From (Tool)Bench to Bedside: The Potential of Necroptosis Inhibitors.

Necroptosis is a regulated caspase-independent form of necrotic cell death that results in an inflammatory phenotype. This process contributes profoundly to the pathophysiology of numerous neurodegenerative, cardiovascular, infectious, malignant, and inflammatory diseases. Receptor-interacting protein kinase 1 (RIPK1), RIPK3, and the mixed lineage kinase domain-like protein (MLKL) pseudokinase have been identified as the key components of necroptosis signaling and are the most promising targets for therapeutic intervention. Here, we review recent developments in the field of small-molecule inhibitors of necroptosis signaling, provide guidelines for their use as chemical probes to study necroptosis, and assess the therapeutic challenges and opportunities of such inhibitors in the treatment of a range of clinical indications.

Synthesis of antimicrobial glucosamides as bacterial quorum sensing mechanism inhibitors.

Bacteria communicate with one another and regulate their pathogenicity through a phenomenon known as quorum sensing (QS). When the bacterial colony reaches a threshold density, the QS system induces the production of virulence factors and the formation of biofilms, a powerful defence system against the host's immune responses. The glucosamine monomer has been shown to disrupt the bacterial QS system by inhibiting autoinducer (AI) signalling molecules such as the acyl-homoserine lactones (AHLs). In this study, the synthesis of acetoxy-glucosamides 8, hydroxy-glucosamides 9 and 3-oxo-glucosamides 12 was performed via the 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) and N,N'-dicyclohexylcarbodiimide (DCC) coupling methods. All of the synthesized compounds were tested against two bacterial strains, P. aeruginosa MH602 (LasI/R-type QS) and E. coli MT102 (LuxI/R-type QS), for QS inhibitory activity. The most active compound 9b showed 79.1% QS inhibition against P. aeruginosa MH602 and 98.4% against E. coli MT102, while compound 12b showed 64.5% inhibition against P. aeruginosa MH602 and 88.1% against E. coli MT102 strain at 2mM concentration. The ability of the compounds to inhibit the production of the virulence factor pyocyanin and biofilm formation in the P. aeruginosa (PA14) strain was also examined. Finally, computational docking studies were performed with the LasR receptor protein.

Synthesis, Characterization and Anti-Cancer Activity of Hydrazide Derivatives Incorporating a Quinoline Moiety.

Identification of the novel (E)-N'-((2-chloro-7-methoxyquinolin-3-yl)methylene)-3-(phenylthio)propanehydrazide scaffold 18 has led to the development of a new series of biologically active hydrazide compounds. The parent compound 18 and new quinoline derivatives 19-26 were prepared from the corresponding quinoline hydrazones and substituted carboxylic acids using EDC-mediated peptide coupling reactions. Further modification of the parent compound 18 was achieved by replacement of the quinoline moiety with other aromatic systems. All the newly synthesized compounds were evaluated for their anti-cancer activity against the SH-SY5Y and Kelly neuroblastoma cell lines, as well as the MDA-MB-231 and MCF-7 breast adenocarcinoma cell lines. Analogues 19 and 22 significantly reduced the cell viability of neuroblastoma cancer cells with micromolar potency and significant selectivity over normal cells. The quinoline hydrazide 22 also induced G1 cell cycle arrest, as well as upregulation of the p27(kip1) cell cycle regulating protein.

Design, synthesis and evaluation of N-aryl-glyoxamide derivatives as structurally novel bacterial quorum sensing inhibitors.

Bacteria cooperatively regulate the expression of many phenotypes through a mechanism called quorum sensing (QS). Many Gram-negative bacteria use an N-acyl homoserine lactone (AHL)-mediated QS system to control biofilm formation and virulence factor production. In recent years, quorum sensing inhibitors (QSIs) have become attractive tools to overcome antimicrobial resistance exhibited by various pathogenic bacteria. In the present study, we report the design and synthesis of novel N-arylisatin-based glyoxamide derivatives via the ring-opening reaction of N-aryl isatins with cyclic and acylic amines, and amino acid esters. The QSI activity of the synthesized compounds was determined in the LasR-expressing Pseudomonas aeruginosa MH602 and LuxR-expressing Escherichia coli MT102 reporter strains. Compounds 31 and 32 exhibited the greatest QSI activity in P. aeruginosa MH602, with 48.7% and 42.7% reduction in QS activity at 250 µM, respectively, while compounds 31 and 34 showed 73.6% and 43.7% QSI activity in E. coli MT102. In addition, the ability of these compounds to inhibit the production of pyocyanin in P. aeruginosa (PA14) was also determined, with compound 28 showing 47% inhibition at 250 µM. Furthermore, computational docking studies were performed on the LasR receptor protein of P. aeruginosa, which showed that formation of a hydrogen bonding network played a major role in influencing the QS inhibitory activity. We envisage that these novel non-AHL glyoxamide derivatives could become a new tool for the study of QS and potentially for the treatment of bacterial infections.

