DRUG-DELIVERY OF ANTISENSE MOLECULES TO THE BRAIN FOR TREATMENT OF ALZHEIMERS-DISEASE AND CEREBRAL AIDS

Antisense oligonucleotides (ODNs) and peptide nucleic acids (PNAs) are potential therapeutics for eradication of malignancies, viral infecti ons, and other pathologies. However, ODNs and PNAs in general are unab le to cross cellular membranes and blood-tissue barriers, such as the blood-brain barrier (BBB), which is only permeable to lipophilic molec ules of molecular weight <600 Da. Cellular delivery systems based on c onjugates of streptavidin (SA) and the OX26 monoclonal antibody direct ed to the transferrin receptor may be employed as a universal carrier for the transport of monobiotinylated peptides, ODNs, or PNAs. 3'-Biot inylation of phosphodiester (PO)-ODN produces complete protection of O DN against serum and cellular 3'-exonucleases, facilitating the conjug ation to avidin-based delivery systems and maintaining the activation of RNase H. These delivery systems markedly increased the cellular upt ake and antisense efficacy of 3'-biotinylated ODNs in models of Alzhei mer's disease and HIV-AIDS. In vivo brain delivery studies demonstrate d that 3'-protected PO-ODNs and PO-phosphorothioate(PS)-ODN hybrids co ntaining a single PO linkage are subjected to endonuclease degradation in vivo. On the contrary PS-ODNs, which were also protected at 3'-ter minus by biotinylation, are metabolically stable in vivo and resistant to exo/endonuclease degradation.;However because of the strong bindin g of these oligomers to plasma protein, PS-ODNs are poorly transported into the brain through the BBB by the OX26-SA delivery vector followi ng intravenous administration. PNAs are also resistant to exo/endonucl ease and protease degradation, and these molecules biotinylated at the amino terminal group were transported into the brain by the OX26-SA d elivery system with brain uptake levels comparable to that of morphine . Using the rev gene of HIV as a model target, RNase protection assays and cell-free translation arrest showed that the PNA-OX26-SA conjugat e maintained active recognition and inactivation of target mRNA, respe ctively. The overall experimental evidence suggests that PNA-OX26-SA c onjugates represent optimal antisense molecules for drug delivery to t he brain.