Developing inhibitors of bacterial DNA-repair and SOS response pathways Jacob Bradbury 1,2 , Timothy R. Walsh 2 , Thomas Lanyon-Hogg 1
1 Dept. of Pharmacology, University of Oxford, UK, 2 INEOS Oxford Institute, University of Oxford, UK
Antimicrobial resistance (AMR) has the potential to make many life-saving medical advances redundant, causing 10 million deaths per year by 2050. 1 New compounds with novel targets are required to address the challenge of AMR. 2 One such target is the DNA damage repair process which allows bacterial survival under stress from antibiotics or immune attack. Loading of the DNA repair enzyme AddAB onto damaged DNA facilitates double stranded break repair and upregulates the SOS response, which activates virulence, persistence, and resistance mechanisms. 4 IMP1700 inhibits AddAB, potentiating the DNA damaging antibiotic Ciprofloxacin (CFX) and inhibiting the SOS response in methicillin-resistant Staphylococcus aureus (MRSA). 3 IMP1700 contains a fluoroquinolone (FQ) motif associated with ‘black box’ toxicity and understanding of the structure-activity relationship (SAR) of this series is limited, both of which hinder future translation. To investigate the SAR of IMP1700 and develop improved lead compounds, over 90 analogues were synthesised (Fig. 1A), and two high-throughput assays were developed to assess compound activity. Firstly, compound growth inhibition was determined with and without half-minimum inhibitory concentration (MIC) of CFX to probe DNA- repair inhibition (Fig. 1B) and fold increase in potency with CFX (∆CFX) calculated. Secondly, SOS response inhibition after activation by CFX was measured using a reporter system expressing GFP under control of an SOS-responsive promoter (Fig. 1C). OXF077 showed greater synergy with CFX-induced DNA damage than IMP1700 (∆CFX = 260 and 106-fold, respectively) and stronger SOS inhibition (IC 50 = 75 and 132 nM, respectively). Interestingly, a selection of compounds, such as OXF030 and OXF031 showed only SOS response inhibition (IC 50 =455 and 607 nM, respectively) without strong synergy with CFX-induced DNA damage, suggesting the potential existence of a second target or mechanism of action (Fig. 1D). OXF030 also does not contain the CFX core associated with off-target ‘black-box’ toxicity. Overall, this work has uncovered a divergent SAR in DNA-repair and SOS response inhibitors, suggesting a new mechanism of action for this series which could provide a useful tool to combat the threat of AMR. Figure 1: A) DNA repair and SOS response inhibitors of interest. B) Growth inhibition with half MIC CFX (solid line) and without (dashed line). C) SOS response inhibition measured in GFP reporter assay. D) Comparison of ∆CFX and SOS response inhibition with 1.25 µM of compound.
References 1. O’Neill, Tackling drug-resistant infections globally: final report and recommendations , 2016. A. Cook and G. D. Wright, Sci Transl Med , 2022, DOI:10.1126/scitranslmed.abo7793. S. Q. Lim, K. P. Ha, R. S. Clarke, L. A. Gavin, D. T. Cook, J. A. Hutton, C. L. Sutherell, A. M. Edwards, L. E. Evans, E. W. Tate and T. Lanyon-Hogg, Bioorg Med Chem , 2019, DOI:10.1016/j.bmc.2019.06.025. Lanyon-Hogg, Future Med Chem , 2021, 13, 143–155. DOI:10.4155/fmc-2020-0310
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© The Author(s), 2023
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