Thiopurine
The thiopurine drugs are purine antimetabolites widely used in the treatment of acute lymphoblastic leukemia, autoimmune disorders, and organ transplant recipients.
Metabolism is catalyzed by S-methyltransferase.
Litigation over patents covering diagnostic kits to monitor the dosing of these drugs led to a US Supreme Court case, Mayo Collaborative Services v. Prometheus Laboratories, Inc. that dramatically changed the nature of patent law in the United States.