Inhibition of mitochondria induces apoptosis and reduces telomere length and activity in acute myeloid leukemia stem cells

Acute myeloid leukemia (AML) is a highly lethal hematological malignancy in adults and children. Abnormal proliferation of leukemia stem cells (LSC) with CD34+ and CD38- phenotypes are the main clinical features of AML. Patients with AML face drug resistance and treatment failure due to a default in stem and progenitor cells. Therefore, defining LSC properties is necessary for targeting leukemia-initiating cells. Mitochondrial mass and activity increase in AML initiating cells compared with normal stem cells. This idea has offered the inhibition of the mitochondrial translation machinery to reduce the number of leukemia-initiating cells in patients with AML Tigecycline is an FDA-approved microbial antibiotic that inhibits oxidative phosphorylation in mitochondria, resulting in the suppression of leukemia cell proliferation with little toxicity to normal cells. Thus, the present study was conducted to evaluate whether LSC is influenced by mitochondrial inhibition. We measured the IC50 of tigecycline in KG-1a AML cell lines. KG-1a AML cell lines were separated into CD34+ and CD34- cells by MACS. In the following, these cells were treated with 20 mu M (IC50) tigecycline. The expression of Annexin/PI, Caspase 3, apoptotic genes (BCL2, BCLX, BAX, BAD, and P53) and proteins (P53, BAX, BCL2 and Caspase 9) was evaluated in CD34+, CD34- and KG-1a AML cells. In addition, the telomere length and expression of hTERT were evaluated in this study. The results indicated that BCl2 (gene and protein) and BCLX gene dramatically decreased. In addition, BAD, BAX, and P53 gene and protein expression significantly increased in CD34+ AML cells compared to CD34- AML cells. The results also suggested that tigecycline induced intrinsic (Cleaved-caspase 9/Pro-Caspase 9 ratio) and p53-mediated apoptosis. Furthermore, hTERT gene expression and telomere length decreased in the tigecycline-treated groups. Taken together, our findings indicate that inhibition of mitochondrial activity with tigecycline can induce apoptosis in cancer stem cells and can be used as a novel method for cancer therapy. One of the main causes of treatment failure in patients with acute myeloid leukemia is the existence of cancer stem cells. Cancer stem cells have abundant mitochondria mass and high oxygen consumption compared with normal cells. Tigecycline suppresses leukemia cell proliferation by inhibiting oxidative metabolism. In this study, we have shown that the inhibition of mitochondrial activity by tigecycline affects cancer stem cells in comparison with other cells.