Plasma basic fibroblast growth factor and bone marrow fibrosis in clonal myeloproliferative disorders

Bone marrow fibrosis in primary myelofibrosis: pathogenic mechanisms and the role of TGF-β

Primary myelofibrosis (PMF) is a Philadelphia chromosome negative myeloproliferative neoplasm (MPN) with adverse prognosis and is associated with bone marrow fibrosis and extramedullary hematopoiesis. Even though the discovery of the Janus kinase 2 (JAK2), thrombopoietin receptor (MPL) and calreticulin (CALR) mutations have brought new insights into the complex pathogenesis of MPNs, the etiology of fibrosis is not well understood. Furthermore, since JAK2 inhibitors do not lead to reversal of fibrosis further understanding of the biology of fibrotic process is needed for future therapeutic discovery. Transforming growth factor beta (TGF-β) is implicated as an important cytokine in pathogenesis of bone marrow fibrosis. Various mouse models have been developed and have established the role of TGF-β in the pathogenesis of fibrosis. Understanding the molecular alterations that lead to TGF-β mediated effects on bone marrow microenvironment can uncover newer therapeutic targets against myelofibrosis. Inhibition of the TGF-β pathway in conjunction with other therapies might prove useful in the reversal of bone marrow fibrosis in PMF.

Cytokine Regulation of Microenvironmental Cells in Myeloproliferative Neoplasms

The term myeloproliferative neoplasms (MPN) refers to a heterogeneous group of diseases including not only polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF), but also chronic myeloid leukemia (CML), and systemic mastocytosis (SM). Despite the clinical and biological differences between these diseases, common pathophysiological mechanisms have been identified in MPN. First, aberrant tyrosine kinase signaling due to somatic mutations in certain driver genes is common to these MPN. Second, alterations of the bone marrow microenvironment are found in all MPN types and have been implicated in the pathogenesis of the diseases. Finally, elevated levels of proinflammatory and microenvironment-regulating cytokines are commonly found in all MPN-variants. In this paper, we review the effects of MPN-related oncogenes on cytokine expression and release and describe common as well as distinct pathogenetic mechanisms underlying microenvironmental changes in various MPN. Furthermore, targeting of the microenvironment in MPN is discussed. Such novel therapies may enhance the efficacy and may overcome resistance to established tyrosine kinase inhibitor treatment in these patients. Nevertheless, additional basic studies on the complex interplay of neoplastic and stromal cells are required in order to optimize targeting strategies and to translate these concepts into clinical application.

Bone marrow fibrosis may be an effective independent predictor of the 'TKI drug response level' in chronic myeloid leukemia

OBJECTIVES

The aim of this study was to assess bone marrow (BM) fibrosis and dysplasia in chronic myeloid leukemia (CML) patients receiving the first-generation tyrosine kinase inhibitor (TKI), imatinib, or second-generation TKIs, dasatinib, and nilotinib. We further investigated whether CML under TKI is associated with dysplastic BM changes during the clinicopathological course of the disease.

METHODS

In total, pre-treatment BM paraffin blocks of biopsy specimens were available for 41 adult patients diagnosed with chronic phase CML. Post-treatment BM aspirate clot and core biopsy samples were reviewed for fibrosis and dyshematopoiesis.

RESULTS

Overall, 13 (31.7%) patients achieved a complete cytogenetic response with imatinib treatment, with no events. In 25 patients, imatinib was discontinued owing to primary or secondary resistance. In patients with initial dysmyelopoiesis, the rate of BM fibrosis was 82.4 versus 47.6% for other patient groups (P = 0.02). Overall, 24 patients with newly diagnosed CML showed marrow fibrosis, among which 19 (79.1%) had imatinib resistance. However, only 5 out of 15 patients (33.5%) without marrow fibrosis had imatinib resistance (P = 0.08). Discussion Our findings indicate that BM fibrosis is an independent predictor of the 'TKI drug response level' in CML and support its inclusion as a critical pathobiological parameter for decision-making with regard to TKI drug selection de novo, calculation of prognosis at the onset of disease, and monitoring response to TKI in the long-term disease course of CML.

