Naturally Derived Malabaricone B as a Promising Bactericidal Candidate Targeting Multidrug-Resistant Staphylococcus aureus also Possess Synergistic Interactions with Clinical Antibiotics.

The emergence of multidrug-resistant (MDR) superbugs underlines the urgent need for innovative treatment options to tackle resistant bacterial infections. The clinical efficacy of natural products directed our efforts towards developing new antibacterial leads from naturally abundant known chemical structures. The present study aimed to explore an unusual class of phenylacylphenols (malabaricones) from Myristicamalabarica as antibacterial agents. In vitro antibacterial activity was determined via broth microdilution, cell viability, time-kill kinetics, biofilm eradication, intracellular killing, and checkerboard assays. The efficacy was evaluated in vivo in murine neutropenic thigh and skin infection models. Confocal and SEM analyses were used for mechanistic studies. Among the tested isolates, malabaricone B (NS-7) demonstrated the best activity against S. aureus with a favorable selectivity index and concentration-dependent, rapid bactericidal killing kinetics. It displayed equal efficacy against MDR clinical isolates of S. aureus and Enterococci, efficiently clearing S. aureus in intracellular and biofilm tests, with no detectable resistance. In addition, NS-7 synergized with daptomycin and gentamicin. In vivo, NS-7 exhibited significant efficacy against S. aureus infection. Mechanistically, NS-7 damaged S. aureus membrane integrity, resulting in the release of extracellular ATP. The results indicated that NS-7 can act as a naturally derived bactericidal drug lead for anti-staphylococcal therapy.

Oxiconazole Potentiates Gentamicin against Gentamicin-Resistant Staphylococcus aureus In Vitro and In Vivo.

Amid the mounting burden of multidrug-resistant (MDR) bacterial infections on health care worldwide, drug repurposing, a time and cost-effective strategy to identify new applications for drugs approved for other indications, can effectively fill the void in the current antibiotic pipeline. In this study, we have repurposed a topical antifungal agent, oxiconazole, in combination with gentamicin against skin infections caused by multidrug-resistant Staphylococcus aureus. Oxiconazole was identified as having antibacterial activity against S. aureus via whole-cell screening assays against clinically relevant bacterial pathogens. It exhibited a potent in vitro profile, including equipotent activity against clinical drug-susceptible and -resistant S. aureus and Enterococcus spp. Checkerboard assays and time-kill kinetics studies demonstrated its concentration-dependent killing and ability to synergize with the approved antibiotics daptomycin and gentamicin against susceptible and MDR S. aureus strains. Oxiconazole also significantly eradicated preformed S. aureus biofilms in vitro. Eventually, in an assessment of its ability to generate resistant S. aureus mutants via serial passaging, oxiconazole displayed an extremely low propensity for developing stable resistance in S. aureus. Its in vivo efficacy alone and in combination with synergistic antibiotics was assessed in a murine superficial skin infection model of S. aureus, where it strongly synergized with gentamicin, exhibiting superior activity to the untreated control and drug-alone treatment groups. Thus, oxiconazole can be repurposed as an antibacterial alone and in combination with gentamicin against susceptible and gentamicin-resistant S. aureus infections. IMPORTANCE Staphylococcus aureus, which causes the majority of nosocomial and community-acquired infections globally, is a WHO high-priority pathogen for antibiotic research and development. In addition to invasive infections, it is the causative agent of moderate to severe skin infections, with an increasing prevalence of infections caused by MDR strains such as methicillin-resistant S. aureus (MRSA). Our study highlights the repurposing of oxiconazole, a topical antifungal agent, as an ideal candidate for combination therapy with gentamicin against susceptible and drug-resistant S. aureus skin infections due to its extremely low propensity for resistance generation in S. aureus, activity against MDR strains, bactericidal killing kinetics alone and in combination, broad antifungal efficacy, and excellent safety and tolerability profile.

Characterization and antimicrobial evaluation of anthraquinones and triterpenes from Rubia cordifolia.

