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February 15, 2009 (Vol. 29, No. 4)

Second Messengers’ Accumulation Assays

Advanced Tools to Investigate All Compound Classes of GPCR Activation

  • Slow-Acting Agonist Activity

    In a recent presentation, scientists from a large pharmaceutical company summarized studies conducted in their laboratory using the IP-One assay with Gq and Galpha16-coupled receptors.

    One of the key findings of the study was the identification, using IP-One, of slow-acting agonist activity not detected by calcium mobilization.

    High-throughput screening of this class of compounds may present technological limitations when seeking agonists with the calcium flux, the most commonly used existing HTS method for Gq-protein coupled receptor cell-based functional assays.

    Calcium mobilization is a proven and widely used assay. The method can, however, require access to dedicated instrumentation and is limited by its extremely short readout time. These obstacles can increase screening turn-around and can lead to false negatives, particularly when looking for slow-acting agonists. The results presented show evidence of two slow-acting agonists with IP-One, but not with the calcium flux.

  • Characterization of Inverse Agonists

    Click Image To Enlarge +
    Figure 4. Agonist and inverse agonist dose response by using IP-One Terbium.

    This article has shown that with second messengers, all compound classes can be investigated. In addition to the ones cited, this also includes inverse agonists.

    A study presented at the Miptec Conference in Basel, Switzerland, late last year showed the characterization of an inverse agonist by using the IP-One Terbium assay. The identification of an inverse agonist effect on a constitutively active receptor is challenging with the calcium mobilization assay.  However, due to its terbium cryptate technology, IP-One Tb’s properties include high light absorption, sensitivity, enhanced signal-to-noise ratio, low false-positive rate, and full reader compatibility, and these accumulation assays provide efficient sensitivity and assay windows to properly perform a screen in HTS conditions (Figure 4).

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