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

[Image: see text] The interposition of a cleavable linkage by enzymes on the renal brush border membrane constitutes a promising approach for reducing the renal radioactivity levels of radiolabeled low-molecular-weight antibody fragments and constructs (LMW Abs). Herein, we applied the molecular design to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-based reagents for radiotheranostic applications with trivalent radiometals. DOTA or a derivative thereof was conjugated to a Fab through an FGK linkage ([(111)In]In-DO3AiBu-Bn-FGK-Fab or [(111)In]In-DOTA-Bn-FGK-Fab). When injected into mice, both generated radiometabolites, [(111)In]In-DO3AiBu-Bn-F and [(111)In]In-DOTA-Bn-F, by the angiotensin-converting enzyme at similar rates. Both exhibited significantly lower renal radioactivity levels than a (111)In-labeled Fab prepared by the conventional procedure ([(111)In]In-DOTA-Bn-SCN-Fab). The different elimination rates of each radiometabolite from the kidney significantly affected the renal radioactivity levels. [(111)In]In-DO3AiBu-Bn-FGK-Fab preferentially reduced the renal localization without impairing tumor accumulation. These findings would pave the way for developing a DOTA-based radiotheranostic platform for LMW Abs bearing cleavable linkers for renal brush border enzymes.