The biggest challenges of RNAi technology are the stability of siRNA and its delivery efficiency. Chemical modifications such as 2' O-Methyl RNA and 2' Fluoro RNA will increase siRNAs' stability in serum and other medium, while minimize off-target effects. Also, some modification, such as cholesterol modification, will increase tranfection efficiency.
1. Chemical Modification available
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2' O-Methyl phosphoramidites
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2'-O-Me-rA, 2'-O-Me-rC, 2'-O-Me-rG, 2'-O-Me-rU
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Increase stability, minimize off-target effect: Prolong RNAi effect (Long-lasting siRNA)
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2' Fluoro phosphoramidites
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2'-FluoC, 2'-FluoU
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5' modifications
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5'-Amino, 5'-Biotin, 5'-Cholesterol, 5'-Phophorylation and 5'-Thio
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For specific applications (Special Application siRNA)
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3' modification
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3'-Amino
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2. Comparable table of chemically-modified and standard siRNAs
| Critical challenges | Standard siRNA | Chemically-modified siRNA |
| siRNA degradation | The non-modified standard siRNA is easy to be degraded in cell culture process. Although it is effective in most in vitro experiments, its life expectancy is shorter in cell culture. | The chemically-modified siRNA not only increases its life expectancy in serum and cell culture, but also strengthens its in vitro application capability |
| Time of effect | Relative short time effect, under normal circumstances for approximately one week. | The chemically-modified siRNA has long time effect, its effective time is twice as that of the standard siRNA |
| In vivo activity | The standard siRNA has poor stability, usually is not applicable to vivo experiments | The chemically-modified siRNA has strong stability in vivo |
