RENAL DISPOSITION CHARACTERISTICS OF OLIGONUCLEOTIDES MODIFIED AT TERMINAL LINKAGES IN THE PERFUSED RAT-KIDNEY

To clarify the renal disposition characteristics of oligonucleotides at the organ level, the renal handling of model end-capped oligonucleotides, 3'-methoxyethylamine 5'-biotin-decathymidylic acid containing phosphoramidate modifications at 3'- and 5'-terminal internucleoside linkages (T-10) and its phosphorothioate (Ts(10)), were studied in the perfused rat kidney. In a single-pass indicator dilution experiment, venous outflow and urinary excretion patterns and tissue accumulation of radiolabeled oligonucleotides were evaluated under filtering or nonfiltering conditions. No significant binding to bovine serum albumin (BSA) in the perfusate was observed for T-10, whereas more than 90% of Ts(10) bound to BSA. The steady-state distribution volume of T-10 calculated from the venous outflow pattern was larger than that of inulin, which corresponds to the extracellular volume of the kidney, whereas the distribution volume of Ts(10) was larger than that of BSA (the intravascular volume). These results suggested their interaction with the vascular wall, Rapid urinary excretion was observed for T-10, similar to inulin used as a marker of golmerular filtration rate. On the other hand, urinary excretion of Ts(10) was greatly restricted due to its high binding ability (>90%) to BSA in the perfusate. A significant amount of T-10 and Ts(10) was accumulated in the kidney (T-10, 1.8% of injected dose; Ts(10), 1.3%) compared with inulin (0.2%) and BSA (<0.1%). The accumulation of these oligonucleotides was ascribed to both tubular reabsorption and uptake from the capillary side. In addition, the uptake of T-10 from the capillary side was significantly inhibited by simultaneous injection of dextran sulfate, suggesting that the oligonucleotide was taken up as an anionic molecule. These findings will be useful information for the development of delivery systems for antisense oligonucleotides.