Design, synthesis, and antibacterial activity of novel pleuromutilin derivatives bearing an amino thiazolyl ring

A series of novel pleuromutilin derivatives containing the amino thiazolyl ring were designed, synthesized, and evaluated for their antibacterial activities in vitro against Gram-positive clinical bacteria. All the target compounds showed better aqueous solubility compared with the lead compound (10). Most compounds displayed strong antibacterial activities against both susceptible and resistant bacteria, particularly for the compound (12f) which showed extraordinary antibacterial properties superior to amoxicillin and tiamulin. Molecular docking studies revealed that the amino thiazolyl ring, the side chains of the pleuromutilin derivatives, can be adopted in the binding pocket of the 50S ribosomal subunit near the mutilin core. Therefore, our novel findings may provide new insights into the design of novel pleuromutilin derivatives and lay the basis for further studies on these promising antibiotics for human clinical use.     

New strategies for antibacterial drug design: targeting non-multiplying latent bacteria

During the past two decades, the number of antibacterials that has reached the marketplace each year has declined, whilst resistance to existing antibacterials has increased. New antibacterials are needed to replace those that have become less effective as a result of the emergence of a high level of resistance amongst target bacteria. Antibacterials are developed by targeting live multiplying whole bacterial cells, or essential bacterial molecules such as enzymes. Using these targets, libraries of natural, recombinant or chemically synthesised compounds are screened. Most existing antibacterials have been developed by creating novel analogues of established antibacterials, which are themselves derivatives of natural compounds. Recently, live non-multiplying bacteria have been used as targets. Bacteria in such a phase are much more tolerant to antibacterials than logarithmic phase organisms. Targeting of non-multiplying bacteria has the potential to yield new antibacterials that would shorten the duration of therapy. This would be more convenient for the patient, could reduce the incidence of adverse effects of treatment, and might reduce the emergence of antibacterial resistance. However, there is much to learn about non-multiplying bacteria, particularly the mechanisms that lie behind their profound antibacterial tolerance. New terminology has been proposed for susceptibility tests for antibacterial agents against non-multiplying bacteria, namely: the minimum stationary-cidal concentration and the minimum dormicidal concentration, which are defined as the minimum concentrations of drug that will kill stationary and dormant bacteria, respectively. The relationship between the antibiotic susceptibility of stationary and logarithmic phase bacteria is the stationary/logarithmic ratio. This terminology is suitable for both planktonic and biofilm cultures. In the future, it is likely that most antibacterial drug design will be based on existing antibacterial structures, but an increasing number of new molecular antibacterial structures may emerge from screening against multiplying and perhaps non-multiplying bacteria. The genomic approach has been disappointing so far, but it is still hoped that this will produce novel antibacterial agents.     

The millennium bugs--the need for and development of new antibacterials

Global antibacterial resistance is becoming an increasing public health problem. Bacteria resistant to almost all of the available antibacterials have been identified. The pharmaceutical industry and fledgling biotechnology companies are responding to the threat of antibiotic resistance with renewed efforts to discover novel antibacterials in attempts to overcome bacterial resistance. Both short term and long term strategies are being vigorously pursued. Short-term efforts are focused on developing novel antibacterial agents with a narrow spectrum of action to combat the problem of gram-positive resistant bacteria. Long-term approaches include the use of microbial genomic sequencing techniques to discover novel agents active against potentially new bacterial targets. Better use of existing agents using pharmacodynamic data to optimise antibiotic regimens is increasingly being addressed and the hope is that such measures will prevail until the newer agents are available.     

Synthesis and antibacterial activities of novel pleuromutilin derivatives bearing an aminothiophenol moiety

We synthesized a series of novel thioether pleuromutilin derivatives incorporating 2‐aminothiophenol moieties into the C14 side chain via acylation reactions under mild conditions. We evaluated the in‐vitro antibacterial activities of the derivatives against methicillin‐resistant Staphylococcus aureus (MRSA, ATCC 43300), Staphylococcus aureus (ATCC 29213) and Escherichia coli (ATCC 25922). The majority of the synthesized derivatives possessed moderate antibacterial activities. Compound 8 was found to be the most active antibacterial derivative against MRSA. We conducted docking experiments to understand the possible mode of interactions between compounds 8 , 9b , 11a and 50S ribosomal subunit. The docking results proved that there is a reasonable correlation between the binding free energy and the antibacterial activity. Compound 8 was evaluated for its in‐vivo antibacterial activity and showed higher efficacy than tiamulin against MRSA in mouse infection model.     

