MDR-04227

MDR-04227 is a potent and selective small molecule inhibitor of Cathepsin S (CTSS), a lysosomal cysteine protease. While Cathepsin S is well-known for its role in MHC class II-mediated antigen presentation, it also plays a critical role in the central nervous system, particularly within microglia. Following nerve injury, Cathepsin S is upregulated and released by microglia, where it cleaves the chemokine fractalkine (CX3CL1) from neuronal membranes, leading to the activation of microglial CX3CR1 receptors and the subsequent maintenance of neuropathic pain. MDR-04227 was developed by Medivir AB as a therapeutic candidate to interrupt this signaling pathway. Although it progressed into Phase 1 clinical trials to evaluate safety and pharmacokinetics, the development of the compound was eventually halted.