Synthesis and SAR studies of novel benzodiazepinedione-based inhibitors of Clostridium difficile (C. difficile) toxin B (TcdB).

Synthesis and structure-activity relationships (SAR) of a novel series of benzodiazepinedione-based inhibitors of Clostridium difficile toxin B (TcdB) are described. Compounds demonstrating low nanomolar affinity for TcdB, and which possess improved stability in mouse plasma vs. earlier compounds from this series, have been identified. Optimized compound 11d demonstrates a good pharmacokinetic (PK) profile in mouse and hamster and is efficacious in a hamster survival model of Clostridium difficile infection.

Treatment of Clostridium difficile Infection with a Small-Molecule Inhibitor of Toxin UDP-Glucose Hydrolysis Activity.

Clostridium difficile infection (CDI) is the leading cause of hospital-acquired infectious diarrhea, with significant morbidity, mortality, and associated health care costs. The major risk factor for CDI is antimicrobial therapy, which disrupts the normal gut microbiota and allows C. difficile to flourish. Treatment of CDI with antimicrobials is generally effective in the short term, but recurrent infections are frequent and problematic, indicating that improved treatment options are necessary. Symptoms of disease are largely due to two homologous toxins, TcdA and TcdB, which are glucosyltransferases that inhibit host Rho GTPases. As the normal gut microbiota is an important component of resistance to CDI, our goal was to develop an effective nonantimicrobial therapy. Here, we report a highly potent small-molecule inhibitor (VB-82252) of TcdA and TcdB. This compound inhibits the UDP-glucose hydrolysis activity of TcdB and protects cells from intoxication after challenge with either toxin. Oral dosing of the inhibitor prevented inflammation in a murine intrarectal toxin challenge model. In a murine model of recurrent CDI, the inhibitor reduced weight loss and gut inflammation during acute disease and did not cause the recurrent disease that was observed with vancomycin treatment. Lastly, the inhibitor demonstrated efficacy similar to that of vancomycin in a hamster disease model. Overall, these results demonstrate that small-molecule inhibition of C. difficile toxin UDP-glucose hydrolysis activity is a promising nonantimicrobial approach to the treatment of CDI.

Identification and initial optimization of inhibitors of Clostridium difficile (C. difficile) toxin B (TcdB).

The discovery, synthesis and preliminary structure-activity relationship (SAR) of a novel class of inhibitors of Clostridium difficile (C. difficile) toxin B (TcdB) is described. A high throughput screening (HTS) campaign resulted in the identification of moderately active screening hits 1-5 the most potent of which was compound 1 (IC50 = 0.77 µM). In silico docking of an early analog offered suggestions for structural modification which resulted in the design and synthesis of highly potent analogs 13j(IC50 = 1 nM) and 13 l(IC50 = 7 nM) which were chosen as leads for further optimization.