Press Release

Harpoon Therapeutics Launches Immuno-Oncology Pipeline with Compelling Data from Lead Programs at the 2018 American Association for Cancer Research (AACR) Annual Meeting

Preclinical Data Showcase New T Cell Engaging Platform (TriTAC™) and Lead Drugs, HPN424 and HPN536, Targeting Prostate Cancer and Other Solid Tumors

Chicago, IL – April 16, 2018 – (BUSINESS WIRE) – Harpoon Therapeutics, a biotechnology company pioneering a new class of T cell engaging therapeutics based on its proprietary TriTAC platform, presented preclinical data supporting the ongoing development of the platform and its two lead molecules, HPN424 and HPN536. These programs are the first of four programs using TriTAC technology, which has been designed for superior tumor penetration and efficacy in combating solid tumors. The company, which announced a series B financing and a partnership with AbbVie in 2017, anticipates filing investigational new drug (IND) applications and entering the clinic with these two compounds in the next 12 months. Data were presented at the 2018 American Association of Cancer Research (AACR) Annual Meeting in Chicago, held April 14-18, 2018.

“Harpoon created TriTAC as a best-in-class T cell engager platform optimized for the treatment of solid tumors,” said Jerry McMahon, PhD, President and CEO, Harpoon Therapeutics. “The platform allows us to bring the success of T cell engagers targeting hematologic malignancies, like Blincyto®, to solid tumor treatment. At Harpoon, we have optimized serum half-life, maximized tumor penetration, and engineered superior stability and manufacturability. These features have been the foundation for our discovery and development of a robust pipeline of drug candidates targeting PSMA, mesothelin, BCMA and DLL3.”

Harpoon presented preclinical data which highlighted the novel aspects of its proprietary TriTAC platform to potentially overcome the limitations of existing bispecific antibody-based and CAR-T therapies. The TriTAC platform uses a single flexible polypeptide comprised of three binding domains, and is designed to be the smallest, half-life extended T cell engaging format without the potential liabilities associated with conventional bispecific antibodies.

“We are excited to share these preclinical data for HPN424 and HPN536, which are designed to elicit targeted tumor cell destruction for both metastatic castration-resistant prostate cancer (mCRPC) and mesothelin-expressing tumors, respectively, such as lung, ovarian and pancreatic cancers,” said Holger Wesche, PhD, Senior Vice President, Research. “We believe our new data underscore the significant impact our approach could make in advancing the field of immuno-oncology, and look forward to evaluating our compounds in clinical testing.”

HPN424 Data Showed Potent T cell Killing of Prostate Cancer Cells and Serum Half-Life Extension

HPN424 is a 50-kD single polypeptide containing three binding domains — for human PSMA, human serum albumin (HSA) and human CD3. In preclinical studies, HPN424 demonstrated single-digit picomolar potency for PSMA-dependent T cell killing in a panel of human prostate cancer cell lines, which translated to in vivo efficacy with efficacious doses in the low μg/kg range. HPN424 was well tolerated in a multi-dose safety study in non-human primates and showed a serum half-life of 80 hours supporting once-weekly administration for a Phase 1 dose-escalation study in mCRPC patients planned to begin this year.

HPN536 Data Showed Potent Destruction of Mesothelin-Positive Cancer Cells and Evidence of Mechanism in a Primate Study

HPN536 is a 50-kD single polypeptide containing three binding domains — for human mesothelin (MSLN), HSA and human CD3. In preclinical studies, HPN536 demonstrated single-digit picomolar potency for MSLN-dependent T cell killing in a panel of human cancer cell lines derived from mesothelioma, pancreatic, non-small cell lung and ovarian tumors, and in vivo efficacy with efficacious doses in the low μg/kg range. An exploratory safety study in non-human primates showed that HPN536 was well tolerated and supported weekly dosing in humans. The compound was also shown to elicit T cell activation resulting in mesothelial hypertrophy and lymphocyte infiltration, which strongly supports tissue penetration, the mechanism of action of the TriTAC platform, and the planned Phase 1 study.

ABSTRACT INFORMATION

Abstract #1773
Title: “HPN424, a half-life extended, PSMA/CD3-specific TriTAC for the treatment of metastatic prostate cancer”
Date and Time: April 16, 2018, 8:00 AM - 12:00 PM CT
Session: Therapeutic Antibodies, Including Engineered Antibodies 1

Abstract #1781
Title: “HPN536, a T cell-engaging, Mesothelin/CD3-specific TriTAC for the treatment of solid tumors”
Date and Time: April 16, 2018, 8:00 AM - 12:00 PM CT
Session: Therapeutic Antibodies, Including Engineered Antibodies 1

Abstract #3814
Title: “TriTACs are novel T cell-engaging therapeutic proteins optimized for the treatment of solid tumors and for long serum half-life”
Date and Time: April 17, 2018, 8:00 AM - 12:00 PM CT
Session: Therapeutic Antibodies, Including Engineered Antibodies 3

About Harpoon Therapeutics

Harpoon Therapeutics is an immuno-oncology company founded by Patrick Baeuerle, Ph.D., a pioneer in the development of T cell engaging therapies, and MPM Capital. The company is focused on the discovery and development of novel T cell engaging biologics for the treatment of cancer. Harpoon Therapeutics created a novel T cell redirection platform called TriTAC (Tri-specific T cell Activating Construct) to unleash the targeted cell-killing properties of a patient's own immune system through T cell activation. This approach has been optimized to overcome the limitations of existing immunotherapies to penetrate tissues and extend serum exposure for superior efficacy in solid tumors. Harpoon is developing a robust pipeline of TriTAC candidates. Harpoon expects to file INDs for lead candidates HPN424, a prostate-specific membrane antigen (PSMA)-targeting TriTAC, and HPN536, a mesothelin-targeting TriTAC in 2018. For more information, please visit www.harpoontx.com.

Contact

Harpoon Therapeutics:
Susan Kinkead
Kinkead Communications, Inc.
susan@kinkeadcomm.com
415-509-3610