Abstract 965: An oncogenic metabolic switch mediates resistance to NOTCH1 inhibition in T-ALL
Authors: Herranz Daniel , Ambesi-Impiombato1 Alberto , Sudderth Jessica , Sánchez-Martín Marta , Tosello Valeria , Xu Luyao , Castillo Mireia , Cordon-Cardo Carlos , Kung Andrew L. , DeBerardinis Ralph J. , Ferrando Adolfo 
Published: May 2015

Abstract
Activating mutations of NOTCH1 are common in T-cell acute lymphoblastic leukemia (T-ALL), making NOTCH signaling a promising target for drugs such as γ-secretase inhibitors (GSIs), which block a proteolytic cleavage required for NOTCH activation. Aberrant activation of the PI3K-AKT pathway due to mutational loss of PTEN is found in 20% of human T-ALLs and has been linked with in vitro resistance to GSIs. Still, the specific mechanisms driving the antileukemic effects of NOTCH inhibition and the role of PTEN loss in resistance to anti-NOTCH therapies in T-ALL remain poorly understood. Here we used a mouse model of NOTCH1-induced leukemia built into conditional-inducible Pten knockout mice to demonstrate that genetic loss of Pten results in GSI resistance, accelerated mortality and progression under therapy in vivo. Importantly, gene expression profiling of tumor cells upon NOTCH inhibition showed that while NOTCH direct target genes are downregulated in both Pten-positive and Pten-deleted tumors, Pten loss results in global reversal of much of the transcriptional effects of NOTCH inhibition. Thus, Pten loss rescued the downregulation of genes involved in anabolic pathways and the upregulation of genes involved in catabolic pathways and autophagy induced by GSI treatment in Pten wild type leukemias. Consistently, electron microscopy and LC3 analysis demonstrated increased autophagy in NOTCH1 induced tumors upon GSI treatment, which was reversed upon Pten deletion. Moreover, global metabolomics analyses demonstrated that NOTCH inactivation induces a global anabolic shutdown in T-ALL with a marked block of glycolysis and glutaminolysis in Pten wild type tumor cells. Of note, flux studies using 13C-labeled glucose and 13C-labeled glutamine pointed to decreased metabolism with a specific block in glutaminolysis as critical effectors of the antileukemic effects of GSIs in T-ALL. Notably, each of the metabolic effects associated with NOTCH inhibition was effectively reversed upon genetic loss of Pten, supporting that metabolic rescue induced by Pten loss may mediate resistance to GSI therapy. Consistently, treatment with methyl pyruvate, a membrane soluble metabolite, effectively rescued the antileukemic effects of NOTCH inhibition, while, inhibition of glutaminolysis with a glutaminase inhibitor (BPTES) strongly and synergistically enhanced the antileukemic effects of NOTCH inhibition in T-ALL.
Overall, these results formally demonstrate that loss of PTEN induces in vivo resistance to NOTCH inhibition in T-ALL; highlight the fundamental role of NOTCH1 in the control of tumor cell metabolism; implicates sustained carbon metabolism induced by Pten loss as mechanism of resistance to GSI therapy; and provide the framework for the development of novel therapies targeting glutaminolysis and cell metabolism in T-ALL.
Citation Format: Daniel Herranz, Alberto Ambesi-Impiombato1, Jessica Sudderth, Marta Sánchez-Martín, Valeria Tosello, Luyao Xu, Mireia Castillo, Carlos Cordon-Cardo, Andrew L. Kung, Ralph J. DeBerardinis, Adolfo Ferrando. An oncogenic metabolic switch mediates resistance to NOTCH1 inhibition in T-ALL. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 965. doi:10.1158/1538-7445.AM2014-965