Sorafenib as monotherapy or in association with cytarabine and clofarabine for the treatment of relapsed/refractory FLT3 ITD-positive advanced acute myeloid leukemia

Leukoreductive response to the combination of sorafenib and chemotherapy in hyperleukocytosis of FLT3-ITD mutated pediatric AML

Twelve to 22% of pediatric acute myeloid leukemia (AML) patients present with hyperleukocytosis, which is one of the main risk factors of early death due to its clinical complications: leukostasis, causing pulmonary or central nervous system injuries, tumor lysis syndrome, and disseminated intravascular coagulation. Sorafenib is a multi-kinase inhibitor that blocks the Fms-Related Tyrosine Kinase 3 receptor (FLT3) in AML patients with a FLT3-internal tandem duplication (FLT3-ITD), leading to a reduction of proliferation. Here we report four de novo diagnosed or relapsed pediatric FLT3-ITD-positive AML patients with hyperleukocytosis, which were treated with sorafenib in combination with cytoreductive chemotherapy prior to the start of the induction phase. We observed a fast reduction of white blood cells in peripheral blood and bone marrow. This resulted in a rapid clinical stabilization of the patients. Adverse side effects-such as dermatologic toxicity, elevation of transaminases and hypertension-occurred but were mild and inductive chemotherapy could be started in parallel or subsequently. This implies sorafenib as a safe and effective treatment option in combination with chemotherapy during cytoreductive prephase for children with this life-threatening condition.

Synergistic cytotoxicity of sorafenib with busulfan and nucleoside analogs in human FMS-like tyrosine kinase 3 internal tandem duplications-positive acute myeloid leukemia cells

Clofarabine (Clo), fludarabine (Flu), and busulfan (Bu) are used in pretransplantation conditioning therapy for patients with myeloid leukemia. To further improve their efficacy in FMS-like tyrosine kinase 3 internal tandem duplications (FLT3-ITD)-positive acute myeloid leukemia (AML), we investigated their synergism with sorafenib (Sor). Exposure of FLT3-ITD-positive MV-4-11 and MOLM 13 cells to Bu+Clo+Flu+Sor resulted in synergistic cytotoxicity; no such synergism was observed in the FLT3-wild type THP-1 and KBM3/Bu250(6) cell lines. The drug synergism in MV-4-11 cells could be attributed to activation of DNA damage response, histone 3 modifications, inhibition of prosurvival kinases, and activation of apoptosis. Further, the phosphorylation of kinases, including FLT3, MAPK kinase (MEK), and AKT, was inhibited. The FLT3-ITD substrate STAT5 and its target gene PIM 2 product decreased when cells were exposed to Sor alone, Bu+Clo+Flu, and Bu+Clo+Flu+Sor. The level of the proapoptotic protein p53 upregulated modulator of apoptosis (PUMA) increased, whereas the level of prosurvival protein MCL-1 decreased when cells were exposed to Bu+Clo+Flu+Sor. The interactions of PUMA with MCL-1 and/or BCL-2 were enhanced when cells were exposed to Bu+Clo+Flu or Bu+Clo+Flu+Sor. The changes in the level of these proteins, which are involved in mitochondrial control of apoptosis, correlate with changes in mitochondrial membrane potential. Bu+Clo+Flu+Sor decreased mitochondrial membrane potential by 60% and caused leakage of cytochrome c, second mitochondria-derived activator of caspases (SMAC)/direct IAP Binding protein with low pI (DIABLO), and AIF from the mitochondria to the cytoplasm, caspase activation, and cell death, suggesting the activation of apoptosis. Analogous, synergistic cytotoxicity in response to Bu, Clo, Flu, and Sor was observed in mononuclear cells isolated from FLT3-ITD-positive AML patients. Although our previous studies were aimed at standardizing the conditioning regimen, the new findings suggest that patients with abnormal expression of FLT3 might further benefit from individualizing treatment through the addition of Sor to Bu+Clo+Flu, thereby providing personalized pretransplantation therapy.