Benzinga | Jun 4, 2021 10:44AM EDT

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-na?ve 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.