Mutant FLT3: A Direct Target of Sorafenib in Acute Myelogenous Leukemia

Weiguo Zhang; Marina Konopleva; Yue-xi Shi; Teresa McQueen; David Harris; Xiaoyang Ling; Zeev Estrov; Alfonso Quintás-Cardama; Donald Small; Jorge Cortes; Michael Andreeff

Disclosures

J Natl Cancer Inst. 2008;100(3):184-198. 

In This Article

Abstract and Introduction

Background: Internal tandem duplication (ITD) mutations in the juxtamembrane domain–coding sequence of the Fmslike tyrosine kinase 3 (FLT3) gene have been identified in 30% of acute myeloid leukemia (AML) patients and are associated with a poor prognosis. The kinase inhibitor sorafenib induces growth arrest and apoptosis at much lower concentrations in AML cell lines that harbor FLT3-ITD mutations than in AML cell lines with wild-type FLT3.
Methods: The antileukemic activity of sorafenib was investigated in isogenic murine Ba/F3 AML cell lines that expressed mutant (ITD, D835G, and D835Y) or wild-type human FLT3, in primary human AML cells, and in a mouse leukemia xenograft model. Effects of sorafenib on apoptosis and signaling in AML cell lines were investigated by flow cytometry and immunoblot analysis, respectively, and the in vivo effects were determined by monitoring the survival of leukemia xenograft–bearing mice treated with sorafenib (groups of 15 mice). In a phase 1 clinical trial, 16 patients with refractory or relapsed AML were treated with sorafenib on different dose schedules. We determined their FLT3 mutation status by a polymerase chain reaction assay and analyzed clinical responses by standard criteria. All statistical tests were two-sided.
Results: Sorafenib was 1000- to 3000-fold more effective in inducing growth arrest and apoptosis in Ba/F3 cells with FLT3-ITD or D835G mutations than in Ba/F3 cells with FLT3-D835Y mutant or wild-type FLT3 and inhibited the phosphorylation of tyrosine residues in ITD mutant but not wild-type FLT3 protein. In a mouse model, sorafenib decreased the leukemia burden and prolonged survival (median survival in the sorafenib-treated group vs the vehicle-treated group = 36.5 vs 16 days, difference = 20.5 days, 95% confidence interval = 20.3 to 21.3 days; P = .0018). Sorafenib reduced the percentage of leukemia blasts in the peripheral blood and the bone marrow of AML patients with FLT3-ITD (median percentages before and after sorafenib: 81% vs 7.5% [P = .016] and 75.5% vs 34% [P = .05], respectively) but not in patients without this mutation.
Conclusion: Sorafenib may have therapeutic efficacy in AML patients whose cells harbor FLT3-ITD mutations.

The Fms-like tyrosine kinase 3 (FLT3) gene encodes a receptor that, when activated by its ligand (FLT3 ligand), supports the survival, proliferation, and differentiation of primitive hematopoietic progenitor cells . Activating mutations in the FLT3 gene, including internal tandem duplications (ITDs) and missense point mutations in the tyrosine kinase domain, are the most frequently observed molecular abnormalities in blood cells of patients with acute myeloid leukemia (AML); these mutations lead to overexpression or constitutive activation of the tyrosine kinase.[1] Internal tandem duplications of the juxtamembrane domain in the FLT3 gene are associated with a poor prognosis.[2] Recently, activating point mutations that involve the D835 residue in the second tyrosine kinase domain were found to be associated with worse disease-free survival in young AML patients.[3] One of the downstream targets of activating FLT3 mutations is the Raf/MEK/ERK signaling pathway.[4] We have previously shown that extracellular signal-regulated kinase (ERK) is constitutively phosphorylated in the majority of primary AML samples[5] and that phosphorylated ERK is associated with poor prognosis in AML, even in the absence of FLT3 gene abnormalities.[6] These observations suggest that activation of ERK itself, either by FLT3 gene mutation or by other factors, such as RAS mutations, may contribute to the survival of AML blast cells.

Inhibitors of several signaling pathways have been developed and are currently in different stages of clinical development, including the FLT3 tyrosine kinase inhibitors lestaurtinib [CEP-701[7]], PKC412, SU11248, and AG1296;[8–10] the MEK1/2 inhibitor CI1040 (PD184352);[11] and PTK787/ZK 222584, which target all vascular endothelial growth factor receptor (VEGFR) tyrosine kinases.[12] However, these agents have not been particularly successful in the treatment of AML when used alone.[7,9,12] It is conceivable that a compound that concomitantly affects several target may be more efficacious than one that targets a single protein.

One such multifunctional kinase inhibitor is sorafenib. Sorafenib was initially designed as a small-molecule inhibitor of c-Raf kinase but has also been shown to inhibit the activities of FLT3, VEGFR-2, VEGFR-3, and members of the platelet-derived growth factor receptor family (ie, PDGFR-beta and Kit).[13,14] Sorafenib was recently approved by the US Food and Drug Administration for the treatment of renal cell and hepatocellular carcinomas. In this study, we investigated the efficacy and mechanisms of action of sorafenib in AML cells harboring FLT3 mutations.

Comments

3090D553-9492-4563-8681-AD288FA52ACE
Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.
Post as:

processing....