4'-Thio-2'-deoxycytidine
4-Thio-2-deoxycytidine is an orally bioavailable 4-thio modified 2-deoxycytidine analog, with potential antineoplastic activity. Upon administration of 4-thio-2-deoxycytidine (TdCyd), this cytidine analog gets incorporated into DNA during replication and inhibits the activity of DNA methyltransferase 1 (DNMT1), which blocks DNA hypermethylation. This results in DNMT1 depletion, hypomethylation of DNA, and the reactivation of tumor suppressor genes that were silenced by hypermethylation; this results in antitumor activity and an inhibition of tumor cell proliferation.