On December 16, 2025 Ratio Therapeutics Inc. (Ratio), a pharmaceutical company employing innovative technologies to develop best-in-class radiopharmaceuticals for cancer treatment and monitoring, reported that dosing of the first cohort has been completed in the ATLAS trial, a Phase 1/2 open-label study evaluating the safety, tolerability, and efficacy of the company’s lead therapeutic radiopharmaceutical, [Ac-225]-RTX-2358, targeting fibroblast activation protein‑α (FAP) in patients with relapsed or refractory soft tissue sarcomas.
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"Advancing [Ac-225]-RTX-2358 into the clinic represents a major milestone for our company and reflects years of dedicated and innovative work by our team," said John Babich, Ph.D., President and Chief Scientific Officer of Ratio. "The preclinical and early human experience point to a strong therapeutic profile for our drug in sarcoma, with encouraging signs of activity in additional FAP-expressing cancers. Initiation of this trial marks the entry of our first therapeutic into the clinic and underscores our commitment to developing innovative radiotherapies that can bring new treatment options to cancer patients."
"This study represents an important step in exploring a novel therapeutic approach for patients with relapsed or refractory sarcoma, a population with limited treatment options," said Dr. Sandra D’Angelo, MD, a Medical Oncologist specializing in the care of patients with sarcoma at Memorial Sloan Kettering Cancer Center. "Radiopharmaceuticals are transforming cancer treatment by delivering radiation directly to tumors with far greater precision and decreased side effects. Ratio’s technology is designed to further enhance these benefits, and we look forward to exploring the potential of [Ac-225]-RTX-2358 to provide a meaningful impact for patients suffering from this challenging disease."
About the ATLAS Trial
The ATLAS trial is a Phase 1/2 open-label clinical trial (clinicaltrials.gov identifier, NCT07156565) designed to assess the safety, tolerability, dosimetry, biodistribution, pharmacokinetics, and preliminary anti-tumor activity of [Ac-225]-RTX-2358, a highly selective, FAP targeted radiotherapeutic labeled with Actinium 225, in patients with relapsed or refractory soft tissue sarcomas that express FAP.
The study consists of two phases: an ascending administered activity phase (Phase 1) and an expansion phase (Phase 2). For patients to be eligible to receive treatment, FAP expression will be assessed using a [Cu-64]-LNTH-1363S PET scan. In the Phase 1 portion, patients with FAP positive sarcomas will receive intravenous injections of [Ac-225]-RTX-2358 once every eight weeks, for up to six treatment cycles over a 12-month period. Using a standard 3+3 dose escalation design, participants will be assigned to one of three groups, each receiving an increasing dose level to determine the maximum tolerated dose and establish a recommended dose for the expansion phase. Cohort expansion will be allowed to a max of 10 patients per cohort, enabling up to 26 patients to be treated and evaluated during the Phase 1 portion of the trial. This will allow better characterization of safety and tolerability as well as the assessment of preliminary efficacy. Safety data from each group will be reviewed by an independent Safety Review Committee before dose escalation proceeds. The Phase 2 portion of the study will evaluate the efficacy and safety of [Ac-225]-RTX-2358 in up to 50 patients. [Ac-225]-RTX-2358 is being manufactured by Pharmalogic. [Cu-64]-LNTH-1363S is being provided by Lantheus and manufactured by PharmaLogic.
Dr. D’Angelo provides consulting and advisory services to Ratio Therapeutics.
(Press release, Ratio Therapeutics, DEC 16, 2025, https://ratiotx.com/2025/12/16/ratio-therapeutics-has-successfully-dosed-the-first-cohort-in-its-phase-1-2-study-evaluating-a-novel-fap-targeted-radiopharmaceutical-in-patients-with-late-stage-aggressive-sarcomas/ [SID1234661461])