The activity of antimicrobial peptoids against multidrug-resistant ocular pathogens.

BACKGROUND: Ocular infections caused by antibiotic-resistant pathogens can result in partial or complete vision loss. The development of pan-resistant microbial strains poses a significant challenge for clinicians as there are limited antimicrobial options available. Synthetic peptoids, which are sequence-specific oligo-N-substituted glycines, offer potential as alternative antimicrobial agents to target multidrug-resistant bacteria. METHODS: The antimicrobial activity of synthesised peptoids against multidrug-resistant (MDR) ocular pathogens was evaluated using the microbroth dilution method. Hemolytic propensity was assessed using mammalian erythrocytes. Peptoids were also incubated with proteolytic enzymes, after which their minimum inhibitory activity against bacteria was re-evaluated. RESULTS: Several alkylated and brominated peptoids showed good inhibitory activity against multidrug-resistant Pseudomonas aeruginosa strains at concentrations of ≤15 µg mL-1 (≤12 µM). Similarly, most brominated compounds inhibited the growth of methicillin-resistant Staphylococcus aureus at 1.9 to 15 µg mL-1 (12 µM). The N-terminally alkylated peptoids caused less toxicity to erythrocytes. The peptoid denoted as TM5 had a high therapeutic index, being non-toxic to either erythrocytes or corneal epithelial cells, even at 15 to 22 times its MIC. Additionally, the peptoids were resistant to protease activity. CONCLUSIONS: Peptoids studied here demonstrated potent activity against various multidrug-resistant ocular pathogens. Their properties make them promising candidates for controlling vision-related morbidity associated with eye infections by antibiotic-resistant strains.

Synthesis of Novel Quinazolinone Analogues for Quorum Sensing Inhibition.

As bacteria continue to develop resistance mechanisms against antimicrobials, an alternative method to tackle this global concern must be developed. As the pqs system is the most well-known and responsible for biofilm and pyocyanin production, quinazolinone inhibitors of the pqs system in P. aeruginosa were developed. Molecular docking following a rationalised medicinal chemistry approach was adopted to design these analogues. An analysis of docking data suggested that compound 6b could bind with the key residues in the ligand binding domain of PqsR in a similar fashion to the known antagonist M64. The modification of cyclic groups at the 3-position of the quinazolinone core, the introduction of a halogen at the aromatic core and the modification of the terminal group with aromatic and aliphatic chains were investigated to guide the synthesis of a library of 16 quinazolinone analogues. All quinazolinone analogues were tested in vitro for pqs inhibition, with the most active compounds 6b and 6e being tested for biofilm and growth inhibition in P. aeruginosa (PAO1). Compound 6b displayed the highest pqs inhibitory activity (73.4%, 72.1% and 53.7% at 100, 50 and 25 µM, respectively) with no bacterial growth inhibition. However, compounds 6b and 6e only inhibited biofilm formation by 10% and 5%, respectively.

Pyrimido[1,2-a]benzimidazoles as inhibitors of oncoproteins ubiquitin specific protease 5 and MYCN in the childhood cancer neuroblastoma.

The MYCN oncogene and histone deacetylases (HDACs) are key driver genes in the childhood cancer, neuroblastoma. We recently described a novel pyridobenzimidazole analogue, SE486-11, which enhanced the therapeutic effectiveness of HDAC inhibitors by increasing MYCN ubiquitination through effects on the deubiquitinase, ubiquitin-specific protease 5 (USP5). Here we describe the synthesis of a novel series of pyrimido[1,2-a]benzimidazole derivatives, and an evaluation of their cytopathic effects against non-malignant and human neuroblastoma cell lines. Among the tested analogues, 4-(4-methoxyphenyl)benzo[4,5]imidazo[1,2-a]pyrimidine (3a) was the most active compound against neuroblastoma cells (IC50 ≤ 2 µM), with low cytotoxicity (IC50 ≥ 15 µM) to normal cells. We show compound 3a bound to USP5 protein (Kd = 0.47 µM) in vitro and synergistically enhanced the efficacy of HDAC inhibitors against neuroblastoma cells. Moreover, knockdown of USP5 and MYCN in treated neuroblastoma cells showed that both USP5 and MYCN expression was necessary for the cytopathic activity of compound 3a, thus providing a clinically relevant rationale for further development of this of pyrimido[1,2-a]benzimidazole.

Tuning the Anthranilamide Peptidomimetic Design to Selectively Target Planktonic Bacteria and Biofilm.

