Tacrolimus (FK506)S5003

FK-506 and cyclosporin A block translocation of the cytoplasmic component without affecting synthesis of the nuclear subunit in T lymphocytes. ^[1] FK-506 prevents T-cell proliferation by inhibiting a Ca(2+)-dependent event required for induction of interleukin-2 transcription. ^[2] FK 506 binds to distinct families of intracellular proteins (immunophilins) termed cyclophilins and FK 506-binding proteins (FKBPs). FK-506 specifically inhibits cellular calcineurin at drug concentrations that inhibit interleukin 2 production in activated T cells. ^[3] FK-506 and CsA exert nearly identical biological effects in cells by inhibiting the same subset of early calcium-associated events involved in lymphokine expression, apoptosis, and degranulation. FK-506 binds to a family of intracellular receptors termed the FK-506 binding proteins (FKBPs). ^[4]