Local bone marrow renin-angiotensin system in primitive, definitive and neoplastic haematopoiesis

The locally active ligand peptides, mediators, receptors and signalling pathways of the haematopoietic BM (bone marrow) autocrine/paracrine RAS (renin-angiotensin system) affect the essential steps of definitive blood cell production. Haematopoiesis, erythropoiesis, myelopoiesis, formation of monocytic and lymphocytic lineages, thrombopoiesis and other stromal cellular elements are regulated by the local BM RAS. The local BM RAS is present and active even in primitive embryonic haematopoiesis. ACE (angiotensin-converting enzyme) is expressed on the surface of the first endothelial and haematopoietic cells, forming the marrow cavity in the embryo. ACE marks early haematopoietic precursor cells and long-term blood-forming CD34(+) BM cells. The local autocrine tissue BM RAS may also be active in neoplastic haematopoiesis. Critical RAS mediators such as renin, ACE, AngII (angiotensin II) and angiotensinogen have been identified in leukaemic blast cells. The local tissue RAS influences tumour growth and metastases in an autocrine and paracrine fashion via the modulation of numerous carcinogenic events, such as angiogenesis, apoptosis, cellular proliferation, immune responses, cell signalling and extracellular matrix formation. The aim of the present review is to outline the known functions of the local BM RAS within the context of primitive, definitive and neoplastic haematopoiesis. Targeting the actions of local RAS molecules could represent a valuable therapeutic option for the management of neoplastic disorders.

Allografting for Bosutinib, Imatinib, Nilotinib, Dasatinib, and Interferon Resistant Chronic Myeloid Leukemia without ABL Kinase Mutation

The current treatment of chronic phase chronic myeloid leukemia (CML) consists of oral tyrosine kinase inhibitors (TKIs). However, high-risk CML may present with an aggressive course which may result in blastic crisis or a "difficult-to-manage" state with available treatments. The aim of this paper is to report a patient with complicated CML resistant to treatment and progressed despite the administration of bosutinib, imatinib mesylate, nilotinib, dasatinib, interferon alpha 2a, cytotoxic chemotherapy, and allogeneic hematopoietic stem cell transplantation. The striking point of this case story is that no Abl kinase domain mutation against TKIs has been detected during this very complicated disease course of CML. Meanwhile, challenging cases will always be present despite the hope and progress in CML in the TKI era.

Acute myelogenous leukemia cells with the MLL-ELL translocation convert morphologically and functionally into adherent myofibroblasts

Bone marrow-myofibroblasts, a major component of bone marrow-stroma, are reported to originate from hematopoietic stem cells. We show in this paper that non-adherent leukemia blasts can change into myofibroblasts. When myeloblasts from two cases of acute myelogenous leukemia with a fusion product comprising mixed lineage leukemia and RNA polymerase II elongation factor, were cultured long term, their morphology changed to that of myofibroblasts with similar molecular characteristics to the parental myeloblasts. The original leukemia blasts, when cultured on the leukemia blast-derived myofibroblasts, grew extensively. Leukemia blasts can create their own microenvironment for proliferation.

Molecularly targeted therapies in myelodysplastic syndromes and acute myeloid leukemias

Although there has been significant progress in acute myeloid leukemia (AML) treatment in younger adults during the last decade, standard induction therapy still fails to induce remission in up to 40% of AML patients. Additionally, relapses are common in 50-70% of patients who achieve a complete remission, and only 20-30% of patients enjoy long-term disease-free survival. The natural history of myelodysplastic syndrome (MDS) is variable, with about half of the patients dying from cytopenic complications, and an additional 20-30% transforming to AML. The advanced age of the majority of MDS patients limits the therapeutic strategies often to supportive care. To address these shortcomings, much effort has been directed toward the development of novel treatment strategies that target the evolution and proliferation of malignant clones. Presented here is an overview of molecularly targeted therapies currently being tested in AML and MDS patients, with a focus on FMS-like tyrosine kinase 3 inhibitors, farnesyltransferase inhibitors, antiangiogenesis agents, DNA hypomethylation agents, and histone deacetylase inhibitors.