7-Hydroxy-(E)-3-phenylmethylene-chroman-4-one analogues as efflux pump inhibitors against Mycobacterium smegmatis mc² 155

Prevention and potential remedies for antibiotic resistance: current research and future prospects

The increasing threat of antibiotic resistance and shrinking treatment options for infections have pushed mankind into a difficult position. The looming threat of the return of the pre-antibiotic era has caused a sense of urgency to protect and conserve the potency of antibiotic therapy. One of the perverse effects of antibiotic resistance is the dissemination of its causative agents from non-clinically important strains to clinically important strains and vice versa. The popular saying "Prevention is better than cure" is appropriate for tackling antibiotic resistance. On the one hand, new and effective antibiotics are required; on the other hand, better measures for the use of antibiotics, along with increased awareness in the general public related to antibiotic use, are essential. Awareness, especially of appropriate antibiotic use, antibiotic resistance, its dissemination, and potential threats, can help greatly in controlling the use and abuse of antibiotics, and the containment of antibiotic resistance. Antibiotic drugs' effectiveness can be enhanced by producing novel antibiotic analogs or adding adjuvants to current antibiotics. Combinatorial therapy of antibiotics has proven successful in treating multidrug-resistant (MDR) bacterial infections. This review aims to highlight the current global situation of antibiotic resistance and discuss the methods used to monitor, prevent, inhibit, or reverse bacterial resistance mechanisms in the fight against antibiotic resistance.

Synthesis and evaluation of a new class of MIF-inhibitors in activated macrophage cells and in experimental septic shock in mice

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine with enzymatic activities. Anti-inflammatory effects of MIF enzyme inhibitors indicate a link between its cytokine- and catalytic activities. Herein the synthesis, docking, and bioactivity of substituted benzylidene-1-indanone and -1-tetralone derivatives as MIF-tautomerase inhibitors is reported. Many of these substituted benzylidene-1-tetralones and -indan-1-ones were potent MIF-tautomerase inhibitors (IC₅₀ < 10 μmol/L), and the most potent inhibitors were the 1-indanone derivatives 16 and 20. Some of these compounds acted as selective enolase or ketonase inhibitors. In addition, compounds 16, 20, 26, 37 and 61 efficiently inhibited NO, TNFα and IL-6 production in lipopolysaccharide-induced macrophages. Compound 20, 37 and 61 also inhibited ROS generation, and compound 26 and 37 abolished activation of NF-κB. Compound 37 significantly augmented hypothermia induced by high dose of lipopolysaccharide in mice. The possible mechanisms of action were explored using molecular modelling and docking, as well as molecular dynamics simulations.

Computational analysis and in vitro evaluation of TMF 104, for its antioxidant, antimicrobial, and anticancer efficacies

Benzylidene chromanones are small molecules, structurally similar to active phytochemicals. Herein, we report one novel benzylidene chromanone, TMF 104, for its bio-efficacies. Its computational docking for Vanin-1, antioxidant, free radical scavenging capacities, antimicrobial effects, and anticancer efficacy were analyzed. TMF 104 predicated strong binging to Vanin-1 protein with a docking energy of -8.1 kcal/mol. The compound dose-dependently exhibited free-radical scavenging and antioxidant activities when tested in vitro. The compound also had remarkable activity against Salmonella typhimurium, Enterococcus faecalis, Staphylococcus aureus, and Escherichia coli with minimum inhibitory concentration values of 1.5, 2.0, 12.5, and 13.5 μg/ml, respectively. The compound was also effective against Bacillus cereus and Pseudomonas aeruginosa albeit at higher concentrations. TMF 104 dose-dependently inhibited the proliferation of MCF-7, NCI H460, and Caki-1 cells with respective GI₅₀ values of 24.51, 21.95, and 32.95 μg/ml, whereas the compound was toxic to normal Vero cells at much higher concentration of 264.70 μg/ml. The compound also aided in apoptosis and increased the sub G₀ /G₁ phase of the cell cycle in all three cancer cells tested. Our study identified a novel, potent benzylidene analogue with potent antioxidant, antimicrobial, and anticancer activities, which drives further attention for further research.

