Bcl-2 resistant mitochondrial toxicity mediated by the isoquinoline carboxamide PK11195 involves de novo generation of reactive oxygen species

• Published in: British journal of cancer Vol. 84; no. 10; pp. 1397 - 1404
• Main Authors: FENNELL, D. A, CORBO, M, PALLASKA, A, COTTER, F. E
• Format: Journal Article
• Language: English
• Published: Basingstoke Nature Publishing Group 18-05-2001
• Subjects: Antineoplastic agents; Antineoplastic Agents - toxicity; Apoptosis; Benzodiazepines; Biological and medical sciences; Cancer research; Cancer therapies; Cell culture; Cell death; Cell Death - drug effects; Cytotoxicity; Dose-Response Relationship, Drug; General aspects; Genes, bcl-2; HL-60 Cells; Humans; Hydrogen Peroxide - metabolism; Intracellular Membranes - drug effects; Intracellular Membranes - physiology; Isoquinolines - toxicity; K562 Cells; Ligands; Lymphoma; Medical research; Medical sciences; Membrane Potentials - drug effects; Mitochondria - drug effects; Mitochondria - physiology; Mitochondrial DNA; Oxidative stress; Permeability; Pharmacology. Drug treatments; Physiology; PK 11195; Proteins; Proto-Oncogene Proteins c-bcl-2 - genetics; Proto-Oncogene Proteins c-bcl-2 - metabolism; Reactive Oxygen Species - physiology; Receptors, GABA-A - drug effects; Receptors, GABA-A - physiology; Regular; Toxicity; Transfection; Tumor Cells, Cultured; United Kingdom > UK; Antineoplastic agent; Human; Promyelocytic leukemia; Oxidative stress; Isoquinoline derivatives; Acute; Cytotoxicity; Malignant hemopathy; Benzodiazepine receptor; In vitro; HL60 cell line; Mitochondria; C-Onc gene; Established cell line; Carboxamide; Mechanism of action; Protooncogene
• ISSN: 0007-0920; 1532-1827; 1532-1827
• DOI: 10.1054/bjoc.2001.1788

Resistance to apoptosis is a major obstacle preventing effective therapy for malignancy. Mitochondria localized anti-death proteins of the Bcl-2 family play a central role in inhibiting apoptosis and therefore present valid targets for novel therapy. The peripheral benzodiazepine receptor (PBR) shares a close physical association with the permeability transition pore complex (PTPC), a pivotal regulator of cell death located at mitochondrial contact sites. In this study we investigated the cytotoxicity of the PBR ligand, PK11195, in the micromolar concentration range. PK11195 induced antioxidant inhibitable collapse of the inner mitochondrial membrane potential (DeltaPsi(m)) and mitochondrial swelling in HL60 human leukaemia cells, but not in SUDHL4 lymphoma cells (which exhibited a higher level of reduced glutathione and relative tolerance to chemotherapy or pro-oxidant induced DeltaPsi(m)dissipation). PK11195 induced the production of hydrogen peroxide that was not inhibited by Bcl-2 transfection, nor depletion of mitochondrial DNA. ROS production was however blocked by protonophore, implicating a requirement for DeltaPsi(m). Our findings suggest that PK11195-induced cytotoxicity relies upon Bcl-2 resistant generation of oxidative stress; a process only observed at concentrations several orders of magnitude higher that required to saturate its receptor.