Morpholine-modified Ru-based agents with multiple antibacterial mechanisms as metalloantibiotic candidates against Staphylococcus aureus infection.

Multidrug-resistant bacteria resulting from the abuse and overuse of antibiotics have become a huge crisis in global public health security. Therefore, it is urgently needed to develop new antibacterial drugs with unique mechanisms of action. As a versatile moiety, morpholine has been widely employed to enhance the potency of numerous bioactive molecules. In this study, a series of ruthenium-based antibacterial agents modified with the morpholine moiety were designed and characterized, aiming to obtain a promising metalloantibiotic with a multitarget mechanism. Antibacterial activity screening demonstrated that the most active complex Ru(ii)-3 exhibited the strongest potency against Staphylococcus aureus (S. aureus) with an MIC value of only 0.78 µg mL-1, which is better than most clinically used antibiotics. Notably, Ru(ii)-3 not only possessed excellent bactericidal efficacy, but could also overcome bacterial resistance. Importantly, Ru(ii)-3 very efficiently removed biofilms produced by bacteria, inhibited the secretion of bacterial exotoxins, and enhanced the activity of many existing antibiotics. The results of mechanism studies confirmed that Ru(ii)-3 could destroy the bacterial membrane and induce ROS production in bacteria. Furthermore, animal infection models confirmed that Ru(ii)-3 showed significant anti-infective activity in vivo. Overall, this work demonstrated that a morpholine-modified ruthenium-based agent is a promising antibiotic candidate in tackling the crisis of drug-resistant bacteria.

Evaluation of multi-target iridium(iii)-based metallodrugs in combating antimicrobial resistance and infections caused by Staphylococcus aureus.

The rapid emergence and spread of multidrug-resistant bacteria pose a serious challenge to human life and health, necessitating the development of novel antibacterial agents. Herein, to address this challenge, three iridium-based antibacterial agents were prepared and their antimicrobial activity were explored. Importantly, the three complexes all showed robust potency against S. aureus with MIC values in the range of 1.9-7.9 µg mL-1. Notably, the most active complex Ir3 also exhibited relative stability in mammalian fluids and a significant antibacterial effect on clinically isolated drug-resistant bacteria. Mechanism studies further demonstrated that the complex Ir3 can kill S. aureus by disrupting the integrity of the bacterial membrane and inducing ROS production. This multi-target advantage allows Ir3 to not only effectively combat bacterial resistance but also efficiently clear the bacterial biofilm. In addition, when used together, complex Ir3 could enhance the antibacterial potency of some clinical antibiotics against S. aureus. Moreover, both G. mellonella wax worms and mouse infection model demonstrated that Ir3 has low toxicity and robust anti-infective efficacy in vivo. Overall, complex Ir3 can serve as a new antibacterial agent for combating Gram-positive bacterial infections.

Design, synthesis, anti-infective potency and mechanism study of novel Ru-based complexes containing substituted adamantane as antibacterial agents.

Infections caused by Staphylococcus aureus (S. aureus) are increasing difficult to treat because this pathogen is easily resistant to antibiotics. However, the development of novel antibacterial agents with high antimicrobial activity and low frequency of resistance remains a huge challenge. Here, building on the coupling strategy, an adamantane moiety was linked to the membrane-active Ru-based structure and then developed three novel metalloantibiotics: [Ru(bpy)2(L)](PF6)2 (Ru1) (bpy = 2,2-bipyridine, L = amantadine modified ligand), [Ru(dmb)2(L)](PF6)2 (Ru2) (dmb = 4,4'-dimethyl-2,2'-bipyridine) and [Ru(dpa)2(L)](PF6)2 (Ru3), (dpa = 2,2'-dipyridylamine). Notably, complex Ru1 was identified to be the best candidate agent, showing greater efficacy against S. aureus than most of clinical antibiotics and low resistance frequencies. Mechanism studies demonstrated that Ru1 could not only increase the permeability of bacterial cell membrane and then caused the leakage of bacterial contents, but also promoted the production of reactive oxygen species (ROS) in bacteria. Importantly, complex Ru1 inhibited the biofilm formation, exotoxin secretion and increased the potency of some clinical used antibiotics. In addition, Ru1 showed low toxic in vivo and excellent anti-infective efficacy in two animal infection model. Thus, Ru-based metalloantibiotic bearing adamantane moiety are promising antibacterial agents, providing a certain research basis for the future antibiotics research.