Chemical investigation of roots of the plant, Rubia cordifolia Linn, led to the isolation of an undescribed anthraquinone, cordifoquinone R, determined as 1,2-dihydroxy-6-methoxyanthracene-9,10-dione (6) based on the 1D and 2D NMR analyses and HRESIMS. Ten other known compounds viz.1,4-dihydroxy-2-methoxyanthracene-9,10-dione (1), rubiadin (2), xanthopurpurin (3), 1-methoxy-3-hydroxy-2-carbomethoxy-9,10-anthraquinone (4), alizarin (5), ß-sitosterol glucoside (7), scopoletin (8), oleanolic acid, (9), pomolic acid (10), queretaroic acid (11) were also isolated. Out of these compounds, 4, 10, and 11 are first reported from this plant species. Compounds 2, 3, 6, 7, and 10 showed activity in the range of 16-32 µg/ml against S. aureus ATCC 29213.

Heterocyclic Diaryliodonium-Based Inhibitors of Carbapenem-Resistant Acinetobacter baumannii.

Finding new therapeutic strategies against Gram-negative pathogens such as Acinetobacter baumannii is challenging. Starting from diphenyleneiodonium (dPI) salts, which are moderate Gram-positive antibacterials, we synthesized a focused heterocyclic library and found a potent inhibitor of patient-derived multidrug-resistant Acinetobacter baumannii strains that significantly reduced bacterial burden in an animal model of infection caused by carbapenem-resistant Acinetobacter baumannii (CRAB), listed as a priority 1 critical pathogen by the World Health Organization. Next, using advanced chemoproteomics platforms and activity-based protein profiling (ABPP), we identified and biochemically validated betaine aldehyde dehydrogenase (BetB), an enzyme that is involved in the metabolism and maintenance of osmolarity, as a potential target for this compound. Together, using a new class of heterocyclic iodonium salts, a potent CRAB inhibitor was identified, and our study lays the foundation for the identification of new druggable targets against this critical pathogen. IMPORTANCE Discovery of novel antibiotics targeting multidrug-resistant (MDR) pathogens such as A. baumannii is an urgent, unmet medical need. Our work has highlighted the potential of this unique scaffold to annihilate MDR A. baumannii alone and in combination with amikacin both in vitro and in animals, that too without inducing resistance. Further in depth analysis identified central metabolism to be a putative target. Taken together, these experiments lay down the foundation for effective management of infections caused due to highly MDR pathogens.

Antimicrobial efficacy of a hemilabile Pt(II)-NHC compound against drug-resistant S. aureus and Enterococcus.

Three platinum(II)-N-heterocyclic carbene (NHC) compounds [Pt(L1)Cl](PF6) (1), [Pt(L2)(COD)](PF6)2 (2) and [Pt(L2)Cl2] (3) were synthesized bearing pyridyl-functionalized butenyl-tethered (L1H) and n-butyl tethered (L2H) NHC ligands, and their antibacterial activity against clinically relevant human pathogens was evaluated. Complex 1 was designed to have one of its metal coordination sites masked with a hemilabile butenyl group. The antibacterial activity spectrum against the ESKAPE panel of pathogens shows superior activity of 1 compared to 2 and 3 against the Gram-positive S. aureus pathogen. Complex 1 showed equipotent activity against clinical drug-resistant S. aureus and Enterococcus isolates. Furthermore, 1 demonstrated concentration-dependent bactericidal activity with a long post-antibiotic effect, eradicated preformed S. aureus biofilm and synergized with gentamicin and minocycline for combinatorial antimicrobial therapy. Under in vivo conditions, 1 displayed potent activity in reducing bacterial load in a murine thigh infection model, similar to vancomycin, albeit at 2.5× less dosage. An array of experiments reveals key characteristics for the hemilabile complex 1 as a potential anti-staphylococcal drug.

Developing the Natural Prenylflavone Artocarpin from Artocarpus hirsutus as a Potential Lead Targeting Pathogenic, Multidrug-Resistant Staphylococcus aureus, Persisters and Biofilms with No Detectable Resistance.

