Cellular Intrinsic Mechanism Affecting The Outcome Of AML Treatment With Ara-C In a Syngeneic Mouse Model

Acute myeloid leukemia (AML) is a deadly form of hematologic malignancy. Refractoriness to treatment in AML represents a common reason for treatment failure. However, the underlying biological mechanisms are not clear. Mouse models of types of leukemia have proved valuable in the identification of mechanisms responsible for leukemogenesis and in the evaluation of efficacy of therapeutics. In this work, we established and characterized a mouse model of AML, by transplantation of BXH-2 derived myeloid leukemic cells into syngeneic mice. The recipient mice developed leukemia shortly following transplantation, with the presence of blast cells in peripheral blood and infiltrated organs. We then developed an efficacious Ara-C-based regimen for the treatment of AML in mice, which was comprised of two courses of ten daily intraperitoneal injections of 50 mg/kg of Ara-C with a 5-day break. Using this immunocompetent mouse model, we proved that leukemic cell load was correlated with the survival of leukemia mice. We also demonstrated that the sensitivity of leukemia cells to Ara-C could significantly affect the survival of AML mice. To examine the difference between sensitive and resistant leukemic cells at the molecular level, genome-wide expression in these cells was profiled, revealing that overall 366 and 212 genes became upreglated or downregulated, respectively, in the resistant cells. Many of these genes are involved in the regulation of cell cycle, cellular proliferation, and apoptosis. Among them, the differential expression levels of Dnmt3L, Plau, Bcl2, CD72, Uba7 and Pdrg1 genes are further validated by quantitative PCR. These genes are known to be related with cellular differentiation and apoptosis pathway. Interestingly, the Ara-C resistant leukemic cells retained sensitivity to an inhibitor of anti-apoptosis proteins, ABT-737, and the treatment with this inhibitor prolonged life span of mice engrafted with resistant leukemic cells. These results suggest that leukemic load and leukemic cell intrinsic resistance can affect the outcome of AML treatment with Ara-C. Incorporation of apoptosis inhibitors, such as ABT-737, into traditional cytotoxic regimens merits consideration for the treatment of a subset of, especially, Ara-C insensitive, patients with AML.