Figure 3. Administration of r NA-targeting drugs in the Central Nervous System. Several ways of administration have been developed to overcome the blood brain barrier and to deliver molecules that target the r in the brain. intracranial delivery of oligonucleotides has been tested in rats and mice to target SOD1 and APP r to treat amyotrofic lateral sclerosis (ALS) and Alzheimer disease (AD) respectively. r ecently, intracranial delivery of antagoNATs targeting BDNF-AS showed to increase BDNF levels in mice brain suggesting a challenging application to prevent neurodegeration as- sociated low levels of BDNF in AD. The same strategy was used to target TGF2β in a study of phase ii to delivery chemoteraphy for glioblastoma (GBM). intranasal administration of sir targeting the Telomerase (Ter T) has been successfully used and will be potentially applied in the future to human being. intrathecal administration, commonly used in pain relief cures, can be applied in the future for the delivery of drugs in the CSF (Blue line) to treat diseases affecting the CNS. siRNAs to translocate through the cell membranes necessitating the development of novel delivery methods. Recently, we sug- gested a broadly applicable method to upregulate gene expression by use of AntagoNAT oligonucleotides targeted to derepress nat- ural antisense (mostly lncRNAs) mediated inhibition (see below and ref. 98). However, as with any therapeutic strategy, it is important to balance efficacy with possible adverse and off-target effects. In fact, despite encouraging results from preclinical and clini- cal studies and the significant progress which has been made in developing these agents as drugs, some hurdles may still exist. For example, several studies have determined that oligonucle- otides can bind serum proteins affecting coagulation,99 that they may cause activation of the immune system100-102 and that their administration can lead to elevated transaminases, suggesting liver damage.103 However, direct administration to CNS may bypass some or all of these latter potential concerns. More studies are nonetheless needed to fully assess risk profiles with centrally administered oligonucleotides. Finally, while extremely challenging to identify, small mol- ecules targeting RNA would arguably be the most attractive tools for regulating lncRNA activity. The interaction between small molecules and lncRNA can potentially disrupt the native confor- mation of the RNA, altering its activity and/or protein-binding ability. Gene therapy is a promising tool for the treatment of human diseases that cannot be cured by conventional treatments. The expression of genes epigenetically regulated by lncRNAs can be specifically modulated by targeting regulatory noncoding transcripts. This strategy has the particular advantage of induc- ing long lasting changes in gene expression through modulation of epigenetic events. Furthermore, targeting lncRNAs can poten- tially restore the expression of a silenced gene which would be out of reach for conventional drugs. Direct delivery of RNA-targeting drugs into the CNS. The blood brain barrier (BBB) protects the brain by forming a highly selec- tive barrier that blocks the entry of large, hydrophilic molecules. The BBB also makes delivery of drugs affecting neurologic dis- orders challenging. Intravenous or intraperitoneal administra- tion of drugs usually shows very low uptake into the brain. Our group and others have pursued a strategy to bypass this obstacle through intracerebroventricular104,105 or intrathecal administra- tion of oligonucleotides into the cerebrospinal fluid (CSF).106-111 Administration of oligonucleotides directly into the brain (interstitial, intracranial or intracerebroventricular) has indeed been fairly successful in animal models and human (Fig. 3). For example, an oligonucleotide with a phosphorothioate back- bone targeting superoxide dismutase 1 (SOD1) was continuously infused into the right lateral ventricle of rats via a surgically implanted catheter in the skull connected to a subcutaneously embedded osmotic pump.109 Treatment showed a reduction in SOD1 mRNA and protein levels in the brain and spinal cord. Mutated forms of SOD1 are responsible for familial amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease caused by preferential loss of neurons in the upper and lower motor pathways, a disease for which current treatments are mar- ginally beneficial. Another case where direct administration is promising is that of intracerebroventricular delivery of ASO’s to treat Alzheimer disease. Point mutations in the human APP gene in the protein region targeted by BACE1, results in familial AD. Recent work by Chauhan et al. shows that mice injected directly www.landesbioscience.com rNA Biology 865