Exploitation of Antibiotic Resistance as a Novel Drug Target: Development of a β-Lactamase-Activated Antibacterial Prodrug

Synthesis and antibacterial medicinal evaluation of carbothioamido hydrazonyl thiazolylquinolone with multitargeting antimicrobial potential to combat increasingly global resistance

The global microbial resistance is a serious threat to human health, and multitargeting compounds are considered to be promising to combat microbial resistance. In this work, a series of new thiazolylquinolones with multitargeting antimicrobial potential were developed through multi-step reactions using triethoxymethane and substituted anilines as start materials. Their structures were confirmed by 1H NMR, 13C NMR and HRMS spectra. Antimicrobial evaluation revealed that some of the target compounds could effectively inhibit microbial growth. Especially, carbothioamido hydrazonyl aminothiazolyl quinolone 8a showed strong inhibitory activity toward drug-resistant Staphylococcus aureus with MIC value of 0.0047 mM, which was 5-fold more active than that of norfloxacin. The highly active compound 8a exhibited negligible hemolysis, no significant toxicity in vitro and in vivo, low drug resistance, as well as rapidly bactericidal effects, which suggested its favorable druggability. Furthermore, compound 8a was able to effectively disrupt the integrity of the bacterial membrane, intercalate into DNA and inhibit the activity of topoisomerase IV, suggesting multitargeting mechanism of action. Compound 8a could form hydrogen bonds and hydrophobic interactions with DNA-topoisomerase IV complex, indicating the insertion of aminothiazolyl moiety was beneficial to improve antibacterial efficiency. These findings indicated that the active carbothioamido hydrazonyl aminothiazolyl quinolone 8a as a chemical therapeutic candidate demonstrated immense potential to tackle drug-resistant bacterial infections.

Smart Galactosidase-Responsive Antimicrobial Dendron: Towards More Biocompatible Membrane-Disruptive Agents

Antimicrobial resistance is a global healthcare challenge that urgently needs the development of new therapeutic agents. Antimicrobial peptides and mimics thereof are promising candidates but mostly suffer from inherent toxicity issues due to the non-selective binding of cationic groups with mammalian cells. To overcome this toxicity issue, this work herein reports the synthesis of a smart antimicrobial dendron with masked cationic groups (Gal-Dendron) that could be uncaged in the presence of β-galactosidase enzyme to form the activated Enz-Dendron and confer antimicrobial activity. Enz-Dendron show bacteriostatic activity toward Gram-negative (P. aeruginosa and E. coli) and Gram-positive (S. aureus) bacteria with minimum inhibitory concentration values of 96 µm and exerted its antimicrobial mechanism via a membrane disruption pathway, as indicated by inner and outer membrane permeabilization assays. Crucially, toxicity studies confirmed that the masked prodrug Gal-Dendron exhibited low hemolysis and is at least 2.4 times less toxic than the uncaged cationic Enz-Dendron, thus demonstrating the advantage of masking the cationic groups with responsive immolative linkers to overcome toxicity and selectivity issues. Overall, this study highlights the potential of designing new membrane-disruptive antimicrobial agents that are more biocompatible via the amine uncaging strategy.

Rapid Detection of Bacterial Resistance to β-Lactam Antibiotics with a Relay-Response Chemiluminescence Assay

Bacterial resistance caused by β-lactamases has been a major threat to public health around the world, seriously weakening the efficacy of β-lactam antibiotics, the most widely used therapeutic agents against infectious diseases. To detect the bacterial resistance to β-lactam antibiotics, particularly specific type of β-lactam antibiotics, in a rapid manner, we report herein a relay-response chemiluminescence assay. This assay mainly consists of two reagents: a β-lactam-caged thiophenol and a thiophenol-sensitive chemiluminescence reporter, both of which are synthetically feasible. The selective hydrolysis of β-lactam by β-lactamase leads to the releasing of free thiophenol, which then triggers the emission of a chemiluminescence signal in a relay manner. Three thiophenol-caged β-lactams, structural analogues of cephalothin, cefotaxime, and meropenem, respectively, have been synthesized. And the application of this assay with these analogues of β-lactam antibiotics allows fast detection of β-lactamase-expressing resistant bacteria and, more impressively, provides detailed information on the resistant scope of bacteria.

Synthesis of ciprofloxacin-linked 1,2,3-triazole conjugates as potent antibacterial agents using click chemistry: exploring their function as DNA gyrase inhibitors via in silico- and in vitro-based studies

The antibacterial efficacy of some newly developed C-3 carboxylic group-containing ciprofloxacin-linked 1,2,3-triazole conjugates was studied. Twenty-one compounds from three different series of triazoles were synthesized using click chemistry and evaluated for their antibacterial activity against nine different pathogenic strains, including three Gram-positive strains, i.e. Enterococcus faecalis (ATCC29212), Staphylococcus aureus (ATCC25923), Staphylococcus epidermidis (clinical isolate), and six Gram-negative bacterial strains, i.e. Escherichia coli (ATCC25922), Pseudomonas aeruginosa (ATCC27853), Salmonella typhi (clinical isolate), Proteus mirabilis (clinical isolate), Acinetobacter baumannii (clinical isolate) and Klebsiella pneumonia (clinical isolate). Among the compounds, 10, 10a, 10b, 10c, 10d, 11a, 11f, 12c, 12e and 12f showed excellent activity with MIC values upto 12.5 μg mL-1, whereas the control ciprofloxacin showed MIC values of 0.781-25 μg mL-1 towards various strains. In addition, the low toxicity profile of the synthesized molecules revealed that they are potent antibiotics. Molecular docking and MD analysis were performed using the protein structure of E. coli DNA gyrase B, which was further corroborated with an in vitro assay to evaluate the inhibition of DNA gyrase. The analysis revealed that compound 10b was the most potent inhibitor of DNA gyrase compared to ciprofloxacin, which was employed as the positive control. Furthermore, the structure of two title compounds (11a and 12d) was characterized using single-crystal analysis.

