Evaluation of Synthetic Ligands as Staphylococcal Nuclease Inhibitors for Potential Anti-MRSA Therapy

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Mitigation of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) is challenging as the pathogen is resistant to a large number of therapeutic antibiotics. Hence, there is an impending need to develop alternate and effective therapeutic approaches in order to counter life-threatening MRSA infections. The current study is an endeavor to address this important and contemporary issue and highlights the prospect of deploying rationally designed small synthetic ligands and target the staphylococcal nuclease enzyme or MNase, which is a key virulence factor present in the pathogen. The present study demonstrates that an anthraquinone-based ligand (C1) could render a non-competitive inhibition, decrease the turnover number as well as catalytic efficiency of MNase, with an IC50 value of 323 nM. A potentially therapeutic C1-loaded HSA nanocarrier (C1-HNC) was developed, which rendered a sustained and protease-triggered release of the payload in presence of the cell-free extract of a clinical MRSA strain. Interestingly, the eluates from the payload nanocarrier could significantly inhibit MNase-catalyzed DNA cleavage. In another study, it was demonstrated that a benzimidazole-based ligand C2 could significantly inhibit MNase, preserve the integrity of the DNA scaffold and promote higher sequestration of MRSA by DNA, which in turn, enhanced the uptake of the DNA-entrapped-pathogen by activated macrophage-like cells. In continuation of the efforts to identify synthetic MNase inhibitors, model in vitro experiments revealed that a napthalimide-based ligand C1 could inhibit MNase, enhance MRSA entrapment in DNA and mediate enhanced pathogen uptake by activated macrophage-like cells. A pluronic F-127 nano-micellar carrier loaded with C1 was developed, wherein the anti-adhesion activity of both the carrier as well as the payload was leveraged in tandem, resulting in significant inhibition of MRSA adhesion onto collagen. Interestingly, the biocompatible C1-loaded nano-micellar arsenal could also hinder MRSA biofilm formation on orthopaedic titanium wire. The present study contributes to the continuous endeavor of discovering anti-MRSA therapeutics and demonstrates the potential of synthetic MNase inhibitors that can not only curb the virulence of MRSA but also empower the host innate immune cells for effective mitigation of infections caused by the pathogen.
Supervisor: Ramesh, Aiyagari
MRSA, Nuclease, Inhibitor, Macrophage, Adhesion, Orthopaedic Implant, MRSA, Nuclease, Inhibitor, Macrophage, Adhesion, Orthopaedic Implant