No it can’t. But in a recent report (1) scientists show how
using tiny gold particles they were able to deliver a therapeutic agent called
siRNA to cells and tissues.
siRNA are two short stretches of ribonucleic acid (RNA),
chemically very similar to DNA. siRNA molecules whose sequence is properly
designed can be very powerful in reducing the level of a target gene’s
activity, most commonly by stopping the production of the protein the gene
encodes for. In their paper, the authors focused on a protein called
endothelial growth factor receptor, or EGFR, which is known to be hyperactive
in certain types of cancer. As you probably figured out by now, reducing the
levels of EGFR protein by siRNA might therefore be a very powerful way of helping
some cancer patients. This study did not involve any human patients, but it did
show that gold nanoparticles coated with siRNA molecules designed to reduce
EGFR levels were successful in doing so in cultured cells and even in the skin
of mice.
The facts that EGFR is hyperactive in some malignancies as
well as that siRNA can reduce levels of proteins have been known for decades.
So why has it taken so long for the scientists to come up with an effective way
of combining the two pieces of knowledge into something effective. The problem
is, putting siRNA into cells, especially when they are a part of a living
organism, is not a straightforward task. It’s a bit simpler when the cells grow
in culture – we can mix siRNA with some chemicals or stick it into modified
viruses, which have the natural ability to inject DNA or RNA into cells. But
when it comes to patients, using these chemicals or viruses is not something
you can get patients to agree to easily. The mentioned chemicals can be simply
toxic and viruses are, well, viruses. These two methods can not only be harmful
to cells or organisms, but they can also modify the so-called gene expression,
i.e. set of genes that are active in given cells. For example, cells in our
bodies usually know that they have been infected by a virus and they activate
all sorts of genes to alert the body’s immune system, often resulting in
phenomena such as inflammation. Scientists do have means of checking how the
profile of active genes inside cells changes after they’ve been subject to a
certain type of treatment, and one of the fascinating things about the gold
nanoparticles was that they changed the activity of only seven genes in
cultured cells. Is that a lot? Well, a chemical reagent used to deliver the
same siRNA to the same cells affected 427 genes. On top of that, the siRNA
delivered on gold nanoparticles was still about 50% active after 4 days, at
which time the siRNA delivered by the compared chemical completely lost its
activity. But most importantly, when tested in animals, the gold-delivered
siRNA managed to get into the majority of cells, stayed active in there for a
long time, exerted a prominent effect, and no obvious signs of toxicity were
apparent in the skin (site of application) or any other tested organ.
This approach, obviously, has its limitations. In the
mentioned study, the researchers applied the gold nanoparticles only to the
skin. They did not mention or speculate about how the golden spheres could be
delivered to another organ. After all, it’s not only skin that might require some
siRNA. Direct injections might be effective, but this certainly requires
testing. Additionally, it would be hard to imagine this technique being used
systematically, say, to treat metastatic cancer. After all the authors point
out just how localised the action of this method is. Nonetheless, this is a
very promising discovery that seems to have a whole multitude of pros and
limited number of cons. Hopefully, in the near future some of our conditions
will get treated by rubbing some gold into our skin…
1. Topical delivery of siRNA-based spherical nucleic acid nanoparticle conjugates for gene regulation.
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