RNA Therapeutics Beyond Vaccines: siRNA and ASOs

From gene to protein, and where RNA fits

Our genes, made of DNA, act like a master recipe book stored safely in each cell. To make a protein, the cell first copies the relevant recipe into a working message called messenger RNA, or mRNA. This message then travels to the cell's protein factories, where it is read and the protein is built. Proteins do almost all the work in the body, so problems in this process cause many diseases. Traditional drugs usually act on proteins after they are made. RNA therapeutics work a step earlier, targeting the messenger RNA itself. By intercepting the message, they can reduce or change the amount of a specific protein, offering a precise way to tackle the root cause of some conditions.

How siRNA medicines work

Small interfering RNA, or siRNA, medicines use a natural process that cells already possess to silence genes. The medicine is a small piece of RNA designed to exactly match the messenger RNA of a disease-causing gene. When it enters the cell, it guides the cell's own machinery to find and destroy that specific message. Without the message, the harmful protein is no longer made. Because the match is so precise, siRNA can be highly targeted. A key challenge has been delivering these fragile molecules to the right cells, but clever chemistry and delivery methods, particularly to the liver, have made this possible. Several siRNA medicines are now licensed, including treatments that dramatically lower harmful cholesterol or treat rare inherited diseases.

How antisense oligonucleotides work

Antisense oligonucleotides, or ASOs, are short, custom-made strands of genetic material that bind to a chosen messenger RNA like a mirror image. Depending on their design, they can do several things. Some flag the message for destruction, reducing a harmful protein, much like siRNA but by a different route. Others can change how the message is edited and assembled, correcting a faulty instruction so the cell makes a working protein instead of a broken one. This second ability is remarkable, because it can restore a missing function rather than only switching something off. ASOs have transformed the outlook for some devastating inherited conditions, and because each one is tailored to a specific genetic message, they can be designed for very rare diseases.

What they can treat

RNA therapeutics have had their biggest early impact on rare inherited diseases, where a single faulty gene is responsible. Licensed medicines now treat conditions such as spinal muscular atrophy, a serious muscle-wasting disease of babies and children, and certain inherited nerve and liver disorders, changing lives that once had few options. Beyond rare diseases, siRNA medicines that lower cholesterol point to a future role in common conditions like heart disease, where they may need dosing only a few times a year. Researchers are exploring RNA approaches for high blood pressure, viral infections, some cancers and neurological diseases. As delivery to different organs improves, the range of treatable conditions is expected to grow considerably over the coming years.

Benefits, limits and the future

The appeal of RNA therapeutics is their precision: they can be designed to target almost any gene, including ones that older drugs could never reach, and some work for months from a single dose. This makes them especially valuable for rare diseases and for long-term conditions where taking daily tablets is difficult. There are limits, though. Delivering the medicine to organs beyond the liver remains challenging, treatments can be very expensive, and long-term safety continues to be studied. In the UK, medicines are assessed by the MHRA for safety and by NICE for value before NHS use; this article does not give doses. As the science matures, RNA medicines are likely to become a mainstream part of treating both rare and common diseases.