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

• Published in: Cancer research (Chicago, Ill.) Vol. 64; no. 10; pp. 3607 - 3616
• Main Authors: HAO, Ji-Hui, MING YU, LIU, Feng-Ting, NEWLAND, Adrian C, LI JIA
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Association for Cancer Research 15.05.2004
• Subjects: Antineoplastic agents; Apoptosis - drug effects; Apoptosis Regulatory Proteins; bcl-2-Associated X Protein; Benzamides - pharmacology; Benzopyrans - pharmacology; Biological and medical sciences; Carbonyl Cyanide m-Chlorophenyl Hydrazone - pharmacology; Cytochromes c - secretion; Drug Synergism; HL-60 Cells; Humans; K562 Cells; Leukemia, T-Cell - drug therapy; Leukemia, T-Cell - metabolism; Leukemia, T-Cell - pathology; Medical sciences; Membrane Glycoproteins - pharmacology; Mitochondria - drug effects; Mitochondria - metabolism; Nitriles - pharmacology; Oxidative Phosphorylation - drug effects; Oxygen Consumption - drug effects; Pharmacology. Drug treatments; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - antagonists & inhibitors; TNF-Related Apoptosis-Inducing Ligand; Tumor Necrosis Factor-alpha - pharmacology; Tumors; Uncoupling Agents - pharmacology; Human; Mitochondria; Cell death; C-Onc gene; Leukemia; TNF related apoptosis inducing ligand; Malignant hemopathy; Inhibitor; Respiration; Protooncogene; Apoptosis
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.CAN-03-3648

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.