Dose-Expansion Study of OBI-999, a Globo H-Targeting Antibody-Drug Conjugate, in Patients with Advanced Solid Tumors

BACKGROUND: OBI-999 is an antibody-drug conjugate consisting of the Globo H-targeting antibody OBI-888 linked to the cytotoxic payload monomethyl auristatin E. In a dose-escalation study, the OBI-999 recommended phase 2 dose (RP2D) was 1.2 mg/kg every 3 weeks. This dose-expansion study evaluated the efficacy and safety of OBI-999 in patients with pancreatic cancer, colorectal cancer (CRC), or other tumor types ("basket cohort") and tumoral Globo-H H-scores ≥100 (NCT04084366). PATIENTS AND METHODS: Patients were treated at the RP2D of OBI-999. We assessed response, progression-free survival (PFS), treatment-emergent adverse events (TEAEs), and pharmacokinetics of OBI-999. RESULTS: Of 29 patients treated, 23 were evaluable for response. Eight (34.8%) had stable disease): pancreatic cancer, 4 of 7; CRC, 2 of 8; basket cohort, 2 of 8. No objective response was noted. The median time on treatment was 22 days. No association between H-score and tumor size reduction was noted. Median PFS was 3.3 months, 1.3 months, and 1.4 months in the pancreatic, CRC, and basket cohorts, respectively. One patient (3.4%) experienced a serious TEAE related to OBI-999 (febrile neutropenia) that led to discontinuation of OBI-999; the TEAE resolved 3 days after onset. OBI‑999 showed consistent pharmacokinetics with comparable exposure at the RP2D across cohorts. CONCLUSION: OBI-999 had a favorable safety profile. Although 34.8% of patients had disease stabilization, no objective response was noted, likely owing to inefficient antigen binding, suboptimal systemic exposure at the tolerated dose, and complex tumor biology.