Ansatrienin A is an ansamycin antibiotic and antifungal agent first isolated from S. collinus and S. rishiriensis. In fetal rat long bones, it is an inhibitor of parathyroid hormone-induced calcium release (IC50 = 64 nM), which is a measure of bone resorption, and pp60c-srcM kinase (IC50 = 100 nM). It also inhibits TNF-α-induced expression of intercellular adhesion molecule-1 (ICAM-1; IC50 = 570 nM). Early in vitro studies showed that ansatrienin A potentiates the chemotherapeutic action of 5-fluorouracil , cisplatin , bleomycin , mitomycin C , and 6-mercaptopurine. It is an oxidized form of ansatrienin B .