Merus NV announces the publication of an abstract on petosemtamab monotherapy in previously treated squamous cell carcinoma of the head and neck for oral presentation in plenary at the AACR

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

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

“We are excited about these data demonstrating the clinically significant efficacy and durability of petosemtamab in previously treated head and neck cancer. We look forward to sharing additional details at the AACR Clinical Trials Plenary Session and on our upcoming investor call,” said Dr. Andrew Joe, Merus Chief Medical Officer.

Petosemtamab (MCLA-158: EGFR x LGR5 Biclonic^®): Solid tumors
Enrollment Continues in Dose Expansion in Phase 1/2 Trial, Including in Combination with Keytruda (pembrolizumab)

Petosemtamab is in clinical development as the expansion portion 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 an investigational cohort of 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 Principal Investigator, Ezra EW Cohen, MD, Moores Cancer Center, UC San Diego Health.

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

• As of the data cut-off date of November 28, 2022, 49 previously treated HNSCC patients (pts) were treated with petosemtamab 1500 mg IV every other week.
• Patient population:
  • The median age was 63 years (range 31 to 77); 78% were men
  • The median number of previous lines of systemic therapy was 2 (range 1-4); including anti-PD-1/PD-L1 in 96% of patients, platinum-based chemotherapy in 92% of patients; 2 pts received previous cetuximab
  • The most frequent locations of the primary tumor were oropharynx (35%), oral cavity (31%) and larynx (16%).
• Efficacy was evaluated in 42 patients who received ≥ 2 treatment cycles (≥ 8 weeks) with ≥ 1 post-baseline tumor evaluation or experienced early progressive disease:
  • Antitumor activity among the 42 pts:
    • The overall response rate (ORR) was 35.7% (15/42), based on RECIST 1.1 by investigator assessment, including 1 complete response (ongoing after 18 months), 12 partial responses (PR), and 2 PR not confirmed with ongoing treatment at the data cutoff
    • The median duration of response (DOR) was 6.0 months (95% CI = 3.3-not calculable) and the median PFS was 5.0 months (95% CI = 3.2 -6.8) with 17 pts who continued with the therapy at the data cutoff
• Petosemtamab continued to demonstrate a manageable safety profile:
  • Of 78 patients treated with the recommended phase 2 dose of 1500 mg every other week (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%), acneiform dermatitis (24%/1%), decreased blood magnesium (19 %/5%), erythema (19%/0%), diarrhea (19%/0%); IRRs (composite term) were reported in 74/21% of patients, mostly at the first infusion, and all resolved. 5 pts (6%) discontinued treatment due to IRR on day 1.

Presentation details:
Qualification: 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: Plenary Session of Clinical Trials
Session: Promising new antitumor strategies in early phase clinical trials
Date: Monday, April 17, 2023
Time: 10:15 a.m. to 12:15 p.m. Eastern Time
Presentation #: CT012

Regulatory Update

Merus met with the US Food and Drug Administration (FDA) at an end-of-phase meeting to discuss interim results from the previously treated HNSCC cohort from the phase 1/2 trial of petosemtamab. The FDA recognized that 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 that a randomized clinical trial in previously treated (2L/3L) or untreated (first-line) HNSCC may support a possible registration. In addition, Merus believes that a randomized registry 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 acquiring data to confirm an appropriate dose for future randomized clinical trials.

“Based on our end-of-phase meeting with the FDA, we believe we have options in our development pathway for petosemtamab in head and neck squamous cell carcinoma and are excited to continue the investigation of this important potential new therapy for the patients,” Bill said. Lundberg, MD, president and CEO of Merus. “I am proud of the progress we are making toward our ambition to become a fully integrated American products company.”

The abstract can be found in the conference. website.

Information from company conference calls and webcasts
Merus will host an investor conference call and webcast on April 17, 2023 at 6:30 PM ET. A replay will be available after the end of the call on the Investors and Media section of our website for a limited time.

Date and Time: April 17, 2023 at 6:30 pm ET
Webcast link: Available on our website
Tick: Toll Free: 1 (800) 715-9871 / International: 1 (646) 307-19631
Conference ID: 4032258

About petosemtamab
Petosemtamab, or MCLA-158, is a bispecific Biclonics^® Full-length low-fucose human IgG1 antibody directed at 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 EGFR-dependent signaling inhibition, LGR5 binding leading to EGFR internalization and degradation in cancer cells, and increased antibody-dependent cell-mediated cytotoxicity ( ADCC) and antibody-dependent cell phagocytosis (ADCP). ) activity.