New host-directed therapeutics for the treatment of Clostridioides difficile infection

Frequent and excessive use of antibiotics prime patients to Clostridioides difficile infection (CDI) that leads to fatal pseudomembranous colitis, with limited treatment options. In earlier reports, we used a drug repurposing strategy and identified amoxapine (an antidepressant), doxapram (a breathing stimulant), and trifluoperazine (an antipsychotic), which provided significant protection to mice against lethal infections with several pathogens, including C. difficile. However, the mechanisms of action of these drugs were not known. Here we provide evidence that all three drugs offered protection against experimental CDI by reducing bacterial burden and toxin levels, although the drugs were neither bacteriostatic nor bactericidal in nature and had minimal impact on the composition of the microbiota. Drug-mediated protection was dependent on the presence of the microbiota, implicating its role in evoking host defenses that promoted protective immunity. By utilizing RNA-seq, we identified that each drug increased expression of several innate immune response-related genes, including those involved in the recruitment of neutrophils, production of interleukin (IL)-33, and the IL-22 signaling pathway. The RNA-seq data on selected genes were confirmed by qRT-PCR and protein assays. Focusing on amoxapine, which had the best anti-CDI outcome, we demonstrated that neutralization of IL-33 or depletion of neutrophils resulted in loss of drug efficacy. Overall, our lead drugs promote disease alleviation and survival in the murine model through activation of IL-33 and by clearing the pathogen through host defense mechanisms that critically include an early influx of neutrophils. Thirty hours post-infection with Clostridioides difficile spores, cecal tissue was harvested for total RNA isolation and subjected to RNAseq analysis. Data represent RNA pooled from 5 mice/group.