title: Mixed agonist/antagonist activity of an FK-506-related immunosuppressant: biological and biochemical characterization.
abstract: FK-506 blocks T cell activation by preventing lymphokine gene transcription through formation of a complex with FKBP12 that inhibits calcineurin phosphatase activity. Immunosuppressive FK-506 analogs (agonists) have been generated whose potency correlates with calcineurin inhibition. Nonimmunosuppressive antagonist analogs have also been identified, including L-685,818, which binds to FKBP12 but does not inhibit calcineurin. We describe a novel property of FK-506 analog, characterized as a mixed agonist/antagonist immunosuppressive activity. It is displayed by L-688,617, the 32 O-methoxyethoxymethyl derivative of the agonist L-683,590 (C21-ethyl). Although it binds to FKBP12 similarly to L-683,590, L-688,617 incompletely suppressed T cell proliferation induced by optimal activation and enhanced that induced by supraoptimal activation. In the latter situation, L-688,617 suppressed IL-2 production only partially but blocked activation-driven cell death. Moreover, a 1000-fold molar excess of L-688,617 antagonized the immunosuppressive activity of L-683,590. L-688,617 inhibited calcineurin phosphatase activity in cells only partially. The unique agonist/antagonist activity of L-688,617 may therefore reflect its high affinity for FKBP12, combined with a reduced ability of the drug-FKBP12 complex to inhibit calcineurin function. However, in a cell-free system, L-688,617 completely blocked this function when a large excess of FKBP12 over calcineurin was present, suggesting that the intracellular concentration of FKBP12 may be a limiting factor that prevents full agonist activity of L-688,617 in cells.
authors.affiliation: Department of Immunology, Merck Research Laboratories, Rahway, New Jersey, USA.
authors.forename: F J
authors.initials: FJ
authors.lastname: Dumont
authors.forename: H
authors.initials: H
authors.lastname: Ok
authors.forename: S
authors.initials: S
authors.lastname: Lin
authors.forename: C A
authors.initials: CA
authors.lastname: Kastner
authors.forename: J
authors.initials: J
authors.lastname: Cryan
authors.forename: M M
authors.initials: MM
authors.lastname: Martin
authors.forename: G
authors.initials: G
authors.lastname: Wiederrecht
authors.forename: M J
authors.initials: MJ
authors.lastname: Staruch
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002478:Cells, Cultured / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007376:Interleukin-2 / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009550:Nigericin / Q000031:analogs & derivatives / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects*; D016559:Tacrolimus / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D007166:Immunosuppressive Agents; D007376:Interleukin-2; C098493:L 688617; C079136:L 683590; C012410:lonomycin; D009550:Nigericin; D016559:Tacrolimus