Safety and efficacy of IBI389, an anti-CLDN18.2/CD3 bispecific antibody, in patients with advanced pancreatic ductal adenocarcinoma: Preliminary results from a phase 1 study.

4011 Background: CLDN18.2 expression has been observed in various solid tumors. In pancreatic ductal adenocarcinoma (PDAC), positive CLDN18.2 expression was reported in nearly 60% patients (pts), indicating its potential as a novel target for anti-tumor therapy. IBI389 is an anti-CLDN18.2/CD3 bispecific antibody that induces immune synapse formations by linking CD3 molecules in T-cell receptor complexes and CLDN18.2 antigens on the membrane of tumor cells. Herein, we report preliminary result from a phase I study to evaluate safety and efficacy of IBI389 in pts with PDAC. Methods: EligibleCLDN18.2-positivepts with locally advanced, refractory or metastaticPDAC who failed or were intolerant to standard treatments were enrolled. IBI389 monotherapy was intravenously administered at 6 dose levels (5-600 µg/kg, Q3W or Q2W) during the 2-stage dose escalation and the dose expansion. In dose levels ≥ 30 µg/kg, the step-up dosing strategy with priming dose of 3 to 10 µg/kg was applied. The primary objective was safety. Secondary objective was efficacy assessed by investigator per RECIST v1.1 including objective response rate (ORR) and disease control rate (DCR). Results: As of January 9, 2024, a total of 64 CLDN18.2-positive PDAC pts were enrolled (males: 64.1%, females:35.9%, median age: 60.0 years, stage IV: 84.4%). All patients received prior therapy with a median of 2 lines (range: 1 to 5). Treatment-related adverse events (TRAEs) occurred in 62 (96.9%) pts including 35 (54.7%) pts had grade ≥3 TRAEs. The most common grade ≥3 TRAEs (≥5%) were gamma-glutamyl transferase increased (20.3%), lymphocyte count decreased (9.4%) and nausea (7.8%). Cytokine release syndrome (CRS) related adverse events occurred in 33 (51.6%) pts with no grade ≥3 CRS occurred. TEAEs leading to dose interruption and treatment discontinuation occurred in 24 (37.5%) and 3 (4.7%) pts. Preliminary efficacy of IBI389 was observed in pts with CLDN18.2 expression ≥10% (immunohistochemistry 2+/3+) at 600 µg/kg. As of January 31, 2024, there were 23 evaluable pts including 7 pts with PR and 9 pts with SD. The ORR was 30.4% (95%CI: 13.2-52.9) and DCR was 69.6% (95%CI: 47.1-86.8). The median duration of response (DoR) and progression-free survival (PFS) was not reached. More updated data on safety and efficacy will be presented at the meeting. Conclusions: IBI389 showed manageable safety profiles in pts with advanced PDAC. Preliminary efficacy was observed, including in pts with relatively low expression of CLDN18.2. Clinical trial information: NCT05164458 .