The multi-targeted receptor tyrosine kinase inhibitor, linifanib (ABT-869), induces apoptosis and inhibits proliferation of leukemia cells through phosphoinositide-3 kinase (PI3K)/AKT-dependent signaling pathways

Acute Myelogenous Leukemia (AML) is an adult and pediatric disorder characterized by the abnormal differentiation and proliferation of hematopoietic stem cells. Mutations in the FMS-like tyrosine kinase 3 (FLT3), an important regulator of hematopoiesis, have been found in one-third of AML patients. Two major types of mutations include an internal tandem duplication (ITD) in the juxtamembrane domain of the receptor (23% of AML patients) and the other a point mutation on the aspartic acid 835 of the kinase domain of the receptor (8–12% of patients with AML). Adults and children with AML, particularly those with the ITD mutation have a poor clinical prognosis. Mutations in FLT3 lead to autophosphorylation and constitutive activation of downstream signaling pathways that affect proliferation, differentiation, and apoptosis. In these studies, the mechanism of action of a newly identified small molecule multi-targeted receptor tyrosine kinase inhibitor (RTKI), linifanib (ABT-869) was identified in Ba/F3 FLT3 ITD mutant cells. It was found that linifanib induces apoptosis and inhibits proliferation in ITD mutant cells in vitro at nanomolar concentrations. In addition, it was determined that apoptosis occurring after treatment occurs rapidly within ITD mutant cells and through a mechanism involving signaling through the phosphoinositide-3-kinase (PI3K)/AKT pathway and Glycogen Synthase Kinase-3β. Additionally, in vitro combination studies revealed that combining linifanib with PI3K inhibitor, LY294002 antagonized linifanib-induced apoptotic and anti-proliferative effects, stressing the importance of this pathway at triggering linifanib-induced effects. In vivo, it was also determined that linifanib delays the progression of ITD mutant cell driven disease and prolongs life span in NOD/SCID treated mice. These preclinical studies suggest that linifanib is effective at inducing apoptosis and inhibiting proliferation through the PI3K pathway. These studies identify a new target, Glycogen Synthase Kinase-3β, to be used for treatment in AML. They also provide insight for the use of selected kinase inhibitors in combination with linifanib to yield better treatment strategies for patients with AML.