Preclinical development of potential therapies for a rare and untreatable inflammatory bone condition
In 1933, a radiologist named William A. Jones coined the term cherubism to describe a rare inflammatory bone condition of the jaw after he observed three members of a family with swollen cheeks and upturned eyes. In 2001, Yasuyoshi Ueki, MD, PhD, then at the Harvard School of Dental Medicine, and colleagues determined that mutations in the SH3BP2 (SH3-domain binding protein 2) gene caused cherubism. Because of this discovery, doctors today can test for mutations in the SH3BP2 gene to confirm their suspicion that a child has this rare condition.
But, unfortunately, doctors can’t do much else for these children beyond a precise diagnosis. No therapy has been established for cherubism, and doctors don’t operate on children with mild forms of cherubism because much of the time, the condition—after appearing suddenly in early childhood between the ages of about 2 and 5 years—spontaneously resolves in adolescence.
Some children, however, contend with severe effects. Children with severe facial swelling or jawbone destruction may have bulging eyes, trouble breathing through the nose, or missing or displaced teeth. Children with such severe effects may require surgery to improve their ability to see, breathe, or eat. In these cases, surgeons are not curing the disease but rather helping these children manage everyday activities that other children take for granted.
Ueki, who is now an associate professor at the University of Missouri–Kansas City School of Dentistry, continues to study cherubism in the lab. He recently published three journal articles detailing his ongoing research on cherubism and the functions of SH3BP2, and his most recent projects could someday lead to the development of prevention and treatment strategies for people with the condition.
A possible method of preventing jawbone destruction
For their experiments in the research lab, Ueki’s team genetically modified mice so that they would have the signs of inflammation that mirror the human version of cherubism. Inflammation was evident in the soft tissues of genetically modified mice as early as 2 weeks of age. The inflammation progressively worsened at 3 weeks and 7 weeks.
Because inflammatory conditions are generally associated with an elevated level of tumor necrosis factor alpha (TNF-alpha) in tissues, Ueki treated mice having the SH3BP2 mutations with a drug that blocks TNF-alpha function.
TNF-alpha-blocking drugs have already proved helpful to people with rheumatoid arthritis and other inflammatory conditions that are more common than cherubism. For example, the drug known as etanercept relieves the symptoms of moderate to severe rheumatoid arthritis and psoriasis by blocking TNF-alpha function.
Twice a week for seven weeks, Ueki’s team injected etanercept under the skin of one-week-old genetically modified mice. Control mice were injected with a solution that did not contain the drug. The researchers reported in the May 2014 issue of the Journal of Bone and Mineral Research that the drug prevented facial skin inflammation and reduced the total area of bone erosion from the jaws of genetically modified mice. When the researchers stopped injecting the drug after seven weeks, the young mice developed facial skin inflammation and jawbone destruction.
With this TNF-alpha-blocking approach, timing is everything. As expected, the drug did not reduce inflammation in 10-week-old genetically modified mice that already had signs of active inflammation.
Ueki’s studies with mice demonstrated three things:
- Etanercept can prevent facial swelling and jawbone destruction in young mice.
- The TNF-blocking drug needs to be given continuously to prevent facial swelling and jawbone destruction.
- Etanercept does not help mice that already have facial swelling and jawbone destruction.
A possible treatment approach
Because blocking TNF-alpha with etanercept didn’t help genetically modified mice that already had signs of cherubism, Ueki’s team devised another approach for those mice. In the February 2015 issue of Bone, they reported that mice with signs of cherubism were helped by transplantation of bone marrow from healthy donor mice. The treatment reduced inflammation and inflammatory bone loss.
Bone marrow transplantation is an established therapy for people with certain cancers, such as leukemia (cancer of the blood and bone marrow). Because cancer treatments kill the healthy blood cells along with the cancer cells, doctors give some people with leukemia an infusion of healthy bone marrow cells from a donor. The donor’s healthy bone marrow cells help the person with leukemia reestablish a continuous supply of healthy cells in the body.
Before transplanting bone marrow from healthy donor mice into genetically modified mice, Ueki’s team treated the genetically modified mice with a cancer drug that kills unhealthy cells in the bone marrow. For the genetically modified mice with developing inflammation (6 weeks old) and fully established inflammation (10 weeks old), bone marrow transplantation worked. The treatment reduced inflammation, facial swelling, and progressive bone loss.
Another possible treatment approach
Ueki’s team has designed experiments to systematically explore and resolve questions surrounding the development, progression, and spontaneous regression of cherubism-related inflammation and bone loss. In September 2014 in Cell Reports, they published findings that may explain why children with cherubism show signs suddenly between the ages of 2 and 5 years and why the swollen cheeks and other signs tend to resolve during puberty.
Using lab mice, they traced the molecular pathways for development of cherubism and described possible triggers. One trigger could be bacteria found in dental plaque. They hypothesized that interventions in toddlers to reduce oral bacteria could in turn reduce or delay the signs of cherubism. However, germ-free genetically modified mice still developed signs of cherubism so control of bacteria in the mouth alone would not be sufficient to prevent the development of the condition.
They also hypothesized that a drug that inhibits the activity of a protein known as SYK (spleen tyrosine kinase) might block the pathway that leads to the inflammation associated with cherubism. The results of their experiments suggested that mutations in SH3BP2 activated a pathway in certain immune cells in response to bacteria, such as those found in dental plaque. They showed that SYK is part of the pathway that leads to TNF-alpha production, and blocking the activity of SYK in those immune cells could prevent inflammation.
Clinical trials have been conducted with investigational drugs that inhibit the activity of SYK in people with common diseases, such as rheumatoid arthritis, asthma, and other diseases, but not yet for people with cherubism. Preclinical researchers like Ueki rely on clinical collaborators to translate their scientific findings into therapeutic approaches for people.
Applications beyond the rare condition
Because Ueki has discovered that cherubism shares molecular pathways with more common inflammatory diseases, the approaches he’s developing for a rare condition may find applications in the treatment of much more common diseases. See the NIDCR Science News in Brief called "Shared Pathways: Innovative studies of cherubism may aid development of therapies for common inflammatory bone diseases."
- Yoshitaka T, Ishida S, Mukai T, Kittaka M, Reichenberger EJ, Ueki Y. Etanercept administration to neonatal SH3BP2 knock-in cherubism mice prevents TNF-α-induced inflammation and bone loss. J Bone Miner Res. 2014;29(5):1170-82. doi: 10.1002/jbmr.2125.
- Yoshitaka T, Kittaka M, Ishida S, Mizuno N, Mukai T, Ueki Y. Bone marrow transplantation improves autoinflammation and inflammatory bone loss in SH3BP2 knock-in cherubism mice. Bone. 2015 Feb;71:201-209. doi: 10.1016/j.bone.2014.10.021.
- Yoshitaka T, Mukai T, Kittaka M, Alford LM, Masrani S, Ishida S, Yamaguchi K, Yamada M, Mizuno N, Olsen BR, Reichenberger EJ, Ueki Y. Enhanced TLR-MYD88 signaling stimulates autoinflammation in SH3BP2 cherubism mice and defines the etiology of cherubism. Cell Rep. 2014 Sep 25;8(6):1752-66. doi: 10.1016/j.celrep.2014.08.023.
- NIH Grant 5R01DE020835