Bifunctional Probes of Cathepsin Protease Activity and pH Reveal Alterations in Endolysosomal pH during Bacterial Infection

Cysteine cathepsins are lysosomal proteases involved in regulation of both normal cellular processes and disease. Biochemical studies with peptide substrates indicate that cathepsins have optimal activity at acidic pH and highly attenuated activity at neutral pH. In contrast, there is mounting evidence that cathepsins have biological roles in environments that have non-acidic pH. To further define the specific pH environments where cathepsins act, we designed bifunctional activity-based probes (ABPs) that allow simultaneous analysis of cathepsin protease activity and pH. We use these probes to analyze the steady-state environment of cathepsin activity in macrophages and to measure dynamic changes in activity and pH upon stimulation. We show that Salmonella typhimurium induces a change in lysosomal pH that ultimately impairs cathepsin activity in both infected cells and a fraction of bystander cells, highlighting a mechanism by which Salmonella can simultaneously flourish within host cells and alter the behavior of nearby uninfected cells

Improved quenched fluorescent probe for imaging of cysteine cathepsin activity

Item does not contain fulltextThe cysteine cathepsins are a family of proteases that play important roles in both normal cellular physiology and many human diseases. In cancer, the activity of many of the cysteine cathepsins is upregulated and can be exploited for tumor imaging. Here we present the design and synthesis of a new class of quenched fluorescent activity-based probes (qABPs) containing a phenoxymethyl ketone (PMK) electrophile. These reagents show enhanced in vivo properties and broad reactivity resulting in dramatically improved labeling and tumor imaging properties compared to those of previously reported ABPs

Non-invasive Imaging of Idiopathic Pulmonary Fibrosis Using Cathepsin Protease Probes

Idiopathic pulmonary fibrosis (IPF) is a lethal, chronic, progressive disease characterized by formation of scar tissue within the lungs. Because it is a disease of unknown etiology, it is difficult to diagnose, to predict disease course and to devise treatment strategies. Recent evidence suggests that activated macrophages play key roles in the pathology of IPF. Therefore, imaging probes that specifically recognize these pools of activated immune cells could provide valuable information about how these cells contribute to the pathobiology of the disease. Here we demonstrate that cysteine cathepsintargeted imaging probes can be used to monitor the contribution of macrophages to fibrotic disease progression in the bleomycin-induced murine model of pulmonary fibrosis. Furthermore, we show that the probes highlight regions of macrophage involvement in fibrosis in human biopsy tissues from IPF patients. Finally, we present first-in-human results demonstrating non-invasive imaging of active cathepsins in fibrotic lesions of patients with IPF. Together, our findings validate small molecule cysteine cathepsin probes for clinical PET imaging and suggest that they have the potential to be used to generate mechanistically-informative molecular information regarding cellular drivers of IPF disease severity and progression