Drug 'repurposing' has some well known success - most famously perhaps the development of the erectile-dysfunction drug Viagra from a failed drug to treat angina.
However, despite these valuable repurposing cases, a new study produced by the University of Cambridge Judge Business School has found that only 2% of new molecules entering clinical trials were ultimately launched in an area other than the one they were initially tested in.
The study, titled: “Renovation as innovation: is repurposing the future of drug discovery research?” – was coauthored by Arthur Neuberger, PhD candidate in pharmacology and biochemistry at the University of Cambridge; Nektarios Oraiopoulos, University Lecturer at Cambridge Judge Business School; and Donald Drakeman, Fellow in Health Management at Cambridge Judge Business School.
The study published in the journal Drug Discovery Today is based on US Food and Drug Administration approvals and the full clinical development history of 834 new molecular entities in a 32-year period starting in 1980. The study noted that there had been “compelling stories” by repurposing advocates, along with some estimates of repurposing success rates ranging from 30–75%, but no data to support such projections.
The study, as reported by University of Cambridge Judge Business School, cautioned against relying too much on the “excitement” that has surrounded some high-profile repurposing successes. Most repurposing attempts and successes have come in the same therapeutic area as originally tested, the study found, which is “outside of the main theme of repurposing, that of finding entirely new uses for existing molecules.”
“Turning base metal into gold has been difficult for a long time, and repurposing is unlikely to fill our future medicine cabinets singlehandedly,” the paper concluded, so research to discover new compounds is essential despite “inexorably increasing” new drug development costs.
“We felt it was important to look at a more extensive dataset than the handful of success stories that surround drug repurposing,” said study coauthor Nektarios Oraiopoulos of Cambridge Judge Business School.
“Attempting to repurpose some drugs can be a good approach given the rising costs of new drug development, but the data shows a low overall success rate for repurposing – particularly in producing successes in a new disease setting.”
The study found that drug companies attempted to expand use in the same therapeutic area (for example, testing a breast cancer drug for ovarian cancer) for 31% of products approved by the FDA, and those extensions had a high success rate of 67%.
Those percentages drop significantly in seeking to repurpose successful drugs in different therapeutic areas: 18% of products were tried in another area, with a 33% success rate.
“The alchemy involved in turning failures into successes is even more complicated,” the study found. “Only 16% were tried in another indication and most were in the same therapeutic area, with only 10% of the initial failures tried in a different area altogether.”
The success rate was just 9% whether the therapeutic areas were the same or different.
Yet the study points out that “rewards can be substantial” for this type of failed-to-successful repurposing: infliximab and etanercept, both initially developed for treating sepsis (overreaction of the immune system to infection or injury), were later approved to treat rheumatoid arthritis and are now among the world’s 10 top-selling drugs.
There were no predictive patterns among successfully repurposed products – with similar success rates for small and large molecules, and successes distributed across a wide range of therapeutic areas.
The study concludes that for products resulting from large amounts of time and resources in research, development, testing and manufacturing, “there can be good reasons to consider the possibility of repurposing, even after an initial clinical failure.”
Yet, “as promising as repurposing might be, basic research remains essential. It will not only help us understand where failed drugs might have a second chance, but, more importantly, will also continue to create a fertile environment for the often-unexpected discoveries that can launch entirely new classes of medicine.”
References
Arthur Neuberger, Nektarios Oraiopoulos and Donald L.Drakeman, "Renovation as innovation: is repurposing the future of drug discovery research?" Drug Discovery Today (2017). www.sciencedirect.com/science/article/pii/S1359644618302459?via%3Dihub
