Drug Discovery and Therapeutic Targets for Pharmacological Modulators of Aquaporin Channels

The human genome encodes 13 aquaporin isoforms with characteristic substrate specificity that are expressed at specific locations throughout the body. Of these isoforms, AQPs 1-4 serve important functions in renal water reabsorption. Consequently, specific AQP inhibitors have been proposed as 'aquaretics', a new class of drugs suitable to induce diuresis without concomitant salt wasting. Furthermore, animal experiments suggested that AQP4 inhibitors could be useful to treat some forms of brain edema. Other proposed applications for AQP inhibitors involve amongst others treatment of diabetes, inflammatory skin diseases and cancer. However, few of these putative applications have been critically evaluated against current forms of therapy. Furthermore, development of AQP inhibitors remains difficult and despite numerous efforts during at least the last 15 years very few AQP inhibitors have been described. Moreover, none of the hitherto described substances have been developed to a level where meaningful verification of proposed AQP drug targets in preclinical or clinical settings was possible. Nonetheless, encouraging progress towards development of such substances has been made during recent years. Novel cell-based assays facilitate high throughput screening of chemical compound libraries for hit discovery. AQP 3D structures have been solved for 10 isoforms, which can support rapidly evolving computational hit discovery methods, as well as hit to lead programs. In this chapter, we will provide a critical review of current evidence supporting relevance of AQPs as drug targets, describe current methods for AQP inhibitor discovery and will try to highlight challenges that remain before successful AQP inhibitor development. (Less)