Discovery and structure - activity relationships of 2,4,5-trimethoxyphenyl pyrimidine derivatives as selective D5 receptor partial agonists.

Dopamine receptors are therapeutic targets for the treatment of various neurological and psychiatric disorders, including Parkinson's and Alzheimer's. Previously, PF-06649751 (tavapadon), PF-2562 and PW0464 have been discovered as potent and selective G protein-biased D1/D5 receptor agonists with optimal pharmacokinetic properties. However, no selective D5R agonist has been reported yet. In this context, we designed and synthesized forty non-catecholamines-based pyrimidine derivatives and identified four pyrimidine derivatives as selective D5R partial agonists. Using cAMP-based GloSensor assay in transiently transfected HEK293T cells with human D1 or D5 receptors, we discovered that compound 5c (4-(4-bromophenyl)-6-(2,4,5-trimethoxyphenyl)pyrimidin-2-amine) exhibited modest D5R agonist activity. This leads us to explore various modifications of this scaffold to improve the D5 agonist potency and efficacy. Using molecular docking, and rational design followed by their evaluation at D1 and D5 receptors for agonist activity, we identified three new derivatives, 5j, 5h, and 5e. The most potent compound of this series 5j (4-(4-iodophenyl)-6-(2,4,5-trimethoxyphenyl)pyrimidin-2-amine), exhibited EC50 of 269.7 ± 6.6 nM. Mice microsomal stability studies revealed that 5j is quite stable (>70 % at 1 hr). Furthermore, pharmacokinetic analysis of 5j (20 mg/kg, p.o) in C57BL/6j mice showed that 5j is readily absorbed via oral route of dosing and also enters into the brain (plasma Tmax: 1 h, Cmax: 51.10 ± 13.51 ng/ml; Brain Tmax: 0.5 h, Cmax: 22.54 ± 4.08 ng/ml). We further determined the in-vivo effect of 5j on cognition in scopolamine-induced amnesia in C57BL/6j mice. We observed that 5j (10 mg/kg, p.o) alleviated scopolamine-induced impairment in short-term memory and social recognition, which were blocked by D1/D5 antagonist SCH23390 (0.1 mg/kg, i.p.). Furthermore, 5j did not exhibit any cytotoxicity (up to 10 µM) or in vivo acute toxicity up to 200 mg/kg (p.o). These results strongly suggest that 5j could be further developed for treating neurological disorders wherein the D5 receptors play pivotal roles.

Intramolecular Diffusion in α-Synuclein: It Depends on How You Measure It.

Intramolecular protein diffusion, the motion of one part of the polypeptide chain relative to another part, is a fundamental aspect of protein folding and may modulate amyloidogenesis of disease-associated intrinsically disordered proteins. Much work has determined such diffusion coefficients using a variety of probes, but there has been an apparent discrepancy between measurements using long-range probes, such as fluorescence resonance energy transfer, and short-range probes, such as Trp-Cys quenching. In this work, we make both such measurements on the same protein, α-synuclein, and confirm that such discrepancy exists. Molecular dynamics simulations suggest that such differences result from a diffusion coefficient that depends on the spatial distance between probes. Diffusional estimates in good quantitative agreement with experiment are obtained by accounting for the distinct distance ranges probed by fluorescence resonance energy transfer and Trp-Cys quenching.

Nortriptyline inhibits aggregation and neurotoxicity of alpha-synuclein by enhancing reconfiguration of the monomeric form.

The pathology of Parkinson's disease and other synucleinopathies is characterized by the formation of intracellular inclusions comprised primarily of misfolded, fibrillar α-synuclein (α-syn). One strategy to slow disease progression is to prevent the misfolding and aggregation of its native monomeric form. Here we present findings that support the contention that the tricyclic antidepressant compound nortriptyline (NOR) has disease-modifying potential for synucleinopathies. Findings from in vitro aggregation and kinetics assays support the view that NOR inhibits aggregation of α-syn by directly binding to the soluble, monomeric form, and by enhancing reconfiguration of the monomer, inhibits formation of toxic conformations of the protein. We go on to demonstrate that NOR inhibits the accumulation, aggregation and neurotoxicity of α-syn in multiple cell and animal models. These findings suggest that NOR, a compound with established safety and efficacy for treatment of depression, may slow progression of α-syn pathology by directly binding to soluble, native, α-syn, thereby inhibiting pathological aggregation and preserving its normal functions.

