Small interfering RNA (siRNA) drugs are a type of treatment that targets and silences specific genes involved in genetic disorders. Yet, these drugs face difficulties because they can inadvertently silence genes that are not the intended targets, leading to unwanted side effects. A research group from Nagoya University in Japan has successfully modified siRNA using formamide to minimize the chances of these off-target effects, thereby enhancing the safety of siRNA therapies for genetic conditions. Their findings have been reported in Nucleic Acids Research.
siRNAs are short, double-stranded RNA molecules that interact with messenger RNA (mRNA) – the template for protein production – to prevent its expression. By targeting and silencing the genes responsible for producing harmful proteins, siRNAs have the potential to treat a variety of genetic diseases.
Nonetheless, the effectiveness of siRNA treatments can be compromised by off-target effects. These occur when siRNAs mistakenly interact with mRNA strands that are not their intended targets. Such interactions can disrupt critical genes, leading to harmful changes in cellular functions and negatively affecting the immune system.
A key factor contributing to off-target effects is a seven-nucleotide sequence known as the seed region, found in the guide strand of the siRNA. This region plays a vital role in identifying the correct target. Off-target effects often arise when this seed region matches with non-target mRNA strands.
Professor Hiroshi Abe noted, “Off-target effects likely occur when there are unintended non-target mRNAs that can base pair with the siRNA’s seed region. We discovered that we could minimize these effects by altering the pairing capacity or the stability of the double-strand in this seed region through chemical modifications. This approach ensures a stable complex forms only when the entire guide strand properly binds to the intended target mRNA.”
Professor Abe and his student Kohei Nomura utilized a formamide modification in this critical area of the siRNA. Formamide can prevent the formation of hydrogen bonds, which are essential for maintaining the stability of the mRNA double helix. By disrupting these hydrogen bonds, formamide causes the mRNA strands to destabilize and separate. This decrease in strand stability makes it difficult for non-target mRNAs to bind with the seed region of the siRNA, thereby lowering the risk of off-target interactions.
“Our modification effectively reduces off-target effects with greater efficiency than current chemical modifications,” Abe explained. “By implementing the modification at just one position, we achieved the desired outcomes and allowed for more versatile siRNA sequence designs.”
The chemically modified siRNAs developed through this technique are expected to lead to siRNA drugs with fewer side effects. Nomura sees the potential for this research to contribute to the development of siRNA therapies for conditions such as hereditary transthyretin amyloidosis, acute hepatic porphyria, primary hyperoxaluria type 1, primary hypercholesterolemia, and mixed dyslipidemia.
