Skip to content
Bending the Curve Trial by Trial
?

Purine analoguesIn useRational design

Thioguanine

Also known as 6-thioguanine, 6-TG, Tabloid

A guanine-based purine analogue taken by mouth, made in the same programme as mercaptopurine. Its 2025 US label lists remission induction and consolidation in acute nonlymphocytic leukaemias and does not recommend maintenance use.

From discovery to approval

  1. c. 1951 · Earliest report found

    In Elion's 1988 Nobel lecture, 6-thioguanine and 6-mercaptopurine came from a screen of over 100 purines in Lactobacillus casei by 1951: replacing oxygen with sulfur at the 6-position of guanine and hypoxanthine gave inhibitors of purine use. She calls thioguanine the 2-amino-6-mercapto derivative with strong antimetabolic activity. A 1956 paper reported its effects in mammals (title only).[2][3][4]

  2. 1966-01-18 · FDA regular · 15 years after first description

    Thioguanine tablets, NDA 012429, original approval, classed as a new molecular entity with priority review in the Drugs@FDA history. The original label and letter are not available there, so the indication at approval is not stated here. The type regular is an inference: no accelerated-approval wording was found. The 2025 label lists remission induction and consolidation in acute nonlymphocytic leukaemias.[4]

How it works

Thioguanine is incorporated into the DNA and RNA of human bone marrow cells; with five daily doses the label reports more than 100 times as much incorporated as after one dose, with up to virtually all residual DNA guanine replaced.[1]

Where it came from and why

The programme aimed to find antagonists of the nucleic acid bases that could stop rapidly dividing cells. Elion says 6-thioguanine and 6-mercaptopurine were both active in rodent tumours and leukaemias at the Sloan-Kettering Institute.

Cancers

  • Acute nonlymphocytic leukaemias

    The 2025 US label lists remission induction and consolidation in acute nonlymphocytic leukaemias, and says combination chemotherapy including thioguanine gives more frequent remission induction and longer remission than thioguanine alone.[1]

Worth knowing

  • The label does not recommend thioguanine for maintenance or other long-term continuous treatment because of the high risk of liver toxicity.[1]
  • The label states that thioguanine is not effective in chronic lymphocytic leukaemia, Hodgkin's lymphoma, multiple myeloma or solid tumours.[1]
  • The label states that in animals and humans there is usually complete cross-resistance between Purinethol (mercaptopurine) and Tabloid thioguanine.[1]
  • The Drugs@FDA history lists the original application (NDA 012429) as approved on 18 January 1966, a new molecular entity with priority review; the original label is not available there.[4]

References

  1. Waylis Therapeutics LLC. Tabloid (thioguanine): prescribing information. DailyMed, set ID 44b0c461-47fb-4106-ba11-6ed85530235c, published 10 January 2025. Read 26 October 2026. Source
  2. Elion GB. The purine path to chemotherapy. Nobel Lecture, 8 December 1988. NobelPrize.org (lecture text, 22 pages). Source
  3. Philips FS, Sternberg SS, Hamilton LD, Clarke DA, et al. Effects of thioguanine in mammals. Cancer. 1956;9(6):1092-101. PubMedDOI
  4. U.S. Food and Drug Administration. Drugs@FDA: Approval date(s) and history, letters, labels, reviews for NDA 012429 (thioguanine). Page read 2026-10-26. Source