Bcl-2 inhibitors sensitize tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis by uncoupling of mitochondrial respiration in human leukemic CEM cells

Cancer Res. 2004 May 15;64(10):3607-16. doi: 10.1158/0008-5472.CAN-03-3648.

Abstract

Previous studies have shown that the lymphoblastic leukemia CEM cell line is resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis because of a low expression of caspase-8. Bcl-2 inhibitors, BH3I-2' and HA14-1, are small cell-permeable nonpeptide compounds, are able to induce apoptosis by mediating cytochrome c release, and also lead to dissipation of the mitochondrial membrane potential (DeltaPsim). This study aimed to use the Bcl-2 inhibitors to sensitize CEM cells to TRAIL-induced apoptosis by switching on the mitochondrial apoptotic pathway. We found that a low dose of BH3I-2' or HA14-1, which did not induce cytochrome c release, greatly sensitized CEM cells to TRAIL-induced apoptosis. In a similar manner to the classical uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP), both BH3I-2' and HA14-1 induced a reduction in DeltaPsim, a generation of reactive oxygen species (ROS), an increased mitochondrial respiration, and a decreased ATP synthesis. This uncoupling function of the Bcl-2 inhibitors was responsible for the synergy with TRAIL-induced apoptosis. CCCP per se did not induce apoptosis but again sensitized CEM cells to TRAIL-induced apoptosis by uncoupling mitochondrial respiration. The uncoupling effect facilitated TRAIL-induced Bax conformational change and cytochrome c release from mitochondria. Inhibition of caspases failed to block TRAIL-mediated cell death when mitochondrial respiration was uncoupled. We observed that BH3I-2', HA14-1, or CCCP can overcome resistance to TRAIL-induced apoptosis in TRAIL-resistant cell lines, such as CEM, HL-60, and U937. Our results suggest that the uncoupling of mitochondrial respiration can sensitize leukemic cells to TRAIL-induced apoptosis. However, caspase activation per se does not represent an irreversible point of commitment to TRAIL-induced cell death when mitochondrial respiration is uncoupled.

MeSH terms

  • Apoptosis / drug effects*
  • Apoptosis Regulatory Proteins
  • Benzamides / pharmacology*
  • Benzopyrans / pharmacology*
  • Carbonyl Cyanide m-Chlorophenyl Hydrazone / pharmacology
  • Cytochromes c / metabolism
  • Drug Synergism
  • HL-60 Cells
  • Humans
  • K562 Cells
  • Leukemia, T-Cell / drug therapy*
  • Leukemia, T-Cell / metabolism
  • Leukemia, T-Cell / pathology
  • Membrane Glycoproteins / pharmacology*
  • Mitochondria / drug effects*
  • Mitochondria / metabolism
  • Nitriles / pharmacology*
  • Oxidative Phosphorylation / drug effects
  • Oxygen Consumption / drug effects
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / antagonists & inhibitors*
  • TNF-Related Apoptosis-Inducing Ligand
  • Tumor Necrosis Factor-alpha / pharmacology*
  • Uncoupling Agents / pharmacology*
  • bcl-2-Associated X Protein

Substances

  • 3-iodo-5-chloro-N-(2-chloro-5-((4-chlorophenyl)sulphonyl)phenyl)-2-hydroxybenzamide
  • Apoptosis Regulatory Proteins
  • BAX protein, human
  • Benzamides
  • Benzopyrans
  • Membrane Glycoproteins
  • Nitriles
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • TNF-Related Apoptosis-Inducing Ligand
  • TNFSF10 protein, human
  • Tumor Necrosis Factor-alpha
  • Uncoupling Agents
  • bcl-2-Associated X Protein
  • ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate
  • Carbonyl Cyanide m-Chlorophenyl Hydrazone
  • Cytochromes c