Optimising dosing strategies of antibacterials utilising pharmacodynamic principles: impact on the development of resistance

Evolving antimicrobial resistance is of global concern. The impact of decreased susceptibility to current antibacterials coupled with the decline in the marketing of new agents with novel mechanisms of action places a tremendous burden on clinicians to appropriately use available agents. Optimising antibacterial dose administration through the use of pharmacodynamic principles can aid clinicians in accomplishing this task more effectively. Methods to achieve this include: continuous or prolonged infusion, or the use of smaller doses administered more frequently for the time-dependent beta-lactam agents; or higher, less frequent dose administration of the concentration-dependent aminoglycosides and fluoroquinolones. Pharmacodynamic breakpoints, which are predictive of clinical and/or microbiological success in the treatment of infection, have been determined for many classes of antibacterials, including the fluoroquinolones, aminoglycosides and beta-lactams. Although surpassing these values may predict efficacy, it may not prevent the development of resistance. Recent studies seek to determine the pharmacodynamic breakpoints that prevent the development of resistance. Numerous studies to this point have determined these values in fluoroquinolones in both Gram-positive and Gram-negative bacteria. However, among the other antibacterial classes, there is a lack of sufficient data. Additionally, a new term, the mutant prevention concentration, has been based on the concentrations above which resistance is unlikely to occur. Future work is needed to fully characterise these target concentrations that prevent resistance.     

Conclusions: the future of antimicrobial therapy - Augmentin and beyond

Since most infectious microorganisms inevitably develop resistance to any agents used to combat them, there has been a constant need to produce improved, more potent, antimicrobials. At least in part, the emergence and spread of resistant organisms has been provoked by inappropriate over-use of antibacterials. In the last decade, many fewer new antibacterials have been developed but overall prescribing has continued to increase. Consensus prescribing principles have now been defined with the aim of optimising therapy and preventing further increases in, or even to prompt a reduction in, the prevalence of resistance to antibacterial agents. Whilst it is important to encourage continued development of new classes of antibacterials, it is also vital to make the best use of available agents. The development of new dosages and formulations of amoxicillin/clavulanate allows this agent to continue to fill the important role in therapy which it has occupied, and continues to occupy, 25 years after it was launched.     

Retapamulin: an antibacterial with a novel mode of action in an age of emerging resistance to Staphylococcus aureus

Staphylococcus aureus (S. aureus) is the leading cause of nosocomial infections and responsible for more than 11 million skin and soft tissue infections annually. Impetigo is a common skin infection and the most common bacterial skin infection in children aged two to five years. The emergence of S. aureus isolates resistant to commonly utilized antibacterials for skin infections (beta-lactams, erythromycin, fluoroquinolones and mupirocin) makes successful treatment an ongoing challenge. To treat skin infections such as impetigo, antibacterials with a short dosing schedule and low propensity to develop resistance should be used. In 2007, retapamulin was the first agent for human use approved in the pleuromutilin class of antibacterials in the United States (U.S.), and is the first topical antibacterial indicated to treat impetigo in over 20 years. In vitro, retapamulin is highly potent against S. aureus and has a lower propensity to develop resistance than mupirocin. In clinical studies, the convenient five-day b.i.d. (twice-daily) dosing of retapamulin is highly effective against impetigo due to methicillin- susceptible S. aureus and Streptococcus pyogenes and may play an important role in limiting the development of resistance against systemic agents.     

