Inhibrx Biosciences reported interim data from the phase 2 portion of its HexAgon study showing a higher objective response rate when its OX40 agonist, INBRX-106, was added to Merck & Co.’s Keytruda in patients with head and neck squamous cell carcinoma (HNSCC). The results have led the company to move forward with additional clinical development plans for the candidate.
The HexAgon study randomized 68 patients with treatment-naïve, metastatic or unresectable recurrent HNSCC. All participants had high PD-L1 expression, with a combined positive score (CPS) of at least 20. Patients received either Keytruda as a monotherapy or in combination with Inhibrx’s hexavalent OX40 agonist, INBRX-106.
At an interim analysis, the objective response rate (ORR) in the combination arm was 44%, compared with 21.4% in the Keytruda-only cohort. According to Inhibrx, the ORR in the control arm aligned with findings from Merck’s phase 3 trial, which reported a 23.3% response rate in a similar group of HNSCC patients with high PD-L1 expression.
The interim data also showed three complete responses among patients treated with INBRX-106 and Keytruda, while no complete responses were reported in the Keytruda control arm. Inhibrx said the response data provided enough of a signal to expand its research and development efforts around the candidate.
“We believe we don’t just have more responders, but better responders, with the majority of responders in the combination arm exceeding 50% in tumor shrinkage [and] with three patients achieving complete response so far,” Inhibrx Chief Executive Officer Mark Lappe said during a call with analysts discussing the findings on Monday.
Lappe also said the company believes the majority of responders in the combination arm experienced tumor shrinkage exceeding 50%, and referenced the complete responses observed in the study.
Inhibrx said it expects to share progression-free survival data from the HexAgon study in the fourth quarter. The company modeled the study design on Merck’s trial by focusing on patients with high PD-L1 expression in an effort to generate a clear signal on whether INBRX-106 adds to the efficacy of Keytruda.
The company plans to begin the phase 3 portion of the HexAgon trial in the third quarter. In parallel, Inhibrx plans to expand development into additional indications, beginning with a perioperative study in non-small cell lung cancer (NSCLC). Studies in front-line metastatic NSCLC are planned for next year.
Inhibrx also said it has identified opportunities to combine INBRX-106 with vaccines, T-cell engagers, and CAR-T therapies. The company’s development strategy reflects its view that OX40 agonism may hold greater promise in earlier-stage patients with more active and responsive immune systems.
Multiple companies have pursued OX40 agonists in oncology treatment pathways based on evidence that the mechanism drives T-cell expansion and other effects that could enhance checkpoint inhibitors. Companies including AstraZeneca, Bristol Myers Squibb, GSK, Pfizer, and Roche struggled to translate preclinical promise into clinical efficacy. Inhibrx has identified the bivalent design of earlier OX40 agonists as a potential reason for those outcomes, which contributed to the development of its hexavalent INBRX-106 candidate.
Inhibrx Biosciences has reported encouraging midphase clinical results showing higher response rates when INBRX-106 is combined with Keytruda in patients with head and neck cancer. The findings highlight a potentially stronger immunotherapy approach that may improve outcomes for difficult-to-treat cancers.
Study Overview: INBRX-106 and Keytruda Combination
The Inhibrx study evaluated INBRX-106, an investigational immune-activating therapy, in combination with Keytruda, a widely used PD-1 inhibitor. The goal of the trial was to assess whether the combination could enhance tumor response rates compared to existing treatment options.
Early results from the midphase study suggest improved anti-tumor activity in head and neck cancer patients receiving the combination therapy.
Why the Inhibrx Approach Matters
The Inhibrx strategy focuses on enhancing immune system engagement in cancer therapy. By combining INBRX-106 with Keytruda, researchers aim to overcome resistance mechanisms often seen in head and neck cancers.
If further validated, the Inhibrx approach could expand treatment options for patients with limited response to current immunotherapies.
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