Repurposing of Antibiotics: Sense or Non-sense

Miconazole and phenothiazine hinder the quorum sensing regulated virulence in Pseudomonas aeruginosa

Antibiotic resistance is a major health problem worldwide. Pseudomonas aeruginosa is a Gram-negative pathogen with an arsenal of virulence factors and elevated antimicrobial resistance. It is a leading cause of nosocomial infections with high morbidity and mortality. The significant time and effort required to develop new antibiotics can be circumvented using alternative therapeutic strategies, including anti-virulence targets. This study aimed to investigate the anti-virulence activity of the FDA-approved drugs miconazole and phenothiazine against P. aeruginosa. The phenotypic effect of sub-inhibitory concentrations of miconazole and phenothiazine on biofilm, pyocyanin, protease, rhamnolipid and hemolysin activities in PAO1 strain was examined. qRT-PCR was used to assess the effect of drugs on quorum-sensing genes that regulate virulence. Further, the anti-virulence potential of miconazole and phenothiazine was evaluated in silico and in vivo. Miconazole showed significant inhibition of Pseudomonas virulence by reducing biofilm-formation approximately 45-48%, hemolytic-activity by 59%, pyocyanin-production by 47-49%, rhamnolipid-activity by approximately 42-47% and protease activity by 36-40%. While, phenothiazine showed lower anti-virulence activity, it inhibited biofilm (31-35%), pyocyanin (37-39%), protease (32-40%), rhamnolipid (35-40%) and hemolytic activity (47-56%). Similarly, there was significantly reduced expression of RhlR, PqsR, LasI and LasR following treatment with miconazole, but less so with phenothiazine. In-silico analysis revealed that miconazole had higher binding affinity than phenothiazine to LasR, RhlR, and PqsR QS-proteins. Furthermore, there was 100% survival in mice injected with PAO1 treated with miconazole. In conclusion, miconazole and phenothiazine are promising anti-virulence agents for P. aeruginosa.

Modification of the Antibiotic, Colistin, with Dextrin Causes Enhanced Cytotoxicity and Triggers Apoptosis in Myeloid Leukemia

Introduction

Acute myeloid leukemia (AML) remains difficult to treat due to its heterogeneity in molecular landscape, epigenetics and cell signaling alterations. Precision medicine is a major goal in AML therapy towards developing agents that can be used to treat patients with different 'subtypes' in combination with current chemotherapies. We have previously developed dextrin-colistin conjugates to combat the rise in multi-drug resistant bacterial infections and overcome dose-limiting nephrotoxicity. Recent evidence of colistin's anticancer activity, mediated through inhibition of intracellular lysine-specific histone demethylase 1 (LSD1/KDM1A), suggests that dextrin-colistin conjugates could be used to treat cancer cells, including AML. This study aimed to evaluate whether dextrin conjugation (which reduces in vivo toxicity and prolongs plasma half-life) could enhance colistin's cytotoxic effects in myeloid leukemia cell lines and compare the intracellular uptake and localization of the free and conjugated antibiotic.

Results

Our results identified a conjugate (containing 8000 g/mol dextrin with 1 mol% succinoylation) that caused significantly increased toxicity in myeloid leukemia cells, compared to free colistin. Dextrin conjugation altered the mechanism of cell death by colistin, from necrosis to caspase 3/7-dependent apoptosis. In contrast, conjugation via a reversible ester linker, instead of an amide, had no effect on the mechanism of the colistin-induced cell death. Live cell confocal microscopy of fluorescently labelled compounds showed both free and dextrin-conjugated colistins were endocytosed and co-localized in lysosomes, and increasing the degree of modification by succinoylation of dextrin significantly reduced colistin internalization.

Discussion

Whilst clinical translation of dextrin-colistin conjugates for the treatment of AML is unlikely due to the potential to promote antimicrobial resistance (AMR) and the relatively high colistin concentrations required for anticancer activity, the ability to potentiate the effectiveness of an anticancer drug by polymer conjugation, while reducing side effects and improving biodistribution of the drug, is very attractive, and this approach warrants further investigation.

Repurposing of anti-malarial drugs for the treatment of tuberculosis: realistic strategy or fanciful dead end?

