Exploring the potential of high-molar activity Samarium-153 for targeted radionuclide therapy with [153Sm]Sm-DOTA-TATE

Samarium-153 is a promising theranostic radionuclide but low molar activities (Am) resulting from its current production route renders it unsuitable for targeted radionu-clide therapy (TRNT). Recent efforts combining neutron activation of 152Sm in the SCK CEN BR2 reactor with mass separation at CERN/MEDICIS yielded high Am 153Sm. In this proof-of-concept study we further evaluated the potential of high Am 153Sm for TRNT by radiolabeling to DOTA-TATE, a well-established carrier molecule binding the somatostatin receptor 2 (SSTR2) that is highly expressed in gastroenteropancreatic neuroendocrine tumors. DOTA-TATE was labeled with 153Sm and remained stable up to 7 days in relevant media. The binding specificity and high internalization rate were validated on SSTR2-expressing CA20948 cells. In vitro biological evaluation showed that [153Sm]Sm-DOTA-TATE was able to reduce CA20948 cell viability and clonogenic potential in an activity-dependent manner. Biodistribution studies in healthy and CA20948 xenografted mice revealed that [153Sm]Sm-DOTA-TATE was rapidly cleared and profound tumor uptake and retention was observed whilst these were limited in normal tissues. This proof-of-concept study showed the potential of mass-separated 153Sm for TRNT and could open doors towards wider applications of mass separation in medical isotope production.