title: Mechanisms of antileukemic activity of the novel Bcl-2 homology domain-3 mimetic GX15-070 (obatoclax).
abstract: In this study, we investigated the mechanism of apoptosis induction of obatoclax (GX15-070), a novel Bcl-2 homology domain-3 (BH3) mimetic, in acute myeloid leukemia (AML) cell lines and primary AML samples. Obatoclax inhibited cell growth of HL-60, U937, OCI-AML3, and KG-1 cell lines. Apoptosis induction contributed to the observed antiproliferative effects at concentrations of this agent that mirror its affinity for antiapoptotic Bcl-2 proteins. We show that obatoclax can promote the release of cytochrome c from isolated leukemia cell mitochondria and that apoptosis induced by this agent is preceded by the release of Bak from Mcl-1, liberation of Bim from both Bcl-2 and Mcl-1, and the formation of an active Bak/Bax complex. Notably, apoptosis was diminished, but not fully prevented, in the absence of Bak/Bax or Bim, suggesting that obatoclax has additional targets that contribute to its cytotoxicity. At growth inhibitory doses that did not induce apoptosis or decrease viability, obatoclax induced an S-G(2) cell-cycle block. Obatoclax induced apoptosis in AML CD34+ progenitor cells with an average IC(50) of 3.59 +/- 1.23 micromol/L although clonogenicity was inhibited at concentrations of 75 to 100 nmol/L. Obatoclax synergized with the novel BH3 mimetic ABT-737 to induce apoptosis in OCI-AML3 cells and synergistically induced apoptosis in combination with AraC in leukemic cell lines and in primary AML samples. In conclusion, we show that obatoclax potently induces apoptosis and decreases leukemia cell proliferation and may be used in a novel therapeutic strategy for AML alone and in combination with other targeted agents and chemotherapeutics.
authors.affiliation: Section of Molecular Hematology and Therapy, Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
authors.forename: Marina
authors.initials: M
authors.lastname: Konopleva
authors.forename: Julie
authors.initials: J
authors.lastname: Watt
authors.forename: Rooha
authors.initials: R
authors.lastname: Contractor
authors.forename: Twee
authors.initials: T
authors.lastname: Tsao
authors.forename: David
authors.initials: D
authors.lastname: Harris
authors.forename: Zeev
authors.initials: Z
authors.lastname: Estrov
authors.forename: William
authors.initials: W
authors.lastname: Bornmann
authors.forename: Hagop
authors.initials: H
authors.lastname: Kantarjian
authors.forename: Jean
authors.initials: J
authors.lastname: Viallet
authors.forename: Ismael
authors.initials: I
authors.lastname: Samudio
authors.forename: Michael
authors.initials: M
authors.lastname: Andreeff
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D051777:AraC Transcription Factor / Q000494:pharmacology; D032701:Biomimetics; D001713:Biphenyl Compounds / Q000494:pharmacology; D002478:Cells, Cultured; D004357:Drug Synergism; D018922:HL-60 Cells; D006801:Humans; D007211:Indoles; D007938:Leukemia / Q000188:drug therapy*; D051379:Mice; D018345:Mice, Knockout; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000378:metabolism; D009596:Nitrophenols / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology* / Q000627:therapeutic use*; D013449:Sulfonamides / Q000494:pharmacology; D014410:Tumor Stem Cell Assay; D020298:U937 Cells
chemical_list: C501332:ABT-737; D000970:Antineoplastic Agents; D051777:AraC Transcription Factor; D001713:Biphenyl Compounds; D007211:Indoles; C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D009596:Nitrophenols; D010879:Piperazines; D019253:Proto-Oncogene Proteins c-bcl-2; D011758:Pyrroles; D013449:Sulfonamides; C520962:obatoclax