QStatin, a Selective Inhibitor of Quorum Sensing in Vibrio Species( SmcR with an EC50 of 208.9 nM).

Because 377B6 [1-(5-bromothiophene-2-sulfonyl)-1H-pyrazole](QStatin) showed the strongest inhibition of SmcR activity without significant growth attenuation of V. vulnificus. SmcR activity was assessed by measuring the RLU level for V. vulnificus WT (pBB1) in the presence of different concentrations of QStatin, which revealed that the half-maximal effective concentration (EC50) of QStatin was 208.9 nM.

The plasmid pBB1 carrying the LuxRVh homologue-activated lux operon was conjugally transferred into the V. vulnificus wild-type (WT) strain, the ΔsmcR mutant, or the ΔluxO mutant. These V. vulnificus reporter strains were grown overnight, diluted 1:1,000 in fresh LBS, and treated with hit molecules. RLU values were calculated every hour. To determine the EC50, QStatin (10^?12 to 10^?4 M) or 2% DMSO as a control was added to the V. vulnificus WT reporter strain and RLU was measured after 5 h. The percentage of SmcR activity of the sample at a given concentration of QStatin was determined using the following equation: percent SmcR activity = sample RLU/control RLU × 100. The EC50 of QStatin (the concentration reducing the SmcR activity to 50%) was calculated from a plot of the percentages of SmcR activity versus QStatin concentrations using GraphPad Prism 6.0.