There is a pressing need to develop new antimicrobials to help combat the increase in antibiotic resistance that is occurring worldwide. In the current research, short amphiphilic antibacterial and antibiofilm agents were produced by tuning the hydrophobic and cationic groups of anthranilamide peptidomimetics. The attachment of a lysine cationic group at the tail position increased activity against E. coli by >16-fold (from >125 µM to 15.6 µM) and greatly reduced cytotoxicity against mammalian cells (from ≤20 µM to ≥150 µM). These compounds showed significant disruption of preformed biofilms of S. aureus at micromolar concentrations.

Effective PFAS degradation by electrochemical oxidation methods-recent progress and requirement.

The presence of per- and poly-fluoroalkyl substances (PFASs) in water is of global concern due to their high stability and toxicity even at very low concentrations. There are several technologies for the remediation of PFASs, but most of them are inadequate either due to limited effectiveness, high cost, or production of a large amount of sludge. Electrochemical oxidation (EO) technology shows great potential for large-scale application in the degradation of PFASs due to its simple procedure, low loading of chemicals, and least amount of waste. Here, we have reviewed the recent progress in EO methods for PFAS degradation, focusing on the last 10 years, to explore an efficient, cost-effective, and environmentally benign remediation technology. The effects of important parameters (e.g., anode material, current density, solution pH, electrolyte, plate distance, and electrical connector type) are summarized and evaluated. Also, the energy consumption, the consequence of different PFASs functional groups, and water matrices are discussed to provide an insight that is pivotal for developing new EO materials and technologies. The proposed degradation pathways of shorter-chain PFAS by-products during EO of PFAS are also discussed.

Novel quinazolinone disulfide analogues as pqs quorum sensing inhibitors against Pseudomonas aeruginosa.

It is well established that the quorum sensing (QS) in Pseudomonas aeruginosa is primarily responsible for the synthesis and the release of several virulence factors including pyocyanin and are involved in biofilm formation. In the Pseudomonas quinolone signal (PQS) system, autoinducers such as PQS and HHQ bind and activate the transcription regulator protein receptor PqsR (MvfR). Targeting PqsR with competitive inhibitors could be a promising strategy to inhibit QS in P. aeruginosa to overcome antimicrobial resistance. In this study, we have designed and synthesized a series of novel quinazolinone disulfide-containing competitive inhibitor of PqsR. The most potent analogue 8q efficiently inhibited the pqs system with an IC50 value of 4.5 µM. It also showed complete suppression of pyocyanin production and a significant reduction in biofilm formation by P. aeruginosa (PAO1) with low cytotoxicity. Additionally, 8q produced synergy in combination with known antibiotics such as ciprofloxacin and tobramycin. Finally, molecular docking analysis suggested that compound 8q could bind with the ligand-binding domain of PqsR in a similar fashion to the native ligand.

Cholic Acid-Based Antimicrobial Peptide Mimics as Antibacterial Agents.

There is a significant and urgent need for the development of novel antibacterial agents to tackle the increasing incidence of antibiotic resistance. Cholic acid-based small molecular antimicrobial peptide mimics are reported as potential new leads to treat bacterial infection. Here, we describe the design, synthesis and biological evaluation of cholic acid-based small molecular antimicrobial peptide mimics. The synthesis of cholic acid analogues involves the attachment of a hydrophobic moiety at the carboxyl terminal of the cholic acid scaffold, followed by the installation of one to three amino acid residues on the hydroxyl groups present on the cholic acid scaffold. Structure-activity relationship studies suggest that the tryptophan moiety is important for high antibacterial activity. Moreover, a minimum of +2 charge is also important for antimicrobial activity. In particular, analogues containing lysine-like residues showed the highest antibacterial potency against Gram-positive S. aureus. All di-substituted analogues possess high antimicrobial activity against both Gram-positive S. aureus as well as Gram-negative E. coli and P. aeruginosa. Analogues 17c and 17d with a combination of these features were found to be the most potent in this study. These compounds were able to depolarise the bacterial membrane, suggesting that they are potential antimicrobial pore forming agents.

Synthesis of Alkyne-Substituted Dihydropyrrolones as Bacterial Quorum-Sensing Inhibitors of Pseudomonas aeruginosa.

The Quorum-sensing system in Pseudomonas aeruginosa is responsible for the pathogenicity and the production of virulence factors and biofilm formation. Dihydropyrrolones were previously found to act as inhibitors of QS-dependent bacterial phenotypes. In this study, a range of dihydropyrrolone (DHP) analogues was synthesized via the lactone-lactam conversion of lactone intermediates followed by the formation of novel acetylene analogues of dihydropyrrolones from brominated dihydropyrrolones via Sonogashira coupling reactions in moderate to high yields. Upon biological testing, the most potent compounds, 39-40 and 44, showed higher bacterial quorum-sensing inhibitory (QSI) activity against P. aeruginosa reporter strain at 62.5 µM. Structure-activity relationship studies revealed that di-alkynyl substituent at the exocyclic position of DHPs possessed higher QSI activities than those of mono-alkynyl DHPs. Moreover, a hexyl-substituent at C3 of DHPs was beneficial to QSI activity while a phenyl substituent at C4 of DHPs was detrimental to QSI activity of analogues.

