Background: Bacterial biofilms are a cause of a number of infections and are associated
with specific drug resistance. In particular, dental biofilm can consist of up to 100 bacterial species
and may result in the diseases in the teeth and the surrounding tissues, including dental caries and
periodontal diseases. Moreover, pathogens from the dental biofilm can migrate to other organs and
lead to systemic diseases. Thus, it is important to search for inhibitors of dental biofilm formation.
The series of 1,4-disubstitued thiosemicarbazide derivatives were evaluated for their ability to inhibit
mono-species Streptococcus mutans or Streptococcus sanguinis biofilm formation.
Methods: The Minimum Biofilm Inhibitory Concentration (MBIC) is defined as the lowest concentration
of an antimicrobial agent required to inhibit the formation of biofilm. MBIC was determined
spectrophotometrically. Molecular docking was performed using Glide from the Schrödinger suite
of software. The grid file was generated indicating acarbose as a reference ligand. The compounds
were modeled using LigPrep protocol from the Schrödinger suite of software. Molecular docking
was performed using the SP (standard precision) protocol of Glide. Molecular dynamics studies of
ligand-receptor complexes was performed using Desmond v. 220.127.116.11.4.
Results: The series of 1,4-disubstituted thiosemicarbazide derivatives were synthesized and investigated
for their ability to inhibit S. mutans or S. sanguinis biofilm. The most active compounds
caused inhibition of S. sanguinis and S. mutans biofilm formation in the concentration of 7.81
µg/ml- 62.5 µg/ml. We showed, that growth of S. mutans and S. sanguinis biofilm was faster and
higher in presence of sucrose. Additionally it was harder to inhibit the growth of biofilm in BHIbroth
with the presence of sucrose, than the biofilm growing in BHI without sucrose. It seems that
colonization by tested caries bacteria depends on sucrose content in medium. Based on above in
vitro anti-biofilm data, we postulated that the mechanism of antibacterial activity of the investigated
compounds might be connected with the inhibition of mono-species bacteria biofilm formation. In
order to demonstrate that the investigated compounds may inhibit the enzyme glucansucrase and
thus, biofilm formation, we performed molecular docking and molecular dynamics of the studied
compounds to glucansucrase crystal structure. The obtained results reveal that the thiosemicarbazide
derivatives can be used as potential inhibitors of dental biofilm formation, acting possibly
through inhibition of glucansucrase.
Conclusion: In this study we showed that some of tested thiosemicarbazide derivatives can be used
as potential inhibitors for mono-species cultures of S. mutans or S. sanguinis biofilm. The possible
blocking mechanism of mono-species biofilm formation was proposed via molecular modelling
technique. The data suggested that this mechanism may involve the glucansucrase inhibition as it
was demonstrated that tested derivatives occupy the same binding pocket in this enzyme as acarbose,
commonly known inhibitor of glucosylotransferases. Therefore, it is possible that tested derivatives
could be used in prevention of dental caries.