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The artificial nucleobase 1,3-diaza-2-oxophenoxazine (tC O ) and its derivative G-clamp strongly bind to guanine and, when incorporated into double-stranded DNA, significantly increase the stability of the latter. As the phenoxazine skeleton is a constituent of major pharmaceuticals, we hypothesized that oligonucleotides (ONs) containing phenoxazine bases would induce property changes related to intracellular uptake and migration in tissues. In this study, we designed and synthesized a novel G-clamp-linker antisense oligonucleotide (ASO) in which a G-clamp base with a flexible linker was introduced into the 5'-end of an ASO targeting mouse long non-coding RNA metastasis-associated lung adenocarcinoma transcript 1 (mMALAT1). Compared to unconjugated ASO, the G-clamp-linker ASO induced significantly more effective knockdown of mMALAT1 in mouse skeletal muscle. The ASOs conjugated with 2'-deoxyribonucleotide(s) bearing a tC O nucleobase at the 5'-end exhibited a similar knockdown effect in skeletal muscle. Thus, it may be possible to improve therapeutic effects against skeletal muscle diseases, such as muscular dystrophy, by using ONs with incorporated phenoxazine nucleobases., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

We previously reported that reducing-environment-responsive prodrug-type small interfering RNA (siRNA) bearing 2'-O-methyldithiomethyl (2'-O-MDTM) uridine exhibits efficient knockdown activity and nuclease resistance. In this report, we describe the preparation of 2'-O-MDTM oligonucleotides modified not only at uridine but also at adenosine, guanosine and cytidine residues by post-synthetic modification. Precursor oligonucleotides bearing 2'-O-(2,4,6-trimethoxybenzylthiomethyl) (2'-O-TMBTM) adenosine, guanosine, and cytidine were reacted with dimethyl(methylthio)sulfonium tetrafluoroborate to form 2'-O-MDTM oligonucleotides in the same manner as the oligonucleotide bearing 2'-O-TMBTM uridine. Furthermore, the oligonucleotides bearing 2'-O-MDTM adenosine, guanosine, and cytidine were efficiently converted into corresponding natural 2'-hydroxy oligonucleotides under the cytosol-mimetic reducing condition., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A number of cell-penetrating peptides (CPPs) have been characterized and their usefulness as delivery tools has been clarified. As one of the CPPs, model amphipathic peptide (MAP) was developed by integrating both hydrophobic and hydrophilic amino acids in its sequence. In our previous work, we designed MAP(Aib) by replacing five alanine (Ala) residues on the hydrophobic face of the helix in the MAP sequence with α-aminoisobutyric acid (Aib) residues, and the replacement resulted in higher helix propensity, stronger resistance to protease, and higher cell membrane permeability than MAP. As a next step, we examined the efficiency of oligonucleotide (ODN) delivery into cells by MAP(Aib) in comparison with that by MAP. The electrostatically formed MAP(Aib)/ODN complex was more easily taken up by cells than the MAP/ODN complex, and the ODN delivery by MAP(Aib) was via an endocytic pathway. We demonstrated that the incorporation of Aib residues into CPPs enhances the delivery of hydrophilic molecules, such as ODN, into cells., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A continuing problem in the area of oligonucleotide-based therapeutics is the poor access of these molecules to their sites of action in the nucleus or cytosol. A number of approaches to this problem have emerged. One of the most interesting is the use of ligand-oligonucleotide conjugates to promote receptor mediated cell uptake and delivery. Here we provide an overview of recent developments regarding targeted conjugates, including use of peptides, carbohydrates and small molecules as ligands. Additionally we discuss our own experience with this approach and point out both advantages and limitations., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

DNA is continuously damaged by endogenous and exogenous factors such as oxidative stress or DNA alkylating agents. These damaged nucleobases are removed by DNA N-glycosylase and form apurinic/apyrimidinic sites (AP sites) as intermediates in the base excision repair (BER) pathway. AP sites are also representative DNA damages formed by spontaneous hydrolysis. The AP sites block DNA polymerase and a mismatch nucleobase is inserted opposite the AP sites by polymerization to cause acute toxicities and mutations. Thus, AP site specific compounds have attracted much attention for therapeutic and diagnostic purposes. In this study, we have developed nucleobase-polyamine conjugates as the AP site binding ligand by expecting that the nucleobase part would play a role in the specific recognition of the nucleobase opposite the AP site by the Watson-Crick base pair formation and that the polyamine part should contribute to the access of the ligand to the AP site by a non-specific interaction to the DNA phosphate backbone. The nucleobase conjugated with 3,3'-diaminodipropylamine (A-ligand, G-ligand, C-ligand, T-ligand and U-ligand) showed a specific stabilization of the duplex containing the AP site depending on the complementary combination with the nucleobase opposite the AP site; that is A-ligand to T, G-ligand to C, C-ligand to G, T- and U-ligand to A. The thermodynamic binding parameters clearly indicated that the specific stabilization is due to specific binding of the ligands to the complementary AP site. These results have suggested that the complementary base pairs of the Watson-Crick type are formed at the AP site., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Using the membrane-modifying peptide, trichorovin-XIIa (TV-XIIa), which is an 11-residual peptaibol isolated from the fungus Trichoderma viride, we synthesized covalent conjugates of 20-mer oligonucleotide with TV-XIIa to examine the potential use of TV-XIIa in cellular delivery. The results indicated that the conjugates were progressively taken up by human lung carcinoma A549 cells. Next, the antisense effects of the conjugates on p53 protein expression were examined. The p53 expression was significantly decreased by ca. 20-50% in the presence of the conjugates upon treatment with the transfection solution at the concentration of 5 μM., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

8-Oxoguanosine (8-oxoG) is a representative metabolite derived by the oxidation of guanosine (G) and is regarded as a marker of oxidative stress in the cells. We previously reported the 8-oxoG-clamp as the first fluorescent probe for detection of 8-oxoG. In this study, new 8-oxoG-clamp derivatives having a variety of N-functional groups were synthesized and their recognition properties were investigated. The sp(3) oxygen atom of the carbamate unit was revealed to play a significant role in the hydrogen bonding interactions, and the pyrene group produced higher stability with 8-oxoG compared with the original 8-oxoG-clamp.