The U.S. FDA has granted Orphan Drug Designation to 225Ac-SSO110.
Initial safety results from the SANTANA-225 trial for ES-SCLC and MCC are anticipated in 2026.
This treatment shows promise for a wide array of neuroendocrine cancers.
BERLIN, Nov. 11, 2025 — Ariceum Therapeutics (Ariceum), a firm specializing in targeted radiotherapeutics to innovate cancer treatment, today revealed that the first patient has received a dose in the SANTANA-225 Phase 1/2 trial. This study evaluates 225Ac-SSO110 for treating extensive stage small cell lung cancer (ES-SCLC) and Merkel Cell Carcinoma (MCC). 225Ac-SSO110 is an Actinium-225-labeled antagonist of the somatostatin type 2 receptor (SSTR2), positioned as a potential leading treatment. SSTR2 is notably overexpressed in neuroendocrine tumors compared to healthy tissue, establishing it as an optimal target for radioligand therapies (RLTs).
The SANTANA-225 clinical trial () is a worldwide, open-label Phase 1/2 investigation designed to evaluate the safety, tolerability, initial effectiveness, and optimal Phase 2 dosage of 225Ac-SSO110. This applies to patients with ES-SCLC receiving first-line maintenance therapy with checkpoint inhibitors (CPI) or MCC patients undergoing first-line CPI therapy. The study aims to recruit around 20 patients for its dose escalation phase, followed by additional expansion cohorts. In February 2025, the U.S. Food and Drug Administration (FDA) granted Orphan Drug Designation (ODD) to 225Ac-SSO110 for addressing ES-SCLC.
“Radioligand therapies (RLTs) are transforming precision oncology by allowing radiation to be delivered directly to tumor cells, thereby reducing exposure to healthy tissue,” stated Germo Gericke, MD, Chief Medical Officer at Ariceum Therapeutics. He added, “225Ac-SSO110 represents the initial SSTR2 antagonist RLT undergoing clinical development. It is engineered to administer higher alpha radiation doses precisely to patients’ tumors while ensuring a favorable safety profile for those with neuroendocrine cancers, such as ES-SCLC and MCC. Administering the first dose to a patient in the SANTANA-225 trial marks a pivotal achievement for our primary program and a key milestone in meeting critical patient needs in these severe cancers. We anticipate releasing preliminary safety data from the SANTANA-225 trial in 2026, which could facilitate its use in further neuroendocrine tumor indications and further confirm 225Ac-SSO110’s unique mechanism of action.”
ES-SCLC is a lethal and virulent cancer, signifying a substantial unmet medical need given the scarcity of available treatment choices for patients. A majority, two-thirds, of SCLC patients are diagnosed at a metastatic advanced stage, leading to a grim prognosis and a 5-10% five-year survival rate. MCC, Merkel Cell Carcinoma, is an uncommon yet aggressive form of skin cancer with few therapeutic options, also exhibiting low survival rates for patients unresponsive to initial CPI therapy. Both ES-SCLC and MCC are neuroendocrine tumors that commonly exhibit SSTR2 expression, positioning them as strong initial candidates for SSTR2-targeted treatment. 225Ac-SSO110 is the inaugural SSTR2-targeting antagonist, labeled with Actinium-225, to enter human trials in conjunction with CPI for these neuroendocrine tumor types. This initiative addresses areas of critical unmet need and establishes a basis for potential expansion into other SSTR2-expressing cancers.
About Ariceum Therapeutics
Ariceum Therapeutics is an oncology company in the clinical stage, committed to transforming future patient care through targeted radiotherapeutics for challenging and aggressive cancers. The company’s primary initiative, 225Ac-SSO110, a new antagonist of the somatostatin type 2 receptor (SSTR2) with potential to be a leading treatment, is presently being assessed in the Phase 1/2 SANTANA-225 study. It aims to be the first maintenance radiotherapy for extensive stage small cell lung cancer (ES-SCLC) and Merkel Cell Carcinoma (MCC)—both conditions characterized by restricted treatment options and unfavorable prognoses. Ariceum is additionally advancing ATT001, an innovative radiolabeled I-123 PARP inhibitor intended to provide subcellular precision radiotherapy for aggressive solid tumors.
With its headquarters in Berlin, Ariceum maintains operations across Germany, Switzerland, Australia, the United Kingdom, and the United States. The company benefits from the backing of prominent international life sciences investors, such as EQT Life Sciences, HealthCap, Pureos Bioventures, Andera Partners, and Earlybird Venture Capital.
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