In vitro activity: Zebularine is a cytidine analogue containing a 2-(1H)-pyrimidinone ring, originally synthesized as a cytidine deaminase inhibitor. Zebularine is shown to form a tight, covalent complex with bacterial methyltransferases. In N. crassa, zebularine inhibits DNA methylation and reactivates a gene previously silenced by methylation. Zebularine is a global inhibitor of DNA methylation, similar to 5-Aza-CR, rather than a selective inhibitor. Zebularine induces the myogenic phenotype in 10T1/2 cells, which is a phenomenon unique to DNA methylation inhibitors. Zebularine reactivates a silenced p16 gene and demethylates its promoter region in T24 bladder carcinoma cells. Zebularine is only slightly cytotoxic to T24 cells. Zebularine is preferentially incorporated into DNA and exhibits greater cell growth inhibition and gene expression in cancer cell lines compared to normal fibroblasts. In addition, zebularine preferentially depletes DNA methyltransferase 1 (DNMT1) and induces expression of cancer-related antigen genes in cancer cells relative to normal fibroblasts.

Cell Assay: For methylation analysis, 10T1/2 cells and T24 cells are treated with the various concentrations of zebularine. For 10T1/2 cells, the medium is changed 24 hours after the initial drug treatment, whereas for T24 cells, the medium is changed 24 hours or 48 hours after the initial drug treatment. DNA and RNA are harvested from 10T1/2 cells 72 hours after initial drug treatment and from T24 cells 96 hours after initial drug treatment. The methylation status of the indicated DNA regions is measured in two separate and independent experiments, both of which are done in duplicate.