Nature, one of the most renowned scientific journals of the world, has published a compelling study performed by a Japanese group, in which these researchers investigate the use of statins for the treatment of achondroplasia. (1)
Statins are a family of drugs widely used to reduce blood cholesterol levels, with the goal of reducing the risk of an individual to have a cardiac attack or to have another attack in the future. However, statins have been shown to have several other potential therapeutic effects in a number of different situations, from preventing excessive scarring in healing processes to positive effects in animal disease models such as Alzheimer dementia. (2)
Another aspect of statins is that they have been shown to exert anti-proliferative actions in cancer cell models, with some investigators suggesting that they could be included as "add-ons" in the treatment of malignant diseases (3).
Nevertheless, the reason why the Japanese group chose statins to be tested in their mutant fibroblast growth factor receptor 3 (FGFR3) / achondroplasia model was the finding that statins have been shown to ameliorate osteoarthritis, likely to have positive effects in chondrocytes.(4)
However, before taking a look in this interesting work by Yamashita and coworkers, in respect to the eventual new readers, let's just point out some concepts about FGFR3 and its mode of action, so to make it easier to understand the topic.
FGFR3 and cell proliferation
If you have read past articles published in this blog you probably know that FGFR3 is an agent that usually promotes cell growth and proliferation. The relevant exception is exactly the chondrocyte living in the growth plate, in which FGFR3 works as a natural growth brake. In achondroplasia, FGFR3 has its structure altered (mutated) and this change makes it more active than normal, thus increasing the brake potency. The result is well known: long bones grow significantly less than expected and other bone structures are affected as well. It is noteworthy that regardless of the cell or tissue, FGFR3 uses the same chemical signaling cascades to exert its effects. The difference is not in the FGFR3 mode of action itself, but in the cell where it is working.
We could think in a chemical/signaling cascade or pathway as a domino chain (Figure 1).
Figure 1. Starting a chain reaction.
The finger (a FGF) taps the first block (FGFR3) and in sequence, it takes down the second, which in turn does the same with the third one till the last one of the row. Figure 2 depicts the main chemical cascades inside the cell that respond to the activation of FGFR3. The letters you see in the figure are acronyms for several reactive proteins (or enzymes) interacting one another to send the signal to the cell nucleus. These chemical cascades are amazing in the sense that what is going on is simply the transfer of electric charges from one molecule to another. How they know what to do with them is something to think about (they don't have GPS, do they?). You can find more about this topic in other articles of the blog.
Figure 2. FGFR3 main signaling cascades (MAPK, PI3K-AKT and JAK-STAT).
As mentioned above, in all cells, when FGFR3 is activated (turned on, or electrically charged) it will trigger the cascades shown in Figure 2, which will take the electric charge to the cell nucleus, which in turn will respond with other chemical reactions making the cell multiply. The exception is the chondrocyte living inside the cartilage growth plate, in which the opposite happens, when FGFR3 is activated, the nucleus responds by stopping the proliferation machinery.
Now, watch this 14 min illustrative animation provided by Cold Spring Harbor Laboratory, to see how a signaling cascade might work in the molecular level:
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| DNA Learning Center by Cold Spring Harbor Laboratory |
Controlling the signal
FGFR3 is only one of the many growth stimulators present in the cell surface. You might remember from another article here, FGFR3 is like an antenna in the roof of the cell, waiting for the appropriate signals carried by FGFs to transmit the message to the nucleus: "grow". There are many other growth triggers and you can imagine what would happen if all of them were working non stop. Cells and tissues would grow indefinitely causing a lot of problems. Grossly speaking, cancer is like this, the ill cells lose their control systems, or disable them, and start to proliferate at will.
Then, how is this growth control obtained in the normal cell, preventing a cell to freak out?