Coupling a Virulence-Targeting Moiety with Ru-Based AMP Mimics Efficiently Improved Its Anti-Infective Potency and Therapeutic Index.

The surge of antibiotic resistance in Staphylococcus aureus calls for novel drugs that attack new targets. Developing antimicrobial peptides (AMPs) or antivirulence agents (AvAs) is a promising strategy to tackle this challenge. However, AMPs, which kill bacteria by disrupting cell membranes, suffer from low stability and high synthesis cost, while AvAs, which inhibit toxin secretion, have relatively poor bactericidal activity. Here, to address their respective shortcomings, we combined these two different antibacterial activities on the same molecular scaffold and developed a Ru-based metalloantibiotic, termed Ru1. Notably, Ru1 exerted remarkable bactericidal activity (MICS = 460 nM) and attenuated bacterial virulence as well. Mechanistic studies demonstrated that Ru1 had two independent targets: CcpA and bacterial membrane integrity. Based on its dual mechanism of action, Ru1 effectively overcame S. aureus resistance and showed high efficacy in a mouse infection model against S. aureus. This study provides a promising approach to confronting bacterial infections.

Simultaneous Determination of Seven Phenolic Acids, Two Flavonoids, and Tussilagone in Rat Plasma after Administration of Farfarae Flos Extract by LC-MS/MS.

A simple LC-MS/MS method was established for the simultaneous quantitative analysis of concentration of seven phenolic acids, two flavonoids, and tussilagone in biological samples. The lower limit of quantitation of each target compound was less than 10 ng·mL-1. The precision of these three types of compounds was less than 15%, and all accuracy was between 85.9% and 115%. The preliminary pharmacokinetics of these three types of compounds in plasma samples were carried out using LC-MS/MS after administration of Farfarae Flos extract (3.90 and 7.80 g·kg-1) to rats, respectively. The results showed that T max of all ten compounds varied from 0.21 ± 0.04 h to 0.69 ± 0.19 h. Maximum concentrations and area under concentration-time curves of seven analyzed phenolic acids were higher than those of the two flavonoids and tussilagone. Terminal elimination half-life of tussilagone was the shortest among these three types of compounds. The results showed that the developed LC-MS/MS method was suitable for clarifying the pharmacokinetic characteristics of these three types of compounds in plasma after administration of Farfarae Flos extract in rats.

Evaluation of Neuraminidase Inhibitory Activity of Compounds and Extracts from Traditional Medicines by HPLC-FLD.

A simple and effective method was established and validated to determine 4-methylumbelliferone (4-MU) for screening the natural neuraminidase inhibitors (NAIs) from traditional medicines (TMs) by high performance liquid chromatography combined with fluorescence detection (HPLC-FLD). 4-MU and TMs compounds were separated on a Hedera TM ODS column (5 µm, 4.6 × 250 mm) using an isocratic elution of 55% methanol at 35°C. The flow rate was 1 mL min-1. The excitation and emission wavelength were performed at 320 nm and 480 nm. Some extracts of TMs and compounds were selected as examples to demonstrate the feasibility of the new HPLC-FLD method. It was found that the results of most compounds except for the auto fluorescence substances determined by HPLC-FLD were in good agreement with NA enzyme-based inhibitory assays. Comparing to traditional NA enzyme-based inhibitory assays, the HPLC-FLD method could prevent interference from fluorescence pigments of compounds. It was considered a simple, effective, and economical technique for the screening the natural neuraminidase inhibitors from traditional medicines.