Identification of CH2-linked quinolone-aminopyrimidine hybrids as potent anti-MRSA agents: Low resistance potential and lack of cross-resistance with fluoroquinolone antibiotics

The structural optimization of B14, an antibacterial agent we previously obtained, has led to the discovery of a new class of CH2-linked quinolone-aminopyrimidine hybrids with potent anti-MRSA activities. Surprisingly, the hybrids lacking a C-6 fluoro atom at the quinolone nucleus showed equal or even stronger anti-MRSA activities than their corresponding 6-fluoro counterparts, despite the well-established structure-activity relationships (SARs) indicating that the 6-fluoro substituent enhances the antibacterial activity in conventional fluoroquinolone antibiotics. Moreover, these new hybrids, albeit structurally related to conventional fluoroquinolones, showed no cross-resistance with fluoroquinolone drugs. The most active compound, 15m, exhibited excellent activities with a MIC value of 0.39 μg/mL against both fluoroquinolone-sensitive strain USA500 and -resistant MRSA isolate Mu50. Further resistance development studies indicated MRSA is unlikely to acquire resistance against 15m. Moreover, 15m displayed favorable in vivo half-life and safety profiles. These findings suggest a rationale for further evolution of quinolone antibiotics with a high barrier to resistance.

The landscape of small-molecule prodrugs

Prodrugs are derivatives with superior properties compared with the parent active pharmaceutical ingredient (API), which undergo biotransformation after administration to generate the API in situ. Although sharing this general characteristic, prodrugs encompass a wide range of different chemical structures, therapeutic indications and properties. Here we provide the first holistic analysis of the current landscape of approved prodrugs using cheminformatics and data science approaches to reveal trends in prodrug development. We highlight rationales that underlie prodrug design, their indications, mechanisms of API release, the chemistry of promoieties added to APIs to form prodrugs and the market impact of prodrugs. On the basis of this analysis, we discuss strengths and limitations of current prodrug approaches and suggest areas for future development.

NMR insights into β-Lactamase activity of UVI31+ Protein from Chlamydomonas reinhardtii

β-Lactamases (EC 3.5.2.6) confer resistance against β-lactam group-containing antibiotics in bacteria and higher eukaryotes, including humans. Pathogenic bacterial resistance against β-lactam antibiotics is a primary concern for potential therapeutic developments and drug targets. Here, we report putative β-lactamase activity, sulbactam binding (a β-lactam analogue) in the low μM affinity range, and site-specific interaction studies of a 14 kDa UV- and dark-inducible protein (abbreviated as UVI31+, a BolA homologue) from Chlamydomonas reinhartii. Intriguingly, the solution NMR structure of UVI31 + bears no resemblance to other known β-lactamases; however, the sulbactam binding is found at two sites rich in positively charged residues, mainly at the L2 loop regions and the N-terminus. Using NMR spectroscopy, ITC and MD simulations, we map the ligand binding sites in UVI31 + providing atomic-level insights into its β-lactamase activity. Current study is the first report on β-lactamase activity of UVI31+, a BolA analogue, from C. reinhartii. Furthermore, our mutation studies reveal that the active site serine-55 is crucial for β-lactamase activity.

Prodrug Rewards in Medicinal Chemistry: An Advance and Challenges Approach for Drug Designing

This article emphasizes the importance of prodrugs and their diverse spectrum of effects in the field of developing novel drugs for a variety of biological applications. Prodrugs are chemicals that are supplied inactively, but then go through enzymatic and chemical transformation in vivo to release the active parent medication that can have the desired pharmacological effect. By adding an inactive chemical moiety, prodrugs are improved in a number of ways that contribute to their potency and durability. For the purpose of illustrating the usefulness of the prodrug approach, this review covers examples of prodrugs that have been made available or are now undergoing human trials. Additionally, it included lists of the most common functional groups, carrier linkers, and reactive chemicals that can be used to create prodrugs. The current study also provides a brief introduction, several chemical methods and modifications for creating prodrugs and mutual prodrugs, as well as an explanation of recent advancements and difficulties in the field of prodrug design. The primary chemical carriers employed in the creation of prodrugs, such as esters, amides, imides, NH-acidic carriers, amines, alcohols, carbonyl, carboxylic, and azo-linkages, are also discussed. This review also discusses glycosidic and triglyceride mutually activated prodrugs, which aim to deliver the drugs after bioconversion at the intended site of action. The article also discusses the extensive chemistry and wide variety of applications of recently approved prodrugs, such as antibacterial, anti-inflammatory, cardiovascular, antiplatelet, antihypertensive, atherosclerotic, antiviral, etc. In order to illustrate the prodrug and mutual drug concept's various applications and highlight its many triumphs in overcoming the formulation and delivery of problematic pharmaceuticals, this work represents a thorough guide that includes the synthetic moiety for the reader.

