Merus N.V. Announces Publication of an Abstract on Petosemtamab Monotherapy in Previously Treated Head and Neck Squamous Cell Carcinoma for Plenary Session Oral Presentation at the AACR

Merus N.V. (Nasdaq: MRUS) (Merus, the Company, we, or our), a clinical-stage oncology company developing innovative, full-length multispecific antibodies (Biclonics^® and Triclonics^®), today announced the publication of an abstract for a plenary session oral presentation of interim clinical data on the bispecific antibody petosemtamab in previously treated head and neck squamous cell carcinoma (HNSCC) at the American Association for Cancer Research (AACR) Annual Meeting 2023 taking place in Orlando, Florida April 14-19, 2023.

Petosemtamab, or MCLA-158, is a human IgG1 Biclonics^® designed to bind to cancer cells expressing epidermal growth factor receptor (EGFR) and leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5).

”We are excited by these data demonstrating clinically meaningful efficacy and durability of petosemtamab in previously treated head and neck cancer. We are looking forward to sharing additional details at the AACR clinical trials plenary session and on our upcoming investor call,” said Dr. Andrew Joe, Chief Medical Officer at Merus.

Petosemtamab (MCLA-158: EGFR x LGR5 Biclonics^®): Solid Tumors
Enrollment continues in dose expansion in the phase 1/2 trial, including in combination with Keytruda (pembrolizumab)

Petosemtamab is in clinical development in the expansion part of a phase 1/2 open-label, multicenter trial in advanced solid tumors, including previously treated head and neck squamous cell carcinoma (HNSCC). The Company also initiated a cohort investigating petosemtamab in combination with Keytruda in patients with untreated HNSCC, designed to evaluate safety and clinical activity in this population.

Plenary Session Oral Presentation: Clinical activity of MCLA-158 (petosemtamab), an IgG1 bispecific antibody targeting EGFR and LGR5, in advanced head and neck squamous cell cancer (HNSCC)

The oral presentation will include updated interim data from the ongoing phase 1/2 clinical trial and will be presented by the Principal Investigator, Dr. Ezra EW Cohen, Moores Cancer Center, UC San Diego Health.

The abstract provides information and observations from the ongoing phase 1/2 trial, including:

• As of a November 28, 2022 data cutoff date, 49 previously treated HNSCC patients (pts) were treated with petosemtamab 1500 mg IV every two weeks
• Patient Population:
  • Median age was 63 (range of 31-77); 78% were male
  • Median prior lines of systemic therapy was 2 (range 1-4); including anti-PD-1/PD-L1 in 96% of pts, platinum-based chemotherapy in 92% of pts; 2 pts received prior cetuximab
  • Most frequent primary tumor locations were oropharynx (35%), oral cavity (31%), and larynx (16%)
• 42 pts were evaluable for efficacy, receiving ≥2 treatment cycles (≥8 weeks) with ≥1 post-baseline tumor assessment or experiencing early progressive disease:
  • Antitumor activity among the 42 pts:
    • Overall responses rate (ORR) was 35.7% (15/42), by RECIST 1.1 per investigator assessment including 1 complete response (ongoing after 18 months), 12 partial responses (PRs), and 2 unconfirmed PRs with treatment ongoing at the data cutoff
    • Median duration of response (DOR) was 6.0 months (95%CI=3.3-not calculable) and median progression-free survival was 5.0 months (95%CI=3.2-6.8) with 17 pts continuing on therapy at the data cutoff
• Petosemtamab continued to demonstrate a manageable safety profile:
  • Of 78 pts treated at the recommended phase 2 dose of 1500 mg every two weeks (escalation and all expansion cohorts), the most frequent AEs regardless of causality (all grades/G3-4) were rash (33%/0%), hypotension (26%/6%), dyspnea (26%/4%), nausea (26%/1%), dermatitis acneiform (24%/1%), blood magnesium decreased (19%/5%), erythema (19%/0%), diarrhea (19%/0%); IRRs (composite term) were reported in 74%/21% of pts, mostly at the first infusion, and all resolved. 5 pts (6%) discontinued treatment due to IRRs on Day 1.

Presentation Details:
Title: Clinical activity of MCLA-158 (petosemtamab), an IgG1 bispecific antibody targeting EGFR and LGR5, in advanced head and neck squamous cell cancer (HNSCC)
Session Category: Clinical Trials Plenary Session
Session: Promising Novel Antitumor Strategies in Early Phase Clinical Trials
Date: Monday, April 17, 2023
Time: 10:15 a.m. – 12:15 p.m. ET
Presentation #: CT012

Regulatory Update

Merus met with the U.S. Food and Drug Administration (FDA) in an end-of-phase meeting to discuss interim results from the previously treated HNSCC cohort of the petosemtamab phase 1/2 trial. The FDA recognized recurrent or metastatic HNSCC represents an area of unmet medical need, and provided clear recommendations for the path to potential registration.

Based on the strong clinical data and discussions with the FDA, Merus believes a randomized clinical trial in previously treated (2L/3L) or untreated (front-line) HNSCC may support a possible registration. Additionally, Merus believes a randomized registration trial in HNSCC with an overall response rate endpoint could potentially support accelerated approval and the overall survival results from the same study could potentially verify its clinical benefit to support regular approval. The Company plans to continue to acquire data to confirm a suitable dose for future randomized clinical trials.

“Based on our end-of-phase meeting with the FDA, we believe we have optionality in our development path for petosemtamab in head and neck squamous cell carcinoma and are excited to continue investigation of this important new potential therapy for patients,” said Bill Lundberg, M.D., President, Chief Executive Officer at Merus. “I’m proud of the progress we are making towards our ambition to become a fully integrated US product company.”

The abstract can be found on the conference website.

Company Conference Call and Webcast Information
Merus will hold a conference call and webcast for investors on April 17, 2023 at 6:30 p.m. ET. A replay will be available after the completion of the call in the Investors and Media section of our website for a limited time.

Date & Time: April 17, 2023 at 6:30 p.m. ET
Webcast link: Available on our website
Dial-in: Toll Free: 1 (800) 715-9871 / International: 1 (646) 307-19631
Conference ID: 4032258

About Petosemtamab
Petosemtamab, or MCLA-158, is a bispecific Biclonics^® low-fucose human full-length IgG1 antibody targeting the epidermal growth factor receptor (EGFR) and the leucine-rich repeat containing G-protein-coupled receptor 5 (LGR5). Petosemtamab is designed to exhibit three independent mechanisms of action including inhibition of EGFR-dependent signaling, LGR5 binding leading to EGFR internalization and degradation in cancer cells, and enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) activity.