Nocathiacin I

Clostridioides difficile is a commensal Gram-positive gut bacterium that causes C. difficile-associated diarrhea. Currently available antibacterial therapeutic treatment options are effective except for the repeated recurrences significantly burdening the health care system and causing mortality. The development of new therapeutic modalities including new effective antibiotics with a low rate of recurrence has been unpredictive and exceedingly challenging, requiring continued profiling of many new classes of antibiotics. Nocathiacins and thiazomycins are a class of thiazolyl peptides exhibiting potent and selective broad-spectrum Gram-positive activity including activity against the anaerobe C. difficile. These compounds showed MIC values of 0.015-0.06 μg/mL against C. difficile with more than 100-200-fold selectivity versus commensurate Gram-negative Bacteroides fragilis. Nocathiacin I and one of its analogs exhibited potent in vivo efficacy in the gold-standard hamster model of C. difficile infection, providing 100% protection in this lethal model at 6.25 mg/kg orally twice daily. The efficacy was corroborated by robust reduction of cecum C. difficile burden and proportionate exposure of the compounds in the cecum contents without any systemic absorption. In this paper, details of the results of in vitro, in vivo, pharmacodynamics, and pharmacokinetic studies have been described.

Nocathiacin I, a glycosylated thiopeptide antibiotic, displays excellent antibacterial activities against multidrug resistant bacterial pathogens. Previously, a novel nocathiacin I formulation for intravenous administration has been successfully developed and its aqueous solubility is greatly enhanced for clinical application. The purpose of the present study was to increase the fermentation titer of nocathiacin I and reduce or eliminate analogous impurities by screening the medium ingredients using response surface methodology. After a sysmatic optimization, a water-soluble medium containing quality-controllable components was developed and validated, resulting in an increase in the production of nocathiacin I from 150 to 405.8 mg·L-1 at 150-L scale. Meanwhile, the analogous impurities existed in reported processes were greatly reduced or eliminated. Using optimized medium for fermentation, nocathiacin I with pharmaceutically acceptable quality was easily obtained with a recovery of 67%. In conclusion, the results from the present study offer a practical and efficient fermentation process for the production of nocathiacin I as a therapeutic agent.

The discovery of biofunctional natural products (NPs) has relied on the phenotypic screening of extracts and subsequent laborious work to dereplicate active NPs and define cellular targets. Herein, NPs present as crude extracts, partially purified fractions, and pure compounds were screened directly against molecular target libraries of RNA structural motifs in a library-versus-library fashion. We identified 21 hits with affinity for RNA, including one pure NP, nocathiacin I (NOC-I). The resultant data set of NOC-I-RNA fold interactions was mapped to the human transcriptome to define potential bioactive interactions. Interestingly, one of NOC-I's most preferred RNA folds is present in the nuclease processing site in the oncogenic, noncoding microRNA-18a, which NOC-I binds with low micromolar affinity. This affinity for the RNA translates into the selective inhibition of its nuclease processing in vitro and in prostate cancer cells, in which NOC-I also triggers apoptosis. In principle, adaptation of this combination of experimental and predictive approaches to dereplicate NPs from the other hits (extracts and partially purified fractions) could fundamentally transform the current paradigm and accelerate the discovery of NPs that bind RNA and their simultaneous correlation to biological targets.