Icaritin, a hydrolytic product of icaritin, is isolated from the traditional Chinese medicinal herb epimedium. Icaritin inhibits the proliferation of several tumor cell lines, but its effect on acute myeloid leukemia (AML) and underlying mechanisms remain to be identified. In the present study, we demonstrated that icaritin inhibits the proliferation of human AML cell lines NB4, HL60, and U937, in a dose- and time-dependent manner. Importantly, icaritin showed anti-leukemia activity on bone marrow mononuclear cells from 15 newly diagnosed AML patients. Flow cytometry analyses indicated that icaritin induces AML cells apoptosis. Icaritin induced activation of caspase-9, -3, -7 and the cleavage of PARP as measured by Western blotting. Icaritin downregulates p-ERK and p-AKT and inhibits the expression of c-myc. These results suggest that icaritin is a promising candidate drug for the treatment of AML. The underlying mechanisms of icaritin anti-AML activity are associated with inhibition of the MAPK/ERK and PI3K/AKT signals and downregulation of c-myc.

SummaryNatural genetic diversity offers an important yet largely untapped resource to decipher the molecular mechanisms regulating hematopoietic stem cell (HSC) function. Latexin (Lxn) is a negative stem cell regulatory gene identified on the basis of genetic diversity. By using an Lxn knockout mouse model, we found that Lxn inactivation in vivo led to the physiological expansion of the entire hematopoietic hierarchy. Loss of Lxn enhanced the competitive repopulation capacity and survival of HSCs in a cell-intrinsic manner. Gene profiling of Lxn-null HSCs showed altered expression of genes enriched in cell-matrix and cell-cell interactions. Thrombospondin 1 (Thbs1) was a potential downstream target with a dramatic downregulation in Lxn-null HSCs. Enforced expression of Thbs1 restored the Lxn inactivation-mediated HSC phenotypes. This study reveals that Lxn plays an important role in the maintenance of homeostatic hematopoiesis, and it may lead to development of safe and effective approaches to manipulate HSCs for clinical benefit.

High-risk B-cell acute lymphoblastic leukemia (B-ALL) remains a therapeutic challenge despite advances in the use of tyrosine kinase inhibitors and chimeric-antigen-receptor engineered T cells. Lymphoblastic-leukemia precursors are highly sensitive to oxidative stress. KLF5 is a member of the Krüppel-like family of transcription factors. KLF5 expression is repressed in B-ALL, including BCR-ABL1+ B-ALL. Here, we demonstrate that forced expression of KLF5 in B-ALL cells bypasses the imatinib resistance which is not associated with mutations of BCR-ABL. Expression of Klf5 impaired leukemogenic activity of BCR-ABL1+ B-cell precursors in vitro and in vivo. The complete genetic loss of Klf5 reduced oxidative stress, increased regeneration of reduced glutathione and decreased apoptosis of leukemic precursors. Klf5 regulation of glutathione levels was mediated by its regulation of glutathione-S-transferase Mu 1 (Gstm1), an important regulator of glutathione-mediated detoxification and protein glutathionylation. Expression of Klf5 or the direct Klf5 target gene Gstm1 inhibited clonogenic activity of Klf5∆/∆ leukemic B-cell precursors and unveiled a Klf5-dependent regulatory loop in glutamine-dependent glutathione metabolism. In summary, we describe a novel mechanism of Klf5 B-ALL suppressor activity through its direct role on the metabolism of antioxidant glutathione levels, a crucial positive regulator of leukemic precursor survival.

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