In vivo transfer of antisense oligonucleotides into rat retina using block polycations

Purpose. Antisense oligonucleotides offer a unique opportunity to down regulate specific gene expression. However, the delivery with low toxicity of such molecules to target sites presents a major challenge for their ultimate efficacy. We investigated whether water-soluble, non-toxic copolymeric carriers consisting of polyoxyethylene (PEO) and polyspermine (PS) chains used previously in vitro can be used in vivo to facilitate the delivery of antisense oligonucleotides into rat retinal tissue. Methods, PEO-PS carrier containing 3uM FITC-labeled antisense oligonucleotides targeted to the fibronectin gene were injected intrayitreously. FITC-labeled oligonucleotides without PEO-PS carrier were similarly injected as control. After enucleation and fixation, Smicron retinal sections were prepared and examined by fluorescence and confocal microscopy. Results. Intense fluorescence was observed 2h and 6h post-injection in the inner limiting membrane, and moderate fluorescence in the retinal microvessels. However, by 24h and 36h post-injection, the intensity of fluorescence increased in the retinal microvessels with diminished fluorescence in the inner limiting membrane. In the ganglion cell layer, photoreceptors, and retinal pigment epithelial cells, weak fluorescence was detectable. Injection of oligonucleotides without carriers produced weaker and more diffused fluorescence. Using a DNA-binding dye to identify the nucleus, and confocal microscopy, fluorescence could be assigned to the retinal microvascular endothelial cells and pericytes or smooth muscle cells. No toxic effects resulting from PEO-PS carrier were detected histologically. Conclusion. Delivery of antisense oligonucleotides into retinal microvascular cells may be achieved by using PEO-PS block copolymer. Since retinal endothelial cells and pericytes qverexpress fibronectin in diabetic retinopathy such an intervention may provide a means to arrest fibronectin overexpression and clarify its role in the oathoaenesis of diabetic microaneiooathy.