Antimycobacterial Compound of Cynoglossum lanceolatum Forsk.: Bioassay Guided Isolation, Molecular Docking, Synthesis of Analogs, and a Plausible Mechanism of Action

Tuberculosis (TB) remains a major threat to human health. Due to the prevalence of drug-resistant Mycobacterium tuberculosis (Mtb), it is urgent to discover drugs with new mechanisms of action (MOA) to ensure effectiveness against strains that are resistant to existing TB drugs. Cynoglossum lanceolatum Forsk was used to treat TB in Traditional Chinese Medicine. In this article, shikonin, the anti-Mtb active component, was obtained from the whole herb extract of C. lanceolatum by bioassay-guided isolation. Using the microplate alamar blue assay (MABA), the minimum inhibitory concentration (MIC) of shikonin against Mtb was determined to be 128 μg/mL. In order to obtain a more efficient anti-Mtb molecule, (E)-1-(6-bromo-2,3-dihydrochromen-4-ylidene)thiosemicarbazide was synthesized based on the scaffold of shikonin, which exhibited potent activity against Mtb (MIC=4 μg/mL). These results highlight that both naphthalene-1,4-dione and chroman-4-one are pharmacophores with activities against Mtb. To investigate a plausible mechanism of action, the molecular docking was firstly performed against catalase-peroxidase enzyme (KatG) of Mtb using AutoDock 4 software. The results demonstrated that both shikonin and (E)-1-(6-bromo-2,3-dihydrochromen-4-ylidene)thiosemicarbazide could bind to the active site of Mtb KatG. KatG enzyme activity and intracellular reactive oxygen species (ROS) levels in Mtb cells were then measured by ultraviolet spectrophotometric method and fluorescence microplate reader assay, respectively. The experiments confirmed that above compounds could inhibit the catalytic activity of Mtb KatG, and cause the ROS accumulation in Mtb cells. Therefore, inhibition of KatG may be a novel mechanism of action for these two compounds to fight against Mtb.

Synthesis, Conformational Analysis and ctDNA Binding Studies of Flavonoid Analogues Possessing the 3,5-di-tert-butyl-4-hydroxyphenyl Moiety

Flavanones and their biochemical precursors, chalcones, are naturally occurring compounds and consist of privileged scaffolds used in drug discovery due to their wide range of biological activities. In this work, two novel flavanones (3 and 4), the arylidene flavanone 5, and the chalcone 6, displaying structural analogies with butylated hydroxytoluene (BHT), were synthesized via an aldol reaction. According to the antioxidant activity studies of the synthesized flavanones, the arylidene flavanone 5 was the most potent antioxidant (70.8% interaction with DPPH radical and 77.4% inhibition of lipid peroxidation). In addition, the ability of the synthesized compounds to bind with ctDNA was measured via UV-spectroscopy, revealing that chalcone 6 has the strongest interaction with DNA (Kb = 5.0 × 10−3 M−1), while molecular docking was exploited to simulate the compound-DNA complexes. In an effort to explore the conformational features of the novel synthetic flavanones (3 and 4), arylidene flavanone 5, and chalcone 6, theoretical calculations were applied and the calculation of their physicochemical properties was also performed.

What Approaches to Thwart Bacterial Efflux Pumps-Mediated Resistance?

An effective response that combines prevention and treatment is still the most anticipated solution to the increasing incidence of antimicrobial resistance (AMR). As the phenomenon continues to evolve, AMR is driving an escalation of hard-to-treat infections and mortality rates. Over the years, bacteria have devised a variety of survival tactics to outwit the antibiotic’s effects, yet given their great adaptability, unexpected mechanisms are still to be discovered. Over-expression of efflux pumps (EPs) constitutes the leading strategy of bacterial resistance, and it is also a primary driver in the establishment of multidrug resistance (MDR). Extensive efforts are being made to develop antibiotic resistance breakers (ARBs) with the ultimate goal of re-sensitizing bacteria to medications to which they have become unresponsive. EP inhibitors (EPIs) appear to be the principal group of ARBs used to impair the efflux system machinery. Due to the high toxicity of synthetic EPIs, there is a growing interest in natural, safe, and innocuous ones, whereby plant extracts emerge to be excellent candidates. Besides EPIs, further alternatives are being explored including the development of nanoparticle carriers, biologics, and phage therapy, among others. What roles do EPs play in the occurrence of MDR? What weapons do we have to thwart EP-mediated resistance? What are the obstacles to their development? These are some of the core questions addressed in the present review.

