Synthesis, Characterization, and Antimicrobial Activity of Ultra-Short Cationic β-Peptides

Antibacterial activity of 2-(4-aminopiperidin-4-yl)acetic acid (β3,3-Pip) derivatives and its peptides conjugated with lauric acid through the side chain against methicillin-resistant Staphylococcus aureus (MRSA)

The present work describes the synthesis, characterization, and antibacterial efficacy of cationic β-amino acid derivatives and peptides, H2N-β3,3-Pip(LA)-PEA, P1; and H2N-β3,3-Pip (ULA)-PEA, P2; H2N-β3,3-Pip(LA)-β2,2-Ac6c-PEA, P3; and H2N- β3,3-Pip(ULA)- β2,2-Ac6c-PEA, P4. The compounds P1-P4 were evaluated against the WHO priority multidrug-resistant (MDR) ESKAPE panel pathogens. P2 and P4 exhibited potent activity with MIC values ranging from 3.1 μM to 6.2 μM against MDR pathogens. Further, the kill-kinetics assay demonstrated that P2 and P4 eliminate MRSA in a concentration and time-dependent manner. P2 and P4 also showed the MRSA biofilm prevention and disruption of preformed biofilm. The SEM images and PI permeability assays confirmed the bacterial killing by P2 and P4 through membrane disruption, highlighting their strong bactericidal activity. Additionally, the very low hemolytic and cytotoxic activity of peptides indicate these compounds as promising candidates for further investigation. Subsequently, the compounds P2 and P4 showed synergistic effects with vancomycin. Altogether, the present study highlights the potential of short cationic β-amino acid derivatives and peptides conjugated with lauric acid through the side chain as novel antibacterial agents for combating antimicrobial resistance (AMR).

Synthesis, Characterization, and Antimicrobial Activity of Urea-Containing α/β Hybrid Peptides against Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus aureus

The insertion of β-amino acids and replacement of the amide bond with a urea bond in antimicrobial peptide sequences are promising approaches to enhance the antibacterial activity and improve proteolytic stability. Herein, we describe the synthesis, characterization, and antibacterial activity of short αβ cationic hybrid peptides LAU-Orn-β3,3Ac6c-PEA, DY-01; LAU-Lys-β3,3Ac6c-PEA, DY-02; and LAU-Arg-β3,3Ac6c-PEA, DY-03 in which a C12 lipid chain is conjugated at the N terminus of peptide through urea bonds. Further, we evaluated all the peptides against both Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA) and their multidrug resistant (MDR) clinical isolates. All of the peptides exhibited significant bactericidal efficacy with minimal inhibitory concentration (MIC) values ranging from 2.5 to 6.25 μM (1.4 to 3.9 μg/mL) against P. aeruginosa and its MDR clinical isolates, whereas the MIC values ranging from 0.78 to 6.25 μM (0.45 to 3.9 μg/mL) against MRSA and MDR clinical isolates of S. aureus. To understand the potency and mechanism of action of DY-01 to DY-03, time-kill kinetics, biofilm inhibition and disruption, synergistic interactions with standard antibiotics, swarming motility, scanning electron microscopy (SEM) analyses, and ex vivo infection assay were performed. The SEM images revealed that all of the peptides exert antibacterial activity through a membrane disruption mechanism. Additionally, negligible cytotoxicity was observed against mammalian cell lines RAW 264.7 and J774A.1, with mild hemolysis at higher concentrations. The comprehensive antimicrobial assessments of DY-01 to DY-03 against P. aeruginosa and MRSA highlight their potential for clinical applications in combating resistant microbial infections.