Staph wars: the antibiotic pipeline strikes back

Antibiotic chemotherapy is widely regarded as one of the most significant medical advancements in history. However, the continued misuse of antibiotics has contributed to the rapid rise of antimicrobial resistance (AMR) globally. Staphylococcus aureus, a major human pathogen, has become synonymous with multidrug resistance and is a leading antimicrobial-resistant pathogen causing significant morbidity and mortality worldwide. This review focuses on (1) the targets of current anti-staphylococcal antibiotics and the specific mechanisms that confirm resistance; (2) an in-depth analysis of recently licensed antibiotics approved for the treatment of S. aureus infections; and (3) an examination of the pre-clinical pipeline of anti-staphylococcal compounds. In addition, we examine the molecular mechanism of action of novel antimicrobials and derivatives of existing classes of antibiotics, collate data on the emergence of resistance to new compounds and provide an overview of key data from clinical trials evaluating anti-staphylococcal compounds. We present several successful cases in the development of alternative forms of existing antibiotics that have activity against multidrug-resistant S. aureus. Pre-clinical antimicrobials show promise, but more focus and funding are required to develop novel classes of compounds that can curtail the spread of and sustainably control antimicrobial-resistant S. aureus infections.

Zidovudine-β-Lactam Pronucleoside Strategy for Selective Delivery into Gram-Negative Bacteria Triggered by β-Lactamases

Addressing antibacterial resistance is a major concern of the modern world. The development of new approaches to meet this deadly threat is a critical priority. In this article, we investigate a new approach to negate bacterial resistance: exploit the β-lactam bond cleavage by β-lactamases to selectively trigger antibacterial prodrugs into the bacterial periplasm. Indeed, multidrug-resistant Gram-negative pathogens commonly produce several β-lactamases that are able to inactivate β-lactam antibiotics, our most reliable and widely used therapeutic option. The chemical structure of these prodrugs is based on a monobactam promoiety, covalently attached to the active antibacterial substance, zidovudine (AZT). We describe the synthesis of 10 prodrug analogues (5a-h) in four to nine steps and their biological activity. Selective enzymatic activation by a panel of β-lactamases is demonstrated, and subsequent structure-activity relationships are discussed. The best compounds are further evaluated for their activity on both laboratory strains and clinical isolates, preliminary stability, and toxicity.

Pharmacokinetics of Antibacterial Agents in the Elderly: The Body of Evidence

Infections are important factors contributing to the morbidity and mortality among elderly patients. High rates of consumption of antimicrobial agents by the elderly may result in increased risk of toxic reactions, deteriorating functions of various organs and systems and leading to the prolongation of hospital stay, admission to the intensive care unit, disability, and lethal outcome. Both safety and efficacy of antibiotics are determined by the values of their plasma concentrations, widely affected by physiologic and pathologic age-related changes specific for the elderly population. Drug absorption, distribution, metabolism, and excretion are altered in different extents depending on functional and morphological changes in the cardiovascular system, gastrointestinal tract, liver, and kidneys. Water and fat content, skeletal muscle mass, nutritional status, use of concomitant drugs are other determinants of pharmacokinetics changes observed in the elderly. The choice of a proper dosing regimen is essential to provide effective and safe antibiotic therapy in terms of attainment of certain pharmacodynamic targets. The objective of this review is to perform a structure of evidence on the age-related changes contributing to the alteration of pharmacokinetic parameters in the elderly.

Development and Evaluation of EDTA-Treated Rabbits for Bioavailability Study of Chelating Drugs Using Levofloxacin, Ciprofloxacin, Hemiacetal Ester Prodrugs, and Tetracycline

Laboratory rabbits are fed foods rich with cationic metals, and while fasting cannot empty gastric contents because of their coprophagic habits. This implies that, in rabbits, the oral bioavailability of chelating drugs could be modulated by the slow gastric emptying rates and the interaction (chelation, adsorption) with gastric metals. In the present study, we tried to develop a rabbit model with low amounts of cationic metals in the stomach for preclinical oral bioavailability studies of chelating drugs. The elimination of gastric metals was achieved by preventing food intake and coprophagy and administering a low concentration of EDTA 2Na solution one day before experiments. Control rabbits were fasted but coprophagy was not prevented. The efficacy of rabbits treated with EDTA 2Na was evaluated by comparing the gastric contents, gastric metal contents and gastric pH between EDTA-treated and control rabbits. The treatment with more than 10 mL of 1 mg/mL EDTA 2Na solution decreased the amounts of gastric contents, cationic metals and gastric pH, without causing mucosal damage. The absolute oral bioavailabilities (mean values) of levofloxacin (LFX), ciprofloxacin (CFX) and tetracycline hydrochloride (TC), chelating antibiotics, were significantly higher in EDTA-treated rabbits than those in control rabbits as follows: 119.0 vs. 87.2%, 9.37 vs. 13.7%, and 4.90 vs. 2.59%, respectively. The oral bioavailabilities of these drugs were significantly decreased when Al(OH)₃ was administered concomitantly in both control and EDTA-treated rabbits. In contrast, the absolute oral bioavailabilities of ethoxycarbonyl 1-ethyl hemiacetal ester (EHE) prodrugs of LFX and CFX (LFX-EHE, CFX-EHE), which are non-chelating prodrugs at least in in vitro condition, were comparable between control and EDTA-treated rabbits irrespective of the presence of Al(OH)₃, although some variation was observed among rabbits. The oral bioavailabilities of LFX and CFX from their EHE prodrugs were comparable with LFX and CFX alone, respectively, even in the presence of Al(OH)₃. In conclusion, LFX, CFX and TC exhibited higher oral bioavailabilities in EDTA-treated rabbits than in control rabbits, indicating that the oral bioavailabilities of these chelating drugs are reduced in untreated rabbits. In conclusion, EDTA-treated rabbits were found to exhibit low gastric contents including metals and low gastric pH, without causing mucosal damage. Ester prodrug of CFX was effective in preventing chelate formation with Al(OH)₃ in vitro and in vivo, as well as in the case of ester prodrugs of LFX. EDTA-treated rabbits are expected to provide great advantages in preclinical oral bioavailability studies of various drugs and dosage formulations. However, a marked interspecies difference was still observed in the oral bioavailability of CFX and TC between EDTA-treated rabbits and humans, possibly due to the contribution of adsorptive interaction in rabbits. Further study is necessary to seek out the usefulness of the EDTA-treated rabbit with less gastric contents and metals as an experimental animal.

