Photoactivated inhibition of cathepsin K in a 3D tumor model.

Collagenolytic activity of cathepsin K is important for many physiological and pathological processes including osteoclast-mediated bone degradation, macrophage function and fibroblast-mediated matrix remodeling. Here, we report application of a light-activated inhibitor for controlling activity of cathepsin K in a 3D functional imaging assay. Using prostate carcinoma cell line engineered to overexpress cathepsin K, we demonstrate the utility of the proteolytic assay in living tumor spheroids for the evaluation and quantification of the inhibitor effects on cathepsin K-mediated collagen I degradation. Importantly, we also show that utilizing the ruthenium-caged version of a potent nitrile cathepsin K inhibitor (4), cis-[Ru(bpy)2(4)2](BF4)2 (5), offers significant advantage in terms of effective concentration of the inhibitor and especially its light-activated control in the 3D assay. Our results suggest that light activation provides a suitable, attractive approach for spatial and temporal control of proteolytic activity, which remains a critical, unmet need in treatment of human diseases, especially cancer.