Distribution and stability of antisense phosphorothioate oligonucleotides in rodent brain following direct intraparenchymal controlled-rate infusion

Object. High-flow microinfusion is a novel technique for delivery of compounds directly into brain parenchyma, bypassing the blood-brain barrier. The feasibility of this technique has been demonstrated with low-molecular weight compounds, macromolecular dyes, and proteins. Delivery of antisense oligonucleotides into brain parenchyma represents an additional potential application of this technique not previously described. In this report the authors sought to examine the distribution and disposition of phosphorothioate oligodeoxynucleotide (PS-ODN) for this reason. Methods. An 18-mer ³⁵S-PS-ODN (M, approximately 6000) was infused over 1 hour into the caudate putamen of Fischer 344 rats. At 1, 6, 12, 24, and 48 hours after beginning the infusion, the brains were extracted and analyzed using quantitative autoradiographic techniques. Cerebrospinal fluid (CSF) was also aspirated from the cistema magna and was analyzed to determine the radioactivity and stability of the ³⁵S-PS-ODN. At 1 hour, the infused ODN was uniformly distributed in brain tissue, with a maximum average concentration of 4806.5 ± 210.5 nCi/g. This represents a tissue concentration of 19.2 ± 0.84 μM. Extensive spread into surrounding parenchyma was observed over the ensuing 47 hours. The ³⁵S-PS-ODN radioactivity peaked in the CSF at the end of the 1-hour infusion, containing 1% (50 ± 20 nCi) of the refused radioactivity. Activity then decayed exponential over 11 hours, but stabilized at a lower CSF content of 0.2% (1 ± 0.1 nCi) thereafter. The volume of distribution was 105 ± 7.9 mm³ at 1 hour, representing a volume of distribution/volume of infusion ratio of 5.2. The volume of distribution increased to 443 ± 62.3 mm³ at the end of 48 hours, whereas the average minimum tissue concentration decreased from 15.2 μM to 3.2 μM. Undegraded 18-mer was observed throughout the 48-hour period by means of 20% polyacrylamide/7 M urea gel electrophoresis. The animals tolerated the infusion without evidence of toxicity and minimal structural changes in tissue were observed on histological investigation. Conclusions. The authors found that PS-ODNs can be safely delivered in high concentrations to wide areas of rat brain by using high-flow microinfusion and are stable even after 48 hours in situ.