An Update Review of Approaches to Multiple Action-Based Antibacterials

Many approaches are being pursued to address the major global health challenge posed by the increasing resistance of pathogenic bacteria to antibacterial agents. One of the promising approaches being investigated includes the design and development of multiple action-based small-molecule antibacterials. Aspects of this broad area have been reviewed previously, and recent developments are addressed in this update review covering the literature mainly over the past three years. Considerations encompassing drug combinations, single-molecule hybrids and prodrugs are summarised in regard to the intentional design and development of multiple-action agents with a focus on potential triple or greater activities in bacteria. The hope for such single agents or combinations of single agents is that resistance development will be significantly hindered, and they may be useful in tackling bacterial disease caused by both resistant and non-resistant bacteria.

Biodegradable Cationic and Ionizable Cationic Lipids: A Roadmap for Safer Pharmaceutical Excipients

Cationic and ionizable cationic lipids are broadly applied as auxiliary agents, but their use is associated with adverse effects. If these excipients are rapidly degraded to endogenously occurring metabolites such as amino acids and fatty acids, their toxic potential can be minimized. So far, synthesized and evaluated biodegradable cationic and ionizable cationic lipids already showed promising results in terms of functionality and safety. Within this review, an overview about the different types of such biodegradable lipids, the available building blocks, their synthesis and cleavage by endogenous enzymes is provided. Moreover, the relationship between the structure of the lipids and their toxicity is described. Their application in drug delivery systems is critically discussed and placed in context with the lead compounds used in mRNA vaccines. Moreover, their use as preservatives is reviewed, guidance for their design is provided, and an outlook on future developments is given.

Design and Synthesis of Novel Antimicrobial Agents

The necessity for the discovery of innovative antimicrobials to treat life-threatening diseases has increased as multidrug-resistant bacteria has spread. Due to antibiotics' availability over the counter in many nations, antibiotic resistance is linked to overuse, abuse, and misuse of these drugs. The World Health Organization (WHO) recognized 12 families of bacteria that present the greatest harm to human health, where options of antibiotic therapy are extremely limited. Therefore, this paper reviews possible new ways for the development of novel classes of antibiotics for which there is no pre-existing resistance in human bacterial pathogens. By utilizing research and technology such as nanotechnology and computational methods (such as in silico and Fragment-based drug design (FBDD)), there has been an improvement in antimicrobial actions and selectivity with target sites. Moreover, there are antibiotic alternatives, such as antimicrobial peptides, essential oils, anti-Quorum sensing agents, darobactins, vitamin B6, bacteriophages, odilorhabdins, 18β-glycyrrhetinic acid, and cannabinoids. Additionally, drug repurposing (such as with ticagrelor, mitomycin C, auranofin, pentamidine, and zidovudine) and synthesis of novel antibacterial agents (including lactones, piperidinol, sugar-based bactericides, isoxazole, carbazole, pyrimidine, and pyrazole derivatives) represent novel approaches to treating infectious diseases. Nonetheless, prodrugs (e.g., siderophores) have recently shown to be an excellent platform to design a new generation of antimicrobial agents with better efficacy against multidrug-resistant bacteria. Ultimately, to combat resistant bacteria and to stop the spread of resistant illnesses, regulations and public education regarding the use of antibiotics in hospitals and the agricultural sector should be combined with research and technological advancements.

Current scenario of quinolone hybrids with potential antibacterial activity against ESKAPE pathogens

The ESKAPE (Escherichia coli/E. coli, Staphylococcus aureus/S. aureus, Klebsiella pneumonia/K. pneumoniae, Acinetobacter Baumannii/A. baumannii, Pseudomonas aeroginosa/P. aeroginosa and Enterobacter spp.) pathogens, which could escape or evade common therapies through diverse antimicrobial resistance mechanisms and biofilm formation, are deemed as highly virulent bacteria responsible for life-threatening diseases, calling for novel chemotherapeutics. Quinolones including 2-quinolones and 4-quinolones have occupied a propitious place in drug design and development due to their excellent pharmacological profiles. Quinolones especially fluoroquinolones could inhibit the synthesis of nucleic acid of ESKAPE pathogens, leading to the rupture of bacterial chromosome. However, the resistance of ESKAPE pathogens to quinolones develops rapidly and spreads widely. Accordingly, it has become increasingly urgent to enhance the potency of quinolones against both drug-susceptible and drug-resistant ESKAPE pathogens. Quinolone hybrids can bind with different drug targets simultaneously and have been considered as useful prototypes to circumvent drug resistance. The purpose of this review is to summarize the current scenario (2018-present) of quinolone hybrids with potential antibacterial activity against ESKAPE pathogens, together with the structure-activity relationships and mechanisms of action to facilitate further rational design of more effective candidates.

