Preliminary results of phase I/II study to evaluate safety and efficacy of combination pucotenlimab with epidermal growth factor receptor-ADC (EGFR-ADC) MRG003 in patients with EGFR positive solid tumors.

6013 Background: Pucotenlimab (HX008) is a recombinant humanized PD-1 inhibitor approved for marketing in China, and MRG003 is an EGFR-ADC which has shown promising anti-tumor activity in squamous cell carcinoma of the head and neck (SCCHN) and nasopharyngeal carcinoma (NPC) in multiple clinical studies. In the preclinical studies, the combination of them has demonstrated a synergistic antitumor effect. This study was aimed to assess the safety and efficacy of the combination therapy in patients (pts) with locally advanced or metastatic solid tumors known to express EGFR. Methods: In this Phase I/II dose escalation and expansion study, eligible pts were treated with 3.0 mg/kg HX008 combined with MRG003 every 3 weeks, with an escalated dosing ranging from 1.5 mg/kg to 2.3 mg/kg. The primary endpoints were maximum tolerated dose (MTD), recommended Phase II dose (RP2D) of combination and objective response rate (ORR). Secondary endpoints included duration of response (DOR), disease control rate (DCR), and progression-free survival (PFS). Results: As of 30 January 2024 (cut-off date), 33 pts (9 NPC, 1 SCCHN and 3 other solid tumors pts in Phase I, 14 NPC and 6 SCCHN pts in Phase II) were enrolled in this study with a median age of 52 (31,65), and 25 pts (76%) were male. 11 (33%) pts were ECOG PS 0. The most commonly reported treatment-related adverse events (TRAEs) included pruritus (46%), rash (33%), AST increased (30%), anemia (30%). Grade 3-4 TRAEs occurred in 4 pts (12%), and mainly was white blood cell count decreased (9%) and hypokalemia (6%). The only DLT event occurred in the 2.3mg/kg dose group, and the RP2D of MRG003 determined was 2.0mg/kg by SMC. Out of the 27 evaluable pts, 17 pts achieved PR and 7 pts achieved SD, thus the ORR and DCR were 63.0% (95%CI: 42.4, 80.6) and 88.9% (95%CI: 70.8, 97.7), respectively. In the Phase II, among 9 evaluable EGFR-positive NPC pts progression after first-line treatment of PD-1 plus platinum-based chemotherapy, 2 CR, 5 PR and 2 SD were observed, ORR and DCR were 77.8% (95%CI:40.0, 97.2) and 100% (95%CI:66.4, 100), respectively. Five evaluable systemic treatment naïve SCCHN pts with EGFR-positive, 3 PR and 1 SD were observed, ORR and DCR were 60% (95%CI:14.7, 94.7) and 80% (95%CI:28.4, 99.5), respectively. The DOR and PFS in the study were immature. The longest patient treated has had a DOR for more than 17 months and still ongoing. Conclusions: The Phase I/II study pts treated with HX008 in combination with MRG003 demonstrated good tolerability and encouraging antitumor activity in NPC and SCCHN, especially in PD-1 treatment failed NPC pts. The Phase II study is currently ongoing. Research Sponsor: Shanghai Miracogen Inc. Clinical trial information: NCT05688605.