Synthesis and evaluation of inhibitors of bacterial drug efflux pumps of the major facilitator superfamily

The Discovery of Novel Antimicrobial Agents through the Application of Isocyanide-Based Multicomponent Reactions

Multicomponent reactions (MCR) have been used to synthesize a wide range of analogs from several classes of heterocyclic compounds, with multifaceted medicinal uses. The synthesis of highly functionalized molecules in a single pot is a unique property of MCR, allowing researchers to quickly assemble libraries of compounds of biological interest and uncover novel leads as possible therapeutic agents. Isocyanide-based multicomponent reactions have proven to be extremely effective at swiftly specifying members of compound libraries, particularly in the discovery of drugs. The understanding of structure-activity correlations that drive the development of new goods and technology requires structural variety in these libraries. In today's world, antibiotic resistance is a major ongoing problem that poses risks to public health. The implementation of isocyanide-based multicomponent reactions upholds a significant potential in this regard. By utilizing such reactions, new antimicrobial compounds can be discovered and subsequently used to fight against such concerns. This study discusses the recent developments in antimicrobial medication discovery using isocyanide-based multicomponent reactions (IMCRs). Furthermore, the article emphasizes the potential of IMCRs (Isocyanide-based multicomponent based reactions) in the near future.

Efflux pumps in multidrug-resistant Acinetobacter baumannii: Current status and challenges in the discovery of efflux pumps inhibitors

Acinetobacter baumannii is an ESKAPE pathogen known to cause fatal nosocomial infections. With the surge of multidrug resistance (MDR) in the bacterial system, effective treatment measures have become very limited. The MDR in A. baumannii is contributed by various factors out of which efflux pumps have gained major attention due to their broad substrate specificity and wide distribution among bacterial species. The efflux pumps are involved in the MDR as well as contribute to other physiological processes in bacteria, therefore, it is critically important to inhibit efflux pumps in order to combat emerging resistance. The present review provides insight about the different efflux pump systems in A. baumannii and their role in multidrug resistance. A major focus has been put on the different strategies and alternate therapeutics to inhibit the efflux system. This includes use of different efflux pump inhibitors-natural, synthetic or combinatorial therapy. The use of phage therapy and nanoparticles for inhibiting efflux pumps have also been discussed here. Moreover, the present review provides the knowledge of barriers in development of efflux pump inhibitors (EPIs) and their approval for commercialization. Here, different prospectives have been discussed to improve the therapeutic development process and make it more compatible for clinical use.

Two decades of recent advances of Ugi reactions: synthetic and pharmaceutical applications

Multicomponent reactions (MCRs) are powerful synthetic tools in which more than two starting materials couple with each other to form multi-functionalized compounds in a one-pot process, the so-called "tandem", "domino" or "cascade" reaction, or utilizing an additional step without changing the solvent, the so-called a sequential-addition procedure, to limit the number of synthetic steps, while increasing the complexity and the molecular diversity, which are highly step-economical reactions. The Ugi reaction, one of the most common multicomponent reactions, has recently fascinated chemists with the high diversity brought by its four- or three-component-based isonitrile. The Ugi reaction has been introduced in organic synthesis as a novel, efficient and useful tool for the preparation of libraries of multifunctional peptides, natural products, and heterocyclic compounds with stereochemistry control. In this review, we highlight the recent advances of the Ugi reaction in the last two decades from 2000-2019, mainly in the synthesis of linear or cyclic peptides, heterocyclic compounds with versatile ring sizes, and natural products, as well as the enantioselective Ugi reactions. Meanwhile, the applications of these compounds in pharmaceutical trials are also discussed.

The host generalist phytopathogenic fungus Sclerotinia sclerotiorum differentially expresses multiple metabolic enzymes on two different plant hosts

Sclerotinia sclerotiorum is a necrotrophic fungal pathogen that infects upwards of 400 plant species, including several economically important crops. The molecular processes that underpin broad host range necrotrophy are not fully understood. This study used RNA sequencing to assess whether S. sclerotiorum genes are differentially expressed in response to infection of the two different host crops canola (Brassica napus) and lupin (Lupinus angustifolius). A total of 10,864 of the 11,130 genes in the S. sclerotiorum genome were expressed. Of these, 628 were upregulated in planta relative to in vitro on at least one host, suggesting involvement in the broader infection process. Among these genes were predicted carbohydrate-active enzymes (CAZYmes) and secondary metabolites. A considerably smaller group of 53 genes were differentially expressed between the two plant hosts. Of these host-specific genes, only six were either CAZymes, secondary metabolites or putative effectors. The remaining genes represented a diverse range of functional categories, including several associated with the metabolism and efflux of xenobiotic compounds, such as cytochrome P450s, metal-beta-lactamases, tannases and major facilitator superfamily transporters. These results suggest that S. sclerotiorum may regulate the expression of detoxification-related genes in response to phytotoxins produced by the different host species. To date, this is the first comparative whole transcriptome analysis of S. sclerotiorum during infection of different hosts.

