To repurpose drugs is to find new ways that they can be applied to treat other conditions and illnesses. Although our knowledge of diseases is greater than ever before, the development of novel therapies has yet to catch up. Drug development is slow, expensive and risky. These challenges have made drug repurposing a more attractive option in recent years. Drug repurposing can be quicker, more cost-effective, and less risky than traditional drug development strategies since the bulk of the work is already done. There are many ways to find new uses for old drugs. The process starts with finding evidence that a drug has useful effects, or new targets, outside of its current clinical use. Then the new mechanism is studied and tested. The process ends within traditional drug development, in some cases skipping the already completed safety phases, and instead focuses on how well the drug works for its new purpose.

The barriers to drug repurposing

Despite clear advantages of drug repurposing, there are numerous challenges to this process. The pharmaceutical industry and scientific community tend to focus on new and innovative therapies. While new drugs are certainly needed, an unintended consequence is overlooking many valuable drugs that already exist. Unfortunately, drug repurposing is not as lucrative as new drug development which particularly hurts rare disorders like SCA. With old drugs, patent protection and legal hurdles are also barriers hindering alternative use. And while drug repurposing is financially less risky, there always exists the possibility that a drug will fail somewhere in development. Finally, it is also important to keep in mind that not all drugs can be repurposed. Even if two disorders are similar, this does not mean that similar drugs can be used to treat them both.

Drug repurposing in practice

It is noteworthy that in addition to old drugs, drugs that have previously failed in treating one condition can be considered when developing treatments for other disorders. A notable example is the drug thalidomide, which infamously led to birth defects but has now been repurposed to treat certain blood cancers (Singhal et al., 1999) and leprosy (Teo et al., 2002). There are also several notable recent examples of drug repurposing in SCA. One example is the proposed repurposing of the drug 4-aminopyridine, or 4-AP. This drug, which is also used to treat multiple sclerosis, has been shown to aid with motor symptoms in a mouse model of SCA6. Hopefully, we will see more drugs repurposed to treat SCA and other rare disorders in the near future.

If you would like to learn more about drug repurposing, take a look at our past SCAsource article on drug repurposing in SCA6 or this resource by Findacure.

Snapshot written by Carlos Barba and edited by Dr. David Bushart.

References

1. Singhal, S.; Mehta, J.; Desikan, R.; Ayers, D.; Roberson, P.; Eddlemon, P.; Munshi, N.; Anaissie, E.; Wilson, C.; Dhodapkar, M.; et al. Antitumor Activity of Thalidomide in Refractory Multiple Myeloma. New England Journal of Medicine. 1999, 341 (21), 1565–1571. https://doi.org/10.1056/nejm199911183412102.
2. Teo, S. K.; Resztak, K. E.; Scheffler, M. A.; Kook, K. A.; Zeldis, J. B.; Stirling, D. I.; Thomas, S. D. Thalidomide in the Treatment of Leprosy. Microbes and Infection2002, 4 (11), 1193–1202. https://doi.org/10.1016/s1286-4579(02)01645-3.