No abstract

16Unphysiological reactive oxygen species (ROS) formation is considered an important 17 pathomechanism for several disease phenotypes with high unmet medical need. Therapeutically, 18 antioxidants have failed multiple times. Instead, focusing on only disease-relevant, enzymatic 19sources of ROS appears to be a more promising and highly validated approach. Here the family of 20 five NADPH oxidases (NOX) stands out as drug targets. Validation has been restricted, however, 21 mainly to genetically modified rodents and is lacking in other species including human. It is thus 22 unclear whether the different NOX isoforms are sufficiently distinct to allow selective 23 pharmacological modulation. Here we show for five of the most advanced NOX inhibitors that 24 indeed isoform selectivity can be achieved. NOX1 was most potently (IC 50 ) targeted by ML171 (0.1 25 µM); NOX2, by VAS2870 (0.7 µM); NOX4, by M13 (0.01 µM) and NOX5, by ML090 (0.01 µM). 26Conditions need to be carefully controlled though as previously unrecognized non-specific 27 antioxidant and assay artefacts may limit the interpretation of data and this included, surprisingly, 28 one of the most advanced NOX inhibitors, GKT136901. As proof-of-principle that now also 29 pharmacological and non-rodent target validation of different NOX isoforms is possible, we used a 30 human blood-brain barrier model and NOX inhibitor panel at IC 50 concentrations. The protective 31 efficacy pattern of this panel confirmed the predominant role of NOX4 in stroke from previous 32 genetic models. Our findings strongly encourage further lead optimization efforts for isoform-33 selective NOX inhibitors and clinical development and provide an experimental alternative when 34 genetic validation of a NOX isoform is not an option. 35 [2][3][4]. This paradox was initially explained by these compounds being underdosed, thereby not 41 reaching efficacy. It is now understood, however, that ROS are not only harmful metabolic by-42 products, but also serve important protective, metabolic and signaling functions, such as the 43 regulation of cell proliferation, differentiation, migration and survival, innate immune response, 44 vascular tone, neuronal signaling as well as inflammation [5][6][7][8]. Anti-oxidants are likely to 45 simultaneously interfere with both qualities of ROS, the physiological and pathophysiological ones 46 with overall neutral or even deleterious outcomes. Thus, ROS should not be modulated in a 47

Nitric oxide (NO) is a widely distributed gasotransmitter binding to the heme of soluble guanylate cyclase (sGC) to stimulate the formation of the second messenger cyclic GMP. In disease, two pathomechanisms can occur, scavenging of NO by reactive oxygen species so that sGC is insufficiently stimulated, and oxidative damage of sGC resulting in heme loss and a NO-insensitive apo-form of sGC. To address this therapeutically, two pharmacological principles have entered the clinic or clinical development. sGC stimulators (sGCs) allosterically sensitize sGC for lower NO levels to reach physiological cGMP levels again; sGC activators (sGCa) bind to the empty heme pocket of apo-sGC to recover cGMP formation. Here we show in vitro and in vivo that this dichotomic pharmacology of sGCs/sGC and sGCa/apo-sGC is wrong. Instead apo-sGC is both activated by sGCa and allosterically modulated by sGC stimulators. The sGCs binding site in sGC and apo-sGC, however, is redox sensitive explaining why it has been previously missed in apo-sGC preparations generated for example by using heme oxidants such as 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Moreover, sGCs synergised with sGCa on apo-sGC in a supra-additive manner similar to the synergy between NO and sGCs on sGC. Our findings provide functional evidence including ischemic stroke, where apo-sGC rather than sGC is detectable, for identical modulation of sGC and apo-sGC by sGCs. This necessitates a revision of the dichotomic sGC/apo-sGC pharmacology and expands the therapeutic potential of sGCs and sGCa both individually and in combination.

Nitric oxide (NO) is a widely distributed gasotransmitter binding to the heme of soluble guanylate cyclase (sGC) to stimulate the formation of the second messenger cyclic GMP. In disease, two pathomechanisms can occur, scavenging of NO by reactive oxygen species so that sGC is insufficiently stimulated, and oxidative damage of sGC resulting in heme loss and a NO-insensitive apo-form of sGC. To address this therapeutically, two pharmacological principles have entered the clinic or clinical development. sGC stimulators (sGCs) allosterically sensitize sGC for lower NO levels to reach physiological cGMP levels again; sGC activators (sGCa) bind to the empty heme pocket of apo-sGC to recover cGMP formation. Here we show in vitro and in vivo that this dichotomic pharmacology of sGCs/sGC and sGCa/apo-sGC is wrong. Instead apo-sGC is both activated by sGCa and allosterically modulated by sGC stimulators. The sGCs binding site in sGC and apo-sGC, however, is redox sensitive explaining why it has been previously missed in apo-sGC preparations generated for example by using heme oxidants such as 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Moreover, sGCs synergised with sGCa on apo-sGC in a supra-additive manner similar to the synergy between NO and sGCs on sGC. Our findings provide functional evidence including ischemic stroke, where apo-sGC rather than sGC is detectable, for identical modulation of sGC and apo-sGC by sGCs. This necessitates a revision of the dichotomic sGC/apo-sGC pharmacology and expands the therapeutic potential of sGCs and sGCa both individually and in combination.