Design, synthesis, antimicrobial activity, stability, and mechanism of action of bioresorbable ceragenins

Abstract

Device-related infections (DRIs) from bacterial/fungal biofilms that form on surfaces are a major cause of death in first-world countries. DRIs and the increasing prevalence of antibiotic resistant strains require development of new antimicrobials for improved antimicrobial prophylaxis. New antimicrobial prophylaxis practices necessitate novel agents to combat a broad spectrum of both fungi and bacteria, to be less toxic to patients, and to be locally administrable to prevent perturbations to a patient's microbiome. A class of antimicrobials that we have previously developed to fit these criteria is ceragenins. Here we describe the design, synthesis, and characterization of a new series of ceragenins that is composed of and degrades into endogenous compounds: cholic acid, B alanine, and glycerides. From this series we identify an optimized bioresorbable ceragenin that has comparable antimicrobial activities to other ceragenins, degrades rapidly through the action of lipase and at pH 7.2, and has a similar mechanism of action to previously developed ceragenins.

Fig. 1. Structure of CSA-131.

Fig. 2. Structural design of bioresorbable ceragenins that degrade into endogenous cholic acid, β alanine, and glycerides.

Scheme 1. (a) BnCl, K₂CO₃, DMF (86%); (b) DCC, Boc β alanine, DMAP, DCM (95%); (c) H₂ (500 PSI), Pd–C, MeOH (92%); (d) 1-octanoyl-rac-glycerol, 1-decanoyl-rac-glycerol, 1-lauroyl-rac-glycerol, 1,2-didecanoyl-sn-glycerol, 1,2-dihexanoyl-sn-glycerol, 1,2-dioctanoyl-sn-glycerol or monomyristin, EDCI, DMAP, DCM; (e) HCl in dioxane.

Scheme 2. (a) Decanoic acid, EDCI, DMAP, DCM (69%); (b) TFA, MeOH (48%); (c) 3, EDCI, DMAP, DCM; (d) HCl in dioxane.

Scheme 3. (a) Solketal, EDCI, DMAP, DCM (56%); (b) TFA, MeOH (60%); (c) butanoic acid, EDCI, DMAP, DCM (70%); (d) HCl in dioxane (92%).

Fig. 3. A: Stability of 12 at pH 3.6. B: Stability of 12 at pH 7.2. C: Stability of 12 at pH 10. D: Stability of 12 in the presence of lipase. E: Effects of various concentrations of sodium dodecyl sulfate (SDS), CSA-44, CSA-13, and 12 on absorbance of orange OT dye. F: Effects of CSA-131 or 12 on the fluorescence intensity of DiSC2(5) in the presence of MRSA ATCC BAA-42. CSA-131 or 12 was added at 140 s to achieve 8 μg mL⁻¹ after addition.

Fig. 4. A: Kinetics of 12 against Candida albicans. B: Kinetics of 12 against Pseudomonas aeruginosa. C: MICs of 12, CSA-131, and ciprofloxacin with MRSA through 15 passages (24 h passages). D: Cytotoxicity of 12 and Triton-X when cultured with primary keratinocytes.