It’s a well-known fact within drug discovery that most drugs fail. But one failure does not portend a second; old drugs can be repurposed for new indications that work much better with better safety profiles.
Thalidomide is a famous example. First used in the 1950s to combat morning sickness in pregnant women, the drug tragically led to severe birth defects in thousands of babies. But after studying its mechanisms of actions, scientists realized they could apply thalidomide’s anti-angiogenic properties to stop the growth of blood vessels in hematological cancers. After it was shown that thalidomide can lead to complete remission in some patients with multiple myeloma, the drug has become a key drug prescribed for the disease.
Today, repurposing old drugs is an appealing option for drug developers and investors alike. In 2024, the drug repurposing market was valued at $32.96 billion and is estimated to reach $47.4 billion by 2033.
Drug repurposing in 2026 offers a genuinely compelling set of advantages that are becoming increasingly recognized across the industry.
—Sten Sorensen, Cereno Scientific
“Drug repurposing in 2026 offers a genuinely compelling set of advantages that are becoming increasingly recognized across the industry,” Sten Sorensen, CEO of Cereno Scientific, told DDN. “The most significant is the ability to build on an existing safety and pharmacological foundation — reducing one of the most significant sources of risk and cost in early-stage drug development.”
In May, the FDA announced a new drug repurposing initiative seeking to target unmet needs across many conditions. The announcement states that the FDA is particularly interested in pursuing repurposing strategies for metabolic diseases, neurodegenerative conditions, conditions that affect women’s and men’s health specifically, rare diseases, and substance use disorders.
“Too many patients lack effective treatment options, even when promising science exists,” said former FDA Commissioner Marty Makary in the news release. “Drug repurposing can make better use of available scientific data to deliver effective treatment options for patients in need.”
A welcome change
Initial reactions to the FDA’s announcement from executives working in the drug repurposing space have been optimistic, though they still see challenges ahead. “This initiative is long overdue, but like all new FDA initiatives it will be the details that matter,” Daniel Tillett, CEO of Racura Oncology, told DDN. “The FDA recognizes that there is little or no commercial incentive to pursue labeling changes for drug repurposing if a drug is off patent. Until there is a viable mechanism to recoup the costs involved in running repurposing studies, commercial interest in drug repurposing will remain muted.”
Tillett also noted that if the new use requires a change in formulation, dosage, or length of treatment, then it’s unclear how much of the existing human safety data package will be able to apply to the new label without requiring new human studies. Racura Oncology is repurposing bisantrene — originally developed in the 1980s to be a less toxic alternative to anthracycline chemotherapy — to treat acute myeloid leukemia (AML). Scientists at Racura Oncology discovered that bisantrene can silence the expression of the oncogene c-MYC (cellular myelocytomatosis).
“For our drug, bisantrene, there is a wealth of clinical data from over 40 clinical trials, but most is from the 1980s before the development of GLP, GMP and GCP guidelines. … A question of great relevance to us is how will the agency approach the use of older clinical data into the repurposing process for drugs that never made it to approval?”
Although questions like these will need to be addressed, Sorensen emphasized that the new FDA initiative still represents a step forward. “This is precisely the direction we believed regulators would eventually move towards, and we are excited to see it formalized. The FDA's initiative validates a development strategy that has been central to Cereno Scientific ffrom the very beginning: that established pharmacological foundations, when applied thoughtfully to new and serious indications, can deliver faster, safer, and more capital-efficient paths to transformative new treatments,” he said.
Cereno Scientific is advancing a repurposed drug candidate, CS1, which is a controlled-release reformulation of valproic acid. The company’s researchers discovered that valproic acid acts as a histone deacetylase inhibitor (HDACi) and decided to apply CS1 to treat pulmonary arterial hypertension (PAH).
Sorensen said that the new FDA initiative could help their clinical program move forward in two main ways. “A more structured and supportive regulatory framework for repurposed drugs has the potential to streamline interactions with the FDA, reduce perceived development risk, and accelerate the path toward approval,” he said. “From a partnering perspective, the initiative also matters. Big pharma, when evaluating transactions, views repurposed drugs as a risk, and a clear regulatory signal of support from FDA for repurposed drug development improves the attractiveness of assets like ours in those conversations.”
However, Sorensen added that “demonstrating disease-modification in a complex disease like PAH requires robust, long-duration clinical data, and that takes time and resources regardless of the regulatory environment. Generating the kind of evidence that satisfies both regulators and potential partners remains the central challenge, and one we are addressing head-on through the design of our global Phase 2b study.”
Hope for repurposed drugs
Recent data from Racura Oncology’s Phase 1 trial and Cereno Scientific’s Phase 2a trial represent the potential for repurposed drugs to fill gaps in treatment and showcase the importance of not giving up on a class of drugs.
“In some ways, we are not only repurposing bisantrene as a cardioprotective anticancer agent but also repurposing the anthracyclines as drugs directly relevant to current clinical practice,” said Tillett. “The well-known cardiotoxicity of the anthracyclines has made clinicians reluctant to use them despite their proven broad anticancer efficacy. If we can ameliorate the cardiotoxicity of anthracyclines, while also improving their overall anticancer activity, clinicians may look to use this extremely powerful class of drugs to better treat cancer patients, rather than just as a relic from a bygone era of oncology.
This initiative is long overdue, but like all new FDA initiatives it will be the details that matter.
—Daniel Tillett, Racura Oncology
Other exciting areas that are seeing high activity with repurposed drugs right now include Alzheimer’s disease, where 35 percent of drugs in development are repurposed compounds, and emerging epidemic infectious diseases, in which speed is paramount. Currently, Merck is considering repurposing its COVID antiviral to treat the Ebola outbreak in the Congo. In addition, for rare and orphan diseases where clinical trials are challenging and expensive, foundations like Every Cure are searching through large databases to find FDA-approved drugs that could be quickly applied to a new condition.
The FDA’s initiative specifically mentioned the use of new computational tools like AI to sift through masses of data and identify promising compounds. For example, startup Ignota Labs is using its AI platforms to analyze why previously shelved drug candidates failed, predict underlying mechanisms, refine their molecular profiles, and push them back into clinical development more quickly and sustainably than de novo discovery would allow. Combined with advances in the biological understanding of both basic health and disease mechanisms, drug repurposing today seems poised to transform therapeutics across all disease areas — as long as regulatory bodies and industry partners continue to signal their support.
“Modern science applied to old drugs can provide amazing discoveries,” said Tillett.
