In vitro activity: Ascomycin, isolated from Streptomyces, suppresses immune response in vitro with IC50 of 0.55 nM for mouse mixed lymphocyte. Ascomycin inhibits calcineurin phosphatase with IC50 of 49 nM through formation of an FKBP12-FK520-calcineurin ternary complex. FK520 also accelerate the rate of nerve regeneration, and promotes neurite outgrowth. Ascomycin shows antimalarial effects via inhibition of the chaperone activity of this bifunctional protein.

Kinase Assay: Ascomycin (Immunomycin, FR-900520, FK520) is an ethyl analog of tacrolimus (FK506) with strong immunosuppressant properties. 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. 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. 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

Cell Assay: Ascomycin (FK 520, FR900520) suppressed lymphocyte reaction in a dose dependent fashion. Ascomycin was non-toxic at concentrations less than 3,200 nM, at which the percent inhibition was 18.9%. Ascomycin showed antifungal activity against Aspergillus fumigatus IFO 5840. Ascomycin had no inhibitory effect on bacteria or yeast at 100 μg/ml.