Catechol-substituted siderophore colistin exhibits superior antimicrobial activity than its unmodified polypeptide counterpart

Abstract

Catechol moieties have been covalently coupled to the last-resort polypeptide antibiotic colistin via esterification and amidation reactions, inspired by the superior antimicrobial action of cefiderocol, i.e., a catechol-substituted siderophore cephalosporin. Among the tested strategies, the incorporation of the catechol motif by amidation reduces by 50% the minimum concentration to inhibit the growth of a clinical strain of uropathogenic Escherichia coli (E. coli) in its planktonic form. Its minimum bactericidal concentration is reduced by 25% after chemical modification. The tested modified antibiotic did not show cytotoxicity against human fibroblasts and keratinocytes at bactericidal doses. Additionally, due to the potential nephrotoxicity of colistin, the cytotoxicity of this catechol-substituted siderophore colistin was evaluated in a 3D model of human renal organoids showing no cytotoxicity at the doses tested. The chemical incorporation of catechol groups to existing antibiotics can reduce the doses to exert a fast antimicrobial action reducing the chances to develop antibiotic resistance.

Keywords: Amidation; Antibiotic; Catechol; Colistin; Esterification; Polymyxin E; Siderophore.

Fig. 1

Molecular structure of natural sideromycins of bacterial origin, (a) salmycins, (b) albomycins. Structure of a synthetic cephalosporin (c) ceftazidime and (d) siderophore- cephalosporin conjugates (cefiderocol). Labelled in red the iron chelating moiety

Fig. 2

Design of target reactive sites in the colistin molecule to introduce catechol units by esterification or amidation reactions

Fig. 3

Synthetic scheme for catechol-substituted colistin by (a) esterification or (b) amidation reactions

Fig. 4

(a) ¹H NMR and (b) DOSY spectra of AMI-COL (D₂O, 400 MHz). For the sake of clarification, protons located in the same area of the spectrum are labelled with the same letter

Fig. 5

(a) Bactericidal activity of commercial colistin (blue) and AMI-COL (red) against UTI E. coli. Control sample (untreated bacteria) is shown in green. (b) bacteria growth at MIC concentration for control (untreated samples, green), colistin (600 ppb, blue, ) and AMI-COL (300 ppb, red). Values are shown as Colony Forming Units per mL (CFU/mL). CAMHB stands for Mueller-Hinton Broth 2, and ID-CAMHB stands for iron depleted Mueller-Hinton Broth 2

Fig. 6

Anti-biofilm activity of colistin (blue) and AMI-COL (red). (a) and c), inhibition of biofilm growth. (b) and d), disruption of mature biofilms

Fig. 7

Cytotoxicity studies for colistin (blue) and AMI-COL (red)