PEGylated Self-Assembled Nano-Bacitracin A: Probing the Antibacterial Mechanism and Real-Time Tracing of Target Delivery in Vivo

Abstract

Although nano-self-assemblies of hydrophobic-modified bacitracin A with poly(d,l-lactic- co-glycolic acid) (PLGA) (nano-BA) have demonstrated promising antibacterial activities, the application of nano-BA was severely compromised by low water solubility. In this study, a series of PEGylated PLGA copolymers were selected to conjugate with the N-terminus of bacitracin A to construct PEGylated self-assembled nano-BAs and to further develop nano-self-assemblies of bacitracin A with strong antibacterial potency and high solubility. Compared with nano-BA, all PEGylated nano-BAs, except nano-BA, exhibited strong antibacterial efficiency against both Gram-positive and Gram-negative bacteria by inducing loss of cytoplasmic membrane potential, membrane permeabilization, and leakage of calcein from artificial cell membranes. Studies elucidating the underlying mechanism of PEGylated nano-BAs against Gram-negative bacteria indicated that the strong hydrophobic and van der Waals interactions between PLGA and lipopolysaccharide (LPS) could bind, neutralize, and disassociate LPS, facilitating cellular uptake of the nanoparticles, which could destabilize the membrane, resulting in cell death. Moreover, PEGylated nano-BAs (nano-BA) with a longer PLGA block were expected to occupy a higher local density of BA mass on the surface and result in stronger hydrophobic and van der Waals interactions with LPS, which were responsible for the enhanced antibacterial activity against Gram-positive and emerging antibacterial activity against Gram-negative bacteria, respectively. In vivo imaging verified that PEGylated nano-BAs exhibited higher inflammatory tissue distribution and longer circulation time than nano-BA. Therefore, although PEGylation did not affect antibacterial activity, it is necessary for target delivery and resistance to clearance of the observed PEGylated nano-BAs. In vivo, nano-BA also showed the highest therapeutic index against infection burden in a mouse thigh infection model among the tested formulations, which showed good correlation with the in vitro results. In conclusion, nano-BA showed high efficacy in the treatment of invasive infections. This new approach of constructing nanoantibiotics by modification of commercially available antibiotics with PEGylated copolymers is safe, cost-effective, and environmentally friendly.

Brain-targeted delivery of PEGylated nano-bacitracin A against Penicillin-sensitive and -resistant Pneumococcal meningitis: formulated with RVG29 and Pluronic® P85 unimers

“…In our previous study, the PEGylated Nano-BA 12K based mainly on BA-PEG-PLGA 12K -PEG-BA demonstrated strong antibacterial activities against a broad spectrum of bacteria, including S. pneumonia , yet induced relatively lower toxicity both in vitro and in vivo (Hong et al., 2018 ). The objective of the present research was to evaluate the possibility of using PEGylated Nano-BA 12K to treat both Penicillin-sensitive and -resistant PM.…”

Insights into the antibacterial mechanism of PEGylated nano-bacitracin A against <em>Streptococcus pneumonia</em>: both penicillin-sensitive and penicillin-resistant strains

“…[18][19][20] In our previous study, the PEGylated Nano-BA 12K based mainly on BA-PEG-PLGA 12K -PEG-BA showed strong antibacterial activities against both Gram-positive and Gram-negative bacteria including S. pneumonia, yet induced relatively lower toxicity both in vitro and in vivo. 21 The objective of the present research was to evaluate the possibility of using PEGylated Nano-BA 12K to treat penicillin-resistant S. pneumonia. The antibacterial potency of PEGylated Nano-BA 12K was first tested against 13 isolates of S. pneumonia.…”

An Update on Antimicrobial Peptides (AMPs) and Their Delivery Strategies for Wound Infections

“…Bacitracin in solution, used as control, was effective only against Gram (+) bacteria with MICs between 2 and 4 µM, while MICs against Gram (−) were higher than 128 µM. It was shown as well that PEGylation did not affect antibacterial activity; on the contrary, PEGylated bacitracin-PLGA exhibited high accumulation in inflammatory tissue and prolonged blood circulation [132]. This system could be efficiently used to design novel antibiotic nano-assemblies in the treatment of invasive infections.…”