; an objectives range from 2x–100x; six imaging restoration modes; and a manual microscope mode.

    Fred Koller, Ph.D., president and CEO of Cyntellect, launched the company’s new Celigo™ cytometer at the “High Content East” meeting, emphasizing the system’s ability to image “every cell in every well,”  from edge to edge without edge effects using both brightfield and fluorescence imaging. Cyntellect’s optical technology achieves high-quality large field imaging using a set of mirrors to capture each well in its entirety without moving the plate and without the need to refocus, allowing for rapid, full-plate imaging.

    Celigo provides “uniform illumination with no gradient across the well,” said Dr. Koller, and allows for a combination of label-free imaging and three-color fluorescence. He described the instrument’s capabilities for performing cell-counting assays, cell growth tracking, and confluency studies, for example, and for noninvasive imaging of stem cell cultures without disrupting their three-dimensional colony structures. Celigo can switch from single-cell to colony-counting mode.

    The company has also developed a secretion assay for use on the Celigo that measures the amount of protein secreted by individual cells. The assay can distinguish between high and low secretors and is useful for detecting heterogeneity and instability in cell cultures early in process development, such as for antibody manufacturing.

    The Cellular Imaging and Analysis group at Thermo Fisher Scientific introduced the Cellomics iDev™ intelligent assay development workflow for HCS image analysis at “High Content East”. Users work training image sets of positive and negative biology, applying imaging and analytical algorithms that allow for real-time interaction with the images. The software employs the biological data generated to optimize assay protocols.

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