DISCOVERY OF LESS NEPHROTOXIC FK506 ANALOGS AND DETERMINING IMMUNOPHILIN DEPENDENCE OF IMMUNOSUPPRESSANT NEPHROTOXICITY WITH A NOVEL SINGLE-DOSE RAT CISPLATIN POTENTIATION ASSAY
Kw. Mollison et al., DISCOVERY OF LESS NEPHROTOXIC FK506 ANALOGS AND DETERMINING IMMUNOPHILIN DEPENDENCE OF IMMUNOSUPPRESSANT NEPHROTOXICITY WITH A NOVEL SINGLE-DOSE RAT CISPLATIN POTENTIATION ASSAY, The Journal of pharmacology and experimental therapeutics, 283(3), 1997, pp. 1509-1519
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 in
crease when only one dose of test compound is followed by cisplatin. R
eference nephrotoxins known to act on various sites in kidney tubules,
glomeruli or renal papilla were all detected by the CISPA at single d
oses that without cisplatin gave little change, which showed that this
simple, sensitive assay has broad potential utility for mechanistic s
tudies of nephrotoxicity. We used the CISPA both to probe the nephroto
xic mode of action of immunosuppressants and to search for safer compo
unds. Although several non-nephrotoxic immunosuppressants were inactiv
e, cyclosporine, FK506, ascomycin (C21-ethyl-FK506) and rapamycin were
nephrotoxic in the CISPA at single doses equal to the daily amounts r
equired to reduce creatinine clearance with 14 days of treatment. Simi
lar therapeutic indices were derived comparing toxicity by either meth
od to prevention of rat ear-heart allograft rejection. C18-OH-ascomyci
n, an FK506-binding protein (FKBP) antagonist, reversed in vivo immuno
suppression by FK506 and ascomycin in the rat, and pretreatment in the
CISPA blocked FK506 and ascomycin nephrotoxicity, which showed a comm
on immunophilin dependence. Rapamycin nephrotoxicity was unaffected (a
s with cyclosporine), which indicated that binding to FKBP was not req
uired, Rapamycin nephrotoxicity thus appears mechanistically unrelated
to its immunosuppressive mode of action. Screening with the CISPA ena
bled discovery of A-119435, a less nephrotoxic ascomycin analog having
a 10-fold higher therapeutic index.