Aberrant activation of the PI3K/mTOR pathway promotes resistance to sorafenib in AML.

O Lindblad,J Vallon-Christersson,K Stegmaier,K Stegmaier,K Stegmaier,L Rönnstrand,K Haraldsson,N N Kabir,J U Kazi,J Sun,A Puissant,A Puissant,A Puissant,A Ramos,F Levander,Å Borg,M T Hemann,K Pietras,E Cordero,L Macaulay

doi:10.1038/onc.2016.41

Abstract

Therapy directed against oncogenic FLT3 has been shown to induce response in patients with acute myeloid leukemia (AML), but these responses are almost always transient. To address the mechanism of FLT3 inhibitor resistance, we generated two resistant AML cell lines by sustained treatment with the FLT3 inhibitor sorafenib. Parental cell lines carry the FLT3-ITD (tandem duplication) mutation and are highly responsive to FLT3 inhibitors, whereas resistant cell lines display resistance to multiple FLT3 inhibitors. Sanger sequencing and protein mass-spectrometry did not identify any acquired mutations in FLT3 in the resistant cells. Moreover, sorafenib treatment effectively blocked FLT3 activation in resistant cells, whereas it was unable to block colony formation or cell survival, suggesting that the resistant cells are no longer FLT3 dependent. Gene expression analysis of sensitive and resistant cell lines, as well as of blasts from patients with sorafenib-resistant AML, suggested an enrichment of the PI3K/mTOR pathway in the resistant phenotype, which was further supported by next-generation sequencing and phospho-specific-antibody array analysis. Furthermore, a selective PI3K/mTOR inhibitor, gedatolisib, efficiently blocked proliferation, colony and tumor formation, and induced apoptosis in resistant cell lines. Gedatolisib significantly extended survival of mice in a sorafenib-resistant AML patient-derived xenograft model. Taken together, our data suggest that aberrant activation of the PI3K/mTOR pathway in FLT3-ITD-dependent AML results in resistance to drugs targeting FLT3.

Highlights

Acute myeloid leukemia (AML) is a heterogeneous disease of the blood originating in the bone marrow
Dimethyl sulfoxide-treated cells responded to FLT3 ligand (FL) as expected, sorafenib-treated cells displayed poor FLT3 activation (Figure 1c), suggesting that sorafenib is still capable of inhibiting FLT3 activation in these resistant cells
We have shown that aberrant activation of the PI3K/mTOR pathway leads to FLT3 inhibitor resistance in AML, and that a dual PI3K/mTOR pathway inhibitor effectively blocks the growth of these resistant cells in vitro and in vivo

Summary

Introduction

Acute myeloid leukemia (AML) is a heterogeneous disease of the blood originating in the bone marrow. Overall survival of childhood AML has increased in the past decade, it still remains poor compared with that of childhood acute lymphoblastic leukemia. Survival rates in adults are quite poor and remain virtually unchanged over the last decade.[1] The molecular genetics of AML has been extensively studied. The receptor tyrosine kinase FLT3 is expressed at high levels in almost all AML, and 430% of AML bears an oncogenic FLT3 mutation.[2] The most common FLT3 mutation is an internal tandem duplication (ITD) of the sequence that encodes the juxtamembrane domain, which portends a poor prognosis. Other mutations include point mutations in the kinase domain

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Conclusion