Comparative in vitro efficacy of AR-12 derivatives against Streptococcus pyogenes

Group A Streptococcus (GAS) results in invasive diseases. Our published studies show that AR-12 can directly kill GAS. However, AR-12 is toxic to the human microvascular endothelial cells (HMEC-1 cells) even at its MIC. In this study, we examined various AR-12 pyrrole derivatives, selected the most effective one and used it to combat GAS.

The bacterial numbers after treatment with AR-12 derivatives were assessed using either spectrophotometry or the colony-forming unit assay. The integrity of cell envelope and the contents of proteins and nucleic acids in GAS were sequentially examined by staining with SYTOX Green, SYPRO or propidium iodide. The protein expression was assessed by western blotting. The cytotoxicity of AR-12 derivatives was evaluated using WST-1 assay, the lactate dehydrogenase release assay and Annexin V staining.

We tested AR-12 pyrrole derivatives P12, P12-3 and P12-8 on GAS growth and found that P12 and P12-8 were effective against various M-type strains. Both P12 and P12-8 disrupted the GAS envelope and reduced protein and nucleic acid content in GAS at their MICs. At sub-MIC levels, both P12 and P12-8 inhibited GAS chaperone protein and streptococcal pyrogenic exotoxin B expression. P12 and P12-8 also exhibited a synergistic effect with gentamicin against GAS. However, only P12-8 did not affect cell death at its MIC. Besides its bactericidal efficacy, P12-8 also enhanced the clearance of intracellular bacteria in GAS-infected A549 and HMEC-1 cells.

Among these three AR-12 derivatives, P12-8 had the best potential to be an alternative agent to fight against GAS.