<prompt> Tarcolimus belong to which class of drug?Calcineurin inhibitorm TOR inhibitorHypoxathine inhibitorInosine inhibitor  <response>: Reference: Katzung, Basic Clinical Pharmacology, 13th ed., Pg. 1402.Tacrolimus FK 506 is an immunosuppressant macrolide antibiotic produced by Streptomyces tsukubaensis. It is not chemically related to cyclosporine, but their mechanisms of action are similar. Both drugs bind to cytoplasmic peptidylprolyl isomerases that are abundant in all tissues. While cyclosporine binds to cyclophilin, tacrolimus binds to the immunophilin FK-binding protein FKBP. Both complexes inhibit calcineurin, which is necessary for the activation of the T-cell-specific transcription factor NF-AT. 