A phase 1a dose-escalation, multicenter trial of anti-claudin 18.2 antibody drug conjugate CMG901 in patients with resistant/refractory solid tumors.

352 Background: CMG901, an anti-claudin 18.2 (CLDN18.2) antibody-drug conjugate, has demonstrated potent preclinical anti-cancer activity through monomethyl auristatin E (MMAE)-mediated cytotoxicity with bystander killing, antibody-dependent cellular cytotoxicity, and complement-dependent cytotoxicity. Methods: This Phase 1a trial uses a modified 3+3 dose-escalation design to evaluate the safety, tolerability, pharmacokinetics (PK), and preliminary anti-tumor activity in subjects (ages 18-75 years) with advanced gastric, gastroesophageal junction (GEJ), pancreatic cancers, and other solid tumors. Eligible subjects are refractory and/or intolerant to standard therapies. CLDN18.2 expression was not required for study entry, but was retrospectively tested by the central lab. CMG901 was administered intravenously on Day 1 in 3-week (Q3W) cycle at doses of 0.3, 0.6, 1.2, 1.8, 2.2, 2.6, 3.0, and 3.4 mg/kg. Primary endpoints include safety and tolerability. Major efficacy endpoints include objective response rate (ORR) and disease control rate (DCR) based on RECIST v1.1. Pharmacokinetics (PK) and immunogenicity are also assessed. Results: As of August 4, 2022, 27 subjects (13 gastric/GEJ cancer and 14 pancreatic cancer patients) received CMG901 at dose levels up to 3.4 mg/kg. The median prior lines of systemic therapy were 2 (range: 1 to 5). Drug-related grade ≥3 adverse events (AEs) occurred in 3/27 (11.1%) patients. No drug-related grade 4 or 5 AEs were reported. MTD was not reached. In CLDN18.2-positive gastric/GEJ cancer patients, ORR and DCR were 75.0% and 100%, respectively, with ORR of 100% in the 2.6, 3.0, and 3.4 mg/kg Q3W dose cohorts. Median progression-free survival (mPFS) and median overall survival (mOS) were not reached yet. PK data showed that patients had low systemic exposure to unconjugated MMAE. Subsequent results will be presented. Conclusions: CMG901 was well-tolerated with preliminary promising clinical efficacy in patients with CLDN18.2-positive gastric/GEJ cancer. The Phase 1b dose-expansion trial in gastric/GEJ adenocarcinoma, pancreatic cancer, and other solid tumors is rapidly enrolling, with multiple pivotal (Phases 2 and 3) trials planned. Clinical trial information: NCT04805307 . [Table: see text]