Ascomycin(Immunomycin, FR-900520, FK520) is an ethyl analog of tacrolimus (FK506) with strong immunosuppressant properties. IC50 Value: 0.55 nM [1] Target: in vitro: When we used either CD4+CD8+ thymocytes or peripheral T cells activated by phorbol ester and ionomycin, the cell surface induction of CD5 was also partially blocked by CsA, FK-520 and rapamycin [2]. Ascomycinalso had a 3-fold lower immunosuppressive potency in a popliteal lymph node hyperplasia assay, resulting in an equivalent therapeutic index consistent with a common mechanistic dependence on calcineurin inhibition [3]. in vivo: In 14-day studies, nephrotoxicity was not induced by continuous i.p. infusion of ascomycin at 10 mg/kg/day or daily oral administration (up to 50 mg/kg/day) in rats on a normal diet, nor by continuous i.v. infusion (up to 6 mg/kg/day) in rats on a low salt diet to enhance susceptibility [3].