Discovery of ethyl urea derivatives as inhibitors of islet amyloid polypeptide fibrillization and cytotoxicity

Bovine serum albumin uptake and polypeptide disaggregation studies of hypoglycemic ruthenium(II) uracil Schiff-base complexes

Our prior studies have illustrated that the uracil ruthenium(II) diimino complex, [Ru(H3ucp)Cl(PPh3)] (1) (H4ucp = 2,6-bis-((6-amino-1,3-dimethyluracilimino)methylene)pyridine) displayed high hypoglycemic effects in diet-induced diabetic rats. To rationalize the anti-diabetic effects of 1, three new derivatives have been prepared, cis-[Ru(bpy)2(urdp)]Cl2 (2) (urdp = 2,6-bis-((uracilimino)methylene)pyridine), trans-[RuCl2(PPh3)(urdp)] (3), and cis-[Ru(bpy)2(H4ucp)](PF6)2 (4). Various physicochemical techniques were utilized to characterize the structures of the novel ruthenium compounds. Prior to biomolecular interactions or in vitro studies, the stabilities of 1-4 were monitored in anhydrous DMSO, aqueous phosphate buffer containing 2% DMSO, and dichloromethane (DCM) via UV-Vis spectrophotometry. Time-dependent stability studies showed ligand exchange between DMSO nucleophiles and chloride co-ligands of 1 and 3, which was suppressed in the presence of an excess amount of chloride ions. In addition, the metal complexes 1 and 3 are stable in both DCM and an aqueous phosphate buffer containing 2% DMSO. In the case of compounds 2 and 4 with no chloride co-ligands within their coordination spheres, high stability in aqueous phosphate buffer containing 2% DMSO was observed. Fluorescence emission titrations of the individual ruthenium compounds with bovine serum albumin (BSA) showed that the metal compounds interact non-discriminately within the protein's hydrophobic cavities as moderate to strong binders. The metal complexes were capable of disintegrating mature amylin amyloid fibrils. In vivo glucose metabolism studies in liver (Chang) cell lines confirmed enhanced glucose metabolism as evidenced by the increased glucose utilization and glycogen synthesis in liver cell lines in the presence of complexes 2-4.

1,4-Diurea- and 1,4-Dithiourea-Substituted Aromatic Derivatives Selectively Inhibit α-Synuclein Oligomer Formation In Vitro

Parkinson's disease (PD) is the second most common neurodegenerative disease, affecting the elderly population worldwide. In PD, the misfolding of α-synuclein (α-syn) results in the formation of inclusions referred to as Lewy bodies (LB) in midbrain neurons of the substantia nigra and other specific brain localizations, which is associated with neurodegeneration. There are no approved strategies to reduce the formation of LB in the neurons of patients with PD. Our drug discovery program focuses on the synthesis of urea and thiourea compounds coupled with aminoindole moieties to abrogate α-syn aggregation and to slow down the progression of PD. We synthesized several urea and thiourea analogues with a central 1,4-phenyl diurea/thiourea linkage and evaluated their effectiveness in reducing α-syn aggregation with a special focus on the selective inhibition of oligomer formation among other proteins. We utilized biophysical methods such as thioflavin T (ThT) fluorescence assays, transmission electron microscopy (TEM), photoinduced cross-linking of unmodified proteins (PICUP), as well as M17D intracellular inclusion cell-based assays to evaluate the antiaggregation properties and cellular protection of our best compounds. Our results identified compound 1 as the best compound in reducing α-syn fibril formation via ThT assays. The antioligomer formation of compound 1 was subsequently superseded by compound 2. Both compounds selectively curtailed the oligomer formation of α-syn but not tau 4R isoforms (0N4R, 2N4R) or p-tau (isoform 1N4R). Compounds 1 and 2 failed to abrogate tau 0N3R fibril formation by ThT and atomic force microscopy. Compound 2 was best at reducing the formation of recombinant α-syn fibrils by TEM. In contrast to compound 2, compound 1 reduced the formation of α-syn inclusions in M17D neuroblastoma cells in a dose-dependent manner. Compound 1 may provide molecular scaffolds for the optimization of symmetric molecules for its α-syn antiaggregation activity with potential therapeutic applications and development of small molecules in PD.

