https://ogma.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:45054 Escherichia coli and Pseudomonas aeruginosa, with a clear delineation of the outer and inner membrane as well as the peptidoglycan layer. We suggest that the use of ultrathin cryo-sectioning can be used to better visualize and understand drug interaction mechanisms on the bacterial cell membrane.]]> Wed 26 Oct 2022 11:36:12 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:42541 Wed 24 Aug 2022 16:53:29 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:53705 Wed 10 Jan 2024 11:03:27 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:40008 Enterococcus faecalis/faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, and Enterobacte spp.), have become a public health threat worldwide. Development of new antimicrobial classes and the use of drugs in combination are potential strategies to treat MDR ESKAPE pathogen infections and promote optimal antimicrobial stewardship. Here, the in vitro antimicrobial activity of robenidine analog NCL195 alone or in combination with different concentrations of three outer membrane permeabilizers [ethylenediaminetetraacetic acid (EDTA), polymyxin B nonapeptide (PMBN), and polymyxin B (PMB)] was further evaluated against clinical isolates and reference strains of key Gram-negative bacteria. NCL195 alone was bactericidal against Neisseria meningitidis and Neisseria gonorrhoeae (MIC/MBC = 32 μg/mL) and demonstrated synergistic activity against P. aeruginosa, E. coli, K. pneumoniae, and Enterobacter spp. strains in the presence of subinhibitory concentrations of EDTA, PMBN, or PMB. The additive and/or synergistic effects of NCL195 in combination with EDTA, PMBN, or PMB are promising developments for a new chemical class scaffold to treat Gram-negative infections. Tokuyasu cryo ultramicrotomy was used to visualize the effect of NCL195 on bioluminescent S. aureus membrane morphology. Additionally, NCL195’s favorable pharmacokinetic and pharmacodynamic profile was further explored in in vivo safety studies in mice and preliminary efficacy studies against Gram-positive bacteria. Mice administered two doses of NCL195 (50 mg/kg) by the intraperitoneal (IP) route 4 h apart showed no adverse clinical effects and no observable histological effects in major organs. In bioluminescent Streptococcus pneumoniae and S. aureus murine sepsis challenge models, mice that received two 50 mg/kg doses of NCL195 4 or 6 h apart exhibited significantly reduced bacterial loads and longer survival times than untreated mice. However, further medicinal chemistry and pharmaceutical development to improve potency, solubility, and selectivity is required before efficacy testing in Gram-negative infection models.]]> Wed 06 Jul 2022 11:20:52 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:30033 1 (2,2′-bis[(4-chlorophenyl)methylene]carbonimidic dihydrazide), was active against MRSA and VRE with MIC’s of 8.1 and 4.7 μM, respectively. SAR revealed tolerance for 4-Cl isosteres with 4-F (8), 3-F (9), 3-CH₃ (22), and 4-C(CH₃)₃ (27) (23.7–71 μM) and with 3-Cl (3), 4-CH₃ (21), and 4-CH(CH₃)₂ (26) (8.1–13.0 μM). Imine carbon alkylation identified a methyl/ethyl binding pocket that also accommodated a CH₂OH moiety (75; 2,2′-bis[1-(4-chlorophenyl)-2-hydroxyethylidene]carbonimidic dihydrazide). Analogues 1, 27 (2,2′-bis{[4-(1,1-dimethylethyl)phenyl]methylene}carbonimidic dihydrazide), and 69 (2,2′-bis[1-(4-chlorophenyl)ethylidene]carbonimidic dihydrazide hydrochloride) were active against 24 clinical MRSA and MSSA isolates. No dose-limiting cytotoxicity at ≥2× MIC or hemolysis at ≥8× MIC was observed. Polymyxin B addition engendered Escherichia coli and Pseudomonas aeruginosa Gram-negative activity MIC’s of 4.2–21.6 μM. 1 and 75 displayed excellent microsomal stability, intrinsic clearance, and hepatic extraction ratios with T_1/2 > 247 min, CL_int < 7 μL/min/mg protein, and E_H < 0.22 in both human and mouse liposomes for 1 and in human liposomes for 75.]]> Wed 02 Mar 2022 14:27:39 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:50596 Tue 08 Aug 2023 11:56:57 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:34739 50 was as low as 0.2 μM with corresponding MLCs as low as 2.8 μM. This is in contrast to metronidazole which required 24 h to exhibit inhibitory activity. A modified adherence assay, developed for this study, demonstrated that three of the compounds inhibited in vitro adherence of the parasite. The lead compound exhibited rapid giardicidal activity (<5hr). In addition, microscopy studies demonstrated damage to the plasma membrane of trophozoites. In conclusion, a class of aminoguanidines, represented by robenidine, has shown antigiardial activity warranting further investigation.]]