Screening of Natural Products and Approved Oncology Drug Libraries for Activity against Clostridioides difficile

Clostridioides difficile is the most common cause of healthcare-associated diarrhea. Infection of the gastrointestinal tract with this Gram-positive, obligate anaerobe can lead to potentially life-threatening conditions in the antibiotic-treated populace. New therapeutics are urgently needed to treat this infection and prevent its recurrence. Here, we screened two libraries from the National Cancer Institute, namely, the natural product set III library (117 compounds) and the approved oncology drugs set V library (114 compounds), against C. difficile. In the two libraries screened, 17 compounds from the natural product set III library and 7 compounds from the approved oncology drugs set V library were found to exhibit anticlostridial activity. The most potent FDA-approved drugs (mitomycin C and mithramycin A) and a promising natural product (aureomycin) were further screened against 20 clinical isolates of C. difficile. The anticancer drugs, mitomycin C (MIC50 = 0.25 μg/ml) and mithramycin A (MIC50 = 0.015 μg/ml), and the naturally derived tetracycline derivative, aureomycin (MIC50 = 0.06 μg/ml), exhibited potent activity against C. difficile strains. Mithramycin A and aureomycin were further found to inhibit toxin production by this pathogen. Given their efficacy, these compounds can provide a quick supplement to current treatment to address the unmet needs in treating C. difficile infection and preventing its recurrence.