iTeos Therapeutics and its development partner GSK have started the Phase 3 GALAXIES Lung-301 trial of belrestotug plus dostarlimab doublet in patients with certain types of non-small cell lung cancer (NSCLC).

Belrestotug (EOS-448) is a monoclonal antibody (mAb) that targets T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domains (TIGIT).

Dostarlimab, which is branded as Jemperli, is a cancer immunotherapy developed by GSK.

It will be assessed along with dostarlimab against placebo plus pembrolizumab in patients with previously untreated, unresectable, locally advanced, or metastatic PD-L1 selected NSCLC.

The GALAXIES Lung-301 trial is a multicentre study that will be conducted in a randomised, double-blind, placebo-controlled manner.

It will feature around 1,000 NSCLC patients across North America, South America, Europe, and Asia.

The late-stage trial’s primary endpoints include progression-free survival and overall survival.  

Patients will be randomly assigned in a 1:1 ratio to receive either an intravenous infusion of the belrestotug + dostarlimab combination or a placebo + pembrolizumab regimen.

iTeos Therapeutics president and CEO Michel Detheux said: “Nearly 70% of patients with first-line PD-L1 high non-small cell lung cancer rely upon a chemotherapy-free regimen. We believe belrestotug + dostarlimab are poised to potentially advance the therapeutic regimen in this setting and establish new benchmarks.

“Based on our high-quality doublet exceeding its pre-defined efficacy criteria for clinically relevant activity in an interim assessment from the Phase 2 GALAXIES Lung-201 study, we believe initiating the Phase 3 programme with this patient population will serve as the foundation to our broader strategy and marks our first step in building a franchise.”

Last month, the Nasdaq-listed iTeos Therapeutics reported interim findings from the Phase 2 GALAXIES Lung-201 trial assessing the belrestotug + dostarlimab combination in previously untreated, locally advanced, or metastatic PD-L1 selected NSCLC.  

The findings surpassed predefined efficacy criteria for clinically relevant activity and demonstrated a safety profile consistent with the TIGIT:PD-1 inhibitor class.  

In addition, significant tumour reduction was observed across all doses of belrestotug plus dostarlimab compared to dostarlimab monotherapy, indicating clinically meaningful efficacy.

GSK and iTeos Therapeutics forged their partnership in June 2021 to jointly develop and co-commercialise EOS-448 for cancer treatment.