In the same way there are many growth inducers (think positive), there are also growth inhibitors (the negative), other molecules the body produces to balance the positive ones. Each cell is prepared to stop the activity of an activated enzyme, through some, let's say janitor systems. When a protein like FGFR3 is activated, not only it attracts the next one in its classic chemical cascade (e.g.: MAPK), but also will call the attention of others that exist to knock down its activity. These clearing systems bind to the activated molecule and either make it inactive again by dispersing the electric charge (recycle) or simply by degrading it.
So, this seems to be the link between statins and FGFR3 seen in the exciting work by Yamashita et al.: it looks like the statins tested were capable to drive the chondrocyte janitor system towards the activated FGFR3, causing its faster degradation.
Well, how could this help us in achondroplasia? The FGFR3 mutation that causes achondroplasia not only makes the enzyme more active but also make it active for longer. In the study by Yamashita et al., the statins were able to attenuate the effects of the mutation by leading FGFR3 to degradation through one of the cell janitors called proteasome pathway.
Statins under the spotlight
The work by Yamashita et al. has at least one major breakthrough in terms of scientific advance. Instead of performing their main tests only in animal cells, which is easier, they used human stem cells derived from tissue from donors bearing tanatophoric dysplasia type 1 (TD1) and achondroplasia mutations. You might remember that there are other activating mutations identified in FGFR3 causing more or less severe clinical features. TD1 is one the most severe syndromes linked to FGFR3 mutations.
The researchers also prepared normal human stem cells to behave like chondrocytes and in some of them they implanted an altered FGFR3 bearing the achondroplasia mutation (the others were used as controls, to allow comparisons). These cells presented disfunctions similar to the ones we see in real achondroplastic chondrocytes. When exposed to statins these altered cells showed improvement in their chemical activities and growth, reacting closer to what the comparative normal cells did. Furthermore, the stem cells derived from TD1 and achondroplasia were exposed to statins and had their disfunction diminished.
The authors also tested a statin, rosuvastatin (RSV), in a mouse model of achondroplasia, and found significant improvement in growth of some of the bones more affected by the mutation (Figure 3).
Figure 3. Effects of exposure to rosuvastatin in wild type (control) and achondroplasia like mice.
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Statins for achondroplasia ?
The authors ended up by proposing that statins could be used in therapy for achondroplasia, pending learning which statin, or statins, would be more adequate for children, and the right doses as well. Having being in the market for decades, the safety profile of statins is very well known, although data on its risk profile in children is still scarce. In their study, they treated the animals with a dose which is comparable to the largest dose used in the real life to treat high cholesterol levels in adult humans and, at this dose, the risk of liver, renal and muscle toxicity is higher.
In this context, there are some genetic and inflammatory conditions, such as systemic lupus erithematosus and familial hypercholesterolemia, that lead to high cholesterol levels in children, and in consequence increasing the risk of cardiovascular complications early in life. These conditions have been treated with statins and to assess the safety of this drug family in these groups, Researchers have been publishing a number of studies, reviews and analyses.(6-8) Although the doses used in these studies were lower than the doses used by Yamashita and coworkers in their work, the reported safety outcomes are reassuring: so far there have been reported only rare serious adverse events in the children population treated with statins.
Pros and cons
Let's see what other experts in the area have commented about the study by Yamashita et al. In the News and Views section of the same Nature issue where the work by the Japanese group was published, Olsen (9) commented that the results shown might lead one to think on the use of statins to treat achondroplasia, but that extreme care should be taken in consideration to keep the appropriate level of cholesterol in children taking these drugs.
In an article published in the online version of The Scientist, Yandell (10) interviewed some of the experts in the field. One of them, Laurence Legeai-Mallet (INSERM Institute, Paris), who participated in some of the studies performed with BMN-111, the CNP analogue now in clinical trials, noted that the bone growth effect was not dramatic, and that the animal model used showed only a mild phenotype (the achondroplasia characteristics). Dr Andrea Superti-Furga, from the University of Lausanne, one of the great world authorities in skeletal dysplasias, mentioned that the work was a wonderful proof of concept of the use of statins for the treatment of achondroplasia, but it also raised a lot of questions. You can find out more about these and other scientists on the right side of the blog page, clicking on their respective links.
