Journal Article

Sequential Dosing in Chemosensitization: Targeting the PI3K/Akt/mTOR Pathway in Neuroblastoma

Westhoff, Mike-Andrew, Enzenmüller, Stefanie, Faham, Najmeh, Marx, Daniela, Gonzalez, Patrick, Nonnenmacher, Lisa, Fulda, Simone, Jennewein, Claudia, Debatin, Klaus-Michael

2013

Overview

Breaking resistance to chemotherapy is a major goal of combination therapy in many tumors, including advanced neuroblastoma. We recently demonstrated that increased activity of the PI3K/Akt network is associated with poor prognosis, thus providing an ideal target for chemosensitization. Here we show that targeted therapy using the PI3K/mTOR inhibitor NVP-BEZ235 significantly enhances doxorubicin-induced apoptosis in neuroblastoma cells. Importantly, this increase in apoptosis was dependent on scheduling: while pretreatment with the inhibitor reduced doxorubicin-induced apoptosis, the sensitizing effect in co-treatment could further be increased by delayed addition of the inhibitor post chemotherapy. Desensitization for doxorubicin-induced apoptosis seemed to be mediated by a combination of cell cycle-arrest and autophagy induction, whereas sensitization was found to occur at the level of mitochondria within one hour of NVP-BEZ235 posttreatment, leading to a rapid loss of mitochondrial membrane potential with subsequent cytochrome c release and caspase-3 activation. Within the relevant time span we observed marked alterations in a ∼30 kDa protein associated with mitochondrial proteins and identified it as VDAC1/Porin protein, an integral part of the mitochondrial permeability transition pore complex. VDAC1 is negatively regulated by the PI3K/Akt pathway via GSK3β and inhibition of GSK3β, which is activated when Akt is blocked, ablated the sensitizing effect of NVP-BEZ235 posttreatment. Our findings show that cancer cells can be sensitized for chemotherapy induced cell death - at least in part - by NVP-BEZ235-mediated modulation of VDAC1. More generally, we show data that suggest that sequential dosing, in particular when multiple inhibitors of a single pathway are used in the optimal sequence, has important implications for the general design of combination therapies involving molecular targeted approaches towards the PI3K/Akt/mTOR signaling network.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: 1-Phosphatidylinositol 3-kinase / Ablation / AKT protein / Anthracyclines / Antineoplastic Agents - administration & dosage / Antineoplastic Combined Chemotherapy Protocols - administration & dosage / Apoptosis / Apoptosis - drug effects / Authorship / B cells / Biology / Breast cancer / Cancer / Cancer therapies / Caspase / Caspase-3 / Cell cycle / Cell death / Cell Line, Tumor / Chemosensitization / Chemotherapy / Cytochrome / Cytochrome c / Desensitization / Doxorubicin / Doxorubicin - administration & dosage / Drug dosages / Drug Synergism / Enzyme Inhibitors - administration & dosage / Fatalities / Glycogen Synthase Kinase 3 - antagonists & inhibitors / Glycogen Synthase Kinase 3 beta / Humans / Imidazoles - administration & dosage / Inhibitors / Kinases / Medical prognosis / Medicine / Membrane permeability / Membrane potential / Membrane Potential, Mitochondrial - drug effects / Mitochondria / Mitochondrial permeability transition pore / Neuroblastoma / Neuroblastoma - drug therapy / Neuroblastoma - metabolism / Neuroblastoma - pathology / Neuroblastoma cells / Neuroblasts / Pediatrics / Permeability / Phagocytosis / Phosphatidylinositol 3-Kinases - antagonists & inhibitors / Prognosis / Proteins / Proto-Oncogene Proteins c-akt - antagonists & inhibitors / Quinolines - administration & dosage / Sensitizing / Sequential scheduling / Signal Transduction - drug effects / Signaling / TOR protein / TOR Serine-Threonine Kinases - antagonists & inhibitors / Tumors / Voltage-Dependent Anion Channel 1 - metabolism