Emerging Target-Directed Approaches for the Treatment and Diagnosis of Microbial Infections

With the rising levels of drug resistance, developing efficient antimicrobial therapies has become a priority. A promising strategy is the conjugation of antibiotics with relevant moieties that can potentiate their activity by target-directing. The conjugation of siderophores with antibiotics allows them to act as Trojan horses by hijacking the microorganisms' highly developed iron transport systems and using them to carry the antibiotic into the cell. Through the analysis of relevant examples of the past decade, this Perspective aims to reveal the potential of siderophore-antibiotic Trojan horses for the treatment of infections and the role of siderophores in diagnostic techniques. Other conjugated molecules will be the subject of discussion, namely those involving vitamin B12, carbohydrates, and amino acids, as well as conjugated compounds targeting protein degradation and β-lactamase activated prodrugs.

Fighting antibiotic resistance-strategies and (pre)clinical developments to find new antibacterials

Antibacterial resistance is one of the greatest threats to human health. The development of new therapeutics against bacterial pathogens has slowed drastically since the approvals of the first antibiotics in the early and mid-20^th century. Most of the currently investigated drug leads are modifications of approved antibacterials, many of which are derived from natural products. In this review, we highlight the challenges, advancements and current standing of the clinical and preclinical antibacterial research pipeline. Additionally, we present novel strategies for rejuvenating the discovery process and advocate for renewed and enthusiastic investment in the antibacterial discovery pipeline.

β-Lactamase-Mediated Fragmentation: Historical Perspectives and Recent Advances in Diagnostics, Imaging, and Antibacterial Design

The discovery of β-lactam (BL) antibiotics in the early 20th century represented a remarkable advancement in human medicine, allowing for the widespread treatment of infectious diseases that had plagued humanity throughout history. Yet, this triumph was followed closely by the emergence of β-lactamase (BLase), a bacterial weapon to destroy BLs. BLase production is a primary mechanism of resistance to BL antibiotics, and the spread of new homologues with expanded hydrolytic activity represents a pressing threat to global health. Nonetheless, researchers have developed strategies that take advantage of this defense mechanism, exploiting BLase activity in the creation of probes, diagnostic tools, and even novel antibiotics selective for resistant organisms. Early discoveries in the 1960s and 1970s demonstrating that certain BLs expel a leaving group upon BLase cleavage have spawned an entire field dedicated to employing this selective release mechanism, termed BLase-mediated fragmentation. Chemical probes have been developed for imaging and studying BLase-expressing organisms in the laboratory and diagnosing BL-resistant infections in the clinic. Perhaps most promising, new antibiotics have been developed that use BLase-mediated fragmentation to selectively release cytotoxic chemical "warheads" at the site of infection, reducing off-target effects and allowing for the repurposing of putative antibiotics against resistant organisms. This Review will provide some historical background to the emergence of this field and highlight some exciting recent reports that demonstrate the promise of this unique release mechanism.

Strategies and progresses for enhancing targeted antibiotic delivery

Antibiotic resistance is a global health issue and a potential risk for society. Antibiotics administered through conventional formulations are devoid of targeting effect and often spread to various undesired body sites, leading to sub-lethal concentrations at the site of action and thus resulting in emergence of resistance, as well as side effects. Moreover, we have a very slim antibiotic pipeline. Drug-delivery systems have been designed to control the rate, time, and site of drug release, and innovative approaches for antibiotic delivery provide a glint of hope for addressing these issues. This review elaborates different delivery strategies and approaches employed to overcome the limitations of conventional antibiotic therapy. These include antibiotic conjugates, prodrugs, and nanocarriers for local and targeted antibiotic release. In addition, a wide range of stimuli-responsive nanocarriers and biological carriers for targeted antibiotic delivery are discussed. The potential advantages and limitations of targeted antibiotic delivery strategies are described along with possible solutions to avoid these limitations. A number of antibiotics successfully delivered through these approaches with attained outcomes and potentials are reviewed.

Adenosine triphosphate-activated prodrug system for on-demand bacterial inactivation and wound disinfection

The prodrug approach has emerged as a promising solution to combat bacterial resistance and enhance treatment efficacy against bacterial infections. Here, we report an adenosine triphosphate (ATP)-activated prodrug system for on-demand treatment of bacterial infection. The prodrug system benefits from the synergistic action of zeolitic imidazolate framework-8 and polyacrylamide hydrogel microsphere, which simultaneously transports indole-3-acetic acid and horseradish peroxidase in a single carrier while preventing the premature activation of indole-3-acetic acid. The ATP-responsive characteristic of zeolitic imidazolate framework-8 allows the prodrug system to be activated by the ATP secreted by bacteria to generate reactive oxygen species (ROS), displaying exceptional broad-spectrum antimicrobial ability. Upon disruption of the bacterial membrane by ROS, the leaked intracellular ATP from dead bacteria can accelerate the activation of the prodrug system to further enhance antibacterial efficiency. In vivo experiments in a mouse model demonstrates the applicability of the prodrug system for wound disinfection with minimal side effects.

Prodrugs are increasingly promising in tackling bacterial resistance and efficacy of treatment. Here, the authors encapsulated horseradish peroxidase and zeolitic imidazolate framework-8 loaded with indole-3-acetic acid in polyacrylamide hydrogel microspheres for ATP-activated wound disinfection.

