Myriocin is an amino fatty acid antibiotic derived from certain thermophylic fungi, in this case Mycelia sterilia. It is a potent immunosuppressant having 10- to 100-fold more activity than cyclosporin A. Myriocin is a potent inhibitor of serine palmitoyltransferase (Ki = 0.28 nM), the enzyme that catalyzes the first step of sphingolipid biosynthesis. It disrupts substratum adhesion of melanoma cells. It also suppresses cell proliferation in the murine cytotoxic T cell line CTLL-2 (IC50 = 15 nM) via apoptosis. Myriocin suppresses replication of the hepatitis C virus (HCV) in a murine model.