Immunosuppressive agents are widely used in the treatment of autoimmune disease and in treating or preventing transplantation rejection, including the treatment of graft-versus-host disease (GVHD). Common immunosuppressive agents include azathioprine, corticosteroids, cyclophosphamide, methotrexate, 6-mercaptopurine, vincristine, and cyclosporin A. In general, none of these drugs are completely effective, and most are limited by severe toxicity. For example, cyclosporin A, a widely used agent, is significantly toxic to the kidney. In addition, doses needed for effective treatment may increase the patient's susceptibility to infection by a variety of opportunistic invaders.
A number of compounds derived from the Chinese medicinal plant Tripterygium wilfordii (TW) have been identified as having immunosuppressive activity, e.g. in the treatment of autoimmune disease, and in treating or preventing transplantation rejection, including the treatment of graft-versus-host disease (GVHD). Triptolide and certain derivatives and prodrugs thereof have also been reported to show anticancer activity. See, for example, Kupchan et al., 1972, 1977, as well as co-owned U.S. Pat. No. 6,620,843 (September 2003), which is hereby incorporated by reference.
In general, the biological activity per se of triptolide derivatives has been found to be less than that of native triptolide. However, these compounds often provide other benefits relative to native triptolide, in areas such as pharmacokinetics or biodistribution, by virtue of their activity as prodrugs and/or differences in lipid or aqueous solubility. See, for example, Jung et al., U.S. Pat. Nos. 5,972,998 and 6,004,999, Kupchan et al., U.S. Pat. No. 4,005,108, Lipsky et al., U.S. Pat. No. 5,294,443, and Qian et al., U.S. Pat. No. 5,430,054, as well as co-owned U.S. Pat. No. 6,150,539 (Triptolide prodrugs having high aqueous solubility), U.S. Pat. No. 5,962,516 (Immunosuppressive compounds and methods), U.S. Pat. No. 5,843,452 (Immunotherapy composition and method), U.S. Pat. No. 5,759,550 (Method for suppressing xenograft rejection), U.S. Pat. No. 5,663,335 (Immunosuppressive compounds and methods), and U.S. Pat. No. 5,648,376 (Immunosuppressant diterpene compound), and references cited therein.