GlaxoSmithKline PD-1 hopeful dostarlimab fell victim to COVID-19-related inspection delay

GlaxoSmithKline GSK House in Brentford, UK
GlaxoSmithKline is looking at approval for its PD-1 hopeful dostarlimab in the first half of 2021 after pandemic travel restrictions delayed an FDA site inspection. (GlaxoSmithKline)

Many drugmakers last year fell victim to COVID-19 related FDA inspection delays that stalled drug approvals, and GlaxoSmithKline's oncology hopeful dostarlimab was not immune, the British Big Pharma has revealed.

Approval for the drug—picked up in GSK’s $5.1 billion Tesaro buyout—"requires a site inspection of our manufacturing site, the timing of which is contingent on COVID-19 travel restrictions," a company spokesperson said over email.

The FDA was originally due to issue a decision in the second half of 2020 and at present, a new deadline for its verdict hasn’t been set. The site inspection still hasn't occurred, either, but GSK is working with the FDA to schedule the inspection and expects a green light in the first half of 2021, the spokesperson said.

Still, all is not lost for PD-1 blocker dostarlimab, a wannabe treatment for microsatellite instability-high (MSI-H) and microsatellite stable (MSS) endometrial cancer. The PD-1/PD-L1 market has become one of the most crowded in oncology, and an FDA approval for dostarlimab would cue up a seventh drug entry into the space, but few boast approvals in endometrial cancer, which could give GSK's candidate room to breathe.

The drug spurred a benefit in 42% of patients with recurrent or mismatch repair-deficient (dMMR) endometrial cancer whose disease worsened on or after chemotherapy, phase 1 data unveiled in April showed. In GSK’s phase 1 Garnet trial, researchers also linked dostarlimab to a 58% disease control rate; cancer vanished in 13% of patients, while 30% of patients saw some improvement.

RELATED: Regeneron and Sanofi won't dethrone Merck in lung cancer despite strong Libtayo data: analysts

Meanwhile, GSK is assessing the drug in other forms of endometrial cancer, plus non-small cell lung cancer, chemotherapy-resistant ovarian cancer and other solid tumors. In January, the drug showed it could trigger a response in 36.2% of patients with dMMR colorectal cancer.

GSK is far from the only drugmaker to run up against pandemic inspection woes in 2020. Bristol Myers Squibb disappointed investors late last year when it missed its December 31 approval deadline for its CAR-T hopeful, liso-cel—a target for the contingent value rights BMS issued with its Celgene merger. BMS initially blamed the delay on a waylaid FDA inspection at a Lonza plant set to churn out liso-cel, but when the regulator made it out to that site in December, inspectors found shortfalls that flushed BMS—and its investors'—CVR hopes down the drain. 

Meanwhile, the uncertainty surrounding dostarlimab's approval gives GSK's rivals more time to get ahead in the booming PD-1/PD-L1 market. Sanofi and Regeneron, sixth into the field, recently showed their PD-1 inhibitor Libtayo, given alone, cut the risk of death by 43% versus chemotherapy in a 710-subject non-small cell lung cancer trial. With the FDA now weighing approval in that setting, the companies could inch Libtayo toward blockbuster territory, provided their ambitious development plan pans out. 

RELATED: Bristol Myers hematology chief Ahmed's out the door amid CAR-T missteps

Of course, their drug will still have to go up against Merck's Keytruda—the undisputed champion of the first-line NSCLC market, and a player in the endometrial cancer space, too. In September 2019, Merck and Eisai's Keytruda and Lenvima combo bagged its first approvals for certain endometrial cancers in the U.S., and Keytruda has boasted an OK since 2017 to treat MSI-H tumors located anywhere in the body.

Editor's note: This story was updated with comments from GlaxoSmithKline.