BERLIN, November 11, 2025 — Leads & Copy — Ariceum Therapeutics has announced that the first patient has been dosed in its Phase 1/2 SANTANA-225 study of 225Ac-SSO110 for treating extensive stage small cell lung cancer (ES-SCLC) and Merkle Cell Carcinoma (MCC).
225Ac-SSO110 is a potentially first- and best-in-class Actinium-225-labelled antagonist of the somatostatin type 2 receptor (SSTR2). SSTR2 is highly overexpressed in neuroendocrine tumors relative to healthy tissue, making it an ideal target for radioligand therapies (RLTs).
The global, open-label SANTANA-225 clinical trial (NCT06939036) will assess the safety, tolerability, preliminary efficacy, and recommended Phase 2 dose of 225Ac-SSO110 in ES-SCLC patients treated with checkpoint inhibitors (CPI) in first-line maintenance therapy or MCC patients treated with CPI in first-line therapy. The trial expects to enroll approximately 20 patients in the dose escalation phase, followed by expansion cohorts. In February 2025, the U.S. Food and Drug Administration (FDA) granted 225Ac-SSO110 Orphan Drug Designation (ODD) for ES-SCLC treatment.
Ariceum Therapeutics Chief Medical Officer Dr. Germo Gericke said that RLTs redefine precision oncology by enabling targeted radiation delivery directly to tumor cells while minimizing exposure to healthy tissue. Dr. Gericke also noted that 225Ac-SSO110 is the first SSTR2 antagonist RLT in clinical development, designed to deliver higher doses of alpha radiation directly to patients’ tumors while maintaining a favorable safety profile for individuals with neuroendocrine cancers, including ES-SCLC and MCC.
Ariceum expects to report initial safety data from the SANTANA-225 trial in 2026, which may support expansion into additional neuroendocrine tumor indications and further validate the differentiated mechanism of action of 225Ac-SSO110. Dosing the first patient in the SANTANA-225 trial is a significant step for the lead program and an important milestone towards addressing urgent patient needs in these aggressive cancers.
ES-SCLC, a deadly and aggressive cancer, presents a significant unmet medical need due to limited treatment options. Two-thirds of SCLC patients are diagnosed at an advanced stage where the disease has metastasized, resulting in a poor prognosis and a 5-10% five-year survival rate. MCC, a rare and aggressive skin cancer with limited treatment options, also has low survival rates in patients who do not respond to first-line CPI therapy. Both ES-SCLC and MCC are neuroendocrine tumors that frequently express SSTR2, making them compelling initial indications for SSTR2-targeted therapy.
225Ac-SSO110 is the first SSTR2-targeting antagonist radiolabeled with Actinium-225 to undergo human trials in combination with CPI for these neuroendocrine tumor indications, addressing areas of high unmet need and laying the foundation for potential expansion to other SSTR2-expressing cancers.
Ariceum Therapeutics is a clinical-stage oncology company dedicated to redefining the future of care through targeted radiotherapeutics for patients with aggressive and hard-to-treat cancers. The company’s lead program, 225Ac-SSO110, a novel antagonist of the somatostatin type 2 receptor (SSTR2) with best-in-class potential, is currently being investigated in the Phase 1/2 SANTANA-225 study as the first maintenance radiotherapy for extensive stage small cell lung cancer (ES-SCLC) and Merkel Cell Carcinoma (MCC).
Ariceum is also developing ATT001, a novel radiolabeled I-123 PARP inhibitor designed to deliver subcellular precision radiotherapy to aggressive solid tumors. Headquartered in Berlin, Ariceum operates across Germany, Switzerland, Australia, the United Kingdom, and the United States. The company is supported by leading global life sciences investors, including EQT Life Sciences, HealthCap, Pureos Bioventures, Andera Partners, and Earlybird Venture Capital.
Investor Contact:
Kevin Lui
Director, Investor Relations
kevin.lui@precisionaq.com
Media Contact:
Genevieve Britton
Group Account Director, Public Relations
genevieve.britton@precisionaq.com
Source: Ariceum Therapeutics
