Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2024

Targeting bacterial transcription for effective antimicrobial solutions (#39)

Cheuk Hei Kan 1 , Yangyi Qiu 2 , Xiao Yang 1 , Cong Ma 2
  1. Department of Microbiology, The Chinese University of Hong Kong, Hong Kong
  2. Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong

In response to the threat of antimicrobial resistance and the urgent need for novel antibiotics, this study explores a promising avenue by targeting bacterial transcription. Unlike conventional drugs that focus on the core enzyme of RNA polymerase (RNAP), which often leads to the emergence of antibiotic-resistant bacteria, our research delves into the realm of protein-protein interactions between highly conserved yet exclusive transcription factors in bacteria and RNAP. 

Using a docking model, we have optimised our compounds, demonstrating potent antimicrobial activity and promising druggability. Broth microdilution assays revealed the remarkable efficacy of our compounds against Gram-positive bacteria, including drug-resistant strains of Staphylococcus aureus. The minimum inhibitory concentrations (MICs) for these compounds were <1 µg/mL. Also, time-kill kinetics studies demonstrated that using concentrations of ≥4-fold the MIC and exposing bacteria for >4 hours effectively eradicated the bacterial population, demonstrating enhanced bactericidal activity. 

Furthermore, cytotoxicity assays confirmed that our compounds exhibited minimal harm to human liver and lung cells. Their 50% cytotoxicity concentration (CC50) values were significantly higher than those of the chemotherapeutic agent cisplatin (≥100 vs. 5 µM), emphasising their potential as safe and selective options. Additional assessments of their pharmacological properties included haemolysis assays and Caco-2 cell permeability assays. The haemolysis assays indicated a low propensity for red blood cell lysis, with haemolytic values remaining well below the suggested non-haemolytic threshold of 10%. Moreover, the results of the Caco-2 cell permeability assays demonstrated high apparent permeability values exceeding 10-5 cm/s, indicating the compounds’ potential for efficient cell membrane permeation. These two properties enable compounds to be administrated orally or intravenously. Finally, the animal experiments demonstrated that our compounds could rescue 30% of mice with bacteraemia, showcasing their efficacy in vivo. 

In conclusion, our study introduces a novel approach of targeting protein-protein interactions between transcription factors and bacterial RNAP in the quest for new antibiotics. The synthesised compounds exhibit potent antimicrobial activity with minimal cytotoxicity, underscoring their potential as safe and selective options. Importantly, the absence of antimicrobial resistance development in sub-inhibitory concentrations against S. aureus highlights their potential as future clinically available antibiotics, paving the way for innovative antimicrobial solutions. 

  1. Qiu, Y., Chan, S. T., Lin, L., Shek, T. L., Tsang, T. F., Zhang, Y., . . . & Ma, C. (2019). Nusbiarylins, a new class of antimicrobial agents: Rational design of bacterial transcription inhibitors targeting the interaction between the NusB and NusE proteins. Bioorganic Chemistry, 92, 103203.
  2. Yang, X., Luo, M. J., Yeung, A. C., Lewis, P. J., Chan, P. K., Ip, M., & Ma, C. (2017). First-in-class inhibitor of ribosomal RNA synthesis with antimicrobial activity against Staphylococcus aureus. Biochemistry, 56(38), 5049-5052.