Iminated aminoglycosides in self-emulsifying drug delivery systems: Dual approach to break down the microbial defense

Aminoglycosides are well known, cationic antimicrobial drugs. However, biofilm-based antibiotic resistance significantly limits their efficacy. Masking the polycationic character of these drugs, followed by incorporation into self-emulsifying drug delivery systems (SEDDS) can improve biofilm eradication.

Imine derivatives were synthesized via coupling with trans-cinnamaldehyde and characterized regarding degree of substitution, logP, cytotoxicity and antimicrobial efficacy on the opportunistic human pathogens Escherichia coli, Staphylococcus aureus and Candida albicans. Imines were loaded into newly developed SEDDS formulations and the antimicrobial efficacy was assessed on these pathogens in planktonic state and after biofilm formation.

Successful synthesis of imine derivatives with almost entirely masked amine groups was confirmed by NMR, FT-IR, TLC and MS. Imines exhibited a marked elevation in logP value of 8 units for kanamycin and 7.7 units for tobramycin. They showed low toxicity profiles while fully preserving antimicrobial efficacy on all tested pathogens. Incorporation into SEDDS resulted in nanoemulsions, which exhibited equal antimicrobial efficacy on the model germs compared to the corresponding aminoglycosides. Moreover, the biofilm eradication assay revealed superior anti-biofilm properties of the nanoemulsions. Native aminoglycosides were largely prone to reduced microbial susceptibility due to biofilm formation, while the combination of SEDDS with iminated aminoglycosides provided overall enhanced biofilm eradication.