Department of Surgery, Oncology, and Gastroenterology, University of Padova, Padova, Italy
Gloria Scattolin
Department of Surgery, Oncology, and Gastroenterology, University of Padova, Padova, Italy
Barbara Buldini
Pediatric Hemato Oncology, Maternal and Child Health Department, University of Padova, Padova, Italy
Samuela Francescato
Pediatric Hemato Oncology, Maternal and Child Health Department, University of Padova, Padova, Italy
Giuseppe Basso
Pediatric Hemato Oncology, Maternal and Child Health Department, University of Padova, Padova, Italy; Italian Institute for Genomic Medicine, Turin, Italy
Sonia A. Minuzzo
Department of Surgery, Oncology, and Gastroenterology, University of Padova, Padova, Italy
Stefano Indraccolo
Veneto Institute of Oncology IOV – IRCCS, Padova, Italy; Department of Surgery, Oncology, and Gastroenterology, University of Padova, Padova, Italy
Donna M. D'Agostino
Veneto Institute of Oncology IOV – IRCCS, Padova, Italy; Department of Biomedical Sciences, University of Padova, Padova, Italy
Vincenzo Ciminale
Veneto Institute of Oncology IOV – IRCCS, Padova, Italy; Department of Surgery, Oncology, and Gastroenterology, University of Padova, Padova, Italy; Corresponding author. postal address: Oncology and Immunology Section, Department of Surgery, Oncology and Gastroenterology, University of Padova, Via Gattamelata 64, 35128 Padova, Italy.
mTOR activation is a hallmark of T-cell acute lymphoblastic leukemia (T-ALL) and is associated with resistance to glucocorticoid (GC)-based chemotherapy. We previously showed that altering redox homeostasis primes T-ALL cells to GC-induced apoptosis. Here we investigated the connection between the mTOR pathway and redox homeostasis using pharmacological inhibitors and gene silencing.In vitro studies performed on T-ALL cell lines and CG-resistant patient-derived T-ALL xenograft (PDX) cells showed that the mTOR inhibitor everolimus increased reactive oxygen species (ROS) levels, augmented lipid peroxidation, and activated the ROS-controlled transcription factor NRF2. These effects were accompanied by a decrease in the levels of NADPH and of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway (PPP), which is a major source of cytosolic NADPH needed for maintaining the cellular ROS-scavenging capacity. The mTOR inhibitor everolimus induced mitochondrial inner membrane depolarization and dose-dependent apoptosis of T-ALL cells, but did not kill normal T-cells. Importantly, the combination of everolimus and the GC dexamethasone had a synergistic effect on killing T-ALL cells. The effects of mTOR inhibition were blunted by ROS scavengers and phenocopied by siRNA-mediated G6PD silencing. In vivo studies of NOD/SCID mice inoculated with refractory T-ALL PDX demonstrated that everolimus overcame dexamethasone resistance in conditions of high tumor burden that mimicked the clinical setting of acute leukemia.These findings provide insight into the crosstalk between mTOR and ROS homeostasis in T-ALL cells and furnish mechanistic evidence to support the combination of glucocorticoids with mTOR inhibitors as a therapeutic avenue for treating refractory T-ALL.
