MEK Inhibition Sensitizes Precursor B-Cell Acute Lymphoblastic Leukemia (B-ALL) Cells to Dexamethasone through Modulation of mTOR Activity and Stimulation of Autophagy

PLoS One. 2016 May 19;11(5):e0155893. doi: 10.1371/journal.pone.0155893. eCollection 2016.

Abstract

Resistance to glucocorticosteroids (GCs) is a major adverse prognostic factor in B-ALL, but the molecular mechanisms leading to GC resistance are not completely understood. Herein, we sought to elucidate the molecular background of GC resistance in B-ALL and characterize the therapeutic potential of targeted intervention in these mechanisms. Using exploratory bioinformatic approaches, we found that resistant cells exhibited significantly higher expression of MEK/ERK (MAPK) pathway components. We found that GC-resistant ALL cell lines had markedly higher baseline activity of MEK and small-molecule MEK1/2 inhibitor selumetinib increased GCs-induced cell death. MEK inhibitor similarly increased in vitro dexamethasone activity in primary ALL blasts from 19 of 22 tested patients. To further confirm these observations, we overexpressed a constitutively active MEK mutant in GC-sensitive cells and found that forced MEK activity induced resistance to dexamethasone. Since recent studies highlight the role GC-induced autophagy upstream of apoptotic cell death, we assessed LC3 processing, MDC staining and GFP-LC3 relocalization in cells incubated with either DEX, SEL or combination of drugs. Unlike either drug alone, only their combination markedly increased these markers of autophagy. These changes were associated with decreased mTOR activity and blocked 4E-BP1 phosphorylation. In cells with silenced beclin-1 (BCN1), required for autophagosome formation, the synergy of DEX and SEL was markedly reduced. Taken together, we show that MEK inhibitor selumetinib enhances dexamethasone toxicity in GC-resistant B-ALL cells. The underlying mechanism of this interaction involves inhibition of mTOR signaling pathway and modulation of autophagy markers, likely reflecting induction of this process and required for cell death. Thus, our data demonstrate that modulation of MEK/ERK pathway is an attractive therapeutic strategy overcoming GC resistance in B-ALL patients.

MeSH terms

  • Apoptosis
  • Autophagy*
  • Benzimidazoles / pharmacology
  • Cell Death
  • Cell Line, Tumor
  • Computational Biology
  • Dexamethasone / pharmacology*
  • Flow Cytometry
  • Gene Expression Regulation, Enzymologic
  • Humans
  • MAP Kinase Kinase Kinase 1 / antagonists & inhibitors
  • MAP Kinase Kinase Kinase 1 / metabolism*
  • MAP Kinase Signaling System
  • Microscopy, Fluorescence
  • Precursor B-Cell Lymphoblastic Leukemia-Lymphoma / drug therapy*
  • Precursor B-Cell Lymphoblastic Leukemia-Lymphoma / pathology
  • RNA, Small Interfering / metabolism
  • TOR Serine-Threonine Kinases / metabolism*

Substances

  • AZD 6244
  • Benzimidazoles
  • RNA, Small Interfering
  • Dexamethasone
  • MTOR protein, human
  • TOR Serine-Threonine Kinases
  • MAP Kinase Kinase Kinase 1

Grant support

This work has been supported solely by a National Science Center grant, #NCN/2011/01/B/NZ4/04829.