First-in-human dose-escalation study of anti-EGFR ADC MRG003 in patients with relapsed/refractory solid tumors.

3550 Background: MRG003 is a novel antibody drug conjugate (ADC) composed of a fully human anti-EGFR IgG1 monoclonal antibody conjugated to a microtubule disrupting agent monomethyl auristatin E (MMAE). MRG003 is presently being tested in an ongoing phase I study for safety, pharmacokinetics, and preliminary antitumor activity in patients (pts) with solid tumors (CTR20180310). Methods: In the phase I dose escalation study of a traditional (3+3) design, pts with relapsed or refractory cancers received single agent MRG003 once every 3 weeks (Q3W) for a maximum of 8 treatment cycles. The starting dose of MRG003 is 0.1 mg/kg, followed by 0.3, 0.6, 1.0, 1.5, 2.0, 2.5, and 3.0 mg/kg. Observations included adverse events (AEs), dose-limiting toxicity (DLT), and antitumor activity which is assessed every two cycles. Results: A total of twenty-two pts with colorectal (CRC, n = 15), nasopharyngeal (NPC, n = 3), head and neck (H&N, n = 2), esophageal (EC, n = 1), and duodenal (DC, n = 1) cancer were enrolled in the dose escalation. The median age of pts was 56.5 years. The MTD identified was 2.5 mg/kg. Commonly observed adverse events were anemia (50%), AST increase (41%), decreased appetite (41%), rash (36%), pruritus (36%), asthenia (36%), and proteinuria (32%). Majority of AEs were mild to moderate in severity. EGFR expression in patients’ tumor samples was determined retrospectively by a validated IHC method in a central laboratory. Nine out of 22 pts tested were EGFR positive. Among these 9 EGFR positive pts, one with NPC in the 2.5 mg/kg cohort had partial response, four had stable disease (one with H&N in the 1.5 mg/kg, one each with NPC and H&N in the 2.0 mg/kg, and one with EC in the 2.5 mg/kg cohorts). The disease control rate (DCR) at doses ≥1.5 mg/kg was 100% for the EGFR positive pts. Conclusions: The dose escalation study of MRG003 showed manageable safety profiles and encouraging preliminary antitumor activity in pts with EGFR-positive solid tumors. MRG003 is currently being evaluated as a single agent in phase I dose expansion cohorts to further assess safety, PK, and antitumor activity. Clinical trial information: CTR20180310 .