Fluorinated quorum sensing inhibitors: enhancement of potency through conformational control.

The bacterial quorum sensing (QS) system is a target for non-lethal antibacterial agents that do not encourage the development of resistance. QS inhibitors commonly contain a polar "head" moiety and a lipidic "tail" moiety. In this work, we synthesised novel QS inhibitor candidates in which the lipidic "tail" is decorated with stereospecifically positioned fluorine atoms. The presence of fluorine is shown to bias the molecules into distinctive conformations that are pre-organised for binding to the QS receptor. This translates into significant increases in QS inhibitory potency.

Natural Product Rottlerin Derivatives Targeting Quorum Sensing.

Rottlerin is a natural product consisting of chalcone and flavonoid scaffolds, both of which have previously shown quorum sensing (QS) inhibition in various bacteria. Therefore, the unique rottlerin scaffold highlights great potential in inhibiting the QS system of Pseudomonas aeruginosa. Rottlerin analogues were synthesised by modifications at its chalcone- and methylene-bridged acetophenone moieties. The synthesis of analogues was achieved using an established five-step synthetic strategy for chalcone derivatives and utilising the Mannich reaction at C6 of the chromene to construct morpholine analogues. Several pyranochromene chalcone derivatives were also generated using aldol conditions. All the synthetic rottlerin derivatives were screened for QS inhibition and growth inhibition against the related LasR QS system. The pyranochromene chalcone structures displayed high QS inhibitory activity with the most potent compounds, 8b and 8d, achieving QS inhibition of 49.4% and 40.6% and no effect on bacterial growth inhibition at 31 µM, respectively. Both compounds also displayed moderate biofilm inhibitory activity and reduced the production of pyocyanin.

Polyphenylglyoxamide-Based Amphiphilic Small Molecular Peptidomimetics as Antibacterial Agents with Anti-Biofilm Activity.

The rapid emergence of drug-resistant bacteria is a major global health concern. Antimicrobial peptides (AMPs) and peptidomimetics have arisen as a new class of antibacterial agents in recent years in an attempt to overcome antibiotic resistance. A library of phenylglyoxamide-based small molecular peptidomimetics was synthesised by incorporating an N-alkylsulfonyl hydrophobic group with varying alkyl chain lengths and a hydrophilic cationic group into a glyoxamide core appended to phenyl ring systems. The quaternary ammonium iodide salts 16d and 17c showed excellent minimum inhibitory concentration (MIC) of 4 and 8 µM (2.9 and 5.6 µg/mL) against Staphylococcus aureus, respectively, while the guanidinium hydrochloride salt 34a showed an MIC of 16 µM (8.5 µg/mL) against Escherichia coli. Additionally, the quaternary ammonium iodide salt 17c inhibited 70% S. aureus biofilm formation at 16 µM. It also disrupted 44% of pre-established S. aureus biofilms at 32 µM and 28% of pre-established E. coli biofilms 64 µM, respectively. A cytoplasmic membrane permeability study indicated that the synthesised peptidomimetics acted via disruption and depolarisation of membranes. Moreover, the quaternary ammonium iodide salts 16d and 17c were non-toxic against human cells at their therapeutic dosages against S. aureus.

Novel Seleno- and Thio-Urea Containing Dihydropyrrol-2-One Analogues as Antibacterial Agents.

The quorum sensing (QS) system in multi-drug-resistant bacteria such as P. aeruginosa is primarily responsible for the development of antibiotic resistance and is considered an attractive target for antimicrobial drug discovery. In this study, we synthesised a series of novel selenourea and thiourea-containing dihydropyrrol-2-one (DHP) analogues as LasR antagonists. The selenium DHP derivatives displayed significantly better quorum-sensing inhibition (QSI) activities than the corresponding sulphur analogues. The most potent analogue 3e efficiently inhibited the las QS system by 81% at 125 µM and 53% at 31 µM. Additionally, all the compounds were screened for their minimum inhibitory concentration (MIC) against the Gram-positive bacterium S. aureus, and interestingly, only the selenium analogues showed antibacterial activity, with 3c and 3e being the most potent with a MIC of 15.6 µM.

Design, Synthesis and Biological Evaluation of Biphenylglyoxamide-Based Small Molecular Antimicrobial Peptide Mimics as Antibacterial Agents.

