Reversal of Tetracycline Resistance in Escherichia coli by Noncytotoxic bis(Tryptophan)s

Resorcinol-based Bolaamphiphilic Quaternary Ammonium Compounds

Quaternary ammonium compounds (QACs) play crucial disinfectant roles in healthcare, industry, and domestic settings. Most commercially utilized QACs like benzalkonium chloride have a common architectural theme, leading to a rise in bacterial resistance and urgent need for novel structural classes. Some potent QACs such as chlorhexidine (CHX) and octenidine (OCT) feature a bolaamphiphilic architecture, comprised of two cationic centers at the molecular periphery and a non-polar region connecting them; these compounds show promise to elude bacterial resistance mechanisms. Inspired by such structures, we synthesized a series of 43 biscationic amphiphilic compounds focused on a resorcinol core, featuring flexibility of linker lengths, alkyl tails, and relative substituent positioning, to study their structure activity relationships (SARs). Antibacterial activity evaluation against a panel of gram-positive and gram-negative strains, including ESKAPE pathogens (A. baumannii, P. aeruginosa), were encouraging, with minimum inhibitory concentrations (MICs) of 0.5-4 μM against all tested strains for select compounds. Ten prepared compounds bearing either 17 or 18 total side chain carbons demonstrated uniformly strong antibacterial activity against P. aeruginosa (MIC 4-16 μM) and 6 other strains (MIC ≤4 μM), irrespective of cationic spacing. These findings promise to further extend the application of bolaamphiphilic QACs as a novel class of disinfectants.

Molecular mechanisms and therapeutic significance of Tryptophan Metabolism and signaling in cancer

Tryptophan (Trp) metabolism involves three primary pathways: the kynurenine (Kyn) pathway (KP), the 5-hydroxytryptamine (serotonin, 5-HT) pathway, and the indole pathway. Under normal physiological conditions, Trp metabolism plays crucial roles in regulating inflammation, immunity, and neuronal function. Key rate-limiting enzymes such as indoleamine-2,3-dioxygenase (IDO), Trp-2,3-dioxygenase (TDO), and kynurenine monooxygenase (KMO) drive these metabolic processes. Imbalances in Trp metabolism are linked to various cancers and often correlate with poor prognosis and adverse clinical characteristics. Dysregulated Trp metabolism fosters tumor growth and immune evasion primarily by creating an immunosuppressive tumor microenvironment (TME). Activation of the KP results in the production of immunosuppressive metabolites like Kyn, which modulate immune responses and promote oncogenesis mainly through interaction with the aryl hydrocarbon receptor (AHR). Targeting Trp metabolism therapeutically has shown significant potential, especially with the development of small-molecule inhibitors for IDO1, TDO, and other key enzymes. These inhibitors disrupt the immunosuppressive signals within the TME, potentially restoring effective anti-tumor immune responses. Recently, IDO1 inhibitors have been tested in clinical trials, showing the potential to enhance the effects of existing cancer therapies. However, mixed results in later-stage trials underscore the need for a deeper understanding of Trp metabolism and its complex role in cancer. Recent advancements have also explored combining Trp metabolism inhibitors with other treatments, such as immune checkpoint inhibitors, chemotherapy, and radiotherapy, to enhance therapeutic efficacy and overcome resistance mechanisms. This review summarizes the current understanding of Trp metabolism and signaling in cancer, detailing the oncogenic mechanisms and clinical significance of dysregulated Trp metabolism. Additionally, it provides insights into the challenges in developing Trp-targeted therapies and future research directions aimed at optimizing these therapeutic strategies and improving patient outcomes.

