Patent ID: 8309704

Claim:
A method of producing a siRNA duplex wherein entry of an antisense strand of the siRNA duplex into a RISC complex is promoted, the method comprising: (a) selecting a first siRNA duplex comprising a sense strand and an antisense strand, each strand having a 5′ end and a 3′ end, wherein the first siRNA duplex directs cleavage by a RISC complex at a phosphodiester bond within a desired target mRNA, the first siRNA duplex having a base pairing strength between 5 base pairs from the antisense strand 5′ end (AS 5′) and the sense strand 3′ end (S 3′) relative to a base pairing strength between 5 base pairs from the antisense strand 3′ end (AS 3′) and the sense strand 5′ end (S 5′), and (b) synthesizing a substituted siRNA duplex comprising one or more substituted base pairs with respect to the first siRNA duplex, wherein the substituted siRNA duplex comprises a sense strand and an antisense strand, each strand having a 5′ end and a 3′ end, and wherein the substituted siRNA duplex directs cleavage by the RISC complex at the same phosphodiester bond within the desired target mRNA, the substituted siRNA duplex having a base pairing strength between 5 base pairs from the AS 5′ and the S 3′ relative to a base pairing strength between 5 base pairs from the AS 3′ and the S 5′, wherein the one or more substituted base pairs comprise at least one mismatched base pair and wherein the one or more substituted base pairs are within the 5 base pairs from the AS 5′ and the S 3′, such that the base pairing strength between the 5 base pairs from the AS 5′ and the S 3′ of the substituted siRNA duplex relative to the base pairing strength between the 5 base pairs from the AS 3′ and the S ′5 of the substituted siRNA duplex is lessened as compared to the base pairing strength between the AS 5′ and the S 3′ of the first siRNA duplex relative to the base pairing strength between the AS3′ and the S 5′ of the first siRNA duplex, such that entry of the antisense strand of the substituted siRNA duplex into the RISC complex is promoted relative to the antisense strand of the first siRNA duplex.