BWC0977, a broad-spectrum antibacterial clinical candidate to treat multidrug resistant infections

Abstract

The global crisis of antimicrobial resistance (AMR) necessitates the development of broad-spectrum antibacterial drugs effective against multi-drug resistant (MDR) pathogens. BWC0977, a Novel Bacterial Topoisomerase Inhibitor (NBTI) selectively inhibits bacterial DNA replication via inhibition of DNA gyrase and topoisomerase IV. BWC0977 exhibited a minimum inhibitory concentration (MIC₉₀) of 0.03-2 µg/mL against a global panel of MDR Gram-negative bacteria including Enterobacterales and non-fermenters, Gram-positive bacteria, anaerobes and biothreat pathogens. BWC0977 retains activity against isolates resistant to fluoroquinolones (FQs), carbapenems and colistin and demonstrates efficacy against multiple pathogens in two rodent species with significantly higher drug levels in the epithelial lining fluid of infected lungs. In healthy volunteers, single-ascending doses of BWC0977 administered intravenously ( https://clinicaltrials.gov/study/NCT05088421 ) was found to be safe, well tolerated (primary endpoint) and achieved dose-proportional exposures (secondary endpoint) consistent with modelled data from preclinical studies. Here, we show that BWC0977 has the potential to treat a range of critical-care infections including MDR bacterial pneumonias.

Fig. 1. Structure-Activity Relationship (SAR) leading to the selection of BWC0977 as the clinical candidate.

The synthesis of the screening hit, compound 1 and the progressive synthesis of different compounds based on medicinal chemistry inputs towards improving the compound properties. The latter included enhanced potency, broad-spectrum antibacterial activity, optimal physico-chemical properties while mitigating tox liability leading to the selection of the clinical candidate, compound 9 or BWC0977. Abbreviations: Eco, Escherichia coli; Pae, Pseudomonas aeruginosa; Aba, Acinetobacter baumannii; Kpn, Klebsiella pneumoniae.

Fig. 2. Dose-fractionation and determination of PK-PD drivers of efficacy for BWC0977, either administered subcutaneously in a neutropenic P. aeruginosa infected mice thigh model (A & B) or administered via intravenous infusion in a neutropenic P. aeruginosa infected rat lung infection model (C & D).

Dose-fractionation of BWC0977 performed in P. aeruginosa infected mice (per dose n = 4 /cage, 8 thigh samples, right & left of each). A BWC0977 was administered subcutaneously at 160 mg/kg total daily dose delivered as a single, two doses or 4 doses over a 24 h period and the CFU burden monitored at various time points. Polymyxin (25 mg/kg) was used as the comparator drug. Data plotted as mean ± SD. B Aggregate plot of BWC0977 efficacy following dose-ranging studies (per dose n = 4/cage, 8 thigh samples, right & left of each) in a neutropenic mice thigh model infected with multiple isolates of P. aeruginosa, A. baumannii, K. pneumoniae and E. coli with pre-existing multidrug resistance mechanisms (Supplementary Table 6). Data plotted as mean ± SD. C Multiple isolates of P. aeruginosa, A. baumannii, K. pneumoniae and E. coli with different resistance mechanisms (Supplementary Table 7) were used for dose-ranging studies and the ΔLog₁₀CFU/gm lung from each animal (n = 2 per treatment group) is plotted as a function of fAUC₂₄/MIC for ease of comparison across isolates. D The PK-PD index that best described the in vivo efficacy of BWC0977 against P. aeruginosa in the neutropenic rat lung infection model. Dose-fractionation was carried out with BWC0977 as per the details shown in Supplementary Table 8. Log₁₀CFU/gm lung from each animal is plotted as a function of fAUC₂₄/MIC, fC_max/MIC and %T > MIC. fAUC₂₄/MIC was identified as the appropriate driver translating to BWC0977 efficacy.

Fig. 3. Determination of pharmacokinetics (PK) in the plasma and epithelial lining fluid (ELF) in neutropenic mice and rats following infection with Pseudomonas aeruginosa.

