Molecular insights into the pathogenesis of B-cell and myeloid malignancies : therapeutic implications

Abstract

Hematological malignancies originate from hematopoietic cells in the bone marrow or the lymphatic system. In this thesis, I study the molecular pathogenesis of Hodgkin lymphoma (HL), mantle cell lymphoma (MCL), and myeloproliferative neoplasms (MPNs), and explore the underlying therapeutic implication in these diseases.

In paper I, we profiled the DNA methylation signature in blood cells from monozygotic triplets, two of which had developed HL. Isolated CD34+ hematopoietic cells, marginal zonelike and naïve B-cells, and switched memory B-cells were compared for the difference in global DNA methylation between the triplets with the one without HL. Shared differences were found in naïve B-cells and marginal zone-like B-cells. One region in chromosome 18 was found to be hyper-methylated in the naïve B-cells, while 21 genomic regions on 10 chromosomes were hyper-methylated in marginal-zone like B-cells derived from the HL triplets. These findings may indicate a role of aberrant DNA methylation in HL pathogenesis.

In paper II, we probed new therapeutic strategies for MPNs. The activating JAK2V617 mutation drives MPN development. Treatment with JAK2 inhibitors frequently leads to therapeutic failure, and the underlying mechanism is elusive. We observed that the JAK2 inhibitor LY2784544 caused the transient decrease in viability and proliferation of the JAK2V617-bearing cell line HEL, but induced the accumulation of leukemic stem cell (CD34+) cells. The stem cell factor KLF4 was highly expressed upon LY2784544 treatment, whereas silencing of KLF4 attenuated the accumulation of LY2784544-induced accumulation of CD34+ cells. A similar effect was also identified in cells treated with the telomerase inhibitor GRN163L after LY2784544 incubation. Thus, targeting KLF4 combined with a JAK2 inhibitor, or combination of telomerase inhibitor and JAK2 inhibitors may potentially be used as a novel treatment strategy for MPN patients.

In paper III, we investigated the role of 5-lipoxygenase (5-LOX) in MCL and evaluated the effect of inhibition of 5-LOX as a therapeutic strategy. Human B lymphocytes express 5-LOX and 5-LOX-activating protein (FLAP), and can convert arachidonic acid to leukotriene B4. MCL cells express large amounts of 5-LOX, but the function and mechanism of activation of 5-LOX in B lymphocytes are unclear. We demonstrated that the intrinsic 5-LOX pathway in the MCL cell line JeKo-1 has an essential role in the migration and adhesion of these cells. 5- LOX and FLAP inhibitors reduced the migration induced by the chemoattractant CXCL12. The knockout of the 5-LOX gene also decreased the migration of JeKo-1 cells. Furthermore, the above inhibitors inhibited adherence of JeKo-1 cells to stromal cells. The inhibitors were as potent as the Bruton tyrosine kinase inhibitor ibrutinib, a therapeutic agent in MCL treatment, to inhibit migration and adherence of MCL cells. Our results suggest that inhibition of the 5-LOX pathway may be an important strategy in the treatment of certain B-cell malignancies.

Taken together, the findings presented in this thesis contribute to better understandings of the molecular pathogenesis of HL, MCL, and MPNs, and are implicated in the rational development of novel therapeutic strategies for these malignancies.