The field of regenerative medicine holds considerable promise for treating diseases that are currently intractable. Although many researchers are adopting the strategy of cell transplantation for ...tissue repair, an alternative approach to therapy is to manipulate the stem cell microenvironment, or niche, to facilitate repair by endogenous stem cells. The niche is highly dynamic, with multiple opportunities for intervention. These include administration of small molecules, biologics or biomaterials that target specific aspects of the niche, such as cell-cell and cell-extracellular matrix interactions, to stimulate expansion or differentiation of stem cells, or to cause reversion of differentiated cells to stem cells. Nevertheless, there are several challenges in targeting the niche therapeutically, not least that of achieving specificity of delivery and responses. We envisage that successful treatments in regenerative medicine will involve different combinations of factors to target stem cells and niche cells, applied at different times to effect recovery according to the dynamics of stem cell-niche interactions.
In recent years, technical developments in mouse genetics and imaging equipment have substantially advanced our understanding of hematopoietic stem cells (HSCs) and their niche. The availability of ...numerous Cre strains for targeting HSCs and microenvironmental cells provides extensive flexibility in experimental design, but it can also pose significant challenges due to strain-specific differences in cell specificity. Here we outline various genetic approaches for isolating, detecting, and ablating HSCs and niche components and provide a guide for advantages and caveats to consider. We also discuss opportunities and limitations presented by imaging technologies that allow investigation of HSC behavior in situ.
A guide to the various genetic approaches and imaging technologies used to study HSCs and niche components is presented here.
Long-acting IFNα induces durable molecular responses in myeloproliferative neoplasms. Emerging studies, including Saleiro et al. recently published in Nature Communications, have identified promising ...candidates that may synergise with IFNα by targeting stem cell function or feedback loops that mediate treatment resistance.
The DNA hypomethylating agents (HMA) azacitidine (AZA) and decitabine (DAC) improve survival and transfusion independence in myelodysplastic syndrome (MDS) and enable a low intensity cytotoxic ...treatment for aged AML patients unsuitable for intensive chemotherapy, particularly in combination with novel agents. The proposed mechanism of AZA and DAC relies on active DNA replication and therefore patient responses are only observed after multiple cycles of treatment. Although extended dosing may provide the optimal scheduling, the reliance of injectable formulation of the drug limits it to intermittent treatment. Recently, an oral formulation of AZA demonstrated significantly improved patient relapse free survival (RFS) and overall survival (OS) when used as maintenance after chemotherapy for AML. In addition, both DAC and AZA were found to be highly effective to improve survival in elderly patients with AML through combination with other drugs. These recent exciting results have changed the therapeutic paradigm for elderly patients with AML. In light of this, we review current knowledge on HMA mechanism of action, clinical trials exploring dosing and scheduling, and recent HMA combination therapies to enhance efficacy.
DNA hypomethylating agents (HMA) are a promising treatment alternative to chemotherapy for elderly patients with myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML). This article summarizes key progress made on HMA research including proposed mechanisms, optimal scheduling and dosing, and clinical trials of combination therapies.
The genetic events that contribute to the pathogenesis of acute myeloid leukemia are among the best characterized of all human malignancies. However, with notable exceptions such as acute ...promyelocytic leukemia, significant improvements in outcome based on these insights have not been forthcoming. Acute myeloid leukemia is a paradigm of cancer stem (or leukemia initiating) cells with hierarchy analogous to that seen in hematopoiesis. Normal hematopoiesis requires complex bidirectional interactions between the bone marrow microenvironment (or niche) and hematopoietic stem cells (HSCs). These interactions are critical for the maintenance of normal HSC quiescence and perturbations can influence HSC self-renewal. Leukemia stem cells (LSCs), which also possess limitless self-renewal, may hijack these homeostatic mechanisms, take refuge within the sanctuary of the niche during chemotherapy, and consequently contribute to eventual disease relapse. We will discuss the emerging evidence supporting the importance of the bone marrow microenvironment in LSC survival and consider the physiologic interactions of HSCs and the niche that inform our understanding of microenvironment support of LSCs. Finally, we will discuss approaches for the rational development of therapies that target the microenvironment.
AKT activation is associated with many malignancies, where AKT acts, in part, by inhibiting FOXO tumor suppressors. We show a converse role for AKT/FOXOs in acute myeloid leukemia (AML). Rather than ...decreased FOXO activity, we observed that FOXOs are active in ∼40% of AML patient samples regardless of genetic subtype. We also observe this activity in human MLL-AF9 leukemia allele-induced AML in mice, where either activation of Akt or compound deletion of
FoxO1/3/4 reduced leukemic cell growth, with the latter markedly diminishing leukemia-initiating cell (LIC) function in vivo and improving animal survival. FOXO inhibition resulted in myeloid maturation and subsequent AML cell death. FOXO activation inversely correlated with JNK/c-JUN signaling, and leukemic cells resistant to FOXO inhibition responded to JNK inhibition. These data reveal a molecular role for AKT/FOXO and JNK/c-JUN in maintaining a differentiation blockade that can be targeted to inhibit leukemias with a range of genetic lesions.
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► Unlike other cancers, acute myeloid leukemia (AML) is maintained by low AKT and high FOXO ► FOXOs are required to maintain leukemia-initiating cells (LICs) ► Resistance to FOXO depletion is mediated by JNK/c-JUN signaling ► Elevated FOXOs present in 40% of AML patients regardless of genetic subtype
The FOXO tumor suppressor, although downregulated in many cancers, is active in a large portion of acute myeloid leukemias, where it maintains the immature state of leukemia-initiating cells. When FOXO is inhibited, myeloid leukemia cells differentiate and die.
Abstract Acute myeloid leukaemia (AML) is an aggressive blood cancer caused by the proliferation of immature myeloid cells. The genetic abnormalities underlying AML affect signal transduction ...pathways, transcription factors and epigenetic modifiers. In solid tumours, it is emerging that the genetic landscape of the tumour has a direct effect on the anti-tumour immune responses and response to immunotherapeutic treatment. However, there remains little information as to whether genetic abnormalities affect anti-leukemic immune responses. This review discusses current knowledge of AML antigens and immune responses to AML with a particular focus on the role of T cells and natural killer cells. Understanding immune responses to AML has implications for the development and use of immunotherapies to treat AML patients with distinct genetic abnormalities.
A key characteristic of hematopoietic stem cells (HSCs) is the ability to self-renew. Genetic deletion of β-catenin during fetal HSC development leads to impairment of self-renewal while β-catenin is ...dispensable in fully developed adult HSCs. Whether β-catenin is required for maintenance of fully developed CML leukemia stem cells (LSCs) is unknown. Here, we use a conditional mouse model to show that deletion of β-catenin after CML initiation does not lead to a significant increase in survival. However, deletion of β-catenin synergizes with imatinib (IM) to delay disease recurrence after imatinib discontinuation and to abrogate CML stem cells. These effects can be mimicked by pharmacologic inhibition of β-catenin via modulation of prostaglandin signaling. Treatment with the cyclooxygenase inhibitor indomethacin reduces β-catenin levels and leads to a reduction in LSCs. In conclusion, inhibiting β-catenin by genetic inactivation or pharmacologic modulation is an effective combination therapy with imatinib and targets CML stem cells.
► β- catenin is required for the maintenance of CML stem cells ► β-catenin deletion suppresses CML recurrence after imatinib withdrawal ► β-catenin deletion synergizes with imatinib to target CML stem cells ► COX inhibitors reduce β-catenin levels in CML stem cells and are synergistic with imatinib
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