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Blog | 25 February 2019

The importance of drug repurposing for rare disease

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Drug repurposing, simply put, is the studying of drugs already approved to treat one disease to see if they can treat another disease or condition for which they are not approved.

Drug repurposing is faster and cheaper than traditional drug discovery and therefore offers hope to rare disease patients where small disease populations can make the conventional model commercially unviable.

Bringing treatments to patients in time

There are 7000 identified rare diseases however only 400 have a licensed treatment. Bringing a new pharmaceutical drug to the market takes 10-15 years, at a cost of one to two billion dollars, with a success rate of 5%. As nearly 95% of rare diseases have no treatment option at all this process takes too long, is too expensive and is very likely to fail.

On the other hand, repurposed drugs can reach the patient as a marketed treatment in around 3-5 years and has a success rate of 3 in every 10 drugs investigated.

Patients do not have the luxury of being able to wait, they need a new approach where treatments can be brought to the patient with more speed. Drug repurposing is one of the ways we can accelerate treatments for rare, acute and neglected diseases.

Reducing the rare disease drug price tag

Bringing a new therapeutic to the clinic will cost in the region of one to two billion US Dollars. This can make some rare diseases unappealing for pharmaceutical companies who, due to small patient numbers, will either stand to make little return on their investment or not have their drug adopted by health boards globally due to the huge price tag.

Existing drugs have already gone through extensive research and trials meaning much of this work does not need to be repeated or can be achieved much more quickly. Bypassing these early and substantial research costs brings the development price tag down considerably making it more attractive to drug developers and payers. A repurposed drug can progress to clinical trials for as little as $500,000 after it’s been validated on disease models.

Balancing the risk of rare disease drug development

For every ten new drugs that reach Phase 1 clinical trials only one will reach the market. Even before a drug reaches Phase 1, for every 10,000 chemical entities that enter the research pipeline only one will make it to become an approved treatment. This risk is considerable and funding for research into rare disease often falls to patient groups for whom the investment is worth it. However, the challenge of raising the considerable sums of money required and accessing the expertise required means this is not a viable option for most support groups and charities.

Repurposing existing drugs requires a collaborative approach between academia, industry, governmental bodies and patient organisations. This way of working helps to reduce the risks involved and with costs at a fraction of that of creating a new therapeutic, it has the potential to revolutionise the drug pipeline for rare disease and empower a larger number of patient organisations to drive for treatments in their conditions.

Proven track record

Drug repurposing is often overlooked as it is not considered novel. However, with many of the adverse reactions already known, the risk of drugs failing because of side effects (toxicity) is greatly reduced. The success rate for repurposed drugs is 5 times higher than for developing new drugs making it an exciting field of research and drug discovery.

Here are some examples of drugs that have been successfully repurposed, many of which have provided viable treatment options for rare disease patients:
1.     Probably the most famous repurposing case is that of thalidomide. First used as a sedative in the 1950’s thalidomide is infamous for causing birth defects in babies of women who were prescribed it to treat nausea whilst pregnant. It was, however, successfully and safely repurposed in 1998 to treat leprosy and in 2006 to treat the blood cancer multiple myeloma.


2.     Discovered in 1972 on Easter Island, rapamycin, also known as Sirolimus, is produced by a soil bacterium Streptomyces hygroscopicus. Its ability to suppress the immune system led to its original approved use to prevent rejection in organ transplantation in 1999. It has since been successfully repurposed to treat two rare diseases, autoimmune lymphoproliferative syndrome (ALPS) and lymphangioleiomyomatosis, a lung disease.


3.     Lomitapide was originally used to lower cholesterol and triglycerides. It went on to be approved in 2012 by the Food and Drug Administration (FDA) and in 2013 by the European Commission to treat patients with the rare genetic disease homozygous familial hypercholesterolemia.


4.     Originally intended as a chemotherapy for T-cell related leukaemias, pentostatin was unsuccessful, however it was repurposed successfully to treat a rare B-cell related leukaemia, hairy cell leukaemia.


5.     All-trans retinoic acid (ATRA) is a derivative of vitamin A historically used to treat severe acne. Whilst it has no anti-cancer properties on its own, ATRA when combined with traditional chemotherapy induced complete remission in 90% of patients with the rare blood cancer acute promyelocytic leukaemia.


6.     Sildenafil was originally developed by Pfizer as a treatment for hypertension and angina pectoris. During the Phase 1 cardiovascular trials, long lasting erections were noted as a side effect, which led to Pfizer’s team led by Dr. David Brown (Chief Scientific Officer , Healx) to repurpose sildenafil into the first erectile dysfunction treatment Viagra in 1998.


7.     Lonafarnib, a farnesyltransferase inhibitor, originally developed to treat cancers was repurposed for use in the rare disease progeria when it was discovered that these inhibitors blocked the attachment of farnesyl groups onto the progeria-associated protein progerin.


8.     The hormone treatment tamoxifen was approved in 1977 to treat metastatic breast cancers.  After 30 years it was repurposed to treat bipolar disorder after it was discovered that it blocks an enzyme called PKC, which goes into overdrive during manic phases.


9.     Zidovudine (AZT) was a failed cancer drug that went on to become the first antiviral approved for HIV/AIDS in 1987. This drug could see a further incarnation as it has been identified as a target for treating carbapenem-resistant Enterobacteriaceae when used in combination with an antibiotic called tigecycline.


10.  In 2017 the successful repurposing of plant-derived fortified food substances known as nutraceuticals showed that they can prevent the transcription of the mutated gene responsible for familial dysautonomia in patients’ brains. Familial dysautonomia is a debilitating rare genetic disease that impacts the development and function of the autonomic nervous system. Patients on a multi-nutraceutical regime who were also subject to dietary changes saw a significantly reduction or elimination of symptoms and a restoration of nervous system function.


Healx is a tech company from the Cambridge Cluster (UK), focussed on accelerating treatments for rare diseases. It integrates artificial intelligence with deep pharmacology to translate therapies into the clinic within 24 months. Thereby, dramatically reducing the time and cost compared to conventional drug discovery.
To achieve this goal, Healx developed the most comprehensive AI-based drug discovery platform for rare diseases: Healnet. With the objective to translate 100 rare disease treatments towards the clinic by 2025.

For more information on our recent project Fragile X visit https://healx.io/our-work/fragile-x-case-study/