In vitro antibacterial activity of AZD0914, a new spiropyrimidinetrione DNA gyrase/topoisomerase inhibitor with potent activity against Gram-positive, fastidious Gram-Negative, and atypical bacteria.

AZD0914 is a new spiropyrimidinetrione bacterial DNA gyrase/topoisomerase inhibitor with potent in vitro antibacterial activity against key Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Streptococcus pyogenes, and Streptococcus agalactiae), fastidious Gram-negative (Haemophilus influenzae and Neisseria gonorrhoeae), atypical (Legionella pneumophila), and anaerobic (Clostridium difficile) bacterial species, including isolates with known resistance to fluoroquinolones. AZD0914 works via inhibition of DNA biosynthesis and accumulation of double-strand cleavages; this mechanism of inhibition differs from those of other marketed antibacterial compounds. AZD0914 stabilizes and arrests the cleaved covalent complex of gyrase with double-strand broken DNA under permissive conditions and thus blocks religation of the double-strand cleaved DNA to form fused circular DNA. Whereas this mechanism is similar to that seen with fluoroquinolones, it is mechanistically distinct. AZD0914 exhibited low frequencies of spontaneous resistance in S. aureus, and if mutants were obtained, the mutations mapped to gyrB. Additionally, no cross-resistance was observed for AZD0914 against recent bacterial clinical isolates demonstrating resistance to fluoroquinolones or other drug classes, including macrolides, ß-lactams, glycopeptides, and oxazolidinones. AZD0914 was bactericidal in both minimum bactericidal concentration and in vitro time-kill studies. In in vitro checkerboard/synergy testing with 17 comparator antibacterials, only additivity/indifference was observed. The potent in vitro antibacterial activity (including activity against fluoroquinolone-resistant isolates), low frequency of resistance, lack of cross-resistance, and bactericidal activity of AZD0914 support its continued development.

Characterization of the novel DNA gyrase inhibitor AZD0914: low resistance potential and lack of cross-resistance in Neisseria gonorrhoeae.

The unmet medical need for novel intervention strategies to treat Neisseria gonorrhoeae infections is significant and increasing, as rapidly emerging resistance in this pathogen is threatening to eliminate the currently available treatment options. AZD0914 is a novel bacterial gyrase inhibitor that possesses potent in vitro activities against isolates with high-level resistance to ciprofloxacin and extended-spectrum cephalosporins, and it is currently in clinical development for the treatment of N. gonorrhoeae infections. The propensity to develop resistance against AZD0914 was examined in N. gonorrhoeae and found to be extremely low, a finding supported by similar studies with Staphylococcus aureus. The genetic characterization of both first-step and second-step mutants that exhibited decreased susceptibilities to AZD0914 identified substitutions in the conserved GyrB TOPRIM domain, confirming DNA gyrase as the primary target of AZD0914 and providing differentiation from fluoroquinolones. The analysis of available bacterial gyrase and topoisomerase IV structures, including those bound to fluoroquinolone and nonfluoroquinolone inhibitors, has allowed the rationalization of the lack of cross-resistance that AZD0914 shares with fluoroquinolones. Microbiological susceptibility data also indicate that the topoisomerase inhibition mechanisms are subtly different between N. gonorrhoeae and other bacterial species. Taken together, these data support the progression of AZD0914 as a novel treatment option for the oral treatment of N. gonorrhoeae infections.

Microbiological interaction studies between ceftazidime-avibactam and pulmonary surfactant and between ceftazidime-avibactam and antibacterial agents of other classes.