The genus Artocarpus, a nutraceutical, is widely used in traditional medicine for treatment of many chronic diseases including infections. Artocarpus hirsutus Lam., an evergreen tree endogenous to the Western Ghats of India, is a well-documented medicinal plant in Hortus Malabaricus, the oldest comprehensive printed book on the natural plant wealth of Asia. Herein we describe artocarpin, a major isoprenyl flavonoid isolated from the stem bark of A. hirsutus Lam., as the explanation behind the indigenous knowledge reported for treatment of various skin ailments. Artocarpin, a noncytotoxic, isoprenyl flavonoid, is rapidly bactericidal against multiple World Health Organization (WHO) priority 2 pathogens including multidrug-resistant Staphylococcus aureus and Enterococcus sp. with an extended postantibiotic effect. Artocarpin (AH-5) synergizes with gentamicin and linezolid, inhibits bacteria in different physiological states, including under biofilm and in macrophages, and does not induce resistance in S. aureus despite repeated exposure. Artocarpin induces rapid cellular lysis, as confirmed by fluorescence microscopy and scanning electron microscopy analysis as well as by measuring the significantly increased extracellular and concomitantly decreased intracellular adenosine triphosphate levels. When tested in vivo, AH-5 is almost as effective as vancomycin in reducing bacterial load in murine thigh and skin infection models, which is comparable to standard of care (SoC) antibiotics. This is highly significant since AH-5 is a direct natural entity that has been evaluated without any pharmaceutical modification and expresses robust in vitro and in vivo antibacterial activity, which is comparable to highly optimized SoC comparators and further could be considered as an effective clinical, antibacterial drug lead.

Pyrvinium pamoate potentiates levofloxacin against levofloxacin-resistant Staphylococcus aureus.

Background: Drug repurposing is a viable approach to expediting the tedious conventional drug discovery process, given rapidly increasing bacterial resistance. In this context, we have repurposed pyrvinium pamoate (PP) for its antibacterial activity against Staphylococcus aureus. Methods: US FDA-approved non-antibiotics were screened against clinically relevant bacterial pathogens to identify antibacterials. The hits were further evaluated utilizing a variety of preclinical parameters, following which in vivo efficacy was estimated in isolation and in combination in a murine neutropenic thigh infection model. Result: The screening identified PP exhibiting potent activity against S. aureus along with concentration-dependent killing. PP also showed a post-antibiotic effect of >22 h and significantly eradicated preformed S. aureus biofilms and intracellular S. aureus at 1× and 5× MIC, respectively. PP synergized with levofloxacin both in vitro and in vivo, resulting in ∼1.5 and ∼0.5 log10 CFU/g reduction against susceptible and resistant S. aureus infections, respectively, as compared with untreated control. Conclusion: Pyrvinium potentiates levofloxacin against levofloxacin-resistant S. aureus.

Treatment of drug-resistant bacterial infections urgently requires novel antibiotic combinations that can help in reducing the dose of antibiotic required as well as decreasing the emergence of resistance. In this context, pyrvinium pamoate is active as an antibacterial against clinically drug-resistant Staphylococcus aureus and combines well with levofloxacin against levofloxacin-resistant S. aureus. Given the paucity of available treatments for multidrug-resistant S. aureus, this is a very welcome new addition to the antibiotic arsenal.

Nitazoxanide potentiates linezolid against linezolid-resistant Staphylococcus aureus in vitro and in vivo.

