Resistance is not Futile:Discovery and development of peptide antibiotics composed of D amino acids
Abstract: Since the discovery of penicillin in 1928, many antibiotics
targeting different kinds of bacterial species have been developed. Extensive and improper
use of antibiotics has triggered a "bacterial resistance" problem. The biggest challenge in
developing new antibiotics is that the bacterial strains may become resistant to newly
developed drugs even during laboratory development befor... read moree clinical trials in humans.
Vancomycin is one of the "last resort" antibiotics used in the treatment of life
threatening hospital infections. Since the isolation and identification of a
vancomycin-resistant strain in 1988, it is of the highest and gravest of concern that
vancomycin-resistance can be spread to multi-drug resistant pathogenic bacteria such as
Methicillin-resistant Staphylococcus aureus (MRSA) that is responsible for lethal
infections in immune-compromised subjects, such as those afflicted with AIDS, and organ
transplant patients. In such a scenario, there will be no more available drugs for the
treatment of such patients and the biggest advantage the modern medicine has thrived upon
would be taken away. The aim of this dissertation is to develop stable, protease resistant
peptides composed of D-amino acids as antibiotics that bind D-Alanyl-D-Alanine termini of
vancomycin-sensitive bacteria and D-Alanyl-D-Lactate termini of vancomycin-resistant
bacteria with a mechanism of action similar to that of vancomycin based on mirror-image
phage display concept. We have identified several L-peptides that bind the enantiomer of
vancomycin-sensitive and resistance bacterial cell wall termini by screening phage display
libraries displaying 7-12 residue linear, cyclic and bicyclic random peptides against
enantiomers of derivatives of the β-lactam antibiotic cephalosporin, that mimic the
D-Ala-D-Ala termini of peptidoglycan structures in bacterial cell walls, crucial for
crosslinking and providing structural integrity to the cell. In addition, enantiomers of
the cell wall crosslinking pentapeptide precursors, including those that contain
D-Ala-D-Lac were also used. After evaluating the binding specificity of each identified
peptide to its target molecule via ELISA, a total of 94 peptides (linear, cyclic, and
bicyclic) identified from such screen were synthesized as their mirror image versions
(D-peptides). Antibacterial activity assays established that some of these D-peptides
(linear, cyclic and bicyclic) have antibacterial activity against vancomycin-sensitive and
vancomycin-resistant bacteria with a MIC values ranging from 8 μg/ml to 64 μg/ml. Taken
together, we have a used a hitherto unused unified chemical-biological approach that can be
used to generate a wide range of D-peptides that can act as antibiotics and will pave the
way for a new family of antimicrobial compounds.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Chemistry.
Advisor: Krishna Kumar.
Committee: Joshua Kritzer, Tomi Sawyer, and Samuel Thomas.
Keyword: Chemistry.read less