Establishment of 68Ga-DOTA-Based Pretargeted Radioimmunodiagnosis.

DOTA-radiometal (DOTA: 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) hapten complexes of β-emitters (177Lu or 90Y) and α-emitters (225Ac) can be selectively targeted to tumors using an antitumor/anti-DOTA bispecific antibody (BsAb) approach in pretargeted radioimmunotherapy (DOTA-PRIT). Clinical translation of DOTA-PRIT may be accelerated by the development of a 68Ga companion diagnostic for PET imaging. Here, we report a novel radiohapten, which uses a 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA) chelator for 68Ga labeling while retaining 175Lu in a benzyl-DOTA moiety for high-affinity antibody recognition (NODAGA-Pr; Pr = Proteus). Radiolabeling of NODAGA-Pr with 68Ga showed high radiochemical yield and purity, and in vitro studies confirmed high radiostability and negligible serum-protein binding. In vivo, using a DOTA-PRIT system targeting the GPA33 antigen in a human colorectal cancer mouse model, [68Ga]Ga-NODAGA-Pr demonstrated efficient tumor uptake and high-contrast PET imaging. Additional studies using an established DOTA-hapten test system─human embryonic kidney 293T cells expressing a transmembrane-anchored anti-DOTA scFv huC825 further confirmed its in vivo PRIT performance. These findings support [68Ga]Ga-NODAGA-Pr as a promising agent for pretargeted immunoPET and for imaging engineered cells expressing a radiohapten capture reporter gene, with favorable pharmacokinetics and tumor targeting well matched to existing therapeutic DOTA-radiohaptens.