Rituximab and 17‐allylamino‐17‐demethoxygeldanamycin induce synergistic apoptosis in B‐cell chronic lymphocytic leukaemia

Summary Treatment options for chronic lymphocytic leukaemia (CLL) are limited and eventually fail because of the development of toxicities or drug resistance. Thus, identification of new therapeutic strategies and targets is a high priority. The semisynthetic geldanamycin derivative 17‐allylamino‐17‐demethoxygeldanamycin (17‐AAG) inhibits heat shock protein 90 (Hsp90) binding to client proteins, thereby leading to their degradation. We demonstrate that at biologically active and clinically attainable levels (1 μmol/l), 17‐AAG treatment of CLL B cells in vitro causes modest apoptosis as well as decreased AKT protein levels. Given the potential activation of AKT following antibody therapy in CLL, we evaluated the combination of 17‐AAG and rituximab. These agents produced synergistic cytotoxicity of CLL cells in vitro . However, rituximab‐mediated antibody‐dependent cellular cytotoxicity was modestly reduced with 17‐AAG, and complement‐dependent cytotoxicity was not altered. We conclude that the combination of Hsp90 inhibitors with therapeutic antibodies, such as rituximab may represent a novel strategy to enhance therapeutic response in CLL. Furthermore, our data indicates that AKT and Hsp70 protein levels are relevant pharmacodynamic endpoints to monitor the in vivo effect of 17‐AAG therapy.