How coronavirus damages lung cells within mere hours

How coronavirus damages lung cells within mere hours

What if scientists knew exactly what impact the SARS-CoV-2 virus had inside our lung cells, within the first few hours of being infected? Could they use that information to find drugs that would disrupt the virus' replication process before it ever gets fully underway? The discovery that several existing FDA-approved drugs--including some originally designed to fight cancer--can stop coronavirus in its tracks indicates the answer is a resounding yes.

A research team simultaneously infected tens of thousands of human lung cells with the SARS-CoV-2 virus, and then tracked precisely what happens in all of those cells during the first few moments after infection. As if that was not complicated enough, the team had to cool their entire high-containment research facility inside the NEIDL to a brisk 61 degrees Fahrenheit.

The result of that challenging and massive undertaking? The team has revealed the most comprehensive map to date of all the molecular activities that are triggered inside lung cells at the onset of coronavirus infection. They also discovered there are at least 18 existing, FDA-approved drugs that could potentially be repurposed to combat COVID-19 infections shortly after a person becomes infected. Experimentally, five of those drugs reduced coronavirus spread in human lung cells by more than 90 percent. Their findings were recently published in Molecular Cell.

Now, academic and industry collaborators from around the world are in contact with the team about next steps to move their findings from bench to bedside, the researchers say. (Although COVID-19 vaccines are starting to be rolled out, it's expected to take the better part of a year for enough people to be vaccinated to create herd immunity. And there are no guarantees that the current vaccine formulations will be as effective against future SARS-CoV-2 strains that could emerge over time.) More effective and well-timed therapeutic interventions could help reduce the overall number of deaths related to COVID-19 infections.

"What makes this research unusual is that we looked at very early time points [of infection], at just one hour after the virus infects lung cells. It was scary to see that the virus already starts to damage the cells so early during infection," says  one of the study's senior investigators.

"The most striking aspect is how many molecular pathways are impacted by the virus," says  another of the study's senior investigators. "The virus does wholesale remodeling of the lung cells--it's amazing the degree to which the virus commandeers the cells it infects."

Viruses can't replicate themselves because they lack the molecular machinery for manufacturing proteins--that's why they rely on infecting cells to hijack the cells' internal machinery and use it to spread their own genetic material. When SARS-CoV-2 takes over, it completely changes the cells' metabolic processes, the author says, and even damages the cells' nuclear membranes within three to six hours after infection, which the team found surprising. In contrast, "cells infected with the deadly Ebola virus don't show any obvious structural changes at these early time points of infection, and even at late stages of infection, the nuclear membrane is still intact," the author says.

The nuclear membrane surrounds the nucleus, which holds the majority of a cell's genetic information and controls and regulates normal cellular functions. With the cell nucleus compromised by SARS-CoV-2, things rapidly take a bad turn for the entire cell. Under siege, the cells--which normally play a role in maintaining the essential gas exchange of oxygen and carbon dioxide that occurs when we breathe--die. As the cells die, they also emit distress signals that boost inflammation, triggering a cascade of biological activity that speeds up cell death and can eventually lead to pneumonia, acute respiratory distress, and lung failure.

The team leveraged the CReM's organoid expertise to grow human lung air sac cells, the type of cell that lines the inside of lungs. Air sac cells are usually difficult to grow and maintain in traditional culture and difficult to extract directly from patients for research purposes. That's why much coronavirus research to date by other labs has relied on the use of more readily available cell types, like kidney cells from monkeys. The problem with that is kidney cells from monkeys don't react the same way to coronavirus infection as lung cells from humans do, making them a poor model for studying the virus--whatever is learned from them doesn't easily translate into clinically relevant findings for treating human patients.

"Our organoids, developed by our CReM faculty, are engineered from stem cells--they're not identical to the living, breathing cells inside our bodies, but they are the closest thing to it," says  one of the study's senior authors.

In another recent study using the CReM's engineered human lung cells, the research team confirmed that existing drugs remdesivir and camostat are effective in combating the virus, though neither is a perfect fix for controlling the inflammation that COVID-19 causes. Remdesivir, a broad-use antiviral, has already been used clinically in coronavirus patients. But based on the new study's findings that the virus does serious damage to cells within hours, setting off inflammation, the researchers say there's likely not much that antiviral drugs like remdesivir can do once an infection has advanced to the point where someone would need to be put on a ventilator in the ICU. "[Giving remdesivir] can't save lives if the disease has already progressed," the author says.

Seeing how masterfully SARS-CoV-2 commandeers human cells and subverts them to do the manufacturing work of replicating the viral genome, it reminded the researchers of another deadly invader.

The team screened a number of cancer drugs as part of their study and found that several of them are able to block SARS-CoV-2 from multiplying. Like viruses, cancer cells want to replicate their own genomes, dividing over and over again. To do that, they need to produce a lot of pyrimidine, a basic building block for genetic material. Interrupting the production of pyrimidine--using a cancer drug designed for that purpose--also blocks the SARS-CoV-2 genome from being built. But the author cautions that cancer drugs typically have a lot of side effects. "Do we really want to use that heavy stuff against a virus?" the author says. More studies will be needed to weigh the pros and cons of such an approach.