Microglial-associated responses to comorbid amyloid pathology and hyperhomocysteinemia in an aged knock-in mouse model of Alzheimer's disease.

BACKGROUND: Elevated blood homocysteine levels, termed hyperhomocysteinemia (HHcy), is a prevalent risk factor for Alzheimer's disease (AD) in elderly populations. While dietary supplementation of B-vitamins is a generally effective method to lower homocysteine levels, there is little if any benefit to cognition. In the context of amyloid pathology, dietary-induced HHcy is known to enhance amyloid deposition and certain inflammatory responses. Little is known, however, about whether there is a more specific effect on microglia resulting from combined amyloid and HHcy pathologies. METHODS: The present study used a knock-in mouse model of amyloidosis, aged to 12 months, given 8 weeks of B-vitamin deficiency-induced HHcy to better understand how microglia are affected in this comorbidity context. RESULTS: We found that HHcy-inducing diet increased amyloid plaque burden, altered the neuroinflammatory milieu, and upregulated the expression of multiple damage-associated and "homeostatic" microglial genes. CONCLUSIONS: Taken together, these data indicate complex effects of comorbid pathologies on microglial function that are not driven solely by increased amyloid burden. Given the highly dynamic nature of microglia, their central role in AD pathology, and the frequent occurrence of various comorbidities in AD patients, it is increasingly important to understand how microglia respond to mixed pathological processes.

Targeting human central nervous system protein kinases: An isoform selective p38αMAPK inhibitor that attenuates disease progression in Alzheimer's disease mouse models.

The first kinase inhibitor drug approval in 2001 initiated a remarkable decade of tyrosine kinase inhibitor drugs for oncology indications, but a void exists for serine/threonine protein kinase inhibitor drugs and central nervous system indications. Stress kinases are of special interest in neurological and neuropsychiatric disorders due to their involvement in synaptic dysfunction and complex disease susceptibility. Clinical and preclinical evidence implicates the stress related kinase p38αMAPK as a potential neurotherapeutic target, but isoform selective p38αMAPK inhibitor candidates are lacking and the mixed kinase inhibitor drugs that are promising in peripheral tissue disease indications have limitations for neurologic indications. Therefore, pursuit of the neurotherapeutic hypothesis requires kinase isoform selective inhibitors with appropriate neuropharmacology features. Synaptic dysfunction disorders offer a potential for enhanced pharmacological efficacy due to stress-induced activation of p38αMAPK in both neurons and glia, the interacting cellular components of the synaptic pathophysiological axis, to be modulated. We report a novel isoform selective p38αMAPK inhibitor, MW01-18-150SRM (=MW150), that is efficacious in suppression of hippocampal-dependent associative and spatial memory deficits in two distinct synaptic dysfunction mouse models. A synthetic scheme for biocompatible product and positive outcomes from pharmacological screens are presented. The high-resolution crystallographic structure of the p38αMAPK/MW150 complex documents active site binding, reveals a potential low energy conformation of the bound inhibitor, and suggests a structural explanation for MW150's exquisite target selectivity. As far as we are aware, MW150 is without precedent as an isoform selective p38MAPK inhibitor or as a kinase inhibitor capable of modulating in vivo stress related behavior.

Beyond amyloid: getting real about nonamyloid targets in Alzheimer's disease.

For decades, researchers have focused primarily on a pathway initiated by amyloid beta aggregation, amyloid deposition, and accumulation in the brain as the key mechanism underlying the disease and the most important treatment target. However, evidence increasingly suggests that amyloid is deposited early during the course of disease, even prior to the onset of clinical symptoms. Thus, targeting amyloid in patients with mild to moderate Alzheimer's disease (AD), as past failed clinical trials have done, may be insufficient to halt further disease progression. Scientists are investigating other molecular and cellular pathways and processes that contribute to AD pathogenesis. Thus, the Alzheimer's Association's Research Roundtable convened a meeting in April 2012 to move beyond amyloid and explore AD as a complex multifactorial disease, with the goal of using a more inclusive perspective to identify novel treatment strategies.

Targeting protein kinases in central nervous system disorders.

Protein kinases are a growing drug target class in disorders in peripheral tissues, but the development of kinase-targeted therapies for central nervous system (CNS) diseases remains a challenge, largely owing to issues associated specifically with CNS drug discovery. However, several candidate therapeutics that target CNS protein kinases are now in various stages of preclinical and clinical development. We review candidate compounds and discuss selected CNS protein kinases that are emerging as important therapeutic targets. In addition, we analyse trends in small-molecule properties that correlate with key challenges in CNS drug discovery, such as blood-brain barrier penetrance and cytochrome P450-mediated metabolism, and discuss the potential of future approaches that will integrate molecular-fragment expansion with pharmacoinformatics to address these challenges.

De novo and molecular target-independent discovery of orally bioavailable lead compounds for neurological disorders.

