A new class of protein drugs have shown amenability to multiple isotopes, paving the way for faster radiopharmaceutical drug development. 

Biotechnology company Molecular Partners announced preclinical data showing its Radio-DARPins are suitable to different isotopes, each specific for a different tumour target.  

DARPin (Designed Ankyrin Repeat Protein) therapeutics are a novel class of protein drugs based on natural binding proteins, which have been clinically validated across several therapeutic areas and developed through to the registrational stage.  

The key properties of DARPins – intrinsic high affinity and specificity, small size, flexible architecture, and high stability – offer unmatched advantages to drug design, such as multi-specificity, broad target range, and tuneable half-life. 

The results of studies in tumour-bearing mice show highly comparable biodistribution profiles for both Radio-DARPin candidates labelled with Lutetium-177 (177Lu) or with Lead-203 (203Pb), with similar uptake and washout rates. Imaging with 177Lu can be indicative of behaviour with the therapeutic isotope Actinium-225 (225Ac), and similarly with 203Pb for 212Pb.  

The preclinical data was revealed at the Global Radiopharmaceuticals Development Summit, which took place in Shanghai, China on March 19–20. 

“Our recent data confirms that our Radio-DARPin-vector design allows interchangeability of alpha-isotopes, including 212Pb and 225Ac,” said Patrick Amstutz, CEO of Molecular Partners.  

“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.”  

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