Critical structural insights into selective small-molecule and peptide inhibitors of human urokinase-type plasminogen activator.

Human urokinase-type plasminogen activator (uPA) is a trypsin-like serine protease that plays a crucial role in plasminogen activation and extracellular matrix (ECM) remodelling. Dysregulation of the interactions of uPA with its receptor (uPAR) has been strongly associated with tumour invasion, metastasis, angiogenesis, inflammation and tissue remodelling, making uPA a very promising therapeutic target. Overexpression of uPA in tumours compared to healthy tissue is significantly associated with worse clinicopathological features and poorer patient survival in many types of cancer. Despite the biological significance of uPA, the development of selective inhibitors remains challenging due to the high structural similarity of the conserved proteolytic domain of the serine protease family. This review summarises advances in the field of human uPA inhibition, with a particular emphasis on structural insight that underpin the design of selective small-molecule and peptide-based inhibitors. We discuss the three-dimensional structure of the uPA catalytic domain and the properties of the binding site that can be exploited to enhance inhibitor specificity. The primary focus is on structure-activity relationships (SAR) and crystallographic studies, which have contributed to the development of compounds targeting uPA. The ADME (Absorption, Distribution, Metabolism, and Excretion) and drug-likeness analysis revealed that many potent uPA inhibitors possess pharmacokinetic limitations, including poor gastrointestinal absorption, high polarity, and low solubility, which may restrict their clinical applicability. The results emphasize the importance of balancing inhibitory potency with favourable physicochemical and pharmacokinetic properties during the development of clinically effective urokinase inhibitors. This review highlights the current challenges associated with developing uPA inhibitors into clinically useful drugs. A better understanding of the structure and mechanism of action of uPA inhibitors will provide a valuable foundation for the rational design of a new generation of compounds effective against uPA, intended for use in the treatment of cancer and other diseases.