Acute myeloid leukemias are a group of malignant hemopathies characterized by a poor prognosis for survival. The discovery of oncogenic mutations in the FLT3 gene (eq FLT3-ITD) has led to the development of new tyrosine kinase inhibitors such as quizartinib. But complete remissions of patients remains difficult because these new TKIs are not able to completely eradicate all leukemia cells. Residual leukemia cells persist during treatment with quizartinib and lead to the rapid emergence of drug-resistant leukemia. Since mitochondrial oxidative metabolism supports the survival of leukemia cells after exposure to several anticancer drugs, we characterized the metabolism of leukemia cells that persisted within quizartinib treatment and developed metabolic strategies to eradicate them.
First, we evaluated glycolysis activity in FLT3-ITD leukemia cell lines (MOLM13 / MOLM14 / MV4-11) under quizartinib treatment (5-10nM). Quizartinib reduced extracellular acidification rate ECAR, but this glycolytic activity is not fully inhibited (50% of untreated condition). These results obtained using the XFe24 Seahorse were in agreement with the metabolomic analysis carried out in a medium containing isotopic U-13C6 glucose. Next we evaluated mitochondrial oxidative phosphorylation in FLT3-ITD leukemia cell lines. After treatment with quizartinib, the basal and maximal oxygen consumption (OCR) of leukemia cells decreased. Metabolomic analysis using isotopic glucose U-13C6 or glutamine U-13C5 have shown that pyruvate derived from glucose was weakly oxidized in the mitochondria of untreated or quizartinib-treated cells. In contrast, a large amount of glutamine was oxidized by the tricarboxylic acid (TCA) cycle in untreated FLT3-ITD cells. Quizartinib reduced but did not abolish the complete oxidation of glutamine in leukemia cells. This result showed that even in the presence of quizartinib, FLT3-ITD cells maintained partially oxygen consumption trough glutamine oxidation.
L-asparaginases (Kidrolase, Erwinase) are enzymes capable of hydrolyzing amino acids such as asparagine and glutamine. These clinical drugs have been approved for the treatment of chronic lymphocytic leukemia (CLL) and pediatric acute myeloid leukemia. We have shown that L-asparaginases weakly induced cell death in FLT3-ITD leukemia cells. Interestingly, our isobologram analysis showed that L-asparaginase acted synergistically with quizartinib to induce apoptosis. To determine whether glutamine metabolism also promoted the persistence of AML under treatment with quizartinib, we treated MOLM13 with quizartinib for several days. After long-term treatment, the percentage of surviving cells (annexin-V negative) was less than 5%. These persistent cells were characterized by an increased mitochondrial membrane potential (Δψm) and mitochondrial ROS. After treatment with the combination of L-asparaginase and quizartinib, the percentage of persistent cells decreased drastically. The combination of L-asparaginase and quizartinib was also more effective than quizartinib alone in reducing the size and number of colonies of MOLM13 in a model based on the formation of leukemia colonies growing in methylcellulose.
Persistent leukemia cells that survive after exposure to FLT3 inhibitor quizartinib can be targeted by the clinical drug L-asparaginases. This metabolic strategy could reduce the emergence of leukemic cells resistant to quizartinib.
Kluza:Daiichi-Sankyo: Research Funding.
Asterisk with author names denotes non-ASH members.