BACKGROUND: Antimicrobial resistance is a growing menace, claiming millions of lives all over the world. In this context, drug repurposing is one approach gaining interest as a suitable alternative to conventional drug discovery and development. METHODS: Whole-cell assays were used to screen FDA-approved drugs to identify novel antimicrobial agents active against bacterial pathogens. Following identification of nitazoxanide, its various characteristics, such as antimicrobial activity against MDR isolates, time-kill kinetics, ability to synergize with approved drugs, antibiofilm activity and ability to generate resistance in Staphylococcus aureus, were determined, followed by determination of its in vivo potential against MDR S. aureus. RESULTS: Nitazoxanide demonstrated a potent in vitro antistaphylococcal profile, including equipotent activity against clinical drug-resistant S. aureus and Enterococcus spp. Nitazoxanide exhibited concentration-dependent killing, significantly eradicated preformed S. aureus biofilm and S. aureus did not generate resistance to it. Nitazoxanide strongly synergized with linezolid both in vitro and in vivo against linezolid-susceptible and -resistant S. aureus, displaying superior activity to untreated control and drug-alone treatment groups. CONCLUSIONS: Nitazoxanide can be utilized in combination with linezolid against infections caused by linezolid-resistant S. aureus as it exhibits strong synergism in vitro and in vivo.

Cudraflavone C from Artocarpus hirsutus as a Promising Inhibitor of Pathogenic, Multidrug-Resistant S. aureus, Persisters, and Biofilms: A New Insight into a Rational Explanation of Traditional Wisdom.

Artocarpus hirsutus Lam., or wild jack, a perennial tree of the Western Ghats of peninsular India, serves as a rich source of flavonoids. The indigenous knowledge of this multipurpose flora chronicles the efficient property of its bark as a natural treatment for various skin infections. Herein, we describe a rational explanation of this traditional knowledge via a broader evaluation of inhibitory activity of one of its phytoconstituents, cudraflavone C (Cud C), a prenyl flavone isolated from stem bark against diverse multidrug-resistant Staphylococcus aureus along with decidedly potent synergy combinations with a standard drug, gentamycin, especially against gentamycin-resistant S. aureus NRS 10119. Cud C exhibited equipotent MIC (4 µg/mL) against a varied array of MDR strains comprising MRSA, VRSA, and VRE and was nontoxic toward eukaryotic cells with a sizable selectivity index (SI 25-50). Cud C displayed concentration-dependent bactericidal activity against planktonic cells, an excellent biofilm disruption property exceeding that of levofloxacin and vancomycin against preformed S. aureus biofilm, and an enhanced capability to kill intracellular S. aureus more potently than vancomycin, thus exemplifying its position as an antibacterial lead candidate. In addition, S. aureus was unable to generate resistance to Cud C even after exposure for more than 40 days, whereas it generated resistance to levofloxacin within ∼20 days of exposure. Therefore, the naturally occurring prenylflavone Cud C can be accounted for as one of the reasons for the reported antibacterial properties of the bark of A. hirsutus. Taken together, detailed biological studies propose that Cud C can be considered as an effective antibacterial drug candidate against MDR S. aureus, which is fast becoming a significant threat to public health worldwide.

Synthesis and structure-activity relationship of new chalcone linked 5-phenyl-3-isoxazolecarboxylic acid methyl esters potentially active against drug resistant Mycobacterium tuberculosis.

In search of novel therapeutic agents active against emerging drug-resistant Mycobacterium tuberculosis and to counter the long treatment protocol of existing drugs, herein we present synthesis and biological evaluation of a new series of 5-phenyl-3-isoxazolecarboxylic acid methyl ester-chalcone hybrids. Among 35 synthesized compounds, 32 analogues displayed potent in-vitro activity against Mycobacterium tuberculosis H37Rv with MIC 0.12-16 µg/mL. Cell viability test against Vero cells indicated 29 compounds to be non-cytotoxic (CC50 > 20 µg/mL & SI > 10). Most potent compounds with MIC 0.12 µg/mL (7 b, 7j, 7 ab) exhibited selectivity index (SI) in excess of 320. Further studies on activity against drug-resistant Mycobacterium tuberculosis revealed 7j as the most potent compound with MIC 0.03-0.5 µg/mL. Time-kill kinetic study suggested compound 7j displaying concentration-dependent bactericidal killing activity with relatively comparable potency to that of current first-line anti-TB drugs. Taken together, 7j presents a novel hit with potential to be translated into a potent antimycobacterial.

