GSK has shared encouraging data from its Phase I BEHOLD-1 clinical trial of mocertatug rezetecan (Mo-Rez), an antibody-drug conjugate targeting B7-H4 in gynaecological cancers.
At the highest assessed doses, Mo-Rez achieved confirmed objective response rates of 62% in patients with platinum-resistant ovarian cancer and 67% in those with recurrent or advanced endometrial cancer.
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The BEHOLD-1 trial is evaluating the Mo-Rez injection’s tolerability, safety and efficacy.
Phase Ia involved dose assessment in patients with advanced solid tumours, with intravenous administration every three weeks until progression or the emergence of adverse effects. In Phase Ib, patients were randomised to specific doses to further evaluate the therapy’s effects.
A total of 224 patients are enrolled, with 44 in Phase Ia and 180 in Phase Ib, focusing on platinum-resistant ovarian cancer and endometrial cancer.
The trial’s primary goals are to determine dose-limiting toxicity in Phase Ia and to confirm response rates in Phase Ib, using RECIST 1.1 criteria.
GSK senior vice-president and oncology R&D global head Hesham Abdullah said: “Treatment of gynaecological cancers remains a major challenge, with a pressing need for new therapies that offer improved response rates.
“With Mo-Rez, we now have compelling evidence of a promising clinical profile, with response rates that support accelerating development into five pivotal global Phase III trials later this year across ovarian and endometrial cancers, including earlier line settings.”
Adverse events at the highest dose included nausea, neutropenia, and anaemia. Treatment-related adverse events led to treatment interruptions in many cases but rarely required discontinuation. The most common treatment-related adverse event was nausea.
Grade 3 or higher adverse events were observed in over half of the patients within both cancer types, primarily affecting haematological function.
The occurrence of interstitial lung disease was minimal and mild. An interim analysis showed that the median duration of treatment response remains undetermined. Based on these results, the recommended dosage for upcoming Phase III trials, BEHOLD-Ovarian01 and BEHOLD-Endometrial01, is set at 5.8mg/kg.
