Decitabine is believed to exert its antineoplastic effects following its conversion to decitabine triphosphate, where the drug directly incorporates into DNA and inhibits DNA methyltransferase, the enzyme that is responsible for methylating newly synthesized DNA in mammalian cells. This results in hypomethylation of DNA and cellular differentiation or apoptosis. Decitabine inhibits DNA methylation in vitro, which is achieved at concentrations that do not cause major suppression of DNA synthesis. Decitabine-induced hypomethylation in neoplastic cells may restore normal function to genes that are critical for the control of cellular differentiation and proliferation. In rapidly dividing cells, the cytotoxicity of decitabine may also be attributed to the formation of covalent adducts between DNA methyltransferase and decitabine that has been incorporated into DNA. Non-proliferating cells are relatively insensitive to decitabine. Decitabine is cell cycle specific and acts peripherally in the S phase of the cell cycle. It does not inhibit the progression of cells from the G1 to S phase.
Decitabine is an analogue of the natural nucleoside 2’-deoxycytidine. It functions in the same way as 5-Azacytidine. The antineoplastic activity of this drug is dependent on its intracellular conversion to its 5'-triphosphate metabolite.
The exact route of elimination and metabolic fate of decitabine is not known in humans. One of the pathways of elimination of decitabine appears to be deamination by cytidine deaminase found principally in the liver but also in granulocytes, intestinal epithelium and whole blood.
There is no known antidote for overdosage with decitabine. Higher doses are associated with increased myelosuppression including prolonged neutropenia and thrombocytopenia.