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

Abstract

High-flow microinfusion is a novel technique for delivery of compounds directly into the 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 the brain parenchyma represents an additional potential application of this technique not previously described. In this report, the authors examined the distribution and disposition of phosphorothioate oligodeoxynucleotide (PS-ODN) infused for this reason. An 18-mer (35)S-PS-ODN (molecular weight 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 cisterna magna and analyzed for radioactivity and stability of the (35)S-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 microM. Extensive spread into surrounding parenchyma was observed over the ensuing 47 hours. The (35)S-PS-ODN radioactivity peaked in the CSF at the end of the 1-hour infusion, containing 10% (50 +/- 20 nCi) of the infused radioactivity. Activity then decayed exponentially over 11 hours, stabilizing at a lower CSF content of 0.2% (1 +/- 0.1 nCi). The volume of distribution (V(d)) was 105 +/- 7.9 mm3 at 1 hour, representing a ratio of V(d)/V(i) (volume of infusion) of 5.2. The V(d) increased to 443.4 +/- 62.3 mm(3) at the end of 48 hours, whereas the average minimum tissue concentration decreased from 15.2 to 3.2 microM. Undegraded 18-mer was seen throughout the 48-hour period using 20% polyacrylamide/7M urea gel electrophoresis. The animals tolerated the infusion without evidence of toxicity, and minimal structural changes in tissue were observed on histological examination. Thus, PS-ODN can be safely delivered in high concentrations to wide areas of the rat brain by using high-flow microinfusion, and the concentrations remain stable even after 48 hours in situ.