Novel flavagline‐like compounds with potent Fli‐1 inhibitory activity suppress diverse types of leukemia

Abstract

E26 transformation‐specific (ETS) gene family contains a common DNA‐binding domain, the ETS domain, responsible for sequence‐specific DNA recognition on target promoters. The Fli‐1 oncogene, a member of ETS gene family, plays a critical role in hematopoiesis and is overexpressed in diverse hematological malignancies. This ETS transcription factor regulates genes controlling several hallmarks of cancer and thus represents an excellent target for cancer therapy. By screening compounds isolated from the medicinal plant Dysoxylum binectariferum in China, we identified two chemically related flavagline‐like compounds including 4′‐demethoxy‐3′,4′‐methylenedioxyrocaglaol and rocaglaol that strongly inhibited Fli‐1 transactivation ability. These compounds altered expression of Fli‐1 target genes including GATA1, EKLF, SHIP1, and BCL2. Consequently, the flavagline‐like compounds suppressed proliferation, induced apoptosis, and promoted erythroid differentiation of leukemic cells in culture. These compounds also suppressed erythroleukemogenesis in vivo in a Fli‐1‐driven mouse model. Mechanistically, the compounds blocked c‐Raf‐MEK‐MAPK/ERK signaling, reduced phosphorylation of eukaryotic translation initiation factor 4E (eIF4E), and inhibited Fli‐1 protein synthesis. Consistent with its high expression in myelomas, B‐cell lymphoma, and B chronic lymphocytic leukemia (B‐CLL), pharmacological inhibition of Fli‐1 by the flavagline‐like compounds or genetic knock‐down via shRNA significantly hindered proliferation of corresponding cell lines and patients’ samples. These results uncover a critical role of Fli‐1 in growth and survival of various hematological malignancies and point to flavagline‐like agents as lead compounds for the development of anti‐Fli‐1 drugs to treat leukemias/lymphomas overexpressing Fli‐1.

FLI1 promotes protein translation via the transcriptional regulation of MKNK1 expression

“…The authors have previously reported that the anti-FLI1 A1544 and A1545 compounds downregulate the phosphorylation of eIF4E in leukemic cell lines (22). Accordingly, in this study, the expression of MKNK1, an upstream regulator of eIF4E, was found to be lower in the HEL cells treated with the A1544 and A1545 compounds (3 µM), compared to the control DMSO-treated cells (Fig.…”

“…pathway. Previous studies have suggested that MYC (cMYC) expression is downstream of the MKNK1 pathway (22,24). However, in this study, while the anti-FLI1 compounds, A1544 and A1545, and the specific MKNK1 inhibitor, CGP57380, markedly inhibited MKNK1 and downstream phospho-eIF4A expression, the level of MYC remained unaltered by treatment with A1544 and A1545 (Fig.…”

“…Accordingly, several classes of compounds with a potent anti-FLI1 activity have recently been identified (18)(19)(20)(21)(22). Among these, two flavagline-like compounds exhibiting potent FLI1 inhibition were also identified (22). These compounds suppress c-Raf-MEK-MAPK/ERK signaling, resulting in the reduced phosphorylation of eIF4E and the inhibition of FLI1 protein synthesis.…”

“…For drug treatment, the HEL cells were treated with 3 µM of A1544, A1545 (22) and CGP57380 and 24 h later subjected to either western blot analysis or RT-qPCR. The drug CGP57380 was obtained from Selleckchem.…”

“…The inhibitor of MKNK1 (CGP57380) was obtained from Selleckchem. The Fli-1 inhibitors, A1544 and A1545, were used as previously described (22).…”