*3.6.3 RNA aptamers*

Aptamers are oligoribonucleotides that form 3D structures and function like proteins, such as ligands and antibodies [42]. For example, pegaptanib, which is an aptamer drug developed for the treatment of macular degeneration, blocks vascular endothelial growth factor (VEGF) by preventing its binding to VEGF receptors [42]. Although there are no reports about the mRNA knockdown using aptamers up to date, the aptamers that simulate RNA-binding proteins may be utilized to modulate mRNA levels by affecting the mRNA-AS transcript interactions.

### **3.7 Drug delivery system (DDS)**

The introduction of oligonucleotides to cells requires transfection reagents using liposomes, e.g., Lipofectamine (Thermo Fisher Scientific Inc., Waltham, MA, USA) and using iron nanoparticles, e.g., MATra A reagent (IBA, Göttingen, Germany) or PolyMag Magnetofection reagent (OZ Biosciences, Marseille, France).

To improve the *in vivo* delivery of sense oligonucleotides, several techniques have been developed [32, 33]. Because LNA is efficiently accumulated in the liver [34], *iNOS* sense oligonucleotides were modified with LNAs [38].

Recently, *N*-acetylgalactosamine (GalNAc) has been conjugated at the ends of the oligonucleotides to efficiently deliver the oligonucleotides to the liver [11, 43]. Because the liver and kidney receive high blood flow and permeability of their capillaries is high, sense oligonucleotides conjugated with GalNAc will improve the delivery and accumulation in these organs. To cross the blood-brain barrier, *Bdnf*-AntagoNATs in liposomes were delivered by nasal approaches [44, 45]. Additionally, aptamers capable of entering the cells may facilitate the delivery of oligonucleotides into the cells [42].

Because guinea pigs maintain a functional *MX1* gene for the IFN-alpha1 pathway, they were infected with influenza virus to verify that the AS transcript-mRNA

*The Natural Antisense Transcript-Targeted Regulation Technology Using Sense Oligonucleotides… DOI: http://dx.doi.org/10.5772/intechopen.108281*

regulatory axis exerts *in vivo* control of innate immunity [46]. When an AS oligoribonucleotide (asORN) to guinea pig *IFN-A1* mRNA in poly (D,L-lactide-co-glycolide (PLGA) nanoparticles was pulmonary-administered, it inhibited *in vivo* viral proliferation by modulating *IFN-A1* mRNA levels. Although this experiment is not NATRE technology, PLGA nanoparticles can be used to deliver sense oligonucleotides to animals. Various lipid nanoparticles (LNPs) have been used to deliver nucleic acids, including oligonucleotides, in the body [47]. New-generation LNPs can deliver long RNA, such as LNP-based mRNA vaccines for COVID-19 [47].
