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J Biomol Screen. 2013 Apr;18(4):420-9. doi: 10.1177/1087057112466697. Epub 2012 Nov 15.

Flow cytometry enables a high-throughput homogeneous fluorescent antibody-binding assay for cytotoxic T cell lytic granule exocytosis.

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University of Connecticut at Storrs, Storrs, CT 06269-3125, USA.


We developed a homogeneous phenotypic fluorescence end-point assay for cytotoxic T lymphocyte lytic granule exocytosis. This flow cytometric assay measures binding of an antibody to a luminal epitope of a lysosomal membrane protein (LAMP-1) that is exposed by exocytosis to the extracellular solution. Washing to remove unbound antibody is not required. Confirming the assay's ability to detect novel active compounds, we screened at a concentration of 50 µM a synthetic diversity library of 91 compounds in a 96-well plate format, identifying 17 compounds that blocked by 90% or more. The actions of six structurally related tetracyano-hexahydroisoindole compounds that inhibited by ~90% at a concentration of 10 µM were investigated further. Four reduced elevations in intracellular Ca(2+); it is likely that depolarization of the cells' membrane potential underlies the effect for at least two of the compounds. Another compound was found to be a potent inhibitor of the activation of the mitogen-activated protein (MAP) kinase ERK. Finally, we transferred the assay to a 384-well format and screened the Prestwick Compound Library using high-throughput flow cytometry. Our results indicate that our assay will likely be a useful means of screening libraries for novel compounds with important biological activities.

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