Rational design, synthesis and testing of novel tricyclic topoisomerase inhibitors for the treatment of bacterial infections part 1.

The alarming reduction in drug effectiveness against bacterial infections has created an urgent need for the development of new antibacterial agents that circumvent bacterial resistance mechanisms. We report here a series of DNA gyrase and topoisomerase IV inhibitors that demonstrate potent activity against a range of Gram-positive and selected Gram-negative organisms, including clinically-relevant and drug-resistant strains. In part 1, we present a detailed structure activity relationship (SAR) analysis that led to the discovery of our previously disclosed compound, REDX05931, which has a minimum inhibitory concentration (MIC) of 0.06 µg mL-1 against fluoroquinolone-resistant Staphylococcus aureus. Although in vitro hERG and CYP inhibition precluded further development, it validates a rational design approach to address this urgent unmet medical need and provides a scaffold for further optimisation, which is presented in part 2.

Rational design, synthesis and testing of novel tricyclic topoisomerase inhibitors for the treatment of bacterial infections part 2.

Building on our previously-reported novel tricyclic topoisomerase inhibitors (NTTIs), we disclose the discovery of REDX07965, which has an MIC90 of 0.5 µg mL-1 against Staphylococcus aureus, favourable in vitro pharmacokinetic properties, selectivity versus human topoisomerase II and an acceptable toxicity profile. The results herein validate a rational design approach to address the urgent unmet medical need for novel antibiotics.

Protection of Escherichia coli cells against extreme turgor by activation of MscS and MscL mechanosensitive channels: identification of genes required for MscS activity.

Mechanosensitive channels are ubiquitous amongst bacterial cells and have been proposed to have major roles in the adaptation to osmotic stress, in particular in the management of transitions from high to low osmolarity environments. Electrophysiological measurements have identified multiple channels in Escherichia coli cells. One gene, mscL, encoding a large conductance channel has previously been described, but null mutants were without well-defined phenotypes. Here, we report the characterization of a new gene family required for MscS function, YggB and KefA, which has enabled a rigorous test of the role of the channels. The channel determined by KefA does not appear to have a major role in managing the transition from high to low osmolarity. In contrast, analysis of mutants of E.coli lacking YggB and MscL shows that mechanosensitive channels are designed to open at a pressure change just below that which would cause cell disruption leading to death.