Chromanone-A Prerogative Therapeutic Scaffold: An Overview

Chromanone or Chroman-4-one is the most important and interesting heterobicyclic compound and acts as a building block in medicinal chemistry for isolation, designing and synthesis of novel lead compounds. Structurally, absence of a double bond in chromanone between C-2 and C-3 shows a minor difference from chromone but exhibits significant variations in biological activities. In the present review, various studies published on synthesis, pharmacological evaluation on chroman-4-one analogues are addressed to signify the importance of chromanone as a versatile scaffold exhibiting a wide range of pharmacological activities. But, due to poor yield in the case of chemical synthesis and expensive isolation procedure from natural compounds, more studies are required to provide the most effective and cost-effective methods to synthesize novel chromanone analogs to give leads to chemistry community. Considering the versatility of chromanone, this review is designed to impart comprehensive, critical and authoritative information about chromanone template in drug designing and development.

Structure activity evaluation and computational analysis identify potent, novel 3-benzylidene chroman-4-one analogs with anti-fungal, anti-oxidant, and anti-cancer activities

SIGNIFICANCE

3-Benzylidene chroman-4-ones share close homology with naturally occurring bioactive compounds.

OBJECTIVES

This study evaluated the antifungal, antioxidant, and anticancer activities of novel 3-benzylidene chromanone analogs with respect to their structure-activity relationships.

METHODS

Compounds 45e-64e were synthesized inhouse. Aspergillus niger (MTCC 1344) Aspergillus flavus and Botrytis cinerea were the fungal strains tested. Computational docking analysis was carried out for vanin-1, estrogen receptor (ER), and Akt proteins using Auto-dock vina. Free radical scavenging and total antioxidant capacity was analyzed using spectrophotometric methods. MCF-7 (breast cancer) cell line was used for anticancer assays. Flow cytometry was used to detect cell cycle and apoptosis.

RESULTS

Out of the twenty compounds screened, compounds 47e, 50e, 52e, 57e, and 61e that possessed either methoxy and ethoxy/methyl/isopropyl group exhibited very good activity against all fungi. Compounds possessing methoxy group alone showed moderate activity and compounds devoid of methoxy, and ethoxy groups did not show any activity. When computationally analyzed against target proteins for antioxidant properties, the compounds exhibited excellent binging efficacy to vanin-1 and ERs. These predictions were translated in the in vitro free-radical scavenging and antioxidant assays. The compounds exhibited anti-proliferative efficacy in breast cancer cell line, increased the sub-G₀/G₁ cell cycle populations and total apoptosis in MCF-7 cells. Additionally, the compounds also depicted excelling binging energy when computationally analyzed for Akt enzyme binding.

CONCLUSION

In summary, our study identified potential analogs of 3-benzylidene chroman-4-one molecules with excellent anti-fungal, anti-oxidant, and anticancer activities which demand further research for drug developments.

Potential of 1-(1-napthylmethyl)-piperazine, an efflux pump inhibitor against cadmium-induced multidrug resistance in Salmonella enterica serovar Typhi as an adjunct to antibiotics

This study was focused on elucidating inhibition of antibiotic efflux mechanism of cadmium adapted (CdA) Salmonella Typhi Ty2 cells. Herein, upregulated expression of efflux genes (acrB, tolC) and their regulators (soxS, marA) was observed in CdA Ty2 cells by qRT-PCR. The pathogen further elevated the expression of these genes even in the presence of three efflux pump inhibitors (EPIs), i.e., Phe-Arg-β-naphthylamide, 1-(1-naphthyl-methyl)piperazine, and 5-hydroxy-2-methyl-1,4-naphthoquinone, perhaps by sensing the pressure of the latter in addition to cadmium stress. Interaction of different EPIs with efflux pumps of CdA Ty2 cells was confirmed using ethidium bromide (EtBr) accumulation and efflux assay. All the EPIs could cause retention of EtBr which was indicated by increased fluorescence units. Considering this potential of EPIs, retention of antibiotics was evaluated in CdA Ty2 cells wherein EPIs were used in combination with selected antibiotics (instead of EtBr). A decrease in the effective concentration of antibiotics was observed. This was further validated using the clinical isolates. The data revealed the efficiency of EPIs as they could inhibit the efflux potential of even the overexpressed efflux pumps. Thus, combination of EPI(s)-antibiotics may be exploited in future as one of the strategies for combating metal induced antibiotic resistance.

