Chapter 9: Pharmacological Targeting of Human Tissue Kallikrein-Related Peptidases

Kallikreins are important enzymes historically known for their participation in the generation of the vasoactive peptides kinins. They are distinguished into plasma kallikrein and the tissue kallikreins, recently renamed kallikrein-related peptidases (KLKs). KLKs constitute the largest serine protease gene family within the human genome that comprises 15 members. It is now well established that KLKs acting individually or in complex tissue-specific proteolytic cascades regulate important physiological processes (i.e., skin desquamation, semen liquefaction, CNS physiology), while their deregulation has been implicated in pathological conditions, including asthma, neurodegeneration, and cancer promotion or inhibition. Therefore, KLKs represent new important targets for pharmacological intervention. The present overview describes the development of different classes of novel inhibitors (or activators) of KLKs that were either designed based on known substrate specificity and protease inhibitor bioscaffolds or isolated by phage display or library screening. These include peptides, engineered protease inhibitors, small organic molecules, and human monoclonal antibodies. These molecules were tested in various animal models for skin disorders, cancer, or asthma, and were found to exhibit potency and efficacy. It is expected that such compounds will enter the market, in the near future, for the treatment of severe diseases some, currently, without alternative therapy.