Background: Recurrent pharyngotonsillitis due to Streptococcus pyogenes develops regardless
of whether infecting strains are resistant or susceptible to first-line antimicrobials. Causation for
recurrent infection is associated with the use of first-line antimicrobials that fail to penetrate deep tissue
and host cell membranes, enabling intracellular S. pyogenes to survive throughout repeated rounds
of antimicrobial therapy.
Objective: To determine whether simvastatin, a therapeutic approved for use in the treatment of hypercholesterolemia,
and ML141, a first-in-class small molecule inhibitor with specificity for human
CDC42, limit host cell invasion by S. pyogenes.
Methods: Assays to assess host cell invasion, bactericidal activity, host cell viability, actin depolymerization,
and fibronectin binding were performed using the RAW 267.4 macrophage cell line and
Human Umbilical Vein Endothelial Cells (HUVEC) infected with S. pyogenes (90-226) and treated
with simvastatin, ML141, structural analogs of ML141, or vehicle control.
Results: Simvastatin and ML141 decreased intracellular infection by S. pyogenes in a dose-dependent
manner. Inhibition by simvastatin persisted following 1 h washout whereas inhibition by ML141 was
reversed. During S. pyogenes infection, actin stress fibers depolymerized in vehicle control treated
cells, yet remained intact in simvastatin and in ML141 treated cells. Consistent with the previous characterization
of ML141, simvastatin decreased host cell binding to fibronectin. Structural analogs of
ML141, designated as the RSM series, decreased intracellular infection through non-cytotoxic, nonbactericidal
Conclusion: Our findings demonstrate the potential of repurposing simvastatin and of developing
CDC42-targeted therapeutics for eradicating intracellular S. pyogenes infection to break the cycle of
recurrent infection through a host-directed approach.