Merck to Acquire Harpoon Therapeutics, Further Diversifying Oncology Pipeline

Merck, known as MSD outside of the United States and Canada, and Harpoon Therapeutics, Inc. announced that the companies have entered into a definitive agreement under which Merck, through a subsidiary, will acquire Harpoon for $23.00 per share in cash for an approximate total equity value of $680 million.

“At Merck, we continue to enhance our oncology pipeline through strategic acquisitions that complement our current portfolio and advance breakthrough science to help address the needs of people with cancer worldwide,” said Dr. Dean Y. Li, president, Merck Research Laboratories. “This agreement reflects the creativity and commitment of scientists and clinical development teams at Harpoon. We look forward to further evaluating HPN328 in innovative combinations with other pipeline candidates.”

Harpoon has developed a portfolio of novel T-cell engagers that employ the company’s proprietary Tri-specific T cell Activating Construct (TriTAC) platform, an engineered protein technology designed to direct a patient’s own immune cells to kill tumor cells, and ProTriTAC™ platform, applying a prodrug concept to its TriTAC platform to create a therapeutic T-cell engager that is designed to remain inactive until it reaches the tumor.

“At Harpoon, we have always been committed to advancing our cancer immunotherapy candidates to improve the lives of patients. With Merck’s recognized leadership in oncology clinical development and global commercial footprint, our lead candidate, HPN328, is well positioned moving forward,” said Julie Eastland, president and chief executive officer, Harpoon Therapeutics. “The talented, passionate and dedicated Harpoon team has made great progress over the past eight years in leveraging our research platform to develop an innovative suite of candidates, and we are pleased that Merck has recognized the significant potential of our pipeline. I want to personally thank all of our key stakeholders, including our entire team at Harpoon, trial participants, physicians and our shareholders, who have supported us.”

Harpoon’s lead candidate, HPN328, is a T-cell engager targeting delta-like ligand 3 (DLL3), an inhibitory canonical Notch ligand that is expressed at high levels in small cell lung cancer (SCLC) and neuroendocrine tumors. HPN328 is currently being evaluated in a Phase 1/2 clinical trial (NCT04471727) evaluating the safety, tolerability and pharmacokinetics of HPN328 monotherapy in patients with advanced cancers associated with expression of DLL3. The study is also evaluating HPN328 in combination with atezolizumab in patients with SCLC. In October 2023, Harpoon announced the presentation of positive interim tolerability and response data for HPN328 in certain patients with SCLC and neuroendocrine tumors.

Additional pipeline candidates include HPN217 targeting B-cell maturation antigen (BCMA), currently in Phase 1 clinical development for the treatment of patients with relapsed/refractory multiple myeloma, and several preclinical stage candidates, including HPN601, a conditionally activated targeting epithelial cell adhesion molecule (EpCAM) for the treatment of certain patients with EpCAM expressing tumors.

Under the terms of the agreement, Merck, through a subsidiary, will acquire all outstanding shares of Harpoon Therapeutics, Inc. for a price per share of $23.00 in cash. The Board of Directors of Harpoon has unanimously approved the transaction. Closing of the acquisition is subject to certain conditions, including approval of the merger by Harpoon’s stockholders, the expiration of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act, and other customary conditions. The transaction is expected to close in the first half of 2024 and will be accounted for as an asset acquisition. Merck expects to record a charge (non-tax deductible) of approximately $650 million, or approximately $0.26 per share, that will be included in non-GAAP results in the quarter that the transaction closes.