Harpoon Therapeutics Announces Updated Interim Tolerability and Response Data from Phase 1/2 Clinical Trial of T Cell Engager HPN328 at ESMO Congress 2023

• Confirmed response rate 35% (11/31), across all tumor types and patient cohorts treated with 1 mg priming dose, including three confirmed, complete responses
  • 32% (6/19) confirmed response rate in patients with small cell lung cancer (SCLC), including one confirmed complete response
  • 42% (5/12) confirmed response rate in other neuroendocrine tumor types, including two confirmed complete responses
• Generally well tolerated; cytokine release syndrome (CRS) most common, predominantly low-grade, with no Gr3 CRS in 1 mg priming dose cohorts
• Enrollment in monotherapy dose cohorts nearing completion, on track to select Phase 2 dose(s) by end of 2023
• Results will be presented in a poster session at ESMO Congress 2023 on Monday, October 23, 2023 and management will hold a webcast at 8:00 a.m. ET / 2:00 p.m. CEST to review the data, following the poster presentation

SOUTH SAN FRANCISCO, Calif., Oct. 21, 2023 (GLOBE NEWSWIRE) -- Harpoon Therapeutics, Inc. (NASDAQ:HARP), a clinical-stage immunotherapy company developing novel T cell engagers, today announced the updated interim monotherapy data from its Phase 1/2 clinical trial evaluating HPN328 in small cell lung cancer (SCLC) and other neuroendocrine tumor types in a poster at the European Society of Medical Oncology Congress (ESMO) 2023. HPN328 targets delta-like ligand 3 (DLL3) and is derived from Harpoon's proprietary Tri-specific T cell Activating Construct (TriTAC^®) platform designed to recruit a patient's own immune cells to kill tumor cells.

HPN328 was generally well tolerated across all dose cohorts (N=71). Treatment-related adverse events (TRAEs) occurred in 67 patients (94%), and Grade ≥ 3 TRAEs in 18 patients (25%). CRS was most common (59%) and was primarily Grade 1 or 2. No dose limiting toxicities (DLT) occurred at target doses, and the target maximum tolerated dose (MTD) has not been reached as of the data cut off on September 12, 2023.

The preliminary response data for evaluable patients treated in 1 mg priming dose cohorts showed confirmed response rate of 35% (11/31) across all tumor types. In SCLC, the confirmed response rate was 32% (6/19) with one confirmed complete response. In patients with other neuroendocrine tumor types, such as prostate cancer, small cell cervical, small cell bladder, and large cell lung cancer, 42% (5/12) confirmed response rate was observed, including two confirmed complete responses in small cell bladder and small cell cervical tumor types. The duration of response data in the 1 mg priming dose cohorts continues to mature.

"HPN328's antitumor activity and tolerability profile are promising given the aggressive nature of SCLC and other neuroendocrine tumor types included in the study. The preliminary response data from the 1 mg priming dose cohorts suggests HPN328's activity in a broad spectrum of tumor types with similar histology," said Noura Choudhury, M.D., of Memorial Sloan Kettering Cancer Center, Principal Investigator in this study. "I look forward to continuing to study this promising candidate to potentially improve outcomes for patients with very limited treatment options and aggressive cancers."

"The interim data provides a solid foundation for the next steps in our future clinical development plans for HPN328, underscoring its potential to serve patients with high unmet medical needs. It enables us to rapidly move towards identifying the recommended Phase 2 regimen(s) in the monotherapy setting by the end of this year and supports the initiation of potential registrational studies in multiple tumor types in 2024," said Luke Walker, M.D., Chief Medical Officer of Harpoon Therapeutics.

The poster (presentation #698P) is now available on the ESMO website and under the Publications section on Harpoon's website.

Webcast Registration Information

The live webcast will take place on Monday, October 23, 2023, from 8:00 a.m. to 9:00 a.m. ET / 2:00 p.m. to 3:00 p.m. CEST. To register for the event, please click here. A replay of the webcast will be available shortly after the live event and can be accessed at the same weblink.

About HPN328

HPN328 targets delta-like canonical Notch ligand 3 (DLL3) and is based on Harpoon's proprietary Tri-specific T cell Activating Construct (TriTAC^®) platform designed to recruit a patient's own immune cells to kill tumor cells. HPN328 is being evaluated as monotherapy in an ongoing open-label, multicenter two-part study to assess the safety, tolerability, and pharmacokinetics in patients with advanced cancers associated with expression of DLL3.

In March 2022, the U.S. Food and Drug Administration (FDA) granted Orphan Drug Designation to HPN328 for the treatment of SCLC.

About Harpoon Therapeutics

Harpoon Therapeutics is a clinical-stage immunotherapy company developing a novel class of T cell engagers that harness the power of the body's immune system to treat patients suffering from cancer and other diseases. T cell engagers are engineered proteins that direct a patient's own T cells to kill target cells that express specific proteins, or antigens, carried by the target cells. Using its proprietary Tri-specific T cell Activating Construct (TriTAC^®) platform, Harpoon is developing a pipeline of novel TriTACs initially focused on the treatment of solid tumors and hematologic malignancies. Harpoon has also developed a proprietary ProTriTAC™ platform, which applies a prodrug concept to its TriTAC platform to create a therapeutic T cell engager that remains inactive until it reaches the tumor. Harpoon's third proprietary technology platform, extended release TriTAC-XR, is designed to mitigate cytokine release syndrome. For additional information about Harpoon Therapeutics, please visit www.harpoontx.com.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "continue," "look forward," "move towards," "potential," "suggest," "will," and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward-looking statements. These forward-looking statements are based on Harpoon Therapeutics' expectations and assumptions as of the date of this press release. Each of these forward-looking statements involves risks and uncertainties that could cause Harpoon Therapeutics' clinical development programs, future results or performance to differ significantly from those expressed or implied by the forward-looking statements. Forward-looking statements contained in this press release include, but are not limited to, statements about the expected timing, progress, and results of Harpoon Therapeutics' clinical trials, the association of interim clinical data and preclinical results with potential treatment outcomes and other statements that are not historical fact. Many factors may cause differences between current expectations and actual results, including unexpected safety or efficacy data observed during clinical studies, preliminary data and trends may not be predictive of future data or results, may not demonstrate safety or efficacy or lead to regulatory approval by the FDA or other regulatory agencies, clinical trial site activation or enrollment rates that are lower than expected, changes in expected or existing competition, changes in the regulatory environment, the uncertainties and timing of the regulatory approval process, the timing and results of unexpected litigation or other disputes, and the sufficiency of Harpoon Therapeutics' cash resources. These and other factors that may cause Harpoon Therapeutics' actual results to differ from those expressed or implied in the forward-looking statements in this press release are discussed in Harpoon Therapeutics' filings with the U.S. Securities and Exchange Commission, including under "Risk Factors" in Harpoon Therapeutics' quarterly report on Form 10-Q for the quarter ended June 30, 2023, and future filings by Harpoon Therapeutics. Except as required by law, Harpoon Therapeutics assumes no obligation to update any forward-looking statements contained herein to reflect any change in expectations, even as new information becomes available.

Contact:

Ana Kapor

Harpoon Therapeutics

[email protected]