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Blood. 2016 Feb 18;127(7):882-92. doi: 10.1182/blood-2015-05-646497. Epub 2015 Aug 18.

Proteasome inhibitors induce FLT3-ITD degradation through autophagy in AML cells.

Author information

1
Cancer Research Center of Toulouse, Unité Mixte de Recherche (UMR)1037 INSERM, ERL5294 Centre National de la Recherche Scientifique (CNRS), Toulouse, France; Université Toulouse III Paul Sabatier, Toulouse, France;
2
Cancer Research Center of Toulouse, Unité Mixte de Recherche (UMR)1037 INSERM, ERL5294 Centre National de la Recherche Scientifique (CNRS), Toulouse, France; Université Toulouse III Paul Sabatier, Toulouse, France; Laboratoire d'Hématologie.
3
Service d'Hématologie, Institut Universitaire du Cancer de Toulouse Oncopole, Toulouse, France; Institut Cochin, Département Développement, Reproduction, Cancer, CNRS, UMR 8104, INSERM U1016, Paris, France; and.
4
Cancer Research Center of Toulouse, Unité Mixte de Recherche (UMR)1037 INSERM, ERL5294 Centre National de la Recherche Scientifique (CNRS), Toulouse, France; Université Toulouse III Paul Sabatier, Toulouse, France; Université Paris Descartes, Faculté de Médecine Sorbonne Paris Cité, Paris, France.

Abstract

Internal tandem duplication of the Fms-like tyrosine kinase-3 receptor (FLT3) internal tandem duplication (ITD) is found in 30% of acute myeloid leukemia (AML) and is associated with a poor outcome. In addition to tyrosine kinase inhibitors, therapeutic strategies that modulate the expression of FLT3-ITD are also promising. We show that AML samples bearing FLT3-ITD mutations are more sensitive to proteasome inhibitors than wild-type samples and this sensitivity is strongly correlated with a higher FLT3-ITD allelic burden. Using pharmacologic inhibitors of autophagy, specific downregulation of key autophagy proteins including Vps34, autophagy gene (Atg)5, Atg12, Atg13, biochemical, and microscopy studies, we demonstrated that proteasome inhibitors induced cytotoxic autophagy in AML cells. FLT3-ITD molecules were detectable within autophagosomes after bortezomib treatment indicating that autophagy induction was responsible for the early degradation of FLT3-ITD, which preceded the inhibition of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK), PI3K/AKT, and STAT5 pathways, and subsequent activation of cell death. Moreover, proteasome inhibitors overcome resistance to quizartinib induced by mutations in the kinase domain of FLT3, suggesting that these compounds may prevent the emergence of mutant clones arising from tyrosine kinase inhibitor treatments. In xenograft mice models, bortezomib stimulated the conversion of LC3-I to LC3-II, indicating induction of autophagy in vivo, downregulated FLT3-ITD protein expression and improved overall survival. Therefore, selecting patients according to FLT3-ITD mutations could be a new way to detect a significant clinical activity of proteasome inhibitors in AML patients.

PMID:
26286850
DOI:
10.1182/blood-2015-05-646497
[Indexed for MEDLINE]
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