Rasmus Nielsen Klitgaard:
Antibiotic Drug Discovery. Potentiation of the quinolones and targeting the initiation of DNA replication

Date: 28-02-2018    Supervisor: Anders Løbner-Olesen

Antibiotic resistance has been deemed as one of the biggest threats to the global public health by the World health Organization. In 2050, an estimated 10 million deaths per year will be attributed to antimicrobial resistance, thus proper action needs to be taken to stop this negative development. An important mean in the arms race against antibiotic resistance is the discovery and development of novel antibiotics, but also preserving the efficacy of the antibiotics that are already in clinical use.

In paper I, we search for ciprofloxacin helper drug targets in an effort to preserve the use of this widely applied antibiotic. Using a combined genetic and transcriptomic approach, the AcrAB-TolC efflux pump and the SOS response genes, RecA and RecC, are identified as potential targets for helper drugs in Escherichia coli strains with low-level ciprofloxacin resistance. In addition, our results also indicate that reversing high-level ciprofloxacin resistance is likely not plausible.

In paper II, we present two novel cell based screens for identifying inhibitors of the chromosomal DNA replication initiation in bacteria. The screens are based on growth rescue of cells that rigorously over-initiate the DNA replication, due to either increased regeneration of the active ATP bound form of the replication initiator protein DnaA, or by being deficient in the process known as regulatory inactivation of DnaA (RIDA). Screening a library of 400 microbial extracts, revealed the iron chelator deferoxamine as a compound that rescues the growth of over-initiating cells. Albeit not by decreasing the replication initiation frequency, but by reducing the production of reactive oxygen species. Substantiating the model that oxidative DNA damage and its repair promotes the lethal action of hyper-replication.

In paper III, we constructed and verified a novel high throughput, cell based, fluorescence screen for inhibitors of chromosome replication initiation in bacteria. The screen utilizes an E. coli mutant that is resistant to replication initiation inhibitors and holds a fluorescence reporter system for DNA replication inhibitors. This screen was also subjected to the above-mentioned library of microbial extracts, though it did not lead to any positive hits.