O-methyl rich fully stabilized oligonucleotides

1. A double-stranded nucleic acid comprising an antisense strand and a sense strand, wherein:

the antisense strand comprises at least 14 contiguous nucleotides, a 5′ end and a 3′ end, and has complementarity to a target;

the sense strand comprises at least 13 contiguous nucleotides, a 5′ end and a 3′ end, and has complementarity to the antisense strand;

the antisense strand comprises at least 85% 2′-O-methyl modifications;

the nucleotides at positions 2 and 14 from the 5′ end of the antisense strand comprise a non-2′-O-methyl modification; and

the nucleotides at positions 7, 9, 10, and 11 from the 3′ end of the sense strand comprise a non-2′-O-methyl modification or the nucleotides at positions 7, 10, and 11 from the 3′ end of the sense strand comprise a non-2′-O-methyl modification.

2. The double-stranded nucleic acid of claim 1 , wherein the antisense strand comprises perfect or less than perfect complementarity to the target, optionally wherein the target comprises mammalian or viral mRNA.

3. The double-stranded nucleic acid of claim 2 , wherein the antisense strand comprises 20 contiguous nucleotides or 22 contiguous nucleotides.

4. The double-stranded nucleic acid of claim 2 , wherein the antisense strand comprises a 5′ vinyl phosphonate.

5. The double-stranded nucleic acid of claim 1 , wherein the antisense strand comprises at least 90% 2′-O-methyl modified nucleotides.

6. The double-stranded nucleic acid of claim 2 , wherein one or more nucleotide mismatches are present at positions 2, 6, and 12 from the 5′ end of sense strand.

7. The double-stranded nucleic acid of claim 1 , wherein the nucleotide at position 20 from the 5′ end of the antisense strand comprises a non-2′-O-methyl modification.

8. The double-stranded nucleic acid of claim 1 , wherein one or more nucleotides at positions 1-7 from the 3′ end of the antisense strand are connected to adjacent nucleotides via phosphorothioate linkages.

9. The double-stranded nucleic acid of claim 1 , wherein the nucleotides at positions 1-6 from the 3′ end or 1-7 from the 3′ end of the antisense strand are connected to adjacent nucleotides via phosphorothioate linkages.

10. The double-stranded nucleic acid of claim 1 , wherein the nucleotides at positions 2 and 14 from the 5′ end of the antisense strand comprise a 2′-F modification or 2′-H modification, or a 2′-OH moiety.

11. The double-stranded nucleic acid of claim 1 , wherein the antisense strand comprises between 15 and 22 contiguous nucleotides.

12. The double-stranded nucleic acid of claim 1 , wherein the sense strand comprises between 15 and 20 contiguous nucleotides.

13. The double-stranded nucleic acid of claim 1 , wherein the nucleotides at positions 1 and 2 from the 3′ end of sense strand and/or the nucleotides at positions 1 and 2 from the 5′ end of sense strand are connected to adjacent nucleotides via phosphorothioate linkages.

14. The double-stranded nucleic acid of claim 1 , wherein the sense strand comprises a hydrophobic molecule at the 3′ end of the sense strand.

15. The double-stranded nucleic acid of claim 1 , wherein the sense strand comprises one or more nucleotide mismatches between the antisense strand and the sense strand.

16. The double-stranded nucleic acid of claim 1 , wherein the antisense strand comprises a 5′ phosphate, a 5′-alkyl phosphonate, a 5′ alkylene phosphonate, or a 5′ alkenyl phosphonate.

17. The double-stranded nucleic acid of claim 1 , wherein the double-stranded nucleic acid comprises 4-16 phosphorothioate linkages or 8-13 phosphorothioate linkages.

18. The double-stranded nucleic acid of claim 1 , wherein the double-stranded nucleic acid comprises double-stranded region of 15 base pairs to 20 base pairs.

19. The double-stranded nucleic acid of claim 1 , wherein the sense strand comprises at least 80% 2′-O-methyl modified nucleotides, at least 90% 2′-O-methyl modified nucleotides, or 100% 2′-O-methyl modified nucleotides.

20. The double-stranded nucleic acid of claim 1 , wherein the sense strand comprises 15 contiguous nucleotides, 18 contiguous nucleotides, or 20 contiguous nucleotides.