β-Lactamase-Responsive Hydrogel Drug Delivery Platform for Bacteria-Triggered Cargo Release

Antibiotic resistance is a growing public health threat that complicates the treatment of infections. β-Lactamase enzymes, which hydrolyze the β-lactam ring present in many common antibiotics, are a major cause of this resistance and are produced by a broad range of bacterial pathogens. Here, we developed hydrogels that degrade specifically in the presence of β-lactamases and β-lactamase-producing bacteria as a platform for bacteria-triggered drug delivery. A maleimide-functionalized β-lactamase-cleavable cephalosporin was used as a crosslinker in the fabrication of hydrogels through end-crosslinked polymerization with multiarm thiol-terminated poly(ethylene glycol) macromers via Michael-type addition. We demonstrated that only hydrogels containing the responsive crosslinker were degraded by β-lactamases and β-lactamase-producing bacteria in vitro and in an ex vivo porcine skin infection model. Fluorescent polystyrene nanoparticles, encapsulated in the hydrogels as model cargo, were released at rates that closely tracked hydrogel wet mass loss, confirming β-lactamase-triggered controlled cargo release. Nonresponsive hydrogels, lacking the β-lactam crosslinker, remained stable in the presence of β-lactamases and β-lactamase-producing bacteria and exhibited no change in mass or nanoparticle release. Furthermore, the responsive hydrogels remained stable in non-β-lactamase enzymes, including collagenases and lipases. These hydrogels have the potential to be used as a bacteria-triggered drug delivery system to control unnecessary exposure to encapsulated antimicrobials, which can provide effective infection treatment without exacerbating resistance.

Stimuli-Responsive Antibacterial Materials: Molecular Structures, Design Principles, and Biomedical Applications

Infections are regarded as the most severe complication associated with human health, which are urgent to be solved. Stimuli-responsive materials are appealing therapeutic platforms for antibacterial treatments, which provide great potential for accurate theranostics. In this review, the advantages, the response mechanisms, and the key design principles of stimuli-responsive antibacterial materials are highlighted. The biomedical applications, the current challenges, and future directions of stimuli-responsive antibacterial materials are also discussed. First, the categories of stimuli-responsive antibacterial materials are comprehensively itemized based on different sources of stimuli, including external physical environmental stimuli (e.g., temperature, light, electricity, salt, etc.) and bacterial metabolites stimuli (e.g., acid, enzyme, redox, etc.). Second, structural characteristics, design principles, and biomedical applications of the responsive materials are discussed, and the underlying interrelationships are revealed. The molecular structures and design principles are closely related to the sources of stimuli. Finally, the challenging issues of stimuli-responsive materials are proposed. This review will provide scientific guidance to promote the clinical applications of stimuli-responsive antibacterial materials.

Dimensionless parameter predicts bacterial prodrug success

Understanding mechanisms of antibiotic failure is foundational to combating the growing threat of multidrug-resistant bacteria. Prodrugs-which are converted into a pharmacologically active compound after administration-represent a growing class of therapeutics for treating bacterial infections but are understudied in the context of antibiotic failure. We hypothesize that strategies that rely on pathogen-specific pathways for prodrug conversion are susceptible to competing rates of prodrug activation and bacterial replication, which could lead to treatment escape and failure. Here, we construct a mathematical model of prodrug kinetics to predict rate-dependent conditions under which bacteria escape prodrug treatment. From this model, we derive a dimensionless parameter we call the Bacterial Advantage Heuristic (BAH) that predicts the transition between prodrug escape and successful treatment across a range of time scales (1-104  h), bacterial carrying capacities (5 × 104 -105  CFU/µl), and Michaelis constants (KM  = 0.747-7.47 mM). To verify these predictions in vitro, we use two models of bacteria-prodrug competition: (i) an antimicrobial peptide hairpin that is enzymatically activated by bacterial surface proteases and (ii) a thiomaltose-conjugated trimethoprim that is internalized by bacterial maltodextrin transporters and hydrolyzed by free thiols. We observe that prodrug failure occurs at BAH values above the same critical threshold predicted by the model. Furthermore, we demonstrate two examples of how failing prodrugs can be rescued by decreasing the BAH below the critical threshold via (i) substrate design and (ii) nutrient control. We envision such dimensionless parameters serving as supportive pharmacokinetic quantities that guide the design and administration of prodrug therapeutics.

Towards the sustainable discovery and development of new antibiotics

An ever-increasing demand for novel antimicrobials to treat life-threatening infections caused by the global spread of multidrug-resistant bacterial pathogens stands in stark contrast to the current level of investment in their development, particularly in the fields of natural-product-derived and synthetic small molecules. New agents displaying innovative chemistry and modes of action are desperately needed worldwide to tackle the public health menace posed by antimicrobial resistance. Here, our consortium presents a strategic blueprint to substantially improve our ability to discover and develop new antibiotics. We propose both short-term and long-term solutions to overcome the most urgent limitations in the various sectors of research and funding, aiming to bridge the gap between academic, industrial and political stakeholders, and to unite interdisciplinary expertise in order to efficiently fuel the translational pipeline for the benefit of future generations.

Antimicrobial resistance is an increasing threat to public health and encouraging the development of new antimicrobials is one of the most important ways to address the problem. This Roadmap article aims to bring together industrial, academic and political partners, and proposes both short-term and long-term solutions to this challenge.

