Abstract
Infections by carbapenem-resistant A. baumannii (CRAB), a widespread nosocomial pathogen, are becoming increasingly difficult to prevent and treat. Therefore, there is an urgent need for discovery of novel antibiotics against CRAB. Programmable, precision antisense antibiotics, e.g., based on the nucleic acid mimic PNA (peptide nucleic acid) have shown promise in this respect in the form of PNA-BPP (bacteria penetrating peptide) conjugates targeting essential bacterial genes. In the present study, we designed and synthesized a series of PNA-BPPs targeting the translation initiation region of the ftsZ, acpP, or rne gene of CRAB strains. The antimicrobial activity of the compounds and effects on gene expression level was compared to that of analogous mismatch PNA controls. Three antisense conjugates (KFF)3K-eg1-(acpP)PNA (5639), (KFF)3K-eg1-(ftsZ)PNA (5612), and (KFF)3-K-eg1-(rne)PNA (5656) exhibited complete growth inhibition against several CRAB strains at 1-2, 2-8, and 2 µM, respectively, and the compounds were bactericidal at 1-2× MIC. The bactericidal effect was correlated to reduction of target gene mRNA level using RT-qPCR, and the compounds showed no bacterial membrane disruption activity at 1-2× MIC. PNA5612 was tested against a series of 12 CRAB isolates and all were sensitive at 2-8 µM. In addition, the conjugates exhibited no cellular toxicity in the HepG2 cell line (up to 20 μM) and did not shown significant antibacterial activity against other Gram negatives (E. coli, P. aeruginosa). These results provide a starting point for discovery of antisense precision designer antibiotics for specific treatment of CRAB infections.