细菌外排泵与抗生素耐药的相关性

抗生素耐药与临床用药紧密相关,一直以来都受到广泛关注。除了药物失活、靶点改变这些已经熟知的耐药机制以外,细菌外排泵的作用也是抗生素耐药的重要原因。外排泵在细菌中普遍存在并且底物十分广泛,其表达对多种细菌的先天耐药和后天耐药都有贡献。对于金黄色葡萄球菌、大肠杆菌、绿脓杆菌等细菌,外排泵导致的耐药是其耐药的主要原因,因此在临床用药过程中,外排泵产生的耐药成了不可忽略的因素。这也给新药研发提供了新的思路,已经有研究以外排泵为靶点开发新药,而开发能够规避外排泵作用的新型抗生素也是克服外排泵耐药的一个途径。本文从分类,结构,调控以及抑制剂等方面对近年来细菌外排转运体方面的研究进行综述,为进一步的探索提供参考。     

抗菌药物应用与医疗质量控制

加强医疗机构抗菌药物临床应用管理,促进抗菌药物合理使用,是有效控制细菌耐药,加强医疗质量和医疗安全的重要保证.应在抗菌药物应用的不同环节加强医疗质量控制与管理,主要措施包括:建立健全抗菌药物合理应用的管理组织和制度,加强抗菌药物使用的监测、监督和反馈,加强对医务人员的培训,对抗菌药物实施分级管理,加强病原微生物检测,建立健全抗菌药物临床应用的预警机制,加强围手术期抗菌药物预防性应用的管理等.     

Pleuromutilin antibacterial agents: patent review 2001 – 2006

Derivatives of the naturally occurring pleuromutilin, of which certain analogs were successfully developed in veterinary medicine, have regained interest in the past few years as promising antibacterial agents with potential for human use. This review provides an overview of patents related to pleuromutilin derivatives during 2001 – 2006. Representative compounds along with their antibacterial activities are selected for this purpose, and a section focuses on pleuromutilins in clinical development and practice, in particular retapamulin. Most of the patents reveal the usefulness of different analogs as antibacterial agents effective against multi-drug-resistant organisms, whereas one patent disclosed the in vitro effectiveness of pleuromutilins against Helicobacter pylori. Few patents disclosed novel formulations, methods of preparation in order to improve efficacy, delivery, stability upon storage and synthesis of pleuromutilins.     

When will the genomics investment pay off for antibacterial discovery?

Effective solutions to antibacterial resistance are among the key unmet medical needs driving the antibacterial industry. A major thrust in a number of companies is the development of agents with new modes of action in order to bypass the increasing emergence of antibacterial resistance. However, few antibacterials marketed in the last 30 years have novel modes of action. Most recently, genomics and target-based screening technologies have been emphasized as a means to facilitate this and expedite the antibacterial discovery process. And although no new antibacterials have yet been marketed as result of these technologies, genomics has delivered well-validated novel bacterial targets as well as a host of genetic approaches to support the antibacterial discovery process. Likewise, high throughput screening technologies have delivered the capacity to perform robust screenings of large compound collections to identify target inhibitors for lead generation. One of the principal challenges still facing antibacterial discovery is to become proficient at optimizing target inhibitors into broad-spectrum antibacterials with appropriate in vivo properties. Genomics-based technologies clearly have the potential for additional application throughout the discovery process especially in the areas of structural biology and safety assessment.     

Natural products--the future scaffolds for novel antibiotics?

Natural products have played a pivotal role in antibiotic drug discovery with most antibacterial drugs being derived from a natural product or natural product lead. However, the rapid onset of resistance to most antibacterial drugs diminishes their effectiveness considerably and necessitates a constant supply of new antibiotics for effective treatment of infections. The natural product templates of actinonin, pleuromutilin, ramoplanin and tiacumicin B, which are compounds undergoing clinical evaluation, represent templates not found in currently marketed antibacterial drugs. In addition, the new templates present in the recently discovered lead antibacterials arylomycin, GE23077, mannopeptimycin, muraymycin/caprazamycin, nocathiacin and ECO-0501, are discussed. Despite extensive efforts to identify antibiotic leads from molecular targets, only the peptide deformylase inhibitor LBM-415 is currently in clinical trials. It is proposed that new antibacterial assays which combine cell-based screening with molecular targets could offer better prospects for lead discovery.     

Antibacterial use in community practice: assessing quantity, indications and appropriateness, and relationship to the development of antibacterial resistance.