There has been an increasing interest in the development of antimicrobial peptides (AMPs) and their synthetic mimics as a novel class of antibiotics to overcome the rapid emergence of antibiotic resistance. Recently, phenylglyoxamide-based small molecular AMP mimics have been identified as potential leads to treat bacterial infections. In this study, a new series of biphenylglyoxamide-based small molecular AMP mimics were synthesised from the ring-opening reaction of N-sulfonylisatin bearing a biphenyl backbone with a diamine, followed by the conversion into tertiary ammonium chloride, quaternary ammonium iodide and guanidinium hydrochloride salts. Structure-activity relationship studies of the analogues identified the octanesulfonyl group as being essential for both Gram-positive and Gram-negative antibacterial activity, while the biphenyl backbone was important for Gram-negative antibacterial activity. The most potent analogue was identified to be chloro-substituted quaternary ammonium iodide salt 15c, which possesses antibacterial activity against both Gram-positive (MIC against Staphylococcus aureus = 8 µM) and Gram-negative bacteria (MIC against Escherichia coli = 16 µM, Pseudomonas aeruginosa = 63 µM) and disrupted 35% of pre-established S. aureus biofilms at 32 µM. Cytoplasmic membrane permeability and tethered bilayer lipid membranes (tBLMs) studies suggested that 15c acts as a bacterial membrane disruptor. In addition, in vitro toxicity studies showed that the potent compounds are non-toxic against human cells at therapeutic dosages.

Dihydropyrrolones as bacterial quorum sensing inhibitors.

Bacteria regulate their pathogenicity and biofilm formation through quorum sensing (QS), which is an intercellular communication system mediated by the binding of signaling molecules to QS receptors such as LasR. In this study, a range of dihydropyrrolone (DHP) analogues were synthesized via the lactone-lactam conversion of lactone intermediates. The synthesized compounds were tested for their ability to inhibit QS, biofilm formation and bacterial growth of Pseudomonas aeruginosa. The compounds were also docked into a LasR crystal structure to rationalize the observed structure-activity relationships. The most active compound identified in this study was compound 9i, which showed 63.1% QS inhibition of at 31.25 µM and 60% biofilm reduction at 250 µM with only moderate toxicity towards bacterial cell growth.

Design, synthesis and biological evaluation of 1,2,3-triazole based 2-aminobenzimidazoles as novel inhibitors of LasR dependent quorum sensing in Pseudomonas aeruginosa.

Bacteria regulate their phenotype, growth and population via a signalling pathway known as quorum sensing. In this process, bacteria produce signalling molecules (autoinducers) to recognize their population density. Inhibiting this quorum sensing signalling pathway is one of the potential methods to treat bacterial infection. 2-Aminobenimdazoles are reported to be the strongest inhibitors of quorum sensing against wild-type P. aeruginosa. 1,2,3-Triazole based acyl homoserine lactones are found to be good inhibitors of the quorum sensing LasR receptor. Hence, in our current study, forty 1,2,3-triazole based 2-aminobenzimdazoles were synthesized and characterized using IR, NMR, MS and elemental analysis. A single crystal was developed for N-(1H-benzo[d]imidazol-2-yl)-2-(4-nonyl-1H-1,2,3-triazol-1-yl)acetamide (6d). All final compounds were screened for in vitro quorum sensing inhibitory activity against Pseudomonas aeruginosa. The quorum sensing inhibitory activity was determined in the LasR expressing P. aeruginosa MH602 reporter strain by measuring green fluorescent protein production. Among the title compounds, N-(1H-benzo[d]imidazol-2-yl)-2-(4-(4-chlorophenyl)-1H-1,2,3-triazol-1-yl)acetamide (6i) exhibited good quorum sensing inhibitory activity of 64.99% at 250 µM. N-(1H-Benzo[d]imidazol-2-yl)-2-(4-(4-nitrophenyl)-1H-1,2,3-triazol-1-yl)acetamide (6p) exhibited the most promising quorum sensing inhibitory activity with 68.23, 67.10 and 63.67% inhibition at 250, 125 and 62.5 µM, respectively. N-(1H-Benzo[d]imidazol-2-yl)-2-(4-(4-(trifluoromethyl)phenyl)-1H-1,2,3-triazol-1-yl)acetamide (6o) and N-(5,6-dimethyl-1H-benzo[d]imidazol-2-yl)-2-(4-(4-(trifluoromethyl)phenyl)-1H-1,2,3-triazol-1-yl)acetamide (7l) also exhibited 64.25% and 65.80% quorum sensing inhibition at 250 µM. Compound 6p, the most active quorum sensing inhibitor, also displayed low cytotoxicity at the tested concentrations (25, 50 and 100 µM) against normal human embryonic kidney cell lines. Finally, a docking study using Schrodinger Glide elucidated the possible putative binding mode of the significantly active compound 6p at the active site of the target LasR receptor (PDB ID: 2UV0).

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.