Synthesis and evaluation of new quinazoline-benzimidazole hybrids as potent anti-microbial agents against multidrug resistant Staphylococcus aureus and Mycobacterium tuberculosis.

Owing to the rapid rise in antibiotic resistance, infectious diseases have become serious threat to public health. There is an urgent need to develop new antimicrobial agents with diverse chemical structures and novel mechanisms of action to overcome the resistance. In recent years, Quinazoline-benzimidazole hybrids have emerged as a new class of antimicrobial agents active against S. aureus and M. tuberculosis. In the current study, we designed and synthesized fifteen new Quinazoline-benzimidazole hybrids and evaluated them for their antimicrobial activity against S. aureus ATCC 29213 and M. tuberculosis H37Rv. These studies led to the identification of nine potent antibacterial agents 8a, 8b, 8c, 8d, 8f, 8g, 8h, 8i and 10c with MICs in the range of 4-64 µg/mL. Further, these selected compounds were found to possess potent antibacterial potential against a panel of drug-resistant clinical isolates which include methicillin and vancomycin-resistant S. aureus. The selected compounds were found to be less toxic to Vero cells (CC50 = 40-≥200 µg/mL) and demonstrated a favourable selectivity index. Based on the encouraging results obtained these new benzimidazol-2-yl quinazoline derivatives have emerged as promising antimicrobial agents for the treatment of MDR- S. aureus and Mycobacterial infections.

Design, synthesis, in silico, and in vitro evaluation of 3-phenylpyrazole acetamide derivatives as antimycobacterial agents.

Mycobacterium tuberculosis (Mtb) is one of the most dangerous pathogens affecting immunocompetent and immunocompromised patients worldwide. Novel molecules, which are efficient and can reduce the duration of therapy against drug-resistant strains, are an urgent unmet need of the hour. In our current study, a series of new 2-(3-phenyl-1H-pyrazol-1-yl)acetamide and N'-benzylidene-2-(3-phenyl-1H-pyrazol-1-yl)acetohydrazide derivatives were designed, synthesized, and evaluated for their antimycobacterial potential. The biological evaluation revealed that 6b, 6m, 6l, 7a, and 7k exhibited selective and potent inhibitory activity against Mtb. Furthermore, compounds 6m and 7h were found to be nontoxic to Vero cells with CC50 of greater than 20 and 80 mg/ml, respectively, and exhibited promising selectivity indices (SI) of greater than 666 and 320, respectively. All derivatives exhibited excellent ADME (absorption, distribution, metabolism, and excretion) properties in silico. Also, all the derivatives were found compliant with Lipinski's rule of five, showing their druggability profile. Molecular docking insights of these derivatives have shown outstanding binding energies on the mycobacterial membrane protein large transporters. These results indicate that this scaffold may lead to a potential antimycobacterial drug candidate in the discovery of antitubercular agents.

Synthesis of novel 4,5-dihydropyrrolo[1,2-a]quinoxalines, pyrrolo[1,2-a]quinoxalin]-2-ones and their antituberculosis and anticancer activity.

A facile strategy was developed for the synthesis of biologically important 4,5-dihydropyrrolo[1,2-a]quinoxalines and pyrrolo[1,2-a]quinoxalin]-2-ones by treating 2-(1H-pyrrol-1-yl)anilines with imidazo[1,2-a]pyridine-3-carbaldehyde or isatin, using amidosulfonic acid (NH3 SO3 ) as a solid catalyst in water at room temperature. The protocol has been extended to electrophile ninhydrin. The catalyst could be recycled for six times without the loss of activity. The compounds were evaluated for their antituberculosis, antibacterial, and anticancer activities. It is worth noting that compounds 3d and 3e demonstrated a minimum inhibitory concentration value of 6.25 µM against Mycobacterium tuberculosis H37Rv, whereas compounds 3d, 3g, 5d, 5e, and 5i showed a remarkable inhibition of A549, DU145, HeLa, HepG2, MCF-7, and B16-F10 cell lines, respectively. Staphylococcus aureus was inhibited by compounds 5b, 5e, 5d, 5g, and 5l at 32 µg/ml.