Efficacy and Mechanisms of Flavonoids against the Emerging Opportunistic Nontuberculous Mycobacteria

Nontuberculous mycobacteria (NTM) are the causative agent of severe chronic pulmonary diseases and is accountable for post-traumatic wound infections, lymphadenitis, endometritis, cutaneous, eye infections and disseminated diseases. These infections are extremely challenging to treat due to multidrug resistance, which encompasses the classical and existing antituberculosis agents. Hence, current studies are aimed to appraise the antimycobacterial activity of flavonoids against NTM, their capacity to synergize with pharmacological agents and their ability to block virulence. Flavonoids have potential antimycobacterial effects at minor quantities by themselves or in synergistic combinations. A cocktail of flavonoids used with existing antimycobacterial agents is a strategy to lessen side effects. The present review focuses on recent studies on naturally occurring flavonoids and their antimycobacterial effects, underlying mechanisms and synergistic effects in a cocktail with traditional agents.

Antibiotic resistance breakers: current approaches and future directions

Infections of antibiotic-resistant pathogens pose an ever-increasing threat to mankind. The investigation of novel approaches for tackling the antimicrobial resistance crisis must be part of any global response to this problem if an untimely reversion to the pre-penicillin era of medicine is to be avoided. One such promising avenue of research involves so-called antibiotic resistance breakers (ARBs), capable of re-sensitising resistant bacteria to antibiotics. Although some ARBs have previously been employed in the clinical setting, such as the β-lactam inhibitors, we posit that the broader field of ARB research can yet yield a greater diversity of more effective therapeutic agents than have been previously achieved. This review introduces the area of ARB research, summarises the current state of ARB development with emphasis on the various major classes of ARBs currently being investigated and their modes of action, and offers a perspective on the future direction of the field.

In silico fight against novel coronavirus by finding chromone derivatives as inhibitor of coronavirus main proteases enzyme

Novel coronavirus, 2019-nCoV is a danger to the world and is spreading rapidly. Very little structural information about 2019-nCoV make this situation more difficult for drug designing. Benzylidenechromanones, naturally occurring oxygen heterocyclic compounds, having capability to inhibit various protein and receptors, have been designed here to block mutant variety of coronavirus main protease enzyme (SARC-CoV-2 Mpro) isolated from 2019-nCoV with the assistance of molecular docking, bioinformatics and molecular electrostatic potential. (Z)-3-(4'-chlorobenzylidene)-thiochroman-4-one showed highest binding affinity to the protein. Binding of a compound to this protein actually inhibits the replication and transcription of the virus and, ultimately, stop the virus multiplication. Incorporation of any functional groups to the basic benzylidenechromanones enhances their binding ability. Chloro and bromo substitutions amplify the binding affinity. ADME studies of all these compounds indicate they are lipophilic, high gastro intestine absorbable and blood-brain barrier permeable. The outcome reveals that the investigated benzylidenechromanones can be examined in the case of 2019-nCoV as potent inhibitory drug of SARC-CoV-2 Mpro, for their strong inhibition ability, high reactivity and effective pharmacological properties.

The Roles of Flavonols/Flavonoids in Neurodegeneration and Neuroinflammation

The inflammatory process in the human body is a physiological response involving many cellular types and mediators. It results in scar formation to separate the damaged area from the surrounding healthy tissue. Because of increased blood-brain barrier permeability following inflammation, leukocytes infiltrate the CNS and are also supplemented by proinflammatory mediators. However, an acute inflammatory process after cerebral trauma or stroke may also result in a prolonged lesion formation, leading to a severe neuronal loss. The prolonged inflammatory process in the CNS may cause serious damage to the neuronal system. It may lead to CNS damage in such a way that endangers functional integration and proinflammatory system balance. Effects of different flavonoid species on ischemia-reperfusion injury and cognition and function have also been shown in experimental studies. Flavonoids are presented broadly in plants and diets. They are believed to have various bioactive effects including anti-viral, anti-inflammatory, cardioprotective, anti-diabetic, anti-cancer, anti-aging, etc. Quercetine is the predominant dietary flavonoid. Main sources are tea, onion, and apple. It is demonstrated that the frequently consumed food like soybean, peanut, mustard, rice, sesame, olive, potatoes, onion, and oats contain flavonoids. Catechin and its derivates which are isolated from tea leaves have antioxidant activity but in low doses, their prooxidant effects are also reported. Ipriflavone which is a synthetic flavonoid may increase total calcium in bone. In this review, the effects of flavonoids species on the inflammatory process in the neurodegenerative process were examined as general.

