A synthetic peptide targeting the BH4 domain of Bcl-2 induces apoptosis in multiple myeloma and follicular lymphoma cells alone or in combination with agents targeting the BH3-binding pocket of Bcl-2

// Andrew R. Lavik 1 , Fei Zhong 1, * , Ming-Jin Chang 1, * , Edward Greenberg 1, 2 , Yuvraj Choudhary 1 , Mitchell R. Smith 3, 4 , Karen S. McColl 1 , John Pink 4 , Frederic J. Reu 3, 4 , Shigemi Matsuyama 1, 4 , Clark W. Distelhorst 1, 4 1 Division of Hematology/Oncology, Case Western Reserve University School of Medicine and University Hospitals Case Medical Center, Cleveland, Ohio, USA 2 Department of Medicine, MetroHealth Medical Center and Case Western Reserve University School of Medicine, Cleveland, Ohio, USA 3 Department of Translational Hematology and Oncology Research, Taussig Cancer Institute, The Cleveland Clinic Foundation, Cleveland, Ohio, USA 4 Case Comprehensive Cancer Center, Cleveland, Ohio, USA * These authors have contributed equally to this work Correspondence to: Clark W. Distelhorst, e-mail: cwd@case.edu Keywords: Bcl-2, inositol 1,4,5-trisphosphate receptor, ABT-199, Bruton's tyrosine kinase, lymphoid malignancy Received: April 03, 2015      Accepted: July 01, 2015      Published: July 11, 2015 ABSTRACT Bcl-2 inhibits apoptosis by two distinct mechanisms but only one is targeted to treat Bcl-2-positive malignancies. In this mechanism, the BH1-3 domains of Bcl-2 form a hydrophobic pocket, binding and inhibiting pro-apoptotic proteins, including Bim. In the other mechanism, the BH4 domain mediates interaction of Bcl-2 with inositol 1,4, 5-trisphosphate receptors (IP 3 Rs), inhibiting pro-apoptotic Ca 2+ signals. The current anti-Bcl-2 agents, ABT-263 (Navitoclax) and ABT-199 (Venetoclax), induce apoptosis by displacing pro-apoptotic proteins from the hydrophobic pocket, but do not inhibit Bcl-2-IP 3 R interaction. Therefore, to target this interaction we developed BIRD-2 (Bcl-2 IP 3 Receptor Disruptor-2), a decoy peptide that binds to the BH4 domain, blocking Bcl-2-IP 3 R interaction and thus inducing Ca 2+ -mediated apoptosis in chronic lymphocytic leukemia, multiple myeloma, and follicular lymphoma cells, including cells resistant to ABT-263, ABT-199, or the Bruton's tyrosine kinase inhibitor Ibrutinib. Moreover, combining BIRD-2 with ABT-263 or ABT-199 enhances apoptosis induction compared to single agent treatment. Overall, these findings provide strong rationale for developing novel therapeutic agents that mimic the action of BIRD-2 in targeting the BH4 domain of Bcl-2 and disrupting Bcl-2-IP 3 R interaction.