panobinostat and Myeloproliferative-Disorders

Overexpression of high mobility group AT-hook 2 (Hmga2), which is negatively regulated by MIRLET7 micro RNAs through 3'-untranslated region (3'UTR), causes proliferative haematopoiesis mimicking myeloproliferative neoplasms (MPNs) and contributes to progression of myelofibrosis in mice. Thus, we investigated HMGA2 mRNA expression in 66 patients with MPNs including 23 polycythaemia vera (PV), 33 essential thrombocythaemia (ET) and 10 primary myelofibrosis (PMF). HMGA2 mRNA expression, especially variant 1 with 3'UTR that contains MIRLET7-specific sites, rather than variant 2 lacking 3'UTR, is frequently deregulated due to decreased MIRLET7 expression in granulocytes from over 20% of PV and ET, and in either granulocytes or CD34(+) cells from 100% of PMF. Patients with deregulated HMGA2 mRNA expression were significantly more likely to show splenomegaly, high serum lactate dehydrogenase values, and methylation of the CDKN2A promoter compared with other patients without deregulation of HMGA2. A histone deacetylase inhibitor, panobinostat, significantly increased MIRLET7 expression and reduced variant 1 of HMGA2 mRNA expression, but not variant 2, in both U937 cells and PMF-derived CD34(+) cells. Moreover, both panobinostat and small interfering RNA of HMGA2 demethylated the CDKN2A promoter in U937 cells. In conclusion, the frequently dysregulated MIRLET7/HMGA2 axis could be a therapeutic target in MPNs.

Topics: Aged; Aged, 80 and over; Antineoplastic Agents; Case-Control Studies; Cyclin-Dependent Kinase Inhibitor p16; DNA Methylation; DNA, Neoplasm; Female; Gene Expression Regulation, Neoplastic; HMGA2 Protein; Humans; Hydroxamic Acids; Indoles; Male; MicroRNAs; Middle Aged; Myeloproliferative Disorders; Panobinostat; Promoter Regions, Genetic; RNA, Messenger; RNA, Neoplasm; Tumor Cells, Cultured

Drug-induced thrombocytopenia often results from dysregulation of normal megakaryocytopoiesis. In this study, we investigated the mechanisms responsible for thrombocytopenia associated with the use of Panobinostat (LBH589), a histone deacetylase inhibitor with promising anti-cancer activities. The effects of LBH589 were tested on the cellular and molecular aspects of megakaryocytopoiesis by utilizing an ex vivo system in which mature megakaryocytes (MK) and platelets were generated from human primary CD34(+) cells. We demonstrated that LBH589 did not affect MK proliferation or lineage commitment but inhibited MK maturation and platelet formation. Although LBH589 treatment of primary MK resulted in hyperacetylation of histones, it did not interfere with the expression of genes that play important roles during megakaryocytopoiesis. Instead, we found that LBH589 induced post-translational modifications of tubulin, a nonhistone protein that is the major component of the microtubule cytoskeleton. We then demonstrated that LBH589 treatment induced hyperacetylation of tubulin and alteration of microtubule dynamics and organization required for proper MK maturation and platelet formation. This study provides new insights into the mechanisms underlying LBH589-induced thrombocytopenia and provides a rationale for using tubulin as a target for selective histone deacetylase inhibitor therapies to treat thrombocytosis in patients with myeloproliferative neoplasms.

Topics: Acetylation; Blood Platelets; Cell Proliferation; Cells, Cultured; Hematologic Neoplasms; Histone Deacetylase Inhibitors; Humans; Hydroxamic Acids; Indoles; Megakaryocytes; Myeloproliferative Disorders; Panobinostat; Protein Processing, Post-Translational; Thrombocytopenia; Thrombopoiesis; Tubulin