SU11657, a FLT3-Targeted Tyrosine Kinase, Has Pro-Apoptotic Activity on Leukemia Cells In Vitro.

Fms-related tyrosine kinase3 (Flt3) is the most commonly mutated gene in human acute myeloid leukemia (AML) and has implicated in its pathogenesis. Constitutive activation of the Flt3 receptor tyrosine kinase, have been linked either by internal tandem duplication (ITD) of the juxtamembrane region or by point mutation in the second tyrosine kinase domain (TKD). To investigate the effect in vitro of SU11657, a new compound FLT3 kinase inhibitors, we analyzed human cell lines from AML patients (MV4-11 and HL60) and blast from patients AML using a wide range of concentrations (1nM-10μM) of this novel agent. In HL-60, FLT3-wt cell line, used as negative control does not show relevant effect after treatment with SU11657. Instead, in MV4-11, FLT3-ITD cell line, we observed a decrease dose-dependent in cell viability after treatment with SU11657. The effects of this compound on cell cycle progression show an accumulation of G1/S phase and an induction of apoptosis at 1-10nM concentration after 24h of treatment. First we observed a dephosphorylation of FLT3 on Tyr⁵⁹¹ in whole cell extracts from MV4-11 cells after treatment with SU11657 100nM. We also demonstrated a hypophosphorylation of AKT on Ser⁴⁷³ and a consequently dephosphorylation of BAD on Ser¹³⁶ at nanomolar concentration. We observed a dephosphorylation of STAT-5 to 100nM of SU11657 at 24h.

We evaluated the effects of this new compound in AML primary progenitors that showed FLT3-ITD, FLt3-TKD and FLT3-wt. In the patients with mutation ITD and TKD was evident a modification of cell cycle progression with a decrease in G2/M phase and an increase of subdiploid peak. The effect of SU11657 in patients FLT3-wt was not relevant.

Our study thus showed a potential therapeutic usefulness of the drug in treatment of AML. Study of signal transductions and gene profile expression will contribute to further understanding of the drug mechanisms.