Unveiling the potent activity of a synthetic ion transporter against multidrug-resistant Gram-positive bacteria and biofilms

The increasing prevalence of drug-resistant infections caused by Gram-positive bacteria poses a significant threat to public healthcare. These pathogens exhibit not only smart resistance mechanisms but also form impenetrable biofilms on various surfaces, rendering them resilient to conventional therapies. In this study, we present the potent antibacterial activity of a synthetic ion transporter T against multi-drug resistant (MDR) Gram-positive pathogens, with minimum inhibitory concentration (MIC) values ranging from 0.5 to 2 μg mL-1. The compound demonstrates high selectivity with negligible toxicity towards mammalian cells (HC50 = 810 μg mL-1). It exhibits fast killing kinetics, completely eliminating >5 log bacterial cells within 12 h. Moreover, the compound displays efficacy against both planktonic bacteria and preformed biofilms of methicillin-resistant S. aureus (MRSA), reducing the bacterial burden within the biofilm by 2 log. Mechanistic investigations reveal that the ion transporter depolarizes the bacterial membrane potential and enhances membrane permeability. Additionally, it generates reactive oxygen species, contributing to its bactericidal activity. Notably, MRSA did not exhibit detectable resistance to the ion transporter even after serial passaging for 10 days. Collectively, this novel class of ion transporter holds promise as a therapeutic candidate for combating infections caused by multi-drug resistant Gram-positive bacteria.

Pyridyl-Linked Hetero Hydrazones: Transmembrane H+/Cl- Symporters with Efficient Antibacterial Activity

The development of potent antibacterial agents has become increasingly difficult as bacteria continue to evolve and develop resistance to antibiotics. It is therefore imperative to find effective antimicrobial agents that can address the evolving challenges posed by infectious diseases and antimicrobial resistance. Using artificial transmembrane ion transporters is an emerging and promising avenue to address this issue. We report pyridyl-linked hetero hydrazones as highly efficient transmembrane HCl symporters. These compounds offer an appropriate HCl binding site through cooperative protonation, followed by recognition of chloride ions. HCl transport by these compounds inhibits the growth of different Gram-negative bacterial strains with high efficacy by affecting the cell envelope homeostasis. This specific class of compounds holds substantial promise in the ongoing pursuit of developing highly efficient antibacterial agents.

Antimicrobial and Adjuvant Potencies of Di-n-alkyl Substituted Diazalariat Ethers

Lariat ethers are macrocyclic polyethers-crown ethers-to which sidearms are appended. 4,13-Diaza-18-crown-6 having twin alkyl chains at the nitrogens show biological activity. They exhibit antibiotic activity, but when co-administered at with an FDA-approved antibiotic, the latter's potency is often strongly enhanced. Potency enhancements and resistance reversals have been documented in vitro for a range of Gram-negative and Gram-positive bacteria with a variety of antimicrobials. Strains of E. coli and Staphylococcus aureus having resistance to a range of drugs have been studied and the potency enhancements (checkerboards) are reported here. Drugs included in the present study are ampicillin, cefepime, chlortetracycline, ciprofloxacin, doxycycline, kanamycin, minocycline, norfloxacin, oxycycline, penicillin G, and tetracycline. Enhancements of norfloxacin potency against S. aureus 1199B of up to 128-fold were observed. The properties of these lariat ethers have been studied to determine solubility, their membrane penetration, cytotoxicity and mammalian cell survival, and their effect on bacterial efflux pumps. It is shown that in some cases, the lariat ethers have complex antimicrobials with considerable selectivity. Based on these observations, including 1:1 complexation between lariat ethers and antimicrobials and the cytotoxicity of the MeI salts showing a separation index of 32-fold, they hold significant potential for further development.

Host defense peptide mimicking cyclic peptoid polymers exerting strong activity against drug-resistant bacteria

Extensive use of antibiotics accelerates the emergence of drug-resistant bacteria and related infections. Host defense peptides (HDPs) have been studied as promising and potential therapeutic candidates. However, their clinical applications of HDPs are limited due to their high cost of synthesis and low stability upon proteolysis. Therefore, HDP mimics have become a new approach to address the challenge of bacterial resistance. In this work, we design the amphiphilic peptoid polymers by mimicking the positively charged and hydrophobic structures of HDPs and synthesize a series of cyclic peptoid polymers efficiently via the polymerization on α-amino acid N-substituted glycine N-carboxyanhydrides (α-NNCAs) using 1,8-diazabicycloundec-7-ene (DBU) as the initiator. The optimal cyclic peptoid polymer, poly(Naeg_0.7Npfbg_0.3)₂₀, displays strong antibacterial activities against drug-resistant bacteria, but low hemolysis and cytotoxicity. In addition, the mode-of-action study indicates that the antibacterial mechanism is associated with bacterial membrane interaction. Our study implies that HDP mimicking cyclic peptoid polymers have potential application in treating drug-resistant bacterial infections.

