Hydroxychalcone inhibitors of Streptococcus mutans glucosyl transferases and biofilms as potential anticaries agents

• Low micromolar inhibitors of S. mutans biofilm and Gtf are identified.
• The lead compounds are E and Z isomers of hydroxychalcones.
• The Z isomers of chalcones produced more potent anti-biofilm activities.
• Chalcones with a 3-OH group on ring A showed better selectivity for biofilm inhibition.
• These compounds do not affect bacterial growth.

Streptococcus mutans has been implicated as the major etiological agent in the initiation and the development of dental caries due to its robust capacity to form tenacious biofilms. Ideal therapeutics for this disease will aim to selectively inhibit the biofilm formation process while preserving the natural bacterial flora of the mouth. Several studies have demonstrated the efficacies of flavonols on S. mutans biofilms and have suggested the mechanism of action through their effect on S. mutans glucosyltransferases (Gtfs). These enzymes metabolize sucrose into water insoluble and soluble glucans, which are an integral measure of the dental caries pathogenesis. Numerous studies have shown that flavonols and polyphenols can inhibit Gtf and biofilm formation at millimolar concentrations. We have screened a group of 14 hydroxychalcones, synthetic precursors of flavonols, in an S. mutans biofilm assay. Several of these compounds emerged to be biofilm inhibitors at low micro-molar concentrations. Chalcones that contained a 3-OH group on ring A exhibited selectivity for biofilm inhibition. Moreover, we synthesized 6 additional analogs of the lead compound and evaluated their potential activity and selectivity against S. mutans biofilms. The most active compound identified from these studies had an IC50 value of 44 μM against biofilm and MIC50 value of 468 μM against growth displaying >10-fold selectivity inhibition towards biofilm. The lead compound displayed a dose dependent inhibition of S. mutans Gtfs. The lead compound also did not affect the growth of two commensal species (Streptococcus sanguinis and Streptococcus gordonii) at least up to 200 μM, indicating that it can selectively inhibit cariogenic biofilms, while leaving commensal and/or beneficial microbes intact. Thus non-toxic compounds have the potential utility in public oral health regimes.

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