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| A nanostar nanoparticle (1) |
In the blog post titled Nanoparticles Light up Brain Tumors published by Jackie, a comment was put forth asking if drug delivery would be possible with this newfound nanotechnology approach to detecting brain tumors. I found an article that directly answers this question in a positive light.
In a collaborative study involving scientists from Northwestern University, and Sunkyunkwan University in South Korea, the scientists were able to induce apoptosis and decrease cell viability in HeLa Cell (from Dr. Islas’s lecture) via the use of nanoparticles (2). What is interesting to note here is that similar to Jackie’s article, the nanoparticles used here were also composed of gold. However, the construction of the nanoparticles were shaped like a star, thus the scientists in this study termed their nanoparticle, gold nanostars (AuNS). Based on previous studies, the scientists knew that a nucleolar phosphoprotein called nucleolin has the ability to act as a transport protein, and thus can be used to transport “anti-cancer ligands from the cell surface to the nucleus.” Unlike previous studies, the scientists here took advantage of this unique property of nucleolin to shuttle across their AuNS to the nucleus. However, just sending “empty” AuNS will do nothing to the cell (at the metabolic/mortality level). The ingenious aspect of this experiment was that the scientists (with the help of previous studies) decided to integrate AS1411 (an aptamer) with their AuNS. A small aside, aptamers are small strands of DNA that identify and bind to specific target molecules. In addition, from henceforth, the aptamer will be called Apt for easier notation. Also, it has been proven that by engineering this small piece of DNA (AS1411), it can actually cause the cell to stop DNA repair and induce immediate apoptosis (destroying Hallmark 3)! Another key aspect to this study was that they were able to visualize exactly how their AuNS were interacting with the nucleus, thus leading to a more concrete mechanistic understanding of how the AuNS caused the cell to apoptose/die!
Specific Mechanism
The basic idea of the mechanism is illustrated in Figure 1 - more details follow below.
As
a first test to verify that the Apt-AuNS actually traveled to the
nucleus, the scientists setup two tests: 1. with the Apt (Cy5-Apt-AuNS)
and 2. without Apt (Cy5-cApt-AuNS). The Cy5 is a fluorescent molecule
that shines red when light is stimulated to it. Also, the control used,
cApt was appropriate because it was an aptamer, but didn’t have the
therapeutic effects of AS1411. Thus, by using a fancy microscope known
as confocal fluorescence microscope, the scientists were able to measure
quantitatively how much each “hybrid” molecule was taken into the
nucleus. They found that the hybrid with the therapeutic component
(+Apt) had taken up more of the molecule than compared to its control
version (Figure 3). As the second test, using high-resolution TEM (tunnelling electron microscopes), the scientists were able to see exactly what was happening to the nucleus once the therapeutic component was added to the cancer cell (HeLa cells). It was seen that once the Apt made its way through the cell and into the nucleus, the once cancerous cell initiated folding of the nucleus. Specifically, over 60% of the HeLa cells had nuclear deformities. The key is that since they observed these foldings in only the HeLa cells that were treated with Apt and not in cApt, they could conclude that it was due to the AS1411 that caused this folding to take place. Thus, the scientists were able to observe and conclude that there is an interaction between the AS1411 molecule and the nucleus that causes apoptosis to ensue. Exactly how this signal pathway takes place is still not well understood so further research in this area needs to be done.
Another key finding from this experiment was the correlation between nuclear folding and cell activity that was observed. One of the types of cell activity they measured was cell viability. They found (you guessed it) that the more number of folds the cell had, the higher the probability that the cell would die immediately. This is particularly interesting because if we could induce HeLa cells to form more nuclear folds, than the probability that the cell will continue with the process of apoptosis increases dramatically. Thus, the chances of removing the tumor/cancer also increases dramatically as well, since this is a targeted chemotherapy at work!
Questions:
1. Are squamous cell carcinomas (like HeLa cells) the only type of cells with a receptor for nucleolin? If this is the case, then it would seem that only carcinomas can be treated with this approach.
2. At the beginning of the article, the researchers mentioned that they had to block/inhibit several functions of nucleolin in order for Apt to induce apoptosis. Why does blocking these functions result in Apt to induce apoptosis? I believe that there has to be some signal transduction pathway that gets inhibited as a result of these changes, but specifically what are they? Maybe if we know this information, we can possibly “broaden the net” and target other types of cancers as well.
These are just my thoughts.....
