Cancer Therapy: Preclinical Heat Shock Protein 90 Inhibitor BIIB021 (CNF2024) Depletes NF-κB and Sensitizes Hodgkin's Lymphoma Cells for Natural Killer Cell–Mediated Cytotoxicity Boris Böll, 1,2 Farag Eltaib, 1 Katrin S. Reiners, 1 Bastian von Tresckow, 1,2 Samir Tawadros, 1 Venkateswara R. Simhadri, 1 Francis J. Burrows, 3 Karen Lundgren, 4 Hinrich P. Hansen, 1 Andreas Engert, 1 and Elke Pogge von Strandmann 1 Abstract Purpose: In Hodgkin's lymphoma, constitutive activation of NF-κB promotes tumor cell survival and proliferation. The molecular chaperone heat shock protein 90 (HSP90) has immune regulatory activity and supports the activation of NF-κB in Hodgkin's lympho- ma cells. Experimental Design: We analyzed the effect of HSP90 inhibition on viability and NF-κB activity in Hodgkin's lymphoma cells and the consequences for their recognition and killing through natural killer (NK) cells. Results: The novel orally administrable HSP90 inhibitor BIIB021 (CNF2024) inhibited Hodgkin's lymphoma cell viability at low nanomolar concentrations in synergy with doxorubicin and gemcitabine. Annexin V/7-aminoactinomycin D binding assay re- vealed that BIIB021 selectively induced cell death in Hodgkin's lymphoma cells but not in lymphocytes from healthy individuals. We observed that BIIB021 inhibited the constitutive activity of NF-κB and this was independent of IκB mutations. Furthermore, we analyzed the effect of HSP90 inhibition on NK cell–mediated cytotoxicity. BIIB021 induced the expression of ligands for the activating NK cell receptor NKG2D on Hodg- kin's lymphoma cells resulting in an increased susceptibility to NK cell–mediated kill- ing. In a xenograft model of Hodgkin's lymphoma, HSP90 inhibition significantly delayed tumor growth. Conclusions: HSP90 inhibition has direct antitumor activity in Hodgkin's lymphoma in vitro and in vivo. Moreover, HSP90 inhibition may sensitize Hodgkin's lymphoma cells for NK cell–mediated killing via up-regulation of ligands engaging activating NK cell receptors. (Clin Cancer Res 2009;15(16):5108–16) The ubiquitously expressed molecular chaperone heat shock protein 90 (HSP90) promotes tumor cell survival and prolifer- ation by maintaining conformation, stability, and activity of several key oncogenic client proteins (1). Formation of HSP90 cochaperone complexes is essential for the function of HSP90 and requires ATP hydrolysis by a NH 2 -terminal ATPase. HSP90 inhibitors, such as the ansamycin 17-N-allylamino-17- demethoxygeldanamycin (17-AAG), inhibit ATPase function re- sulting in ubiquitination and proteasomal degradation of the client proteins (1, 2). Consequently, inhibition of HSP90 in- duces cell death in a broad variety of solid and hematologic tu- mor cell lines in vitro (2). However, 17-AAG has significant clinical limitations, including weak target potency and low aqueous solubility (3). Furthermore, initial clinical trials have suggested low bioavailability and considerable toxicity of 17- AAG, prompting the development of novel small-molecule HSP90 inhibitors such as the orally administrable purine scaf- fold BIIB021 (CNF2024; refs. 4–8). Besides stabilizing oncogenic proteins, HSP90 is critically in- volved in antitumor immunity (9). As recently reported, HSP90 inhibition decreases the cell surface MHC-I expression and im- pairs loading of MHC-I with peptides, suggesting an unfavor- able effect of HSP90 inhibition on tumor cell recognition by CD8 + T cells (10). Furthermore, inhibition of HSP90 has been shown to decrease antigen presentation and cytokine secretion by dendritic cells (11). However, the effect of HSP90 inhibition on natural killer (NK) cells, innate lymphocytes that detect MHC-I-negative cells, is less well understood. Authors' Affiliations: 1 Laboratory of Immunotherapy, Department of Hematology and Oncology, University Hospital Cologne; 2 Center of Molecular Medicine, University of Cologne, Cologne, Germany; 3 Aarden Pharmaceuticals; and 4 Biogen Idec, San Diego, California Received 2/4/09; revised 3/20/09; accepted 5/1/09; published OnlineFirst 8/11/09. Grant support: Köln Fortune Program (B. Böll and B. von Tresckow) and Deutsche Krebshilfe (E.P. von Strandmann). Thecostsofpublicationofthisarticleweredefrayedinpartbythepaymentof page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicatethis fact. Requests for reprints: Boris Böll, Department of Internal Medicine I, Univer- sity Hospital Cologne, Kerpener Street 62, 50937 Cologne, Germany. Phone: 49-2214786033; Fax: 49-22147888745; E-mail: boris.boell@uk.koeln.de. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-09-0213 5108 Clin Cancer Res 2009;15(16) August 15, 2009 www.aacrjournals.org Research. on June 6, 2020. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from Published OnlineFirst August 11, 2009; DOI: 10.1158/1078-0432.CCR-09-0213