(481) Evaluating the anti-bacterial effects of a MEK1/2 inhibitor compound on Staphylococcus aureus isolates obtained from people with cystic fibrosis

Background: One of the most prevalent bacteria colonizing the lungs in people with cystic fibrosis (PwCF) is Staphylococcus aureus (S. aureus). Challenges associated with S. aureus infection include the emergence of antibiotic resistance that limits therapeutic options to eradicate infection. As antibiotic resistant strains become more prevalent, it will become increasingly important to have alternative therapeutics to treat infections. Pharmacologic compounds targeting the mammalian serine/threonine protein kinases MEK1 and MEK2 (MEK1/2) for inhibition have been investigated for their anti-inflammatory effects on leukocytes and epithelial cells. However, it has recently been demonstrated that MEK1/2 inhibitor compounds exert direct anti-bacterial effects on S. aureus, likely through interaction with bacterial serine/threonine protein kinases. Our laboratory is investigating the therapeutic anti-inflammatory and anti-bacterial potential of MEK1/2 inhibitor compounds, with the hypothesis that MEK1/2 inhibitors reduce detrimental inflammation in CF without impairing host-defense mechanisms. However, little is known whether bacterial strains causing recurrent and chronic S. aureus infections in PwCF are susceptible to direct anti-bacterial effects of MEK1/2 inhibitor compounds. In this study we evaluated if a MEK1/2 inhibitor compound exerts anti-bacterial effects on S. aureus CF clinical isolates.

Methods: To test the hypothesis that a MEK1/2 inhibitor compound exerts direct anti-bacterial effects on clinically relevant S. aureus strains, we performed experiments with the community-associated MRSA strain USA300 and S. aureus isolates obtained from PwCF. After overnight culture, S. aureus CF isolates and wildtype S. aureus (USA300) were sub-cultured and treated with vehicle; 5, 25, or 50 µM of the MEK1/2 inhibitor compound ATR-002; or Gentamicin as a control. OD600 readings were collected at 6h to determine the effect of ATR-002 on bacterial growth and CFU were enumerated from cultures.

Results: The addition of 25 and 50 µM of ATR-002 has a robust antibacterial effect on S. aureus USA300 compared to vehicle-treated controls throughout a 6-hour growth assay. In addition, data from eight S. aureus isolates from PwCF demonstrate similar sensitivity to the direct anti-bacterial effects by addition of the ATR-002 compound.

Conclusions: Our preliminary data suggest that MEK1/2 inhibitors have direct anti-bacterial effects on clinically relevant strains of S. aureus in addition to their anti-inflammatory effects on mammalian cells. Future studies include evaluating additional S. aureus isolates from PwCF, examining the effects of MEK1/2 inhibitor compounds on S. aureus biofilms, determining if other common CF bacterial pathogens can be inhibited by MEK1/2 inhibitor compounds, and characterizing MEK1/2 inhibitor effects in a multi-microorganism co-culture system.

Acknowledgements: Supported by the Cystic Fibrosis Foundation awards LONG19F5-CI, LONG21R3, and MCCOY19R0. CF clinical isolates were provided by Dr. Daniel Wozniak’s lab at The Ohio State University.

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