Life can be unexpectedly difficult for children with congenital vascular malformations. These rare, congenital vascular abnormalities cause swelling, deformities, thrombosis, or bleeding, but above all chronic pain. Playing with friends or getting through a full day at school is not a given for many patients.

However, an existing drug, originally developed for a completely different condition, can make all the difference.

The story of pediatric hematologist-oncologist and clinical pharmacologist Maroeska te Loo shows how powerful drug repurposing can be. In 2025, her team at Radboudumc won the Drug Repurposing Venture Challenge (DRVC) organized by ZonMw and FAST with a plan to make the drug sirolimus officially available to patients with congenital vascular malformations.

Their experience shows what is possible when science, entrepreneurship, and patient care come together.

An unexpected breakthrough
Fortunately, congenital vascular malformations are rare, affecting approximately one in 5,000 to 10,000 children. However, in complex cases—tangles of abnormal veins or lymphatic vessels—the impact can be enormous. Te Loo recalls a patient who changed everything: a ten-year-old boy with a lymphatic vascular malformation in both legs. The pain was so severe that he arrived at the consultation in a wheelchair. Existing pain medication offered little relief.

Around the same time, research appeared that suggested a surprising possibility. In mouse models, sirolimus, an immunosuppressant used after kidney transplants, was found to have an effect on vascular malformations. The drug inhibits the so-called mTOR pathway, a biological mechanism that controls the growth of cells and blood vessels.

In vascular malformations, this “engine” runs at full speed, as it were. After consulting with the patient and his parents, the team decided to try an experimental treatment, starting cautiously with a low dose due to possible side effects. Three months later, the boy walked into the consultation room himself. His mother had only one complaint: her son was playing outside again – and was difficult to get inside in the evening.

From practical experience to clinical evidence
The result was no coincidence. Encouraged by this success, the team treated more patients with sirolimus, often with similar results. This led to a clinical study that ran from 2017 to 2021. Despite the rarity of the condition, so many patients signed up that a waiting list was even created.

The results were convincing:

• 90% of children experience a significant reduction in pain.
• 70% of adults also benefit significantly.
• Side effects remain relatively mild thanks to low dosages.

International research confirms these findings. In clinical practice, sirolimus is now increasingly being used in these patients. But there is a problem: the drug is not officially registered for this indication.

Why registration is crucial
Off-label use of a medicine may work well, but it carries risks. For example, if a medicine is used less for its original indication, production may decline. This could jeopardize availability for other patient groups. At the same time, new, targeted therapies are being developed for specific genetic mutations that cause vascular malformations. These treatments are promising, but also likely to be very expensive.

Sirolimus has an important strength: it acts on a central biological mechanism and can therefore work in a broader group of patients. In order to keep the drug available in the future, official registration for this indication is therefore necessary. And that is anything but simple.

The step towards entrepreneurship
A registration process requires much more than just scientific evidence. Consider:

• regulatory expertise
• pharmacoeconomic analyses
• production and formulation development
• investments for clinical studies

That is why the Radboudumc team decided to seek help from experts in the biotech and drug development world.

At that very moment, the Drug Repurposing Venture Challenge offered a unique opportunity.

This challenge helps researchers translate their scientific ideas into realistic business plans for the development and registration of existing drugs for new applications.

After months of preparation, the team presented its plan in a pitch to a jury of experts. Questions about budgets, clinical studies, side effects, and market access followed in rapid succession. The plan was convincing. On October 8, 2025, the Radboudumc team was declared the winner of the Drug Repurposing Venture Challenge.

The next step
With the €20,000 prize money, the team is now taking the next step: applying for orphan drug designation for the new formulation of sirolimus. This status for orphan drugs offers important advantages, such as market exclusivity and additional support during development.

This makes the project more attractive to investors and pharmaceutical partners. Interest is already there: shortly after the award ceremony, two companies came forward to explore possible collaboration. According to Te Loo, this is no coincidence. The team not only brings scientific expertise to the table, but also a strong international network and close collaboration with patients.

An inspiration for new teams
The story of sirolimus shows how a clinical observation can develop into an innovative development route for an existing drug. With the right support, drug repurposing can deliver new treatments faster, more affordably, and more effectively to patients who urgently need them.

And that is exactly what the Drug Repurposing Venture Challenge 2026 is for.

Do you have a promising idea for a new application of an existing drug? Then this challenge can help you take the next step: from scientific insight to real impact for patients.

Maybe the next success story will be your team’s.