Fungal metabolites. Part 11. A potent immunosuppressive activity found in Isaria sinclairii metabolite.

A potent immunosuppressive activity was found in the culture broth of the fungus Isaria sinclairii (ATCC 24400). The metabolite, ISP-I ((2S,3R,4R)-(E)-2-amino-3,4-dihydroxy-2- hydroxymethyl-14-oxoeicos-6-enoic acid, myriocin = thermozymocidin) suppressed the proliferation of lymphocytes in mouse allogeneic mixed lymphocyte reaction, but had no effect on the growth of human tumor cell lines. It also suppressed the appearance of plaque-forming cells in response to sheep red blood cells and the generation of allo-reactive cytotoxic T lymphocytes in mice after intraperitoneal or oral administration. The metabolite was 10- to 100-fold more potent than cyclosporin A as an immunosuppressive agent of the immune response in vitro and in vivo, and appears to be a candidate for clinical application as a powerful immunosuppressant.