The human Airway Chip that the Wyss team developed for these studies is a microfluidic device about the size of a USB memory stick that contains two parallel channels separated by a porous membrane. Human lung airway cells are grown in one channel that is perfused with air, while human blood vessel cells are grown in the other channel, which is perfused with liquid culture medium to mimic blood flow. Cells grown in this device naturally differentiate into multiple airway-specific cell types in proportions that are similar to those in the human airway, and develop traits observed in living lungs such as cilia and the ability to produce and move mucus. Airway Chip cells also have higher levels of angiotensin-converting enzyme-2 (ACE2) receptor protein, which plays a central role in lung physiology and is used by SARS-CoV-2 to infect cells.
“Our biggest challenge in shifting our focus to SARS-CoV-2 was that we don’t have lab facilities with the necessary infrastructure to safely study dangerous pathogens. To get around that problem, we designed a SARS-CoV-2 pseudovirus that expresses the SARS-CoV-2 spike protein, so that we could identify drugs that interfere with the spike protein’s ability to bind to human lung cells’ ACE2 receptors,” said Bai, who is a postdoctoral fellow at the Wyss Institute and co-lead author. “A secondary goal was to demonstrate that these types of studies could be carried out by other Organ Chip researchers who similarly have this technology, but lack access to lab facilities required to study highly infectious viruses.”
Armed with the pseudovirus that allowed them to study SARS-CoV-2 infection, the team first perfused the Airway Chips’ blood vessel channel with several approved drugs, including amodiaquine, toremifene, clomiphene, chloroquine, hydroxychloroquine, arbidol, verapamil, and amiodarone, all of which have exhibited activity against other related viruses in previous studies. However, in contrast to static culture studies, they were able to perfuse the drug through the channels of the chip using a clinically relevant dose to mimic how the drug would be distributed to tissues in our bodies. After 24 hours they introduced SARS-CoV-2 pseudovirus into the Airway Chips’ air channel to mimic infection by airborne viruses, like that in a cough or sneeze.
Only three of these drugs ⎯ amodiaquine, toremifene, and clomiphene ⎯ significantly prevented viral entry without producing cell damage in the Airway Chips. The most potent drug, amodiaquine, reduced infection by about 60 percent. The team also performed spectrometry measurements with the assistance of Steve Gygi’s group at Harvard Medical School to assess how the drugs impacted the airway cells. These studies revealed that amodiaquine produced distinct and broader protein changes than the other antimalarial drugs.
The researchers had a lead drug candidate.
All hands on deck
Despite the promise of amodiaquine, the team still needed to demonstrate that it worked against the real infectious SARS-CoV-2 virus. With the help of a new COVID-19-focused grant from DARPA, Ingber teamed up with Matthew Frieman at the University of Maryland School of Medicin and Benjamin tenOever at the Icahn School of Medicine at Mount Sinai, both of whom already had biosafety labs set up to study infectious pathogens.
This collaboration created a drug discovery ecosystem that combines the human emulation capability of the Wyss Institute’s Organ Chips with Frieman’s and tenOever’s expertise in the interactions between viruses and their host cells. The Frieman lab tested amodiaquine and its active metabolite, desethylamodiaquine, against native SARS-CoV-2 via high-throughput assays in cells in vitro, and confirmed that the drug inhibited viral infection.