Finally, it seems that statins could be used to treat achondroplasia, provided the right steps were taken before, to understand how it really works in the growth plate cartilage, what is the actual intensity of the effect and what would be the implications for other aspects of the child health with its use in large doses for a long period of time. For instance, lowering too much the cholesterol levels with a statin in a child could be harmful for his/her development.
This is not the end
A great aspect of this study is the rescue of an old family of drugs to repurpose it for a new clinical indication. The same has been done with meclizine, a drug used for motion sickness which has been shown to promote bone growth in an achondroplasia model in another recent study. (10)
Two major key advantages of these "old" drugs are that their safety profiles are largely known, and their costs are low. This, in turn, brings another challenge to the stage. To perform all the research needed to allow a drug to be commercially prescribed, the researcher must fulfill an enormous volume of tests, from verifying the reproducibility of the results, understanding the drug mechanism of action, checking its toxicity, to most crucial of all, performing tests in the affected individuals to prove the therapeutic concept. This is a very expensive path to be pursued and a huge challenge to be beaten when there is no patent protecting the drug and, in consequence, the investment needed. For a common disease these challenges would be already hard, but for rare conditions the barrier is indeed taller. Who would invest millions to prove that an old drug without patent could treat achondroplasia or similar rare conditions? To let you have another view of this topic, I invite you to read this short article by Dr Nicolas Sireau, the head of the Alkaptonuria Society, a physician and father of two kids with alkaptonuria, and one of the most combative leaders in favor of rare diseases (thank you Ines, from Beyond Achondroplasia).
Finally, while a recent study by the Tufts CSDD stated that a new drug could cost up to USD 2.6 billion, the Doctors Without Borders (Medecins Sans Frontiers) contests these figures saying that a drug could be developed at far lower costs, let's say the costs of 4 or 5 top soccer/football players in Europe.
Food for thoughts
There are some doubts about the capacity of statins to significantly rescue the bone growth in achondroplasia. It seems that a large dose would be necessary to see results, which brings the questioning about risks. But, what if the dose needed to promote FGFR3 degradation was not that large? Could the statins be combined with other drugs, such as meclizine, found to be potentially therapeutic in achondroplasia to rescue bone growth? In such a combination, there would be a drug inhibiting the MAPK cascade (meclizine) while the other would be accelerating the FGFR3 degradation. Two different mechanisms of action to reduce the FGFR3 signaling to promote bone growth. Could this also allow for lower doses of both drugs? To answer all these and many other questions, research must be performed first.
References
1. Yamashita A et al. Statin treatment rescues FGFR3 skeletal dysplasia phenotypes. Nature (17 September 2014) | doi:10.1038/nature13775.
2. Barone E et al. Statins more than cholesterol lowering agents in Alzheimer disease: their pleiotropic functions as potential therapeutic targets. Biochem Pharmacol 2014; 88(4): 605-16.
3. Pisanti S et al. Novel prospects of statins as therapeutic agents in cancer. Pharmacol Res 2014 Oct;88:84-98. doi: 10.1016/j.phrs.2014.06.013. Epub 2014 Jul 5.
4. Yudoh K, Karasawa R. Statin prevents chondrocyte aging and degeneration of articular cartilage in osteoarthritis (OA). Aging (Albany NY). 2010 Dec;2(12):990-8. Free access.
5. Feng S et al. Fibroblast growth factor receptors: multifactorial contributors to tumor initiation and progression. Histol Histopathol (2014) 29: 000-000. Free access.
6. Schanberg LE et al. Use of atorvastatin in systemic lupus erythematosus in children and adolescents.Arthritis Rheum 2012;64(1):285-96. Free access.
7. Vuorio A et al. Statins for children with familial hypercholesterolemia. Cochrane Database Syst Rev. 2014 Jul 23;7:CD006401. Free access.
10. Yandell K. Statins Stimulate Bone Growth? The Scientist 2014. Free access.
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