21. A pharmaceutical composition comprising one or more double-stranded nucleic acids of claim 1 , and a pharmaceutically acceptable carrier.

22. A double-stranded nucleic acid comprising an antisense strand and a sense strand, wherein:

the antisense strand comprises at least 14 contiguous nucleotides, a 5′ end and a 3′ end, and has complementarity to a target;

the sense strand comprises at least 13 contiguous nucleotides, a 5′ end and a 3′ end, and has complementarity to the antisense strand;

the antisense strand comprises at least 85% 2′-O-methyl modifications;

the nucleotides at positions 2 and 14 from the 5′ end of the first oligonucleotide are modified with 2′-F;

the sense strand comprises 100% 2′-O-methyl modifications; and

the nucleotides at positions 1-6 from the 3′ end, or positions 1-7 from the 3′ end, of the antisense strand are connected to adjacent nucleotides via phosphorothioate linkages.

23. A branched oligonucleotide compound capable of mediating RNA silencing in a cell, comprising two or more double-stranded nucleic acids, wherein the nucleic acids (N) are connected to one another by one or more moieties selected from a linker (L), a spacer (S) and optionally a branching point (B), wherein:

each double-stranded nucleic acid comprises an antisense strand and a sense strand, wherein each antisense strand comprises at least 14 contiguous nucleotides, a 5′ end and a 3′ end, and at least one antisense strand comprises at least 85% 2′-O-methyl modifications;

wherein the nucleotides at positions 2 and 14 from the 5′ end of the at least one antisense strand comprise a non-2′- O-methyl modification; and

wherein one or more nucleotides at positions 1-7 from the 3′ end of at least one antisense strand are connected to adjacent nucleotides via phosphorothioate linkages.

24. The branched oligonucleotide compound of claim 23 , wherein:

each antisense strand comprises at least 85% 2′-O-methyl modifications;

the nucleotides at positions 2 and 14 from the 5′ end of each antisense strand comprise a non-2′- O-methyl modification;

one or more nucleotides at positions 1-7 from the 3′ end of each antisense strand are connected to adjacent nucleotides via phosphorothioate linkages;

the nucleotides at positions 1 and 2 from the 5′ end of the sense and antisense strands are connected to adjacent nucleotides via phosphorothioate linkages;

each double-stranded nucleic acid is independently connected to a linker, spacer or branching point at the 3′ end or at the 5′ end of the sense strand or the antisense strand;

the compound further comprises a hydrophobic moiety attached to the terminal 5′ position of the branched oligonucleotide compound;

the nucleotide at position 20 from the 5′ end of the antisense strand comprises a non-2′-O-methyl modification;

the antisense strand comprises 15, 16, 17, 18, 19, 20, 21, or 22 contiguous nucleotides; and

the sense strand comprises 15, 16, 17, 18, 19, or 20 contiguous nucleotides.

25. The branched oligonucleotide compound of claim 24 , wherein the hydrophobic moiety comprises an alkyl, alkenyl, or aryl moiety; a vitamin or cholesterol derivative; a lipophilic amino acid; or a combination thereof.

26. The branched oligonucleotide compound of claim 23 , wherein each linker is independently selected from an ethylene glycol chain, an alkyl chain, a peptide, RNA, DNA, a phosphate, a phosphonate, a phosphoramidate, an ester, an amide, a triazole, or combinations thereof; and

wherein any carbon or oxygen atom of the linker is optionally replaced with a nitrogen atom, bears a hydroxyl substituent, or bears an oxo substituent.

27. The branched oligonucleotide compound of claim 23 , wherein the nucleotides at position 7, 10, and 11 from the 3′ end of the sense strand comprise a non-2′-O-methyl modification.

28. The branched oligonucleotide compound of claim 23 , wherein the non-2′-O-methyl modification comprises a 2′-F modification or 2′-H modification, or 2′-OH moiety.

29. The branched oligonucleotide compound of claim 23 , wherein:

the antisense strand comprises at least 90% 2′-O-methyl modified nucleotides; and/or

the sense strand comprises at least 80% 2′-O-methyl modified nucleotides, at least 90% 2′-O-methyl modified nucleotides, or 100% 2′-O-methyl modified nucleotides.