For an antibacterial agent to be considered for clinical studies in nosocomial pneumonia (NP), it should be active in the presence of pulmonary surfactant. Furthermore, owing to the common practice of treating such infections with more than one antibacterial agent, it should be free of antagonistic interactions with agents of other classes. The aim of this study was to demonstrate the effect of pulmonary surfactant on the activity of ceftazidime and ceftazidime-avibactam and to determine the interaction (if any) of ceftazidime-avibactam and six antimicrobial agents common in the treatment of NP. Minimum inhibitory concentration (MIC) determination for ceftazidime and ceftazidime-avibactam was performed with and without the presence of four concentrations of bovine pulmonary surfactant, and a chequerboard assay was used to determine any interaction between ceftazidime and ceftazidime-avibactam with tobramycin, levofloxacin, linezolid, vancomycin, tigecycline and colistin. Here we report that the in vitro antimicrobial activity of ceftazidime-avibactam against ß-lactamase-producing Gram-negative bacteria remained unaltered in the presence of pulmonary surfactant at concentrations that antagonised the antimicrobial activity of daptomycin. Furthermore, in chequerboard interaction studies, an absence of antagonism was demonstrated between ceftazidime-avibactam and six antimicrobial agents of different classes when tested against aerobic species frequently isolated from NP. The results support the further investigation of ceftazidime-avibactam as a potential treatment for NP caused by susceptible bacteria.

Antibacterial inhibitors of Gram-positive thymidylate kinase: structure-activity relationships and chiral preference of a new hydrophobic binding region.

Thymidylate kinase (TMK), an essential enzyme in bacterial DNA biosynthesis, is an attractive therapeutic target for the development of novel antibacterial agents, and we continue to explore TMK inhibitors with improved potency, protein binding, and pharmacokinetic potential. A structure-guided design approach was employed to exploit a previously unexplored region in Staphylococcus aureus TMK via novel interactions. These efforts produced compound 39, with 3 nM IC50 against S. aureus TMK and 2 µg/mL MIC against methicillin-resistant S. aureus (MRSA). This compound exhibits a striking inverted chiral preference for binding relative to earlier compounds and also has improved physical properties and pharmacokinetics over previously published compounds. An example of this new series was efficacious in a murine S. aureus infection model, suggesting that compounds like 39 are options for further work toward a new Gram-positive antibiotic by maintaining a balance of microbiological potency, low clearance, and low protein binding that can result in lower efficacious doses.

Discovery of selective and potent inhibitors of gram-positive bacterial thymidylate kinase (TMK).

Thymidylate kinase (TMK) is an essential enzyme in bacterial DNA synthesis. The deoxythymidine monophosphate (dTMP) substrate binding pocket was targeted in a rational-design, structure-supported effort, yielding a unique series of antibacterial agents showing a novel, induced-fit binding mode. Lead optimization, aided by X-ray crystallography, led to picomolar inhibitors of both Streptococcus pneumoniae and Staphylococcus aureus TMK. MICs < 1 µg/mL were achieved against methicillin-resistant S. aureus (MRSA), S. pneumoniae, and vancomycin-resistant Enterococcus (VRE). Log D adjustments yielded single diastereomers 14 (TK-666) and 46, showing a broad antibacterial spectrum against Gram-positive bacteria and excellent selectivity against the human thymidylate kinase ortholog.

In vivo validation of thymidylate kinase (TMK) with a rationally designed, selective antibacterial compound.

There is an urgent need for new antibacterials that pinpoint novel targets and thereby avoid existing resistance mechanisms. We have created novel synthetic antibacterials through structure-based drug design that specifically target bacterial thymidylate kinase (TMK), a nucleotide kinase essential in the DNA synthesis pathway. A high-resolution structure shows compound TK-666 binding partly in the thymidine monophosphate substrate site, but also forming new induced-fit interactions that give picomolar affinity. TK-666 has potent, broad-spectrum Gram-positive microbiological activity (including activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus), bactericidal action with rapid killing kinetics, excellent target selectivity over the human ortholog, and low resistance rates. We demonstrate in vivo efficacy against S. aureus in a murine infected-thigh model. This work presents the first validation of TMK as a compelling antibacterial target and provides a rationale for pursuing novel clinical candidates for treating Gram-positive infections through TMK.