IN-VIVO STABILITY, DISPOSITION AND METABOLISM OF A HYBRID OLIGONUCLEOTIDE PHOSPHOROTHIOATE IN RATS

Oligodeoxynucleotide phosphorothioates containing segments of 2'-O-met hyloligoribonucleotide phosphorothioates at both 3'- and 5'-ends (hybr id oligonucleotide) have been shown to be potent antisense agents, In the present study, in vivo biostability, disposition, and excretion of a 25-mer hybrid oligonucleotide were determined in rats after i.v. bo lus administration of the S-35-labeled oligonucleotide at a dose of 30 mg/kg. The plasma disappearance curve for the hybrid oligonucleotide could be described by a two-compartmental model, with half-lives of 0. 34 and 52.02 hr, respectively. The majority of the radioactivity in pl asma was associated with the intact hybrid oligonucleotide. Urinary ex cretion represented the major pathway of elimination, with 21.98 +/- 3 .21% (mean +/- SD) of the administered dose excreted within 24 hr and 38.13 +/- 2.99% over 240 hr post-dosing. The majority of the radioacti vity in urine was associated with the degradative products with lower molecular weights, but the intact form was also detected by HPLC analy sis. Fecal excretion was a minor pathway of elimination with 2.34 +/- 0.13% of the administered dose excreted over 24 hr and 6.74 +/- 0.40% over 240hr post-dosing. A wide tissue distribution of hybrid oligonucl eotide was observed based on radioactivity levels, and analysis by HPL C showed that the majority of the radioactivity in tissues was associa ted with the intact hybrid oligonucleotide. Further analyses of the ex perimental data provided a comprehensive pharmacokinetic analysis of h ybrid oligonucleotide in each tissue. Compared with a previously exami ned oligodeoxynudeotide phosphorothioate (GEM 91) that has a similar n ucleotide sequence, the hybrid oligonucleotide had a shorter distribut ion half-life and a longer elimination half-life, based on the quantit ation of radioactivity in plasma. Although it had a similar tissue dis tribution pattern compared with other oligonucleotide phosphorothioate s such as GEM 91, the hybrid oligonucleotide was more stable in vivo, which may be important in the development of antisense oligonucleotide s as therapeutic agents.