Possible New Antivirals Against COVID-19 and Herpes

Peptoids (blue, left) pierce the protective layer of a virus and cause its disintegration and inactivation (right). Credit: Maxwell Biosciences

In addition to antibodies and white blood cells, the immune system uses peptides to fight viruses and other pathogens. Synthetic peptides could enhance this defense, but don’t last long in the body, so researchers are developing stable peptide mimics. Today, scientists report success using mimics known as peptoids to treat animals with herpes virus infections. These small synthetic molecules could one day cure or prevent many types of infections, including COVID-19.

The researchers will present their results at the fall meeting of the American Chemical Society (ACS). ACS Fall 2021 is a hybrid meeting held virtually and in person from August 22-26, and on-demand content will be available August 30 – September 30. The meeting includes more than 7,000 presentations on a wide range of scientific topics.

“In the body, antimicrobial peptides such as LL-37 help control viruses, bacteria, fungi, cancer cells, and even parasites,” said Annelise Barron, Ph.D., one of the lead researchers on the project. But peptides are cleared quickly by enzymes, so they are not ideal drug candidates. Instead, she and her colleagues emulated the key biophysical properties of LL-37 in smaller, more stable molecules called peptoids. “Peptoids are easy to make,” says Barron, of Stanford University. “And unlike peptides, they’re not broken down quickly by enzymes, so they can be used at a much lower dose.”

Peptides consist of short sequences of amino acids, with side chains attached to carbon atoms in the backbone of the molecules. This structure is easily broken down by enzymes. In peptoids, the side chains are instead linked to nitrogens in the molecular backbone, forming a structure that is resistant to enzymes. They were first created in 1992 by Ronald Zuckermann, Ph.D. of Chiron Corp., later Barron’s postdoctoral advisor. Unlike other types of peptide mimetics that require laborious, multi-step organic chemistry to produce, peptoids are simple and inexpensive to make with an automated synthesizer and readily available chemicals, she says. “You can make them almost as easily as bread in a bread machine.”

Barron, Zuckermann, Gill Diamond, Ph.D., of the University of Louisville, and others founded Maxwell Biosciences to develop peptoids as clinical candidates to prevent or treat viral infections. They recently reported results with their latest peptoid sequences, which were designed to be less toxic to humans than previous versions. In lab dishes, the compounds inactivated SARS-CoV-2, which causes COVID-19, and herpes simplex virus-1 (HSV-1), which causes oral cold sores, rendering the viruses unable to infect cultured human cells.

Now the researchers report in vivo results, showing that the peptoids safely prevent herpes infections in mice when dabbed on their lips. Diamond’s team is conducting additional experiments to confirm the mouse’s findings. In addition, they will investigate the effectiveness of the peptoids against strains of HSV-1 that are resistant to acyclovir, the best current U.S. Food and Drug Administration-approved antiviral treatment for this condition, Barron says.

The researchers are also preparing to test peptoids for activity against SARS-CoV-2 in mice. “COVID-19 infection involves the whole body, once someone gets really sick from it, we’ll do this test intravenously as well as look at the delivery to the lungs,” Barron says.

But these antimicrobial molecules could have many more applications. Work is underway at Stanford to investigate their impact on ear and lung infections. And Barron has sent peptoid samples to experts in other labs to test for a range of viruses, showing promising results in lab-scale studies against the flu, the common cold virus, and hepatitis B and C.” In their in vitro studies, a team found that two of the peptoids were the most potent antivirals ever identified against MERS and older SARS coronaviruses,” said Barron. Other labs are testing the peptoids as antifungals for respiratory and gut, and as anti-infective coatings for contact lenses, catheters, and implanted hip and knee joints.

Diamond and Barron are investigating how these broad-spectrum connections work. They appear to pierce and break the viral envelope and also bind to the RNA or DNA of the virus. That multiple mechanism has the advantage of inactivating the virus, unlike standard antivirals, which slow viral replication but still allow viruses to infect cells, Barron says. It also makes it less likely that pathogens will develop resistance.

Barron expects clinical trials to begin within the year. If successful, she says, peptoids can be given preemptively — for example, before a plane trip to protect a passenger from COVID-19 — or after an infection sets in, such as when a person feels the telltale tingling of an approaching cold sore.

A recorded media briefing on this topic will be posted on Tuesday, August 24 at 9:00 a.m. Eastern time at www.acs.org/acsfall2021briefings.

The researchers acknowledge support and funding from Maxwell Biosciences, the National Institutes of Health and the Molecular Foundry through the United States Department of Energy.

Title

Potent antiviral activity against HSV-1 and SARS-CoV-2 by antimicrobial peptoids

Abstract

Viral infections, such as those caused by Herpes Simplex Virus-1 (HSV-1) and SARS-CoV-2, affect millions of people every year. However, few antivirals can effectively treat these infections. The standard approach to antiviral drug development involves the identification of a unique viral target, followed by the design of an agent that addresses that target. Antimicrobial peptides (AMPs) represent a new source of potential antiviral drugs. AMPs have been shown to inactivate numerous different enveloped viruses through the disruption of their viral envelopes. However, the clinical development of AMPs as antimicrobial therapies has been hampered by a number of factors, most notably their enzymatically labile structure as peptides. We explored the antiviral potential of peptoid mimics of AMPs (sequence-specific N-substituted glycine oligomers). These peptoids have the distinct advantage of being insensitive to proteases and also exhibit increased bioavailability and stability. Our results demonstrate that several peptoids exhibit potent in vitro antiviral activity against both HSV-1 and SARS-CoV-2 when incubated prior to infection. In other words, they have a direct effect on the viral structure, making the viral particles appear to become non-infectious. Visualization by cryo-EM shows disruption of the viral envelope similar to what has been observed with AMP activity against other viruses. Furthermore, we have not observed cytotoxicity against primary cultures of oral epithelial cells. These results suggest a general or biomimetic mechanism, possibly due to the differences between the composition of the phospholipid headgroup of viral envelopes and host cell membranes, underscoring the potential of this class of molecules as safe and effective broad-spectrum antivirals. We discuss how and why different molecular features among 10 peptoid candidates can influence both antiviral activity and selectivity. Finally, we will discuss promising new results indicating antiviral peptoid activity against rhinovirus and hepatitis B virus.