TY - JOUR T1 - Discovery of Less Nephrotoxic FK506 Analogs and Determining Immunophilin Dependence of Immunosuppressant Nephrotoxicity with a Novel Single-Dose Rat Cisplatin Potentiation Assay JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 1509 LP - 1519 VL - 283 IS - 3 AU - Karl W. Mollison AU - Thomas A. Fey AU - Ruth A. Krause AU - Janet M. Andrews AU - Pat T. Bretheim AU - Julie A. Brandt AU - Megumi Kawai AU - Rolf Wagner AU - Gin C. Hsieh AU - Jay R. Luly Y1 - 1997/12/01 UR - http://jpet.aspetjournals.org/content/283/3/1509.abstract N2 - Comparing nephrotoxicity of numerous drug analogs is impractical with chronic in vivo models. We devised a new cisplatin potentiation assay (CISPA) that sensitively detects renal injury as a serum creatinine increase when only one dose of test compound is followed by cisplatin. Reference nephrotoxins known to act on various sites in kidney tubules, glomeruli or renal papilla were all detected by the CISPA at single doses that without cisplatin gave little change, which showed that this simple, sensitive assay has broad potential utility for mechanistic studies of nephrotoxicity. We used the CISPA both to probe the nephrotoxic mode of action of immunosuppressants and to search for safer compounds. Although several non-nephrotoxic immunosuppressants were inactive, cyclosporine, FK506, ascomycin (C21-ethyl-FK506) and rapamycin were nephrotoxic in the CISPA at single doses equal to the daily amounts required to reduce creatinine clearance with 14 days of treatment. Similar therapeutic indices were derived comparing toxicity by either method to prevention of rat ear-heart allograft rejection. C18-OH-ascomycin, an FK506-binding protein (FKBP) antagonist, reversed in vivoimmunosuppression by FK506 and ascomycin in the rat, and pretreatment in the CISPA blocked FK506 and ascomycin nephrotoxicity, which showed a common immunophilin dependence. Rapamycin nephrotoxicity was unaffected (as with cyclosporine), which indicated that binding to FKBP was not required. Rapamycin nephrotoxicity thus appears mechanistically unrelated to its immunosuppressive mode of action. Screening with the CISPA enabled discovery of A-119435, a less nephrotoxic ascomycin analog having a 10-fold higher therapeutic index. The American Society for Pharmacology and Experimental Therapeutics ER -