Differential interaction of human renal p-glycoprotein with various
metabolites and analogues of cyclosporine a.
Charuk, Jeffrey H. M., Pui Y. Wong, and Reinhart A. F. Reithmeier.
MRC Group in Membrane Biology, Departments of Medicine and
Biochemistry, Room 7344, Medical Sciences Building, University of
Toronto, Toronto, Ontario, Canada, M5S 1A8, Department of Clinical
Biochemistry, Toronto General Hospital, Toronto, Ontario, Canada, M5G
2C4, Telephone: 416-978-7739, FAX: 416-978-8765
APStracts 2:0017F, 1995.
The interactions of P-glycoprotein with several analogues and
metabolites of cyclosporine A were studied to gain a better
understanding of this immunosuppres-sant's mechanism of excretion and
nephrotoxicity. The incorporation of [3H]-azidopine into human
renal P-glycoprotein in the presence of varying concentrations of
different cyclosporines was quantitated. Competitive [3H]
-azidopine photolabelling and [3H]drug transport assays of CHRC5
multidrug-resistant cells were also conducted to evaluate the effects
of the cyclosporines on P-glycoprotein function. Cyclosporines A
(K0.5=20nM) and G (K0.5=40nM) blocked [3H]-azidopine
photolabelling of renal P-glycoprotein at very low concentrations
while higher concentrations of cyclosporine C (K0.5=500nM) and
metabolites 1 17 and 21 (K0.5=200nM) were required to inhibit
photolabelling. Metabolites H, and 8, were ineffective at inhibiting
[3H]azidopine photolabelling of the human renal P-glycoprotein.
Similarly, cyclosporines A, C and G also inhibited
[3H]azidopine photolabelling of P-glycoprotein in multidrug
-resistant C5 cells best, while the various metabolites were less
effective. Cyclosporines A, C and G also enhanced the cellular
accumulation of [3H]cyclosporine A and several other
[3H]labelled compounds known to be transported by P
-glycoprotein in multidrug-resistant C5 cells. The differential
affinities of cyclosporine A metabolites for P-glycoprotein suggest
there is considerable drug-binding site specificity. Our current
hypothesis is that cyclosporine A may be more nephrotoxic than its
metabolites by virtue of its superior ability to bind to and
competitively inhibit the urinary excretion of an endogenous P
-glycoprotein substrate. Our findings provide the basis for the future
design and testing of new cyclosporine derivatives that have
immunosuppressive activity yet may be less nephrotoxic because of
their poor interaction with renal P-glycoprotein.
Received 3 November 1994; accepted in final form 6 February 1995.
APS Manuscript Number F395-4.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 February 1995.