Abstract P185: Preliminary antitumor activity of MCLA-158, an IgG1 bispecific antibody targeting EGFR and LGR5, in advanced head and neck squamous cell carcinoma

Abstract In the expansion part of an ongoing phase 1 study, MCLA-158 is being investigated at the recommended phase 2 dose (RP2D) in patients (pts) with advanced solid tumors, including head and neck squamous cell carcinoma (HNSCC). Epidermal growth factor receptor (EGFR) and WNT signaling are known oncogenic and mitogenic drivers in several cancers, including HNSCC. MCLA-158 is a human common light chain IgG1 bispecific antibody with enhanced antibody-dependent cellular cytotoxicity (ADCC) activity. It targets EGFR and the leucine-rich, repeat-containing, G-protein coupled receptor 5 (LGR5), a transmembrane receptor associated with tumor initiating cells, particularly cancer stem cells. Potent antitumor activity was seen with MCLA-158 in pt-derived HNSCC xenograft models. The RP2D of MCLA-158 was determined to be 1500 mg every 2 weeks (q2w), with 4-week cycles, during the dose escalation part of the study, based on safety, PK and receptor occupancy prediction. A maximum tolerated dose was not reached. The primary objective of the expansion part is to characterize the safety and tolerability of single-agent MCLA-158 and confirm the RP2D. Secondary objectives include assessment of antitumor activity (investigator-assessed overall response rate [ORR] per RECIST 1.1 and duration of response). Key eligibility criteria include prior exposure to standard therapy, ECOG performance status (PS) 0-1, measurable disease (RECIST 1.1), and availability of a baseline tumor biopsy. At the interim data cutoff date of 15 June 2021, 7 pts with advanced recurrent/metastatic HNSCC were enrolled and treated in the expansion phase. Median age was 63 years (range 50-74), ECOG PS 0/1: 2/5. Primary tumor locations were oropharynx (2 pts), hypopharynx (1 pts), larynx (3 pts), and unknown primary (1 pt). All pts had a histology of squamous cell carcinoma. Prior treatment included platinum-based chemotherapy in all pts, and anti-PD-1/PD-L1 in 6 pts. No pts received prior cetuximab. A median of 3 treatment cycles (range 1-8) were administered to the 7 pts, 4 of whom were continuing with therapy at the cutoff. Of the 5 pts who had a postbaseline assessment, 2 had confirmed partial responses (5+ and 8 cycles initiated), and 2 pts had stable disease (reduction in the sum of target lesions of 7% and 17%; 4+ and 5 cycles initiated, respectively). Scheduled first postbaseline tumor assessments for 2 pts occurred after the data cutoff date. Among 26 pts who were treated at the RP2D in the dose escalation and expansion cohorts, the most frequent adverse events regardless of causality (all grades/grade 3) were infusion-related reactions (73%/8%), rash (39%/0%), asthenia (35%/4%), decreased appetite (27%/4%), nausea (27%/4%), and acneiform dermatitis (23%/4%). There were no treatment-related grade 4 or 5 adverse events. In conclusion, MCLA-158 shows promising signs of antitumor activity in pretreated HNSCC, and a well-tolerated and favorable safety profile. Citation Format: Antoine Hollebecque, Irene Brana, Lara Iglesias, Caroline Even, Kato Shumei, Marc Díez García, Mateo Bover, Patricia Martin-Romano, Rocio Garcia-Carbonero, Guillen Argilés, Josep Tabernero, Rajan Khanna, Viktoriya Stalbovskaya, Jeroen Lammerts van Bueren, Kees Bol, Mohamed Bekradda, Andrew Joe, Ernesto Wasserman, Ezra E.W. Cohen. Preliminary antitumor activity of MCLA-158, an IgG1 bispecific antibody targeting EGFR and LGR5, in advanced head and neck squamous cell carcinoma [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P185.