Harpoon Therapeutics Granted Orphan Drug Designation for Small Cell Lung Cancer Treatment

Harpoon Therapeutics, Inc. recently announced the US FDA has granted Orphan Drug Designation for HPN328, a delta like ligand 3- (DLL3) targeting TriTAC, for the treatment of small cell lung cancer (SCLC). A Phase 1/2 clinical trial is currently ongoing for HPN328 in the SCLC patient population.

“Orphan Drug Designation for HPN328 is a significant milestone that underscores the need for additional treatments for patients suffering from small cell lung cancer and HPN328’s potential to contribute to this unmet medical need,” stated Julie Eastland, President and CEO, Harpoon Therapeutics. “We are pleased with the clinical progress of HPN328 and remain focused on dose escalation with the goal to determine the recommended Phase 2 dose by the end of this year.”

The FDA’s Orphan Drug Designation program provides orphan status to drugs defined as those intended for the safe and effective treatment, diagnosis or prevention of rare diseases that affect fewer than 200,000 people in the United States. Orphan Drug Designation qualifies the sponsor of the drug for certain development incentives, including tax credits for qualified clinical testing, prescription drug user fee exemptions and potential eligibility for seven-year marketing exclusivity upon FDA approval.

HPN328 is a TriTAC that binds to human and non-human primate DLL3, CD3ε, and albumin with similar affinities. The Phase 1/2 trial is an open-label study of HPN328 as monotherapy to assess the safety, tolerability and pharmacokinetics in patients with advanced cancers associated with expression of DLL3. The first part of the trial is designed to determine a dose for additional clinical investigations.

As of the December 13, 2021 clinical update provided by Harpoon, 15 patients had been enrolled in dose cohorts ranging from 15 µg to 7200 µg per week using both fixed and step dose administration once weekly by intravenous infusion. Enrolled patients had a median of 2 lines (range 1 to 5) of prior therapy and included small cell lung cancer patients who had relapsed after platinum chemotherapy and patients with other malignancies with high grade neuroendocrine tumors associated with DLL3 expression. HPN328 has been well tolerated with Grade 1-2 cytokine release syndrome (CRS) reported in 33% of patients, no DLTs observed and MTD had not been reached. Among four patients with small cell lung cancer receiving the two highest doses tested to date, 1215 µg fixed dose and 3600-7200 µg step dose, three had target lesion reduction, including 1 confirmed RECIST partial response. The patient with a cPR experienced a target lesion reduction of 53% at week 10.

Following dose escalation, Harpoon may further evaluate the safety and efficacy of HPN328 in additional parallel cohorts. The primary outcome measure will be to determine efficacy for the Phase 2 dose based on the overall response rate as determined by RECIST. For additional information about the trial, please visit clinicaltrials.gov using the identifier NCT04471727.

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. HPN424 targets PSMA and is in a Phase 1/2a trial for metastatic castration-resistant prostate cancer. 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 more information, visit www.harpoontx.com.