NF- B and FLIP in arsenic trioxide (ATO)–induced apoptosis in myelodysplastic syndromes (MDSs)

Tumor necrosis factor (TNF)– , a potent stimulus of nuclear factorB (NFB), is up-regulated in myelodysplastic syndrome (MDS). Here, we show that bone marrow mononuclear cells (BMMCs) and purified CD34 cells from patients with low-grade/early-stage MDS (refractory anemia/refractory anemia with ring sideroblasts [RA/RARS]) have low levels of NFB activity in nuclear extracts comparable with normal marrow, while patients with RA with excess blasts (RAEB) show significantly increased levels of activity (P .008). Exogenous TNFenhanced NFB nuclear translocation in MDS BMMCs above baseline levels. Treatment with arsenic trioxide (ATO; 2-200 M) inhibited NFB activity in normal marrow, primary MDS, and ML1 cells, even in the presence of exogenous TNF(20 ng/mL), and downregulated NFB–dependent antiapoptotic proteins, B-cell leukemia XL (Bcl-XL), Bcl-2, X-linked inhibitor of apoptosis (XIAP), and Fas-associated death domain (FADD)–like interleukin-1 –converting enzyme (FLICE) inhibitory protein (FLIP), leading to apoptosis. However, overexpression of FLIP resulted in increased NFB activity and rendered ML1 cells resistant to ATO-induced apoptosis. These data are consistent with theobservedup-regulationofFLIPandresistance to apoptosis with advanced MDS, where ATO as a single agent may show only limited efficacy. However, the data also suggest that combinations of ATO with agents that interfere with other pathways, such as FLIP autoamplification via NFB, may have considerable therapeutic activity. (Blood. 2005;106:3917-3925)