Most use of antibacterials occurs in community practice; however, despite the widespread belief of inappropriate use and the resultant increase in antibacterial resistance, little data exist describing antibacterial use in this setting. A MEDLINE search of English-language articles was conducted for epidemiological studies assessing quantity, indication and appropriateness of antibacterial use in community practice. A 1983 study of international antibacterial use described considerable disparities in quantity of use between countries. Subsequent longitudinal studies from the US, Canada, Australia and the UK described changing patterns of antibacterial use. No increase in the total rate of antibacterial use was reported by any of the 4 countries; however, all countries reported increased use of newer and/or broad-spectrum agents (e.g. fluoroquinolones, amoxicillin-clavulanic acid, cephalosporins and new macrolides] coupled with decreased use of older and/or narrow-spectrum agents [e.g. phenoxymethylpenicillin (penicillin V), erythromycin, ampicillin and tetracycline). Most (approximately three-quarters) use of antibacterials was in the treatment of respiratory tract infections. Prescribing rates for respiratory tract infections of presumed viral aetiology (e.g. the common cold) ranged from 17 to 60% in the UK and US, respectively. Among indications for which antibacterials were indicated, the appropriateness of antibacterial use received little study. Correspondingly, the rates of antibacterial resistance among common respiratory pathogens (Streptococcus pneumoniae and Haemophilus influenzae) have increased significantly in the past decade, although disparities exist between countries. Antibacterial use is considered a major factor in the development of antibacterial resistance, although the relationship between community antibacterial use and resistance has been poorly described. Further study of antibacterial usage patterns and associated resistance patterns is fundamental to the development of methods to reduce unnecessary and inappropriate use, thereby slowing the development of antibacterial resistance in the community.     

抗耐药菌药物研究进展

近年来医药界十分关注抗耐药菌药物研究，有两种主要抗耐甲氧西林金黄色葡萄球菌（MRSA），耐青霉素肺炎链球菌（PRSP），耐万古霉素肠球菌（VRE）等革兰阳性耐药菌的新药上市，有一批新广谱抗生素临床应用，还有若干颇具开发前景的化合物正在研究中，本文分3个部分综述了近年来研究进展（1）新型结构，新作用机制、新作用靶位的新药研究；（2）抗生素与合成抗菌药的结构修饰；（3）增强与保护抗菌药物性能的物质诸如抗菌增强剂，抗生素酶抑制剂，膜渗透性增强剂，外排泵抑制剂等研究。     

截短侧耳素衍生物ZYY-12h对MRSA菌株的抑菌作用及作用机制研究

摘要：目的 探究截短侧耳素衍生物ZYY-12h对耐甲氧西林金黄色葡萄球菌(MRSA)的抑菌效果及作用机制。方法 采用抑菌圈法和微量肉汤稀释法测定MRSA菌株对ZYY-12h的敏感性，在此基础上绘制时间-杀菌曲线；再测量经ZYY-12h处理后的MRSA细菌悬液A260、通过SDS-PAGE电泳观察细菌可溶性蛋白的含量变化和扫描电子显微镜(SEM)观察细菌的形态结构变化来探究其抑菌机制。结果 ZYY-12h对MRSA菌株有较强的抑菌活性，其最小抑菌浓度(MIC)为0.125 mg/mL，最小杀菌浓度(MBC)为0.5 mg/mL；经ZYY-12h处理后细菌细胞膜的通透性明显变大，菌体可溶性蛋白含量明显减少，且细菌的外部超微形态结构发生改变。结论 截短侧耳素衍生物ZYY-12h对MRSA菌株有明显的抑制作用，且在高浓度下有杀菌作用，其作用机制与改变细菌的膜通透性和抑制细菌蛋白质合成有关。     

