Approach to the discovery of novel, selective inhibitors of p56^lck tyrosine kinase: Identification of non‐hydroxylated chromones as p56^lck inhibitors

The protein tyrosine kinase p56^Ick, 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 p56^Ick inhibitors, which are potential immunosuppressants. A non‐radioactive assay for p56^Ick tyrosine kinase activity has been developed and adapted for high volume screening. This assay does not require purified enzyme. p56^Ick 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 p56^Ick. Following the kinase reaction in the presence of test compound, autophosphorylated p56^Ick is detected with a biotinylated monoclonal antibody to phosphotyrosine. Using the approach described in this report, three simple chromones have been identified that inhibit p56^Ick autophosphorylation with low micromolar potencies and exhibit some selectivity for p56^Ick over the serine/threonine and other tyrosine kinases tested. These compounds constitute a novel group of p56^Ick tyrosine kinase inhibitors. ©1995 Wiley‐Liss, Inc.