A Targeted Click-to-Release Activation of the Last-Resort Antibiotic Colistin Reduces its Renal Cell Toxicity.

The use of highly potent but very toxic antibiotics such as colistin has become inevitable due to the rise of antimicrobial resistance. We aimed for a chemically-triggered, controlled release of colistin at the infection site to lower its systemic toxicity by harnessing the power of click-to-release reactions. Kinetic experiments with nine tetrazines and three dienophiles demonstrated a fast release via an inverse-electron-demand Diels-Alder reaction between trans-cyclooctenes (TCO) and the amine-functionalized tetrazine Tz7. The antibiotic activity of colistin against Escherichia coli was masked by TCO units, but restored upon reaction with d-Ubi-Tz, a tetrazine functionalised with the bacterial binding peptide d-Ubi29-41. While standard TCO did not improve toxicity against human proximal tubular kidney HK-2 cells, the installation of an aspartic acid-modified TCO masking group reduced the overall charge of the peptide and entry to the kidney cells, thereby dramatically lowering its toxicity. The analog Col-(TCO-Asp)1 had favourable pharmacokinetic properties in mice and was successfully activated locally in the lung by d-Ubi-Tz in an in vivo infection model, whereas it remained inactive and non-harmful without the chemical trigger. This study constitutes the first example of a systemically acting two-component antibiotic with improved drug tolerability.

Studies of antibacterial activity (in vitro and in vivo) and mode of action for des-acyl tridecaptins (DATs).

Tridecaptins comprise a class of linear cationic lipopeptides with an N-terminal fatty acyl moiety. These 13-mer antimicrobial peptides consist of a combination of d- and l-amino acids, conferring increased proteolytic stability. Intriguingly, they are biosynthesized by non-ribosomal peptide synthetases in the same bacterial species that also produce the cyclic polymyxins displaying similar fatty acid tails. Previously, the des-acyl analog of TriA1 (termed H-TriA1) was found to possess very weak antibacterial activity, albeit it potentiated the effect of several antibiotics. In the present study, two series of des-acyl tridecaptins were explored with the aim of improving the direct antibacterial effect. At the same time, overall physico-chemical properties were modulated by amino acid substitution(s) to diminish the risk of undesired levels of hemolysis and to avoid an impairment of mammalian cell viability, since these properties are typically associated with highly hydrophobic cationic peptides. Microbiology and biophysics tools were used to determine bacterial uptake, while circular dichroism and isothermal calorimetry were used to probe the mode of action. Several analogs had improved antibacterial activity (as compared to that of H-TriA1) against Enterobacteriaceae. Optimization enabled identification of the lead compound 29 that showed a good ADMET profile as well as in vivo efficacy in a variety of mouse models of infection.