Chemiluminescent probes for imaging cysteine cathepsin activity

The cysteine cathepsins are a family of proteases that are widely expressed in diverse cell types. However, because their activity is highly upregulated at sites of inflammation, they are ideal targets for imaging a range of disease pathologies including cancer, atherosclerosis, fibrosis and others. While significant advances have been made in generation of activatable ‘smart’ probes for cathepsin activity, virtually all of these agents use fluorescent reporters which require a laser light source to induce a signal from the probe. We describe here the development and application of chemiluminescent probes for imaging cysteine cathepsin activity in cells and tissues. These probes provide rapid signal generation with low background in cells and tissues without the need for a light source. We demonstrate that a cathepsin probe containing an optimal peptide sequence can be used topically to detect activity in tumor tissues, demonstrating the potential value of this approach for real-time diagnosis of cancer as well as other conditions involving inflammation.