Recreating the Bone Marrow Microenvironment to Model Leukemic Stem Cell Quiescence

Abstract

The main challenge in the treatment of acute myeloid leukemia (AML) is relapse, as it has no good treatment options and 90% of relapsed patients die as a result. It is now well accepted that relapse is due to a persisting subset of AML cells known as leukemia-initiating cells or leukemic stem cells (LSCs). Hematopoietic stem cells (HSCs) reside in the bone marrow microenvironment (BMM), a specialized niche that coordinates HSC self-renewal, proliferation, and differentiation. HSCs are divided into two types: long-term HSCs (LT-HSCs) and short-term HSCs, where LT-HSCs are typically quiescent and act as a reserve of HSCs. Like LT-HSCs, a quiescent population of LSCs also exist. Like LT-HSCs, quiescent LSCs have low metabolic activity and receive pro-survival signals from the BMM, making them resistant to drugs, and upon discontinuation of therapy, they can become activated and re-establish the disease. Several studies have shown that the activation of quiescent LSCs may sensitize them to cytotoxic drugs. However, it is very difficult to experimentally model the quiescence-inducing BMM. Here we report that culturing AML cells with bone marrow stromal cells, transforming growth factor beta-1 and hypoxia in a three-dimensional system can replicate the quiescence-driving BMM. A quiescent-like state of the AML cells was confirmed by reduced cell proliferation, increased percentage of cells in the G0 cell cycle phase and a decrease in absolute cell numbers, expression of markers of quiescence, and reduced metabolic activity. Furthermore, the culture could be established as co-axial microbeads, enabling high-throughput screening, which has been used to identify combination drug treatments that could break BMM-mediated LSC quiescence, enabling the eradication of quiescent LSCs.

Understanding the interaction between leukaemia stem cells and their microenvironment to improve therapeutic approaches

“…Currently, there are many efforts to develop in vitro 3D systems to model the leukaemic niche. Examples of such systems include BM‐MSCs trapped in scaffolds (Aljitawi et al, 2014; O'Reilly, Zeinabad, Nolan, et al, 2021), and scaffolds built with decellularized material (Li et al, 2018). These systems provide the opportunity to study leukaemic cell responses in the context of a microenvironment.…”

Drug Resistance Mechanisms of Acute Myeloid Leukemia Stem Cells

“…Cell populations with low ROS were rich in quiescent LSCs, which was associated with drug resistance/ recurrence, compared to cell populations with high ROS (63). Eimear OR et al simulated BM-induced dormancy of KG1a cells in vitro by using a hydrogel-based layered co-culture system based on bone mesenchymal stem cells (BMSCs), adding TNFb-1 and HIFs (64). This model is valuable for targeted drugs screening to treat dormant LSCs in the microenvironment.…”

“…Eimear OR et al. simulated BM-induced dormancy of KG1a cells in vitro by using a hydrogel-based layered co-culture system based on bone mesenchymal stem cells (BMSCs), adding TNFβ-1 and HIFs ( 64 ). This model is valuable for targeted drugs screening to treat dormant LSCs in the microenvironment.…”

Chronic myeloid leukemia: cytogenetics and molecular biology’s part in the comprehension and management of the pathology and treatment evolution

“…The microenvironment is also involved in resistance via surrounding stromal cells which act on LSCs by stopping their cell cycle through growth factors and cytokines [39]. For example CXCR4, a chemokine receptor, is inhibited by the oncoprotein BCR-ABL1, causing the modification of the interactions between the medullary stroma and the LSCs [40]. TKI resistance generates TKI failure which is manifested on the cytogenetic level by the appearance of ACA.…”