MITOTIC PERTURBATION IS A KEY MECHANISM OF ACTION OF DECITABINE IN MYELOID TUMOR TREATMENT

Abstract

Introduction: Decitabine (DAC) is an epigenetic drug clinically used for the treatment of myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). However, its exact mechanism of action is unclear. Methods: To uncover the mechanisms underlying resistance to HMA, we performed genome-scale CRISPR activation screen using murine MDS/AML cells expressing ASXL1 and SETBP1 mutants (cSAM). Results: Our genome-wide CRISPR-dCas9 activation screen using MDS-derived AML cells indicates that mitotic regulation is critical for 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 or antecedent hematological disorders. This DAC-induced mitotic disruption and apoptosis are significantly attenuated in DNMT1-depleted cells. In contrast, overexpression of Dnmt1, but not the catalytically inactive mutant, enhances DAC-induced mitotic defects in myeloid tumors. We also demonstrate that DAC-induced mitotic disruption is enhanced by pharmacological inhibition of the ATR-CLSPN-CHK1 pathway. In addition, transcriptome and metabolome analyses combined with our screen revealed the involvement of cholesterol metabolism in DAC resistance. Inhibition of cholesterol synthesis using statins delayed mitotic progression, suggesting that cholesterol is also important for proper mitosis. Moreover, co-treatment with DAC and statin caused mitotic catastrophe and showed synergistic growth-inhibitory effects in leukemia cells. Conclusions: 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 disrupt mitosis through aberrant DNMT1-DNA covalent bonds.