Transient Low Doses of DNA-Demethylating Agents Exert Durable Antitumor Effects on Hematological and Epithelial Tumor Cells

SummaryReversal of promoter DNA hypermethylation and associated gene silencing is an attractive cancer therapy approach. The DNA methylation inhibitors decitabine and azacitidine are efficacious for hematological neoplasms at lower, less toxic, doses. Experimentally, high doses induce rapid DNA damage and cytotoxicity, which do not explain the prolonged time to response observed in patients. We show that transient exposure of cultured and primary leukemic and epithelial tumor cells to clinically relevant nanomolar doses, without causing immediate cytotoxicity, produce an antitumor “memory” response, including inhibition of subpopulations of cancer stem-like cells. These effects are accompanied by sustained decreases in genomewide promoter DNA methylation, gene reexpression, and antitumor changes in key cellular regulatory pathways. Low-dose decitabine and azacitidine may have broad applicability for cancer management.

► Transient DAC or AZA sustains antitumor responses and reduces self-renewal
► Acute cytotoxicity does not appear to account for the lasting effects of the drugs
► Low-dose DAC causes sustained global DNA demethylation and gene reexpression
► Low-dose DAC or AZA sustains antitumor responses through key signaling pathways