Inhibition of Bcl-2 antiapoptotic members by obatoclax potently enhances sorafenib-induced apoptosis in human myeloid leukemia cells through a Bim-dependent process

Abstract

Interactions between the multikinase in-hibitor sorafenib and the BH3-mimetic obatoclax (GX15-070) were examined in human acute myeloid leukemia (AML) cells. Treatment with sorafenib/obatoclax induced pronounced apoptosis in and reduced the clonogenic growth of multiple AML lines and primary AML cells but not normal CD34 cells. Sorafenib triggered rapid and pronounced Mcl-1 down-regulation accompanied by enhanced binding of Bim to Bcl-2 and Bcl-xL, effects that were abolished by obatoclax coadministration. Notably, shRNA knock-down of Bim, Bak, or Bax, but not Noxa, significantly attenuated obatoclax/ sorafenib lethality, whereas ectopic expression of Mcl-1 exerted a protective effect. Furthermore, exposure of leuke-mia cells to sorafenib and obatoclax markedly induced autophagy, reflected by rapid and pronounced LC3 processing and LC3-green fluorescent protein (GFP) punctate formation. Multiple autophagy inhibitors or VPS34 knockdown, significantly potentiated sorafenib/obatoclax lethality, indicating a cytoprotective role for autophagy in this setting. Finally, studies in a xenograft mouse model revealed that combined sorafenib/obatoclax treatment markedly reduced tumor growth and significantly prolonged survival in association with Mcl-1 down-regulation and apoptosis induction, whereas agents administered individually had only modest effects. These findings suggest that combining sorafenib with agents that inhibit Mcl-1 and Bcl-2/Bcl-xL such as obatoclax may represent a novel and potentially effective strategy in AML. (Blood. 2012; 119(25):6089-6098)

Degradation of Keap1 activates BH3-only proteins Bim and PUMA during hepatocyte lipoapoptosis

“…GFP-LC3 lentiviral particles have been described previously. 53 After PA treatment, cells overexpressing GFP-LC3 were fixed with freshly prepared 4% paraformaldehyde in phosphate-buffered saline for 10 min at 37 1C, mounted onto slides in medium containing DAPI (Prolong Gold Antifade, Molecular Probes, Eugene, OR, USA) and analyzed using a Nikon Eclipse Ti confocal microscope. Individual cellular fluorescence was visualized using excitation and emission filters of 490 and 520 nm, respectively.…”

Targeting the mitochondria in acute myeloid leukemia

“…BH3 mimetic obatoclax combined with tyrosine kinase inhibitor sorafenib potentiated apoptosis and reduced clonogenic growth of primary AML cells and AML cell lines. Additionally, this combined treatment in a xenograft mouse model reduced tumor growth, induced apoptosis, and prolonged survival [27]. In another study, Bcl-2/Bcl-xL antagonist ABT-737 combined with mammalian Target of Rapamycin complex 1 and 2 (mTORC1/2) inhibitor INK128 induced cell death in various AML cell lines and primary AML cells carrying mutations in FLT3, IDH2, NPM1 and kirsten rat sarcoma viral oncogene homolog (Kras) genes.…”

CAF-Secreted IGFBPs Regulate Breast Cancer Cell Anoikis

“…Given the well-documented role that Bcl-2 family members play in modulating cytochrome c release from the mitochondria (22), we hypothesized that Bcl-2 family members were regulated in some fashion by CAF-secreted factors. To address this possibility, we treated 10A cells that were exposed to conditioned media with obatoclax, a drug that mimics the actions of pro-apoptotic BH3 only proteins by interfering with antiapoptotic Bcl-2 family members (23). As expected, addition of obatoclax to 10A cells treated with CAF conditioned media reversed the protection from caspase activation (Fig.…”