NAD depletion occurs after excitotoxic insults and oxidative stress and causes neuronal death in several rodent models of neurodegenerative conditions, including models for brain ischemia/reperfusion injury and Wallerian degeneration. We have recently discovered that NAD depletion is also the primary cause of neuronal death induced by exposure to a misfolded and toxic form of the amyloidogenic prion protein (TPrP). NAD replenishment reversed the fate of TPrP-injured neurons in culture and improved motor function in a mouse model of prion disease. Therefore, our study established NAD restoration as a new therapeutic target for protein misfolding neurodegenerative diseases, a family of diseases that includes Alzheimer's, Parkinson's, prion diseases and amyotrophic lateral sclerosis (ALS). We developed a high- throughput screening strategy to identify NAD-dependent neuroprotective small molecules in the misfolded protein toxicity paradigm and then conducted a screening campaign. We identified and selected four chemical series providing complete neuroprotection and preserving NAD levels with nanomolar potency. One compound was tested in a murine model of ALS and improved the mice's muscle strength and motor function. We will conduct molecular mode of action studies for each chemical series, in conjunction with potency and drug metabolism and pharmacokinetic (DMPK) studies, to guide selection of the top lead. Lead optimization will be done through iterative rounds of structure-activity relationship studies and subjecting analogs to a series of in vitro and in vivo assays for potency, selectivity and absence of undesired off-target effects, as well as favorable DMPK properties including brain penetration. This workplan will deliver a novel small molecule neuroprotectant poised for investigational new drug (IND)?enabling studies and ultimately for the treatment of neurological conditions linked to a deficit in NAD.
NAD is a metabolite essential for cell survival; NAD depletion is involved in a number of neurodegenerative conditions including brain ischemia, nerve degeneration after axotomy and, as we have discovered, misfolded protein toxicity. We have identified chemical compounds replenishing NAD, rescuing cells in vitro and, for one of them, showing therapeutic benefit in a mouse model of amyotrophic lateral sclerosis. In this project, we will select and optimize these compounds to deliver a new potent, selective and bio-available neuroprotectant.