Auranofin increases the affinity of phorbol dibutyrate receptors in chronic lymphocytic leukemia cells (B cells).

Previous studies have shown that auranofin (AF), a lipophilic gold I complex, modulates metabolic events in leukocytes stimulated by phorbol esters, whose major cellular binding site is now known to be the Ca++/phospholipid-dependent protein kinase (protein kinase C). In these experiments we have investigated the effect of AF on the binding of phorbol dibutyrate (PDBu) to human chronic lymphocytic leukemia (CLL) B cells. AF enhanced binding of PDBu to its receptor in CLL cells by a) causing an increase in the affinity of PDBu receptors from Kd 20.3 nM to 7.3 nM, and b) enhancing translocation of PDBu receptors to the cell membrane. The increase in PDBu binding induced by AF in whole cells was only partially reversible by EGTA or the intracellular Ca++ antagonist TMB-8. Studies performed with quin-2-labeled cells showed that 100 microM AF caused a mean (+/- SD) rise in cytosolic Ca++ levels from 0.41 (0.12) to 0.85 (0.33) (n = 5). Thus the mechanism by which AF increases binding of PDBu to its receptor appears to be partially dependent on Ca++. These effects of AF occurred at cellular levels achieved in mononuclear cells during chrysotherapy of patients with rheumatoid arthritis.