Harpoon Therapeutics Presents Preclinical Data for TriTAC-XR Platform that Supports Potential for Improved Safety by Minimizing Cytokine Release Syndrome

TriTAC-XR demonstrates extended release mechanism that confirms accumulation of active drug which improves therapeutic index

SOUTH SAN FRANCISCO, Calif., April 12, 2022 (GLOBE NEWSWIRE) — Harpoon Therapeutics, Inc. (NASDAQ: HARP), a clinical-stage immunotherapy company developing novel T cell engagers, today presented a poster with preclinical data for its TriTAC-XR T cell engager platform at the American Association for Cancer Research (AACR) Annual Meeting being held in New Orleans from April 8-13, 2022.

The poster titled “TriTAC-XR is an extended-release T cell engager platform that improves safety by minimizing cytokine release syndrome” showed preclinical data describing the capabilities of the novel platform in animal models. Harpoon is committed to developing best-in-class T cell engagers. TriTAC-XR, our third such platform, is designed to minimize on-target cytokine release syndrome (CRS), a characteristic of many T cell engagers that can lead to dose limiting toxicities and can reduce the efficacy of these potent anti-tumor drugs.

“We are pleased with these recent animal data showing that our TriTAC-XR T cell engager platform mitigates CRS while maintaining activity. This may enable use of T cell engagers to direct immune cells to targets outside oncology, to treat autoimmune and other non-oncology diseases,” said Holger Wesche, Ph.D., Chief Scientific Officer of Harpoon Therapeutics. “The results showing the gradual accumulation of active drug with a reduced Cmax/Cmin profile may represent a new approach to managing CRS.”

Preclinical data from the TriTAC-XR platform demonstrated:

• TriTAC-XR is an extended-release T cell engager platform designed to mitigate cytokine release syndrome by releasing active T cell engagers from an inactive prodrug in a temporally controlled fashion, thus avoiding the very high exposures (Cmax) that occur shortly after administration with constitutively active molecules.
• Single doses of FLT3 and CD19 as well as weekly doses of CD20 TriTAC-XR produced similar PD effects with significantly lower cytokines than a comparable TriTAC in animal models.
• The expected safety improvement of TriTAC-XR could enable the treatment of non-oncology diseases in addition to solid tumors and hematologic malignancies.

Harpoon’s first platform, the constitutively active TriTAC, is designed to minimize off-target toxicities, and is ideal for targets with limited on-target liabilities. The ProTriTAC platform offers similar advantages and adds an element of spatial control, with activation directed primarily to the tumor microenvironment. This spatial control of activation may address on-target tissue damage, hence enabling an expansion of the T cell engager target space. The TriTAC-XR adds improved temporal control and is designed to be activated in the systemic circulation at a predefined rate to minimize on-target CRS.

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. HPN217 targets BCMA and is in a Phase 1/2 trial for relapsed, refractory multiple myeloma. HPN328 targets DLL3 and is in a Phase 1/2 trial for small cell lung cancer and other DLL3-associated tumors. HPN536 targets mesothelin and is in a Phase 1/2a trial for cancers expressing mesothelin, initially focused on ovarian and pancreatic cancers. 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. The company’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.

Cautionary Note on 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 “could,” “expect,” “may,” “target,” 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 development and advancement of Harpoon Therapeutics’ platforms and product candidates, including progress, timing, scope, design and interim results of clinical trials, ability of TriTAC-XR T cell engager platform to mitigate toxicities, such as cytokine release syndrome, and ability of TriTAC-XR T cell engagers to direct immune cells to targets outside oncology, to treat autoimmune and other non-oncology diseases, the candidate’s safety and tolerability profile, 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, unanticipated or greater than anticipated impacts or delays due to COVID-19, 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’ annual report on Form 10-K for the year ended December 31, 2021 and other 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.

Contacts:

Harpoon Therapeutics, Inc.
Georgia Erbez
Chief Financial Officer
650-443-7400
media@harpoontx.com

ICR Westwicke
Robert H. Uhl
Managing Director
858-356-5932
robert.uhl@westwicke.com