Sinusoidal endothelial cells are damaged and display enhanced autophagy in myelodysplastic syndromes

Nature or Nurture? Role of the Bone Marrow Microenvironment in the Genesis and Maintenance of Myelodysplastic Syndromes

Myelodysplastic syndrome (MDS) are clonal haematopoietic stem cell (HSC) disorders driven by a complex combination(s) of changes within the genome that result in heterogeneity in both clinical phenotype and disease outcomes. MDS is among the most common of the haematological cancers and its incidence markedly increases with age. Currently available treatments have limited success, with <5% of patients undergoing allogeneic HSC transplantation, a procedure that offers the only possible cure. Critical contributions of the bone marrow microenvironment to the MDS have recently been investigated. Although the better understanding of the underlying biology, particularly genetics of haematopoietic stem cells, has led to better disease and risk classification; however, the role that the bone marrow microenvironment plays in the development of MDS remains largely unclear. This review provides a comprehensive overview of the latest developments in understanding the aetiology of MDS, particularly focussing on understanding how HSCs and the surrounding immune/non-immune bone marrow niche interacts together.

Evaluation of bone marrow microenvironment could change how myelodysplastic syndromes are diagnosed and treated

Myelodysplastic syndromes are a heterogeneous group of clonal hematopoietic disorders. However, the therapies used against the hematopoietic stem cells clones have limited efficacy; they slow the evolution toward acute myeloid leukemia rather than stop clonal evolution and eradicate the disease. The progress made in recent years regarding the role of the bone marrow microenvironment in disease evolution may contribute to progress in this area. This review presents the recent updates on the role of the bone marrow microenvironment in myelodysplastic syndromes pathogenesis and tries to find answers regarding how this information could improve myelodysplastic syndromes diagnosis and therapy.

Loss of ASXL1 triggers an apoptotic response in human hematopoietic stem and progenitor cells

ASXL1 is frequently mutated in myelodysplastic syndrome and other hematological malignancies. It has been reported that a loss of ASXL1 leads to a reduction of H3K27me3 via the polycomb repressive complex 2 (PRC2). To determine the role of ASXL1 loss in normal hematopoietic stem and progenitor cells, cord blood CD34⁺ cells were transduced with independent small hairpin interfering RNA lentiviral vectors against ASXL1 and cultured under myeloid and erythroid permissive conditions. Knockdown of ASXL1 led to a significant reduction in stem-cell frequency and a reduced cell expansion along the myeloid lineage. Cell expansion along the erythroid lineage was also reduced significantly and was accompanied by an increase in apoptosis of erythroid progenitor cells throughout differentiation and by an accumulation of cells in the G₀/G₁ phase. Bone marrow stromal cells supported the growth of immature erythroid cells, but did not alter the adverse phenotype of ASXL1 knockdown. Chromatin immunoprecipitation revealed no loss of H3K27me3 in myeloid progenitor cells, but demonstrated a loss of H3K27me3 on the HOXA and the p21 locus in erythroid progenitors. We conclude that ASXL1 is essential for erythroid development and differentiation and that the aberrant differentiation is, at least in part, facilitated via PRC2.

Progression of a solitary plasmacytoma to multiple myeloma. A population-based registry of the northern Netherlands

Plasmacytoma is characterized by a local accumulation of monoclonal plasma cells without criteria for multiple myeloma (MM). The current treatment regimen is local radiotherapy. However, more than 50% of patients develop MM within 2 years after treatment. A population-based registry was consulted for the diagnosis of solitary plasmacytoma between 1988 and 2011. Progression to MM and prognostic features for progression to MM were scored, including hypoxia inducible factors (HIF), vascular endothelial growth factor (VEGF, also termed VEGFA) and micro-vessel density (MVD) expression in biopsy material. A total of 76 patients were included, 34% having extramedullary plasmacytoma (EMP) while 66% had a solitary plasmacytoma of the bone (SBP). Median follow-up was 89 months, (7-293 months). In Seventy per cent of SBP patients developed MM with a median time to progression of 19 months (5-293). Three patients (12%) with EMP developed MM. High expression of VEGF and HIF-2α (also termed EPAS1) was demonstrated in conjunction with an increased MVD in 66% of the patients. No association could be shown between angiogenesis parameters and progression to MM. In conclusion, this population-based study demonstrates that SBP patients have a higher risk of developing MM following local radiotherapy, indicating that this group might benefit from added systemic chemotherapy.

18F-FDG PET increases visibility of bone lesions in relapsed multiple myeloma: is this hypoxia-driven?

INTRODUCTION

Whole-body x-ray (WBX) is used for detecting skeleton abnormalities in patients with multiple myeloma (MM). An alternative might be 18F-FDG PET, which makes use of metabolic changes of malignant cells. The aims of this study were to evaluate whether 18F-FDG PET detects more lesions compared with WBX in patients with relapsing MM and to define its prognostic value. In addition 1-α-D-(5-deoxy-5-[F]-fluoroarabinofuranosyl)-2-nitroimidazole (18F-FAZA) scan and immunohistochemical staining on bone marrow were performed to define whether FDG uptake coincides with angiogenesis-related tumor hypoxia.

PATIENTS AND METHODS

18F-FDG PET (n = 44) and 18F-FAZA-PET (n = 5) were performed in patients with relapsed MM. Bone marrow biopsies (n = 20) were evaluated for hypoxia inducible factors (HIF) 1α and 2α, vascular endothelial growth factor, glucose transport proteins 1 and 3, and the microvessel density.

RESULTS

New lesions were more frequently demonstrated on 18F-FDG PET than on WBX (P = 0.000001). 18F-FDG PET was not predictive for progression-free survival and overall survival. Immunohistochemical staining on bone marrow biopsies demonstrated a significant increase in microvessel density and elevated expression of vascular endothelial growth factor, HIF-2α, and glucose transport protein 3 by the malignant plasma cells. However, HIF-1α expression and 18F-FAZA scan results were negative.

CONCLUSIONS

Our results demonstrate that 18F-FDG PET is relevant for diagnostic purposes compared with WBX in relapsing MM. The enhanced uptake of 18F-FDG PET is likely related to the activation of the HIF-2α signaling pathway but probably independent of hypoxia-induced signaling in view of the negative findings on both 18F-FAZA-PET and HIF-1α expression.