探討選擇性抑制劑cabozantinib在in vitro及in vivo 針對帶有 FLT3-ITD突變之難治型急性骨髓性白血病的抑殺效果

Abstract

FLT3-ITD internal tandem duplication (ITD) mutations occur in 30% of acute myeloid leukemia (AML) patients. In clinical studies, patients with FLT3-ITD mutation are associated with adverse prognosis, and hence FLT3 is considered to be a potential target for AML therapies. Many FLT3 inhibitors have been developed and are undergoing clinical investigation. However, emerging of drug resistance after treatment has become an obstacle for full recovery. Development of new FLT3 inhibitors is urgently needed for better therapeutic strategies. Cabozantinib is a multikinase inhibitor that targets MET, VEGFR2, RET, KIT, TIE-2, and FLT3. It was found to be selectively cytotoxic to AML cells harboring FLT3-ITD in previous study. By using MTS assay and western blot analysis, we first confirmed the selective cytotoxicity of cabozantinib to FLT3-ITD cell line MV4-11 (IC50< 10nM) in vitro. After drug treatment, inhibition of active FLT3 and its downstream signaling pathway was detected as well. In xenograft model, cabozantinib effectively suppressed MV4-11 tumor growth through FLT3 inhibition and increased the survival of mice (p<0.01). To evaluate the possible application of cabozantinib in AML patients with chemotherapeutic resistance, we also tested a cell line MV4-11R established in our lab beforehand, which is resistant to cytarabine, a chemotherapeutic agent for AML. The results showed that MV4-11R was sensitive to cabozantinib in vitro. Valid inhibition of MV4-11R tumor growth and the extension of survival after treatment could be found in vivo. To evaluate the efficacy of cabozantinib, we further investigated several factors, which have been identified to confer drug resistance. Compared to normal condition, cabozantinib inhibited MV4-11 and MV4-11R cell growth with increased IC50 under either FL stimulation or stromal environment, implicating less drug sensitivity. Higher concentration of cabozantinib treatment in a short period still displayed strong inhibition on FLT3 pathway. The inhibitory effect of cabozantinib on FLT3 pathway could be influenced by human plasma environment. Moreover, we examined the sensitivity of primary bone marrow mononuclear cells to cabozantinib ex vivo. Reduction of cell viability and decreased level of phosphorylated FLT3 were both detected in FLT3-ITD AML cells. In brief, these results demonstrate cabozantinib as an effective inhibitor for FLT3-ITD AML cells growth both in vitro and in vivo, and it could be a potential target therapeutic agent for AML treatment. Further investigation on underlying drug resistance of cabozantinib is needed.