Nuclease resistant double-stranded ribonucleic acid

1. A method of increasing the nuclease resistance of a dsRNA, comprising the steps of:

(a) identifying in the nucleotide sequences of the antisense strand of an unmodified dsRNA all occurrences of the dinucleotides 5′-ua-3′, 5′-ca-3′, 5′-ug-3′, 5′-uu-3′, 5′-cc-3′, 5′-uc-3′ and 5′-cu-3′; and

(b) replacing the 5′-uridines and/or 5′-cytidines in all occurrences of at least one of the dinucleotides identified in (a) with 2′-modified uridines and/or cytidines, respectively;

wherein the replacement of 5′-uridines and 5′-cytidines by 2′-modified uridines and cytidines, respectively, is carried out stepwise and results in a modified dsRNA, wherein

(a′) in a first step, all uridines in a 5′-ua-3′ sequence context are replaced by 2′-modified uridines, and,

(b′) in a further step, all cytidines in a 5′-ca-3′ sequence context are replaced by the respective 2′-modified nucleotides, and,

(c′) in a subsequent optional step, all uridines in a 5′-ug-3′ sequence context are replaced by the respective 2′-modified nucleotides, and,

(d′) in a subsequent optional step, all 5′-uridines in a 5′-uu-3′ sequence context are replaced by the respective 2′-modified nucleotides, and

(e′) in a subsequent optional step, all 5′-cytidines in a 5′-cc-3′ sequence context are replaced by the respective 2′-modified nucleotides, and,

(f) in a subsequent optional step, all uridines in a 5′-uc-3′ sequence context are replaced by the respective 2′-modified nucleotides, and,

(g′) in a subsequent optional step, all cytidines in a 5′-cu-3′ sequence context are replaced by the respective 2′-modified nucleotides,

wherein after all of steps (a′) and (b′), the stability of the modified dsRNA(s) in biological samples after the replacement in each of the subsequent optional steps (c′), (d′), (e′) (f′), and (g′), if present, is measured by a nucleotide degradation assay and compared to the stability of the dsRNA(s) immediately prior to that subsequent optional step to determine whether to carry out the subsequent optional step, wherein the subsequent optional step is carried out if the modified dsRNA demonstrates greater stability than the modified dsRNA(s) immediately prior to that subsequent optional step, and the subsequent optional step is not carried out if the modified dsRNA demonstrates no greater stability than the modified dsRNA(s) immediately prior to that subsequent optional step.

2. The method of claim 1 , wherein all of the 5′-uridines and/or 5′-cytidines in at least three of the dinucleotides identified in (a) are replaced by 2′-modified uridines and/or cytidines, respectively.

3. The method of claim 1 , wherein all of the 5′-uridines and/or 5′-cytidines in at least four of the dinucleotides identified in (a) are replaced by 2′-modified uridines and/or cytidines, respectively.

4. The method of claim 1 , wherein all of the 5′-uridines and/or 5′-cytidines in at least five of the dinucleotides identified in (a) are replaced by 2′-modified uridines and/or cytidines, respectively.

5. The method of claim 3 , wherein the said four dinucleotides are 5′-ua-3′, 5′-ug-3′, 5′-uu-3′, and 5′-ca-3′.

6. A method of increasing the nuclease resistance of a dsRNA, comprising the steps of:

(a) identifying in the nucleotide sequences of the antisense strand of an unmodified dsRNA all occurrences of the dinucleotides 5′-ua-3′, 5′-ca-3′, 5′-ug-3′, 5′-uu-3′, 5′-cc-3′, 5′-uc-3′ and 5′-cu-3′, and identifying in the nucleotide sequences of the sense strand of the dsRNA all occurrences of the dinucleotides 5′-ua-3′, 5′-ca-3′, 5′-ug-3′, 5′-uu-3′, 5′-cc-3′, 5′-uc-3′ and 5′-cu-3; and

(b) replacing the 5′-uridines and/or 5′-cytidines in all occurrences of at least one of the dinucleotides identified in (a) with 2′-modified uridines and/or cytidines, respectively;

wherein the replacement of 5′-uridines and 5′-cytidines by 2′-modified uridines and cytidines, respectively, is carried out stepwise and results in a modified dsRNA, wherein

(a′) in a first step, all uridines in a 5′-ua-3′ sequence context are replaced by 2′-modified uridines, and,

(b′) in a further step, all cytidines in a 5′-ca-3′ sequence context are replaced by the respective 2′-modified nucleotides, and,

(c′) in a subsequent optional step, all uridines in a 5′-ug-3′ sequence context are replaced by the respective 2′-modified nucleotides, and,

(d′) in a subsequent optional step, all 5′-uridines in a 5′-uu-3′ sequence context are replaced by the respective 2′-modified nucleotides, and

(e′) in a subsequent optional step, all 5′-cytidines in a 5′-cc-3′ sequence context are replaced by the respective 2′-modified nucleotides, and,

(f′) in a subsequent optional step, all uridines in a 5′-uc-3′ sequence context are replaced by the respective 2′-modified nucleotides, and,

(g′) in a subsequent optional step, all cytidines in a 5′-cu-3′ sequence context are replaced by the respective 2′-modified nucleotides,

wherein after all of steps (a′) and (b′), the stability of the modified dsRNA(s) in biological samples after the replacement in each of the subsequent optional steps (c′), (d′), (e′) (f′), and (g′), if present, is measured by a nucleotide degradation assay and compared to the stability of the dsRNA(s) immediately prior to that subsequent optional step to determine whether to carry out the subsequent optional step, wherein the subsequent optional step is carried out if the modified dsRNA demonstrates greater stability than the modified dsRNA(s) immediately prior to that subsequent optional step, and the subsequent optional step is not carried out if the modified dsRNA demonstrates no greater stability than the modified dsRNA(s) immediately prior to that subsequent optional step.

7. The method of claim 6 , wherein all of the 5′-uridines and/or 5′-cytidines in at least three of the dinucleotides identified in (a) are replaced by 2′-modified uridines and/or cytidines, respectively.

8. The method of claim 6 , wherein all of the 5′-uridines and/or 5′-cytidines in at least four of the dinucleotides identified in (a) are replaced by 2′-modified uridines and/or cytidines, respectively.

9. The method of claim 6 , wherein all of the 5′-uridines and/or 5′-cytidines in at least five of the dinucleotides identified in (a) are replaced by 2′-modified uridines and/or cytidines, respectively.

10. The method of claim 8 , wherein said four dinucleotides are 5′-ua-3′, 5′-ug-3′, 5′-uu-3′, and 5′-ca-3′.