Feedback Disruption Shows Promise for Addressing Antiviral Drug Resistance

Researchers in California have developed a new class of resistance-proof drugs called feedback disruptors that could transform treatment of viral diseases.

“Antiviral drug resistance is a huge problem that affects millions of people around the world,” says Sonali Chaturvedi, PhD, a researcher with Gladstone Institutes, an independent, non-profit biomedical research organization based in San Fransciso. “That’s why I care so deeply about designing therapies that are resistance-proof.”

Viruses in the herpesvirus family, for example, are leading causes of birth defects, blindness, and failed organ transplants worldwide. Existing herpesvirus drugs work by poisoning the replication machinery that viruses use to multiply inside an infected cell. However, the specific viral proteins targeted by these drugs can swiftly develop just a small number of changes, or mutations, that enable them to evade the attack.

For this reason, Chaturvedi and colleagues looked for ways to disrupt viral feedback circuits.  Viral proteins that are critical for virus growth become toxic to cells at high levels. So these proteins turn off their own production when the level gets too high to prevent the cells they depend on from dying—a system known as a negative feedback loop. Feedback disruptors target and break these genetic feedback loops, causing infected cells to self-destruct and stopping infection in its tracks.

This feedback-disrupting approach arose from an earlier discovery in the lab of coauthor Leor Weinberger, PhD, of a key feedback loop in cytomegalovirus (CMV), a common type of herpesvirus. Within an infected cell, this loop regulates the production of IE86, a protein needed for the virus to multiply. Once IE86 reaches high enough levels, it switches off its own production until its concentration subsides and stabilizes. This is because too much IE86 is toxic to cells.

In lab experiments, when the team introduced genetic alterations to “cut the brakes” on the loop, IE86 production soared, destroying infected cells before more virus could be made. “It’s counterintuitive, because we’re ramping up production of a viral protein, but ultimately this counteracts infection instead of worsening it,” says Chaturvedi.

The scientists realized that if they could develop a drug to disrupt this loop, they could potentially treat CMV infection while avoiding drug resistance. “This study shows that resistance to feedback disruptors requires the virus to make numerous mutations at multiple different genomic locations, to essentially reconstitute a new feedback circuit,” says Weinberger, who is the William and Ute Bowes Distinguished Professor and director of the Center for Cell Circuitry at Gladstone. “The likelihood of this occurring is vanishingly small and lab experiments recapitulated this; the virus had little problem evolving resistance to current antivirals, but was unable to evolve resistance to feedback disruptors.”

Employing biochemical experiments, mathematical modeling, and synthetic biology, the researchers developed a small piece of synthetic DNA that binds to IE86 and prevents it from blocking its own production. Additional lab experiments demonstrated that this feedback disruptor indeed killed CMV-infected cells, but left healthy cells unharmed.

In one key experiment, the team showed that the feedback disruptor continued to be effective against CMV in cells for many months, without the virus ever developing resistance. In contrast, CMV can become resistant to the antiviral drug acyclovir in just 2 days. They also found that mice infected with a version of CMV fared better when treated with a feedback disruptor than with a placebo.

Next, the team demonstrated that feedback disruptors could be developed to target similar feedback loops used by other viruses, beginning with herpes simplex virus 1 (HSV-1), the leading infectious cause of blindness. They found that, after infection with HSV-1, the eyes of mice that had been treated with feedback disruptors experienced a significant drop in viral infection.

In addition, the researchers developed a feedback disruptor against SARS-CoV-2, the virus that causes COVID-19, showing promising antiviral effects in cell experiments.

“This is very encouraging because it suggests that the feedback-disruptor strategy is not limited to DNA-based viruses like CMV and HSV-1, but can also be designed for RNA viruses like SARS-CoV-2,” says Chaturvedi.

The findings were reported in the journal Cell.