Bis(Tryptophan) Amphiphiles Form Ion Conducting Pores and Enhance Antimicrobial Activity against Resistant Bacteria

The compounds referred to as bis(tryptophan)s (BTs) have shown activity as antimicrobials. The hypothesis that the activity of these novel amphiphiles results from insertion in bilayer membranes and transport of cations is supported by planar bilayer voltage-clamp studies reported herein. In addition, fluorescence studies of propidium iodide penetration of vital bacteria confirmed enhanced permeability. It was also found that BTs having either meta-phenylene or n-dodecylene linkers function as effective adjuvants to enhance the properties of FDA-approved antimicrobials against organisms such as S. aureus. In one example, a BT-mediated synergistic effect enhanced the potency of norfloxacin against S. aureus by 128-fold. In order to determine if related compounds in which tryptophan was replaced by other common amino acids (H₂N-Aaa-linker-Aaa-NH₂) we active, a family of analogs have been prepared, characterized, and tested as controls for both antimicrobial activity and as adjuvants for other antimicrobials against both Gram-negative and Gram-positive bacteria. The most active of the compounds surveyed remain the bis(tryptophan) derivatives.

Biomedically Relevant Applications of Bolaamphiphiles and Bolaamphiphile-Containing Materials

Bolaamphiphiles (BAs) are structurally segmented molecules with rich assembly characteristics and diverse physical properties. Interest in BAs as standalone active agents or as constituents of more complex therapeutic formulations has increased substantially in recent years. The preorganized amphiphilicity of BAs allows for a range of biological activities including applications that rely on multivalency. This review summarizes BA-related research in biomedically relevant areas. In particular, we review BA-related literature in four areas: gene delivery, antimicrobial materials, hydrogels, and prodrugs. We also discuss several distinguishing characteristics of BAs that impact their utility as biomedically relevant compounds.

Switchable foldamer ion channels with antibacterial activity

Synthetic ion channels may have applications in treating channelopathies and as new classes of antibiotics, particularly if ion flow through the channels can be controlled. Here we describe triazole-capped octameric α-aminoisobutyric acid (Aib) foldamers that "switch on" ion channel activity in phospholipid bilayers upon copper(ii) chloride addition; activity is "switched off" upon copper(ii) extraction. X-ray crystallography showed that CuCl2 complexation gave chloro-bridged foldamer dimers, with hydrogen bonds between dimers producing channels within the crystal structure. These interactions suggest a pathway for foldamer self-assembly into membrane ion channels. The copper(ii)-foldamer complexes showed antibacterial activity against B. megaterium strain DSM319 that was similar to the peptaibol antibiotic alamethicin, but with 90% lower hemolytic activity.

Small molecule anion transporters display in vitro antimicrobial activity against clinically relevant bacterial strains

Highly active transmembrane anion transporters have demonstrated their activity against antibiotic-resistant and clinically relevant bacterial strains.

