Virginia Via Research Day Book 2026

Graduate Student Research Biomedical

02 UNVEILING THE HIDDEN POTENTIAL OF TAFENOQUINE AS A NOVEL THERAPEUTIC FOR CLOSTRIDIOIDES DIFFICILE

Ahmed A. Abouelkhair, DVM, MS, Dipl.ACVM; Nader S. Abutaleb, PharmD, MS, PhD; Mohamed N. Seleem, DVM, MS, PhD Corresponding author: aabouelkhair@vt.edu

Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University; Blacksburg, Virginia

difficile. Tafenoquine was selected for comprehensive evaluation. In vitro assays assessed bactericidal activity, inhibition of spore outgrowth, and activity against vancomycin-resistant Enterococcus (VRE). A macromolecular synthesis assay was used to explore the drug's mechanism of action alongside the protein binding assays. In vivo efficacy was evaluated using a lethal murine CDI model, where survival and recurrence outcomes were compared to those of vancomycin. Pharmacokinetic characteristics relevant to intestinal drug exposure were also examined. Results: Tafenoquine demonstrated rapid bactericidal activity, killing C. difficile within 4 hours. It strongly inhibited spore outgrowth and exhibited potent activity against VRE. Mechanistic analysis revealed disruption of fatty acid synthesis as a primary mode of action. In the murine CDI model, tafenoquine provided 83.3% survival and completely prevented recurrence, outperforming vancomycin, which showed recurrence in surviving animals. Additionally, tafenoquine’s slow systemic absorption (12–14 hours to peak plasma levels) suggests prolonged intestinal exposure, potentially enhancing its therapeutic effectiveness against CDI.

Background/Context: Clostridioides difficile infection (CDI) remains the leading cause of antibiotic-associated diarrhea in the United States and is responsible for an estimated 12,800 deaths annually. Despite the availability of vancomycin (VAN) and fidaxomicin (FDX), recurrence rates remain unacceptably high (~30%), and high treatment costs further limit accessibility. This underscores the urgent need for new, effective, and affordable therapeutics. Drug repurposing provides a rapid and cost-efficient strategy for identifying novel anti-C. difficile agents from existing FDA-approved compounds. Objective/Hypothesis: This study aimed to identify FDA-approved drugs with potent anti-C. difficile activity and evaluate their potential as therapeutic candidates. We hypothesized that tafenoquine (TQ), an FDA-approved oral antimalarial drug identified during high-throughput screening, would demonstrate robust bactericidal activity, inhibit spore outgrowth, and provide superior protection against CDI recurrence compared to vancomycin with unique mechanism of action. Methods: A library of approximately 3,800 FDA-approved compounds was screened to identify agents with growth-inhibitory activity against C.

Conclusions: Tafenoquine exhibits exceptional in vitro and in vivo anti-C. difficile activity and effectively prevents disease recurrence, highlighting its potential as a promising repurposed therapeutic candidate. By overcoming key limitations of current treatments, particularly recurrence, TQ represents a strong lead molecule for future CDI drug development. Further preclinical and clinical studies are warranted to define its safety profile, pharmacodynamics, and clinical applicability.

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