By Deena Beasley

(Reuters) – The U.S. National Institutes of Health on Thursday launched a clinical trial of fostamatinib, currently used to treat a blood platelet-destroying autoimmune disorder, in patients hospitalized with severe COVID-19, the disease caused by the novel coronavirus.

The tablets, sold under the brand name Tavalisse by Rigel Pharmaceuticals Inc, have shown in lab and animal studies the ability to block production of sticky, web-like substances that the immune system produces to trap foreign invaders.

For reasons that are still not clearly understood, the immune systems of some COVID-19 patients can overreact, creating an inflammatory cascade that can be toxic to organs, cause blood clots and worsen pneumonia.

Fostamatinib is designed to block activity of an enzyme that regulates parts of the body’s immune response, including “neutrophil extracellular traps,” or NETs, that white blood cells release to ensnare and kill pathogens.

“I am most excited about this drug because I know that as a targeted therapy it inhibits NETs, which we think is a big contributor to mortality,” said Dr. Richard Childs, clinical director of the National Heart, Lung, and Blood Institute.

The randomized, placebo-controlled Phase 2 trial will enroll 60 patients at the NIH Clinical Center in Bethesda, Maryland, Inova Health System’s Northern Virginia hospital and possibly other Inova locations.

The primary objective is evaluation of safety.

The trial is likely to take two or three months, and Rigel is considering how a larger study might be conducted, said Raul Rodriguez, the company’s chief executive officer.

Other immune system-modulating drugs are being used in COVID-19 patients, including the decades-old steroid dexamethasone, which is so far the only medication shown to improve their chance of survival.

“The problem is the steroid is a non-targeted therapy. It will also hit parts of the immune system that are very important for fighting off the virus or other infections,” Childs said. “Some patients that get COVID will get a bacterial infection … we see that all the time with influenza.”

Researchers at Imperial College London are also running an open-label study of fostamatinib in patients with COVID-19 pneumonia.

The drug is approved in the United States and Europe for treating adult chronic immune thrombocytopenia, a rare autoimmune disorder in which the body’s immune system destroys healthy platelets, leading to easy or excessive bruising and bleeding.

(Reporting by Deena Beasley; Editing by Timothy Gardner)