Nanotechnology, Nanomedicine, and the Kidney

The kidneys are vital organs performing several essential functions. Their primary function is the filtration of blood and the removal of metabolic waste products as well as fluid homeostasis. Renal filtration is the main pathway for drug removal, highlighting the importance of this organ to the growing field of nanomedicine. The kidneys (i) have a key role in the transport and clearance of nanoparticles (NPs), (ii) are exposed to potential NPs’ toxicity, and (iii) are the targets of diseases that nanomedicine can study, detect, and treat. In this review, we aim to summarize the latest research on kidney-nanoparticle interaction. We first give a brief overview of the kidney’s anatomy and renal filtration, describe how nanoparticle characteristics influence their renal clearance, and the approaches taken to image and treat the kidney, including drug delivery and tissue engineering. Finally, we discuss the future and some of the challenges faced by nanomedicine.

Pan-proteome profiling of emerging and re-emerging zoonotic pathogen Orientia tsutsugamushi for getting insight into microbial pathogenesis

With the occurrence and evolution of antibiotic and multidrug resistance in bacteria most of the existing remedies are becoming ineffective. The pan-proteome exploration of the bacterial pathogens helps to identify the wide spectrum therapeutic targets which will be effective against all strains in a species. The current study is focused on the pan-proteome profiling of zoonotic pathogen Orientia tsutsugamushi (Ott) for the identification of potential therapeutic targets. The pan-proteome of Ott is estimated to be extensive in nature that has 1429 protein clusters, out of which 694 were core, 391 were accessory, and 344 were unique. It was revealed that 622 proteins were essential, 222 proteins were virulent factors, and 42 proteins were involved in antibiotic resistance. The potential therapeutic targets were further classified into eleven broad classes among which gene expression and regulation, transport, and metabolism were dominant. The biological interactome analysis of therapeutic targets revealed that an ample amount of interactions were present among the proteins involved in DNA replication, ribosome assembly, cellwall metabolism, cell division, and antimicrobial resistance. The predicted therapeutic targets from the pan-proteome of Ott are involved in various biological processes, virulence, and antibiotic resistance; hence envisioned as potential candidates for drug discovery to combat scrub typhus.

Novel Cephalosporin Conjugates Display Potent and Selective Inhibition of Imipenemase-Type Metallo-β-Lactamases

In an attempt to exploit the hydrolytic mechanism by which β-lactamases degrade cephalosporins, we designed and synthesized a series of novel cephalosporin prodrugs aimed at delivering thiol-based inhibitors of metallo-β-lactamases (MBLs) in a spatiotemporally controlled fashion. While enzymatic hydrolysis of the β-lactam ring was observed, it was not accompanied by inhibitor release. Nonetheless, the cephalosporin prodrugs, especially thiomandelic acid conjugate (8), demonstrated potent inhibition of IMP-type MBLs. In addition, conjugate 8 was also found to greatly reduce the minimum inhibitory concentration of meropenem against IMP-producing bacteria. The results of kinetic experiments indicate that these prodrugs inhibit IMP-type MBLs by acting as slowly turned-over substrates. Structure-activity relationship studies revealed that both phenyl and carboxyl moieties of 8 are crucial for its potency. Furthermore, modeling studies indicate that productive interactions of the thiomandelic acid moiety of 8 with Trp28 within the IMP active site may contribute to its potency and selectivity.

Recent advances in prodrug-based nanoparticle therapeutics

Extensive research into prodrug modification of active pharmaceutical ingredients and nanoparticle drug delivery systems has led to unprecedented levels of control over the pharmacological properties of drugs and resulted in the approval of many prodrug or nanoparticle-based therapies. In recent years, the combination of these two strategies into prodrug-based nanoparticle drug delivery systems (PNDDS) has been explored as a way to further advance nanomedicine and identify novel therapies for difficult-to-treat indications. Many of the PNDDS currently in the clinical development pipeline are expected to enter the market in the coming years, making the rapidly evolving field of PNDDS highly relevant to pharmaceutical scientists. This review paper is intended to introduce PNDDS to the novice reader while also updating those working in the field with a comprehensive summary of recent efforts. To that end, first, an overview of FDA-approved prodrugs is provided to familiarize the reader with their advantages over traditional small molecule drugs and to describe the chemistries that can be used to create them. Because this article is part of a themed issue on nanoparticles, only a brief introduction to nanoparticle-based drug delivery systems is provided summarizing their successful application and unfulfilled opportunities. Finally, the review's centerpiece is a detailed discussion of rationally designed PNDDS formulations in development that successfully leverage the strengths of prodrug and nanoparticle approaches to yield highly effective therapeutic options for the treatment of many diseases.

Cephalosporin Prodrug Inhibitors Overcome Metallo-β-Lactamase Driven Antibiotic Resistance

The increasing prevalence of metallo-β-lactamase (MBL)-expressing bacteria presents a worrying trend in antibiotic resistance. MBLs rely on active site zinc ions for their hydrolytic activity and the pursuit of MBL-inhibitors has therefore involved the investigation of zinc chelators. To ensure that such chelators specifically target MBLs, a series of cephalosporin prodrugs of two potent zinc-binders: dipicolinic acid (DPA) and 8-thioquinoline (8-TQ) was prepared. Although both DPA and 8-TQ bind free zinc very tightly (Kd values in the low nm range), the corresponding cephalosporin conjugates do not. The cephalosporin conjugates are efficiently hydrolyzed by MBLs to release DPA or 8-TQ, as confirmed by using both NMR and LC-MS studies. Notably, the cephalosporin prodrugs of DPA and 8-TQ show potent inhibitory activity against NDM, VIM, and IMP classes of MBLs and display potent synergy with meropenem against MBL-expressing clinical isolates of K. pneumoniae and E. coli.

