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Insights into the Spectrum of Activity and Mechanism of Action of MGB-BP-3

Hind, Charlotte; Clifford, Melanie; Woolley, Charlotte; Harmer, Jane; McGee, Leah M.C.; Tyson-Hirst, Izaak; Tait, Henry J.; Brooke, Daniel P.; Dancer, Stephanie J.; Hunter, Iain S.; Suckling, Colin J.; Beveridge, Rebecca; Parkinson, John A.; Sutton, J. Mark; Scott, Fraser J.


Charlotte Hind

Melanie Clifford

Charlotte Woolley

Jane Harmer

Leah M.C. McGee

Izaak Tyson-Hirst

Henry J. Tait

Daniel P. Brooke

Iain S. Hunter

Colin J. Suckling

Rebecca Beveridge

John A. Parkinson

J. Mark Sutton

Fraser J. Scott


MGB-BP-3 is a potential first-in-class antibiotic, a Strathclyde Minor Groove Binder (S-MGB), that has successfully completed Phase IIa clinical trials for the treatment of Clostridioides difficile associated disease. Its precise mechanism of action and the origin of limited activity against Gram-negative pathogens are relatively unknown. Herein, treatment with MGB-BP-3 alone significantly inhibited the bacterial growth of the Gram-positive, but not Gram-negative, bacteria as expected. Synergy assays revealed that inefficient intracellular accumulation, through both permeation and efflux, is the likely reason for lack of Gram-negative activity. MGB-BP-3 has strong interactions with its intracellular target, DNA, in both Gram-negative and Gram-positive bacteria, revealed through ultraviolet–visible (UV–vis) thermal melting and fluorescence intercalator displacement assays. MGB-BP-3 was confirmed to bind to dsDNA as a dimer using nano-electrospray ionization mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. Type II bacterial topoisomerase inhibition assays revealed that MGB-BP-3 was able to interfere with the supercoiling action of gyrase and the relaxation and decatenation actions of topoisomerase IV of both Staphylococcus aureus and Escherichia coli. However, no evidence of stabilization of the cleavage complexes was observed, such as for fluoroquinolones, confirmed by a lack of induction of DSBs and the SOS response in E. coli reporter strains. These results highlight additional mechanisms of action of MGB-BP-3, including interference of the action of type II bacterial topoisomerases. While MGB-BP-3′s lack of Gram-negative activity was confirmed, and an understanding of this presented, the recognition that MGB-BP-3 can target DNA of Gram-negative organisms will enable further iterations of design to achieve a Gram-negative active S-MGB.

Journal Article Type Article
Acceptance Date Nov 10, 2022
Online Publication Date Nov 29, 2022
Publication Date 2022-12
Deposit Date Dec 15, 2022
Publicly Available Date Dec 15, 2022
Publisher American Chemical Society
Peer Reviewed Peer Reviewed
Volume 8
Issue 12
Pages 2552-2563
Keywords Strathclyde minor groove binders, DNA binding, synergy, Gram-positive, Gram-negative, topoisomerase
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