Shares of Harpoon Therapeutics saw a significant increase of 39% to $9.57 in premarket trading following positive results from its Phase 1/2 clinical trial evaluating HPN328. The trial focused on small cell lung cancer and other neuroendocrine tumor types.

HPN328, which targets delta-like ligand 3, is derived from Harpoon's proprietary Tri-specific T cell Activating Construct platform. The platform aims to mobilize a patient's own immune cells to effectively kill tumor cells.

During the trial, HPN328 was well tolerated across all dose cohorts, with no dose limiting toxicities observed at the targeted doses. Out of the 67 patients, treatment-related adverse events occurred but were manageable. Importantly, the maximum tolerated dose has not been reached as of the data cut off on Sept. 12.

Preliminary response data for patients treated with a 1 mg priming dose showcased a promising confirmed response rate of 35% across all tumor types. The duration of response data in the 1 mg priming dose cohorts is still maturing, indicating further positive developments.

Harpoon's plans involve identifying the recommended Phase 2 regimen for monotherapy by the end of this year. Furthermore, they aim to commence registrational studies in multiple tumor types starting in 2024.

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