Tezacitabine is a synthetic pyrimidine nucleoside analogue with potential antineoplastic activity. Phosphorylated by cellular kinases, tezacitabine is converted into its active diphosphate and triphosphate metabolites. Tezacitabine diphosphate binds to and irreversibly inhibits the activity of the enzyme ribonucleotide reductase (RNR), which may result in the inhibition of DNA synthesis in tumor cells and tumor cell apoptosis.