Penicillin-bound polyacrylate nanoparticles: restoring the activity of beta-lactam antibiotics against MRSA

Abstract

This report describes the preparation of antibacterially active emulsified polyacrylate nanoparticles in which a penicillin antibiotic is covalently conjugated onto the polymeric framework. These nanoparticles were prepared in water by emulsion polymerization of an acrylated penicillin analogue pre-dissolved in a 7:3 (w:w) mixture of butyl acrylate and styrene in the presence of sodium dodecyl sulfate (surfactant) and potassium persulfate (radical initiator). Dynamic light scattering analysis and atomic force microscopy images show that the emulsions contain nanoparticles of approximately 40 nm in diameter. The nanoparticles have equipotent in vitro antibacterial properties against methicillin-susceptible and methicillin-resistant forms of Staphylococcus aureus and indefinite stability toward beta-lactamase.

Figure 1

Acrylated penicillin monomers 1–5 used to prepare drug-conjugated nanoparticles NP1–5, respectively.

Figure 2

Penicillin G (6) and penicillin ester 7 used for preparing drug-encapsulated nanoparticles NP6 and NP7, respectively.

Figure 3

Kirby-Bauer studies of NP1 using S. aureus (ATCC 25923). Assays were performed first in the absence of added penicillinase protein (left image) and then in the presence of 100 μg of penicillinase added to the agar (right image). The control, penicillin G, lost all of its activity in the presence of the enzyme while NP1 retained its original activity at all 3 drug amounts, as noted. The cloudy white spots appearing in the inhibition zones in the penicillinase-treated plate (right) appear to be due to uneven diffusion of the polymer through the agar in the presence of the added protein, which we have observed occasionally in Kirby-Bauer experiments (and seen around the edges of the wells), and not from surviving bacterial colonies. These spots were sampled and cultured on agar to confirm that no surviving bacteria were present.

Figure 4

AFM images show the particles from the NP1 and NP4 emulsions are uniformly in the range of 25 to 40 nm in diameter.

Scheme 1

Emulsion polymerization to make antibiotic-conjugated polyacrylate nanoparticles in water.

Scheme 2

Synthesis of penicillin acrylamide monomer 1.

Scheme 3

Synthesis of penicillin monomer 4.

Scheme 4

Representative example of an emulsion polymerization using acrylated penicillin monomer 1.