Abstract
Abstract 2151 Fms-like tyrosine kinase-3 (FLT3) inhibitors have recently been introduced to overcome the dismal prognosis of acute myeloid leukemia (AML) with FLT3/ITD mutations. However, while ciculating blasts are rapidly eliminated, bone marrow (BM) responses are in general less impressive (Zhang et al., JCI 2009). One potential explanation for the reduced bone marrow response compared to the striking activity against circulating blast cells may be microenvironmental resistance to FLT3 inhibitors, including protection of FLT3/ITD+ blasts through the SDF-1 (CXCL12)/CXCR4 axis (Zeng et al., BLOOD 2009) and novel strategies to overcome microenvironmental resistance may further enhance the clinical benefit of FLT3 inhibitors. Here we investigated the role of p53 in bone marrow stromal cells in stromal cell-mediated resistance to FLT3 inhibition in FLT3/ITD AML. We confirmed that Mdm2-p53 interaction and mutant FLT3 signaling in leukemic blasts were inhibited by the Mdm2 inhibitor Nutlin-3a and the selective FLT3 inhibitor FI-700, respectively, as previously reported (Kojima et al., BLOOD 2004; Kojima et al., LEUKEMIA 2009). BM samples were obtained from normal individuals or from FLT3/ITD AML patients with more than 70% leukemia cells after informed consent. BM-derived stromal cells were seeded in 12-well plates in MEM-alpha medium and exposed to Nutlin-3a for 24 hours, gamma-irradiated (2 Gy), or treated with 100 nM doxorubicin. The wells were then washed three times and AML cells were added. Cell cycle distribution was determined by propidium iodide staining and apoptosis by Annexin V binding. In FLT3/ITD AML cell lines and primary cells, apoptosis was induced by FI-700, but apoptosis induction was diminished under stromal coculture conditions (43.2 ± 0.5% versus 17.0 ± 1.2% in MOLM-13; p Disclosures: No relevant conflicts of interest to declare.
Published Version
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