Goutham B. Manjunath

Small Molecular Antibacterial Peptoid Mimics: The Simpler the Better!

The emergence of multidrug resistant bacteria compounded by the depleting arsenal of antibiotics has accelerated efforts toward development of antibiotics with novel mechanisms of action. In this report, we present a series of small molecular antibacterial peptoid mimics which exhibit high in vitro potency against a variety of Gram-positive and Gram-negative bacteria, including drug-resistant species such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium. The highlight of these compounds is their superior activity against the major nosocomial pathogen Pseudomonas aeruginosa. Nontoxic toward mammalian cells, these rapidly bactericidal compounds primarily act by permeabilization and depolarization of bacterial membrane. Synthetically simple and selectively antibacterial, these compounds can be developed into a newer class of therapeutic agents against multidrug resistant bacterial species.

Polymers with tunable side-chain amphiphilicity as non-hemolytic antibacterial agents

Quaternized polymers mimicking the antimicrobial peptides were created by tuning the side-chain amphiphilicity using a first-time approach of post-functionalization. They displayed excellent efficacy against pathogenic bacteria even in human plasma and membrane disruptive mode of action. The optimized polymers and degraded products were non-hemolytic.

Broad Spectrum Antibacterial and Antifungal Polymeric Paint Materials: Synthesis, Structure–Activity Relationship, and Membrane-Active Mode of Action

Microbial attachment and subsequent colonization onto surfaces lead to the spread of deadly community-acquired and hospital-acquired (nosocomial) infections. Noncovalent immobilization of water insoluble and organo-soluble cationic polymers onto a surface is a facile approach to prevent microbial contamination. In the present study, we described the synthesis of water insoluble and organo-soluble polymeric materials and demonstrated their structure-activity relationship against various human pathogenic bacteria including drug-resistant strains such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), and beta lactam-resistant Klebsiella pneumoniae as well as pathogenic fungi such as Candida spp. and Cryptococcus spp. The polymer coated surfaces completely inactivated both bacteria and fungi upon contact (5 log reduction with respect to control). Linear polymers were more active and found to have a higher killing rate than the branched polymers. The polymer coated surfaces also exhibited significant activity in various complex mammalian fluids such as serum, plasma, and blood and showed negligible hemolysis at an amount much higher than minimum inhibitory amounts (MIAs). These polymers were found to have excellent compatibility with other medically relevant polymers (polylactic acid, PLA) and commercial paint. The cationic hydrophobic polymer coatings disrupted the lipid membrane of both bacteria and fungi and thus showed a membrane-active mode of action. Further, bacteria did not develop resistance against these membrane-active polymers in sharp contrast to conventional antibiotics and lipopeptides, thus the polymers hold great promise to be used as coating materials for developing permanent antimicrobial paint.

Membrane active vancomycin analogues: a strategy to combat bacterial resistance.

The alarming growth of antibiotic resistant superbugs such as vancomycin-resistant Enterococci and Staphylococci has become a major global health hazard. To address this issue, we report the development of lipophilic cationic vancomycin analogues possessing excellent antibacterial activity against several drug-resistant strains. Compared to vancomycin, efficacy greater than 1000-fold was demonstrated against vancomycin-resistant Enterococci (VRE). Significantly, unlike vancomycin, these compounds were shown to be bactericidal at low concentrations and did not induce bacterial resistance. An optimized compound in the series, compared to vancomycin, showed higher activity in methicillin-resistant Staphylococcus aureus (MRSA) infected mouse model and exhibited superior antibacterial activity in whole blood with no observed toxicity. The remarkable activity of these compounds is attributed to the incorporation of a new membrane disruption mechanism into vancomycin and opens up a great opportunity for the development of novel antibiotics.

Membrane Active Small Molecules Show Selective Broad Spectrum Antibacterial Activity with No Detectable Resistance and Eradicate Biofilms

Treating bacterial biofilms with conventional antibiotics is limited due to ineffectiveness of the drugs and higher propensity to develop bacterial resistance. Development of new classes of antibacterial therapeutics with alternative mechanisms of action has become imperative. Herein, we report the design, synthesis, and biological evaluations of novel membrane-active small molecules featuring two positive charges, four nonpeptidic amide groups, and variable hydrophobic/hydrophilic (amphiphilic) character. The biocides synthesized via a facile methodology not only displayed good antibacterial activity against wild-type bacteria but also showed high activity against various drug-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium (VRE), and β-lactam-resistant Klebsiella pneumoniae. Further, these biocides not only inhibited the formation of biofilms but also disrupted the established S. aureus and E. coli biofilms. The membrane-active biocides hindered the propensity to develop bacterial resistance. Moreover, the biocides showed negligible toxicity against mammalian cells and thus bear potential to be used as therapeutic agents.

Tackling vancomycin-resistant bacteria with 'lipophilic-vancomycin-carbohydrate conjugates'.

Vancomycin, a glycopeptide antibiotic, has long been a drug of choice for life-threatening Gram-positive bacterial infections. Vancomycin confers its antibacterial activity by inhibiting bacterial cell wall biosynthesis. However, over the time, vancomycin has also been rendered ineffective by vancomycin-resistant bacteria (VRB). These bacteria developed resistance to it by alteration of cell wall precursor from D-Ala-D-Ala to D-Ala-D-Lac (vancomycin-resistant Enterococci, VRE), which leads to manifold reduction in the binding constant and results in the loss of antibacterial activity. Herein, we report various vancomycin–sugar analogs, based on a simple design rationale, which exhibit increased binding affinity to VRB, thereby resensitizing VRB to vancomycin. Optimized vancomycin–sugar conjugate exhibited 150-fold increase in affinity for N,N′-diacetyl-Lys-D-Ala-D-Lac compared with vancomycin. This improved binding affinity was also reflected in its antibacterial activity, wherein the MIC value was brought down from 750 to 36 μM against VRE (VanA phenotype). To further sensitize against VRE, we appended lipophilic alkyl chain to optimized vancomycin–sugar conjugate. This lipophilic–vancomycin–sugar conjugate was >1000-fold (MIC=0.7 μM) and 250-fold (MIC=1 μM) more effective against VanA and VanB strains of VRE, respectively, compared with vancomycin. Therefore, this synthetically simple approach could lead to the development of new generation of glycopeptide antibiotics, which can be clinically used to tackle VRB infections.

