Gilead stops phase 3 TIGIT trial, doubling down on other studies and pumping $320M into partner Arcus

Arcus Biosciences and Gilead Sciences are rethinking their TIGIT strategy. Gilead is stopping a phase 3 lung cancer TIGIT clinical trial—and walking away from another project—but reaffirming its commitment to Arcus by pumping a further $320 million into the biotech.

Gilead struck a far-reaching, 10-year deal with Arcus in 2020, when it paid $175 million upfront for rights to the PD-1 checkpoint inhibitor zimberelimab and options on the rest of the biotech’s pipeline. The next year, Gilead took up options on three programs, including the anti-TIGIT antibody domvanalimab and CD73 candidate quemliclustat, in return for another $725 million.

The partners shared details of tweaks to the strategy after markets closed Monday. Arcus and Gilead are stopping a phase 3 clinical trial of their TIGIT-PD-1 antibody combination in first-line locally advanced or metastatic, PD-L1-high non-small cell lung cancer (NSCLC). The partners said the action will allow them to prioritize trials with a “higher unmet need for patients with lung and gastrointestinal cancers.”

Enrollment in the trial, ARC-10, began almost three years ago, and the partners were targeting a primary completion date of Aug. 31. The decision to stop the study comes months after leaked data suggested that Roche’s rival TIGIT candidate could improve overall survival in the ARC-10 patient population. Arcus polled (PDF) oncologists after the data leak and learned that most expect the rival drug to win approval.

Roche began its pivotal trial in PD-L1-high NSCLC 11 months before ARC-10 got underway and expects to have final survival data in the second half of 2024. Neither Gilead nor Arcus referenced Roche in their update. 

Arcus and Gilead are continuing a phase 3 NSCLC trial that is enrolling patients of any PD-L1 status, a broader population than in ARC-10, and are planning a new registrational phase 3 lung cancer study that includes the domvanalimab plus zimberelimab regimen. Arcus’ corporate presentation said (PDF) the new phase 3 trial, plus a planned phase 2 study, are in settings where it could be first to market.

The partners are continuing a phase 3 gastrointestinal cancer clinical trial, too, and expect to complete enrollment in that study and the active NSCLC trial this year. Stopping ARC-10 could “potentially accelerate” the studies, according to the companies.

Arcus and Gilead shared the new plan alongside other changes to their collaboration. Gilead is leaving Arcus to run a phase 3 trial of the small-molecule CD73 inhibitor quemliclustat solo. The Big Biotech took up its option on the candidate in 2021 but said the planned pancreatic cancer trial “will become an Arcus independent study.”

The question of whether Arcus can fund the study received an immediate answer. Gilead is investing a further $320 million in Arcus, increasing its stake to 33% and its total outlay (PDF) on the biotech to $1.7 billion. Arcus will use the cash, which extends its runway into 2027, to fund studies including phase 3 trials of quemliclustat in pancreatic cancer and the HIF2a inhibitor AB521 in kidney cancer.

Gilead paid $21 a share for the additional equity, a 37% premium to Arcus’ closing price yesterday. Arcus' share price jumped 17% to almost $18 in premarket trading in the aftermath of the news. Gilead also added a third director to Arcus’ board, Chief Commercial Officer Johanna Mercier, and changed the governance to streamline decision-making.