Impact of a Novel Anticoccidial Analogue on Systemic Staphylococcus aureus Infection in a Bioluminescent Mouse Model

Abstract

In this study, we investigated the potential of an analogue of robenidine (NCL179) to expand its chemical diversity for the treatment of multidrug-resistant (MDR) bacterial infections. We show that NCL179 exhibits potent bactericidal activity, returning minimum inhibitory concentration/minimum bactericidal concentrations (MICs/MBCs) of 1–2 µg/mL against methicillin-resistant Staphylococcus aureus, MICs/MBCs of 1–2 µg/mL against methicillin-resistant S. pseudintermedius and MICs/MBCs of 2–4 µg/mL against vancomycin-resistant enterococci. NCL179 showed synergistic activity against clinical isolates and reference strains of Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa in the presence of sub-inhibitory concentrations of colistin, whereas NCL179 alone had no activity. Mice given oral NCL179 at 10 mg/kg and 50 mg/kg (4 × doses, 4 h apart) showed no adverse clinical effects and no observable histological effects in any of the organs examined. In a bioluminescent S. aureus sepsis challenge model, mice that received four oral doses of NCL179 at 50 mg/kg at 4 h intervals exhibited significantly reduced bacterial loads, longer survival times and higher overall survival rates than the vehicle-only treated mice. These results support NCL179 as a valid candidate for further development to treat MDR bacterial infections as a stand-alone antibiotic or in combination with existing antibiotic classes.

In Vitro Activity of Robenidine Analogues NCL259 and NCL265 against Gram-Negative Pathogens

“…NCL265 (MIC range 2–32 μg/mL) demonstrated more potent antimicrobial activity against a variety of Gram-negative human and animal isolates, including human KAPE pathogens compared to NCL259 (8–64 μg/mL), suggesting that the smaller size of these monomeric robenidine analogues may enable penetration of the Gram-negative outer membrane through porins (thus reaching the likely target site within the bacterial inner membrane) compared to the larger dimeric guanidine and pyrimidine-based structures. As we have previously shown, much improved MICs were obtained for both molecules in the presence of outer membrane permeabilizers, a feature of both the parent compound (NCL812) and previously described dimeric analogues NCL195 and NCL179 [ 22 , 23 , 25 , 42 ]. Whilst outer membrane permeabilizers such as EDTA may facilitate transport across the outer membrane through destabilization and loss of lipopolysaccharide chains, outer membrane permeabilizers could also affect microbial efflux systems [ 43 , 44 ].…”

“…Given our previous findings that the combination of NCL812, NCL195, or NCL179 with Gram negative outer membrane permeabilizers (EDTA and polymyxins) could result in a synergistic or additive activity against Gram-negative bacteria [ 22 , 23 , 25 , 42 ], we also tested NCL259 or NCL265 activity in combination with PMB. For the Gram-negative bacteria reference strains tested, either a synergistic or additive interaction was observed, reducing the MIC of NCL259 by 8- to 256-fold and the MIC of NCL265 by 4- to 256-fold.…”

Oral administration of a 2-aminopyrimidine robenidine analogue (NCL195) significantly reduces Staphylococcus aureus infection and reduces Escherichia coli infection in combination with sub-inhibitory colistin concentrations in a bioluminescent mouse model

“…Furthermore, mice that received two intraperitoneal doses of 50 mg/kg NCL195 exhibited significantly reduced S. aureus loads compared to untreated mice, but still succumbed to infection (28). Interestingly, we recently showed that mice treated with four 50 mg/kg oral doses of a closely-related robenidine analogue (NCL179) had significant increase in overall survival rate after S. aureus challenge compared to the vehicleonly control (30). This provided the opportunity to investigate the efficacy of oral NCL195 and intraperitoneal colistin combination as a proof of concept of in vivo antimicrobial activity against GNB in a bioluminescent mouse peritonitis-sepsis model.…”