Targeting InhA in drug-resistant Mycobacterium tuberculosis: potent antimycobacterial activity of diaryl ether dehydrozingerone derivatives

Tuberculosis (TB) remains a major global threat, with 10 million new cases and 1.5 million deaths each year. In multidrug-resistant tuberculosis (MDR-TB), resistance is most commonly observed against isoniazid (INH) and rifampicin (RIF), the two frontline drugs. Isoniazid resistance is predominantly linked to mutations in the InhA gene, which encodes an enzyme involved in mycolic acid synthesis, a vital component of the mycobacterial cell wall. Mutations in InhA reduce drug binding, rendering INH ineffective. These morbidity and mortality figures, along with the fact that the rise and global spread of drug-resistant TB, underscores the need for the discovery of novel therapeutics. In this direction, we have previously synthesized, characterized, and screened a library of diaryl ether dehydrozingerone derivatives against mycobacteria and identified two best hits, 7 and 14, based on bacteriostatic activities. The present study aimed to thoroughly investigate the antituberculosis potential of these compounds, particularly regarding drug-resistant TB. Our findings revealed that both compounds exhibited tuberculocidal activity against the standard laboratory strain Mycobacterium tuberculosis (M. tb) H37Rv, with minimal bactericidal concentrations (MBC) of 4μg/ml for compound 7 and 8 μg/ml for compound 14. Next, concentration vs time-kill kinetics of both these compounds showed concentration-dependent bactericidal activities against M. tb and complete pathogen eradication from culture at just 16× MIC. Both compounds were found to be suitable for combination regimens as their interactions with isoniazid and rifampicin against M. tb were observed to be synergistic. Additionally, 7 and 14 exhibited minimal hemolysis against human RBCs and less cytotoxicity was observed against three human cell lines up to 1000 μM. Molecular docking revealed that these compounds bind more effectively to M. tb InhA, including its mutant forms where isoniazid binding is impaired, outperforming both isoniazid and triclosan in binding affinity. Importantly 7 and 14 showed potent activity against drug-susceptible clinical isolates and two isoniazid-resistant M. tb clinical isolates equivalent to that against M. tb H37Rv. The most interesting observation was that both compounds were found to be effective against three multi-drug resistant (MDR) strains of M. tb, thereby depicting their potential against drug-resistant TB. An ex vivo assay on RAW 264 cells infected with M. tb demonstrated a significant reduction in bacterial load at 8× MIC, revealing the fact that these compounds are highly effective against intracellular M. tb H37Rv. To the best of our knowledge, this is the first study that reports promising antimycobacterial potential of 7 and 14 against drug-susceptible, isoniazid-resistant, and MDR tuberculosis which warrants further exploration considering the need for new anti-TB medicine.

Synthesis of novel spiroisoxazolidino hybrids of alantolactone and isoalantolactone via 1,3 dipolar nitrone cycloaddition and its antimicrobial Evaluation

Alantolactone and isoalantolactone are two isomeric sesquiterpene lactones that were isolated from Innula recemosa. Here, we are used for the semisynthesis of novel isoxazolidine hybrids of alantolactone and isoalantolactone through a two-step process: nitrone synthesis followed by nitrone 1,3-dipolar cycloaddition. The formation of the cycloadduct was well characterized via modern spectroscopic techniques such as HRMS, 1H NMR, 13C NMR, DEPT-90, DEPT-135, and 2D NMR. This study also includes the synthesis of dinitrone with glyoxal and terephthalaldehyde, which is used for the dinitrone cycloadduct of alantolactone and isoalantolactone. Both nitrone cycloaddition and dinitrone cycloaddition proceed with high regio- and diastereoselectivity, resulting in the formation of only one isomer. The formation of the α-cycloadducts and the absolute configuration were established through 2D NMR and single-crystal X-ray diffraction analysis. The antimicrobial activity of all synthesized compounds was evaluated against a panel of Gram-positive and Gram-negative pathogens. Compounds 3f and 4f exhibited potential antimicrobial activity against drug-sensitive and -resistant Staphylococcus aureus strains, with minimum inhibitory concentrations ranging from 6 to 10 µM. A time-kill kinetics assay suggested that compounds 3f and 4f are bacteriostatic. Furthermore, scanning electron microscopy analysis confirmed that compounds 3f and 4f cause significant morphological alternations and exert potent antibacterial effects by causing substantial cellular damage.