Peptide Nanostructure-Mediated Antibiotic Delivery by Exploiting H2S-Rich Environment in Clinically Relevant Bacterial Cultures.

Stimuli-responsive self-destructing soft structures serve as versatile hosts for the encapsulation of guest molecules. A new paradigm for H2S-responsive structures, based on a modified tripeptide construct, is presented along with microscopy evidence of its time-dependent rupture. As a medicinally interesting application, we employed these commercial antibiotic-loaded soft structures for successful drug release and inhibition of clinically relevant, drug-susceptible, and methicillin-resistant Staphylococcus aureus.

Vancomycin Derivative Inactivates Carbapenem-Resistant Acinetobacter baumannii and Induces Autophagy.

Vancomycin is a standard drug for the treatment of multidrug-resistant Gram-positive bacterial infections. Albeit, development of resistance (VRE, VRSA) and its inefficacy against persistent infections is a demerit. It is also intrinsically inactive against Gram-negative bacteria. Herein, we report a vancomycin derivative, VanQAmC10, that addresses these challenges. VanQAmC10 was rapidly bactericidal against carbapenem-resistant A. baumannii (6 log10 CFU/mL reduction in 6 h), disrupted A. baumannii biofilms, and eradicated their stationary phase cells. In MRSA infected macrophages, the compound reduced the bacterial burden by 1.3 log10 CFU/mL while vancomycin exhibited a static effect. Further investigation indicated that the compound, unlike vancomycin, promoted the intracellular degradative mechanism, autophagy, in mammalian cells, which may have contributed to its intracellular activity. The findings of the work provide new perspectives on the field of glycopeptide antibiotics.

Copper mediated one-pot synthesis of quinazolinones and exploration of piperazine linked quinazoline derivatives as anti-mycobacterial agents.

A facile method was developed for the synthesis of quinazolinone derivatives in a one-pot condensation reaction via in situ amine generation using ammonia as the amine source and with the formation of four new C-N bonds in good to excellent yields. With the optimised method, we synthesized a library of piperazine linked quinazoline derivatives and the synthesized compounds were evaluated for their inhibitory activity against Mycobacterium tuberculosis. The compounds 8b, 8e, 8f, 8m, 8n and 8v showed potent anti-mycobacterial activity with MIC values of 2-16 µg mL-1. All the synthesized compounds follow Lipinski's rules for drug likeness.

A novel molecular scaffold resensitizes multidrug-resistant S. aureus to fluoroquinolones.

Nosocomial infections arising from opportunistic pathogens, such as Staphylococcus aureus, are growing unabated, compounded by the rapid emergence of antimicrobial resistance. Herein, we demonstrate a new molecular design that exhibits excellent activity against multidrug-resistant S. aureus with no cytotoxicity and resensitizes fluoroquinolones (FQ) towards FQ-resistant methicillin-resistant S. aureus strains, with DNA gyrase B as the likely molecular target as determined by molecular dynamics (MD) simulations.

Synthesis and biological evaluation of 2,4,5-trisubstituted thiazoles as antituberculosis agents effective against drug-resistant tuberculosis.

The dormant and resistant form of Mycobacterium tuberculosis presents a challenge in developing new anti-tubercular drugs. Herein, we report the synthesis and evaluation of trisubstituted thiazoles as antituberculosis agents. The SAR study has identified a requirement of hydrophobic substituent at C2, ester functionality at C4, and various groups with hydrogen bond acceptor character at C5 of thiazole scaffold. This has led to the identification of 13h and 13p as lead compounds. These compounds inhibited the dormant Mycobacterium tuberculosis H37Ra strain and M. tuberculosis H37Rv selectively. Importantly, 13h and 13p were non-toxic to CHO cells. The 13p showed activity against multidrug-resistant tuberculosis isolates.