Synthesis, quorum sensing inhibition and docking studies of 1,5-dihydropyrrol-2-ones.

Gram-negative bacteria such as Pseudomonas aeruginosa and Escherichia coli use N-acylated l-homoserine lactones (AHLs) as autoinducers (AIs) for quorum sensing (QS), a chief regulatory and cell-to-cell communication system. QS is responsible for social adaptation, virulence factor production, biofilm production and antibiotic resistance in bacteria. Fimbrolides, a class of halogenated furanones isolated from the red marine alga Delisea pulchra, have been shown to exhibit promising QS inhibitory activity against various Gram-negative and Gram-positive bacterial strains. In this work, various lactam analogues of fimbrolides viz., 1,5-dihydropyrrol-2-ones, were designed and synthesized via an efficient lactamization protocol. All the synthesized analogues were tested for QS inhibition against the E. coli AHL-monitor strain JB357 gfp (ASV). Compound 17a emerged as the most potent compound, followed by 9c, with AIC40 values (the ratio of synthetic inhibitor to natural AHL signaling molecule that is required to lower GFP expression to 40%) of 1.95 and 19.00, respectively. Finally, the potential binding interactions between the synthesized molecules and the LasR QS receptor were studied by molecular docking. Our results indicate that 1,5-dihydropyrrol-2-ones have the ability to serve as potential leads for the further development of novel QS inhibitors as antimicrobial therapeutics.

Synthesis, biological evaluation and structure-activity relationship studies of isoflavene based Mannich bases with potent anti-cancer activity.

Phenoxodiol, an analogue of the isoflavone natural product daidzein, is a potent anti-cancer agent that has been investigated for the treatment of hormone dependent cancers. This molecular scaffold was reacted with different primary amines and secondary amines under different Mannich conditions to yield either benzoxazine or aminomethyl substituted analogues. These processes enabled the generation of a diverse range of analogues that were required for structure-activity relationship (SAR) studies. The resulting Mannich bases exhibited prominent anti-proliferative effects against SHEP neuroblastoma and MDA-MB-231 breast adenocarcinoma cell lines. Further cytotoxicity studies against MRC-5 normal lung fibroblast cells showed that the isoflavene analogues were selective towards cancer cells.

Synthesis and anticancer evaluation of 3-substituted quinolin-4-ones and 2,3-dihydroquinolin-4-ones.

A series of 3-aryl-5,7-dimethoxyquinolin-4-ones 8 and 3-aryl-5,7-dimethoxy-2,3-dihydroquinolin-4-ones 13 were synthesized in good yields. Demethylation under a range of conditions afforded the corresponding 5-hydroxy and 5,7-dihydroxy derivatives. Biological evaluation against a range of cancer cells lines showed that the quinolin-4-one scaffold was more cytotoxic than the reduced 2,3-dihydroquinolin-4-one scaffold. The most active monohydroxy compound 15f demonstrated 85.9-99% reduction in cell viability against the cell lines tested.

Synthesis of retinoid enhancers based on 2-aminobenzothiazoles for anti-cancer therapy.

Indole-3-amides and dipeptides were produced from 2-aminobenzothiazoles using the PyBop peptide coupling reagent. These analogues were tested in anti-cancer cell viability assays against SH-SY5Y neuroblastoma and MDA-MB-231 breast adenocarcinoma cell lines, and were found to exhibit cytotoxic activities at concentrations ranging from 0.1 to 20µM. These compounds were also found to act additively with a low dosage of 13-cis-retinoic acid in neuroblastoma cells. Then, using neuroblastoma cells transfected to stably overexpress the RARß(2) gene, a SAR was developed for the indole-3-amides. Real-time PCR was also used to demonstrate their RARß(2) agonistic activity.