ORIGINAL ARTICLE: RESEARCH Targeting the Bcl-2 family of proteins in Hodgkin lymphoma: in vitro cytotoxicity, target modulation and drug combination studies of the Bcl-2 homology 3 mimetic ABT-737 AARTHI JAYANTHAN 1 , SCOTT C. HOWARD 2 , TANYA TRIPPETT 3 , TERZAH HORTON 4 , JAMES A. WHITLOCK 5 , LARA DAISLEY 1 , VICTOR LEWIS 1 , & ARU NARENDRAN 1 1 Hughes’ Children’s Cancer Research Centre and the Division of Pediatric Oncology, Alberta Children’s Hospital, Calgary, Alberta, Canada, 2 St. Jude Children’s Research Hospital, Memphis, Tennessee, USA, 3 Memorial Sloane-Kettering Cancer Center, New York, New York, USA, 4 Baylor College of Medicine, Houston, Texas, USA, and 5 Vanderbilt University Medical Center, Nashville, Tennessee, USA (Received 12 September 2008; revised and accepted 31 March 2009) Abstract With currently available treatment, patients with refractory Hodgkin lymphoma (HL) or those who relapse multiple times have an extremely poor prognosis. Therefore, new agents and novel therapeutic approaches are urgently needed. Anti- apoptotic proteins such as Bcl-2 and Bcl-x have been associated with the growth and survival of Hodgkin Reed–Sternberg cells and are potential therapeutic targets. ABT-737 is a small molecule that inhibits the Bcl-2 family of apoptosis regulators. In this study, we show the concentration-dependent and time-dependent cytotoxicity of ABT-737 against cell lines derived from patients with HL. A concurrent reduction in a number of intracellular cell growth and survival related molecules, such as Bcl-2, Bcl-xl, NF-kB and survivin was also seen. Drug combination studies using a panel of conventional and novel therapeutic agents show that ABT-737 potentiates the activity of agents that have inherent anti-lymphoma activity and provide support for the evaluation of ABT-737 in the clinical setting. Keywords: Hodgkin lymphoma, ABT-737, Bcl-2, apoptosis, targeted therapeutics Introduction Though current treatment protocols offer an 80% cure rate for patients with newly diagnosed Hodgkin lymphoma (HL), patients who progress while on therapy or subsequently relapse would benefit from novel therapeutic agents and treatment regimens. Even patients who do not relapse often experience late toxicities, including secondary cancer, heart failure and hypothyroidism. Therefore, new targeted therapies could potentially lead to either decreased therapy intensity, through eliminating radiation or decreasing chemotherapy, or improved efficacy. To this end, we examined the in vitro effect of ABT-737, a novel small molecule that induces apoptosis by inhibiting Bcl-2 and other anti-apoptotic proteins, on two cell lines derived from patients with HL. HL is characterised by the appearance of Hodgkin Reed–Sternberg (H/RS) cells in an inflammatory background. These cells are thought to originate by clonal expansion of germinal centre cells with aberrant immunoglobulin genes, but the exact molecular abnormalities that lead to the increased growth and survival potential of H/RS cells are unknown. Several abnormally activated growth sti- mulatory pathways have been described in H/RS cells. These include the constitutive activation of NF-kB and STAT pathways and defective cell cycle regulation [1–6]. In addition, abnormal expression and/or activation of biological markers associated Correspondence: Aru Narendran, MD, PhD, Division of Pediatric Oncology, Alberta Children’s Hospital, 2888 Shaganappi Trail NW, Calgary, Alberta, Canada T3B 6A8. Tel: þ403-210-6418. Fax: þ403-955-2645. E-mail: a.narendran@ucalgary.ca There is an accompanying commentary that discusses this paper. Please refer to the issue Table of Contents. Leukemia & Lymphoma, July 2009; 50(7): 1174–1182 ISSN 1042-8194 print/ISSN 1029-2403 online Ó 2009 Informa Healthcare USA, Inc. DOI: 10.1080/10428190902943069