Multi-agent chemotherapy overcomes glucocorticoid resistance conferred by a BIM deletion polymorphism in pediatric acute lymphoblastic leukemia.

Sheila Xinxuan Soh,Nan Jiang,John W J Huang,Allen Eng Juh Yeoh,Joshua Yew Suang Lim,S Tiong Ong,Linda Bendall

doi:10.1371/journal.pone.0103435

Abstract

A broad range of anti-cancer agents, including glucocorticoids (GCs) and tyrosine kinase inhibitors (TKIs), kill cells by upregulating the pro-apoptotic BCL2 family member, BIM. A common germline deletion in the BIM gene was recently shown to favor the production of non-apoptotic BIM isoforms, and to predict inferior responses in TKI-treated chronic myeloid leukemia (CML) and EGFR-driven lung cancer patients. Given that both in vitro and in vivo GC resistance are predictive of adverse outcomes in acute lymphoblastic leukemia (ALL), we hypothesized that this polymorphism would mediate GC resistance, and serve as a biomarker of poor response in ALL. Accordingly, we used zinc finger nucleases to generate ALL cell lines with the BIM deletion, and confirmed the ability of the deletion to mediate GC resistance in vitro. In contrast to CML and lung cancer, the BIM deletion did not predict for poorer clinical outcome in a retrospective analysis of 411 pediatric ALL patients who were uniformly treated with GCs and chemotherapy. Underlying the lack of prognostic significance, we found that the chemotherapy agents used in our cohort (vincristine, L-asparaginase, and methotrexate) were each able to induce ALL cell death in a BIM-independent fashion, and resensitize BIM deletion-containing cells to GCs. Together, our work demonstrates how effective therapy can overcome intrinsic resistance in ALL patients, and suggests the potential of using combinations of drugs that work via divergent mechanisms of cell killing to surmount BIM deletion-mediated drug resistance in other cancers.

Highlights

Genome-wide profiling studies of acute lymphoblastic leukemia (ALL) have revealed it to be a highly heterogeneous disease [1]
Because human cell lines vary in their amenability to transfection and genome editing by zinc fingers, we tested the ability of our approach to edit 3 different GC-sensitive ALL cell lines (CCRF-CEM, RS4;11, and PALL-2) [39,40,41] that did not have the polymorphism
We used a genome-editing approach to demonstrate that a common germline variant in the BIM gene is sufficient to confer GC resistance in ALL cell lines

Summary

Introduction

Genome-wide profiling studies of acute lymphoblastic leukemia (ALL) have revealed it to be a highly heterogeneous disease [1]. There have been ongoing efforts to identify genetic factors that could account for this response heterogeneity and serve as prognostic markers for risk stratification or novel druggable targets in order to improve patient outcomes [4,5,6]. Studies correlating genetic variants with clinical phenotypes have been largely based on genetic epidemiology data and lack experimental validation at a mechanistic level. Such mechanistic studies have been hampered in part by the difficulty and cost of generating isogenic cell lines that either possess or lack a mutation of interest. A variety of methods that enable genome engineering to faithfully recapitulate mutations of interest have been developed and these will aid the functional validation of these variants in vitro [16]

Methods

Results

Conclusion