Role of P-glycoprotein in cyclosporine cytotoxicity in the cyclosporine–sirolimus interaction

Abstract

Cyclosporine nephrotoxicity remains a major side effect in solid organ transplantation, and can be exacerbated by concomitant administration of sirolimus. Cyclosporine and sirolimus are P-glycoprotein (Pgp) substrates. We hypothesized that the Pgp activity level may affect cyclosporine cytotoxicity by interfering with the ability of Pgp to remove cyclosporine from within tubular cells, and that an interaction between cyclosporine and sirolimus on Pgp function may explain the enhancement of cyclosporine nephrotoxicity by sirolimus. Cyclosporine cytotoxicity was evaluated in primary cultures of normal human renal epithelial cells (HRECs) by cell viability and cytotoxicity assays. Verapamil, quinine, PSC833, and PGP-4008 were used as Pgp inhibitors. Rhodamine-123 (R-123), a fluorescent substrate of Pgp, was used to assess Pgp-mediated transport. Cellular cyclosporine concentration was measured by high-performance liquid chromatography coupled to tandem mass spectrometry. Pgp expression and function were confirmed in HRECs and cyclosporine and sirolimus were shown to be Pgp inhibitors in this model. Verapamil-induced inhibition of Pgp led to a significant increase in cellular concentration of cyclosporine (P<0.05). Cyclosporine exerted a concentration-dependent cytotoxic effect on HRECs that was significantly increased by inhibition of Pgp activity. Sirolimus exerted an inhibitory effect on R-123 efflux in HRECs and increased cellular cyclosporine concentrations in a dose-dependent manner. These data demonstrate that Pgp plays a critical role in protecting renal epithelial cells from cyclosporine toxicity. The inhibitory effect of sirolimus on Pgp-mediated efflux and the cellular concentration of cyclosporine could explain the exacerbation of cyclosporine nephrotoxicity observed clinically.

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“…21 This enhanced renal tissue exposure when both drugs are combined appears to be mediated by P-glycoprotein (P-gp) inhibition in renal tubular cells. 46 In an in vitro human epithelial renal cell model, Anglicheau and associates 46 demonstrated that rapamycin exerted an inhibitory effect on P-gp and increased intracellular cyclosporine concen-trations and cell death in a dose-dependent manner. The P-gp efflux pump, an ABCB1 (previously multidrug resistance 1) gene product, is a membrane protein that functions as an ATP-dependent exporter.…”

“…These histologic findings have been reported to be associated with mTOR inhibitor monotherapy or in combination therapy with CNI and at therapeutic concentrations, in both animal and human models. 7,11,[16][17][18][21][22][23]46,47 In fact, Piao and associates 47 recently demonstrated, using an in vivo experimental animal model, that combined treatment with cyclosporine and the mTOR inhibitors (rapamycin and everolimus) significantly increased cyclosporine or mTOR inhibitor concentrations in kidney tissue versus treatment with cyclosporine or mTOR inhibitor alone, despite similar whole blood levels of either drug. This increase in tissue concentration of both drugs was associated with an exaggeration in oxidative stress and an aggravation in renal injury with significant deterioration in renal function in the combination therapy group versus with monotherapy.…”

Current Status of Immunosuppression in Liver Transplantation

“…A characteristic cast nephropathy lesion has also been reported with use of mTOR inhibitors. [53][54][55] Renal Sparing Strategies…”

Calcineurin Inhibitor Nephrotoxicity

“…First, there is the observation that both sirolimus and everolimus increase chronic nephrotoxicity of CNIs, both in rats (272) and in humans (273)(274)(275). This is explained by robust evidence that these mTOR inhibitors interact with cyclosporine excretion in tubular epithelial cells through competition for P-glycoprotein (276,277), and hence lead to accumulation of cyclosporine in these cells. Local renal accumulation of cyclosporine was demonstrated in vitro by Anglicheau et al (277) and in vivo by Napoli et al (278) and Podder et al (279).…”

“…This is explained by robust evidence that these mTOR inhibitors interact with cyclosporine excretion in tubular epithelial cells through competition for P-glycoprotein (276,277), and hence lead to accumulation of cyclosporine in these cells. Local renal accumulation of cyclosporine was demonstrated in vitro by Anglicheau et al (277) and in vivo by Napoli et al (278) and Podder et al (279). These latter studies measured increased local renal cyclosporine concentrations in kidney tissue after concomitant treatment with sirolimus in rats.…”