Aryl-Alkyl-Lysines: Agents That Kill Planktonic Cells, Persister Cells, Biofilms of MRSA and Protect Mice from Skin-Infection

Development of synthetic strategies to combat Staphylococcal infections, especially those caused by methicillin resistant Staphyloccus aureus (MRSA), needs immediate attention. In this manuscript we report the ability of aryl-alkyl-lysines, simple membrane active small molecules, to treat infections caused by planktonic cells, persister cells and biofilms of MRSA. A representative compound, NCK-10, did not induce development of resistance in planktonic cells in multiple passages and retained activity in varying environments of pH and salinity. At low concentrations the compound was able to depolarize and permeabilize the membranes of S. aureus persister cells rapidly. Treatment with the compound not only eradicated pre-formed MRSA biofilms, but also brought down viable counts in bacterial biofilms. In a murine model of MRSA skin infection, the compound was more effective than fusidic acid in bringing down the bacterial burden. Overall, this class of molecules bears potential as antibacterial agents against skin-infections.

Glycopeptide Antibiotic To Overcome the Intrinsic Resistance of Gram-Negative Bacteria

The emergence of drug resistance along with a declining pipeline of clinically useful antibiotics has made it vital to develop more effective antimicrobial therapeutics, particularly against difficult-to-treat Gram-negative pathogens (GNPs). Many antibacterial agents, including glycopeptide antibiotics such as vancomycin, are inherently inactive toward GNPs because of their inability to cross the outer membrane of these pathogens. Here, we demonstrate, for the first time, lipophilic cationic (permanent positive charge) vancomycin analogues were able to permeabilize the outer membrane of GNPs and overcome the inherent resistance of GNPs toward glycopeptides. Unlike vancomycin, these analogues were shown to have a high activity against a variety of multidrug-resistant clinical isolates such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. In the murine model of carbapenem-resistant A. baumannii infection, the optimized compound showed potent activity with no observed toxicity. The notable activity of these compounds is attributed to the incorporation of new membrane disruption mechanisms (cytoplasmic membrane depolarization along with outer and inner (cytoplasmic) membrane permeabilization) into vancomycin. Therefore, our results indicate the potential of the present vancomycin analogues to be used against drug-resistant GNPs, thus strengthening the antibiotic arsenal for combating Gram-negative bacterial infections.

Aryl-alkyl-lysines: Membrane-Active Small Molecules Active against Murine Model of Burn Infection.

Infections caused by drug-resistant Gram-negative pathogens continue to be significant contributors to human morbidity. The recent advent of New Delhi metallo-β-lactamase-1 (blaNDM-1) producing pathogens, against which few drugs remain active, has aggravated the problem even further. This paper shows that aryl-alkyl-lysines, membrane-active small molecules, are effective in treating infections caused by Gram-negative pathogens. One of the compounds of the study was effective in killing planktonic cells as well as dispersing biofilms of Gram-negative pathogens. The compound was extremely effective in disrupting preformed biofilms and did not select resistant bacteria in multiple passages. The compound retained activity in different physiological conditions and did not induce any toxic effect in female Balb/c mice until concentrations of 17.5 mg/kg. In a murine model of Acinetobacter baumannii burn infection, the compound was able to bring the bacterial burden down significantly upon topical application for 7 days.

In vivo antibacterial activity and pharmacological properties of the membrane-active glycopeptide antibiotic YV11455.

The membrane-active glycopeptide antibiotic YV11455 is a lipophilic cationic vancomycin analogue that demonstrates rapid and concentration-dependent killing of clinically relevant multidrug-resistant (MDR) Gram-positive bacteria in vitro. YV11455 was 2-fold and 54-270-fold more effective than vancomycin against clinical isolates of vancomycin-sensitive and vancomycin-resistant bacteria, respectively. In this study, the in vivo efficacy, pharmacodynamics, pharmacokinetics and acute toxicology of YV11455 were investigated. In vivo activity and pharmacodynamics were determined in the neutropenic mouse thigh infection model against meticillin-resistant Staphylococcus aureus (MRSA). YV11455 produced dose-dependent reductions in MRSA titres in thigh muscle. When administered intravenously, the 50% effective dose (ED(50)) for YV11455 against MRSA was found to be 3.3 mg/kg body weight, and titres were reduced by up to ca. 3log(10)CFU/g from pre-treatment values at a dosage of 12 mg/kg with single treatment. Single-dose pharmacokinetic studies demonstrated linear kinetics and a prolonged half-life, with an increase in drug exposure (area under the concentration-time curve) compared with vancomycin. The peak plasma concentration following an intravenous dose of 12 mg/kg was 543.5 μg/mL. Acute toxicology studies revealed that YV11455 did not cause any significant alterations in biochemical parameters or histological pictures related to major organs such as the liver and kidney at its pharmacodynamic endpoint (ED(3-log kill)). These findings collectively suggest that YV11455 could be used clinically for the treatment of infections caused by MDR Gram-positive bacteria.