The Odd Couple(s): An Overview of Beta-Lactam Antibiotics Bearing More Than One Pharmacophoric Group

β-lactam antibiotics are among the most important and widely used antimicrobials worldwide and are comprised of a large family of compounds, obtained by chemical modifications of the common scaffolds. Usually these modifications include the addition of active groups, but less frequently, molecules were synthesized in which either two β-lactam rings were joined to create a single bifunctional compound, or the azetidinone ring was joined to another antibiotic scaffold or another molecule with a different activity, in order to create a molecule bearing two different pharmacophoric functions. In this review, we report some examples of these derivatives, highlighting their biological properties and discussing how this strategy can lead to the development of innovative antibiotics that can represent either novel weapons against the rampant increase of antimicrobial resistance, or molecules with a broader spectrum of action.

Targeting the bacterial SOS response for new antimicrobial agents: drug targets, molecular mechanisms and inhibitors

Antimicrobial resistance is a pressing threat to global health, with multidrug-resistant pathogens becoming increasingly prevalent. The bacterial SOS pathway functions in response to DNA damage that occurs during infection, initiating several pro-survival and resistance mechanisms, such as DNA repair and hypermutation. This makes SOS pathway components potential targets that may combat drug-resistant pathogens and decrease resistance emergence. This review discusses the mechanism of the SOS pathway; the structure and function of potential targets AddAB, RecBCD, RecA and LexA; and efforts to develop selective small-molecule inhibitors of these proteins. These inhibitors may serve as valuable tools for target validation and provide the foundations for desperately needed novel antibacterial therapeutics.

Self-Assembled Disulfide Bond Bearing Paclitaxel-Camptothecin Prodrug Nanoparticle for Lung Cancer Therapy

Self-assembled prodrugs (SAPDs), which combine prodrug strategy and the merits of self-assembly, not only represent an appealing type of therapeutics, enabling the spontaneous organization of supramolecular nanocomposites with defined structures in aqueous environments, but also provide a new method to formulate existing drugs for more favorable outcomes. To increase drug loading and combination therapy, we covalently conjugated paclitaxel (PTX) and camptothecin (CPT) through a disulfide linker into a prodrug, designated PTX-S-S-CPT. The successful production of PTX-S-S-CPT prodrug was confirmed by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). This prodrug spontaneously undergoes precipitation in aqueous surroundings. Taking advantage of a flow-focusing microfluidics platform, the prodrug nanoparticles (NPs) have good monodispersity, with good reproducibility and high yield. The as-prepared prodrug NPs were characterized with dynamic light scattering (DLS) and transmission electron microscopy (TEM), demonstrating spherical morphology of around 200 nm in size. In the end, the self-assembled NPs were added to mouse embryonic fibroblast (MEF), mouse lung adenocarcinoma and Lewis lung carcinoma (LLC) cell lines, and human non-small cell lung cancer cell line A549 to evaluate cell viability and toxicity. Due to the redox response with a disulfide bond, the PTX-S-S-CPT prodrug NPs significantly inhibited cancer cell growth, but had no obvious toxicity to healthy cells. This prodrug strategy is promising for co-delivery of PTX and CPT for lung cancer treatment, with reduced side effects on healthy cells.

Antibacterial Prodrugs to Overcome Bacterial Resistance

Bacterial resistance to present antibiotics is emerging at a high pace that makes the development of new treatments a must. At the same time, the development of novel antibiotics for resistant bacteria is a slow-paced process. Amid the massive need for new drug treatments to combat resistance, time and effort preserving approaches, like the prodrug approach, are most needed. Prodrugs are pharmacologically inactive entities of active drugs that undergo biotransformation before eliciting their pharmacological effects. A prodrug strategy can be used to revive drugs discarded due to a lack of appropriate pharmacokinetic and drug-like properties, or high host toxicity. A special advantage of the use of the prodrug approach in the era of bacterial resistance is targeting resistant bacteria by developing prodrugs that require bacterium-specific enzymes to release the active drug. In this article, we review the up-to-date implementation of prodrugs to develop medications that are active against drug-resistant bacteria.

Dual-Pharmacophore Pyrithione-Containing Cephalosporins Kill Both Replicating and Nonreplicating Mycobacterium tuberculosis

The historical view of β-lactams as ineffective antimycobacterials has given way to growing interest in the activity of this class against Mycobacterium tuberculosis (Mtb) in the presence of a β-lactamase inhibitor. However, most antimycobacterial β-lactams kill Mtb only or best when the bacilli are replicating. Here, a screen of 1904 β-lactams led to the identification of cephalosporins substituted with a pyrithione moiety at C3' that are active against Mtb under both replicating and nonreplicating conditions, neither activity requiring a β-lactamase inhibitor. Studies showed that activity against nonreplicating Mtb required the in situ release of the pyrithione, independent of the known class A β-lactamase, BlaC. In contrast, replicating Mtb could be killed both by released pyrithione and by the parent β-lactam. Thus, the antimycobacterial activity of pyrithione-containing cephalosporins arises from two mechanisms that kill mycobacteria in different metabolic states.

Highly selective and wash-free visualization of resistant bacteria with a relebactam-derived fluorogenic probe

An unprecedented relebactam-based fluorogenic probe is reported for the wash-free imaging of resistant bacteria.