Diabetes mellitus drug discovery: insights into targeting feline and human amylin with small molecules

BACKGROUND

Type 2 diabetes (T2D) is a health concern for both humans and cats, with cases rising over the past decade. Around 70% of patients from either species exhibit pancreatic aggregates of islet amyloid polypeptide (IAPP), a protein that proves toxic upon misfolding. These misfolded protein aggregates congregate in the islets of Langerhans of the pancreas, diminishing the capability of β-cells to produce insulin and further perpetuating disease.

OBJECTIVE

Our team's drug discovery program is investigating newly synthesized compounds that could diminish aggregates of both human and feline IAPP, potentially disrupting the progression of T2D.

MATERIAL AND METHODS

We prepared 24 compounds derived from diaryl urea, as ureas have previously demonstrated great potential at reducing accumulations of misfolded proteins. Biophysical methods were employed to analyze the anti-aggregation activity of these compounds at inhibiting and/or disrupting IAPP fibril formation in vitro.

RESULTS

The results demonstrate that compounds 12 and 24 were most effective at reducing the fibrillization and aggregation of both human and feline IAPP. When compared with the control for each experiment, samples treated with either compound 12 or 24 exhibited fewer accumulations of amyloid-like fibrils.

CONCLUSION

Urea-based compounds, such as compounds 12 and 24, may prove crucial in future pre-clinical studies in the search for therapeutics for T2D.

5-Nitro-1,2-benzothiazol-3-amine and N-Ethyl-1-[(ethylcarbamoyl)(5-nitro-1,2-benzothiazol-3-yl)amino]formamide Modulate α-Synuclein and Tau Aggregation

Protein misfolding results in a plethora of known diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, transthyretin-related amyloidosis, type 2 diabetes, Lewy body dementia, and spongiform encephalopathy. To provide a diverse portfolio of therapeutic small molecules with the ability to reduce protein misfolding, we evaluated a set of 13 compounds: 4-(benzo[d]thiazol-2-yl)aniline (BTA) and its derivatives containing urea (1), thiourea (2), sulfonamide (3), triazole (4), and triazine (5) linker. In addition, we explored small modifications on a very potent antioligomer 5-nitro-1,2-benzothiazol-3-amine (5-NBA) (compounds 6-13). This study aims to define the activity of BTA and its derivatives on a variety of prone-to-aggregate proteins such as transthyretin (TTR81-127, TTR101-125), α-synuclein (α-syn), and tau isoform 2N4R (tau 2N4R) through various biophysical methods. Thioflavin T (ThT) fluorescence assay was used to monitor fibril formation of the previously mentioned proteins after treatment with BTA and its derivatives. Antifibrillary activity was confirmed using transmission electron microscopy (TEM). Photoreactive cross-linking assay (PICUP) was utilized to detect antioligomer activity and lead to the identification of 5-NBA (at low micromolar concentration) and compound 13 (at high concentration) as the most promising in reducing oligomerization. 5-NBA and not BTA inhibited the inclusion formation based on the cell-based assay using M17D neuroblastoma cells that express inclusion-prone αS-3K::YFP. 5-NBA abrogated the fibril, oligomer, and inclusion formation in a dose-dependent manner. 5-NBA derivatives could be the key to mitigate protein aggregation. In the future, the results made from this study will provide an initial platform to generate more potent inhibitors of α-syn and tau 2N4R oligomer and fibril formation.

Treatment with semaglutide, a GLP-1 receptor agonist, improves extracellular matrix remodeling in the pancreatic islet of diet-induced obese mice

AIMS

The extracellular matrix (ECM) is fundamental for the normal endocrine functions of pancreatic islet cells and plays key roles in the pathophysiology of type 2 diabetes. Here we investigated the turnover of islet ECM components, including islet amyloid polypeptide (IAPP), in an obese mouse model treated with semaglutide, a glucagon-like peptide type 1 receptor agonist.

