Rvx-2135 Is A Novel, Orally Bioavailable Epigenetic Bet Inhibitor That Synergizes With Cytarabine And Idarubicin To Inhibit Proliferation Of Acute Myeloid Leukemia Cells.

Current treatment of acute myeloid leukemia (AML) often includes a combination of intravenous cytarabine (Ara-C) and an anthracycline such as idarubicin. Bromodomain and extra-terminal domain (BET) proteins contain two bromodomains that bind to acetylated lysines in histones and regulate gene transcription by an epigenetic mechanism. Here we describe a novel small molecule BET inhibitor, RVX-2135, which selectively binds recombinant BET bromodomains of BRD2, BRD3, and BRD4 but not non-BET bromodomains. RVX-2135 inhibited BRD2, BRD3, and BRD4 dual bromodomains binding to acetylated histones in vitro with sub to low micromolar IC50 values. In the human AML cell line MV4-11, RVX-2135 displaced BET proteins from chromatin and significantly reduced expression of c-MYC and BCL-2 mRNAs, with IC50s of 4 and 5 μM, respectively. RVX-2135 inhibited proliferation of cultured MV4-11 cells with an IC50 value of 6 μM, and induced cell cycle arrest and apoptosis. In vivo, nude mice bearing MV4-11 xenografts were treated orally with RVX-2135 at doses of 75 and 120 mg/kg b.i.d, and showed tumor growth inhibition of 77 and 92% respectively. There was a corresponding inhibition of c-MYC and BCL-2 mRNA expression in the xenograft tumors. In combination therapy in vitro, RVX-2135 synergized with idarubicin and cytarabine, with Chou-Talalay9s combination indices of 0.17 and 0.18, respectively. The synergistic effect also translated into increased apoptosis when cytarabine was combined with RVX-2135. Similar data were seen with BET inhibitors from different chemical scaffolds, suggesting that this may represent a promising new class of drugs for AML. Citation Format: Eric Campeau, Ravi Jahagirdar, Jin Wu, Emily M. Gesner, Olesya Kharenko, Raymond Yu, Sarah Attwell, Henrik C. Hansen, Gregory S. Wagner, Kevin G. McLure, Peter R. Young. RVX-2135 is a novel, orally bioavailable epigenetic BET inhibitor that synergizes with cytarabine and idarubicin to inhibit proliferation of acute myeloid leukemia cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr LB-92. doi:10.1158/1538-7445.AM2013-LB-92