Inhibition of autophagy as a treatment strategy for p53 wild-type acute myeloid leukemia

Here we have explored whether inhibition of autophagy can be used as a treatment strategy for acute myeloid leukemia (AML). Steady-state autophagy was measured in leukemic cell lines and primary human CD34(+) AML cells with a large variability in basal autophagy between AMLs observed. The autophagy flux was higher in AMLs classified as poor risk, which are frequently associated with TP53 mutations (TP53(mut)), compared with favorable- and intermediate-risk AMLs. In addition, the higher flux was associated with a higher expression level of several autophagy genes, but was not affected by alterations in p53 expression by knocking down p53 or overexpression of wild-type p53 or p53(R273H). AML CD34(+) cells were more sensitive to the autophagy inhibitor hydroxychloroquine (HCQ) than normal bone marrow CD34(+) cells. Similar, inhibition of autophagy by knockdown of ATG5 or ATG7 triggered apoptosis, which coincided with increased expression of p53. In contrast to wild-type p53 AML (TP53(wt)), HCQ treatment did not trigger a BAX and PUMA-dependent apoptotic response in AMLs harboring TP53(mut). To further characterize autophagy in the leukemic stem cell-enriched cell fraction AML CD34(+) cells were separated into ROS(low) and ROS(high) subfractions. The immature AML CD34(+)-enriched ROS(low) cells maintained higher basal autophagy and showed reduced survival upon HCQ treatment compared with ROS(high) cells. Finally, knockdown of ATG5 inhibits in vivo maintenance of AML CD34(+) cells in NSG mice. These results indicate that targeting autophagy might provide new therapeutic options for treatment of AML since it affects the immature AML subfraction.