Small Peptidic Ionophore for Calcium Transport.

Synthetic calcium transporters are few despite their potential biological significance. Herein, we report small alanine-derived peptides containing pyridyl-triazole motifs for inducing calcium selectivity. The peptides are decorated with hydrophobic alkyl chains to facilitate membrane insertion. The most efficient peptide scaffold has an EC50 value of 0.09 mol % and functions as a calcium carrier.

A minimalistic tetrapeptide amphiphile scaffold for transmembrane pores with a preference for sodium.

Synthetic channels or pores that are easy to synthesize, stable and cation-selective are extremely attractive for the development of therapeutics and materials. Herein, we report a pore developed from a small tetrapeptide scaffold that shows a preference for sodium over lithium/potassium. The sodium selectivity is attributed to the appended oligoether tail at the C-terminus. A peptide dimer is proposed as the predominant cation-transporting pore. Such pyridine containing stable pores can be potentially utilized for the pH modulated ion transport.

Cation-halide transport through peptide pores containing aminopicolinic acid.

Synthetic pores that selectively transport ions of biological significance through membranes could be potentially used in medical diagnostics or therapeutics. Herein, we report cation-selective octapeptide pores derived from alanine and aminopicolinic acid. The ion transport mechanism through the pores has been established to be a cation-chloride symport. The cation-chloride co-transport is biologically essential for the efficient functioning of the central nervous system and has been implicated in diseases such as epilepsy. The pores formed in synthetic lipid bilayers do not exhibit any closing events. The ease of synthesis as well as infinite lifetimes of these pores provides scope for modifying their transport behaviour to develop sensors.

Isoamphipathic antibacterial molecules regulating activity and toxicity through positional isomerism.

Peptidomimetic antimicrobials exhibit a selective interaction with bacterial cells over mammalian cells once they have achieved an optimum amphiphilic balance (hydrophobicity/hydrophilicity) in the molecular architecture. To date, hydrophobicity and cationic charge have been considered the crucial parameters to attain such amphiphilic balance. However, optimization of these properties is not enough to circumvent unwanted toxicity towards mammalian cells. Hence, herein, we report new isoamphipathic antibacterial molecules (IAMs: 1-3) where positional isomerism was introduced as one of the guiding factors for molecular design. This class of molecules displayed good (MIC = 1-8 µg mL-1 or µM) to moderate [MIC = 32-64 µg mL-1 (32.2-64.4 µM)] antibacterial activity against multiple Gram-positive and Gram-negative bacteria. Positional isomerism showed a strong influence on regulating antibacterial activity and toxicity for ortho [IAM-1: MIC = 1-32 µg mL-1 (1-32.2 µM), HC50 = 650 µg mL-1 (654.6 µM)], meta [IAM-2: MIC = 1-16 µg mL-1 (1-16.1 µM), HC50 = 98 µg mL-1 (98.7 µM)] and para [IAM-3: MIC = 1-16 µg mL-1 (1-16.1 µM), HC50 = 160 µg mL-1 (161.1 µM)] isomers. Co-culture studies and investigation of membrane dynamics indicated that ortho isomer, IAM-1 exerted more selective activity towards bacterial over mammalian membranes, compared to meta and para isomers. Furthermore, the mechanism of action of the lead molecule (IAM-1) has been characterized through detailed molecular dynamics simulations. In addition, the lead molecule displayed substantial efficacy against dormant bacteria and mature biofilms, unlike conventional antibiotics. Importantly, IAM-1 exhibited moderate in vivo activity against MRSA wound infection in a murine model with no detectable dermal toxicity. Altogether, the report explored the design and development of isoamphipathic antibacterial molecules to establish the role of positional isomerism in achieving selective and potential antibacterial agents.

Small-Molecular Adjuvants with Weak Membrane Perturbation Potentiate Antibiotics against Gram-Negative Superbugs.

