Isatin Bis-Imidathiazole Hybrids Identified as FtsZ Inhibitors with On-Target Activity Against Staphylococcus aureus

Abstract

In the present study, a series of isatin bis-imidathiazole hybrids was designed and synthesized to develop a new class of heterocyclic compounds with improved antimicrobial activity against pathogens responsible for hospital- and community-acquired infections. A remarkable inhibitory activity against Staphylococcus aureus was demonstrated for a subset of compounds (range: 13.8-90.1 µM) in the absence of toxicity towards epithelial cells and human red blood cells. The best performing derivative was further investigated to measure its anti-biofilm potential and its effectiveness against methicillin-resistant Staphylococcus aureus strains. A structure-activity relationship study of the synthesized molecules led to the recognition of some important structural requirements for the observed antibacterial activity. Molecular docking followed by molecular dynamics (MD) simulations identified the binding site of the active compound FtsZ, a key protein in bacterial cell division, and the mechanism of action, i.e., the inhibition of its polymerization. The overall results may pave the way for a further rational development of isatin hybrids as FtsZ inhibitors, with a broader spectrum of activity against human pathogens and higher potency.

Keywords: FtsZ inhibitors; MRSA; antibacterial activity; isatin bis-imidathiazole hybrids; molecular dynamics simulations.

Chart 1

6k, 6m in ref. [15].

Scheme 1

Synthetic route for obtaining the new derivatives 3–16, 17–20.

Figure 1

Dose–response curves of compound 11 against S. aureus reference strain and the 5 clinical isolates. (a) Sigmoid curves obtained by plotting the percentages of growth inhibition, relative to the positive control (set to 100% of growth), as a function of the tested concentrations (on a logarithm scale). (b) IC₅₀ values obtained for S. aureus strains (mean values and 95% confidence interval).

Figure 2

(A) FtsZ co-crystallized with GTP (in blue) and an inhibitor, PC190723, (in yellow) from PDB 3VOB; (B) 11 in GTP binding pocket (blue region); (C) 11 in interdomain cleft (yellow region).

Figure 3

(A) Per-residue decomposition analysis for the binding of 11 at the interdomain cleft; (B) Close-up of the most interacting FtsZ residues with 11. Hydrogen bonds are highlighted by red dashed lines, and non-polar interactions via gray dashed lines.

Figure 4

Dimerization energy for (A) apo-FtsZ; (B) FtsZ in presence of GTP and Ca²⁺; (C) FtsZ in presence of GTP, Ca²⁺, and 11.

Figure 5

Antibiofilm activity of derivative 11 at different concentrations (μM) against S. aureus. (A) Photograph of a crystal violet stained biofilm produced in a 96-well plate; (B) Biofilm quantification as measured by optical density (OD) at 550 nanometers. *** p < 0.05 for samples treated with 200–25 μM compared to the positive control (ANOVA test and Dunnett’s multiple comparison test).