Molecular Partners (NASDAQ:MOLN) hosted a webcast to discuss clinical imaging and dosimetry data for MP0712, its DLL3-targeting radiotherapeutic program, following a presentation at the Theranostics World Conference in South Africa. Company executives said the data came from a named patient access program conducted under South Africa’s compassionate care framework (Section 21), supervised by Dr. Mike Sathekge of the University of Pretoria and Steve Biko Academic Hospital and CEO of NuMeRI.
Program overview and collaboration with Orano Med
Chief Executive Officer Patrick Amstutz described MP0712 as a “true collaboration” with Orano Med, with Molecular Partners focusing on the DARPin-based targeting vector and engineered half-life, while Orano Med contributes isotope expertise and supply capabilities for lead isotopes. The company is using Lead-203 for imaging, with the therapeutic counterpart expected to use Lead-212.
Imaging results: tumor uptake and healthy organ washout
Executive Vice President of Projects Michael Stumpp and colleagues focused the presentation on imaging results from patients dosed with 185 megabecquerels of Lead-203. Stumpp reviewed a metastatic SCLC case where imaging highlighted liver metastases that were “unknown at the time of diagnosis,” which he said could enable upstaging and more precise treatment decisions. Over multiple time points, the company observed early blood pool activity (including heart and large vessels) that diminished over roughly 24 hours, while lesions became more visible over time.
Stumpp emphasized that healthy organ uptake appeared limited, particularly in the liver and kidneys, while tumors demonstrated increasing uptake and retention. He said tumor lesions showed continued accumulation during the imaging period, with healthy organs demonstrating washout beginning around 24 hours.
The company presented additional maximum-intensity projection images from other patients, including another SCLC patient and a metastatic urothelial (bladder) cancer patient. Stumpp said lesion uptake increased over time and that tumor uptake rose quickly—reaching “probably about 80% in the first 24 hours”—with strong retention and little decline observed in most lesions.
Dosimetry: kidneys and red marrow in focus
Stumpp said dosimetry work concentrated on kidneys and red marrow, which the company identified as potentially dose-limiting based on animal studies. He described a consistent pattern across patients: uptake rose in the first ~24 hours and then declined, with “close clustering” of curves across subjects.
Using these data, Stumpp said absorbed dose estimates for Lead-212 at an initial clinical starting dose of 1 × 75 megabecquerels were “well within” external beam radiation therapy (EBRT) reference limits. He added that the company expects red marrow recovery based on animal data and believes repeat dosing may be feasible, potentially even above EBRT guideline values.
At the highest intended starting activity discussed (200 megabecquerels), Stumpp said kidney absorbed doses remained below the 23 gray EBRT reference limit, while red marrow exposure approached 2 grays—prompting plans for careful monitoring of hematologic recovery.
External expert perspective and phase I/II status
Professor Ken Herrmann, Chair of the Department of Nuclear Medicine at the University of Essen and chairman of Molecular Partners’ Scientific Advisory Board, characterized the first-in-human biodistribution as favorable. He cited low background uptake, visible tumor uptake even at late imaging time points (up to 120–168 hours), and apparent washout from normal organs over time. Herrmann cautioned against over-interpreting dosimetry and underscored the need to proceed to therapy to understand toxicity and response.
Management said the U.S. phase I/II trial is open and ready for screening, with initial patients identified and expected to enter screening “in the coming weeks.” Amstutz said the company plans to update on safety in the first half of the year, with hopes to show early activity signals during the second half of the year. He said response rate evaluation would require more patients at appropriate dose levels and could come “very late in 2026, early 2027.”
Monitoring plan, dosing cadence, and isotope optionality
In the Q&A, Chief Medical Officer Philippe Legenne said red marrow monitoring will include weekly blood draws to track lymphocytes, ANC, and white blood cells. He said the team expects to see some declines and anticipates recovery within two to three weeks, supporting the possibility of redosing. Legenne said the standard plan is four treatment cycles, with the possibility of going up to six based on benefit-risk considerations.
Amstutz and others also discussed interest in the potential to explore Actinium-225, noting that the observed tumor retention over many days could support alternative isotope choices. However, management said it does not have a specific timeline for an actinium track for MP0712 and framed the topic as part of broader strategic flexibility. The company also said it does not plan to build actinium manufacturing capabilities and would pursue partnerships if needed.
Regarding clinical positioning, Amstutz said the initial U.S. development path is likely in later-line SCLC, potentially after patients receive other DLL3 agents such as tarlatamab, and he also outlined interest in potential combinations, including with immuno-oncology approaches such as PD-1 inhibitors and/or T-cell engagers.
The call concluded with management reiterating its focus on advancing MP0712 during the year, while also noting that MP0726 (an ovarian program) is expected to progress toward first-in-human studies and that the company aims to nominate one or two additional internal programs for future development by mid-year.
About Molecular Partners (NASDAQ:MOLN)
Molecular Partners AG is a clinical-stage biopharmaceutical company headquartered in Zurich, Switzerland, specializing in the design and development of DARPin® (Designed Ankyrin Repeat Protein) therapies. These small, modular proteins are engineered to bind with high specificity and affinity to disease-relevant targets. The company’s technology platform aims to deliver novel treatments across multiple therapeutic areas by leveraging the unique properties of DARPins, including stability, tissue penetration and multi-specific binding capabilities.
The company’s development pipeline spans infectious diseases, ophthalmology and oncology.
