Pieris Pharmaceuticals, Inc. (NASDAQ: PIRS) today announced the presentation of data from the phase 1 dose-escalation monotherapy study of PRS-343, a 4-1BB/HER2 bispecific for the treatment of HER2-positive solid tumors, in a late-breaking oral presentation at the Society for Immunotherapy of Cancer (SITC) Annual Meeting. PRS-343 demonstrated single-agent anti-tumor activity, including partial responses, in heavily pre-treated patients across multiple HER2-positive tumors. Beyond demonstrating clinical benefit, PRS-343 showed a potent increase in CD8+ T cell numbers and proliferative index in the tumor microenvironment of responders, indicative of 4-1BB agonism on T cells. PRS-343 was safe and well tolerated at all doses and schedules tested.
"The data presented today demonstrate PRS-343's potential to make a meaningful difference for patients with tumors that are difficult to treat with currently-available therapies," said Geoffrey Y. Ku, medical oncologist at Memorial Sloan Kettering and the principal investigator for the PRS-343 monotherapy trial. "Beyond today's presentation, I look forward to sharing some of these case studies at Pieris' upcoming R&D day alongside emerging data from the study of PRS-343 in combination with atezolizumab."
The ongoing phase 1 first-in-human, open-label multicenter trial has enrolled 53 patients, including 19 patients with gastric cancer, 14 patients with breast cancer, 6 patients with gynecological cancers, and 14 patients with other tumor types. Eleven dose cohorts have been evaluated at a Q3W dosing schedule, with the 11th dose level (8 mg/kg) also being evaluated at a Q2W dosing schedule. Pre- and post- treatment biopsies were obtained from many of the patients. Trial objectives include evaluation of safety and tolerability, characterizing the pharmacokinetic profile, assessing pharmacodynamic and potential immunogenicity effects, and investigating clinical response.
As of the cut-off date of October 23, 2019, 18 patients were evaluable for a response at active dose levels, which began at cohort 9 (2.5 mg/kg).
At the 8 mg/kg Q2W dose level, one patient with stage 4 gastric adenocarcinoma and one patient with stage 4 gynecological carcinoma achieved confirmed partial responses; the remaining patients experienced stable disease, for an overall disease control rate of 100% in this cohort as best response.
Across the remaining active dose levels and schedules, an additional five patients experienced stable disease.
Biomarker data from post-treatment tumor biopsies in patients receiving active dose levels and showing clinical benefit reflected a pronounced increase in CD8+ T cell numbers.
As of the cutoff date, treatment duration across active dose levels is over 30 weeks.
Treatment-related adverse events (AEs) were primarily grade 1 and 2. The most common AEs were infusion related reactions and fatigue. No patients experienced a dose-limiting toxicity and a maximum tolerated dose has not been reached.
"In addition to being the first 4-1BB bispecific to enter the clinic, PRS-343 is our lead immuno-oncology asset, and we believe this dataset serves as early clinical validation of our 4-1BB-targeting immuno-oncology approach and the Anticalin bispecific platform," said Stephen S. Yoder, President and Chief Executive Officer of Pieris. "PRS-343 shows promising signs of efficacy linked to clear biomarker evidence of 4-1BB agonism, in addition to being safe and well tolerated. We look forward to concluding this escalation trial in the near term and initiating an expansion trial informed by the emerging data. We also look forward to initiating clinical development of our 4-1BB/PD-L1 bispecific, PRS-344, with Servier in the first half of next year."