NMR structure‐based optimization of Staphylococcus aureus sortase A pyridazinone inhibitors

Abstract

Staphylococcus aureus is a leading cause of hospital-acquired infections in the United States and is a major health concern as methicillin-resistant S. aureus (MRSA) and other antibiotic resistant strains are common. Compounds that inhibit the S. aureus sortase (SrtA) cysteine transpeptidase may function as potent anti-infective agents as this enzyme attaches virulence factors to the bacterial cell wall. While a variety of SrtA inhibitors have been discovered, the vast majority of these small molecules have not been optimized using structure-based approaches. Here we have used NMR spectroscopy to determine the molecular basis through which pyridazinone-based small molecules inhibit SrtA. These inhibitors covalently modify the active cysteine thiol and partially mimic the natural substrate of SrtA by inducing the closure of an active site loop. Computational and synthetic chemistry methods led to second generation analogs that are ~70-fold more potent than the lead molecule. These optimized molecules exhibit broad-spectrum activity against other types of class A sortases, have reduced cytotoxicity and impair SrtA-mediated protein display on S. aureus cell surface. Our work shows that pyridazinone analogs are attractive candidates for further development into anti-infective agents, and highlights the utility of employing NMR spectroscopy and solubility-optimized small molecules in structure-based drug discovery.

Asymmetric Disulfanylbenzamides as Irreversible and Selective Inhibitors of Staphylococcus aureus Sortase A

“…To date, only a few studies characterized irreversible SrtA inhibitors by their inactivation kinetics . Most of these inhibitors contained the LPAT sorting‐signals but utilized different electrophilic warheads (diazoketone, chloroketone or vinyl sulfone).…”

“…Previous research campaigns investigated competitive‐reversible S. aureus SrtA inhibitors including promising scaffolds such as 2‐morpholinobenzoates, thiadiazoles, 2‐phenylthiazoles, macrocyclic peptides, 2‐phenylbenzoxazoles, and various other inhibitors . However, the most active compounds were found to be irreversible covalent inhibitors containing an electrophilic warhead that reacts with the active‐site Cys126 of SrtA . While having significant inhibition in the low micromolar range, they typically exhibit poor target selectivity or are cytotoxic such as quinones, rhodanines, or benzisothiazolinones .…”

Diverse chemical and biological potentials of various pyridazine and pyridazinone derivatives

“…These optimized molecules exhibit broad-spectrum activity against other types of class A sortases, have reduced cytotoxicity, and impair SrtA-mediated protein exhibit on S. aureus cell surface. Pyridazinone analogues were attractive candidates for further development into anti-infective agents (Chan at al., 2017). Cannabinoid type-2 receptor (CB2R) selective ligands have shown a great potential as therapeutic drugs in various diseases.…”

Design and Synthesis of Small Molecules as Potent Staphylococcus aureus Sortase A Inhibitors

“…Sortase A inhibitors reduce the bacterial virulence caused by adhesion of the surface protein that carries disease-causing components to the host. Since sortase A is not required for the growth of S. aureus , drug resistance owing to sortase A inhibitors is less expected [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ].…”