On June 4, 2021 Harpoon Therapeutics, Inc. (NASDAQ: HARP), a clinical-stage immunotherapy company developing a novel class of T cell engagers, reported a pipeline update on its four clinical stage programs, including updating the interim data presented earlier at ASCO (Free ASCO Whitepaper) from the ongoing dose escalation portion of the Phase 1/2a trial for HPN424 in patients with metastatic castration resistant prostate cancer (mCRPC) (Press release, Harpoon Therapeutics, JUN 4, 2021, View Source [SID1234583615]). Harpoon has four product candidates in clinical trials that are based on its proprietary Tri-specific T cell Activating Construct (TriTAC) platform designed to recruit a patient’s own immune cells to kill tumor cells.
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"We are excited by the clinical data emerging from our four TriTAC programs that are showing tumor size reductions or stable disease, meaningful treatment duration, clinical activity, target engagement, extended half-life, and manageable safety and tolerability profiles in the heavily pretreated patient populations," stated Jerry McMahon, Ph.D., President and CEO, Harpoon Therapeutics. "As we continue to advance to higher doses in each of these programs, we look forward to the initiation of expansion cohorts this year."
"The clinical signals observed in the HPN424 trial and the unconfirmed partial response in the recently initiated HPN328 trial are very encouraging," said Natalie Sacks, M.D., Chief Medical Officer of Harpoon. "Looking across the portfolio, we are encouraged by how our novel technology is performing across multiple tumor types. We are seeing initial signs of clinical activity while effectively managing cytokine-mediated adverse events."
Dose escalation and step dosing for HPN424 Phase 1/2a clinical trial continuing.
As of May 31, 2021, the data cutoff date for the Company’s HPN424 presentation, the Company updated the ASCO (Free ASCO Whitepaper) interim data to describe newly enrolled patients and additional follow-up on existing patients already enrolled in the 300 ng/kg step dose cohort. The company has examined several step dosing regimens in this cohort and had the following observations:
Eight patients most recently enrolled in this cohort were treated with the same modified step dose regimen. Preliminary data from these patients include 3/8 (38%) with PSA declines that occur early in the course of treatment.
For the total 19 patients enrolled in this cohort, 4/19 showed PSA declines, including two patients with PSA30.
The ASCO (Free ASCO Whitepaper) poster presentation, included the following observations:
Antitumor activity includes a confirmed PR per RECIST, PSA declines and CTC reductions.
Fifteen of 74 (20%) pts with >1 post-baseline value had PSA decreases from baseline ranging from -2% to -76%, including 4 pts with PSA50 response and 2 pts with PSA30 response
Treatment duration > 24 weeks observed in 15 of 74 (20%) pts, including 8 of 17 (47%) chemo-naïve patients
Reduction in CTCs was seen in 36 of 64 (56%) patients with available baseline and on-treatment CTC counts
CRS has been transient and manageable with 4% of patients experiencing Grade 3 CRS
CRS and transaminitis events observed most often in Cycle 1, with diminished frequency and severity in subsequent cycles
Introduction of step dose regimens has allowed for the administration of higher target doses, currently at 300ng/kg
HPN536 (mesothelin TriTAC) Phase 1/2a clinical trial continues dose escalation. Dosing has occurred across 10 fixed-dose cohorts of 6 to 560ng/kg and three step dose cohort up to 1200ng/kg, with total enrollment of 60 patients. Tumor types treated include late-stage ovarian (47%), pancreatic (40%) and peritoneal and pleural mesothelioma (13%) cancers. Pharmacokinetic analysis shows median half-life of more than 70 hours for HPN536. Among the relapsed/refractory ovarian cancer patients with at least one post-baseline scan, 11 of 20 (55%) patients showed stability of target lesions, including three patients with target lesion shrinkage. In addition, five of 27 (19%) ovarian cancer patients had a duration of treatment of greater than 24 weeks. As of May 31, 2021, MTD has not been reached. The Company expects to present interim data at a medical conference in 2021.
Dose escalation for HPN217 (BCMA TriTAC) Phase 1/2 clinical trial making good progress. Relapsed/refractory multiple myeloma patients (N=20) have been treated across eight fixed dose cohorts of 5 to 2150 µg weekly, reflecting rapid dose expansion since the trial began. HPN217 has been well tolerated, and no DLTs have been observed as of the May 10, 2021 cutoff date. Pharmacokinetic analysis shows half-life extension to support at least once weekly dosing. A presentation of interim data is anticipated as well as initiation of a dose expansion cohort in the second half of 2021.
Dose escalation for HPN328 (DLL3 TriTAC) Phase 1/2 clinical trial initiated in late 2020 and has shown rapid progress. The first single patient cohort began with a flat dose of 15µg of HPN328 administered once weekly by intravenous infusion and has proceeded to the fourth cohort at a dose of 405µg. Eligible patients include small cell lung cancer patients who have relapsed after platinum chemotherapy and patients with other tumors associated with DLL3 expression. An unconfirmed partial response has been observed for one patient with small cell lung cancer from the 45µg dose cohort. Presentation of initial interim data is planned for the second half of 2021.
IND-enabling studies for HPN601 (EpCAM ProTriTAC) are progressing as planned. HPN601 is a conditionally active T cell engager based on the ProTriTAC platform. EpCAM is expressed in a broad range of solid tumors, including gastrointestinal cancers, potentially enabling HPN601 to address multiple indications with high unmet medical need.
Conference Call and Webcast Today
Harpoon’s management will host a webcast and conference call at 4 p.m. ET / 1 p.m. PT on Friday, June 4, 2021 to review the data presented at ASCO (Free ASCO Whitepaper) and provide an update on its other pipeline programs. The live call may be accessed by dialing 866-951-6894 for domestic callers or 409-216-0624 for international callers and using conference ID # 2657278.
A live webcast of the call will be available from the Events and Presentations section of the company’s website at View Source and will be archived there shortly after the live event.