Atea Pharmaceuticals Inc., of Boston, brought in a $215 million series D financing to support development of its COVID-19 antiviral, which is designed to inhibit the viral RNA polymerase enzyme, a key element in RNA virus replication.

Atea said the FDA cleared AT-527’s IND for a phase II trial of its efficacy and safety in patients, ages 45 to 80, with moderate coronavirus disease with one or more risk factors for poor outcomes, including obesity, hypertension, diabetes or asthma. The estimated enrollment is set at 180 patients for the randomized, parallel assignment, blinded study that is estimated to begin this month and be completed by August. One or two 550-mg tablets of AT-527 or placebo are to be administered on day one followed by one tablet twice a day, plus standard of care, for 10 days.

Jean-Pierre Sommadossi, Atea’s founder, chairman and CEO, said COVID-19 has changed the pace of companies and regulatory agencies addressing the virus. It’s a new world, he told BioWorld, that his company found as it worked the past two and a half months, seven days a week and 14 hours a day to file an IND for AT-527, which Sommadossi said has been in the clinic in Europe but not in the U.S.

The pace, he added, was exemplified by Atea’s back and forth with the FDA, with the agency “requesting we reply within 48 to 72 hours, with the same due diligence on weekends, in the evening, any time.”

Jean-Pierre Sommadossi, founder, chairman and CEO, Atea

Sommadossi said he believes he “will have data in the next couple months that our drug is interacting with non-structural proteins” that are critical in functions to the virus’ replication.

AT-527, an oral, purine nucleotide prodrug, has demonstrated in vitro and in vivo antiviral activity against several enveloped single-stranded RNA viruses, including human flaviviruses and coronaviruses. Data from a phase Ib/IIa trial of AT-527 showed pan-genotypic antiviral activity in cirrhotic and noncirrhotic hepatitis C-infected patients. The data, released in late 2018, showed the drug was safe and well-tolerated with once-daily dosing of 550 mg for seven days.

Atea plans to take some of the series D money to advance its pipeline of direct-acting antivirals that target other severe RNA viral infections. The pipeline includes treatments for hepatitis C, dengue fever and respiratory syncytial virus (RSV).

Atea has several targeted nucleoside prodrugs that it said may be able to treat RSV infections, one of which is AT-899, though it plans to declare its RSV candidate later this year. The company has AT-752, a diastereomer of AT-527 and a purine nucleotide prodrug for treating newly or previously infected patients with dengue virus, which is in a phase I proof-of-concept study. The oral therapy is designed for a short treatment course. It also has AT-787, an oral antiviral combining AT-527 and AT-777, an NS5A inhibitor, for treating hepatitis C.

Atea, founded in 2014, has three development programs for treating the hepatitis C RNA virus flaviviridae that are delayed due to COVID-19. One is in phase II and two are in phase I proof-of-concept studies.

Sommadossi was principal founder of Idenix Pharmaceuticals Inc., bought by Merck & Co. Inc. for $3.85 billion in 2014, and a co-founder of Pharmasset Inc., which was acquired by Gilead Sciences Inc. for $11 billion in 2012. While he was at Idenix, the company discovered, co-developed and co-launched telbuvidine (Tyzeka/Sebivo) to treat hepatitis B and established a pipeline of antiviral therapeutics for treating hepatitis C and HIV/AIDS. Sommadossi has doctorates from the University of Marseilles in France and was a post-doctoral Fogarty fellow at the National Cancer Institute and the Medical College of Virginia.

He brought some former co-workers to Atea with him, including Andrea Corcoran, the company’s executive vice president, legal, who was an executive vice president at Idenix for nine years, and Steven Good, Atea’s executive vice president, preclinical science, who had been senior vice president of preclinical development at Idenix. Adel Mousa, Atea’s executive vice president, chemistry, was also a vice president at Idenix.

The financing was led by Bain Capital Life Sciences plus new investors RA Capital Management, Perceptive Advisors, Rock Springs Capital, Adage Capital Management, funds and accounts managed by T. Rowe Price Associates Inc., Redmile Group and Omega Funds. Existing Atea investors, including Morningside Ventures, Cormorant Asset Management, Ally Bridge Group and Sectoral Asset Management, also participated.