Combination therapy with membrane-targeting compounds is at the forefront because the bacterial membrane is an attractive target considering its role in various multidrug-resistant elements. However, this strategy is crippled by the toxicity associated with these agents. The structural requirements for optimum membrane perturbation and minimum toxicity have not been explored for membrane-targeting antibiotic potentiators or adjuvants. Here, we report the structural influence of different chemical moieties on membrane perturbation, activity, toxicity, and potentiating ability in norspermidine derivatives. It has been shown in this report that weak membrane perturbation, achieved by the incorporation of cyclic hydrophobic moieties, is an effective strategy to design antibiotic adjuvants with negligible in vitro toxicity and activity but good potentiating ability. Aryl or adamantane functionalized derivatives were found to be better resorts as opposed to the acyclic analogues, exhibiting as high as 4096-fold potentiation of multiple classes of antibiotics toward critical Gram-negative superbugs. The mechanism of potentiation was nonspecific, consisting of weak outer-membrane permeabilization, membrane depolarization, and efflux inhibition. This unique concept of "weakly perturbing the membrane" by incorporating cyclic hydrophobic moieties in a chemical design with free amine groups serves as a breakthrough for nontoxic membrane-perturbing adjuvants and has the potential to revitalize the effect of obsolete antibiotics to treat complicated Gram-negative bacterial infections.

Alkyl-Aryl-Vancomycins: Multimodal Glycopeptides with Weak Dependence on the Bacterial Metabolic State.

Resistance to last-resort antibiotics such as vancomycin for Gram-positive bacterial infections necessitates the development of new therapeutics. Furthermore, the ability of bacteria to survive antibiotic therapy through formation of biofilms and persister cells complicates treatment. Toward this, we report alkyl-aryl-vancomycins (AAVs), with high potency against vancomycin-resistant enterococci and staphylococci. Unlike vancomycin, the lead compound AAV-qC10 was bactericidal and weakly dependent on bacterial metabolism. This resulted in complete eradication of non-growing cells of MRSA and disruption of its biofilms. In addition to inhibiting cell wall biosynthesis like vancomycin, AAV-qC10 also depolarizes and permeabilizes the membrane. More importantly, the compound delocalized the cell division protein MinD, thereby impairing bacterial growth through multiple pathways. The potential of AAV-qC10 is exemplified by its superior efficacy against MRSA in a murine thigh infection model as compared to vancomycin. This work paves the way for structural optimization and drug development for combating drug-resistant bacterial infections.

One-Step Curable, Covalently Immobilized Coating for Clinically Relevant Surfaces That Can Kill Bacteria, Fungi, and Influenza Virus.

Microbial attachment and subsequent colonization onto surfaces lead to the spread of deadly community-acquired and hospital-acquired (nosocomial) infections. Cationic polymeric coatings have gained enormous attention to tackle this scenario. However, non-biodegradable cationic polymer coated surfaces suffer from accumulation of microbial debris leading to toxicity and consequent complexities. Synthetic reproducibility and sophisticated coating techniques further limit their application. In this present study, we have developed one-step curable, covalent coatings based on two organo- and water-soluble small molecules, quaternary benzophenone-based ester and quaternary benzophenone-based amide, which can cross-link on surfaces upon UV irradiation. Upon contact, the coating completely killed bacteria and fungi in vitro including drug-resistant pathogens methicillin-resistant Staphylococcus aureus (MRSA) and fluconazole-resistant Candida albicans spp. The coating also showed antiviral activity against notorious influenza virus with 100% killing. The coated surfaces also killed stationary-phase cells of MRSA, which cannot be eradicated by traditional antibiotics. Upon hydrolysis, the surfaces switched to an antifouling state displaying significant reduction in bacterial adherence. To the best of our knowledge, this is the first report of an antimicrobial coating which could kill all of bacteria, fungi, and influenza virus. Taken together, the antimicrobial coating reported herein holds great promise to be developed for further application in healthcare settings.