Reduction of the Renal Radioactivity of ¹¹¹In-DOTA-Labeled Antibody Fragments with a Linkage Cleaved by the Renal Brush Border Membrane Enzymes

The interposition of a cleavable linkage by enzymes onthe renalbrush border membrane constitutes a promising approach for reducingthe renal radioactivity levels of radiolabeled low-molecular-weightantibody fragments and constructs (LMW Abs). Herein, we applied themolecular design to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaceticacid (DOTA)-based reagents for radiotheranostic applications withtrivalent radiometals. DOTA or a derivative thereof was conjugatedto a Fab through an FGK linkage ([In-111]In-DO3AiBu-Bn-FGK-Fab or [In-111]In-DOTA-Bn-FGK-Fab).When injected into mice, both generated radiometabolites, [In-111]In-DO3AiBu-Bn-F and [In-111]In-DOTA-Bn-F,by the angiotensin-converting enzyme at similar rates. Both exhibitedsignificantly lower renal radioactivity levels than a In-111-labeled Fab prepared by the conventional procedure ([In-111]In-DOTA-Bn-SCN-Fab). The different elimination rates of each radiometabolitefrom the kidney significantly affected the renal radioactivity levels.[In-111]In-DO3AiBu-Bn-FGK-Fab preferentiallyreduced the renal localization without impairing tumor accumulation.These findings would pave the way for developing a DOTA-based radiotheranosticplatform for LMW Abs bearing cleavable linkers for renal brush borderenzymes.