Molecular Partners AG presented promising initial human data for its experimental cancer therapy MP0712. The data, including the first human images, show the Radio-DARPin therapy successfully targeting tumors with limited accumulation in healthy organs like the kidneys and liver, a critical hurdle for radiopharmaceuticals.

The presentation marks a significant milestone for MP0712, which is being developed with strategic partner Orano Med for small cell lung cancer (SCLC) and other neuroendocrine cancers. The data was revealed at the Targeted Radiopharmaceuticals Summit Europe, which took place from 10-12 November 2025.

Initial Human Images Show Targeted Delivery

The showcased case study featured a patient with small-cell lung cancer who received MP0712 carrying an imaging payload, lead-203 (²⁰³Pb). The images demonstrated specific uptake of the drug in primary tumors and metastatic lesions, visible at 24 hours and sustained over four days.

Critically, the images showed limited exposure in healthy organs of concern. This targeted delivery is a key indicator of potential efficacy and safety when the drug is used with its therapeutic payload, lead-212 (²¹²Pb), a potent alpha-emitter.

“The images show targeted delivery of MP0712 into tumors and limited exposure in healthy organs of concern such as kidney and liver,” said Dr. Patrick Amstutz, CEO of Molecular Partners.

“This is an important milestone for MP0712, which is indicative of its potential performance in a clinical setting when carrying ²¹²Pb as a therapeutic radioactive payload and providing a strong basis for advancing its clinical development. We are continuing preparations for the upcoming Phase I trial with MP0712 and look forward to advancing additional Radio-DARPin programs in 2026.”

Mechanism of Action

MP0712 is the lead candidate from Molecular Partners’ Radio-DARPin platform. This approach combines the high specificity and small size of DARPin proteins—engineered binding proteins—with the tumor-killing power of [²¹²Pb] for targeted alpha therapy (TAT). The small size of DARPins may help overcome historical limitations of other radioligand therapies, such as poor tumor penetration.

The data presented also shed light on how MP0712 achieves high tumor accumulation. MP0712 is designed to target Delta-like ligand 3 (DLL3), a protein found on the surface of certain cancer cells.

Research shows that MP0712 is rapidly internalized by DLL3-expressing cells, carrying its radioactive payload inside the tumor cell. Furthermore, the DARPin molecule is “half-life engineered” to remain in the bloodstream longer, allowing for continuous delivery to tumors as the DLL3 protein naturally replenishes on the cell surface. This mechanism allows for high tumor uptake even with low DLL3 expression levels.

Next Steps

Molecular Partners has filed a Phase I Investigational New Drug (IND) application with the US Food and Drug Administration (FDA) for MP0712. Pending regulatory clearance, the company expects to initiate a Phase I/IIa clinical trial in the US before the end of 2025.

The study will be a multi-center trial designed to assess the safety of MP0712 and determine a recommended Phase II dose. It will include an initial imaging and dosimetry step using the [²⁰³Pb]-labeled version, followed by treatment with the therapeutic [²¹²Pb] version. Initial clinical data from this trial is anticipated in 2026.

The full imaging and dosimetry dataset from the compassionate use cases is expected to be presented by the NuMeRI team in South Africa at the Theranostics World Congress in January 2026.