> Tue 03 Sep 2019 17:57:16 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:45380 Thu 27 Oct 2022 15:58:15 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:37232 Acinetobacter baumannii [minimum inhibitory concentrations (MIC) mode = 8 μg/ml] and Acinetobacter calcoaceticus (MIC mode = 2 μg/ml). Against Acinetobacter spp., an additivity/indifference of the combination of robenidine/EDTA (0.53 > FICIs > 1.06) and a synergistic effect of the combination of robenidine/PMBN (0.5 < FICI) were obtained. DRIs of robenidine were significantly increased in the presence of both EDTA and PMBN from 2- to 2048-fold. Robenidine exhibited antimicrobial activity against Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa, in the presence of sub-inhibitory concentrations of either EDTA or PMBN. Robenidine also demonstrated potent antibacterial activity against multidrug-resistant Gram-positive pathogens and all Gram-negative pathogens isolated from cases of canine otitis externa in the presence of EDTA. Robenidine did not demonstrate antibiofilm activity against Gram-positive and Gram-negative bacteria. EDTA facilitated biofilm biomass degradation for both Gram-positives and Gram-negatives. The addition of robenidine to EDTA was not associated with any change in the effect on biofilm biomass degradation. The combination of robenidine with EDTA or PMBN has potential for further exploration and pharmaceutical development, such as incorporation into topical and otic formulations for animal and human use.]]> Thu 10 Sep 2020 18:17:17 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:31422 E)-4-methylbenzylidene)hydrazinyl)pyrimidin-2-amine; NCL195) displays potent bactericidal activity against Streptococcus pneumoniae and Staphylococcus aureus by disrupting the cell membrane potential. NCL195 was less cytotoxic to mammalian cell lines than the parent compound, showed low metabolic degradation rates by human and mouse liver microsomes, and exhibited high plasma concentration and low plasma clearance rates in mice. NCL195 was bactericidal against Acinetobacter spp and Neisseria meningitidis and also demonstrated potent activity against A. baumannii, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae and Enterobacter spp. in the presence of sub-inhibitory concentrations of ethylenediaminetetraacetic acid (EDTA) and polymyxin B. These findings demonstrate that NCL195 represents a new chemical lead for further medicinal chemistry and pharmaceutical development to enhance potency, solubility and selectivity against serious bacterial pathogens.]]> Thu 09 Dec 2021 11:03:31 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:41781 (E)‐N′‐((E)‐1‐(4‐chlorophenyl)ethylidene)‐2‐(1‐(4‐chlorophenyl)ethylidene)hydrazine‐1‐carboximidhydrazide displays methicillin‐resistant Staphyoccoccus aureus (MRSA) and vancomycin‐resistant Enterococci (VRE) MICs of 2 μg mL⁻¹. Herein we describe the structure‐activity relationship development of a novel series of guanidine to 2‐aminopyrimidine isosteres that ameliorate the low levels of mammalian cytotoxicity in the lead compound while retaining good antibiotic activity. Removal of the 2‐NH₂ pyrimidine moiety renders these analogues inactive. Introduction of a central 2‐NH₂ triazine moiety saw a 10‐fold activity reduction. Phenyl to cyclohexyl isosteres were inactive. The 4‐BrPh and 4‐CH₃Ph with MIC values of 2 and 4 μg mL⁻¹, against MRSA and VRE respectively, are promising candidates for future development.]]> Thu 01 Sep 2022 12:33:12 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:44889 N′,2-bis((E)-4-chlorobenzylidene)hydrazine-1-carboximidhydrazide) and the introduction of imine alkyl substituents gave good antibiotic activity. Of note was the increased potency of two analogues against vancomycin-resistant Enterococci (VRE), one of which returned a MIC of 0.5 μg mL⁻¹. Five analogues were found to be equipotent or more potent than the lead 1. Introduction of an indole moiety resulted in the most active robenidine analogue against methicillin-resistant S. aureus (MRSA), with a MIC of 1.0 μg mL⁻¹. Imine C=NH isosteres (C=O/C=S) were inactive. Monomeric analogues were 16–64 μg mL⁻¹ active against MRSA and VRE. An analogue that lacks the terminal hydrazide NH moiety showed modest Gram-negative activity at 64 μg mL⁻¹. A 4-tert-butyl analogue was shown to be active against both Gram-positive and -negative strains at 16–64 μg mL⁻¹. In general, additional modifications with aromatic moieties was poorly tolerated, except with concomitant introduction of an imine C-alkyl group. The activity of these analogues against MRSA and VRE ranged from 8 μg mL−1 to inactive (MIC>128 μg mL⁻¹) with the naphthyl and indole analogues. Gram-negative activity was most promising with two compounds at 16 μg mL⁻¹ against E. coli. Against P. aeruginosa, the highest activity observed was with MIC values of 32 μg mL⁻¹ with another two analogues. Combined, these findings support the further development of the (E)-2-benzylidenehydrazine-1-carboximidamide scaffold as a promising scaffold for the development of antibiotics against Gram-positive and Gram-negative strains.]]> Mon 24 Oct 2022 14:46:25 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:50925 256 µg/mL. This resistance was completely reversed in the presence of the efflux pump inhibitor phenylalanine-arginine-beta-naphthylamide (PAβN) to yield MIC values of 8–16 µg/mL and 2–4 µg/mL for NCL259 and NCL256, respectively. When NCL259 and NCL265 were tested against wild-type E. coli isolate BW 25113 and its isogenic multidrug efflux pump subunit AcrB deletion mutant (∆AcrB), the MIC of both compounds against the mutant ∆AcrB isolate was reduced 16-fold compared to the wild-type parent, indicating a significant role for the AcrAB-TolC efflux pump from Enterobacterales in imparting resistance to these robenidine analogues. In vitro cytotoxicity testing revealed that NCL259 and NCL265 had much higher levels of toxicity to a range of human cell lines compared to the parent robenidine, thus precluding their further development as novel antibiotics against Gram-negative pathogens.]]> Fri 11 Aug 2023 15:54:32 AEST ]]>