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February 01, 2012 (Vol. 32, No. 3)

Screening Large Compound Libraries

Challenges Inherent in Primary and Secondary Stages Necessitate Automation of Liquid Handling

  • Small-Scale HTS

    Click Image To Enlarge +
    Figure 1. Dose response curves of compounds over an 8 point dilution series set up using TTP Labtech’s mosquito X1

    The versatility of the mosquito X1 is of value to small academic research groups that need to get maximal use and value from each instrument in their laboratory. Although mosquito HTS is more commonly employed to perform serial dilutions of active compound leads for dose-response curves, Larsen’s group successfully uses the single tipped X1 to perform serial dilutions of each hit compound selected. This group has found that with easy to use, dial-in volumes and transfer protocols, mosquito X1 can easily perform sequential pipetting with minimal re-programming.

    Figure 1 demonstrates the results of an eight-point dilution series of 10 hit compounds on a transiently expressed protein target. In this instance, dose-response curves were successfully achieved with mosquito X1 using lower volumes compared to those used in earlier studies. In addition, single disposable tip usage can be maximized, transferring multiple samples via sequential pipetting of the same sample, saving tip usage and costs.

    This research group also used their mosquito X1 to set up control wells containing identical concentrations of unstable control reagents or low volumes of DMSO identical to those in the compound sample wells. Of greater importance, they also found that mosquito X1 (Figure 2) was especially useful for dry spotting compounds that are labile in aqueous solution.

    Dry spotted compound plates were successfully stored at -20°C, ensuring sample integrity and providing assay-ready plates when required. The ability to pre-prepare plates at this secondary screening stage was highlighted to be of significant benefit to their workflow, while establishing optimal conditions for the set up of transient transfections.

  • Bioassay Development

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    Figure 2. TTP Labtech’s mosquito X1

    Bioassays using transiently expressed protein targets can be a bottleneck in the screening process. The successful establishment and optimization of expression of protein targets within bacterial, mammalian cell lines, yeast or insect cells can be lengthy. Once successful expression is achieved, it is often useful to be able to transfer these cells directly onto compound containing plates, and thus the preparation of pre-prepared plates can be advantageous. Indeed, a number of companies offer pre-prepared plates containing compounds in a ready-to-screen format in biocompatible solvents with no reconstitution needed.

    Such plates, although offering sample integrity and ease of use, are hugely expensive and many small-scale labs cannot justify the cost of commercially pre-prepared plates. Therefore the ability to set up pre-prepared plates using automated liquid-handling instruments such as the mosquito HTS or X1 are of great value to smaller research groups such as this, significantly increasing their screening rate and throughput.

  • Conclusion

    The large array of liquid-handling procedures required in primary and secondary screening of compound libraries makes the automation of liquid handling essential for both the primary and secondary screening stages of drug discovery.

    For small-scale labs that cannot justify the cost of commercially pre-prepared plates and for groups who have bespoke compound or RNAi libraries, the need to be able to accurately carry out compound screening setup using nanoliter volumes is important.

    TTP LabTech’s mosquito HTS and X1 offer precise and accurate nanoliter liquid handling from robust, small footprint instruments. mosquito’s ease of setup and use enables easy integration into a multiuser environment. The use of such instruments eliminates problems encountered in a high-throughput screening environment, reducing manual tedium and risk of error, in addition to the cost and effort involved in the discovery process.

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