Lysosomal pH Decrease in Inflammatory Cells Used To Enable Activatable Imaging of Inflammation with a Sialic Acid Conjugated Profluorophore

Inflammation causes significant morbidity and mortality, necessitating effective in vivo imaging of inflammation. Prior approaches often rely on combination of optical agents with entities specific for proteinaceous biomarkers overexpressed in inflammatory tissues. We herein report a fundamentally new approach to image inflammation by targeting lysosomes undergoing acidification in inflammatory cells with a sialic acid (Sia) conjugated near-infrared profluorophote (pNIR). Sia pNIR contains a sialic acid domain for in vivo targeting of inflamed tissues and a pNIR domain which isomerizes into fluorescent and optoacoustic species in acidic lysosomes. Sia pNIR displays high inflammation-to-healthy tissue signal contrasts in mice treated with Escherichia coli, Staphylococcus aureus, or lipopolysaccharide. In addition, inflammation-associated fluorescence is switched off upon antibiotics treatment in mice. This report shows the potentials of Sia pNIR for activatable dual-modality inflammation imaging, and particularly the use of lysosomes of inflamed cells as a previously unappreciated biomarker for inflammation imaging.