Klin Padiatr 2016; 228 - A22
DOI: 10.1055/s-0036-1582499

Antileukemic activity of the azacitidine in a xenograft model of juvenile myelomonocytic leukemia

CF Krombholz 1, 2, S Fluhr 1, CM Niemeyer 1, C Flotho 1, M Erlacher 1
  • 1Division of Pediatric Hematology and Oncology, Department of Pediatrics and Adolescent Medicine, University Medical Center Freiburg
  • 2Faculty of Biology, University of Freiburg, Germany

Introduction: Juvenile myelomonocytic leukemia (JMML) is an aggressive myeloproliferative disorder of early childhood. Patients present with hepatosplenomegaly, lymphadenopathy and skin rash, and peripheral blood analysis reveals monocytosis and the presence of myeloid precursors. Clinical signs are caused by organ infiltration of proliferating monocytes and granulocytes. JMML cells are characterized by a deregulated activation of the RAS signaling pathway as a result of mutations in KRAS, NRAS, NF1, PTPN11 (encoding SHP2) or CBL. When left untreated, most patients die from respiratory failure due to leukemic lung infiltration. The only curative treatment of JMML so far is allogeneic hematopoietic stem cell transplantation (HSCT), with an overall survival of 60%. DNA hypermethylation in JMML cells is associated with an aggressive disease course and poor outcome. This suggests a key role of epigenetic modifications in JMML pathophysiology. Accordingly, the clinical efficacy of epigenetic treatment with the DNA methyltransferase inhibitor azacitidine was recently demonstrated in a retrospective JMML case series (Cseh et al, Blood 2015). A clinical trial using azacitidine as a front-line therapy is ongoing.

Results: We are currently analyzing the antileukemic activity of azacitidine in our JMML xenotransplantation model. JMML mononuclear cells were transplanted into sublethally irradiated immunodeficient Rag2-/-IL2rg-/- mice. Recipient mice showed key characteristics of JMML, including cachexia and clonal expansion of myelomonocytic progenitor cells that infiltrated bone marrow, spleen, liver and lung (Krombholz et al, Haematologica 2016). Mice were treated with azacitidine, cytarabine or saline. Both azacitidine and cytarabine reduced leukemic burden in the recipient mice, but only azacitidine resulted in a reduction of immature CD34+ cells that contain the leukemia-initiating cells. Reduction of immature stem and progenitor cells was in part due to apoptosis but also due to differentiation. DNA methylation of JMML cells was strongly reduced by azacitidine.

Conclusion: Azacitidine showed clear preclinical efficacy in our JMML xenograft model. Mode of action differed from that of conventional chemotherapy and azacitidine seemed to affect mostly immature JMML cells.

* equal contribution.