Primate Monocytes - CD14, CD16 - Ziegler-Heitbrock

The protein tyrosine kinase inhibitor SU5614 inhibits FLT3 and induces growth arrest and apoptosis in AML-derived cell lines expressing a constitutively activated FLT3

Abstract

Activating mutations of the protein tyrosine kinase (PTK) FLT3 can be found in approximately 30% of patients with acute myeloid leukemia (AML) thereby representing the most frequent single genetic alteration in AML. These mutations occur in the juxtamembrane (FLT3 length mutations, FLT3-LM) and the catalytic (FLT3D835/836) domain of FLT3 and confer IL-3 independent growth to Ba/F3 cells. In the mouse bone marrow transplantation (BMT) model, FLT3-LM induce a myeloproliferative syndrome stressing their transforming activity in vivo. In this study we analyzed the pro-proliferative and anti-apoptotic potential of FLT3 in FLT3-LM/D835 transformed Ba/F3 cells and AML-derived cell lines. SU5614 has inhibitory activity for FLT3 and selectively induces growth arrest, apoptosis and cell cycle arrest in Ba/F3 and AML cell lines expressing a constitutively activated FLT3. In addition, the compound reverts the anti-apoptotic and pro-proliferative activity of FLT3-ligand (FL) in FL-dependent cells. No cytotoxic activity of SU5614 was found in leukemic cell lines which express a nonactivated FLT3 or no FLT3 protein. At the biochemical level, SU5614 downregulated the activity of the hyperphosphorylated FLT3 receptor and its downstream targets STAT3, STAT5 and MAPK and the STAT5 target genes BCL-XL and p21. Our results show that SU5614 is a PTK inhibitor of FLT3 and has anti-proliferative and pro-apoptotic activity in AML-derived cell lines which endogenously express an activated FLT3 receptor. The selective and potent cytotoxicity of FLT3 PTK inhibitors support a clinical strategy of targeting FLT3 as a new molecular treatment option for patients with FLT3-LM/D835 positive AML.