A In neutropenic CD-1 mice, (n = 3/cage, per dose for each time point) thigh infection model, plasma PK was determined following subcutaneous administration of 10, 40, 80 and 120 mg/kg of BWC0977 q24h following infection with Pseudomonas aeruginosa NCTC 13921 and plasma samples taken at 0, 0.5, 1, 2, 4, 6, 8, and 24 h post-dosing (n = 3/cage, per dose for each time point). Data plotted as mean ± SD. (B) The ELF was obtained by instilling 2 ml of sterile saline into the lungs of mice and removing saline from the lungs twice at 0, 0.5, 1, 2, 4, 6, 8 h post-dosing. Plasma protein binding was estimated to be ~87%. Data plotted as mean ± SD. C In the neutropenic rat (n = 3) lung infection model, 100 mg/kg of BWC0977 was administered following infection with P. aeruginosa ATCC27853. The ELF and plasma samples were taken at 0.5, 1 h (during infusion), and post-infusion at 1.25, 1.5, 2, 3, 5, 9, 25 h post-dosing (n = 3, per dose for each time point). The ELF was obtained by instilling 2 ml of sterile saline into the lungs and removing saline from the lungs. The free plasma levels were calculated from the total plasma levels using the plasma protein binding value of 94%. For all evaluations mean per dose/time point ± SD is plotted.

Fig. 4. Plasma and urine pharmacokinetics of BWC0977 following 2-hr intravenous administration in the single-ascending dose (SAD) study in healthy human volunteers. Modelling and prediction of human PK parameters based on experimental data from preclinical species.

The PK of BWC0977 administered as a single intravenous infusion at doses 120, 240, 480, 720 or 1050 mg in healthy volunteers (n = 6 per dose) over 120 min. A The time-concentration response in plasma observed in the ascending dose groups. Mean ± SD from 6 subjects plotted versus time. B Dose proportionality observed with respect to plasma C_max and AUC. Mean ± SD from 6 subjects plotted versus dose (mgs). (C) The amount of drug excreted in urine in the 48 h interval following dose administration was less than dose proportional to increasing dose, with the fraction of dose excreted in urine gradually decreasing from 35% for 120 mg BWC0977 to 20% for 1050 mg BWC0977. Mean ± SD from 6 subjects plotted versus dose (mgs). A model built on simple allometric scaling was used to predict the human PK parameters: C_max (D) & AUC (E) based on a 2-compartment open model. Mean ± SD from 6 subjects plotted for each observed parameter. This was the best-fit model of the mean PK data generated following intravenous bolus / infusion administration of different doses of BWC0977 into mice, rats, guinea pigs and dogs. There was good concordance between the predicted and observed parameters.

Fig. 5. Molecular docking to identify unique residues of (A) Gyrase and (B) Topoisomerase IV involved in key interactions with BWC0977.

The crystal bound conformations of ciprofloxacin mapped to EcGyrase (A), and EcTopoIV (B). The residues which form key ion-mediated interactions are shown as sticks and labelled. Mg²⁺ ions are shown as black spheres and ion-mediated interactions are highlighted with broken lines. The BWC0977 binding orientation determined by molecular docking is also shown as sticks to illustrate the variable binding pockets. All key interaction residues of BWC0977 are minimum 4 atoms away from the ciprofloxacin ligand atoms. Also, the DNA bases where BWC0977 left-hand side (LHS) ring stack are different from ciprofloxacin interacting DNA base pairs. Therefore, none of the BWC0977 interacting amino acid residues are directly involved in ciprofloxacin binding, implicating an unlikely possibility of development of cross-resistance.

Fig. 6. Non-overlapping MIC (µg/ml) between ciprofloxacin (•) and BWC0977 (Δ) across clinical isolates.

Scatter plot of individual MICs of 35–40 fluoroquinolone-resistant clinical isolates of E. coli, A. baumannii and P. aeruginosa, and 98 fluoroquinolone-resistant clinical isolates of K. pneumoniae. The MIC values of BWC0977 and ciprofloxacin are non-overlapping, indicating the lack of cross-resistance between ciprofloxacin and BWC0977, a finding that will support the use of BWC0977 for treating infections caused by fluoroquinolone-resistant bacterial pathogens.