This Article Full Text Full Text (PDF) Supplementary Data Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Konopleva, M. Articles by Andreeff, M. PubMed PubMed Citation Articles by Konopleva, M. Articles by Andreeff, M.

Mechanisms of Antileukemic Activity of the Novel Bcl-2 Homology Domain-3 Mimetic GX15-070 (Obatoclax)

¹ Section of Molecular Hematology and Therapy, Department of Stem Cell Transplantation and Cellular Therapy, Departments of ² Leukemia and ³ Experimental Diagnostic Imaging, The University of Texas M. D. Anderson Cancer Center, Houston, Texas and ⁴ Geminx, Inc., Malvern, Pennsylvania

Requests for reprints: Michael Andreeff, Section of Molecular Hematology and Therapy, Department of Stem Cell Transplantation and Cellular Therapy, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 448, Houston, TX 77030. Phone: 713-792-7261; Fax 713-794-4747; E-mail: mandreef{at}mdanderson.org.

Key Words: obatoclax • apoptosis • AML • Mcl-1 • BH3

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-G₂ cell-cycle block. Obatoclax induced apoptosis in AML CD34+ progenitor cells with an average IC₅₀ of 3.59 ± 1.23 µmol/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. [Cancer Res 2008;68(9):3413–20]