Sensitization of Leukemic Cells for Glucocorticoids by Inhibition of NFκB Activity.

Based on their immunosuppressive and cytotoxic effects, glucocorticoids (GCs) find widespread use as immune-modulatory agents and in (childhood) leukemia, lymphomas and myelomas. Unfortunately, resistance to GCs is a major adverse prognostic factor and occurs in about 20% in newly diagnosed childhood acute lymphoblastic leukemia (ALL) and in more than 50% in relapsed ALL, while acute myeloid leukemia (AML) is largely unresponsive to GCs. In addition, adult AML is more often GC resistant compared to childhood AML. Recently, we observed (van der Heijden et al, Ann Rheum Dis 63: 131-137,2004) that prolonged exposure of human CEM-C7 T cell leukemia cells to the anti-rheumatic drug sulfasalazine (SSZ) sensitized these primary sensitive cells even further for GCs. SSZ is an inhibitor of activation of NFκB that is often therapeutically used in combination with methotrexate and prednisone. Following these observations, two human myeloid leukemia cell lines (THP-1 and U937) with inherent resistance to GCs (IC50 for prednisolone > 250 μM, IC50 dexamethasone > 25 μM) were exposed to SSZ to establish whether this would provoke GC sensitization. Indeed, prolonged SSZ exposure sensitized both myeloid leukemia cells for prednisolone (IC50