Formulation and Biological Evaluation of Mesoporous Silica Nanoparticles Loaded with Combinations of Sortase A Inhibitors and Antimicrobial Peptides

This study aimed to develop synergistic therapies to treat superbug infections through the encapsulation of sortase A inhibitors (SrtAIs; trans-chalcone (TC), curcumin (CUR), quercetin (QC), or berberine chloride (BR)) into MCM-41 mesoporous silica nanoparticles (MSNs) or a phosphonate-modified analogue (MCM-41-PO3-) to overcome their poor aqueous solubility. A resazurin-modified minimum inhibitory concentration (MIC) and checkerboard assays, to measure SrtAI synergy in combination with leading antimicrobial peptides (AMPs; pexiganan (PEX), indolicidin (INDO), and [I5, R8] mastoparan (MASTO)), were determined against methicillin-sensitive (MSSA) and methicillin-resistant (MRSA) Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. The results demonstrated that the MCM-41 and MCM-41-PO3- formulations significantly improved the aqueous solubility of each SrtAI. The MICs for SrtAI/MCM-41-PO3- formulations were lower compared to the SrtAI/MCM-41 formulations against tested bacterial strains, except for the cases of BR/MCM-41 and QC/MCM-41 against P. aeruginosa. Furthermore, the following combinations demonstrated synergy: PEX with TC/MCM-41 (against all strains) or TC/MCM-41-PO3- (against all strains except P. aeruginosa); PEX with BR/MCM-41 or BR/MCM-41-PO3- (against MSSA and MRSA); INDO with QC/MCM-41 or QC/MCM-41-PO3- (against MRSA); and MASTO with CUR/MCM-41 (against E. coli). These combinations also reduced each components' toxicity against human embryonic kidney cells. In conclusion, MCM-41 MSNs provide a platform to enhance SrtAI solubility and demonstrated antimicrobial synergy with AMPs and reduced toxicity, providing novel superbug treatment opportunities.