A molecular signature of dormancy in CD34+CD38- acute myeloid leukaemia cells.

Mazin Gh Al-Asadi,Grace Brindle,Monica Pallis,Marcos Castellanos,Claire H Seedhouse,Ken I Mills,Sean T May,Nigel H Russell

doi:10.18632/oncotarget.22808

Abstract

Dormant leukaemia initiating cells in the bone marrow niche are a crucial therapeutic target for total eradication of acute myeloid leukaemia. To study this cellular subset we created and validated an in vitro model employing the cell line TF-1a, treated with Transforming Growth Factor β1 (TGFβ1) and a mammalian target of rapamycin inhibitor. The treated cells showed decreases in total RNA, Ki-67 and CD71, increased aldehyde dehydrogenase activity, forkhead box 03A (FOX03A) nuclear translocation and growth inhibition, with no evidence of apoptosis or differentiation. Using human genome gene expression profiling we identified a signature enriched for genes involved in adhesion, stemness/inhibition of differentiation and tumour suppression as well as canonical cell cycle regulation. The most upregulated gene was the osteopontin-coding gene SPP1. Dormant cells also demonstrated significantly upregulated beta 3 integrin (ITGB3) and CD44, as well as increased adhesion to their ligands vitronectin and hyaluronic acid as well as to bone marrow stromal cells. Immunocytochemistry of bone marrow biopsies of AML patients confirmed the positive expression of osteopontin in blasts near the para-trabecular bone marrow, whereas osteopontin was rarely detected in mononuclear cell isolates. Unsupervised hierarchical clustering of the dormancy gene signature in primary acute myeloid leukaemia samples from the Cancer Genome Atlas identified a cluster enriched for dormancy genes associated with poor overall survival.

Highlights

Acute myeloid leukaemia (AML) is characterised by a high disease relapse rate despite initial induction of remission
Clonogenic growth was inhibited by Transforming Growth Factor β1 (TGFβ1) or rapamycin individually, and the combination of the two agents blocked the formation of colonies (>95% inhibition, Figure 1A)
TGFβ1 is reported to upregulate the stem-like properties of haematopoietic stem cells (HSC) [14] and leukaemia-initiating cells (LIC) [15], and AML cells with intermediate aldehyde dehydrogenase (ALDH) activity are reported to be highly represented in minimal residual disease AML samples [16]

Summary

Introduction

Acute myeloid leukaemia (AML) is characterised by a high disease relapse rate despite initial induction of remission. The leukaemia-initiating cells (LIC) that survive chemotherapy are likely to be enriched for a dormant subpopulation within the bone marrow niche [1]. The crosstalk between LICs and the bone marrow (BM) niche in which they reside has been implicated www.impactjournals.com/oncotarget in dormancy regulation. Leukaemia cells which are responsible for relapsed AML, similar to normal haematopoietic stem cells (HSCs), reside in a low perfusion microenvironment in the endosteal region of the bone marrow [2,3,4]. The scarcity of nutrients in the poorly-perfused niche is likely to contribute to leukaemia cell dormancy and resistance to chemotherapy. MTOR inhibition by rapamycin can be used to mimic shortage of nutrients [5, 6], and has been employed for the in vitro maintenance of haematopoietic stem cells [7]. The addition of mTOR inhibition to TGFβ1 was reported to potentiate the inhibitory effect of TGFβ1 in transformed cells [11]

Methods

Results

Conclusion