First-in-human trial of M9140, an anti-CEACAM5 antibody drug conjugate (ADC) with exatecan payload, in patients (pts) with metastatic colorectal cancer (mCRC).

3000 Background: CEACAM5 is a cell surface protein with limited expression in adult healthy tissues, but high expression in various adenocarcinomas, particularly in CRC (>90% of pts). M9140 is the first anti-CEACAM5 ADC with a topoisomerase 1 inhibitor (Top1i) payload (exatecan). The ß-glucuronide linker connecting the M9140 antibody backbone to the payload is highly stable in circulation (drug-to-antibody ratio=8). In preclinical models, M9140 has demonstrated strong potency, antitumor activity, and a bystander effect. Methods: This Phase 1 trial (NCT05464030) investigated the safety, tolerability, pharmacokinetics (PK), and preliminary clinical activity of M9140 as monotherapy (Q3W [Day 1 of 21-day cycles]; IV) in adults with CRC (ECOG PS ≤1) who had received ≥2 prior lines of treatment. The primary objectives of Part 1A were to determine the maximum tolerated dose (MTD) and/or recommended dose(s) for expansion (RDE). Results: At data cutoff (19 Jan 2024), 40 pts from the US, EU, and Japan were treated across 7 dose levels (DLs): 0.6 mg/kg, 1.2 mg/kg (n=3, each), 2.4 mg/kg (n=7), 2.6 mg/kg (n=4), 2.8 mg/kg (n=12), 3.0 mg/kg (n=4), and 3.2 mg/kg (n=7, including 3 pts with primary G-CSF prophylaxis). Most pts were heavily pretreated (80% had ≥3 lines of prior treatment; 100% received irinotecan). Overall, 6 pts experienced dose-limiting toxicities (DLTs); the majority were hematological adverse events at DLs 3.0 and 3.2 mg/kg; 1 patient (at 2.8 mg/kg) experienced a Grade 5 sepsis. The most frequently reported Grade ≥3 treatment-emergent adverse events (TEAEs) were neutropenia in 16 (40.0%) pts, thrombocytopenia and anemia in 11 (27.5%) pts each, and WBC decreased in 10 (25.0%) pts. No events of ocular toxicity/interstitial lung disease (ILD) were reported. The best objective response per RECIST v1.1 was partial response (PR) in 4 (10.0%) pts (3 confirmed) (all at DLs ≥2.4 mg/kg); stable disease (SD) in 17 (42.5%), including 6 (15.0%) lasting for ≥100 days and progressive disease (PD) in 6 (15.0%) pts. For a total of 13 (32.5%) pts, the best overall response was not evaluable, including 6 (15.0%) who had no on-treatment tumor assessment yet. The preliminary median progression-free survival (PFS) was 6.7 months (95% CI: 4.6, 8.4). As of data cutoff, 15 (37.5%) pts are continuing treatment. Based on the safety, tolerability, preliminary clinical activity, PK, and PK/pharmacodynamics modeling data, 2.8 mg/kg was declared as the MTD, and 2.4 mg/kg and 2.8 mg/kg were chosen as the RDEs and have been taken forward into a randomized expansion study. Conclusions: M9140 demonstrated encouraging activity in heavily pretreated pts with advanced CRC, with a manageable and predictable safety profile. Contrary to approved ADCs with Top1i payloads, no ILD or ocular toxicities were observed. Evaluation of M9140 in mCRC continues in the dose expansion part of this study. Clinical trial information: NCT05464030 .