The antiviral nucleotide analogs cidofovir and adefovir are novel substrates for human and rat renal organic anion transporter 1

Nephrotoxicity is the dose-limiting clinical adverse effect of cidofovir and adefovir, two potent antiviral therapeutics. Because renal uptake likely plays a role in the etiology of cidofovir- and adefovir-associated nephrotoxicity, we attempted to identify a renal transporter capable of interacting with these therapeutics. A cDNA clone was isolated from a human renal library and designated human organic anion transporter 1 (hOAT1). Northern analysis detected a specific 2.5-kilobase pair hOAT1 transcript only in human kidney. However, reverse transcription-polymerase chain reaction revealed hOATI expression in human brain and skeletal muscle, as well. Immunoblot analysis of human kidney cortex demonstrated that hOATI is an 80- to 90-kilodalton heterogeneous protein modified by abundant N-glycosylation. Xenopus laevis oocytes expressing hOATI supported probenecid-sensitive uptake of [H-3]p-aminohippurate (K-m = 4 mu M), which was trans-stimulated in oocytes preloaded with glutarate. Importantly, both hOAT1 and rat renal organic anion transporter 1 (rROAT1) mediated saturable, probenecid-sensitive uptake of cidofovir, adefovir, and other nucleoside phosphonate antivirals. The affinity of hOAT1 toward cidofovir and adefovir (K-m = 46 and 30 mu M, respectively) was 5- to g-fold higher compared with rROAT1 (K-m = 238 and 270 mu M, respectively). These data indicate that hOATI may significantly contribute to the accumulation of cidofovir and adefovir in renal proximal tubules and, thus, play an active role in the mechanism of nephrotoxicity associated with these antiviral therapeutics.