Researchers Uncover Mechanism of New Antivirals for Herpesviruses

Researchers at Harvard Medical School have made significant strides in understanding a new class of antiviral drugs aimed at combating drug-resistant strains of the herpes simplex virus (HSV). Their work reveals critical mechanisms behind these emerging treatments, which could transform the approach to managing herpesviruses and other DNA viruses. The findings were published in the scientific journal Cell on March 15, 2024.

The study’s co-senior author, Jonathan Abraham, who practices as an infectious disease doctor at Brigham and Women’s Hospital, emphasizes the urgency of developing effective antiviral medications. He has observed many patients with compromised immune systems who suffer from severe HSV infections that defy treatment due to drug resistance. As Abraham notes, “As a clinician, it’s disheartening when medicine can cure a patient of cancer, but the patient requires immunosuppression that leaves them vulnerable to a virus that doesn’t respond to the best drugs we have to treat it.” His dual role as a researcher provides him a unique perspective in the fight against drug-resistant viruses.

New antiviral agents are currently undergoing clinical trials in the United States, with one already approved in Japan. Despite their potential, the mechanisms by which these drugs exert their effects remain largely unknown. Abraham and his colleague Joseph Loparo, a professor of biological chemistry and molecular pharmacology at Harvard, aimed to elucidate these mechanisms through advanced structural biology and imaging techniques.

Decoding the Virus’s Defense Mechanism

The research team utilized cryogenic electron microscopy (cryo-EM) to visualize the HSV-1 helicase-primase complex, which plays a vital role in the virus’s replication cycle. Traditionally, studying these enzymes has been challenging due to their dynamic nature, making it difficult to capture their structures. The introduction of helicase-primase inhibitors (HPIs) allowed the researchers to stabilize these enzymes in a single form, facilitating detailed imaging.

Abraham’s lab focused on the structural aspects of how the HPIs bind to the viral protein, while Loparo’s lab concentrated on real-time observations of how this binding inhibits the enzyme’s function. “A real strength of this study is the combination of high-resolution, atomistic pictures of the viral proteins bound by the inhibitors and real-time imaging of the viral proteins in action,” Loparo stated.

The HSV-1 virus is notorious for its resilience and potential to cause severe health issues, including cold sores and life-threatening infections in immunocompromised individuals. Current FDA-approved antiviral medications primarily target the virus’s DNA polymerase, which is responsible for replicating the viral genome. However, strains of HSV have developed resistance to these existing treatments, prompting the need for innovative alternatives such as HPIs.

Visualizing the Battle Against the Virus

The research team successfully captured near-atomic resolution images of the HSV-1 helicase-primase when bound by various inhibitors. This detailed imaging not only reveals the physical structure of the enzyme but also opens avenues for identifying new drug targets by showcasing potential binding sites that could disrupt the virus’s replication process.

In addition to cryo-EM imaging, the researchers employed optical tweezers to observe the helicase-primase in action. This technique allowed them to manipulate viral DNA and monitor the effects of the HPI drugs on the enzyme’s function. As Loparo explained, “The latest generation of imaging tools, like the tweezers, have given scientists an unprecedented ability to see how the processes of life work at the level of single molecules.”

These findings are not just academic; they offer hope for future drug development aimed at combating resistant viral strains. Abraham and his team believe that their research will lay the groundwork for new antiviral therapies that could improve health outcomes for patients worldwide.

In summary, the groundbreaking work at Harvard Medical School marks a pivotal moment in the ongoing battle against herpesviruses. By understanding how new antiviral drugs interact with viral enzymes, researchers are paving the way for more effective treatments that can address the pressing issue of drug resistance in viral infections.