Active Motif's After incorporation into DNA, 6-Thioguanine disrupts cytosine methylation by DNA methyltransferases in vitro and acts as a DNA demethylating agent in vivo. It reactivates epigenetically silenced genes in acute lymphoblastic leukemia cells by facilitating proteasome-mediated degradation of DNA methyltransferase (DNMT1). 6-Thioguanine incorporates into DNA and induces double-strand breaks which destabilize DNA structure resulting in cytotoxicity. It selectively kills BRCA2-defective tumors and overcomes PARP inhibitor resistance in xenograft model. It has anti-cancer and immunosuppressive activity.