Approach to the discovery of novel, selective inhibitors of p56lck tyrosine kinase: Identification of non‐hydroxylated chromones as p56lck inhibitors

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Abstract
The protein tyrosine kinase p56Ick, which is expressed predominantly in lymphocytes, plays a critical role in optimal T cell activation through the T cell antigen receptor. An approach is presented for the discovery of selective p56Ick inhibitors, which are potential immunosuppressants. A non‐radioactive assay for p56Ick tyrosine kinase activity has been developed and adapted for high volume screening. This assay does not require purified enzyme. p56Ick in the plasma membranes of a human T cell line is purified in situ by immobilization onto the wells of a microtiter plate using an antibody specific for p56Ick. Following the kinase reaction in the presence of test compound, autophosphorylated p56Ick is detected with a biotinylated monoclonal antibody to phosphotyrosine. Using the approach described in this report, three simple chromones have been identified that inhibit p56Ick autophosphorylation with low micromolar potencies and exhibit some selectivity for p56Ick over the serine/threonine and other tyrosine kinases tested. These compounds constitute a novel group of p56Ick tyrosine kinase inhibitors. ©1995 Wiley‐Liss, Inc.