Phase 1 Study of INBRX-105, a TNFRSF9 (4-1BB) and PD-L1 Bispecific Antibody, in Patients with Select Solid Tumors.

[PURPOSE] INBRX-105, a tetravalent, PD-L1-targeted TNFRSF9 (4-1BB) agonist, demonstrated preclinical antitumor activity. This first-in-human study evaluated INBRX-105 in solid tumors.

[PATIENTS AND METHODS] This open-label, 4-part, phase 1 study evaluated INBRX-105 alone or with pembrolizumab in adults with locally advanced/metastatic, unresectable solid tumors (NCT03809624). INBRX-105 was administered intravenously once every 2 weeks or 4 weeks in parts 1 (single-agent dose escalation; 0.001-3 mg/kg) and 2 (single-agent expansion) or once every 3 weeks in parts 3 (combination dose escalation; INBRX-105 0.03-1.0 mg/kg) and 4 (combination expansion). Part 2 enrolled patients with checkpoint inhibitor-relapsed/refractory (CPI-R/R) tumors. Part 4 enrolled patients with CPI-R/R or CPI-naïve disease. The primary endpoint was safety and tolerability of INBRX-105. Preliminary clinical response was a secondary endpoint.

[RESULTS] Of 160 patients assessed, 81 received monotherapy (median age, 65 years; female, 50.6%), and 79 combination therapy (median age, 64 years; female, 38%). The INBRX-105 maximum tolerated dose was 0.3 mg/kg once every 3 weeks. Head and neck squamous cell carcinoma (n = 61) and non-small cell lung cancer (n = 25) were the most common tumor types. The most common any-grade INBRX-105-related adverse events (AE) were fatigue (monotherapy, 35.8%; combination, 17.7%), increased aspartate aminotransferase (25.9%; 15.2%), and nausea (19.8%; 17.7%). INBRX-105-related hepatic AEs occurred in 41 patients [monotherapy, n = 25 (grade ≥3, n = 11); combination, n = 16 (grade ≥3, n = 6)]. In all patients, the objective response rate was 8.8% [monotherapy, 3.7%; combination, 13.9% (CPI-naïve, 30%; CPI-R/R, 8.6%)]; the disease control rate was 43.1%.

[CONCLUSIONS] The low response rates and hepatic safety signals observed do not support further clinical development of INBRX-105.

[SIGNIFICANCE] Tumor resistance to CPIs often develops, underscoring an unmet need. This first-in-human phase 1 trial evaluated INBRX-105-a tetravalent, PD-L1-targeted 4-1BB agonist-alone or with pembrolizumab. Unfortunately, clinical development of INBRX-105 was ended because of hepatotoxicity and limited efficacy. Novel treatment combinations with nonredundant, complementary immunotherapies are needed.