Harpoon Therapeutics Stock Drops After Prostate Cancer Candidate Shows Cytokine-Related Adverse Events

Harpoon Therapeutics Inc (NASDAQ:HARP) has announced interim data from the ongoing dose-escalation portion of a Phase 1/2a trial evaluating HPN424 in patients with metastatic castration-resistant prostate cancer (mCRPC).
Data were presented at the 2021 American Society of Clinical Oncology (ASCO) Annual Meeting.
HPN424 targets prostate-specific membrane antigen (PSMA) and is based on Harpoon's proprietary Tri-specific T cell Activating Construct (TriTAC) platform designed to recruit a patient's immune cells to kill tumor cells.
As of April 23, the data cutoff date, 89 patients have been dosed across 13 cohorts at fixed doses of 1.3 to 160 ng/kg and in step dosing cohorts up to 300ng/kg administered as a weekly intravenous infusion.
Antitumor activity included one confirmed partial response, PSA declines, and circulating tumor cell (CTC) reductions.
Treatment duration of over 24 weeks was observed in 15 of 74 (20%) of patients, including 8 of 17 (47%) chemo-naïve patients.
CRS and transaminitis events were observed most often in Cycle 1, with diminished frequency and severity in subsequent cycles.
Dose Limiting Toxicities (DLTs) were observed at doses ranging from 96 to 300ng/kg and did not limit escalation, and Maximum Tolerated Dose was not reached.
2/89 patients discontinued treatment due to treatment-related AEs.
Harpoon's management will host a webcast and conference call today at 4 p.m. ET.
Price Action: HARP shares are down 24.3% at $15.86 during the market session on the last check Friday.

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