Evaluation of the effect of cobicistat on the in vitro renal transport and cytotoxicity potential of tenofovir

Abstract

A once-daily single-tablet antiretroviral regimen containing tenofovir (TFV) disoproxil fumarate, emtricitabine (FTC), elvitegravir (EVG), and cobicistat (COBI) is an approved combination for the treatment of patients infected with HIV. COBI and TFV have been reported to interact with distinct transporters in renal proximal tubules; while TFV is renally eliminated by a combination of glomerular filtration and tubular secretion via anion transporters OAT1, OAT3, and MRP4, COBI inhibits renal cation transporters, particularly MATE1, resulting in a measurable decrease in the tubular secretion of creatinine. To investigate the potential for a renal drug-drug interaction between TFV and COBI in vitro, the uptake of TFV in the presence and absence of COBI was determined in fresh human renal cortex tissue and in cells expressing the relevant renal transporters. At concentrations exceeding clinical protein-unbound plasma levels, COBI did not significantly inhibit the transport of TFV by the anion transporters OAT1, OAT3, and MRP4 (50% inhibitory concentrations [IC50s] of >15, 6.6, and 8.5 μM, respectively). Conversely, TFV had little or no effect on the cation transporters OCT2 and MATE1 (IC50 > 100 μM). Consistent with studies using individual transporters, no increase in the accumulation of TFV in freshly isolated human renal cortex tissue or renal proximal tubule cells (RPTECs) was observed in the presence of COBI. Finally, COBI alone or in combination with FTC and EVG did not affect the sensitivity to TFV of cultured primary RPTECs or cells coexpressing OAT1 and MRP4. These results illustrate that COBI and TFV interact primarily with distinct renal transporters and indicate a low potential for pharmacokinetic renal drug-drug interaction.

Fig 1

Renal tubular transporters interacting with TFV and COBI. (A) The active tubular secretion of TFV is mediated by the organic anion pathway (OATs and MRP4). (B) COBI interacts with the organic cation pathway involved in the active secretion of creatinine (MATE1) (18).

Fig 2

Effect of COBI and RTV on the transport of tenofovir by OAT1v1 (A), OAT1v2 (B), and OAT3 (C). Cells expressing OATs were incubated with 1.2 μM [³H]TFV and either DMSO or serially diluted tested compounds for 3 to 6 min (OAT1) or 10 min (OAT3) at 37°C. The intracellular level of [³H]TFV was quantified, and the percentage of OAT1- or OAT3-specific uptake relative to that for the untreated control was calculated after subtracting background determined in the presence of 50 μM probenecid. Results represent means ± SD from at least three independent experiments.

Fig 3

Effect of COBI and RTV on the MRP4-mediated efflux of TFV in the absence (A) or presence (B) of human serum. The results represent means ± SD from at least 3 independent measurements. MK-571 (50 μM) was used as a positive-control inhibitor of MRP4 to establish the complete inhibition of TFV transport (0% efflux).

Fig 4

Effect of COBI and RTV on the accumulation of TFV in freshly isolated RPTECs (A) and human renal cortical slices (B). The results represent means ± SD from 4 independent measurements in RPTECs from two separate donors and 3 independent measurements in renal cortical tissue. Probenecid (PBC; 200 μM) was used as a control inhibitor of the active uptake of TFV.

Fig 5

Effect of TFV on the transport of tetraethylammonium (TEA) by renal organic cation transporters OCT2 (A) and MATE1 (B). The results represent means from two independent measurements. The difference in individual measurements was <13.5%. Verapamil (VPL; 100 μM) and quinidine (QND; 100 μM) were used as control inhibitors of OCT2 and MATE1, respectively.