Flt3 inhibitor AC220 is a potent therapy in a mouse model of myeloproliferative disease driven by enhanced wild-type Flt3 signaling

Abstract

High levels of expression of wild-type Flt3 characterize many hematopoietic proliferative diseases and neoplasms, providing a potential therapeutic target. Using the c-Cbl RING finger mutant mouse as a model of a myeloproliferative disease (MPD) driven by wild-type Flt3, in the present study, we show that treatment with the Flt3 kinase inhibitor AC220 blocks MPD development by targeting Flt3 ؉ multipotent progenitors (MPPs). We found that daily administration of AC220 caused a marked reduction in Flt3 expression, induction of quiescence, and a significant loss of MPPs within 4 days. Unexpectedly, a robust Flt3 ligand-associated proliferative recovery response soon followed, preventing further loss of MPPs. However, continued AC220 treatment limited MPP recovery and maintained reduced, steady-state levels of cycling MPPs that express low levels of Flt3. Therefore, a finely tuned balance between the opposing forces of AC220 and Flt3 ligand production was established; whereas the Flt3 ligand blunted the inhibitory effects of AC220, the disease was held in remission for as long as therapy was continued. The net effect is a potent therapy indicating that patients with c-Cbl mutations, or those with similarly enhanced Flt3 signaling, may respond well to AC220 even after the induction of high levels of Flt3 ligand. (Blood. 2012;120(19): 4049-4057) IntroductionThe Flt3 receptor tyrosine kinase is expressed at high levels on most myeloid and lymphoblastic leukemias, 1 and for many years it has been considered a potential target for compounds that inhibit its kinase activity. 2,3 However, it has been difficult to test this possibility because of a lack of both suitable animal models and Flt3 inhibitors with the desired potency, specificity, and pharmacokinetic properties. Recently, we characterized a mouse with an inactivating knock-in mutation in the RING finger domain of the c-Cbl E3 ubiquitin ligase that has provided a model for studying myeloid malignancies driven by enhanced Flt3 signaling. This mouse develops a myeloproliferative disease (MPD) progressing to lethal leukemia that is characterized by markedly elevated WBC counts, splenomegaly, and extensive myeloid cell invasion into peripheral organs. 4 Analysis of Lin Ϫ Sca-1 ϩ c-Kit ϩ (LSK) cells in the BM revealed a marked expansion of cells expressing high levels of Flt3 compared with LSK cells from wild-type and c-Cbl-deficient mice. 4 Furthermore, the Flt3 ϩ LSK cells (defined as multipotent progenitors, MPPs) 5 showed enhanced Flt3 signaling to the Erk and PI3K pathways. When these mice were mated to Flt3 ligand-deficient mice, the doubly mutant mice did not develop leukemia, 4 indicating that Flt3 signaling is an essential component for driving disease development.Mutations in c-Cbl have been identified in 5%-20% of patients within the World Health Organization (WHO) groupings of myelodysplastic syndrome (MDS) and myelodysplastic/myeloproliferative neoplasm (MDS/MPN). 6-14 MDS/MPN patients are further classified into chronic myelomonocytic leukemia, juvenile ...

LAMTOR2 regulates dendritic cell homeostasis through FLT3-dependent mTOR signalling

“…In another mouse model developing MPD due to enhanced wild-type Flt3 signalling, AC220 could hold the disease in remission during the therapy period35. The mice were treated daily for 28 days with 10 mg kg −1 AC220 or vehicle by oral gavage and then killed to investigate the effect on the DC compartment.…”

CBL family E3 ubiquitin ligases control JAK2 ubiquitination and stability in hematopoietic stem cells and myeloid malignancies

“…Of note, inhibitors to two known CBL targets in hematopoietic cells, KIT and FLT3, have been tested in the RF knock-in Cbl C379A/− mice that develop a similar disease but with a longer latency (Rathinam et al 2010). While the FLT3 inhibitor (FLT3i) quizartinib temporarily alleviated CMML development in this model, the c-Kit/Src inhibitor dasatinib failed to impact the disease in Cbl C379A/− mice (Taylor et al 2012;Duyvestyn et al 2014). Based on our new findings, we set out to test whether JAK2 inhibition could abrogate CMML development in Cbl;Cbl-b conditional double-knockout mice.…”

Functions of flt3 in zebrafish hematopoiesis and its relevance to human acute myeloid leukemia

“…41,43 We tested whether AC220 could recapitulate the hematopoietic phenotypes of the flt3 morphants. AC220 (2.5 mmol/L) had no effect on embryo morphology but significantly reduced the expression of l-plastin in the anterior yolk sac at 18 hpf ( Figure 4A-C) and c-myb in the ventral wall of DA at 32 ( Figure 4D-E) and 96 hpf ( Figure 4J-K) as well as rag1 in the thymus at 96 hpf ( Figure 4L-M).…”