Antimicrobial activity of α/β hybrid peptides incorporating tBu-β3,3Ac6c against methicillin-resistant Staphylococcus aureus

The incorporation of β-amino acids into peptides is a promising approach to develop proteolytically stable therapeutic agents. Short α/β hybrid peptides containing tBu-β3,3Ac6cː H2N-Lys-tBu-β3,3Ac6c-PEA, P1; H2N-Orn-tBu-β3,3Ac6c-PEA, P2; H2N-Arg-tBu-β3,3Ac6c-PEA, P3; LA-Lys-tBu-β3,3Ac6c-PEA, P4; LA-Orn-tBu-β3,3Ac6c-PEA, P5; LA-Arg-tBu-β3,3Ac6c-PEA, P6; LAu-Lys-tBu-β3,3Ac6c-PEA, P7; LAu-Orn-tBu-β3,3Ac6c-PEA, P8; and LAu-Arg-tBu-β3,3Ac6c-PEA, P9 were prepared. The antimicrobial efficacies of all the peptides were evaluated against ESKAPE pathogens, along with a small panel of multi-drug resistant (MDR) clinical isolates of S. aureus. Among all the peptides, P4, P6, and P7 showed significant efficacies against P. aeruginosa, S. aureus, and MRSA with an MIC value ranging from 6.25 to 12.5 μM. Further, in vitro, anti-staphylococcal assessment with their antimicrobial synergy of the peptides P4, P6, and P7 was carried out against MRSA, due to its better efficacy. The peptides P6 and P7 exhibited MRSA biofilm inhibition of 70% and 77%, respectively, at 4×MIC concentration. At its MIC concentration, about 19% hemolysis was observed for P4, P6, and P7.

Antifungal Efficacy of Ultrashort β-Peptides against Candida Species: Mechanistic Understanding and Therapeutic Implications

Candidiasis, a condition spurred by the unchecked proliferation of Candida species, poses a formidable global health threat, particularly in immunocompromised individuals. The emergence of drug-resistant strains complicates management strategies, necessitating novel therapeutic avenues. Antimicrobial peptides (AMPs) have garnered attention for their potent antifungal properties and broad-spectrum activity against Candida species. This study assessed the antifungal effectiveness of ultrashort β-peptides against Candida strains, with a specific focus on peptide P3 (LAU-β3,3-Pip-β2,2-Ac6c-PEA). Our findings showed P3's remarkable fungistatic and fungicidal activities against Candida albicans, exhibiting an MIC of 4 μg/mL, comparable to those of standard antifungal drugs. The MIC value remained unchanged in the presence of ADC and BSA, indicating that serum albumin does not diminish the activity of P3. P3 demonstrates synergistic effects when combined with Fluconazole (FLU), Itraconazole (ITR), and Nystatin (NYS) to the extent that it becomes effective at 0.125, 0.125, and 0.03125 μg/mL, respectively. Concentration versus time-kill kinetics showed its time-dependent activity up to the first 12 h against C. albicans, and later concentration also played a role; indeed, at 24 h the whole culture was sterilized at 8× MIC. Post-antifungal effect assays confirmed prolonged suppression of pathogen growth after the removal of P3 from the media for significant durations. More importantly, P3 inhibits hyphae formation and biofilm development of Candida, outperforming Fluconazole with respect to these properties. Mechanistic insights display P3's potential to disrupt fungal cell membrane integrity and dose-dependent inhibition of ergosterol biosynthesis, essential for fungal cell wall integrity. Using the Bradford assay, it was observed that extracellular protein concentrations increased with higher doses of the compound, thereby validating the effect of P3 on membrane integrity. A comparative gene analysis using RT-PCR showed that P3 downregulates ERG3, ERG11, and HWP1, which are crucial for the survival and pathogenicity of C. albicans. The impact of P3 on ERG11 and ERG3 is more effective than that of Fluconazole. Molecular docking studies revealed strong binding of P3 to various isoforms of lanosterol 14-α-demethylase, a key enzyme in ergosterol synthesis. Furthermore, molecular dynamic simulations validated the stability of the most promising docking complex. Overall, our findings underscore P3's potential as a leading candidate for the development of innovative antifungal therapies, warranting further investigation and optimization.