Monomer Dynamics of Alzheimer Peptides and Kinetic Control of Early Aggregation in Alzheimer's Disease.

The rate of reconfiguration-or intramolecular diffusion-of monomeric Alzheimer (Aß) peptides is measured and, under conditions that aggregation is more likely, peptide diffusion slows down significantly, which allows bimolecular associations to be initiated. By using the method of Trp-Cys contact quenching, the rate of reconfiguration is observed to be about five times faster for Aß40 , which aggregates slowly, than that for Aß42 , which aggregates quickly. Furthermore, the rate of reconfiguration for Aß42 speeds up at higher pH, which slows aggregation, and in the presence of the aggregation inhibitor curcumin. The measured reconfiguration rates are able to predict the early aggregation behavior of the Aß peptide and provide a kinetic basis for why Aß42 is more prone to aggregation than Aß40 , despite a difference of only two amino acids.

Therapeutic targeting of Wnt antagonists by small molecules for treatment of osteoporosis.

Wnt signaling is one of the key regulators of bone development and homeostasis. Wnt signaling regulates key biological events, including stem cell fate and osteoblast and osteoclast activity, leading to the maintenance of bone mass and strength. Wnt ligands are secreted glycoproteins that bind to Frizzled (FZD) receptors and their coreceptors, lipoprotein receptor-related proteins-5/6 (LRP5/6). Binding of Wnts to FZD triggers canonical (ß-catenin-dependent) and noncanonical (ß-catenin-independent) pathways. In canonical Wnt signaling, stabilized ß-catenin translocates to the nucleus, where it promotes osteoblast differentiation by activating target genes, including Runx2 and Osterix. The negative regulators of Wnt or so-called Wnt antagonists, including CXXC5, sFRP, sclerostin, DKK1, and Notum, compete for Fzd binding, attenuating Wnt signaling. The critical roles of Wnt signaling in bone homeostasis have been established by various bone diseases caused by mutations in Wnt signaling pathways. Loss-of-function mutations in the LRP5 gene cause osteoporosis-pseudoglioma syndrome, whereas gain-of-function mutations are linked to osteopetrosis characterized by high bone density. Sclerosteosis and Van Buchem disease are caused by mutations affecting the SOST gene, which encodes sclerostin, a natural inhibitor of Wnt signalling. Loss-of-function mutations in SOST result in excessive bone growth, markedly increased bone density, and other skeletal abnormalities due to uncontrolled Wnt activity. Considering the clinical relevance of Wnt signaling, targeting Wnt inhibitors is being intensely pursued using small molecules that act by inhibiting endogenous Wnt agonists. We used a computational biology approach to review current data on pharmacophores of Wnt antagonists, assessing their potential as therapeutic candidates for postmenopausal osteoporosis.

Carbonyl Cytotoxicity Affects Plant Cellular Processes and Detoxifying Enzymes Scavenge These Compounds to Improve Stress Tolerance.

Oxidative stress is ubiquitous in environmental stresses and prevails over the cellular metabolic and phenotypic responses in plants. Reactive oxygen species (ROS) generated under stress affect macromolecules to form another group of toxic compounds called reactive carbonyl compounds (RCCs). These molecules have a longer half-life than ROS and cause carbonyl stress that affects cellular metabolism, cellular homeostasis, and crop productivity. The later effect of oxidative stress in terms of the generation of RCCs and glycation products and their effects on plant processes have not been explored well in plant biology. Therefore, how these molecules are produced and a few important effects of RCCs on plants have been discussed in this review article. Further, the plant adaptive detoxification mechanisms of RCCs have been discussed. The enzymes that were identified in plants to detoxify these cytotoxic compounds have broad substrate specificity and the potential for use in breeding programs. The review should provide a comprehensive understanding of the cytotoxic compounds beyond ROS and subsequently their mitigation strategies for crop improvement programs.

Intramolecular diffusion controls aggregation of the PAPf39 peptide.

The 39-residue fragment of human prostatic acidic phosphatase (PAP) is found in high concentrations in semen and easily form fibrils. Previous work has shown that fibrillization is accelerated with a deletion of the first 8, mostly charged residues and it was hypothesized that fibrillization depended on the dynamics of these peptides. To test this hypothesis we have measured the intramolecular diffusion of the full length and 8-residue deletion peptides at two different pHs and found a correlation with fibrillization lag time. These results can be explained by a simple kinetic model of the early stages of aggregation in which oligomerization is controlled by the rate of peptide reconfiguration.