Overcoming problems of poor drug penetration into bacteria: challenges and strategies for medicinal chemists

INTRODUCTION

Bacterial cell walls and membranes provide essential protection for bacteria against environmental influences. Different bacteria possess different cell envelopes and understanding each of these structures is crucial for the design of effective antibacterial drugs whose targets are intracellular. Optimal properties of drugs that are required for their entry into bacteria are still hard to predict. The guidelines that are suitable and well established for the penetration of a drug into eukaryotic cells are poorly adaptable to the complex world of pathogens. Areas covered: The factors that govern the penetration of anti-infection drugs into bacteria are examined and the available strategies to overcome this therapeutically very important barrier are reviewed. The areas covered include optimization of the physicochemical properties of compounds, utilization of iron-chelating compounds, i.e. siderophores, the use of efflux pump inhibitors, and of carriers such as liposomes. Expert opinion: Although several rules governing permeation have recently been proposed for effective antibacterial drugs, none of them has been so far established as the 'golden' rule. Thus, new research is needed to find a more general approach on how to increase the concentration of antibacterial compounds in bacterial cells.

Fragment-Based Strategy for Investigating and Suppressing the Efflux of Bioactive Small Molecules

Membrane protein-mediated drug efflux is a phenomenon that compromises our ability to treat both infectious diseases and cancer. Accordingly, there is much interest in the development of strategies for suppression of the mechanisms by which therapeutic agents are effluxed. Here, using resistance to the cyclic acyldepsipeptide (ADEP) antibacterial agents as a model, we demonstrate a new counter-efflux strategy wherein a fragment of an actively exported bioactive compound competitively interferes with its efflux and potentiates its activity. A fragment comprising the N-heptenoyldifluorophenylalanine side chain of the pharmacologically optimized ADEPs potentiates the antibacterial activity of the ADEPs against actinobacteria to a greater extent than reserpine, a well-known efflux inhibitor. Beyond their validation of a new approach to studying molecular recognition by drug efflux pumps, our findings have important implications for killing Mycobacterium tuberculosis with ADEPs and reclaiming the efficacies of therapeutic agents whose activity has been compromised by efflux pumps.

Discovery of a new class of natural product-inspired quinazolinone hybrid as potent antileishmanial agents

The high potential of quinazolinone containing natural products and their derivatives in medicinal chemistry led us to discover four novel series of 53 compounds of quinazolinone based on the concept of molecular hybridization. Most of the synthesized analogues exhibited potent leishmanicidal activity against intracellular amastigotes (IC50 from 0.65 ± 0.2 to 7.76 ± 2.1 μM) as compared to miltefosine (IC50 = 8.4 ± 2.1 μM) and nontoxic toward the J-774A.1 cell line and Vero cells. Moreover, activation of Th1 type and suppression of Th2 type immune responses and induction in nitric oxide generation proved that 8a and 8g induce murine macrophages to prevent survival of parasites. Compounds 8a and 8g exhibited significant in vivo inhibition of parasite 73.15 ± 12.69% and 80.93 ± 10.50% against Leishmania donovani /hamster model. Our results indicate that compounds 8a, 8g, and 9f represent a new structural lead for this serious and neglected disease.

Mining the antibiotic resistome

Antibiotic-producing microoganisms are a reservoir of drug resistance genes. Studies of the "antibiotic resistome" can inform antimicrobial drug discovery and explain the emergence of multidrug resistant pathogens. In this issue of Chemistry & Biology, Westman and colleagues take an alternative look at the resistome and identify genes that could be used to detoxify the anticancer compound, doxorubicin.

Recent Advances in Multi-Drug Resistance (MDR) Efflux Pump Inhibitors of Gram-Positive Bacteria S. aureus

The paper focuses on recent achievements in the search for new chemical compounds able to inhibit multidrug resistance (MDR) mechanisms in Gram-positive pathogens. An analysis of the results of the search for new efflux pump inhibitors (EPIs) for Gram-positive bacteria, which have been performed over the last decade, indicates that almost all efforts are focused on the NorA (MFS) efflux pump in S. aureus. Considering the chemical structures of the NorA EPIs that have been identified, it can be observed that the most active agents belong to the families of compounds possessing conjugated double bonds, e.g., chalcones, piperine-like compounds, N-cinnamoylphenalkylamides or citral amide derivatives. Indole-, dihydronaphthyl-, 2-chloro-5-bromo-phenyl- or piperidine moieties seem to be profitable for the EPI properties, as well. These results, together with an increasing knowledge about a variety of efflux pumps that are involved in MDR of Gram-positive pathogens underline that further search for new EPIs should pay more attention to develop MDR efflux protein targets, including SMR, MATE, ABC or other members of the MFS family.

Determination of the concentration of potential efflux pump inhibitors, pheophorbide a and pyropheophorbide a, in the feces of animals by fluorescence spectroscopy

Efflux pumps are vital bacterial components, and research has demonstrated that some plant compounds such as pheophorbide a (php) possess efflux pump inhibitor (EPI) activity. This study determined the quantity of php present in feces as an indicator of EPI activity. Feces were collected from different species of animals fed a variety of feeds. The chlorophyll metabolites php and pyropheophorbide a (pyp) were determined using fluorescense spectroscopy. The average concentrations [μg/g dry matter (DM) feces] of pyp/php in feces were as follows: guinea pig, 180; goat, 150; rabbit, 150; dairy cow, 120; feedlot cattle, 60; rat, <1; pig, <1; chicken, <1. These data indicate that animals consuming "green" diets will excrete feces with concentrations of php/pyp that exceed levels demonstrated to be inhibitory to bacterial efflux pumps (0.5 μg/mL). The natural presence EPIs in the gastrointestinal tract may modulate the activity of microbial efflux pumps and exert selection pressure upon resident microbial populations.