Pharmacokinetics of intrathecal oligodeoxynucleotides.

Background: Intrathecal administration of antisense oligonucleotides is a frequently used technique to alter gene expression for research purposes. However, in the future, antisense oligonucleotides will likely be administered intrathecally to humans for therapeutic purposes. To date, there have been no systematic studies of the pharmacokinetics of intrathecal oligonucleotides. This study was designed to fill that knowledge gap.

Methods: Microdialysis probes were placed intrathecally at the L4, L1, and T11 vertebral levels and epidurally at the L4 vertebral level in pigs. One of the study oligodeoxynucleotides (10-, 18-, or 30-nucleotide-long sequences of the human MDR-1 gene) was injected intrathecally at the L4 level at time 0. Microdialysis samples were obtained for measurement of oligodeoxynucleotide samples at 5-min intervals until 20 min, 10-min intervals until 60 min, and 20-min intervals until 180 min. Noncompartmental pharmacokinetic analysis was performed using PK Solutions software.

Results: Mean residence time and terminal elimination half-life did not differ significantly among the three oligodeoxynucleotides at any sampling site. In contrast, area under the concentration-time curve differed significantly among the oligodeoxynucleotides at all sampling sites and was inversely related to oligodeoxynucleotide length at the L4 and L1 intrathecal sites but not the T11 or epidural sampling sites. Similarly, clearance and volumes of distribution at the L4 level differed significantly among the oligodeoxynucleotides and were directly related to oligodeoxynucleotide length.

Conclusion: The intrathecal pharmacokinetics of oligodeoxynucleotides are largely determined by oligodeoxynucleotide length. This contrasts with smaller drug molecules, such as opioids, for which intrathecal and epidural pharmacokinetics are largely determined by lipid solubility, not size. The potential clinical utility of this information is that oligodeoxynucleotide distribution within the central nervous system may be controllable to some degree by varying oligodeoxynucleotide length.