Cytotoxicity of Antiviral Nucleotides Adefovir and Cidofovir Is Induced by the Expression of Human Renal Organic Anion Transporter 1

. The transport of organic anions in proximal convoluted tubules plays an essential role in the active secretion of a variety of small molecules by the kidney. In addition to other anionic substrates, the human renal organic anion transporter 1 (hOAT1) is capable of transporting the nucleotide analogs adefovir and cidofovir. To investigate the involvement of hOAT1 in the mechanism of nephrotoxicity associated with these two clinically important antiviral agents, Chinese hamster ovary (CHO) cells were stably transfected with hOAT1 cDNA. The resulting CHO hOAT cells showed probenecid-sensitive and pH-dependent uptake of p -aminohippurate ( K m = 15.4 μM, V max = 20.6 pmol/10 6 cells · min), a prototypical organic anion substrate. In addition, the stably expressed hOAT1 mediated efficient transport of adefovir ( K m = 23.8 μM, V max = 46.0 pmol/10 6 cells · min) and cidofovir ( K m = 58.0 μM, V max = 103 pmol/10 6 cells · min) such that the levels of intracellular metabolites of both nucleotides were >100-fold higher in CHO hOAT cells than in parental CHO. Consequently, adefovir and cidofovir were approximately 500-fold and 400-fold more cytotoxic, respectively, in CHO hOAT cells compared to CHO. The cytotoxicity of both drugs in CHO hOAT cells was markedly reduced in the presence of hOAT1 inhibitors. The cyclic prodrug of cidofovir, which exhibits reduced in vivo nephrotoxicity, was a poor substrate for hOAT1 and showed only marginally increased cytotoxicity in CHO hOAT cells. In conclusion, these studies demonstrate that hOAT1 plays a critical role in the organ-specific toxicity of adefovir and cidofovir, and indicates that CHO hOAT cells may represent a useful in vitro model to investigate the potential nephrotoxicity of clinically relevant organic anion agents.