Efficacy of a Mer and Flt3 tyrosine kinase small molecule inhibitor, UNC1666, in acute myeloid leukemia.

Alisa B Lee-Sherick,Gregory Kirkpatrick,Douglas K Graham,Xiaodong Wang,Sean Rinella,H Shelton Earp,Lauren S Page,Weihe Zhang,Craig T Jordan,Qi Wei,Michael A Stashko,Jing Liu,Dehui Zhang,Stephen Frye,Deborah Deryckere,Kelly K Menachof,Amanda A Hill

doi:10.18632/oncotarget.3156

Abstract

Mer and Flt3 receptor tyrosine kinases have been implicated as therapeutic targets in acute myeloid leukemia (AML). In this manuscript we describe UNC1666, a novel ATP-competitive small molecule tyrosine kinase inhibitor, which potently diminishes Mer and Flt3 phosphorylation in AML. Treatment with UNC1666 mediated biochemical and functional effects in AML cell lines expressing Mer or Flt3 internal tandem duplication (ITD), including decreased phosphorylation of Mer, Flt3 and downstream effectors Stat, Akt and Erk, induction of apoptosis in up to 98% of cells, and reduction of colony formation by greater than 90%, compared to treatment with vehicle. These effects were dose-dependent, with inhibition of downstream signaling and functional effects correlating with the degree of Mer or Flt3 kinase inhibition. Treatment of primary AML patient samples expressing Mer and/or Flt3-ITD with UNC1666 also inhibited Mer and Flt3 intracellular signaling, induced apoptosis, and inhibited colony formation. In summary, UNC1666 is a novel potent small molecule tyrosine kinase inhibitor that decreases oncogenic signaling and myeloblast survival, thereby validating dual Mer/Flt3 inhibition as an attractive treatment strategy for AML.

Highlights

Though the treatment of acute myeloid leukemia (AML) has significantly improved over the past 30 years, average five-year survival rates are still less than 60% for pediatric patients and are progressively worse for older adult and elderly patients [1, 2]
We show that this ATP-binding site competitive small molecule potently and selectively inhibits Mer and FMS-like tyrosine kinase 3 (Flt3) kinase activation and downstream signal transduction resulting in growth inhibition and apoptosis of AML cell lines and primary patient myeloblasts
A comprehensive protein kinase profiling panel provided by Carna Biosciences was used to assess off-target kinase inhibition mediated by UNC1666 at a concentration of 46 nM, more than 50-fold higher than its microfluidic capillary electrophoresis (MCE) IC50 values against Mer and Flt3 (Supplemental Table 2)

Summary

Introduction

Though the treatment of acute myeloid leukemia (AML) has significantly improved over the past 30 years, average five-year survival rates are still less than 60% for pediatric patients and are progressively worse for older adult and elderly patients [1, 2]. Inhibition of Mer in AML via RNA interference led to a significant increase in myeloblast apoptosis, decreased colony formation in methylcellulose, and prolonged leukemia-free survival in a murine xenograft model [8]. These findings led us to determine that aberrant Mer expression (rather than activating mutation in the kinase domain) provides a www.impactjournals.com/oncotarget survival advantage in leukemia. Taken together, these data suggest that Mer kinase inhibition may selectively target leukemia cells, while sparing normal bone marrow progenitors

Methods

Results

Conclusion