Pheast Therapeutics Advances PHST001, an IgG4 Anti-CD24 Monoclonal Antibody, into Phase 1b Combination Cohorts
First patient dosed in Phase 1b portion of ongoing Phase 1 study evaluating PHST001 in combination with chemotherapy
Company to present three abstracts at AACR 2026, including preliminary clinical data and two preclinical studies evaluating combination strategies and activity in metastatic models of PHST001
REDWOOD CITY, Calif., March 31, 2026 (GLOBE NEWSWIRE) -- Pheast Therapeutics, a clinical-stage biotechnology company advancing macrophage-directed immunotherapies for cancer, today announced that the first patient has been dosed in the Phase 1b portion of its ongoing Phase 1 study of PHST001, an IgG4 anti-CD24 macrophage checkpoint inhibitor.
“The initiation of the Phase 1b combination cohorts marks an important step forward for PHST001 and reflects the progress of our Phase 1 program,” said Roy Maute, Ph.D., Co-founder and Chief Executive Officer of Pheast Therapeutics. “The safety and biological signals we have seen to-date support advancing PHST001 into combination cohorts with established therapies. Together with the preliminary data we will be presenting at AACR, we are building a strong foundation as we work toward our goal of bringing new options to patients facing cancers with significant unmet need.”
The Phase 1b portion of the study is designed to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary anti-tumor activity of PHST001 in combination with established chemotherapy regimens using a suitable dose identified by the Phase 1a portion. To date, the observed safety profile supports continued monotherapy escalation and advancement into combination regimens. Preliminary clinical and translational findings from the Phase 1a portion of the study, along with supporting preclinical data, will be presented at the American Association for Cancer Research® (AACR) Annual Meeting 2026, taking place April 17–22 in San Diego (see company announcement dated March 17, 2026).
Initial expansion cohorts are actively enrolling patients with advanced ovarian cancer, endometrial cancer, and cholangiocarcinoma. Additional tumor types and combination strategies may be explored as the study progresses.
“Advancing into combination therapy allows us to explore how macrophage activation may enhance the activity of existing treatment approaches,” said Raphaël Rousseau, M.D., Ph.D., Chief Medical Officer of Pheast Therapeutics. “With a dose established for combination evaluation, Phase 1b enables us to further define the potential role of PHST001 across multiple tumor settings.”
PHST001 is designed to block CD24, a macrophage checkpoint that enables tumor cells to evade innate immune clearance through engagement of Siglec-10. By targeting this pathway, PHST001 is intended to promote macrophage-mediated phagocytosis of cancer cells and support anti-tumor immune responses.
About CD24
CD24 is a cell surface protein that plays a key role in tumor immune evasion by engaging Siglec-10, an inhibitory receptor on macrophages. This interaction suppresses macrophage-mediated clearance of cancer cells, allowing tumors to escape destruction by the innate immune system. CD24 was identified as a novel macrophage checkpoint through foundational work by Dr. Amira Barkal, principal founder of Pheast. Along with other co-founders, Drs. Irving Weissman, Ravi Majeti, and Roy Maute, Pheast’s research opened the door to therapeutic strategies targeting CD24 to drive innate immune responses against cancer.
About PHST001
PHST001 is an anti-CD24 macrophage checkpoint inhibitor designed to overcome immune suppression in the tumor microenvironment. CD24 is highly expressed by many human cancers, and high expression of CD24 is a negative prognostic factor in multiple cancer indications. Pheast has engineered PHST001 to be a potential best-in-class antibody designed to induce macrophages to phagocytose cancer cells and initiate a powerful immune response. PHST001-101 is an open-label, multicenter Phase 1 study in patients with advanced solid tumors (ClinicalTrials.gov Identifier: NCT06840886). Primary objectives include safety, tolerability, and dose optimization, with secondary objectives evaluating pharmacokinetics and preliminary anti-tumor activity. PHST001 received FDA Fast Track Designation for the treatment of ovarian cancer in June 2025.
About Pheast Therapeutics
Pheast is a clinical-stage immuno-oncology company focused on activating the innate immune system in the fight against cancer. Founded as a spinout from Stanford University and led by scientific experts in innate immunity and cancer immunotherapy, Pheast is developing novel therapies for some of the most difficult-to-treat and aggressive cancers. Pheast is backed by leading life sciences investors, Catalio Capital Management and ARCH Venture Partners. For more info, visit Pheast.com and connect on LinkedIn.
Contact: media@pheast.com
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