Mitotic perturbation is a key mechanism of action of decitabine in myeloid tumor treatment

Decitabine (DAC) is used clinically for myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). To elucidate its exact mechanism of action, we performed a genome-wide CRISPR-dCas9 activation screen using MDS-derived AML cells and revealed that mitotic regulation plays a pivotal role in DAC resistance. DAC strongly induces abnormal mitosis (abscission failure or tripolar mitosis) in human myeloid tumors at clinical concentrations, especially in those with TP53 mutations and antecedent hematological disorders. This DAC-induced mitotic disruption and apoptosis are significantly attenuated in DNMT1-depleted cells. In contrast, the overexpression of Dnmt1, but not the catalytically inactive mutant, enhances DAC-induced mitotic defects in myeloid tumors. These data challenge the current assumption that DAC inhibits leukemogenesis through DNMT1 inhibition and subsequent DNA hypomethylation and highlight the potent activity of DAC to perturb mitosis through aberrant DNMT1-DNA covalent bonds. This clinically revised mode of action is enhanced by pharmacological inhibition of the ATR-CLSPN-CHK1 pathway. Overall design: Our genome-wide CRISPRa screen revealed the enrichment of genes related to cholesterol metabolism, such as Srebf2, Ldlr, Cyp51 and Pcyt2, in decitabine resistance. Statins are one of the most widely used drugs worldwide and suppress endogenous cholesterol synthesis by inhibiting HMG-CoA reductase. We found that both simvastatin and lovastatin synergized with DAC to inhibit the growth of HL-60 cells and Kasumi-1 cells in several reference models. Therefore, We next performed RNA-seq of HL-60 treated with DAC, simvastatin or both.