Inhibition of Endosteal Vascular Niche Remodeling Rescues Hematopoietic Stem Cell Loss in AML

Delfim Duarte,Reema Khorshed,Olufolake Akinduro,Isabella Y Kong,Nicola Ruivo,Cristina Lo Celso,Stephin J Vervoort,Ralf H Adams,Tom S Weber,Katia De Filippo,Lenny Straszkowski,Heather Ang,Myriam Haltalli,Catriona Mclean,Anjali P Kusumbe,Edwin D Hawkins,Saravana K Ramasamy,Chiara Pirillo,Louise E Purton,Leo M Carlin,Ken R Duffy ,Andrew H Wei

doi:10.1016/j.stem.2017.11.006

Abstract

SummaryBone marrow vascular niches sustain hematopoietic stem cells (HSCs) and are drastically remodeled in leukemia to support pathological functions. Acute myeloid leukemia (AML) cells produce angiogenic factors, which likely contribute to this remodeling, but anti-angiogenic therapies do not improve AML patient outcomes. Using intravital microscopy, we found that AML progression leads to differential remodeling of vasculature in central and endosteal bone marrow regions. Endosteal AML cells produce pro-inflammatory and anti-angiogenic cytokines and gradually degrade endosteal endothelium, stromal cells, and osteoblastic cells, whereas central marrow remains vascularized and splenic vascular niches expand. Remodeled endosteal regions have reduced capacity to support non-leukemic HSCs, correlating with loss of normal hematopoiesis. Preserving endosteal endothelium with the small molecule deferoxamine or a genetic approach rescues HSCs loss, promotes chemotherapeutic efficacy, and enhances survival. These findings suggest that preventing degradation of the endosteal vasculature may improve current paradigms for treating AML.

Highlights

Intravital Microscopy Enables the Study of Acute myeloid leukemia (AML) Cells, Healthy Hematopoietic Cells, and the bone marrow (BM) Microenvironment Simultaneously To study the effects of AML growth on BM vasculature and hematopoietic stem cells (HSCs) as disease propagates through the tissue, we used the well-established MLL-AF9-driven murine model of AML, which recapitulates phenotypic and pathological features of human MLL-rearranged AML (Krivtsov et al, 2006; Somervaille and Cleary, 2006)
Progressive blast expansion was observed from days 8 to 10 post-transplantation with full BM infiltration typically reached between day 20 and 28, with the variation depending on the source of the primary blasts analyzed
AML cells, vasculature, and hematopoietic cells were visualized by intravital microscopy (IVM) performed on mouse calvarium BM (Figure 1C), which has been shown to be representative of long bones’ marrow in terms of stroma composition and ability to support functional HSCs and their homing and engraftment (Lassailly et al, 2013; Lo Celso et al, 2009)

Summary

Methods

For DFO treatment, daily 100mg/kg deferoxamine mesylate (DFO; Sigma) was administered I.P. from day 8 until day 22 posttransplantation of AML blasts, at which time mice were sacrificed and their BM analyzed. Induction chemotherapy for AML was administered when BM infiltration was over 50% by injecting 100mg/kg cytarabine (Ara-C) I.V. for 5 days and 3mg/kg doxorubicin (Doxo) for 3 days. Ara-C was co-delivered with Doxo on days 1 to 3 and alone on days 4 and 5, mimicking the 7+3 regimen used in AML patients (Wunderlich et al, 2013). Both drugs were purchased from Sellekchem, MA or obtained from the Imperial College Healthcare NHS Trust

Results

Discussion

Conclusion