Efflux-mediated drug resistance in bacteria

Drug resistance in bacteria, and especially resistance to multiple antibacterials, has attracted much attention in recent years. In addition to the well known mechanisms, such as inactivation of drugs and alteration of targets, active efflux is now known to play a major role in the resistance of many species to antibacterials. Drug-specific efflux (e.g. that of tetracycline) has been recognised as the major mechanism of resistance to this drug in Gram-negative bacteria. In addition, we now recognise that multidrug efflux pumps are becoming increasingly important. Such pumps play major roles in the antiseptic resistance of Staphylococcus aureus, and fluoroquinolone resistance of S. aureus and Streptococcus pneumoniae. Multidrug pumps, often with very wide substrate specificity, are not only essential for the intrinsic resistance of many Gram-negative bacteria but also produce elevated levels of resistance when overexpressed. Paradoxically, 'advanced' agents for which resistance is unlikely to be caused by traditional mechanisms, such as fluoroquinolones and beta-lactams of the latest generations, are likely to select for overproduction mutants of these pumps and make the bacteria resistant in one step to practically all classes of antibacterial agents. Such overproduction mutants are also selected for by the use of antiseptics and biocides, increasingly incorporated into consumer products, and this is also of major concern. We can consider efflux pumps as potentially effective antibacterial targets. Inhibition of efflux pumps by an efflux pump inhibitor would restore the activity of an agent subject to efflux. An alternative approach is to develop antibacterials that would bypass the action of efflux pumps.     

An update on the role of nitrofurans in the management of urinary tract infections

There have been few recent reviews of the nitrofurans in the literature, and none include recently available data on the use of nitrofurazone (nitrofural) in the prevention of catheter-associated urinary tract infection (CAUTI). Nitrofurazone and nitrofurantoin are the only nitrofurans that have become established in clinical use in the 20th century. These 2 nitrofurans have remained clinically useful against a wide spectrum of gram-positive and gram-negative bacteria, including many strains of common urinary tract pathogens. Today, the primary use of nitrofurantoin is as an oral antibacterial treatment for genitourinary infections. Nitrofurazone is primarily used as a topical antibacterial agent in burns and skin grafts and recently was approved for the prophylaxis of CAUTI. The recent development of a nitrofurazone-impregnated catheter as a novel modality in the prevention of CAUTI reflects a renewed interest in the effectiveness of nitrofurans. In an era when concern about bacterial resistance to many anti-infective agents is growing, the nitrofurans have continued to be active against organisms that have developed resistance to antibacterials. The presence of multiple mechanisms of action for the nitrofurans might be expected to reduce the ability of bacteria to develop resistance. Considering that an emergence of resistance to the nitrofurans has not appreciably occurred after several decades of clinical use, the nitrofurans may be unique among common antibacterial agents in this regard.     

Novel dual-targeting benzimidazole urea inhibitors of DNA gyrase and topoisomerase IV possessing potent antibacterial activity: intelligent design and evolution through the judicious use of structure-guided design and structure-activity relationships

The discovery of new antibacterial agents with novel mechanisms of action is necessary to overcome the problem of bacterial resistance that affects all currently used classes of antibiotics. Bacterial DNA gyrase and topoisomerase IV are well-characterized clinically validated targets of the fluoroquinolone antibiotics which exert their antibacterial activity through inhibition of the catalytic subunits. Inhibition of these targets through interaction with their ATP sites has been less clinically successful. The discovery and characterization of a new class of low molecular weight, synthetic inhibitors of gyrase and topoisomerase IV that bind to the ATP sites are presented. The benzimidazole ureas are dual targeting inhibitors of both enzymes and possess potent antibacterial activity against a wide spectrum of relevant pathogens responsible for hospital- and community-acquired infections. The discovery and optimization of this novel class of antibacterials by the use of structure-guided design, modeling, and structure-activity relationships are described. Data are presented for enzyme inhibition, antibacterial activity, and in vivo efficacy by oral and intravenous administration in two rodent infection models.     

The bacterial cell wall as a source of antibacterial targets

This review focuses on target-based approaches for developing new chemical classes of antibacterial agents aimed at the bacterial cell wall. The clinical success of antibiotics such as beta-lactams and glycopeptides validates this chemotherapeutic strategy and emerging resistance to these agents warrants the development of new antibacterial drugs. Understanding the mechanism of action and resistance to beta-lactams and glycopeptides at a molecular level has supported the development of new agents that prevent transpeptidation and transglycosylation reactions of peptidoglycan polymerisation. The enzymes involved in the synthesis of the peptidoglycan structural unit have also been targeted for antibacterial discovery. The influence of bacterial genetics and genomics, structural biology, assay development and the properties of known inhibitors on these approaches will be discussed in the context of drug discovery.