Dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor NVP-BEZ235 synergizes with chloroquine to induce apoptosis in embryonal rhabdomyosarcoma.

Abstract

Aberrant activation of the phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) pathway has been reported for rhabdomyosarcoma (RMS) and is implicated in survival of tumor cells as well as therapeutic resistance. In the present study, we searched for combination therapies with the dual PI3K/mTOR inhibitor NVP-BEZ235 (BEZ235) in RMS. Here, we identify a synthetic lethal interaction of BEZ235 together with the lysosomotropic agent chloroquine (CQ), which is effective against embryonal rhabdomyosarcoma (ERMS). BEZ235 and CQ at subtoxic concentrations synergize to induce apoptosis in ERMS cells, as confirmed by calculation of combination index (CI). BEZ235 and CQ cooperate to activate caspase-9, -3 and -8, which is crucial for apoptosis induction given that the broad-range caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD.fmk) blocks BEZ235/CQ-induced apoptosis. Additionally, pharmacological inhibition of lysosomal enzymes significantly reduces BEZ235/CQ-induced apoptosis, indicating concomitant activation of the lysosomal compartment. Importantly, BEZ235/CQ-induced apoptosis is significantly inhibited by antioxidants, implying that increased oxidative stress contributes to BEZ235/CQ-induced cell death. Importantly, our molecular studies reveal that BEZ235/CQ-induced apoptosis is mediated by cooperative downregulation of the antiapoptotic BCL-2 family protein MCL-1, since stabilization of MCL-1 by expression of a non-degradable MCL-1 phospho-defective mutant significantly decreases BEZ235/CQ-induced apoptosis. Also, overexpression of antiapoptotic BCL-2 leads to a significant reduction of BEZ235/CQ-induced apoptosis, emphasizing that an intact mitochondrial pathway of apoptosis is required for BEZ235/CQ-induced cell death. This identification of a synthetic lethality of BEZ235 and CQ has important implications for the development of molecular targeted therapies for RMS.

• Authors: Manuela Hugle, Simone Fulda
• Journal: Cancer letters (Cancer Lett) Vol. 360 Issue 1 Pg. 1-9 (Apr 28 2015) ISSN: 1872-7980 [Electronic] Ireland
• PMID: 25637161 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

Chemical References

• BCL2 protein, human
• Imidazoles
• MCL1 protein, human
• Myeloid Cell Leukemia Sequence 1 Protein
• Phosphoinositide-3 Kinase Inhibitors
• Protein Kinase Inhibitors
• Proto-Oncogene Proteins c-bcl-2
• Quinolines
• Reactive Oxygen Species
• Chloroquine
• MTOR protein, human
• Phosphatidylinositol 3-Kinase
• TOR Serine-Threonine Kinases
• Caspases
• dactolisib

Topics

• Antineoplastic Combined Chemotherapy Protocols (pharmacology)
• Apoptosis (drug effects)
• Caspases (metabolism)
• Cell Line, Tumor
• Chloroquine (pharmacology)
• Dose-Response Relationship, Drug
• Drug Synergism
• Enzyme Activation
• Humans
• Imidazoles (pharmacology)
• Lysosomes (drug effects, enzymology)
• Molecular Targeted Therapy
• Mutation
• Myeloid Cell Leukemia Sequence 1 Protein (genetics, metabolism)
• Phosphatidylinositol 3-Kinase (metabolism)
• Phosphoinositide-3 Kinase Inhibitors
• Protein Kinase Inhibitors (pharmacology)
• Proto-Oncogene Proteins c-bcl-2 (genetics, metabolism)
• Quinolines (pharmacology)
• Reactive Oxygen Species (metabolism)
• Rhabdomyosarcoma, Embryonal (enzymology, genetics, pathology)
• Signal Transduction (drug effects)
• TOR Serine-Threonine Kinases (antagonists & inhibitors, metabolism)
• Transfection