Pharmacokinetics and pharmacodynamics of an antisense phosphorothioate oligonucleotide targeting Fas mRNA in mice

ISIS 22023 is a modified phosphorothioate antisense oligonucleotide targeti ng murine Fas mRNA. Treatment of mice with ISIS 22023 reduced Fas expressio n in liver in a concentration-dependent and sequence-specific manner, which completely protected mice from fulminant death induced by agonistic Fas an tibody. In this study, we characterized the relationships in mice between t otal dose administered, dose to the target organ, and ultimately, the intra cellular concentration within target cell types to the pharmacologic activi ty of ISIS 22023. After subcutaneous injection, ISIS 22023 distributed to t he liver rapidly and remained in the liver with the t(1/2) ranging from 11 to 19 days, depending on dose. There were apparent differences in patterns of uptake and elimination in different types of liver cells. Oligonucleotid e appeared within hepatocytes rapidly, whereas the peak concentrations in K upffer cells were delayed until 2 days after dose administration. Hepatocyt es cleared oligonucleotide the most rapidly, whereas Kupffer cells appeared to retain oligonucleotide longer. The reduction of Fas mRNA levels (pharma codynamic response) paralleled the increase of oligonucleotide concentratio n in mouse liver with maximum mRNA reduction of 90% at 2 days after a singl e 50 mg/kg subcutaneous administration. Moreover, the pharmacodynamics of I SIS 22023 correlated better with the pharmacokinetics in hepatocytes, suppo rting the concept that the presence of oligonucleotide in target cells resu lts in reductions in mRNA and, ultimately, pharmacologic activity. These re sults provide a comprehensive understanding of the kinetics of an antisense drug at the site of action and demonstrate that the reductions in mRNA ind uced by this antisense oligonucleotide correlate with its concentrations in cell targets.