BACKGROUND

Drug repurposing offers a strategic alternative to the development of novel compounds, leveraging the known safety and pharmacokinetic profiles of medications, such as linezolid and levofloxacin for tuberculosis (TB). Anti-malarial drugs, including quinolones and artemisinins, are already applied to other diseases and infections and could be promising for TB treatment.

METHODS

This review included studies on the activity of anti-malarial drugs, specifically quinolones and artemisinins, against Mycobacterium tuberculosis complex (MTC), summarizing results from in vitro, in vivo (animal models) studies, and clinical trials. Studies on drugs not primarily developed for TB (doxycycline, sulfonamides) and any novel developed compounds were excluded. Analysis focused on in vitro activity (minimal inhibitory concentrations), synergistic effects, pre-clinical activity, and clinical trials.

RESULTS

Nineteen studies, including one ongoing Phase 1 clinical trial, were analysed: primarily investigating quinolones like mefloquine and chloroquine, and, to a lesser extent, artemisinins. In vitro findings revealed high MIC values for anti-malarials versus standard TB drugs, suggesting a limited activity. Synergistic effects with anti-TB drugs were modest, with some synergy observed in combinations with isoniazid or pyrazinamide. In vivo animal studies showed limited activity of anti-malarials against MTC, except for one study of the combination of chloroquine with isoniazid.

CONCLUSIONS

The repurposing of anti-malarials for TB treatment is limited by high MIC values, poor synergy, and minimal in vivo effects. Concerns about potential toxicity at effective dosages and the risk of antimicrobial resistance, especially where TB and malaria overlap, further question their repurposing. These findings suggest that focusing on novel compounds might be both more beneficial and rewarding.

All-atoms molecular dynamics study to screen potent efflux pump inhibitors against KpnE protein of Klebsiella pneumoniae

The Small Multidrug Resistance efflux pump protein KpnE, plays a pivotal role in multi-drug resistance in Klebsiella pneumoniae. Despite well-documented study of its close homolog, EmrE, from Escherichia coli, the mechanism of drug binding to KpnE remains obscure due to the absence of a high-resolution experimental structure. Herein, we exclusively elucidate its structure-function mechanism and report some of the potent inhibitors through drug repurposing. We used molecular dynamics simulation to develop a dimeric structure of KpnE and explore its dynamics in lipid-mimetic bilayers. Our study identified both semi-open and open conformations of KpnE, highlighting its importance in transport process. Electrostatic surface potential map suggests a considerable degree of similarity between KpnE and EmrE at the binding cleft, mostly occupied by negatively charged residues. We identify key amino acids Glu14, Trp63 and Tyr44, indispensable for ligand recognition. Molecular docking and binding free energy calculations recognizes potential inhibitors like acarbose, rutin and labetalol. Further validations are needed to confirm the therapeutic role of these compounds. Altogether, our membrane dynamics study uncovers the crucial charged patches, lipid-binding sites and flexible loop that could potentiate substrate recognition, transport mechanism and pave the way for development of novel inhibitors against K. pneumoniae.Communicated by Ramaswamy H. Sarma.

The interplay between the gut-brain axis and the microbiome: A perspective on psychiatric and neurodegenerative disorders

What is the effect of our gut microbial flora on brain? Does the gut microbiome have any role in the causation of psychiatric and neurodegenerative diseases? Does the effect of gut microbiota traverse the gut-brain axis? Questions like these have captured the interest and imagination of the scientific community for quite some time now. Research in the quest for answers to these questions, to unravel the potential role of the microbiota inhabiting the gut in controlling brain functions, has progressed manifold over the last two decades. Although the possibility of microbiome as a key susceptibility factor for neurological disorders viz. Parkinson's disease, Alzheimer's disease, multiple sclerosis, and autism spectrum disorder has bolstered by an increase in the clinical and preclinical evidence, the field is still in its infancy. Given the fact that the diversity of the gut microbiota is affected by various factors including the diet and exercise, the interpretation of such data becomes all the more difficult. Also, such studies have been mostly conducted on animal models, so there is a need for randomized controlled trials in human subjects, corroborated by longitudinal studies, to establish if modulating the gut microbiota can unravel novel therapeutic interventions. Exploring the genomic, metagenomic and metabolomic data from clinical subjects with psychiatric and neurological diseases can prove to be a helpful guide in individual treatment selection.