MAIN METHODS

Male one-month-old C57BL/6 mice were fed a control diet (C) or a high-fat diet (HF) for 16 weeks, then treated with semaglutide (subcutaneous 40 μg/kg every three days) for an additional four weeks (HFS). The islets were immunostained and gene expressions were assessed.

KEY FINDINGS

Comparisons refer to HFS vs HF. Thus, IAPP immunolabeling and beta-cell-enriched beta-amyloid precursor protein cleaving enzyme (Bace2, -40 %) and heparanase immunolabeling and gene (Hpse, -40 %) were mitigated by semaglutide. In contrast, perlecan (Hspg2, +900 %) and vascular endothelial growth factor A (Vegfa, +420 %) were enhanced by semaglutide. Also, semaglutide lessened syndecan 4 (Sdc4, -65 %) and hyaluronan synthases (Has1, -45 %; Has2, -65 %) as well as chondroitin sulfate immunolabeling, and collagen type 1 (Col1a1, -60 %) and type 6 (Col6a3, -15 %), lysyl oxidase (Lox, -30 %) and metalloproteinases (Mmp2, -45 %; Mmp9, -60 %).

SIGNIFICANCE

Semaglutide improved the turnover of islet heparan sulfate proteoglycans, hyaluronan, chondroitin sulfate proteoglycans, and collagens in the islet ECM. Such changes should contribute to restoring a healthy islet functional milieu and should reduce the formation of cell-damaging amyloid deposits. Our findings also provide additional evidence for the involvement of islet proteoglycans in the pathophysiology of type 2 diabetes.

Discovery of 4-aminoindole carboxamide derivatives to curtail alpha-synuclein and tau isoform 2N4R oligomer formation

Alzheimer's disease (AD) is a multifactorial, chronic neurodegenerative disease characterized by the presence of extracellular β-amyloid (Aβ) plaques, intraneuronal neurofibrillary tangles (NFTs), activated microglial cells, and an inflammatory state (involving reactive oxygen species production) in the brain. NFTs are comprised of misfolded and hyperphosphorylated forms of the microtubule-binding protein tau. Interestingly, the trimeric form of the 2N4R splice isoform of tau has been found to be more toxic than the trimeric 1N4R isoform in neuron precursor cells. Few drug discovery programs have focused on specific tau isoforms. The present drug discovery project is centered on the anti-aggregation effect of a series of seventeen 4- or 5-aminoindole carboxamides on the 2N4R isoform of tau. The selection of the best compounds was performed using α-synuclein (α-syn). The anti-oligomer and -fibril activities of newly synthesized aminoindole carboxamide derivatives were evaluated with biophysical methods, such as thioflavin T fluorescence assays, photo-induced cross-linking of unmodified proteins, and transmission electron microscopy. To evaluate the reduction of inclusions and cytoprotective effects, M17D neuroblastoma cells expressing inclusion-forming α-syn were treated with the best amide representatives. The 4-aminoindole carboxamide derivatives exhibited a better anti-fibrillar activity compared to their 5-aminoindole counterparts. The amide derivatives 2, 8, and 17 exerted anti-oligomer and anti-fibril activities on α-syn and the 2N4R isoform of tau. At a concentration of 40 μM, compound 8 reduced inclusion formation in M17D neuroblastoma cells expressing inclusion-prone αSynuclein3K::YFP. Our results demonstrate the potential of 4-aminoindole carboxamide derivatives with regard to inhibiting the oligomer formation of α-syn and tau (2N4R isoform) for further optimization prior to pre-clinical studies.

