CLDN18.2–targeting antibody–drug conjugate IBI343 in advanced gastric or gastroesophageal junction adenocarcinoma: a phase 1 trial

Aberrant expression of claudin18.2 (CLDN18.2) has frequently been observed in gastric and gastroesophageal junction (G/GEJ) adenocarcinoma, making it a promising therapeutic target for this aggressive cancer. While a monoclonal antibody targeting CLDN18.2 has been approved for G/GEJ adenocarcinoma, antibody-drug conjugates (ADCs) have also emerged as therapeutic modalities. IBI343 is an ADC consisting of a fully humanized anti-CLDN18.2 monoclonal antibody conjugated to exatecan via site-specific glycol conjugation and a cleavable linker with a drug-to-antibody ratio of 4. Here we present the results from a phase 1 dose escalation and dose expansion study of the IBI343 ADC. A total of 127 patients were enrolled and dosed (19 in the escalation phase and 108 in the expansion phase). Dose-limiting toxicities occurred in two of six participants at a dose of 10 mg kg^-1, including one with myelosuppression (grade 4) and one with both neutropenia (grade 4) and febrile neutropenia (grade 3). Minimal gastrointestinal adverse events (grade ≥3) were observed and no interstitial lung disease was reported. The recommended phase 2 dose of IBI343 was determined to be 6 mg kg^-1 every 3 weeks with a confirmed objective response rate of 29% and median progression-free survival of 5.5 months in CLDN18.2-high (2+/3+ ≥ 75%) G/GEJ adenocarcinoma. IBI343 was well tolerated, with a manageable safety profile and promising efficacy in G/GEJ adenocarcinoma. Further research is required to understand optimal sequencing, and biomarker-informed combination therapy, in G/GEJ tumors given the development of multiple therapies targeting CLDN18.2 in addition to human epidermal growth factor receptor 2 and programmed cell death 1 ligand 1.ClinicalTrials.gov registration: NCT05458219 .