An oral-to-urinalysis fluorescent prodrug platform for IBD theranostics

We developed an oral-to-urinalysis theranostic approach for inflammatory bowel disease (IBD) that aims to improve procedural practicality and safety by enabling diagnosis and treatment monitoring without invasive sampling. The strategy exploits disease-associated changes in intestinal chemistry that alter absorption, using the hydrophobicity shift between a fluorescent prodrug (MB-ASA) and its activated product methylene blue (MB). MB-ASA was synthesized by conjugating MB to 5-aminosalicylic acid (5-ASA), a first-line IBD therapy, via a ROS-responsive urea linkage. Owing to its high hydrophobicity, MB-ASA forms aggregates (hydrodynamic diameter ∼531 nm) that limit uptake by intestinal epithelial cells after oral administration in mice. In the inflamed IBD lumen, elevated reactive oxygen species cleave the urea bond, releasing hydrophilic MB and active 5-ASA. The liberated MB is then more readily absorbed and excreted, enabling IBD detection by monitoring fluorescence in the bladder and in excreted urine. Therapeutic activity was supported by histopathological comparisons before and after oral administration of MB-ASA, consistent with local activation and 5-ASA release. This work introduces a fluorescent prodrug platform that couples oral administration with urine-based fluorescence readouts to support theranostic assessment of IBD.