Using stem cells to treat cancer?
Cancer is a very interesting disease. As I mentioned in a previous blog post, its ability to mutate into countless different forms means that generating effective ways to combat it is no small task. Researchers and physicians usually have to be pretty creative with how they approach treatment- no one drug will help every patient! A very interesting review coming out of Nature talks about a very interesting new way in which scientists are approaching this problem. As was reported by several laboratories, it turns out that stem cells have the natural tendency to migrate towards tumors. Using this principle, biologists are beginning to hijack these stem cells to deliver a wide variety of different things. Here is a brief summary of some of the therapies discussed (for the full story, check out the paper that I linked above!
Figure 1: A colony of stem cells!
Strategy 1: Delivering Therapeutic Proteins
There are many proteins out there that can be used to cause the spontaneous death of cells. One of these proteins is called TRAIL; it binds to a protein called death receptor 4 (ominous, I know!) and causes apoptosis, which is the cells way of destroying itself. By navigating directly to the tumor, stem cells are able to deliver these noxious proteins directly to the cells they wish to kill while sparing the surrounding tissue!
Strategy 2: Stem Cell Mediated Suicide Therapy
In this treatment, stem cells migrate to the tumors of interest and convert a previously harmless drug into one that is pretty nasty! By doing, this the stem cell sacrifices itself while simultaneously preventing the risk of it going on to divide into different things. This also means that dangerous drugs will only appear at the tumor site - if the drug manages to escape and go somewhere else, it won't be toxic because it hasn't been converted any stem cells!
Strategy 3: Nanoparticle delivery
One of the biggest difficulties in getting drugs to their targets is the body's own immune system. Your innate defense system is pretty potent (which is a very good thing!), but it also means that drugs are recognized as foreign entities and are quickly destroyed. To get around this, scientist have begun to surround drugs in nanoparticles, which your body doesn't identify as being a bad thing. This "Trojan horse" method allows your therapeutic of choice to sail past the defenders and make it to the end zone. Touchdown!
Figure 2: What your stem cell friends look like delivering nanoparticles. Close enough, right?
Strategy 4: Oncolytic Virus delivery
Oncolytic viruses are viruses that selectively destroy the rapidly dividing cells characteristic of cancerous tumors. However, the delivery of such viruses is difficult due to the same hiccup described in strategy 3: avoiding host immune defenses. The ability to "hide" within a stem cell allows the virus to remain inconspicuous until the moment is right!
Figure 3: A schematic of the therapies discussed above. Pretty snazzy! Picture courtesy of Nature Reviews Cancer.
But as you may note from the the title of the review, Stem cell-based therapies for cancer treatment: separating hope from hype, not everything is as simple as it seems! The field of stem cell research is still relatively young; thus, there are still a myriad of problems with using stem cells in humans. These issues are too long to list here (contact me if you wish to discuss!), but always take any new revolutionary treatment with a grain of salt. I, however, remain incredibly optimistic that we will circumvent these challenges and that stem cell therapies will soon become routinely used in the clinic!