IN-VIVO DISTRIBUTION AND METABOLISM OF A PHOSPHOROTHIOATE OLIGONUCLEOTIDE WITHIN RAT-LIVER AFTER INTRAVENOUS ADMINISTRATION

In the rat, the liver represents a major site of phosphorothioate olig odeoxynucleotide deposition after i.v. administration. For this reason , we examined the intracellular fate of ISIS 1082, a 21-base heteroseq uence phosphorothioate oligodeoxynucleotide, isolated from parenchymal and nonparenchymal cell types after systemic dosing using established perfusion and separation techniques followed by CGE. Isolated cells w ere further fractionated into nuclear, cytosolic and membrane constitu ents to assess the intracellular localization, distribution and metabo lic profiles as a function of time and dose. After a 10-mg/kg i.v. bol us, intracellular drug levels where maximal after 8 hr and diminished significantly thereafter, suggesting an active efflux mechanism or met abolism. Nonparenchymal (i.e., Kupffer and endothelial) cells containe d approximately 80% of the total organ cellular dose, and this was equ ivalently distributed between the two cell types, while the remaining 20% was associated with hepatocytes. Nonparenchymal cells contained ab undant nuclear, cytosolic and membrane drug levels over a wide dose ra nge. in contrast, at doses of less than 25 mg/kg, hepatocytes containe d significantly less drug with no detectable nuclear-association. Dose s at or above 25 mg/kg appeared to saturate nonparenchymal cell types, whereas hepatocytes continued to accumulate drug in all cellular comp artments, including the nucleus. Our results suggest that although pha rmacokinetic parameters vary as a function of hepatic cell type, signi ficant intracellular delivery can be readily achieved in the liver aft er systemic administration.