Let's talk now about how this finding might result in new medicines. As an example, consider AIDS.
AIDS is caused by a virus called HIV. HIV is a special kind of virus called a retrovirus.
A retrovirus starts out "life" as an RNA. Once it gets into a cell, the RNA is turned into DNA which can then make new virus.
Because HIV starts out as an RNA, it is a wonderful target for RNA interference. The idea is to have someone make microRNAs (miRNAs) that stick to the RNA of HIV and target it for destruction. Simple.
Not so fast. There are lots of problems here. You need to get the miRNA into the cell. You need to have the miRNA remain effective over time. And you need for the miRNA not to be harmful.
The last one is the easiest. There are lots of miRNAs that will work against HIV so you can find the ones that are not harmful. But how do you get the miRNAs into the cell?
You can't just eat an miRNA or inject them into the blood. Our body hates RNAs that it doesn't know (they could be viruses). So the body quickly chews them up.
Scientists are working on creating RNAs that the body can't destroy. But they haven't found one yet that is effective enough to use as a medicine.
Gene therapy is another possibility for getting RNA into a cell. This is where a doctor infects you with a harmless virus that makes the RNA you want. In this case, a harmless virus would be used to destroy a harmful one.
Gene therapy has not been effective so far. It is hard to get the virus into every cell. The body also tends to shut the virus down (the body doesn't know the virus is trying to be helpful). And sometimes where the "harmless" virus lands in our DNA can cause problems like leukemia.
So this problem hasn't been worked out yet. What about the miRNA remaining effective over time?
This is a problem with HIV because HIV is constantly changing. This is why current drugs stop working after a while. The RNA of HIV changes so that the drug won't work anymore.
A changing RNA causes problems for miRNA too. The way a miRNA works is that it sticks to a certain sequence of RNA. For example, imagine an RNA with the sequence UAGC (real miRNA binding sites would be 20 or 25 long).
A miRNA with the sequence AUCG can stick to this RNA. (Remember, U and A stick together and so do G and C.)
It is important for all of the bases to line up for RNA interference to work. Now imagine that a new strain of HIV appears by chance with the sequence AAGC. This one doesn't match up and so is probably resistant to the miRNA we've made.
If it is resistant, then this version of HIV can now can spread. The miRNA we've designed will no longer be effective and this patient will develop AIDS.
The way around this problem is to use many miRNAs. Sort of like combination therapy is used now to treat AIDS.
Combination therapy uses different medicines all at once. These medicines target different parts of HIV. The idea is that it is hard to become resistant to many medicines all at once.
For example, if HIV becomes resistant to a protease inhibitor, it can still be killed off by a fusion or reverse transcriptase inhibitor. The reason for this is that it is very unlikely that an HIV will happen that has the three changes all at once.
If each change is a 1 in a million chance, then the chances of all three happening at the same time is 1 in a million cubed or 1 in a quintillion or so. This is so unlikely that it won't happen.
The same idea is being tried with interfering RNAsuse lots of them against different parts of the HIV RNA all at once. The odds are very unlikely that a resistant strain will develop against all of these RNAs all at once.
We clearly aren't at a cure yet using RNA interference. But this whole avenue of research would not have been possible without the work of Andy Fire and Craig Mello.
In other words, we wouldn't have known about this approach without their work. A whole new class of medicines may now become available because of some basic research done on a tiny worm. No wonder they won the Nobel Prize!