There is immediate potential to enhance success and innovation in drug development by pairing newly emerging approaches in medicinal chemistry and computational biology with knowledge gained from the recent era of high throughput screens and the early years of modern drug discovery when in vivo efficacy was an early "Go/No Go" project management decision. Focused, in-parallel synthetic chemistry platforms, combined with computational analyses serving as decision aids in planning, minimize the total number of compounds synthesized while maximizing the probability of creating bioavailable compounds that sample diverse chemical space. Incorporating a hierarchal strategy that emphasizes early selection of synthesized compounds based on biological or biophysical endpoints presents fewer and more relevant compounds for secondary evaluation of in vivo efficacy using animal screens with disease relevant or clinically translatable endpoints. We summarize here an interdisciplinary approach at the chemistry-biology interface that is used for the rapid discovery of novel lead compounds for neurodegenerative disorders, such as Alzheimer's disease (AD). The chemistry platform uses established chemistries amenable to in-parallel strategies to create synthetic diversifications of the privileged pyridazine chemotype that sample a restricted chemical space. The hierarchal biology platform uses primary screens for in vitro activity and selectivity with the target cell type, and rapid secondary screens for in vivo efficacy and toxicity in animal models with good phenotypic penetrance for disease relevant pathophysiological endpoints or clinically translatable surrogate endpoints. For the AD case study, novel lead compounds were developed in less than two years by a small academic group, and corporate sponsored clinical trials are planned.

Glia as a therapeutic target: selective suppression of human amyloid-beta-induced upregulation of brain proinflammatory cytokine production attenuates neurodegeneration.

A corollary of the neuroinflammation hypothesis is that selective suppression of neurotoxic products produced by excessive glial activation will result in neuroprotection. We report here that daily oral administration to mice of the brain-penetrant compound 4,6-diphenyl-3-(4-(pyrimidin-2-yl)piperazin-1-yl)pyridazine (MW01-5-188WH), a selective inhibitor of proinflammatory cytokine production by activated glia, suppressed the human amyloid-beta (Abeta) 1-42-induced upregulation of interleukin-1beta, tumor necrosis factor-alpha, and S100B in the hippocampus. Suppression of neuroinflammation was accompanied by restoration of hippocampal synaptic dysfunction markers synaptophysin and postsynaptic density-95 back toward control levels. Consistent with the neuropathophysiological improvements, MW01-5-188WH therapy attenuated deficits in Y maze behavior, a hippocampal-linked task. Oral MW01-5-188WH therapy begun 3 weeks after initiation of intracerebroventricular infusion of human Abeta decreased the numbers of activated astrocytes and microglia and the cytokine levels in the hippocampus without modifying amyloid plaque burden or altering peripheral tissue cytokine upregulation in response to an in vivo inflammatory challenge. The results provide a novel integrative chemical biology proof in support of the neuroinflammation hypothesis of disease progression, demonstrate that neurodegeneration can be attenuated independently of plaque modulation by targeting innate brain proinflammatory cytokine responses, and indicate the feasibility of developing efficacious, safe, and selective therapies for neurodegenerative disorders by targeting key glial activation pathways.

Discovery of new chemical classes of synthetic ligands that suppress neuroinflammatory responses.

We used a chemical genomics approach that includes follow up in parallel syntheses to discover a new class of compounds that selectively suppress glial activation. While the mechanism of action remains to be determined, available data and the experimental approach for discovery indicate that the mechanism includes inhibition of gene regulating protein kinases. Specifically, the increased production of IL-1beta and iNOS in response to various activating stimuli, including Abeta1-42, is suppressed while the production of potentially beneficial responses, such as ApoE production, is not inhibited. The increased production of COX-2 and p38 MAPK activation are also not altered, demonstrating the novel nature of potential therapeutic targets compared to currently available drugs. The chemical scaffold is 3-aminopyridazine (3-AP). This is an attractive scaffold because of its potential for diversification by established, facile chemistries and the prior use of a 3-AP scaffold in other central nervous system targeted therapeutics. Therefore, the potential bioavailability of 3-AP derivatives and the demonstrated cellular selectivity demand that future research address the potential efficacy of selective 3-AP derivatives in animal models of disease.

Discovery of a 3-amino-6-phenyl-pyridazine derivative as a new synthetic antineuroinflammatory compound.

Excessive glial activation, with overproduction of cytokines and oxidative stress products, is detrimental and a hallmark of neurodegenerative disease pathology. Suppression of glial activation is a potential therapeutic approach, and protein kinases are targets of some antiinflammatory drugs. To address an unmet need for selective inhibitors of glial activation, we developed a novel 3-amino-6-phenylpyridazine derivative that selectively blocks increased IL-1 beta, iNOS, and NO production by activated glia, without inhibition of potentially beneficial glial functions.