Pheast Therapeutics Begins Phase 1 Trial of PHST001 in Advanced Solid Tumor Patients

REDWOOD CITY, CA, USA | April 14, 2025

Pheast Therapeutics, a private biotech company dedicated to pioneering cancer treatments, has announced the initiation of its Phase 1 clinical trial for PHST001. This innovative treatment is an anti-CD24 macrophage checkpoint inhibitor designed to combat advanced solid tumors.

Roy Maute, Ph.D., co-founder and CEO of Pheast, highlighted the significance of this milestone. He emphasized the potential of PHST001 to offer new treatment possibilities, especially for cancers that have resisted other immunotherapies.

The Phase 1 trial is a multicenter, open-label study that plans to enroll up to 80 participants with advanced relapsed or refractory solid tumors. The study's primary goals focus on the safety and tolerability of PHST001, aiming to determine the recommended dose for subsequent trials. Secondary objectives include analyzing the drug’s pharmacokinetics and observing early signs of its efficacy against tumors.

Dr. Raphaël Rousseau, Chief Medical Officer at Pheast, pointed out the promising preclinical results of PHST001, which demonstrated significant activity across various tumor types and a favorable safety profile. These findings suggest that PHST001 might effectively counteract tumor immune evasion by activating macrophages differently. The initiation of this trial marks the beginning of evaluating PHST001's clinical potential to enhance outcomes for cancer patients.

Dr. Irving Weissman, scientific co-founder of Pheast, elaborated on the mechanism of action. CD24, a crucial protein exploited by tumors to evade immune responses, is targeted by PHST001. This inhibitor was developed following foundational research into the CD24 pathway, representing a step forward in harnessing the innate immune system's capabilities against cancer.

Preclinical studies, shared at the Society for Immunotherapy of Cancer (SITC) 2024, underscored PHST001's potential across multiple cancer types. Unlike other inhibitors, it is specifically designed to target all glyco-variants of CD24. By binding CD24 with high affinity, PHST001 enhances the phagocytosis of cancer cells by macrophages, significantly reducing tumor size in live models. Its pharmacokinetic profile is favorable in non-human primates, and it does not induce immune-mediated toxicity in laboratory studies.

CD24, a cell surface protein, plays a vital role in helping tumors evade immune attacks by interacting with Siglec-10, an inhibitory receptor on macrophages. This interaction hinders the macrophages' ability to clear cancer cells, enabling tumors to avoid destruction by the innate immune system. Pheast’s research, led by Dr. Amira Barkal and co-founders including Drs. Irving Weissman, Ravi Majeti, and Roy Maute, identified CD24 as a novel checkpoint, paving the way for therapies that target it to activate immune responses against cancer.

PHST001, an anti-CD24 macrophage checkpoint inhibitor, is designed to overcome the immune suppression prevalent in tumor environments. CD24 is widely expressed in various human cancers, such as ovarian and triple-negative breast cancer (TNBC), and its high expression often correlates with poor prognosis. Pheast has engineered PHST001 to be a leading antibody, encouraging macrophages to phagocytize cancer cells, thereby initiating a robust immune response.

Pheast Therapeutics is a clinical-stage company focused on leveraging the innate immune system to battle cancer. Established as a Stanford University spinout, it is led by experts in innate immunity and cancer immunotherapy. Pheast is committed to developing groundbreaking therapies for challenging and aggressive cancers, supported by major investors like Catalio Capital Management and ARCH Venture Partners.