Molecular Partners Preclinical Data Shows Radio-DARPin Isotope Interchangeability Across Therapy Programs

Molecular Partners AG presented preclinical data at the 3rd Global Radiopharmaceuticals Development Summit in Shanghai this week showing that its Radio-DARPin vectors maintain highly comparable biodistribution across multiple isotopes, a finding that CEO Patrick Amstutz, Ph.D., says fundamentally changes how the Zurich-Schlieren company can run its oncology pipeline.

The oral presentation, delivered March 19 on the summit's opening day, centered on a property the company calls isotope interchangeability: the same Radio-DARPin vector can be labeled with either the alpha-emitter actinium-225 (225Ac) or lead-212 (212Pb) without requiring a restart of the discovery and development process. Lutetium-177 (177Lu), a beta emitter used for imaging, is also compatible with the platform, positioning Radio-DARPins as tools for both theranostic imaging and targeted alpha therapy within a single program architecture.

"Our recent data confirms that our Radio-DARPin-vector design allows interchangeability of alpha-isotopes, including 212Pb and 225Ac," Amstutz said. "This feature offers us the opportunity and flexibility to evaluate Radio-DARPin candidates in an isotope-agnostic manner and to choose the most suitable therapeutic isotope, as late as with initial clinical data, without having to restart the entire drug discovery and development process — a significant advantage to tailor our candidates to patient needs."

The practical implication for program planning is substantial. Teams running targeted radiopharmaceutical programs typically commit to a specific isotope early, locking in chelation chemistry, manufacturing relationships, and regulatory filings around that choice. Molecular Partners is claiming its platform defers that commitment until early clinical signals are in hand, reducing the cost of switching and potentially allowing isotope selection to track supply availability, which remains a recognized constraint in the 225Ac market.

The platform itself is engineered to address two persistent failure modes in radioligand therapy: kidney accumulation leading to dose-limiting toxicity, and suboptimal tumor uptake. The company says it tackles both through half-life extension technologies and surface engineering approaches applied to the DARPin scaffold, while preserving the clearance and penetration advantages that come with the small protein format.

Underpinning the Shanghai presentation is a manufacturing partnership Molecular Partners signed with Eckert & Ziegler in February 2026. The Berlin-based isotope specialist, described by Molecular Partners as a leading provider of isotope-related components for nuclear medicine and radiation therapy, will provide a comprehensive range of development services for Radio-DARPins using 225Ac as the therapeutic payload and 177Lu as the imaging payload. No financial terms or manufacturing site details were disclosed in the agreement announcement.

Molecular Partners trades on the SIX Swiss Exchange and NASDAQ under the ticker MOLN. The company is headquartered in Zurich-Schlieren, Switzerland, with a U.S. presence in Concord, Massachusetts. Quantitative biodistribution data from the preclinical studies, including tumor uptake figures and kidney-to-tumor ratios across isotopes, was not included in materials released alongside the announcement, and the company has not yet disclosed IND or CTA timelines for any Radio-DARPin program.