The development of novel bacterial cell division protein FtsZ inhibitors to broaden their antibacterial spectrum

Abstract

Antibacterial resistance has become a new global threat for public health, due to the lack of effective strategies to solve it. For example, methicillin-resistantS. aureus (MRSA) which is the most common resistant bacteria, can cause infections with a high rate of mortality. Therefore, there is an urgent need to develop some new types of antibiotics with new drug target and new mechanism of action. FtsZ protein is a bacterial cell division protein, which plays a very important role in the process of cell division. It has been approved to be an attractive drug target for antibiotic drug discovery. There have been many different types of FtsZ inhibitors from natural products to small molecules. However, most of these FtsZ inhibitors only have antibacterial activity against S.aureus, or they have little effect on resistant bacteria and Gram-negative bacteria. In this study, we investigated the synergistic effect of FtsZ inhibitor and beta-lactam antibiotics, and we also developed a series of compounds with broad antibacterial spectrum through structure modification and double warhead strategy. Firstly, we confirmed that the target of compound F332 was FtsZ protein by genetic study and docking study, although the compound F332 was considered as a potential FtsZ inhibitor in our previous study. Then we investigated the synergistic effect of F332 together with beta-lactam antibiotics. The MIC result showed that combination of drugs had synergistic effect and F332 could restore the efficacy of beta-lactam antibiotics in vitro. The highest synergy percentage was the combination of the compound F332 used together with methicillin, which was as high as more than 80% in vitro. These results indicated that the FtsZ inhibitor F332 could restore the efficacy of beta-lactam antibiotics to treat MRSA in vitro. In the next stage, we tried to develop broad spectrum FtsZ inhibitors through the structure modification of F332. We designed and synthesized a series of compounds, and the antibacterial activities of all compounds were evaluated by the MIC test. Some compounds had the antibacterial activity against both S. aureus and E. coli, and the antibacterial spectrum was broadened by adding a amidine group. Furthermore, when one fluorine was replaced by different phenol, the antibacterial activity would increase. The compound 32 and 38 exhibited stronger antibacterial activity against both of S. aureus and E. coli, and the MIC of their antibacterial activity against S. aureus was 4 µg/mL, which increased 8-fold comparing with compound 6, while the antibacterial activity against E. coli was 16 µg/mL and it also increased by 2-fold.These results indicated that the amidine group could be a start point for structure modification to develop more broad-spectrum FtsZ inhibitors with better antibacterial activity. In order to develop more antibiotics for Gram-negative bacterial strains, we tried to use the double warhead strategy to connect two scaffolds of F332 and triclosan by different linkers. The advantage of this method was that it could broaden the antibacterial spectrum of F332 and it could also reduce the toxicity of triclosan. We designed and synthesized a series of new compounds and the antibacterial activities of these compounds were evaluated by the MIC test. The MIC result of the compound 60 exhibited improved antibacterial activity against both S. aureus and E. coli with the MIC of less than 0.25 µg/mL. Furthermore, it also demonstrated excellent antibacterial activity against other Gram-negative bacterial strains with the MIC of less than 0.5 µg/mL, including K. pneumoniae, K. oxytoca and E. cloacae. These results indicated that the double warhead strategy of using the scaffold of FtsZ inhibitors provides a possible method for developing new antibiotics to treat Gram-negative bacterial strains.