Background Alzheimer’s disease (AD) pathology is associated with complex interactions among multiple factors, involving an intertwined network of various signaling pathways. The polypharmacological approach is an emerging therapeutic strategy that has been proposed to overcome the multifactorial nature of AD by targeting multiple pathophysiological factors including amyloid-β (Aβ) and phosphorylated tau. We evaluated a blood-brain barrier penetrating phosphodiesterase 5 (PDE5) inhibitor, mirodenafil (5-ethyl-2-7-n-propyl-3,5-dihydrro-4H-pyrrolo[3,2-d]pyrimidin-4-one), for its therapeutic effects on AD with polypharmacological properties. Methods To evaluate the potential of mirodenafil as a disease-modifying AD agent, mirodenafil was administered to test its effects on the cognitive behaviors of the APP-C105 AD mouse model using the Morris water maze and passive avoidance tests. To investigate the mechanisms of action that underlie the beneficial disease-modifying effects of mirodenafil, human neuroblastoma SH-SY5Y cells and mouse hippocampal HT-22 cells were used to show mirodenafil-induced alterations associated with the cyclic guanosine monophosphate (cGMP)/cGMP-dependent protein kinase (PKG)/cAMP-responsive element-binding protein (CREB) pathway, apoptotic cell death, tau phosphorylation, amyloidogenesis, the autophagy-lysosome pathway, glucocorticoid receptor (GR) transcriptional activity, and the Wnt/β-catenin signaling. Results Here, mirodenafil is demonstrated to improve cognitive behavior in the APP-C105 mouse model. Mirodenafil not only reduced the Aβ and phosphorylated tau burdens in vivo, but also ameliorated AD pathology induced by Aβ through the modulation of the cGMP/PKG/CREB signaling pathway, glycogen synthase kinase 3β (GSK-3β) activity, GR transcriptional activity, and the Wnt/β-catenin signaling in neuronal cells. Interestingly, homodimerization and nuclear localization of GR were inhibited by mirodenafil, but not by other PDE5 inhibitors. In addition, only mirodenafil reduced the expression levels of the Wnt antagonist Dickkopf-1 (Dkk-1), thus activating the Wnt/β-catenin signaling. Conclusions These findings strongly suggest that the PDE5 inhibitor mirodenafil shows promise as a potential polypharmacological drug candidate for AD treatment, acting on multiple key signaling pathways involved in amyloid deposition, phosphorylated tau burden, the cGMP/PKG/CREB pathway, GSK-3β kinase activity, GR signaling, and the Wnt/β-catenin signaling. Mirodenafil administration to the APP-C105 AD mouse model also improved cognitive behavior, demonstrating the potential of mirodenafil as a polypharmacological AD therapeutic agent.

Background The accumulation of amyloid‐b (Ab) in the brain is the primary pathological hallmark of Alzheimer’s disease (AD). Aggregated Ab is associated with cytotoxicity by a variety of mechanisms leading to neuronal apoptosis and synaptic impairments. Here, we present experimental evidence showing that AR1001, a highly selective and potent phosphodiesterase 5 (PDE5) inhibitor, acts as a polypharmacological agent for the treatment of AD by promoting neuronal cell survival and inhibiting Ab accumulation. Method The in vitro toxic effects of Ab were examined using the human neuroblastoma derived SH‐SY5Y cell line and mouse hippocampal neuronal HT‐22 cell line. Cell‐free Thioflavin T (ThT) fluorescence assay and SDS‐PAGE with PICUP (Photo‐Induced Cross‐Linking of Unmodified Proteins) of Ab plaques were employed to test inhibition of Ab aggregate formation and reduction of preformed oligomers and fibrils. To identify transcription factors responsible for inhibitory effects of AR1001 on Amyloid Precursor Protein (APP) / b‐site APP cleaving enzyme 1 (BACE1) expression, the Transcription Factor Profiling Plate Array was used to monitor the activation/inhibition of various transcription factors. 5XFAD transgenic mice were used to evaluate Ab42 induced neurodegeneration and amyloid plaque formation. NSE/APP‐C105 transgenic mice were used to test spatial and learning memory in the Morris water maze test and the passive avoidance test. Result AR1001 markedly increased cGMP levels and activated cGMP/cGMP‐dependent protein kinase/cAMP responsive element‐binding protein (CREB) cascade in Ab‐treated SH‐SY5Y cells, promoting neuronal cell survival. In Ab‐treated HT‐22 cells, downregulation of Glucocorticoid Receptor (GR) transcriptional activity by AR1001 was responsible for reduced expression of APP, BACE1 and Dickkopf‐1 (Dkk1). In addition, AR1001 disrupted pre‐formed Ab42 fibrils in vitro. Interestingly, AR1001 reduced deposition of Aβ plaques in 5XFAD transgenic mouse brain by activating the autophagic process. Finally, AR1001 significantly improved memory functions in NSE/APP‐C105 mice. Conclusion Our findings strongly support that AR1001 has benefits against the accumulation of Ab and cognitive deficits in AD mouse models. We have demonstrated that AR1001 serves as a polypharmacological agent to inhibit PDE5 activity, promoting cell survival, and downregulate GR activity, reducing APP/BACE1 expression.