Synthetic flavonoids with antimicrobial activity: a review

The emergence of drug-resistant microbes left us with a great need for new antimicrobial agents. Flavonoids, with their wide range of biological activities, are good candidates in this respect. Although naturally occurring flavonoids are the most studied ones, semi-synthetic or synthetic flavonoids have proven to have great potential, inhibiting and even killing microbes at concentrations below 1 μg ml^-1 . The substitution pattern of these flavonoids often includes hydroxy groups, halogens or other heteroatomic rings, such as pyridine, piperidine or 1,3-dithiolium cations. However, the great variety in substituents makes it difficult to draw any definitive conclusion regarding their structure-activity relationship.

Synthesis and Biological Evaluation of 3-Benzylidene-4-chromanone Derivatives as Free Radical Scavengers and α-Glucosidase Inhibitors

A series of 3-benzylidene-4-chromanone derivatives (3-20) were synthesized and the structure-activity relationships for antioxidant and α-glucosidase inhibitory activities were evaluated. Among synthesized compounds, compounds 5, 13, 18, which contain catechol moiety, showed the potent 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity (5: EC50 13 µM; 13: EC50 14 µM; 18: EC50 13 µM). The compounds 12, 14, 18 showed higher α-glucosidase inhibitory activity (12: IC50 15 µM; 14: IC50 25 µM; 18: IC50 28 µM). The compound 18 showed both of potent DPPH radical scavenging and α-glucosidase inhibitory activities. These data suggest that 3-benzylidene-4-chromanone derivatives, such as compound 18, may serve as the lead compound for the development of novel α-glucosidase inhibitors with antioxidant activity.

Antibiotic adjuvants: diverse strategies for controlling drug-resistant pathogens

The growing number of bacterial pathogens that are resistant to numerous antibiotics is a cause for concern around the globe. There have been no new broad-spectrum antibiotics developed in the last 40 years, and the drugs we have currently are quickly becoming ineffective. In this article, we explore a range of therapeutic strategies that could be employed in conjunction with antibiotics and may help to prolong the life span of these life-saving drugs. Discussed topics include antiresistance drugs, which are administered to potentiate the effects of current antimicrobials in bacteria where they are no longer (or never were) effective; antivirulence drugs, which are directed against bacterial virulence factors; host-directed therapies, which modulate the host's immune system to facilitate infection clearance; and alternative treatments, which include such therapies as oral rehydration for diarrhea, phage therapy, and probiotics. All of these avenues show promise for the treatment of bacterial infections and should be further investigated to explore their full potential in the face of a postantibiotic era.

Recent advances of chroman-4-one derivatives: synthetic approaches and bioactivities

Chroman-4-one scaffold is a privileged structure in heterocyclic chemistry and drug discovery. Also, chroman-4-ones are important intermediates and interesting building blocks in organic synthesis and drug design. The structural diversity found in the chroman-4-one family led to their division into several categories including benzylidene-4-chromanones, flavanones (2-phenyl-4-chromanones), isoflavanones (3-phenyl-4-chromanones), spirochromanones, and C-4 modified chroman-4-ones such as hydrazones and oxime derivatives. This review addresses the most significant synthetic methods reported on 4-chromanone-derived compounds and consequently emphasizes on the biological relevance of such compounds.

Chromanones: selective and reversible monoamine oxidase B inhibitors with nanomolar potency

Compound 4f was a potent and selective inhibitor for hMAO-B.

Acetophenone derivatives: novel and potent small molecule inhibitors of monoamine oxidase B

Compounds 1j and 2e were both potent and selective MAO-B inhibitors.