Synthetic ionophores as non-resistant antibiotic adjuvants

Antimicrobial resistance is a world-wide health care crisis. New antimicrobials must both exhibit potency and thwart the ability of bacteria to develop resistance to them. We report the use of synthetic ionophores as a new approach to developing non-resistant antimicrobials and adjuvants. Most studies involving amphiphilic antimicrobials have focused on either developing synthetic amphiphiles that show ion transport, or developing non-cytotoxic analogs of such peptidic amphiphiles as colistin. We have rationally designed, prepared, and evaluated crown ether-based synthetic ionophores (‘hydraphiles’) that show selective ion transport through bilayer membranes and are toxic to bacteria. We report here that hydraphiles exhibit a broad range of antimicrobial properties and that they function as adjuvants in concert with FDA-approved antibiotics against multi-drug resistant (MDR) bacteria. Studies described herein demonstrate that benzyl C₁₄ hydraphile (BC₁₄H) shows high efficacy as an antimicrobial. BC₁₄H, at sub-MIC concentrations, forms aggregates of ∼200 nm that interact with the surface of bacteria. Surface-active BC₁₄H then localizes in the bacterial membranes, which increases their permeability. As a result, antibiotic influx into the bacterial cytosol increases in the presence of BC_nHs. Efflux pump inhibition and accumulation of substrate was also observed, likely due to disruption of the cation gradient. As a result, BC₁₄H recovers the activity of norfloxacin by 128-fold against resistant Staphylococcus aureus. BC₁₄H shows extremely low resistance development and is less cytotoxic than colistin. Overall, synthetic ionophores represent a new scaffold for developing efficient and non-resistant antimicrobial-adjuvants.

Antimicrobial resistance is a world-wide health care crisis.

The Role of Terminal Functionality in the Membrane and Antibacterial Activity of Peptaibol-Mimetic Aib Foldamers

Peptaibols are peptide antibiotics that typically feature an N-terminal acetyl cap, a C-terminal aminoalcohol, and a high proportion of α-aminoisobutyric acid (Aib) residues. To establish how each feature might affect the membrane-activity of peptaibols, biomimetic Aib foldamers with different lengths and terminal groups were synthesised. Vesicle assays showed that long foldamers (eleven Aib residues) with hydrophobic termini had the highest ionophoric activity. C-terminal acids or primary amides inhibited activity, while replacement of an N-terminal acetyl with an azide group made little difference. Crystallography showed that N₃ Aib₁₁ CH₂ OTIPS folded into a 3₁₀ helix 2.91 nm long, which is close to the bilayer hydrophobic width. Planar bilayer conductance assays showed discrete ion channels only for N-acetylated foldamers. However long foldamers with hydrophobic termini had the highest antibacterial activity, indicating that ionophoric activity in vesicles was a better indicator of antibacterial activity than the observation of discrete ion channels.

A synthetic channel that efficiently inserts into mammalian cell membranes and destroys cancer cells

A tubular molecule with terminal positively charged amino groups that displays a strong ability to insert into the membrane of mammalian cells.

Penicillin induces alterations in glutamine metabolism in Streptococcus pneumoniae

Penicillin is a bactericidal antibiotic that inhibits the synthesis of the peptidoglycan by targeting penicillin-binding proteins. This study aimed to assess through transcriptional profiling the stress response of S. pneumoniae strains after exposure to lethal penicillin concentrations to understand further the mode of action of penicillin. Two experimental designs (time-course and dose-response) were used for monitoring the effect of penicillin on the transcriptional profile. The expression of some genes previously shown to be modulated by penicillin was altered, including ciaRH, pstS and clpL. Genes of the glnRA and glnPQ operons were among the most downregulated genes in the three strains. These genes are involved in glutamine synthesis and uptake and LC-MS work confirmed that penicillin treatment increases the intracellular glutamine concentrations. Glutamine conferred a protective role against penicillin when added to the culture medium. Glutamine synthetase encoded by glnA catalyses the transformation of glutamate and ammonium into glutamine and its chemical inhibition by the inhibitor L-methionine sulfoximine is shown to sensitize S. pneumoniae to penicillin, including penicillin-resistant clinical isolates. In summary, a combination of RNA-seq and metabolomics revealed that penicillin interferes with glutamine metabolism suggesting strategies that could eventually be exploited for combination therapy or for reversal of resistance.

A unimolecular channel formed by dual helical peptide modified pillar[5]arene: correlating transmembrane transport properties with antimicrobial activity and haemolytic toxicity

Five unimolecular channels with different lengths are presented. The varying length of these channels has significant impact on their transport properties.