TpoR Agonist signaling in AML primary cells

Biologic characterization of SB-559457 (SB), a non-peptidyl hydrazone class of thrombopoietin receptor (Mpl) agonist, revealed toxicity towards human leukemia cells. Anti-proliferative effects followed by significant, non-apoptotic, cell death within 72 hours occurred in 24/26 AML, 0/6 ALL, and 3/6 CML patient samples exposed to SB, but not recombinant human thrombopoietin (rhTpo), in liquid suspension culture. Further investigation revealed increased phosphorylation of p70S6/S6 kinases in SB, but not in rhTpo, treated cells. Expression profiling of cells exposed to SB vs rhTpo revealed statistically significant, ~2-fold changes in GAPDH and REDD1 gene expression, confirmed by QRT-PCR. These genes, induced in energy or hypoxia stressed cells, have been implicated in cell death pathways, and may provide important clues to the mechanism of SB induced, leukemic cell death. These results suggest that nonpeptidyl, hydrazone class Mpl agonists may be clinically useful anti-leukemic agents by virtue of their combined thrombopoietic and anti-leukemic effects. Primary cells collected from 5 patients with acute myeloid leukemia (AML) were stimulated stimulated with MPL receptor agonist (SB559457) or recombinant human Tpo (rhTpo) for 6 hours. Next, RNA was isolated from these cells. RNA was used for gene profile analyis to compare genes regulated in AML cells by SB559457 verus rhTpo. For each sample half of the cells were stimulated with Mpl agonist and half with rhTpo.