Antibacterial activities of poly(amidoamine) dendrimers terminated with amino and poly(ethylene glycol) groups

Abstract

Poly(amidoamine) (PAMAM) dendrimer derivatives have been investigated for their biological applications, especially for delivery of drugs, including antimicrobial drugs to eukaryotic cells, but their effects on bacterial cells are largely unexplored. Herein we report that amino-terminated PAMAM dendrimers are highly toxic to the common Gram-negative pathogen Pseudomonas aeruginosa. The concentration that kills 50% of the bacteria (EC50) was in the range of approximately 0.9-1.5 microg/mL for the generation 5, amino-terminated dendrimers with or without partial (43%) coating of poly(ethylene glycol) (PEG). These EC50 values were lower than that ( approximately 1.9-2.8 microg/mL) for LL-37, a potent antimicrobial peptide expressed in a variety of epithelia. On the contrary, the dendrimers were far less toxic (EC50 > 21 microg/mL) to the Gram-positive pathogen Staphylococcus aureus than LL-37 (EC50 = approximately 1.9 microg/mL). In agreement with the previous studies on other cell types, the dendrimers were not cytotoxic to human corneal epithelial cells at the concentrations that were toxic to P. aeruginosa. Our findings indicate that amino-terminated PAMAM dendrimers and their partially PEG-coated derivatives possess attractive antimicrobial properties, particularly against Gram-negative bacteria, thus expanding the potential biological application of the dendrimers.

Figure 1

Structure of the G3 PAMAM dendrimer possessing ∼32 amino groups at the periphery, and the reaction used in the present study for modifying the commercial G5 PAMAM dendrimer, possessing ∼117 amino groups at its periphery, with PEG consisting of 11 ethylene glycol units (EG₁₁).

Figure 2

MALDI-TOF mass spectra of the G5 PAMAM (a) and PEG–PAMAM (b), showing their average MWs to be 26 575 and 55 249 Da. The peak at ∼13 290 (a) and the shoulder at ∼27 600 Da/charge (b) are likely from the double-charged molecular ions.

Figure 3

Concentration (cfu/mL) of PA, including PA19960 (lab strain) and PA2219 (clinical strain), upon incubation with PAMAM and PEG–PAMAM at various concentrations for 2 h. The data points are the mean of at least three separate experiments, and the error bar represents the standard deviation.

Figure 4

Concentration (cfu/mL) of bacteria SA ATCC 29213 upon incubation with G5 PAMAM and 43% PEG-coated PAMAM (PEG–PAMAM) at various concentrations for 2 h. The data points are the mean of at least three separate experiments, and the error bar represents the standard deviation.

Figure 5

PAMAM cytotoxicity to HCECs measured by MTT survival assay with 0.002% benzalkonium chloride (bac) as the positive control. Percent survival of HCECs upon treatment with PAMAM and PEG–PAMAM at various concentrations is based on an untreated control. The data show the mean from two separate experiments with four replicates per condition, and the error bar represents a standard deviation.