Pathios Therapeutics Announces Promising Clinical Progress for First-in-Class GPR65 Antagonist PTT-4256 at ASCO 2026

OXFORD, UK – 5 June, 2026 High-quality biomarker data confirms successful GPR65 target engagement and intratumoral immune activation Dose-proportional pharmacokinetic profile validates the viability of patient-friendly, once-daily oral dosing Early signals of clinical activity observed in hard-to-treat advanced solid tumors, including documented cases of tumor shrinkage Pathios was proud to announce the presentation of positive preliminary data from its ongoing RAISIC-1 Phase 1/2 clinical trial at the American Society of Clinical Oncology (ASCO) Annual Meeting May 29 – June 2 2026 in Chicago. Key Clinical Highlights Presented at ASCO 2026 The RAISIC-1 trial is evaluating PTT-4256, a first-in-class, orally bioavailable GPR65 antagonist, in adult patients with advanced, refractory solid tumors. The updated data underscores significant milestones across three clinical pillars: High-quality translational biomarker data has confirmed that PTT-4256 is executing its exact design. The compound successfully engages the GPR65 target in patients, effectively shutting down acid-sensing pathways and triggering robust immune system activation directly within the tumor site. Proof of Mechanism: The trial continues to demonstrate that PTT-4256 is generally well-tolerated with an excellent clinical safety margin. Furthermore, a highly predictable, dose-proportional pharmacokinetic (PK) profile has confirmed the viability of a once-daily oral dosing regimen—offering a significant advantage for patient compliance and quality of life. Optimised Safety & Dosing: Even within heavily pre-treated patient cohorts presenting with advanced solid malignancies, Pathios is observing promising early signals of efficacy. The updated findings feature documented cases of objective tumor shrinkage alongside sustained stable disease. Clinical Activity in Hard-to-Treat Cancers: Why This Matters: A New Frontier in Immuno-Oncology Local extracellular acidity is a notorious driver of immunosuppression and a fundamental hallmark of advanced solid tumors. Within this low-pH environment, the proton-sensing receptor GPR65 is activated on key immune cells, polarising them into a deeply protective shield that renders the malignancy resistant to traditional immunotherapies. By successfully targeting and inhibiting this mechanism, Pathios is opening a new frontier in cancer treatment. Reconditioning this hostile microenvironment allows the host’s immune system to recognise and attack the cancer, offering a novel therapeutic pathway for solid tumors that have historically been resistant to standard care. The scientific poster presented at the conference is available on the Pathios website . here Back

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