Modulation of AQP4 for cerebral oedema treatment: Characterisation of proposed blockers and identification of novel molecules

Abstract

Cerebral oedema following traumatic brain injuries and stroke is a major cause of death and long-term cognitive damage. Current treatment options are very limited, mainly relying on either symptom management or risky neurosurgery once the oedema has developed. Since the identification of the water channel AQP4 as a promising target to pharmacologically intervene with the underlying causes of cerebral oedema, many AQP4 pore blockers have been reported. The compounds AER-270 and TGN-020 were reported as AQP4 inhibitors, primarily based on Xenopus oocyte swelling assays, and the prodrug of AER-270 is currently in phase I human trial. Both drugs demonstrated beneficial outcomes in various rodent models of CNS pathology, but their direct effects on AQP4 function are still not clear. Here their in vitro effect on AQP4 was investigated across multiple assay systems. In agreement with earlier reported data, in the work of this thesis AER-270 and TGN-020 inhibited AQP4 when assayed in Xenopus oocytes but not in assays using reconstituted recombinant AQP4 or mammalian cells expressing exogenous or endogenous AQP4. Evidence for other targets than AQP4 was found, which could explain previously observed in vivo results. Dihydropyridines were identified as novel AQP4 modulators, directly blocking the water channel pore and reducing relocalisation to the cell surface. Further drug development for these molecules could address the unmet clinical need for pharmacological treatment by repurposing the clinically used calcium channel blocker. Additionally, adenosine receptors were found to enhance AQP4 function, which should be further explored as an approach to target glymphatic function.