Design And Development Of Experimental Therapeutics

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Design and Development of Drugs and Pharmacologic Probes: The goal of the Drug Design & Development Section is to develop novel agents against pivotal steps involved in the pathophysiology of diseases associated with aging, with particular interest in neurological diseases, exemplified by Alzheimer's disease (AD) and stroke, as well as in systemic diseases, such as diabetes. 1. Alzheimer's Disease: Three series of agents are being developed to treat AD. Selective inhibitors of acetylcholinesterase (AChE), of butyrylcholinesterase (BChE), and of amyloid-beta peptide (Ab) production. 1.1. Cholinesterase inhibitors: Compounds were developed to optimally augment the cholinergic system in the elderly and raise levels of the neurotransmitter, acetylcholine (ACh). Extensive studies involving chemistry, X-ray crystallography, biochemistry and pharmacology resulted in the design and synthesis of novel compounds to differentially inhibit either AChE or BChE in either the brain or periphery for an optimal duration for the potential treatment of a variety of diseases, such as AD, Myasthenia Gravis, and as chemical warfare prophylactics. 1.1A. AChE: Two of our numerous novel synthesized AChE inhibitors are in development for the treatment of AD; specifically, the pure non-competitive inhibitors, phenserine and tolserine. Both are phenylcarbamates of physostigmine that are 70- and 190-fold selective for AChE vs. BChE. Compared to current agents for AD treatment, they have a favorable toxicologic profile and robustly enhance cognition in animal models (undertaken in collaboration with Dr. Donald Ingram, NIA). They possess a long duration of reversible enzyme inhibition, coupled with a short pharmacokinetic half-life. This reduces dosing frequency, decreases body drug exposure and minimizes the dependence of drug action on the individual variations of drug metabolism commonly found in the elderly. In collaboration with Axonyx Inc. (New York, NY), three clinical trials have thus far been completed to evaluate the safety, maximum tolerated dose (MTD), pharmacokinetic (PK), pharmacodynamic (PD) and efficacy profile of phenserine, in healthy elderly and AD subjects. Its clinical development and evaluation continues in one ongoing phase 2 and two phase 3 trials in AD. 1.1B. BChE: In normal brain, some 80% of cholinesterase activity is in the form of AChE and 20% is BChE. AChE activity is concentrated mainly in neurons, while BChE is primarily associated with glial cells. Kinetic evidence indicates a role for BChE, in hydrolysing excess ACh. In advanced AD, however, AChE activity decreases to 15% of normal levels in affected brain regions, whereas BChE activity increases. The normal ratio of BChE to AChE becomes mismatched in AD causing excess metabolism of already depleted levels of ACh. The first available reversible and highly potent BChE inhibitors have been synthesized and are in preclinical assessment to evaluate their potential as AD drug candidates. On going studies are focusing on cognition and the molecular mechanisms underpinning AD. 1.2. Molecular events associated with AD: The reduction in levels of the potentially toxic amyloid-beta peptide (Ab) has emerged as an important therapeutic goal in AD. Key targets for this goal are factors that affect the expression and processing of the Ab precursor protein (APP). Our studies show that phenserine, reduces APP and Ab levels in vivo and in tissue culture without toxicity. This activity is independent of its cholinesterase action, but is post-transcriptional: lowering APP protein levels without affecting mRNA levels. This is mediated via the 5'-untranslated region (UTR) of APP mRNA. Current studies are characterizing mechanisms involved and focusing on these in the design and synthesis of agents that lower APP levels as a way of lower Ab peptide. 2. Stroke and Parkinson's disease: Drugs currently used to treat stroke and PD provide temporary relief of symptoms, but do not prevent the cell death. Our target for drug design is the transcription factor, p53. Its up-regulation is a common feature of several neurodegenerative disorders, and is a gate keeper to the biochemical cascade that leads to apoptosis. We recently designed and synthesized a novel series of tetrahydrobenzothiazole and ?oxazole analogues that inhibit p53 activity. Compounds are in current assessment for neuroprotective action in tissue culture and animal models (collaborators: Drs. Mattson& Ovadia) to select agents of potential for evaluation as drug candidates. 3. Diabetes: Type 2 diabetes is a prevalent disease in the elderly. Present treatments are unsatisfactory. Our target for drug design is the glucagons-like peptide-1 (GLP-1) receptor (R). GLP-1 is secreted from the gut in response to food and is a potent secretagogue ? it binds to the GLP1R on pancreatic beta-cells to induce glucose-dependent insulin secretion, thereby controling plasma glucose levels. We are developing long-acting GLP-1 analogues (collaborator: Dr. Egan). This research aided in the development of the peptide exendin-4 (Ex-4) into clinical studies in type 2 diabetes. Novel chimeric peptides that combine the best features of GLP-1 and Ex-4 have also been designed and are under preclinical assessment in a variety models. We are characterizing the role of the GLP-1R stimulation in the nervous system. GLP-1 analogues possess neurotrophic properties and protect neuronal cells from oxidative and Ab-induced cell death. Neuroprotection in cell culture translated to in vivo studies in classical rodent neurodegeneration models. Current studies are focused on selecting agents for clinical assessment. 4. Inflammation: Inflammation is a critical feature of neurodegereation and also occurs in numerous systemic diseases. Our target is the cytokine, TNF-alpha. Novel, potent TNF-alpha inhibitors are being synthesized on the backbone of thalidomide. They reduce TNF-alpha synthesis post-transcriptionally, via its 3'-UTR, in cell culture studies. These are being assessed in classical animals models to aid in the selection of a clinical cadidate for diseases such as Amyotrophic Lateral Sclerosis.