|M.Sc Student||Eylon Bat-Hen|
|Subject||New Variants of Hybrid Antibiotics as a Strategy to Delay|
Development of Bacterial Resistance
|Department||Department of Chemistry||Supervisor||Professor Timor Baasov|
|Full Thesis text|
The emerging resistance to currently available antibiotics raises an urgent need for the development of new strategies to combat the growing antibacterial resistance.
One strategy to delay the evolution of resistance is the combination therapy in which two or more different antibiotics employing distinct mechanisms of action are used as a mixture-cocktail of drugs. Since the two drugs act through different mechanisms, there is a low probability that the bacteria will simultaneously gain resistance to both drugs. However, the effects of cocktail in vitro do not necessarily correlate to in vivo outcomes due to the varied pharmacokinetic properties of the different drugs in the combination. To address this issue, the approach of "hybrid antibiotic" in which two different drugs are covalently linked was recently developed. This approach can retain the advantages of combination therapy, and yield a powerful drug with potential to delay resistance development.
Our lab has previously reported on the development of two sets of hybrids, ciprofloxacin-neomycin B and ciprofloxacin-kanamycin A. These hybrids demonstrated substantial antibacterial activity, and exhibited antagonistic behavior in comparison to ciprofloxacin. They also showed significant delay in resistance development. By looking the phenotypic and genotypic evolution of resistance,we found that the neomycin B component of the hybrids does not attribute the observed antibacterial activity of the hybrid, although it does help to restrict resistance development to the ciprofloxacin component. It was suggested that the neomycin component blocks the bacterial efflux pumps due to its high hydrophilicity, but reduces the penetration of the hybrid to the cell due to its large size. Based these data, we hypothesized that the aminoglycoside component can be replaced with a smaller, chemically similar structure, so to retain the hydrophilicity of the hybrid and improve the permeability.
The main goal of this thesis was to test the above hypothesis by designing and synthesis of new hybrids that will exhibit better cell permeation and delay resistance development more efficiently.
Toward these ends, a library of new paromamine-ciprofloxacin hybrid structures were synthesized and their antibacterial activity was tested against a wide range of bacterial strains. We found that while the new hybrids exhibit significant antibacterial activity, they also have antagonistic behavior towards the ciprofloxacin component. A case study also showed large delay in resistance development in comparison to ciprofloxacin, but this delay was less significant than that observed in the previous hybrids.
It was reported that aminoglycosides can be converted to amphiphilic compounds that can target bacterial membranes. Moreover, targeting the cell membrane is known to delay resistance development. In view of the above, we synthesized a second library of hybrids in which the free hydroxyl groups are per-benzylated. The per-benzylated hybrids showed significant antibacterial activity against non-pathogenic bacteria, which was similar to that of the per-benzylated-paromamine component of the hybrids. A case study of the hybrid and its paromamine component demonstrated significant delay for both of these compounds. Because the membrane-targeting compounds are often cytotoxic, more biologically tests are needed in order to assess the medical relevance of our per-benzylated hybrids.