Triazole-Bridged Peptides with Enhanced Antimicrobial Activity and Potency against Pathogenic Bacteria

There are still no linear antimicrobial peptides (AMPs) available as a treatment option against bacterial infections. This is caused by several drawbacks that come with AMPs such as limited proteolytic stability and low selectivity against human cells. In this work, we screened a small library of rationally designed new peptides based on the cell-penetrating peptide sC18* toward their antimicrobial activity. We identified several effective novel AMPs and chose one out of this group to further increase its potency. Therefore, we introduced a triazole bridge at different positions to provide a preformed helical structure, assuming that this modification would improve (i) proteolytic stability and (ii) membrane activity. Indeed, placing the triazole bridge within the hydrophilic part of the linear analogue highly increased membrane activity as well as stability against enzymatic digestion. The new peptides, 8A and 8B, demonstrated high activity against several bacterial species tested including pathogenic N. gonorrhoeae and methicillin-resistant S. aureus. Since they exhibited significantly good tolerability against human fibroblast and blood cells, these novel peptides offer true alternatives for future clinical applications and are worth studying in more detail.

Innovative peptide architectures: advancements in foldamers and stapled peptides for drug discovery

INTRODUCTION

Peptide foldamers play a critical role in pharmaceutical research and biomedical applications. This review highlights recent (post-2020) advancements in novel foldamers, synthetic techniques, and their applications in pharmaceutical research.

AREAS COVERED

The authors summarize the structures and applications of peptide foldamers such as α, β, γ-peptides, hydrocarbon-stapled peptides, urea-type foldamers, sulfonic-γ-amino acid foldamers, aromatic foldamers, and peptoids, which tackle the challenges of traditional peptide drugs. Regarding antimicrobial use, foldamers have shown progress in their potential against drug-resistant bacteria. In drug development, peptide foldamers have been used as drug delivery systems (DDS) and protein-protein interaction (PPI) inhibitors.

EXPERT OPINION

These structures exhibit resistance to enzymatic degradation, are promising for therapeutic delivery, and disrupt crucial PPIs associated with diseases such as cancer with specificity, versatility, and stability, which are useful therapeutic properties. However, the complexity and cost of their synthesis, along with the necessity for thorough safety and efficacy assessments, necessitate extensive research and cross-sector collaboration. Advances in synthesis methods, computational modeling, and targeted delivery systems are essential for fully realizing the therapeutic potential of foldamers and integrating them into mainstream medical treatments.

Enhancing the Antimicrobial Properties of Peptides through Cell-Penetrating Peptide Conjugation: A Comprehensive Assessment

Combining antimicrobial peptides (AMPs) with cell-penetrating peptides (CPPs) has shown promise in boosting antimicrobial potency, especially against Gram-negative bacteria. We examined the CPP-AMP interaction with distinct bacterial types based on cell wall differences. Our investigation focused on AMPs incorporating penetratin CPP and dihybrid peptides containing both cell-penetrating TAT protein fragments from the human immunodeficiency virus and Antennapedia peptide (Antp). Assessment of the peptides TAT-AMP, AMP-Antp, and TAT-AMP-Antp revealed their potential against Gram-positive strains (Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus (MRSA), and Bacillus cereus). Peptides TAT-AMP and AMP-Antp using an amyloidogenic AMP from S1 ribosomal protein Thermus thermophilus, at concentrations ranging from 3 to 12 μM, exhibited enhanced antimicrobial activity against B. cereus. TAT-AMP and TAT-AMP-Antp, using an amyloidogenic AMP from the S1 ribosomal protein Pseudomonas aeruginosa, at a concentration of 12 µM, demonstrated potent antimicrobial activity against S. aureus and MRSA. Notably, the TAT-AMP, at a concentration of 12 µM, effectively inhibited Escherichia coli (E. coli) growth and displayed antimicrobial effects similar to gentamicin after 15 h of incubation. Peptide characteristics determined antimicrobial activity against diverse strains. The study highlights the intricate relationship between peptide properties and antimicrobial potential. Mechanisms of AMP action are closely tied to bacterial cell wall attributes. Peptides with the TAT fragment exhibited enhanced antimicrobial activity against S. aureus, MRSA, and P. aeruginosa. Peptides containing only the Antp fragment displayed lower activity. None of the investigated peptides demonstrated cytotoxic or cytostatic effects on either BT-474 cells or human skin fibroblasts. In conclusion, CPP-AMPs offer promise against various bacterial strains, offering insights for targeted antimicrobial development.