B-cell Acute Lymphoblastic Cells Research Articles

Hijacking of the Fibrinolytic System By B-Cell Acute Lymphoblastic Leukaemia and Its Therapeutic Targeting

The fibrinolytic system plays a role in the mobilization of hematopoietic stem cells from their bone marrow microenvironment (BMM), but its function in leukemias is not well understood. The fibrinolytic system consists of the proenzyme plasminogen and its active form, plasmin, a serine protease. The activation of plasmin is tightly regulated by activators such as tissue plasminogen activator (tPA) and various inhibitors. A role of this plasminogen activation system in the microenvironment of solid tumors is being unravelled, but a function of this pathway in the BMM, where hematological cancers usually originate, has so far been elusive. Transcriptome analysis of mesenchymal cells in the BMM of mice with different leukemias had revealed annexin A2 ( Anxa2), an initiator of fibrinolysis, to be differentially expressed. Using an ANXA2-deficient BMM as a model for impaired fibrinolysis, we showed that ANXA2 promotes the activation of plasmin, leading to decreased levels of the extracellular matrix (ECM) protein fibronectin in the BMM and accelerating the progression of BCR-ABL1 + B-cell acute lymphoblastic (B-ALL), but not MLL-AF9 + acute myeloid leukemia. Consistently, induction of B-ALL in tPA-deficient mice led to fibronectin accumulation in the BMM and significant survival prolongation. The dense ECM in an ANXA2-deficient BMM is shown to entrap insulin-like growth factor (IGF) and to specifically reduce mTORC2-dependent signalling and proliferation in B-ALL cells. Conversely, B-ALL cell-derived interleukin (IL)-6 conditions hepatic generation of plasminogen, the precursor of plasmin, perpetuating this circuit. Treatment with -aminocaproic acid (EACA), an anti-hemorrhagic drug, which inhibits plasmin activation, reduces tumor burden and prolongs survival in syngeneic and xenogeneic murine models via increased fibronectin in the BMM. Human data confirm that IGF1 and fibronectin staining in trephine biopsies are correlated and that the mTORC2 pathway is distinctly activated in B-ALL. Higher expression of SERPINF2 (α2-antiplasmin), an inhibitor of plasmin, in human B-ALL cells leads to superior outcome. In summary, B-ALL-derived IL-6 impacts hepatic generation of fibrinolytic agents influencing B-ALL progression via ECM remodeling and regulation of the availability of B-ALL-supportive growth factors. Inhibition of plasmin-mediated degradation of the ECM by EACA may be beneficial as adjunct therapy in B-ALL.

Bone Marrow Niche-Derived Extracellular Matrix-Degrading Enzymes Influence the Progression of B-Cell Acute Lymphoblastic Leukemia

Interactions with the bone marrow microenvironment (BMM) influence the pathophysiology of hematological malignancies. Reciprocally, hematological malignancies remodel the BMM in order to render it more hospitable for malignant progression. Hypothesizing that different leukemias differentially remodel stroma cells in the BMM, we tested differences in the expression of various genes in sorted osteoblastic cells from mice with B-cell acute lymphoblastic (B-ALL), acute myeloid (AML) or chronic myeloid leukemia (CML) or control mice by microarray. This revealed a high expression of various proteases, especially matrix metalloproteinase-9 (MMP-9), in osteoblastic cells isolated from mice with B-ALL. MMP-9 had previously been shown to be produced by leukemia cells.To investigate the physiological relevance of BMM-derived MMP-9 for the progression of B-ALL, we employed the well-established retroviral transduction/transplantation model of BCR-ABL1-dependent B-ALL in MMP-9-deficient or wildtype mice. Deficiency of MMP-9 in the BMM prolonged the survival of mice with B-ALL compared to wildtype mice. Secondary transplantation of bone marrow from wildtype versus MMP-9 knockout (KO) mice with B-ALL led to a significant prolongation of survival of recipients of B-ALL bone marrow from MMP-9 KO mice, suggesting that leukemia-initiating cells are reduced in a MMP-9 KO BMM. In addition, we observed reduced invasion of B-ALL cells into different organs such as spleen, meninges, lungs and liver, which likely underlies the observed prolongation of survival, as well as the reduced degradation of extracellular matrix (ECM) proteins such as laminin and fibronectin in the BMM of MMP-9 deficient mice. Mechanistically, using various in vivo and in vitro assays, as well as mice deficient for the receptor for tumor necrosis factor-α (TNF-α) we have demonstrated that B-ALL cells induce MMP-9-expression in niche cells, such as mesenchymal stem cells (MSC), via a release of high amounts of TNF-α, both in the murine and the human setting. TNF-α-dependent induction of MMP-9 in MSC was mediated via TNF-receptor-1, followed by activation of the downstream target nuclear factor kappa B (NF-kB). Consistently, transplantation of B-ALL-initiating cells, in which TNF-α had been knocked down, led to a significant prolongation of survival in B-ALL mice.Testing whether treatment of mice with B-ALL with an inhibitor of MMP-9 may prolong survival compared to vehicle-treated mice, we indeed found decreased degradation of ECM proteins in the BMM, a decreased leukemia burden in peripheral blood and a significant prolongation of survival. In addition, we observed reduced minimal residual disease in the bone marrow of mice with B-ALL when the mice had been treated with cytarabine and the MMP-9 inhibitor compared to mice treated with cytarabine alone. Experiments on testing the effect of MMP-9 inhibitor treatment on human B-ALL cells in a xenotransplantation model are currently ongoing.In summary, we have demonstrated the role of BMM-derived MMP-9 for B-ALL progression. B-ALL cells self-reinforce the BMM by inducing the production of MMP-9 via the release of TNF-α. Increased production of MMP-9 from the BMM promotes B-ALL progression via increased invasion of leukemic cells into different organs. Our data suggest, that inhibition of MMP-9 may be a feasible strategy as an adjunct to existing therapies. DisclosuresKrause:Glycotope: Consultancy; Glycomimetics Inc. until 06/2016: Consultancy, Research Funding; Merck KgGA in future: Research Funding; European Patent: Patents & Royalties: European Patent No. 16187926.7-1401 “FIBRONECTIN FOR USE IN THE TREATMENT OF LEUKEMIA” .