A phase Ib/II study of ASKB589 (anti-Claudin 18.2 [CLDN18.2] monoclonal antibody) combined with CAPOX and PD-1 inhibitor as first-line treatment for locally advanced, relapsed and metastatic gastric/gastro-esophageal junction (G/GEJ) adenocarcinoma.

Abstract

317 Background: ASKB589 is a humanized IgG1 monoclonal antibody against Claudin 18.2 (CLDN18.2) with high affinity and enhanced antibody-dependent cytotoxicity. We report preliminary safety and efficacy data from an ongoing Phase Ib/II, dose-escalation and expansion study of ASKB589 combined with capecitabine, oxaliplatin(CAPOX) and Sintilimab as first-line treatment of G/GEJ adenocarcinoma (NCT05632939). Methods: The study enrolled G/GEJ adenocarcinoma patients(pts) with CLDN18.2 positive expression. The dose-escalation phase used a 3 + 3 design to determine the maximum tolerated dose (MTD). In expansion, the dose of ASKB589 selected for expansion was based on the safety, tolerability, pharmacokinetics and antitumor activity during escalation phase. Responses were assessed by RECIST 1.1 every 2 cycles (6 weeks). Adverse events (AEs) were graded using CTCAE v5.0. In escalation, pts received ASKB589 intravenously (IV) at doses of 6 mg/kg (n = 3) and 10 mg/kg (n = 6) every 3 weeks (Q3W) combined with CAPOX and Sintilimab. In expansion, all pts received ASKB589 IV at a dose of 6 mg/kg. Results: As of July 20, 2023, 9 pts were enrolled in escalation. No DLT was observed and thus the MTD was not identified. 9(100%)pts had treatment-related adverse events (TRAEs), the most common being nausea (77.8%), hypoproteinemia (66.7%), and hyponatremia (55.6%). While the majority of TRAEs were grade 1 or 2, 1 pt (11.1%) had a grade 3 TRAE (decreased neutrophils [10mg/kg]). In expansion, 26 pts with CLDN18.2 moderate-to-high expression (≥2+ membrane staining intensity in ≥40% of tumor cells) were included in the safety set. 24(92.3%) pts had TRAEs, the most common being nausea (65.4%), vomiting (53.8%), hypoproteinemia (53.8%), anemia (50.0%), fatigue (26.9%) and decreased neutrophils (23.1%). 3 pts (11.5%) had TRAEs of grade ≥3 including hypocalcemia, hypokalemia, decreased neutrophils, fatigue and bone marrow suppression. For the 15 evaluable pts who had at least one post-baseline tumor assessment, 12 pts (80.0%) achieved PR for an unconfirmed objective response rate (ORR) of 80.0%. 3 pts (20.0%) had SD for a disease control rate (DCR) of 100.0%. The PK of ASKB589 at doses of 6mg/kg and 10mg/kg combined with CAPOX and anti-PD1 therapy was consistent with that of monotherapy. Conclusions: ASKB589 combined with CAPOX and PD-1 inhibitor has manageable safety and promising antitumor activity. 6mg/kg is chosen as the recommended dose in subsequent studies. Clinical trial information: NCT05632939 .