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

Development of a novel bioavailable inhibitor of the calmodulin-regulated protein kinase MLCK: a lead compound that attenuates vascular leak

Tissue barriers involving epithelial and endothelial cell layers are critical to homeostasis, regulating passage of water, macromolecules, cells and certain classes of small molecules via two distinct cellular mechanisms, transcellular or paracellular. Endothelial or epithelial barrier dysfunction is a key component of pathophysiology in diverse diseases and injuries that have a broad impact on survival and quality of life. However, effective and safe small molecule therapeutics for these disorders are lacking. Success in development would therefore fill a major unmet medical need across multiple disease areas. Myosin light chain kinase (MLCK), a highly specialized calcium/calmodulin (CaM) regulated protein kinase, modulates barrier function through its regulation of intracellular contractile processes. MLCK levels and activity are increased in various animal models of disease and in human clinical disease samples. Our prior work with a genetic knockout (KO) mouse strain for the long form of MLCK, MLCK210, has identified MLCK as a drug discovery target for endothelial and epithelial barrier dysfunction. We describe here the development of a selective, bioavailable, stable inhibitor of MLCK that attenuates barrier dysfunction in mice comparable to that seen with the MLCK KO mice. The inhibitor compound 6 is stable in human microsomal metabolic stability assays and can be synthesized in a high-yielding and facile synthetic process. These results provide a foundation for and demonstrate the feasibility of future medicinal chemistry refinement studies directed toward the development of novel therapies for disorders involving barrier dysfunction.

Human amyloid β-induced neuroinflammation is an early event in neurodegeneration

Using a human amyloid beta (Abeta) intracerebroventricular infusion mouse model of Alzheimer's disease-related injury, we previously demonstrated that systemic administration of a glial activation inhibitor could suppress neuroinflammation, prevent synaptic damage, and attenuate hippocampal-dependent behavioral deficits. We report that Abeta-induced neuroinflammation is an early event associated with onset and progression of pathophysiology, can be suppressed by the glial inhibitor over a range of intervention start times, and is amenable to suppression without inhibiting peripheral tissue inflammatory responses. Specifically, hippocampal neuroinflammation and neurodegeneration occur in close time proximity at 4-6 weeks after the start of infusion. Intraperitoneal administration of inhibitor for 2-week intervals starting at various times after initiation of Abeta infusion suppresses progression of pathophysiology. The glial inhibitor is a selective suppressor of neuroinflammation, in that it does not block peripheral tissue production of proinflammatory cytokines or markers of B- and T-cell activation after a systemic lipopolysaccharide challenge. These results support a causal link between neuroinflammation and neurodegeneration, have important implications for future therapeutic development, and provide insight into the relative time window for targeting neuroinflammation with positive neurological outcomes.

Aminopyridazines inhibit beta-amyloid-induced glial activation and neuronal damage in vivo

The critical role of chronic inflammation in disease progression continues to be increasingly appreciated across multiple disease areas, especially in neurodegenerative disorders such as Alzheimer's disease. We report that late intervention with a recently discovered aminopyridazine suppressor of glial activation, developed to inhibit both oxidative and inflammatory cytokine pathways, attenuates human amyloid beta (Abeta)-induced glial activation in a murine model. Peripheral administration of the aminopyridazine MW01-070C, beginning 3 weeks after the start of intracerebroventricular infusion of human Abeta1-42, decreased the number of activated astrocytes and microglia and the levels of proinflammatory cytokines interleukin-1beta, tumor necrosis factor-alpha and S100B in the hippocampus. Inhibition of neuroinflammation correlated with a decreased neuron loss, restoration towards control levels of synaptic dysfunction biomarkers in the hippocampus, and diminished amyloid plaque deposition. The results from this in vivo chemical biology approach provide a proof of concept that targeting of key glia inflammatory cytokine pathways can suppress Abeta-induced neuroinflammation in vivo, with resultant attenuation of neuronal damage.

Discovery of a new class of synthetic protein kinase inhibitors that suppress selective aspects of glial activation and protect against beta-amyloid induced injury: a foundation for future medicinal chemistry efforts focused on targeting Alzheimer's disease progression

A prevailing hypothesis in Alzheimer's disease (AD) research is that chronically activated glia may contribute to neuronal dysfunction, through generation of a detrimental state of neuroinflammation. This raises the possibility in drug discovery research of targeting the cycle of untoward glial activation and neuronal dysfunction that characterizes neuroinflammation. Success over the past century with effective anti-inflammatory drug development, in which the molecular targets are intracellular enzymes involved in signal transduction events and cellular homeostasis, demands that a similar approach be tried with neuroinflammation. Suggestive clinical correlations between inflammation markers and AD contribute to the urgency in addressing the hypothesis that targeting selective glial activation processes might be a therapeutic approach complementary to existing drugs and discovery efforts. An academic collaboratorium initiated a rapid inhibitor discovery effort 2 yr ago, focused on development of novel compounds with new mechanisms of action in AD-relevant cellular processes, in order to obtain the small-molecule compounds required to address the neuroinflammation hypothesis and provide a proof of concept for future medicinal chemistry efforts. We summarize here our progress toward this goal in which novel pyridazine-based inhibitors of gene-regulating protein kinases have been discovered. Feasibility studies indicate their potential utility in current medicinal chemistry efforts focused on improvement in molecular properties and the longer term targeting of AD-related pathogenic processes.

Chemical genomics as an emerging paradigm for postgenomic drug discovery

Chemical genomics approaches are evolving to overcome key problems limiting the efficiency of drug discovery in the postgenomic era. Many of these stem from the low success rates in finding drugs for novel genomics targets whose biochemical properties and therapeutic relevance is poorly understood. The fundamental objective of chemical genomics is to find and optimize chemical compounds that can be used to directly test the therapeutic relevance of new targets revealed through genome sequencing. An integrated approach to chemical genomics encompasses a diverse set of tools including quantitative affinity-based screens, computer-directed combinatorial chemistry, and structure-based drug design. The approach is most effectively applied across targets classes whose members are structurally related, and where some members are known to have bona fide therapeutic relevance.

Drugs targeting Alzheimer's disease: some things old and some things new

Enormous effort is now being devoted to developing drugs that slow neurodegeneration in Alzheimer's disease (AD), although insights into AD genetics and molecular pathogenesis only arose in the last 15 years. Acetylcholinesterase inhibitors that temporarily slow loss of cognitive function remain the only approved AD drugs. Discovery of mutations in three genes leading to severe early onset AD was critical in focusing attention on the role of amyloid peptides (Abeta) in neuronal cell death, and enhanced understanding of the biology of these peptides has led to an array of mechanism-based drug discovery strategies. These include inhibitors for Abeta-generating proteases, agents that prevent or reverse Abeta oligomerization, immunotherapies to reduce Abeta in brain and plasma, and drugs to modulate cholesterol-mediated effects on Abeta transport. Strategies are also underway to minimize toxic effects of Abeta fibrils on neurons, and these include antioxidants, blockers of glutamate-mediated excitotoxicity, and modulators of inflammatory responses within the brain. Although several approaches involve new agents for recently discovered targets, many are based on new applications of existing drugs such as statins and nonsteroidal anti-inflammatory drugs. Discovery of abnormally phosphorylated tau protein in neurofibrillary tangles in AD brain has led to strategies for identifying selective inhibitors of tau kinases and central nervous system/brain-permeable drugs that help maintain microtubule integrity. Clearly, a large gap exists between our understanding of the cellular cascades targeted in drug discovery and widespread failure of the nervous system that AD represents. Nevertheless, the pace of recent research clearly supports optimism that slowing progression of AD will soon be possible.