Abstract PR05: Clonal evolution enhances leukemia-propagating cell activity in T-cell acutelymphoblastic leukemia through AKT/mTORC1 pathway activation
Authors: Blackburn Jessica , Liu Sali , Martinez Sarah , Dobrinski Kimberly , Moore Finola , Lobbardi Riadh , Langenau David 
Published: May 2015

Abstract
Leukemia progression and relapse are driven by molecularly distinct and often-rare cancer cells called leukemia-propagating cells (LPCs). If LPCs are retained following treatment, they will ultimately initiate relapse disease. Despite the substantial number of genetic lesions that have been identified in relapse samples and the contention that these mutations likely modulate response to therapy, acquired mutations that increase the overall frequency of tumor propagating cells following continued clonal evolution have not been reported in any cancer to date. Here, we have developed a transgenic zebrafish model where single fluorescently-labeled T-cell acute lymphoblastic leukemia (T-ALL) cells are transplanted into genetically identical recipient fish and functionally assessed for differences in leukemia propagating cell frequency, growth, and dexamethasone resistance. While subclonal variation was observed within single cells from the same primary leukemia, a subset of clones continued to evolve genetic lesions and epigenetic modifications to enhance growth and overall LPC frequency. A majority of evolved clones acquired activated AKT signaling, which simultaneously increased the number of leukemia propagating cells through activating the mTORC1 pathway, enhanced growth by stabilizing Myc protein levels, and rendered T-ALL cells resistant to dexamethasone, which was reversed by combined treatment with an AKT inhibitor. These results were confirmed using large-scale transgenic epistasis experiments and limiting-dilution cell transplantation studies. In total, our data suggest that diagnosis clones can stochastically acquire mutations necessary to survive treatment and drive relapse even before a patient begins treatment, with acquired mutations being independently selected based on important cancer phenotypes including elevated growth rate and leukemia propagating potential. Moreover, our work also identifies combination therapies that utilize dexamethasone and AKT inhibitor can kill LPCs in a subset of refractory T-ALL. Finally, these are the first studies performed in any model to follow single cell evolution as it relates to relapse, utilizing in excess of 6,000 transplant recipient animals and opening new and exciting avenues of study to uncover genetic pathways that drive cancer malignancy.
This abstract is also presented as Poster B23.
Citation Format: Jessica Blackburn, Sali Liu, Sarah Martinez, Kimberly Dobrinski, Finola Moore, Riadh Lobbardi, David Langenau. Clonal evolution enhances leukemia-propagating cell activity in T-cell acutelymphoblastic leukemia through AKT/mTORC1 pathway activation. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr PR05.