Development of First-in-Class PDE5/HAT Directed LigandsModulating Molecular Pathways involved in Synaptic Plasticity

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Alzheimer’s disease (AD) is a complex, multifactorial disease with a significant health and financial societal impact as there are no drugs that effectively counteract the disease. AD is characterized by impaired synaptic plasticity leading to defective hippocampal-dependent memory, which has been found to appear long before the buildup of amyloid plaques and neuronal cell death. This observation suggests that interventions targeting biological pathways that regulate synaptic plasticity may provide a way to slow down, arrest, and/or prevent the progression of neurodegenerative processes. The objective of this proposal is to identify first-in-class small molecules with dual target activity that enhance synaptic plasticity. In preliminary studies, we discovered that two distinct molecular targets, phosphodiesterase 5 (PDE5) and histone acetyltransferase (HAT) are crucial in synaptic plasticity. We developed small molecule PDE5 inhibitors and HAT activators that are able to rescue impaired synaptic plasticity in mouse hippocampal slices. In a proof-of-concept study, we demonstrated that a combination treatment with a PDE5 inhibitor and a HAT activator produces a 6-fold higher rescue of synaptic plasticity compared to treatment with the two compounds alone. These findings indicate that modulating these two targets involved in AD provides a more effective treatment than a single-target therapy. In this proposal, we plan to test the hypothesis that modulating PDE5 and HAT activity via a newly synthesized single molecule will result in a novel AD treatment. The multi-target directed ligand approach will be used to attain a PDE5 inhibitor/HAT activator drug molecule. This approach has emerged as a beneficial strategy for the treatment of complex diseases and presents several advantages with respect to combination therapy, including increased therapeutic efficacy, reduced drug-drug interactions, and simplified drug regimen. Specifically, we will test our hypothesis via the following specific aims: 1) design and synthesis of a library of new dual-target molecules with HAT and PDE5 activity, 2) elucidate the pharmacokinetic/pharmacodynamic properties of our newly synthesized dual-target molecules in vitro and in vivo, and 3) assess synaptic plasticity in mouse hippocampal slices derived from a genetically modified mouse model of amyloid deposition treated with our newly synthesized dual-target ligands. These aims will be addressed through a combination of medicinal chemistry approaches for generating new chemical entities, and biochemical and electrophysiological techniques for testing the biological activity of these new dual target molecules in vitro as well as assessing their in vivo efficacy. Results from these experiments will provide crucial insights into an alternative and novel therapeutic approach for treating AD based on cleverly modulating two molecular targets known to play a significant role in the etiopathology of this disease.