A drug used to treat acute myeloid leukemia (AML). It is also being studied in the treatment of other types of cancer. Thioguanine stops cells from making DNA and RNA and it may kill cancer cells. It is a type of antimetabolite. Also called Tabloid. OR A synthetic guanosine analogue antimetabolite. Phosphorylated by hypoxanthine-guanine phosphoribosyltransferase, thioguanine incorporates into DNA and RNA, resulting in inhibition of DNA and RNA syntheses and cell death. This agent also inhibits glutamine-5-phosphoribosylpyrophosphate amidotransferase, thereby inhibiting purine synthesis.