Recent Advances in the Discovery of Therapeutics to Curtail Islet Amyloid Polypeptide Aggregation for Type 2 Diabetes Treatment

In humans with type 2 diabetes, at least 70% of patients exhibit islet amyloid plaques formed by misfolding islet amyloid polypeptides (IAPP). The oligomeric conformation and accumulation of the IAPP plaques lead to a panoply of cytotoxic effects on the islet β-cells. Currently, no marketed therapies for the prevention or elimination of these amyloid deposits exist, and therefore significant efforts are required to address this gap. To date, most of the experimental treatments are limited to only in vitro stages of testing. In general, the proposed therapeutics use various targeting strategies, such as binding to the N-terminal region of islet amyloid polypeptide on residues 1-19 or the hydrophobic region of IAPP. Other strategies include targeting the peptide self-assembly through π-stacking. These methods are realized by using several different families of compounds, four of which are highlighted in this review: naturally occurring products, small molecules, organometallic compounds, and nanoparticles. Each of these categories holds immense potential to optimize and develop inhibitor(s) of pancreatic amyloidosis in the near future.

Human islet amyloid polypeptide: A therapeutic target for the management of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) and other metabolic disorders are often silent and go unnoticed in patients because of the lack of suitable prognostic and diagnostic markers. The current therapeutic regimens available for managing T2DM do not reverse diabetes; instead, they delay the progression of diabetes. Their efficacy (in principle) may be significantly improved if implemented at earlier stages. The misfolding and aggregation of human islet amyloid polypeptide (hIAPP) or amylin has been associated with a gradual decrease in pancreatic β-cell function and mass in patients with T2DM. Hence, hIAPP has been recognized as a therapeutic target for managing T2DM. This review summarizes hIAPP's role in mediating dysfunction and apoptosis in pancreatic β-cells via induction of endoplasmic reticulum stress, oxidative stress, mitochondrial dysfunction, inflammatory cytokine secretion, autophagy blockade, etc. Furthermore, it explores the possibility of using intermediates of the hIAPP aggregation pathway as potential drug targets for T2DM management. Finally, the effects of common antidiabetic molecules and repurposed drugs; other hIAPP mimetics and peptides; small organic molecules and natural compounds; nanoparticles, nanobodies, and quantum dots; metals and metal complexes; and chaperones that have demonstrated potential to inhibit and/or reverse hIAPP aggregation and can, therefore, be further developed for managing T2DM have been discussed.

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Misfolded species of hIAPP form toxic oligomers in pancreatic β-cells.

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hIAPP amyloids has been detected in the pancreas of about 90% subjects with T2DM.

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Inhibitors of hIAPP aggregation can help manage T2DM.

A Novel Pentapeptide Inhibitor Reduces Amyloid Deposit Formation by Direct Interaction with hIAPP

BACKGROUNDS

The presence of amyloid deposits of human islet amyloid polypeptide (hIAPP) in islet β-cells has been associated with type 2 diabetes occurrence and islet graft failure. Self-assembly into oligomers and fibrils during the process of aggregation by hIAPP can lead to failure and depletion of β-cells. Studies have shown that some critical regions of hIAPP might contribute to the aggregation. Thus, many studies focused on finding the effective molecules, especially the short-peptide inhibitors, that bind to these regions and disrupt the aggregation of hIAPP. In the present study, a novel pentapeptide inhibitor Phe-Leu-Pro-Asn-Phe (FLPNF) was designed and its effectiveness on the inhibition of the formation of amyloid deposits was examined.

METHODS

The binding mode between FLPNF and hIAPP was performed using molecular docking. The effectiveness of FLPNF on inhibiting hIAPP amyloid aggregation was tested by Thioflavin T (ThT) staining. Furthermore, negative stain electron microscopy was used to observe hIAPP fibrils. A biolayer interferometry analysis was used to identify the interaction between FLPNF and hIAPP. In addition, the cytotoxicity toward INS-1 cells was tested by a cell proliferation assay.

RESULTS

FLPNF was predicted to have a compact conformation to bind at the site of hIAPP. FLPNF strongly inhibited the amyloid aggregation of hIAPP at a 10 : 1 molar ratio in vitro. Coincubation of FLPNF with hIAPP decreased the amount of hIAPP fibrils. Furthermore, a direct interaction between FLPNF and hIAPP was confirmed. FLPNF could also decrease the cytotoxic effect of hIAPP.

CONCLUSIONS

The novel pentapeptide inhibitor FLPNF was constructed and inhibited the aggregation through direct binding to hIAPP. It is considered a suitable inhibitor for hIAPP amyloid deposit formation.