“Stapled” antimicrobial peptides could combat antibiotic resistance
August 19, 2019
Antimicrobial peptides are a class of natural molecules with
unique anti-infective properties. While they’ve been viewed as a potential solution
to the urgent problem of multidrug resistant infections, safety and stability
issues have stymied their development for clinical use.
Now, scientists at Dana-Farber Cancer Institute say they have
designed antimicrobial peptides (AMPs) that resolve a major safety challenge of
current AMPs, which kill bacteria by penetrating their outer membranes but also
damage the membranes of mammalian cells, including red blood cells and other
normal tissues.
The researchers used chemical “staples” to create
membrane-selective antimicrobial peptides, termed stapled AMPs (StAMPs), which are
stable, are potent, and punch holes in bacterial membranes to kill the germs while
avoiding harm to the membranes of red blood cells and kidney cells. The team,
headed by Loren D. Walensky, MD, PhD, a physician at Dana-Farber/Boston Children's Cancer and Blood Disorders Center, demonstrated that one such StAMP cured
the majority of mice infected with a highly drug-resistant Gram-negative
bacterium and did not cause toxic side effects. “We hope that our results will
inspire the advancement of StAMPs as a novel class of antibiotics to combat
multidrug resistant infections,” said the investigators, reporting in Nature Biotechnology.
Resistance to existing antibiotics has become a serious,
global threat to the point that treatment options have become very limited for
some types of infections, especially with Gram-negative bacteria, which have
outer membranes that shield them from many antibiotics. “By applying stapling
technology, we hoped to tap into the full potential of antimicrobial peptides
as a therapeutic alternative to traditional antibiotics,” said Rida Mourtada,
PhD, lead author of the study.
Importantly, the investigators found that the bacteria could not develop
resistance to StAMPs, likely because the target is the membrane itself rather
than a particular molecule.
Antimicrobial peptides are naturally produced by all classes
of organisms as a defense against invading microorganisms. They are found, for
example, in plants, insects, and vertebrates including humans. Their ability to kill a wide range of
microorganisms without causing drug resistance has made antimicrobial peptides
a prime candidate for clinical development. “However, the longstanding barrier to
translating natural antimicrobial peptides has been the indiscriminate nature
of membrane destruction, causing non-specific toxicity to normal tissues,” said
Walensky.
The antimicrobial peptides are made up of short chains of amino
acids. They are linear but in the presence of membranes can fold into different
secondary structures, some of which are called alpha-helices, a coiled form. Walensky
and his colleagues have long studied the properties of helical peptides and
have used chemical “staples” – made of hydrocarbon molecules – to brace peptides
into stable conformations that recapitulate their biological properties. In
their current research, they investigated how the properties of diverse stapled
helical antimicrobial peptides determined their ability to penetrate bacterial
membranes – and how they could be modified to avoid damaging normal cell
membranes.
The particular antimicrobial peptide they worked with is
called Magainin-II. Integrating laboratory experimentation and computer simulation,
the scientists studied the effects of inserting chemical staples at various
locations along the length of the peptide helix. Ultimately, they found that
inserting two hydrocarbon staples at specific points along the helix yielded an
antimicrobial peptide that was stable, resistant to being destroyed by enzymes,
was a potent weapon against multidrug resistant Gram-negative bacteria, and
caused little or no damage to red blood cells or kidney cells in culture.
Laboratory testing of this lead compound in panels of Gram-negative
bacteria demonstrated that it was highly effective, even against the most
drug-resistant bacterial isolates provided by the Centers for Disease Control
and Prevention.
In mouse experiments, the StAMP proved capable of curing 75
percent of mice infected with a highly drug-resistant Gram-negative bacterium
using only two doses of the compound and caused no harmful effects.
The authors concluded that peptide stapling can be used to
create antimicrobial peptides “that can kill even the most resistant
Gram-negative bacteria and be administered internally without the toxic side
effects that have long thwarted the clinical translation of AMPs.”
The research was supported in part by National Institutes of
Health grant R35CA197583, a Leukemia and Lymphoma Society Scholar Award to
Walensky, and NIH grant R01GM101135.
Walensky is a scientific advisory board member and consultant
for Aileron Therapeutics.