Ariceum Therapeutics Doses First Patient in SANTANA-225 Phase 1/2 Clinical Trial of 225Ac-SSO110 in Patients with Extensive-Stage Small Cell Lung Cancer or Merkel Cell Carcinoma

225Ac-SSO110 has received U.S. FDA Orphan Drug Designation

Initial safety data from SANTANA-225 in ES-SCLC and MCC expected in 2026

Potential to address a broad range of neuroendocrine cancers

BERLIN, Nov. 11, 2025 (GLOBE NEWSWIRE) -- Ariceum Therapeutics (Ariceum), a targeted radiotherapeutics company dedicated to setting new standards in cancer care, today announced that the first patient has been dosed in the SANTANA-225 Phase 1/2 study of 225Ac-SSO110 for the treatment of 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 SANTANA-225 clinical trial (NCT06939036) is a global, open-label Phase 1/2 study that will assess the safety, tolerability, preliminary efficacy, and recommended Phase 2 dose of 225Ac-SSO110 in patients with ES-SCLC treated with checkpoint inhibitors (CPI) in first-line maintenance therapy or MCC patients treated with CPI in first-line therapy. The trial is expected to enroll approximately 20 patients in the dose escalation phase of the study, followed by expansion cohorts. In February 2025, 225Ac-SSO110 received Orphan Drug Designation (ODD) from the U.S. Food and Drug Administration (FDA) for the treatment of ES-SCLC.

“RLTs are redefining precision oncology by enabling targeted delivery of radiation directly to tumor cells while minimizing exposure to healthy tissue,” said Germo Gericke, MD, Chief Medical Officer of Ariceum Therapeutics. “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. Dosing the first patient in the SANTANA-225 trial is a significant step for our lead program and an important milestone towards addressing urgent patient needs in these aggressive cancers. We expect 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.”

ES-SCLC is a deadly and aggressive cancer that represents a significant unmet medical need due to the limited number of treatment options available to patients. Two-thirds of SCLC patients are diagnosed at an advanced stage where the disease has already metastasized, resulting in a poor prognosis and a 5-10% five-year survival rate. MCC is a rare and aggressive type of skin cancer with limited treatment options that 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.

About Ariceum Therapeutics
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) –two diseases with limited options and poor prognosis. 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.

For further information, please visit www.ariceum-therapeutics.com and follow us on LinkedIn.

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